Next Door Earth Like Planets

This artist’s conception shows a hypothetical habitable planet with two moons orbiting a red dwarf star. Astronomers have found that 6 percent of all red dwarf stars have an Earth-sized planet in the habitable zone, which is warm enough for liquid water on the planet’s surface. Since red dwarf stars are so common, then statistically the closest Earth-like planet should be only 13 light-years away. // David A. Aguilar (CfA)

By Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts

Published: February 6, 2013
 
Using publicly available data from NASA’s Kepler space telescope, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, have found that 6 percent of red dwarf stars have habitable Earth-sized planets. Since red dwarfs are the most common stars in our galaxy, the closest Earth-like planet could be just 13 light-years away.

“We thought we would have to search vast distances to find an Earth-like planet. Now, we realize another Earth is probably in our own backyard waiting to be spotted,” said Courtney Dressing from CfA.

Red dwarf stars are smaller, cooler, and fainter than our Sun. An average red dwarf is only one-third as large and one-thousandth as bright as the Sun. From Earth, no red dwarf is visible to the naked eye.

Despite their dimness, these stars are good places to look for Earth-like planets. Red dwarfs make up three out of every four stars in our galaxy for a total of at least 75 billion. The signal of a transiting planet is larger since the star itself is smaller, so an Earth-sized world blocks more of the star’s disk. And since a planet has to orbit a cool star closer in order to be in the habitable zone, it’s more likely to transit from our point of view.

Dressing culled the Kepler catalog of 158,000 target stars to identify all the red dwarfs. She then reanalyzed those stars to calculate more accurate sizes and temperatures. She found that almost all of those stars were smaller and cooler than previously thought.

Since the size of a transiting planet is determined relative to the star size, based on how much of the star’s disk the planet covers, shrinking the star shrinks the planet. And a cooler star will have a tighter habitable zone.

Dressing identified 95 planetary candidates orbiting red dwarf stars. This implied that at least 60 percent of such stars have planets smaller than Neptune. However, most weren’t quite the right size or temperature to be considered truly Earth-like. Three planetary candidates were both warm and approximately Earth-sized. Statistically, this means that 6 percent of all red dwarf stars should have an Earth-like planet.

“We now know the rate of occurrence of habitable planets around the most common stars in our galaxy,” said David Charbonneau from CfA. “That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought.”

Locating nearby Earth-like worlds may require a dedicated small space telescope or a large network of ground-based telescopes. Follow-up studies with instruments like the Giant Magellan Telescope and James Webb Space Telescope could tell scientists whether any warm, transiting planets have an atmosphere and further probe its chemistry.

Such a world would be different from our own. Orbiting so close to its star, the planet would probably be tidally locked. However, that doesn’t prohibit life since a reasonably thick atmosphere or deep ocean could transport heat around the planet. And while young red dwarf stars emit strong flares of ultraviolet light, an atmosphere could protect life on the planet’s surface. In fact, such stresses could help life evolve. “You don’t need an Earth clone to have life,” said Dressing.

Since red dwarf stars live much longer than Sun-like stars, this discovery raises the interesting possibility that life on such a planet would be much older and more evolved than life on Earth. “We might find an Earth that’s 10 billion years old,” said Charbonneau.

The three habitable-zone planetary candidates identified in this study are Kepler Object of Interest (KOI) 1422.02, which is 90 percent the size of Earth in a 20-day orbit; KOI 2626.01, 1.4 times the size of Earth in a 38-day orbit; and KOI 854.01, 1.7 times the size of Earth in a 56-day orbit. All three are located about 300 to 600 light-years away and orbit stars with temperatures between 5700° and 5900° Fahrenheit (3100° and 3300° Celsius). For comparison, our Sun’s surface is 10000° F (5500° C).

Planets can form in the galactic center (Near a Black Hole)

Fig : In this artist's conception, a protoplanetary disk of gas and dust (red) is being shredded by the powerful gravitational tides of our galaxy's central black hole. // Credit: David A. Aguilar (CfA)
  
By Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts

  
Published: September 12, 2012
 
At first glance, the center of the Milky Way seems like a very inhospitable place to try to form a planet. Stars crowd each other as they whiz through space like cars on a rush-hour freeway. Supernova explosions blast out shock waves and bathe the region in intense radiation. Powerful gravitational forces from a supermassive black hole twist and warp the fabric of space itself.

Yet new research by astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) shows that planets still can form in this cosmic maelstrom. For proof, they point to the recent discovery of a cloud of hydrogen and helium plunging toward the galactic center. They argue that this cloud represents the shredded remains of a planet-forming disk orbiting an unseen star.

“This unfortunate star got tossed toward the central black hole. Now it’s on the ride of its life, and while it will survive the encounter, its protoplanetary disk won’t be so lucky,” said Ruth Murray-Clay of the CfA.

Last year, a team of astronomers discovered the cloud in question using the Very Large Telescope in Chile. The group speculated that it formed when gas streaming from two nearby stars collided, like windblown sand gathering into a dune.

Murray-Clay and colleague Avi Loeb propose a different explanation. Newborn stars retain a surrounding disk of gas and dust for millions of years. If one such star dived toward our galaxy’s central black hole, radiation and gravitational tides would rip apart its disk in a matter of years.

They also identify the likely source of the stray star — a ring of stars known to orbit the galactic center at a distance of about one-tenth of a light-year. Astronomers have detected dozens of young, bright O-type stars in this ring, which suggests that hundreds of fainter Sun-like stars also exist there. Interactions between the stars could fling one inward along with its accompanying disk.

Although this protoplanetary disk is being destroyed, the stars that remain in the ring can hold onto their disks. Therefore, they may form planets despite their hostile surroundings.

As the star continues its plunge over the next year, more and more of the disk’s outer material will be torn away, leaving only a dense core. The stripped gas will swirl down into the maw of the black hole. Friction will heat it to high enough temperatures that it will glow in X-rays.

“It’s fascinating to think about planets forming so close to a black hole,” said Loeb. “If our civilization inhabited such a planet, we could have tested Einstein’s theory of gravity much better, and we could have harvested clean energy from throwing our waste into the black hole.”

Milky way may swarm with nomad planets

Figure : This image is an artistic rendition of a nomad object wandering the interstellar medium. The object is intentionally blurry to represent uncertainty about whether it has an atmosphere. A nomadic object may be an icy body akin to an object found in the outer solar system, a more rocky material akin to asteroids, or even a gas giant similar in composition to the most massive solar system planets and exoplanets.

By Stanford University
Published: February 24, 2012

Our galaxy may be awash in homeless planets, wandering through space instead of orbiting a star. In fact, there may be 100,000 times more nomad planets in the Milky Way than stars, according to a new study by researchers at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) in Stanford, California.

If observations confirm the estimate, this new class of celestial objects will affect current theories of planet formation and could change our understanding of the origin and abundance of life.

“If any of these nomad planets are big enough to have a thick atmosphere, they could have trapped enough heat for bacterial life to exist,” said Louis Strigari from KIPAC. Although nomad planets don’t bask in the warmth of a star, they may generate heat through internal radioactive decay and tectonic activity.

Searches over the past two decades have identified more than 500 planets outside our solar system, almost all of which orbit stars. Last year, researchers detected about a dozen nomad planets, using a technique called gravitational microlensing, which looks for stars whose light is momentarily refocused by the gravity of passing planets.

The research produced evidence that roughly two nomads exist for every typical, main sequence star in our galaxy. The new study estimates that nomads may be up to 50,000 times more common than that.

To arrive at what Strigari called “an astronomical number,” the KIPAC team took into account the known gravitational pull of the Milky Way Galaxy, the amount of matter available to make such objects, and how that matter might divvy itself up into objects ranging from the size of Pluto to larger than Jupiter. Not an easy task, considering no one is quite sure how these bodies form. According to Strigari, some were probably ejected from solar systems, but research indicates that not all of them could have formed in that fashion.

“To paraphrase Dorothy from The Wizard of Oz, if correct, this extrapolation implies that we are not in Kansas anymore, and in fact we never were in Kansas,” said Alan Boss from the Carnegie Institution for Science in Washington, D.C. “The universe is riddled with unseen planetary-mass objects that we are just now able to detect.”

A good count, especially of the smaller objects, will have to wait for the next generation of big survey telescopes, especially the space-based Wide-Field Infrared Survey Telescope and the ground-based Large Synoptic Survey Telescope, both set to begin operation in the early 2020s.

A confirmation of the estimate could lend credence to another possibility mentioned in the paper — that as nomad planets roam their starry pastures, collisions could scatter their microbial flocks to seed life elsewhere.

“Few areas of science have excited as much popular and professional interest in recent times as the prevalence of life in the universe,” said Roger Blandford from KIPAC. “What is wonderful is that we can now start to address this question quantitatively by seeking more of these erstwhile planets and asteroids wandering through interstellar space, and then speculate about hitchhiking bugs.”

Astronomers discover two planets that survived their star's expansion

Fig: Two planets that survived the red-giant expansion of their host star. Illustration by Stéphane Charpinet/Institut de Recherche en Astrophysique et Planétologie in Toulouse, France

By Iowa State University, Ames

Published: December 22, 2011

Astronomers have discovered two Earth-sized planets that survived getting caught in the red-giant expansion of their host star.

Steve Kawaler from Iowa State University helped the research team study data from the Kepler space telescope to confirm that tiny variations of light from a star were actually caused by two planets orbiting it. Stéphane Charpinet from the Institut de Recherche en Astrophysique et Planétologie in Toulouse, France, is the leader of the research team.

“This is a snapshot of what our solar system might look like after several billion more years of evolution,” Kawaler said. “This can help us learn about the future of planetary systems and of our own Sun.”

Kawaler said the researchers have studied pulsations of the planets’ host star, KIC 05807616 — an old star just past its red-giant stage — for about two years. While analyzing the data, Charpinet noticed two tiny variations repeated in 5.76- and 8.23-hour intervals.

He asked other astronomers, including Kawaler, to analyze the original Kepler data and a subsequent set of data to see if they also could see the variations.

“We saw them in the same place and the same periodicity,” Kawaler said. “So we knew they were real.”

That led to the next question: “So what are they?”

Kawaler has studied the fastest and slowest rates that stars could pulsate. Using that result, the team could conclude the variations seen by Kepler were too slow to be from the star itself. So the astronomers started testing the idea that the variations were from two planets orbiting the star.

Astronomers believe the variations from the two planets, KOI 55.01 and KOI 55.02, are caused by reflection of the star’s light on the planets and by temperature differences between the hot day-sides and cooler night-sides of the planets.

The astronomers also report the planets are 76 percent and 87 percent the size of Earth. That makes them among the smallest planets detected around a star other than our Sun.

They further report the planets are close to their host star, only 0.6 percent and 0.76 percent the distance between the Sun and Earth. That means conditions on the planets are harsh with temperatures up to 16,000° Fahrenheit (9,000° Celsius).

That’s so close that the host star’s expansion to a red giant would have engulfed the planets, possibly stripping gas giant planets similar to Jupiter down to their dense cores. The planets also could have contributed to the host star’s unusual loss of mass.

The research team said the discovery of the two planets raises many questions about their ability to survive such harsh conditions. It also raises questions about how planets can affect the evolution of their host stars.

Free-Floating Planets May Be More Common Than Stars

This artist's conception illustrates a Jupiter-like planet alone in the dark of space, floating freely without a parent star.
Image credit: NASA/JPL-Caltech

By Jet Propulsion Laboratory, Pasadena, Calif.
Published: 05.18.11

Astronomers, including a NASA-funded team member, have discovered a new class of Jupiter-sized planets floating alone in the dark of space, away from the light of a star. The team believes these lone worlds were probably ejected from developing planetary systems.

The discovery is based on a joint Japan-New Zealand survey that scanned the center of the Milky Way galaxy during 2006 and 2007, revealing evidence for up to 10 free-floating planets roughly the mass of Jupiter. The isolated orbs, also known as orphan planets, are difficult to spot, and had gone undetected until now. The newfound planets are located at an average approximate distance of 10,000 to 20,000 light-years from Earth.

"Although free-floating planets have been predicted, they finally have been detected, holding major implications for planetary formation and evolution models," said Mario Perez, exoplanet program scientist at NASA Headquarters in Washington.

The discovery indicates there are many more free-floating Jupiter-mass planets that can't be seen. The team estimates there are about twice as many of them as stars. In addition, these worlds are thought to be at least as common as planets that orbit stars. This would add up to hundreds of billions of lone planets in our Milky Way galaxy alone.

"Our survey is like a population census," said David Bennett, a NASA and National Science Foundation-funded co-author of the study from the University of Notre Dame in South Bend, Ind. "We sampled a portion of the galaxy, and based on these data, can estimate overall numbers in the galaxy."

The study, led by Takahiro Sumi from Osaka University in Japan, appears in the May 19 issue of the journal Nature.

The survey is not sensitive to planets smaller than Jupiter and Saturn, but theories suggest lower-mass planets like Earth should be ejected from their stars more often. As a result, they are thought to be more common than free-floating Jupiters.

Previous observations spotted a handful of free-floating, planet-like objects within star-forming clusters, with masses three times that of Jupiter. But scientists suspect the gaseous bodies form more like stars than planets. These small, dim orbs, called brown dwarfs, grow from collapsing balls of gas and dust, but lack the mass to ignite their nuclear fuel and shine with starlight. It is thought the smallest brown dwarfs are approximately the size of large planets.

On the other hand, it is likely that some planets are ejected from their early, turbulent solar systems, due to close gravitational encounters with other planets or stars. Without a star to circle, these planets would move through the galaxy as our sun and other stars do, in stable orbits around the galaxy's center. The discovery of 10 free-floating Jupiters supports the ejection scenario, though it's possible both mechanisms are at play.

"If free-floating planets formed like stars, then we would have expected to see only one or two of them in our survey instead of 10," Bennett said. "Our results suggest that planetary systems often become unstable, with planets being kicked out from their places of birth."

The observations cannot rule out the possibility that some of these planets may have very distant orbits around stars, but other research indicates Jupiter-mass planets in such distant orbits are rare.

The survey, the Microlensing Observations in Astrophysics (MOA), is named in part after a giant wingless, extinct bird family from New Zealand called the moa. A 5.9-foot (1.8-meter) telescope at Mount John University Observatory in New Zealand is used to regularly scan the copious stars at the center of our galaxy for gravitational microlensing events. These occur when something, such as a star or planet, passes in front of another, more distant star. The passing body's gravity warps the light of the background star, causing it to magnify and brighten. Heftier passing bodies, like massive stars, will warp the light of the background star to a greater extent, resulting in brightening events that can last weeks. Small planet-size bodies will cause less of a distortion, and brighten a star for only a few days or less.

A second microlensing survey group, the Optical Gravitational Lensing Experiment (OGLE), contributed to this discovery using a 4.2-foot (1.3 meter) telescope in Chile. The OGLE group also observed many of the same events, and their observations independently confirmed the analysis of the MOA group.

Orbital chaos may destroy Earth

Image: possible orbital chaos collision between Venus and Earth

A force known as orbital chaos may cause our solar system to go haywire, leading to a possible collision between earth and Venus or Mars, according to a study released today.The good news is that the likelihood of such a smash-up is small, around one-in-2500.And even if the planets did careen into one another, it would not happen before another 3.5 billion years.

Indeed, there is a 99 per cent chance that the sun's posse of planets will continue to circle in an orderly pattern throughout the expected life span of our life-giving star, another five billion years, the study found.After that, the sun will likely expand into a red giant, engulfing earth and its other inner planets - Mercury, Venus and Mars - in the process.Astronomers have long been able to calculate the movement of planets with great accuracy hundreds, even thousands of years in advance. This is how eclipses have been predicted. But peering further into the future of celestial mechanics with exactitude is still beyond our reach, said Jacques Laskar, a researcher at the Observatoire de Paris and lead author of the study.

"The most precise long-term solutions for the orbital motion of the solar system are not valid over more than a few tens of millions of years," he said.

Using powerful computers, Mr Laskar and colleague Mickael Gastineau generated numerical simulations of orbital instability over the next five billion years.
Unlike previous models, they took into account Albert Einstein's theory of general relativity. Over a short time span, this made little difference, but over the long haul it resulted in dramatically different orbital paths.The researchers looked at 2501 possible scenarios, 25 of which ended with a severely disrupted solar system.

"There is one scenario in which Mars passes very close to earth," 794 kilometres to be exact, said Mr Laskar."When you come that close, it is almost the same as a collision because the planets get torn apart."

Life on earth, if there still were any, would almost certainly cease to exist.To get a more fine-grained view of how this might unfold, Mr Laskar and Mr Gastineau ran an additional 200 computer models, slightly changing the path of Mars each time.All but five of them ended in a two-way collision involving the sun, earth, Mercury, Venus or Mars. A quarter of them saw earth smashed to pieces.The key to all the scenarios of extreme orbital chaos was the rock closest to the sun, found the study, published in the British journal Nature."Mercury is the trigger, and would be be the first planet to be destabilised because it has the smallest mass," said Mr Laskar.At some point Mercury's orbit would get into resonance with that of Jupiter, throwing the smaller orb even more out of kilter, he said.Once this happens, the so-called "angular momentum" from the much larger Jupiter would wreak havoc on the other inner planets' orbits too.

"The simulations indicate that Mercury, in spite of its diminutive size, poses the greatest risk to our present order," said University of California scientist Gregory Laughlin in a commentary, also published in Nature.

Edited By: Imran Khan
Key Terms: Observatorie de paris,Angular momentum,computer simulations and models
Year: 2009

Planet Smash-Up Sends Vaporized Rock, Hot Lava Flying

This artist's concept shows a celestial body about the size of our moon slamming at great speed into a body the size of Mercury. NASA's Spitzer Space Telescope found evidence that a high-speed collision of this sort occurred a few thousand years ago around a young star, called HD 172555, still in the early stages of planet formation. The star is about 100 light-years from Earth.Spitzer detected the signatures of vaporized and melted rock, in addition to rubble, all flung out from the giant impact. Further evidence from the infrared telescope shows that these two bodies must have been traveling at a velocity relative to each other of at least 10 kilometers per second (about 22,400 miles per hour).As the bodies slammed into each other, a huge flash of light would have been emitted. Rocky surfaces were vaporized and melted, and hot matter was sprayed everywhere. Spitzer detected the vaporized rock in the form of silicon monoxide gas, and the melted rock as a glassy substance called obsidian. On Earth, obsidian can be found around volcanoes, and in black rocks called tektites often found around meteor craters.Shock waves from the collision would have traveled through the planet, throwing rocky rubble into space. Spitzer also detected the signatures of this rubble.In the end, the larger planet is left skinned, stripped of its outer layers. The core of the smaller body and most of its surface were absorbed by the larger one. This merging of rocky bodies is how planets like Earth are thought to form.Astronomers say a similar type of event stripped Mercury of its crust early on in the formation of our solar system, flinging the removed material away from Mercury, out into space and into the sun. Our moon was also formed by this type of high-speed impact: a body the size of Mars is thought to have slammed into a young Earth about 30 to 100 million years after the sun formed. The sun is now 4.5 billion years old. According to this theory, the resulting molten rock, vapor and shattered debris mixed with debris from Earth to form a ring around our planet. Over time, this debris coalesced to make the moon.

NASA's Spitzer Space Telescope has found evidence of a high-speed collision between two burgeoning planets around a young star.

Astronomers say that two rocky bodies, one as least as big as our moon and the other at least as big as Mercury, slammed into each other within the last few thousand years or so — not long ago by cosmic standards. The impact destroyed the smaller body, vaporizing huge amounts of rock and flinging massive plumes of hot lava into space.

Spitzer's infrared detectors were able to pick up the signatures of the vaporized rock, along with pieces of refrozen lava, called tektites.

"This collision had to be huge and incredibly high-speed for rock to have been vaporized and melted," said Carey M. Lisse of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md., lead author of a new paper describing the findings in the Aug. 20 issue of the Astrophysical Journal. "This is a really rare and short-lived event, critical in the formation of Earth-like planets and moons. We're lucky to have witnessed one not long after it happened."

Lisse and his colleagues say the cosmic crash is similar to the one that formed our moon more than 4 billion years ago, when a body the size of Mars rammed into Earth.

"The collision that formed our moon would have been tremendous, enough to melt the surface of Earth," said co-author Geoff Bryden of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Debris from the collision most likely settled into a disk around Earth that eventually coalesced to make the moon. This is about the same scale of impact we're seeing with Spitzer — we don't know if a moon will form or not, but we know a large rocky body's surface was red hot, warped and melted."

Our solar system's early history is rich with similar tales of destruction. Giant impacts are thought to have stripped Mercury of its outer crust, tipped Uranus on its side and spun Venus backward, to name a few examples. Such violence is a routine aspect of planet building. Rocky planets form and grow in size by colliding and sticking together, merging their cores and shedding some of their surfaces. Though things have settled down in our solar system today, impacts still occur, as was observed last month after a small space object crashed into Jupiter.

Lisse and his team observed a star called HD 172555, which is about 12 million years old and located about 100 light-years away in the far southern constellation Pavo, or the Peacock (for comparison, our solar system is 4.5 billion years old). The astronomers used an instrument on Spitzer, called a spectrograph, to break apart the star's light and look for fingerprints of chemicals, in what is called a spectrum. What they found was very strange. "I had never seen anything like this before," said Lisse. "The spectrum was very unusual."

After careful analysis, the researchers identified lots of amorphous silica, or essentially melted glass. Silica can be found on Earth in obsidian rocks and tektites. Obsidian is black, shiny volcanic glass. Tektites are hardened chunks of lava that are thought to form when meteorites hit Earth.

Large quantities of orbiting silicon monoxide gas were also detected, created when much of the rock was vaporized. In addition, the astronomers found rocky rubble that was probably flung out from the planetary wreck.

The mass of the dust and gas observed suggests the combined mass of the two charging bodies was more than twice that of our moon.

Their speed must have been tremendous as well — the two bodies would have to have been traveling at a velocity relative to each other of at least 10 kilometers per second (about 22,400 miles per hour) before the collision.

Spitzer has witnessed the dusty aftermath of large asteroidal impacts before, but did not find evidence for the same type of violence — melted and vaporized rock sprayed everywhere. Instead, large amounts of dust, gravel, and boulder-sized rubble were observed, indicating the collisions might have been slower-paced. "Almost all large impacts are like stately, slow-moving Titanic-versus-the-iceberg collisions, whereas this one must have been a huge fiery blast, over in the blink of an eye and full of fury," said Lisse.

Other authors include C.H. Chen of the Space Telescope Science Institute, Baltimore, Md.; M.C. Wyatt of the University of Cambridge, England; A. Morlok of the Open University, London, England; I. Song of The University of Georgia, Athens, Ga.; and P. Sheehan of the University of Rochester, N.Y.

JPL manages the Spitzer mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared spectrograph, which made the observations in 2004 before the telescope began its "warm" mission, was built by Cornell University, Ithaca, N.Y. Its development was led by Jim Houck of Cornell.

Monday, August 10, 2009

Rogue planet: Nobody's Child

A rogue planet (also known as an interstellar planet, free-floating planet or orphan planet) is an object which has equivalent mass to a planet and is not gravitationally bound to any star, and that therefore moves through space as an independent object. Several astronomers claim to have detected such objects (for example, Cha 110913-773444), but those detections remain unconfirmed pending visitation.Some astronomers refer to these objects as "planets", usually because they believe such objects were planets that were ejected from orbit around a star.However, others believe that the definition of 'planet' should depend on current observable state, and not origin. Additionally, these objects may form on their own (sub brown dwarf)through gas cloud collapse similar to star formation; in which case they would never have been planets.

Retention of heat in interstellar space:

In 1998, David J. Stevenson authored a paper entitled "Possibility of Life Sustaining Planets in Interstellar Space."In this paper, Stevenson theorizes that some wandering objects, that Stevenson refers to as "planets", drift in the vast expanses of cold interstellar space and could possibly sustain a thick atmosphere which would not freeze out due to radiative heat loss. He proposes that atmospheres are preserved by the pressure-induced far infrared radiation opacity of a thick hydrogen-containing atmosphere.It is thought that during planetary system formation, several small protoplanetary bodies may be ejected from the forming system.With the reduced ultraviolet light associated with its increasing distance from the parent star, the planet's predominantly hydrogen and helium containing atmosphere would be easily confined even by an Earth-sized body's gravity.It is calculated that for an Earth-sized object at a kilobar hydrogen atmospheric pressures in which a convective gas adiabat has formed, geothermal energy from residual core radioisotope decay will be sufficient to heat the surface to temperatures above the melting point of water.Thus, it is proposed that interstellar planetary bodies with extensive liquid water oceans may exist. It is further suggested that the bodies are likely to remain geologically active for long periods, providing a geodynamo-created protective magnetosphere and possible sea floor volcanism which could provide an energy source for life.The author admits these bodies will be difficult to detect due to the intrinsically weak thermal microwave radiation emissions emanating from the lower reaches of the atmosphere.A study of simulated planet ejection scenarios has suggested that around five percent of Earth-sized planets with Moon-sized moons would retain their moons after ejection. A large moon would be a source of significant geological tidal heating.

Proplyds of planetars?:

Recently, it has been discovered that some extrasolar planets such as the planemo 2M1207b, orbiting the brown dwarf 2M1207, have debris discs. If some large interstellar objects are considered as stars (brown sub-dwarfs) then the debris could coalesce into planets, meaning the disks are proplyds. If these are considered planets, then the debris would coalesce as moons. The term planetar exists for those accretion masses that seem to fall between stars and planets.

Mega-laser to Probe Secrets of Exoplanets

Artist's impression of a gas giant planet circling the star Gliese 436. The new laser will investigate the internal chemistry of these vast planets (Image: NASA)

Sunday, March 01, 2009

AN AWESOME laser facility, built to provide fusion data for nuclear weapons simulations, will soon be used to probe the secrets of extrasolar planets.

The National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in California was declared ready for action earlier this month. Its vital statistics reveal it to be a powerful beast: its ultraviolet lasers can deliver 500 trillion watts in a 20-nanosecond burst. That power opens up new scientific possibilities.

For instance, Raymond Jeanloz, an astronomer at the University of California, Berkeley, will use the device to recreate the conditions inside Jupiter and other larger planets, where pressures can be 1000 times as great as those at the centre of the Earth.

Jeanloz will fire the lasers at an iron sample 800 micrometres in diameter. The intense heat will vaporise the metal, generating a gas jet so powerful it will send a shock wave through the iron, compressing it to over a billion times atmospheric pressure. By measuring how the metal's crystalline structure and melting point change at these pressures, Jeanloz hopes to shed light on the formation of the hundreds of giant exoplanets that we have discovered in the last two decades. "The chemistry of these planets is completely unexplored," says Jeanloz. "It's never been accessible in the laboratory before."

Next year, Livermore teams will start work on experiments that could ultimately have an even bigger impact. They will use the lasers to ignite a fusion reaction in a ball of hydrogen isotopes. Other labs have triggered fusion, but not a self-sustaining reaction. The Livermore facility should deliver a big enough jolt of energy to trigger a reaction that burns until the fuel is used up. The data produced will feed into attempts to design a commercial fusion power plant.

The same reaction will also aid the management of the US nuclear weapons stockpile. It is more than 15 years since the US tested a nuclear weapon. Engineers use computer simulations to determine if warheads are in working order, but the models need to be calibrated using data from experiments like NIF's fusion reactions.

Astronomers Observe Planet with Wild Temperature Swings

Tour of Planet with Extreme Temperature Swings
Credit: NASA/JPL-Caltech/D. Kasen (UC Santa Cruz)

This image shows a computer simulation of the planet HD 80606b from an observer located at a point in space lying between the Earth and the HD 80606 system. The animation starts 2.2 days before the moment of close approach and ends 8.9 days later. The blue areas are reflected starlight (the blue color arises mainly from absorption by sodium and potassium in the planetary atmosphere). Red regions are areas of the planet that are glowing with their own intrinsic heat.The point of closest approach -- and maximum heating -- occurs about 4.5 seconds into the animation. As the planet whips around the star, we see the evolving thermal storm patterns across its unilluminated side. The planetÍs transit behind its star (as would be seen from Earth four seconds into the animation) is not shown in this simulation.These theoretical models allow astronomers to better understand weather patterns on distant planets. While direct telescopic observations of the atmospheres of such worlds may be many decades away, such simulations give us a clue to what we may see when it becomes possible.


Light From Red-Hot Planet
Credit: NASA/JPL-Caltech/G. Laughlin (UC Santa Cruz)

This figure charts 30 hours of observations taken by NASA's Spitzer Space Telescope of a strongly irradiated exoplanet (an planet orbiting a star beyond our own). Spitzer measured changes in the planet's heat, or infrared light.The lower graph shows precise measurements of infrared light with a wavelength of 8 microns coming from the HD 80606 stellar system. The system consists of a sun-like star and a planetary companion on an extremely eccentric, comet-like orbit. The geometry of the planet-star encounter is shown in the upper part of the figure.As the planet swung through its closest approach to the star, the Spitzer observations indicated that it experienced very rapid heating (as shown by the red curve). Just
before close approach, the planet was eclipsed by the star as seen from Earth, allowing astronomers to determine the amount of energy coming from the planet in comparison to the amount coming from the star.The observations were made in Nov. of 2007, using Spitzer's infrared array camera. They represent a significant first for astronomers, opening the door to studying changes in atmospheric conditions of planets far beyond our own solar system.


Severe Exoplanetary Storm
Credit: NASA/JPL-Caltech/J. Langton (UC Santa Cruz)

These computer-generated images chart the development of severe weather patterns on the highly eccentric exoplanet HD 80606b during the days after its closest approach to its parent star. An exoplanet is a planet that orbits a star other than our sun.
The images were produced by computer simulations that modeled NASA's Spitzer
Space Telescope's measurements of heat radiating from the planet. The six frames are evenly spaced in time, starting from 4.4 days after the planet's close approach to the star, a moment known as "periastron," and running through 8.9 days after periastron. The blue glow of the crescent is starlight that has been scattered and reflected by the planet. The starlight appears blue because the planet is a very efficient absorber of red light. The night side appears reddish orange as it glows with its own internal heat.These theoretical models allow astronomers to better understand weather patterns on distant planets. While direct telescopic observations of the atmospheres of such worlds may be many decades away, such simulations give us a clue to what we may see when it becomes possible.The Spitzer observations themselves spanned the relatively brief period when the heating of the planet was most intense, running from 20 hours prior to 10 hours after periastron. The data were taken in Nov. of 2007.HD 80606b is located 190 light-years away in the constellation Ursa Major. Its star can be seen with binoculars.

Wednesday, January 28, 2009

NASA's Spitzer Space Telescope has observed a planet that heats up to red-hot temperatures in a matter of hours before quickly cooling back down.

The "hot-headed" planet is HD 80606b, a gas giant that orbits a star 190 light-years from Earth. It was already known to be quite unusual, with an orbit shuttling it nearly as far out as Earth is from our sun, and much closer in than our planet Mercury. Astronomers used Spitzer, an infrared observatory, to measure heat emanating from the planet as it whipped behind and close to its star. In just six hours, the planet's temperature rose from 800 to 1,500 Kelvin (980 to 2,240 degrees Fahrenheit).

"We watched the development of one of the fiercest storms in the galaxy," said astronomer Greg Laughlin of the Lick Observatory, University of California at Santa Cruz. "This is the first time that we've detected weather changes in real time on a planet outside our solar system." Laughlin is lead author of a new report about the discovery appearing in the Jan. 29 issue of Nature.

HD 80606b was originally discovered in 2001 by a Swiss planet-hunting team led by Dominique Naef of the Geneva Observatory in Switzerland. Using a method known as the Doppler-velocity technique, the astronomers learned that the planet is wildly eccentric, with an orbit more like a comet's than a planet's. HD 80606b's orbit takes it as far out as 0.85 astronomical units from its star, and as close in as 0.03 astronomical units (one astronomical unit is the distance between Earth and the sun).

The planet takes about 111 days to circle its star, but it spends most of its time at farther distances while zipping through the closest part of its orbit in less than a day. (This is a consequence of Kepler's Second Law of Planetary Motion, which states that orbiting bodies -- planets and comets -- sweep out an equal area in equal time.)

"If you could float above the clouds of this planet, you'd see its sun growing larger and larger at faster and faster rates, increasing in brightness by almost a factor of 1,000," said Laughlin.

Spitzer observed HD 80606b before, during and just after its closest passage to the star in November of 2007, as the planet sizzled under the star's heat. When Laughlin and his colleagues planned the observation, they did not know whether the planet would disappear completely behind the star, an event called a secondary eclipse, or whether it would remain in view. Luckily for the team, the planet did indeed temporarily disappear from view, providing the planet's initial and final temperatures (had the planet had not been eclipsed, the team would have known only the temperature change without knowing the starting point).

The extreme temperature swing observed by Spitzer indicates that the air near the planet's gaseous surface must quickly absorb and lose heat. This type of atmospheric information revealing how a planet responds to sudden changes in heating -- an extreme version of seasonal change -- had never been obtained before for any exoplanet (a planet orbiting another star).

"By studying this planet under such extreme circumstances, we figure out how it handles heat -- does it retain it or dissipate it? In this case, the answer is that the planet releases the heat right away," said Laughlin. "We were essentially able to perform the 'thought experiment' -- what would happen to a planet like Jupiter if we could drag it very close to the sun?"

Laughlin and his colleagues say that a key factor in being able to make the observations is the planet's eccentric orbit. Unlike so-called hot Jupiter planets that remain in tight orbits around their stars, HD 80606b rotates around its axis roughly every 34 hours. Hot Jupiters, on the other hand, are thought to be tidally locked like our moon, so one side always faces their stars. Because HD 80606b spins on its axis many times per orbit, the astronomers were able to measure how its atmosphere responds to being baked by the star.

"The planet is spinning at a fast enough rate for the planet's hot spot to come into view," said co-author Drake Deming of NASA's Goddard Space Flight Center, Greenbelt, Md. "The hot spot can't hide."

Amateur and professional astronomers alike are gearing up to observe HD 80606b this coming Valentine's Day, when it will swing around the front of its star. There's a 15 percent chance that the planet will eclipse its star, an event known as the primary transit. If so, the event would not only be remarkable to see, but would also provide more details about the nature of this temperamental world.

Other authors include Jonathan Langton, Daniel Kasen, Steve Vogt, Eugenio Rivera and Stefano Meschiari from the University of California, Santa Cruz, and Paul Butler of the Carnegie Institution's Department of Terrestrial Magnetism, Washington. NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.

Habitable Planets: Four Types Proposed

The traditional view of our own solar system's habitable zone may be unfairly restrictive. This could also be the case for other systems. Credit: NASA

18 December 2008

The origin of life and the habitability of worlds other than Earth are two of the biggest mysteries facing science today. Much research has been dedicated to these topics, but there is still a lack of definite answers.

Jan Hendrik Bredehöft from the UK's Open University has been considering habitability on other worlds. "I'm one of those guys who takes a piece of meteorite, grinds it up and finds out what the organic chemistry is in there," said Bredehöft.

Based on these types of studies, he has come to believe that habitable worlds can be split into four categories, each with varying likelihoods of being home to extraterrestrial organisms. This has great potential for assisting the search for life in the universe, particularly as technology is now progressing to the stage where direct imaging of extrasolar planets is possible. Bredehöft presented his ideas at Europlanet's latest Planetary Science Congress.

His four groups of habitable worlds are: Earth-like, Mars-Like, Europa-like and water-worlds.

Taking each of these in turn, he considered their potential for hosting complex life. Earth-like words are the first class, and a kind of "control" since we already know such worlds are capable of sustaining complex life. Earth-like worlds feature an appropriate atmosphere, liquid water, moderate temperature ranges, and stable climates.

The second class of planets are those that were once much like Earth, such as Mars and Venus. "For some reason these planets left the classical habitable zone," said Bredehöft. "Mars became too dry, there's very little water left, at least not liquid water. Venus became just so enormously hot due to the greenhouse effect."

Still, Bredehöft believes there is some chance for life to exist on this type of world. He reasons that organisms could have developed when the planet was more hospitable, and this life could maintain a grip even through the hard times. "Once life has established itself it is really hard to kill off," said Bredehöft. "There have been absolutely devastating events in Earth's history that might have wiped out all kinds of life, but usually these served to further enhance biodiversity, rather than destroy it."

A chilly existence

Bodies that possess liquid water, but under an ice layer rather than on the surface, make up the third class of worlds.

Jupiter's moon Europa is a classic example from our own cosmic neighbourhood. Could there be life in places like this? Bredehöft's ideas here are particularly pertinent as often these worlds do not fit neatly into the conventional view of habitable zones. Europa, for example, lies beyond the solar system's temperature zone where water can remain as a liquid on a planet's surface.

However, there is still potential for life.

The traditional view of habitable zones thinks of a local star as being the prime energy source. But on icy worlds like Europa, other factors come into play, such as the gravitational pull of another planet. Worlds with liquid water hidden beneath icy layers could potentially be inhabited by simple organisms despite being far from the conventional habitable zone, so long as energy is provided in some other way.

Water-worlds

The fourth kind of habitable planets are made almost entirely of water. These hypothetical worlds would be Mercury to Earth-sized and would feature extensive oceans. Unlike oceans on Earth, the water on these types of planets would not be in contact with silicates or other rocks.

"These planets can either be completely made of water with high pressure ice at the core, or they can have bodies of liquid water that are separated from a silicate core by a thick layer of high pressure ice," said Bredehöft.

One theory for life's origin on Earth says organic material collected in shallow pools and then became concentrated by clinging to the surface of rocks. Eventually, this early life spread into the wider ocean. Another theory for life's origin is that the necessary chemistry occurred at hydrothermal volcanic vents. On water worlds, however, these scenarios are impossible. Therefore, Bredehöft thinks life is not likely to originate on such planets.

"The amount of water on such a planet would be so huge, you would need unbelievable amounts of carbon components concentrated together for a chance of life. It's far too diluted," said Bredehöft.

Considered opinions

After considering all the facts, Bredehöft said the best bet to find extraterrestrial ecosystems is to hunt for Earth-like planets, after all. However, he doesn't think Earth-like worlds will necessarily have advanced life.

"We don't know whether the level of complexity or the size of organisms living on Earth is essentially a logical outcome of evolution or whether it is just some fluke experienced here," said Bredehöft. "Is having talking intelligent beings on the surface of the planet the pinnacle of evolution? We just assume so because we like to see ourselves as something special."

With the rapid pace of development in planet-hunting technology, it is only a matter of time until we learn much more about exotic extrasolar planets and moons, and are able to glean vital information about their properties. Until then though, scientists like Bredehöft will continue to theorise about discoveries.

So in Bredehöft's carefully considered opinion, what kind of organisms are we most likely to find? "Probably something slimy," he said.

Earth: A borderline planet for life?

A super-Earth like the one in this artist's conception can grow twice as large as Earth with up to 10 times the mass. Super-Earths are likely to be more life-friendly than our world because they would be more geologically active. David A. Aguilar (Harvard-Smithsonian CfA)

January 9, 2008

Our planet is changing before our eyes, and as a result, many species are living on the edge. Yet Earth has been on the edge of habitability from the beginning. New work by astronomers at the Harvard-Smithsonian Center for Astrophysics shows that if Earth had been slightly smaller and less massive, it would not have plate tectonics, the forces that move continents and build mountains. And without plate tectonics, life might never have gained a foothold on our world.

"Plate tectonics are essential to life as we know it," says Diana Valencia of Harvard University. "Our calculations show that bigger is better when it comes to the habitability of rocky planets."

This research was the subject of a press conference at the 211th meeting of the American Astronomical Society.

Plate tectonics involve the movement of huge chunks, or plates, of a planet's surface. Plates spread apart from each other, slide under one another, and even crash into each other, lifting gigantic mountain ranges like the Himalayas. Plate tectonics are powered by magma boiling beneath the surface, much like a bubbling pot of chocolate. The chocolate on top cools and forms a skin or crust, just as magma cools to form the planet's crust.

Plate tectonics are crucial to a planet's habitability because they enable complex chemistry and recycle substances like carbon dioxide, which acts as a thermostat and keeps Earth balmy. Carbon dioxide that was locked into rocks is released when those rocks melt, returning to the atmosphere from volcanos and oceanic ridges.

"Recycling is important even on a planetary scale," Valencia explains.

Valencia and her colleagues, Richard O'Connell and Dimitar Sasselov (Harvard University), examined the extremes to determine whether plate tectonics would be more or less likely on different-sized rocky worlds. In particular, they studied so-called "super-Earths," planets more than twice the size of Earth and up to 10 times as massive. (Any larger, and the planet would gather gas as it forms, becoming like Neptune or even Jupiter.)

The team found that super-Earths would be more geologically active than our planet, experiencing more vigorous plate tectonics due to thinner plates under more stress. Earth itself was found to be a borderline case, not surprisingly since the slightly smaller planet Venus is tectonically inactive.

"It might not be a coincidence that Earth is the largest rocky planet in our solar system, and also the only one with life," says Valencia.

Exoplanet searches have turned up five super-Earths already, although none have life-friendly temperatures. If super-Earths are as common as observations suggest, then it is inevitable that some will enjoy Earth-like orbits, making them excellent havens for life.

"There are not only more potentially habitable planets, but MANY more," states Sasselov, who is director of the Harvard Origins of Life Initiative.

In fact, a super-Earth could prove to be a popular vacation destination to our far-future descendants. Volcanic "rings of fire" could span the globe while the equivalent of Yellowstone Park would bubble with hot springs and burst with hundreds of geysers. Even better, an Earth-like atmosphere would be possible, while the surface gravity would be up to three times that of Earth on the biggest super-Earths.

"If a human were to visit a super-Earth, they might experience a bit more back pain, but it would be worth it to visit such a great tourist spot," Sasselov suggests with a laugh.

He added that although a super-Earth would be twice the size of our home planet, it would have similar geography. Rapid plate tectonics would provide less time for mountains and ocean trenches to form before the surface was recycled, yielding mountains no taller and trenches no deeper than those on Earth. Even the weather might be comparable for a world in an Earth-like orbit.

"The landscape would be familiar. A super-Earth would feel very much like home," says Sasselov.

When worlds collide

Illustrated here in this artist's concept, astronomers may have observed the aftermath of a collision between two protoplanets, one Jupiter-sized and one Neptune-sized, in the system 2M1207. David A. Aguilar (Harvard-Smithsonian CfA)

January 9, 2008

Provided by Harvard-Smithsonian CfA

Astronomers announced today that a mystery object orbiting a star 170 light-years from Earth might have formed from the collision and merger of two protoplanets. The object, known as 2M1207B, has puzzled astronomers since its discovery because it seems to fall outside the spectrum of physical possibility. Its temperature, luminosity, age, and location do not match up with any theory.

"This is a strange enough object that it needs a strange explanation," says Eric Mamajek of the Harvard-Smithsonian Center for Astrophysics (CfA).

The announcement was made in a press conference at the 211th meeting of the American Astronomical Society.

2M1207B orbits a 25-Jupiter-mass brown dwarf called 2M1207A seen in the direction of the constellation Centaurus. Computer models show that 2M1207A is very young, only about 8 million years old; therefore its companion should also be 8 million years old. At that age, it should have cooled to a temperature of less than 1300° F (1000 K). However, observations show that 2M1207B is actually about 2400° F (1600 K). The extra heat might be the result of a protoplanetary collision.

"Most, if not all, planets in our solar system were hit early in their history. A collision created Earth's moon and knocked Uranus on its side," explains Mamajek. "It's quite likely that major collisions happen in other young planetary systems, too."

Given its temperature, astronomers would expect a certain luminosity for 2M1207B, but it is 10 times fainter than expected. In 2006, astronomers suggested that it is obscured by a dusty, edge-on disk. Mamajek and his colleague, Michael Meyer of the University of Arizona, propose an alternative explanation: 2M1207B is small, only about the size of Saturn, and therefore has a smaller-than-expected surface area radiating energy.

They derive a radius of 31,000 miles (50,000 km) for 2M1207B, compared to 37,000 miles (60,000 km) for Saturn. Given typical densities for giant planets, this would give 2M1207B a mass about 80 times Earth (or one-fourth Jupiter). The only plausible way for such a small object to be so hot millions of years after it formed is if it suffered a recent, titanic collision that heated it.

The planets in our solar system assembled from dust, rock, and gas, gradually growing larger over millions of years. But sometimes, two planet-sized objects collided catastrophically. For example, the Moon formed when an object about half the size of Mars hit the proto-Earth. If planet formation works the same way in other star systems, then 2M1207B might be the product of a collision between a Saturn-sized gas giant and a planet about three times the size of Earth. The two smacked into each other and stuck, forming one larger world still boiling from the heat generated in the collision.

"The Earth was hit by something one-tenth its mass, and it's likely that other planets in our solar system were too, including Venus and Uranus," explains Meyer. "If that one-tenth scale holds in other planetary systems, then we could be seeing the aftermath of a collision between a 72 Earth-mass gas giant and an 8 Earth-mass planet, even though such collisions are very unlikely."

Mamajek also points out that the collision theory is reasonable from a timescale point of view. A 2400-degree, Saturn-sized object would radiate its heat away over about 100,000 years. If the system were billions of years old, it is unlikely that we would be looking at the right time, but since the system is young, the chances are much better that we would catch it shortly after the collision while the hot aftermath is still observable.

The collision hypothesis makes several predictions that astronomers can test. Chief among them is a low surface gravity (which depends on a planet's mass and radius). To check this prediction, astronomers will need to get a better spectrum of 2M1207B, a challenge since it is very faint and very close to the brown dwarf 2M1207A. Others are checking the dusty disk theory by looking for signs of polarization in the light from 2M1207B. More answers should be forthcoming within a year or two.

Mamajek emphasizes that while a planet collision may not be the correct explanation for the weirdness of 2M1207B, examples of colliding planets are likely to be found by the next generation of ground-based telescopes.

"Hot, post-collision planets might be a whole new class of objects we will see with the Giant Magellan Telescope."

"Even if we're wrong, I wouldn't be surprised if someone finds a clear-cut case in the next 10 years," Mamajek adds.

Earth-like planets may be common

photo:Astronomers might try to identify Earth-like features on an extrasolar planet (land and seas or a breathable atmosphere, for example) to determine whether it might be habitable.

December 22, 2003

The thought of life elsewhere in the universe captures the collective imagination and compels scientists to search the sky for any sign of cosmic company. To date, about 110 extrasolar planets have been discovered dancing around distant stars, and with roughly one hundred billion stars in our galaxy alone, the possibilities for life out there seem endless. Still, with so many places to look, where should astronomers begin?

University of Washington astronomer Sean Raymond and colleagues think they've found the answer. In recent computer simulations, the team uncovered a set of vital clues that may help observers hone in on life-sustaining planets.

While scientists don't know exactly what conditions give rise to life, they do know a key ingredient: water. According to the recent study, involving 44 computer simulations of late-stage planetary formation, planets in stars' habitable zones, where liquid water can exist, should be quite common. In fact, such planets formed in a quarter of the group's simulations.

But even if a planet would be lucky enough to find itself in this liquid zone, there's no guarantee it actually would have water. That's because when terrestrial planets like Earth form, they are too hot to accommodate water. Farther away from a star, though, conditions are suitable for ice. Astronomers believe that asteroids and other such debris carry ice from this region to inner planets, delivering water upon impact.In our own solar system, Jupiter may have orchestrated this astronomical hailstorm. With more than 300 times the mass of Earth, the gas giant has a gravitational influence capable of steering the contents of the disk that lie between it and the terrestrial planets. "This water-rich rocky stuff is feeling Jupiter's gravity very strongly, and there are two possible outcomes," Raymond explains. "It might get a little too close to Jupiter and get ejected from the solar system, or it could be slowly scattered inward where, in time, it will whack into Earth and deliver a bunch of water."

In any planetary system, therefore, the water content of an Earth-like planet would depend crucially on the orbit of its Jupiter-like neighbor. First, the farther out the giant lives, the more icy material it can herd inward, and the higher the chances for a wet, habitable planet. Second, if the shape of Jupiter's orbit is too elliptical, its gravitational thrust will be stronger in some regions than in others, rendering it more likely to send the water-laden rubble flying off into interstellar space. A more circular orbit would result in a wetter Earth-like planet. In our solar system, Jupiter's orbit is slightly elliptical; hence Earth is 80 percent ocean rather than a landless, flooded world.

photo:The image's most energetic features are the small, bright clouds to the left of the Great Red Spot and in similar locations in the northern hemisphere. Streaks form as clouds are dissipated by Jupiter's intense jet streams that run parallel to the colored bands. The prominent dark band in the northern half of the planet is the location of Jupiter's fastest jet stream, with eastward winds of 300 miles (480 km) per hour. NASA / JPL / Space Science Institute


The recent simulations suggest the universe is littered with an extensive variety of planets and planetary systems, ranging from those with many small, dry planets to massive, habitable planets awash in water. But for every system, the relationship between a Jupiter-like planet and terrestrial planets is the same. And that's key because, while current instruments are not capable of searching for Earth-like planets directly, they can detect Jupiter-like planets. Scientists then can determine which solar systems are most likely to harbor life. That way, when future planet-hunting missions head out in search of wet worlds, they'll be looking in all the right places.

It seems our precious Earth — with its mass, location, and water content — is a relatively typical planet. If that's truly the case, it could be that life, too, is a typical occurrence. For now, we can only contemplate what the twinkle of distant stars hides, but the intriguing possibility of life elsewhere in the universe blazes bright.

"From my point of view," says Raymond, "the chance for life on other planets is looking pretty good."

Twin super-scopes join forces to spy on early solar system

photo:Like other T Tauri stars, the young DG Tau is surrounded by a disk that could eventually spawn planets. NASA / JPL

July 17, 2003

One of the major aspirations of modern astronomy is to capture the feeble light from Earth-sized planets orbiting distant stars. Taking a giant step closer to this lofty goal, a team of astronomers has combined the infrared light collected by two of the world's largest observatories and detected a ring of gas and dust swirling around a star more than 450 light-years distant.

By linking the twin 10-meter Keck telescopes on Mauna Kea in Hawaii in October 2002 and February 2003, the astronomers made detailed measurements of the young star DG Tau and its surrounding disk of hot material. The infrared observations reveal that, while the orbiting disk extends more than 4.5 billion miles from the star (as expected), its inner edge surprisingly lies at least 11 million miles from the central star.

Of the more than 100 extrasolar planets discovered, about a quarter of them lie within 10 million miles of their host star. However, DG Tau has no protoplanetary material that close to itself. The larger-than-anticipated gap between DG Tau and its disk leads astronomers to speculate that either DG Tau's disk is unusually far or that close-in planets have formed farther from their stars and eventually migrated inward.

photo:The two large Keck telscopes can combine their light-gathering power through interferometry to probe the universe deeper than any other optical telescope system on Earth. NASA / JPL

"Studies like this teach us more about how stars form … and how planets eventually form in disks around stars," states Rachel Akeson, leader of the research team and astronomer at the California Institute of Technology in Pasadena.DG Tau is a "T Tauri" star, a newborn at the youngest observable stage in its life that has yet to begin burning its hydrogen core. Brighter T Tauri stars have been seen before, but the powerful resolution of the Keck Interferometer now allows astronomers to study fainter ones like DG Tau, says Akeson.

Thanks to an amazing technique called interferometry, the giant Keck mirrors work together as a single 85-meter glass, resolving finer detail than ever before. While observing the same object, the light collected by the individual telescopes is combined to create a constructive interference pattern. It would be like throwing one rock after another into a lake at just the right pace to create a set of ripples that join up and form a larger, more powerful set of waves.

The results, to be published in an upcoming issue of The Astrophysical Journal Letters, are the first published science observations by the Keck Interferometer. These findings also represent the first complete scientific study using an interferometer in combination with adaptive optics.

Thunderstorms can drive jet streams on all giant planets

photo: Moist convection produces jet streams resembling those observed on Jupiter, Saturn, Uranus, and Neptune. NASA/JPL.

DATE: October 13, 2008

Researchers account for the different number of jet streams on the gas giants based on the expected amount of water vapor found on each planet.Turbulence generated by thunderstorms can drive the multiple east-west jet streams on the giant planets — Jupiter, Saturn, Uranus, and Neptune — and explain a long-standing conundrum concerning the puzzling differences between the two innermost gas giants, Jupiter and Saturn, and the outermost two, Uranus and Neptune.

Scientists have been trying to understand the mechanisms that form the jet streams and control their structure since the Pioneer and Voyager spacecrafts returned the first high-resolution images of the giant planets in the 1970s and 1980s.

The jet streams are narrow rivers of air that flow east-west. On Earth, they are major component of our planet's global circulation and control much of the large-scale weather that the United States and other countries outside of the tropics experience. Analogous jet streams dominate the circulation of Jupiter, Saturn, Uranus, and Neptune, reaching up to 400 mph (600 km/h) on Jupiter and nearly 900 mph (1,500 km/h) on Saturn and Neptune. The question of what causes these jet streams and sets their structure remains one of the most important unsolved problems in the study of planetary atmospheres.

Yuan Lian and Adam Showman of the University of Arizona showed how storms can generate the jet streams during Division of Planetary Sciences of the American Astronomy Society meeting in Ithaca, New York. Lian is a graduate student and Showman is a professor at the university, which is based in Tucson, Arizona.

Lian and Showman performed state-of-the-art computer simulations showing how moist convection — essentially, thunderstorms — can produce patterns of jet streams resembling those on the four giant planets. In the simulations, water vapor condensation generates small hurricane-like storms that interact with each other to form global jet streams. The study is the first to self-consistently describe both the generation of these storms and their interaction with the global circulation.

"Thunderstorms have been known to exist on Jupiter and Saturn since the early 1980s, and it has repeatedly been proposed that they drive the jet streams on these planets, but before now this idea had never been adequately tested," Lian said. "We showed that such storms can indeed drive jet streams similar to those observed."

A long-standing puzzle is the dichotomy between sister planets Jupiter and Saturn on the one hand and Uranus and Neptune on the other. "Unlike Earth, Jupiter and Saturn have about 20 jet streams each, which are associated with the banded cloud patterns on those planets," Showman said. "In contrast, Uranus and Neptune have only three jet streams each. Another conundrum is that the jet stream on the equator flows eastward on Jupiter and Saturn but westward on Uranus and Neptune. Understanding that dichotomy has been a hard nut to crack."

The simulations successfully produced about 20 jet streams each for Jupiter and Saturn and three jet streams each for Uranus and Neptune, consistent with observations. Moreover, the simulations explained the direction of the equatorial winds on all four planets — eastward on Jupiter and Saturn but westward on Uranus and Neptune.

"Previous investigations generally predicted that the equatorial jet stream would have the same direction on all four planets, inconsistent with observations," Lian added. "Our study is among the first to provide an explanation for these differences."

In the simulations, the abundance of water vapor — which is modest on Jupiter and Saturn but expected to be large on Uranus and Neptune — controlled the differences.

The storms produced in the simulations also bear an encouraging resemblance to those observed on Jupiter and Saturn, Showman noted.

Lian cautioned that much work remains to be done. "Our study provides a mechanism that can generate the jets on the giant planets. However, the wind speeds in our computer simulations are generally too weak. Overcoming this discrepancy will require continued improvements in our models."

Astronomers Discover Edge-On Protoplanetary Disk in Quadruple Star System

2002 January 07

Astronomers using the recently commissioned Gemini North telescope in Hawaii have discovered a protoplanetary disk orbiting one of the stars in a newborn quadruple star system. The dusty disk, about three times the size of Pluto's orbit around the Sun, appears nearly edge-on when viewed from Earth.This press release is issued concurrently by the Gemini Observatory, UC Berkeley, the Harvard-Smithsonian CfA and NSF's National Optical Astronomy Observatory (NOAO).

Only about 10 edge-on disks like this disk have been discovered to date. Out of these 10, two are in binary star systems, and this new object is the first one discovered in a quadruple star system. The new observations used a technique known as adaptive optics, which partially corrects for the blurring effects of the Earth's atmosphere in images of astronomical sources.

"This is a remarkable demonstration that adaptive optics can help the largest ground-based telescopes reach their full potential," said Ray Jayawardhana, a Miller Research Fellow at the University of California, Berkeley. "We now have a powerful tool to probe the evolution of protoplanetary disks and to look for newborn Jupiter-like planets."

"The new 8- to 10-meter telescopes really need adaptive optics to achieve the highest possible resolution," said the other leader of the team, Kevin Luhman of the Harvard-Smithsonian Center for Astrophysics. "Adaptive optics has come of age, and has allowed us to image a protoplanetary disk in a quadruple star system for the first time."

The findings were reported today in Washington, DC, at the 199th meeting of the American Astronomical Society by a team led by Jayawardhana and Luhman. Other members of the team are Paola D'Alessio (Instituto de Astronomia, Universidad Nacional Autonoma de Mexico) and John Stauffer (SIRTF Science Center, California Institute of Technology).

Adaptive optics works by flexing a thin mirror many times a second into just the right shape to cancel out the effects of roiling air above the telescope. The technique has become regularly available to astronomers only in the last few years. When used on large telescopes, it allows astronomers to obtain images that are as sharp and sensitive as those from space-based observatories such as the Hubble Space Telescope.

Jayawardhana, Luhman and colleagues combined the University of Hawaii's Hokupa'a adaptive optics system with the 8-meter Gemini North telescope to obtain high-resolution infrared images of a wide binary star system. This binary system is only about two million years old, and is part of a small cluster of stars known as MBM 12, located 900 light-years from Earth.

In the new high-resolution images, one of the stars is revealed to be a pair of two closely orbiting stars. What's more, astronomers saw an additional, much fainter and fuzzier object nearby, with two elongated lobes that are separated by a dark lane. This morphology is the distinct signature of a protoplanetary disk that is being viewed edge-on and is blocking the light from the star at its center. The star's light reflecting off the top and bottom surfaces of the disk produces faint nebulosities on either side of the dark lane.

"What we're looking at is an example of a dusty disk that will probably evolve into a young planetary system over the next several million years," explains Jayawardhana, lead author of a paper describing these results submitted to the Astrophysical Journal. "It's the combination of adaptive optics and a large telescope like Gemini that made this discovery possible. Thanks to these sharp images, now we can study the earliest stages of planet formation in remarkable detail."

"We would never have found this object with normal ground-based imaging. To find something this faint next to a bright star and to resolve its structure, adaptive optics on a big telescope like Gemini was essential," concurs Luhman. Normally, stars with protoplanetary disks are viewed from an angle so that we see the star easily but we see little or nothing of the disk, which is much fainter. Here, we happen to be looking from an angle where the disk blocks the star and makes its presence known."

By analyzing the infrared images of the edge-on disk and the quadruple star system, the research team can learn about both the physical properties of disks from which planets form, and the way in which stars are born in multiple star systems.

Planetary science

photo: Photograph from Apollo 15 orbital unit of the rilles in the vicinity of the crater Aristarchus on the Moon. The arrangement of the two valleys is very similar, although one third in size, to Great Hungarian Plain rivers Danube and Tisza.

Planetary science, also known as planetology and closely related to planetary astronomy, is the science of planets, or planetary systems, and the solar system. Incorporating an interdisciplinary approach, planetary science draws from diverse sciences and may be considered a part of the Earth sciences, or more logically, as its parent field. Research tends to be done by a combination of astronomy, space exploration (particularly robotic spacecraft missions), and comparative, experimental and meteorite work based on Earth. There is also an important theoretical component and considerable use of computer simulation. Astrogeology is a major component of planetary sciences.Planetology is an interdisciplinary science growing out from astronomy and earth science. Its development was determined by the increasing importance of robotics and measuring technology. In general, planetary science studies the planets, their moons, all the bodies and radiations of the Solar System, the various force fields and interactions between the several components of the Solar system.

Its relation to earth sciences

The earth science has a new discipline: geonomy, strongly related to planetary science. Geonómia is a comprehensive science encompassing earth science disciplines and extending a synthesis between them. Geonomy integrates the knowledge collected from the Earth. However, the sequence of collecting data from Earth is much different than from other planets. Earth sciences originated studies in the vicinity of human habitation, and it later expanded to embrace the entire Earth.

Planetary science began in astronomy from studies of the unresolved planets and later increased resolution concerning atmospheric and surface details. One exception was the Moon, which always exhibited details on its surface, due to its proximity to the earth. The gradual increase in instrumental resolution resulted in more detailed geological knowledge about our natural satellite. In this scientific process, astronomical telescopes (and later radio telescopes) and finally space probe robots played important roles.

Planetary science involves many disciplines, although many studies such as mineralogy, petrology, and geochemistry mainly concentrate on the earth. Today cosmochemistry, cosmopetrography, and cosmo-geochemistry also are areas of study. Meteoritics studies the rocky and mineral materials of the Solar System. (Journals concerning meteeoritics include: The Geochimica et Cosmochimica Acta, and the Meteoritics and Planetary Science.)

The most important regular annual conference of this discipline is the Lunar and Planetary Science Conference (LPSC), organized by the Lunar and Planetary Institute in Houston, at NASA Lyndon B. Johnson Space Center (JSC). Held since 1970, the 39th LPSC will occur in 2008.