Mars, methane and mysteries

Artist's impression of Mars Express

Mars may not be as dormant as scientists once thought. The 2004 discovery of methane means that either there is life on Mars, or that volcanic activity continues to generate heat below the martian surface. ESA plans to find out which it is. Either outcome is big news for a planet once thought to be biologically and geologically inactive.

The methane mystery started soon after December 2003, when ESA’s Mars Express arrived in orbit around the red planet. As the Planetary Fourier Spectrometer (PFS) began taking data, Vittorio Formisano, Istituto di Fisica dello Spazio Interplanetario CNR, Rome, and the rest of the instrument team saw a puzzling signal. As well as the atmospheric gases they were anticipating, such as carbon monoxide and water vapour, they also saw methane. “Methane was a surprise, we were not expecting that,” says Agustin Chicarro, ESA Mars Lead Scientist. The reason is that on Earth much of the methane in our atmosphere is released by evolved life forms, such as cattle digesting food. While there are ways to produce methane without life, such as by volcanic activity, it is the possible biological route that has focused attention on the discovery.

The Mars Express detection of methane is not an isolated case. While the spacecraft was en route, two independent teams of astronomers using ground-based telescopes started to see traces of methane. After five years of intensive study, the suite of observations all confirmed the discovery and presented planetary scientists with a big puzzle.

Methane is thought to be stable in the martian atmosphere for around 300 years. So, whatever is generating the methane up there, it is a recent occurrence. In January 2009, a team led by Michael Mumma of NASA’s Goddard Space Flight Center published results that the methane they saw in 2003 was concentrated in three regions of the planet. This showed that the methane was being released at the present time and was being observed before it had time to distribute itself around the planet.

Things then took a strange turn. Instead of taking 300 years to disappear, the methane had almost entirely vanished by early 2006. Clearly something unusual is going on at Mars. “We thought we understood how methane behaved on Mars but if the measurements are correct then we must be missing something big,” says Franck Lefèvre, Université Pierre et Marie Curie, CNRS, Paris and a member of Mars Express’s SPICAM instrument team.

Together with his colleague François Forget, Mars Express Interdisciplinary Scientist in charge of atmospheric studies and also of Université Pierre et Marie Curie, CNRS, Paris, Lefèvre has investigated the disappearance using a computer model of Mars’ climate. “We have tackled the problem as atmospheric physicists, without worrying about the nature of the source of the methane,” he says.

In results published last week they found that, while their computer model can reproduce atmospheric species such as carbon monoxide and ozone, it is unable to reproduce the behaviour of the methane. “Something is removing the methane from the atmosphere 600 times faster than the models can account for,” says Lefèvre. “Consequently, the source must be 600 times more intense than originally assumed, which is considerable even by Earth’s geological standards.”


To remove methane at such a rate, suspicion falls on the surface of the planet. Either the methane is being trapped in the dust there or highly reactive chemicals such as hydrogen peroxide are destroying it, as was hinted by the Viking missions in the 1970s. If the latter, then the surface is much more hostile to organic molecules (those containing carbon) than previously thought. This will make searching for traces of past or present life much tougher and future rovers will have to drill below the martian surface to look for signs of life.

To help get to the bottom of the methane mystery, ESA and the Italian space agency (ASI) are to hold a three-day international workshop in November. The assembled scientists will discuss the results and plan strategies for the future study of methane. At the workshop, the Mars Express PFS team hopes to present a global map of martian methane. “We have made the PFS mapping a priority over the last few months,” says Olivier Witasse, ESA Project Scientist for Mars Express.

In July, ESA agreed with NASA to launch joint missions to Mars. The topic of methane is of such importance that it will be most likely addressed in these future missions. “Understanding the methane on Mars is one of our top priorities,” says Witasse.

However the methane is eventually explained, it makes Mars a more fascinating place than even planetary scientists dreamed.

10 August 2009

Gamma-ray evidence suggests ancient Mars had oceans

This 3-D map superimposes gamma-ray data from Mars Odyssey's Gamma-Ray Spectrometer onto topographic data from the laser altimeter onboard the Mars Global Surveyor. The red arrow indicates the shield volcanoes of Elysium rise
in northern Mars, seen obliquely to the southeast. Blue-to-violet colors at the Elysium rise and highlands stretching to the foreground of the map mark areas poor in potassium. Red-to-yellow colors mark potassium-rich sedimentary deposits in lowlands below the Mars Pathfinder landing site (PF) and Viking 1 landing site (V1). University of Arizona

November 17, 2008

Provided by the University of Arizona

An international team of scientists reports new evidence for the controversial idea that oceans once covered about a third of ancient Mars based on data from the Gamma Ray Spectrometer onboard NASA's Mars Odyssey.

The orbiter's Gamma Ray Spectrometer (GRS), controlled by William Boynton of University of Arizona's (UA) Lunar and Planetary Laboratory, can detect elements buried as much as 13 inches (1/3 meter), below the surface by the gamma rays they emit. That capability led to the instrument's 2002 discovery of water-ice near the surface throughout much of high-latitude Mars.

"We compared Gamma Ray Spectrometer data on potassium, thorium and iron above and below a shoreline believed to mark an ancient ocean that covered a third of Mars' surface, and an inner shoreline believed to mark a younger, smaller ocean," said James M. Dohm, University of Arizona planetary geologist and leader of the international investigation.

"Our investigation posed the question, 'Might we see a greater concentration of these elements within the ancient shorelines because water and rock containing the elements moved from the highlands to the lowlands, where they eventually ponded as large water bodies?'" Dohm said.

Results from Mars Odyssey and other spacecraft suggest that past watery conditions likely leached, transported, and concentrated such elements as potassium, thorium, and iron, Dohm said. "The regions below and above the two shoreline boundaries are like cookie cutouts that can be compared to the regions above the boundaries, as well as the total region."

The younger, inner shoreline is evidence that an ocean about 10 times the size of the Mediterranean Sea, or about the size of North America, existed on the northern plains of Mars a few billion years ago. The larger, more ancient shoreline that covered a third of Mars held an ocean about 20 times the size of the Mediterranean, the researchers estimate.

The potassium-thorium-iron enriched areas occur below the older and younger paleo-ocean boundaries with respect to the entire region, they said. The scientists used data from Mars Global Surveyor's laser altimeter for topographic maps of the regions in their study.

They report their findings in the article, "GRS Evidence and the Possibility of Paleo-oceans on Mars." The article will be published in a special edition of Planetary and Space Science, which stems from a June 2007 workshop on Mars and its Earth analogs held in Trento, Italy.

Scientific debate on the existence of ancient martian oceans marked by shorelines was sparked by several studies almost 20 years ago. One such study, by Baker and colleagues at the UA Lunar and Planetary Laboratory, proposed that a few billion years ago, erupting magma unleashed floods far greater in volume than Brazil's Amazon River. The floods ponded in the northern lowlands of Mars, forming seas and lakes that triggered relatively warmer and wetter conditions that lasted tens of thousands of years.

Spacecraft images going back to Mariner 9 in the early 1970s and the Viking orbiters and landers later in the 1970s show widespread evidence for a watery past for Mars. Images and other information from a flotilla of United States and European Mars orbiters have sharpened the details in the past decade. Results from Mars Global Surveyor, Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter highlight a water-and-ice-sculpted martian landscape.

Scientists studying spacecraft images have a hard time confirming "shoreline" landforms, the researchers said, because Mars shorelines would look different from Earth's shorelines. Earth's coastal shorelines are largely a direct result of powerful tides caused by gravitational interaction between Earth and the Moon, but Mars lacks a sizable moon. Another difference is that lakes or seas on Mars could have formed largely from giant debris flows and liquefied sediments. Still another difference is that Mars oceans may have been ice-covered, which would prevent wave action.

"The GRS adds key information to the long-standing oceans-on-Mars controversy," Dohm said. "But the debate is likely to continue well into the future, perhaps even when scientists can finally walk the martian surface with instruments in hand, with a network of smarter spaceborne, airborne, and ground-based robotic systems in their midst."

Groundwater springs helped shape Mars

Iani Chaos on Mars, an area where Light Toned Deposits, or LTD, are known to be present. ESA/DLR/FU Berlin (G. Neukum)

December 12, 2008

Provided by ESA, Noordwijk, The Netherlands

Data and images from Mars Express suggest that several Light Toned Deposits (LTDs), some of the least understood features on Mars, were formed when large amounts of groundwater burst onto the surface. Scientists propose that groundwater had a greater role in shaping the martian surface than previously believed, and may have sheltered primitive life forms as the planet started drying up.

LTDs — martian sediments that most closely resemble sediments on Earth — are some of the most mysterious sediments on Mars. Causes for their origin remain unknown. Until now, different mechanisms, including volcanic processes, have been proposed for their formation.

LTDs were first discovered by the Viking spacecraft in the late 1970s and since have been at the center of scientific debate. These deposits occur on a large scale in Arabia Terra, Chaotic Terrain, and Valles Marineris, close to the Tharsis volcanic bulge. Now, based on Mars Express data, scientists propose that these sediments are actually younger than originally believed. Angelo P. Rossi and colleagues (ESA) report their findings in a paper published in September 2008. They propose that several LTDs may have been deposited by large-scale springs of groundwater that burst onto the surface, possibly at different times.

Analysis indicates that groundwater had a more wide-ranging and important role in martian history than previously believed. Hydrated minerals, relatively young in age, have been found in the region. Given that the deposits are relatively young in age, and associated with water, they may also have sheltered microbial life from the drier and harsher climate in more recent times on Mars, possibly eliminating the need for a stable atmosphere or a permanent water body.

Scientists find "missing" mineral and clues to Mars mysteries

The scene is heavily eroded terrain to the west of a small canyon in the Nili Fossae region of Mars. It was one of the first areas where researchers on the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) science team detected carbonate in Mars rocks. The spectral information comes from infrared imaging by CRISM, one of six science instruments on NASA's Mars Reconnaissance Orbiter. That coloring is overlaid on a grayscale image from the same orbiter's Context Camera. NASA/JPL/JHUAPL/MSSS/Brown University

December 22, 2008

Provided by Jet Propulsion Laboratory

Researchers using a powerful instrument aboard NASA's Mars Reconnaissance Orbiter have found a long-sought mineral on the martian surface and, with it, unexpected clues to the Red Planet's watery past.

Surveying intact bedrock layers with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), scientists found carbonate minerals, indicating that Mars had neutral to alkaline water when the minerals formed at these locations more than 3.6 billion years ago. Carbonates, which on Earth include limestone and chalk, dissolve quickly in acid. Therefore, their survival until today on Mars challenges suggestions that an exclusively acidic environment later dominated the planet. Instead, it indicates that different types of watery environments existed. The greater the variety of wet environments, the greater the chances one or more of them may have supported life.

"We're excited to have finally found carbonate minerals because they provide more detail about conditions during specific periods of Mars' history," said Scott Murchie, principal investigator for the instrument at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

The findings will appear in the December 19 issue of Science magazine and were announced December 18 at a briefing at the American Geophysical Union's Fall Meeting in San Francisco.

Carbonate rocks are created when water and carbon dioxide interact with calcium, iron or magnesium in volcanic rocks. Carbon dioxide from the atmosphere becomes trapped within the rocks. If all of the carbon dioxide locked in Earth's carbonates were released, our atmosphere would be thicker than that of Venus. Some researchers believe that a thick, carbon dioxide-rich atmosphere kept ancient Mars warm and kept water liquid on its surface long enough to have carved the valley systems observed today.

"The carbonates that CRISM has observed are regional rather than global in nature, and therefore, are too limited to account for enough carbon dioxide to form a thick atmosphere," said Bethany Ehlmann, lead author of the article and a spectrometer team member from Brown University in Providence, Rhode Island.

"Although we have not found the types of carbonate deposits which might have trapped an ancient atmosphere," Ehlmann said, "we have found evidence that not all of Mars experienced an intense, acidic weathering environment 3.5 billion years ago, as has been proposed. We've found at least one region that was potentially more hospitable to life."

The article reports clearly defined carbonate exposures in bedrock layers surrounding the 925-mile (1,490-kilometer) diameter Isidis impact basin, which formed more than 3.6 billion years ago. The best-exposed rocks occur along a trough system called Nili Fossae, which is 414 miles (670 km) long, at the edge of the basin. The region has rocks enriched in olivine, a mineral that can react with water to form carbonate.

"This discovery of carbonates in an intact rock layer, in contact with clays, is an example of how joint observations by CRISM and the telescopic cameras on the Mars Reconnaissance Orbiter are revealing details of distinct environments on Mars," said Sue Smrekar, deputy project scientist for the orbiter at NASA's Jet Propulsion Laboratory in Pasadena, California.

NASA's Phoenix Mars Lander discovered carbonates in soil samples. Researchers had previously found them in Martian meteorites that fell to Earth and in windblown Mars dust observed from orbit. However, the dust and soil could be mixtures from many areas, so the carbonates' origins have been unclear. The latest observations indicate carbonates may have formed over extended periods on early Mars. They also point to specific locations where future rovers and landers could search for possible evidence of past life.

NASA spacecraft detects buried glaciers on Mars

Artist concept of glacier on Mars. NASA/JPL

November 21, 2008

Provided by Jet Propulsion Laboratory

NASA's Mars Reconnaissance Orbiter has revealed vast martian glaciers of water ice under protective blankets of rocky debris at much lower latitudes than any ice previously identified on the Red Planet.

Scientists analyzed data from the spacecraft's ground-penetrating radar and discovered that buried glaciers extend for dozens of miles from the edges of mountains or cliffs. The group reported the results in the November 21 issue of the journal Science. A layer of rocky debris blanketing the ice may have preserved the underground glaciers as remnants from an ice sheet that covered middle latitudes during a past ice age. This discovery is similar to massive ice glaciers that have been detected under rocky coverings in Antarctica.

"Altogether, these glaciers almost certainly represent the largest reservoir of water ice on Mars that is not in the polar caps," said John W. Holt of the University of Texas at Austin, who is lead author of the report. "Just one of the features we examined is three times larger than the city of Los Angeles and up to half a mile thick. And there are many more. In addition to their scientific value, they could be a source of water to support future exploration of Mars."

Scientists have been puzzled by what are known as aprons — gently sloping areas containing rocky deposits at the bases of taller geographical features — since NASA's Viking orbiters first observed them on the martian surface in the 1970s. One theory suggests the aprons are flows of rocky debris lubricated by a small amount ice. Now, the shallow radar instrument on the Mars Reconnaissance Orbiter has provided scientists an answer to this martian puzzle.

"These results are the smoking gun pointing to the presence of large amounts of water ice at these latitudes," said Ali Safaeinili, a shallow radar instruments team member with NASA's Jet Propulsion Laboratory in Pasadena, California.

The spacecraft received radar echoes that indicate radio waves pass through the aprons and reflect off a deeper surface below without significant loss in strength. That is expected if the apron areas are composed of thick ice under a relatively thin covering. The radar does not detect reflections from the interior of these deposits as would occur if they contained significant rock debris. The apparent velocity of radio waves passing through the apron is consistent with a composition of water ice.

Scientists developed the orbiter's shallow radar instrument to examine these mid-latitude geographical features and layered deposits at the martian poles. The Italian Space Agency provided the device.

"We developed the instrument so it could operate on this kind of terrain," said Roberto Seu, leader of the instrument science team at the University of Rome La Sapienza in Italy. "It is now a priority to observe other examples of these aprons to determine whether they are also ice."

Holt and 11 co-authors report the buried glaciers lie in the Hellas Basin region of Mars' southern hemisphere. The radar also has detected similar-appearing aprons extending from cliffs in the northern hemisphere.

"There's an even larger volume of water ice in the northern deposits," said JPL geologist Jeffrey J. Plaut, who will publish results about these deposits in the American Geophysical Union's Geophysical Research Letters. "The fact these features are in the same latitude bands, about 35 to 60 degrees in both hemispheres, points to a climate-driven mechanism for explaining how they got there."

The rocky debris blanket topping the glaciers apparently has protected the ice from vaporizing, which would happen if it were exposed to the atmosphere at these latitudes.

"A key question is, how did the ice get there in the first place?" said James W. Head of Brown University in Providence, Rhode Island. "The tilt of Mars' spin axis sometimes gets much greater than it is now. Climate modeling tells us ice sheets could cover mid-latitude regions of Mars during those high-tilt periods. The buried glaciers make sense as preserved fragments from an ice age millions of years ago. On Earth, such buried glacial ice in Antarctica preserves the record of traces of ancient organisms and past climate history."

Mars on ice

photo:Spacecraft observations of Mars show different physical properties of layers in a region called Terra Meridiani. These differences suggest that the environment on this part of Mars varied through time as these layers were formed. NASA / JPL / Arizona State University

December 28, 2003

Just as an armada of probes is beginning an assault on the Red Planet, scientists have upped the ante for finding convincing evidence for similarities between our world and it. The latest findings from NASA's Mars Odyssey and Global Surveyor orbiters indicate the seemingly dry and dusty world may have recently climbed out of the grips of a true ice age. No woolly mammoths or rhinos accompanied a martian ice age, but with a familiar-sounding climate change and fresh discoveries of water-carved gullies, glacier-like flows, and buried ice, Mars may be more Earth-like than we ever thought.

By combining the latest infrared satellite maps with known patterns of past changes in Mars' orbit and tilt, a team of American and Ukrainian geologists believes the Red Planet may have been frozen in a geologically recent ice age just 400,000 to 2.1 million years ago. The proof appears to lie in layers upon layers of distinctly different rock deposits scattered from mid-latitudes to the poles that point to a variation in the environment through time as each layer formed.

Reporting their results in the December 18 issue of the journal Nature, the authors argue that, just like on Earth, variations in the obliquity of Mars' axis drives large-scale changes in climate. While Earth's axial tilt has only varied between 22 to 24.5 degrees in the past 10 million years, Mars has experienced a more extreme wobble, ranging from 14 to 48 degrees.

This epoch of higher tilt is suggested to be the very driver for inducing ice ages on Mars that brought the distribution of water-ice from the polar regions down to mid-latitudes equivalent to southern United States and Saudi Arabia here on Earth. As the maritan poles warmed, water vapor formed and crept to the southernly latitudes where they got dumped as ice water mixed with dust. Glaciers may have overrun Mars of the past. Now, in a warmer, interglacial period, this thick deposit is in the process of degrading and retreating.

"These results show Mars is not a dead planet, but it undergoes climate changes that are even more pronounced than on Earth," says team leader James Head of Brown University.

This research bodes well for NASA and their 'follow-the-water' strategy for Mars exploration. "The extreme climate changes on Mars are providing us with predictions we can test with upcoming Mars missions, such as Europe's Mars Express and NASA's Mars Exploration Rovers," explains team member and Brown scientist John Mustard.

With a sensitive climate so similar to that of the Earth, hopes have been raised that our neighboring planet may indeed hold promise of present-day water. "Among the climate changes that occurred during these extremes is warming of the poles and partial melting of water at high altitudes," Mustard continues. "This clearly broadens the environments in which life might occur on Mars."

Rocks on Mars hold key to climate history

photo: Sequences of cyclic sedimentary rock layers exposed in an unnamed crater in Arabia Terra, Mars. Topography, Caltech; HiRISE Image, NASA/JPL/University of Arizona


Scientists found evidence of ancient climate change on Mars caused by regular variation in the planet's tilt. On Earth, similar "astronomical forcing" of climate drives ice-age cycles.

Provided by Caltech, Pasadena, California
December 5, 2008

Using stereo topographic maps obtained by processing data from the high-resolution camera onboard NASA's Mars Reconnaissance Orbiter, Caltech scientists Kevin Lewis, Oded Aharonson, and John Grotzinger, identified and measured layered rock outcrops within four craters in the Red Planet's Arabia Terra region. The layering in different outcrops occurs at scales ranging from a few meters to tens of meters, but at each location the layers all have similar thicknesses and exhibit similar features.

Based on a pattern of layers within layers measured at Becquerel crater, the scientists propose that each layer formed during a period of about 100,000 years and that the same cyclical climate changes produced these layers.

In addition, every 10 layers were bundled together into larger units, which were laid down during an approximately one-million-year period. In the Becquerel crater, the 10-layer pattern is repeated at least 10 times. This one-million-year cycle corresponds to a known pattern of change in Mars' obliquity caused by solar system dynamics .

"Due to the scale of the layers, small variations in Mars' orbit are the best candidate for the implied climate changes. These are the very same changes that have been shown to set the pacing of ice ages on the Earth and can also lead to cyclic layering of sediments," said Lewis.

Earth's tilt on its axis varies between 22.1 and 24.5° over a 41,000-year period. The tilt is responsible for seasonal variation in climate, because the portion of Earth that is tipped toward the Sun receives more sunlight hours during a day and gradually changes throughout the year. During phases of lower obliquity, polar regions are less subject to seasonal variations, leading to periods of glaciation.

Mars' tilt varies by tens of degrees throughout a 100,000-year cycle, producing even more dramatic variation. When the obliquity is low, the poles are the coldest places on the planet, while the Sun is located near the equator all the time. This could cause volatiles in the atmosphere, like water and carbon dioxide, to migrate poleward, where they'd be locked up as ice.

When the obliquity is higher, the poles get relatively more sunlight, and those materials would migrate away. "That affects the volatiles budget. If you move carbon dioxide away from the poles, the atmospheric pressure would increase, which may cause a difference in the ability of winds to transport and deposit sand," Aharonson said. This is one effect that could change the layers' deposition rate such as those seen by the researchers in the four craters.

The changing tilt would also change the stability of surface water, which alters the ability of sand grains to stick together and cement to form the rock layers.

"The whole climate system would be different," Aharonson said.

However, such large climate changes would influence a variety of geologic processes on the surface. While the researchers cannot tie the formation of the rhythmic bedding on Mars to any particular geologic process, "strength of the paper is that we can draw conclusions without having to specify the precise depositional process," Aharonson said.

"This study gives us a hint of how the ancient climate of Mars operated and shows a much more predictable and regular environment than you would guess from other geologic features that indicate catastrophic floods, volcanic eruptions, and impact events," Lewis said. "More work will be required to understand the full extent of the information contained within these natural geologic archives," he said.

"One of the fun things about this project is that we were able to use techniques on Mars that are the bread and butter of studies of stratigraphy on Earth," said Aharonson. "We substituted a high-resolution camera in orbit around Mars and stereo processing for a geologist's Brunton Compass and mapboard, and were able to derive the same quantitative information on the same scale. This enabled conclusions that have qualitative meaning similar to those we chase on Earth."

Frost on Mars

This image shows bluish-white frost seen on the Martian surface near NASA's Phoenix Mars Lander. The image was taken by the lander's Surface Stereo Imager on the 131st Martian day, or sol, of the mission (Oct. 7, 2008). Frost is expected to continue to appear in images as fall, then winter approach Mars' northern plains.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

Image credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University

Date: October 8, 2008

Mars May Be Cozy Place for Hardy Microbes

October 19, 2006

A class of especially hardy microbes that live in some of the harshest Earthly environments could flourish on cold Mars and other chilly planets, according to a research team of astronomers and microbiologists.

In a two-year laboratory study, the researchers discovered that some cold-adapted microorganisms not only survived but reproduced at 30 degrees Fahrenheit, just below the freezing point of water. The microbes also developed a defense mechanism that protected them from cold temperatures. The researchers are members of a unique collaboration of astronomers from the Space Telescope Science Institute and microbiologists from the University of Maryland Biotechnology Institute's Center of Marine Biotechnology in Baltimore, Md. Their results appear on the International Journal of Astrobiology website.

"The low temperature limit for life is particularly important since, in both the solar system and the Milky Way Galaxy, cold environments are much more common than hot environments," said Neill Reid, an astronomer at the Space Telescope Science Institute and leader of the research team. "Our results show that the lowest temperatures at which these organisms can thrive fall within the temperature range experienced on present-day Mars, and could permit survival and growth, particularly beneath Mars's surface. This could expand the realm of the habitable zone, the area in which life could exist, to colder Mars-like planets."

Most stars in our galaxy are cooler than our Sun. The zone around these stars that is suitable for Earth-like temperatures would be smaller and narrower than the so-called habitable zone around our Sun. Therefore, the majority of planets would likely be colder than Earth.

In their two-year study, the scientists tested the coldest temperature limits for two types of one-cell organisms: halophiles and methanogens. They are among a group of microbes collectively called extremophiles, so-named because they live in hot springs, acidic fields, salty lakes, and polar ice caps under conditions that would kill humans, animals, and plants. Halophiles flourish in salty water, such as the Great Salt Lake, and have DNA repair systems to protect them from extremely high radiation doses. Methanogens are capable of growth on simple compounds like hydrogen and carbon dioxide for energy and can turn their waste into methane.

The halophiles and methanogens used in the experiments are from Antarctic lakes. In the laboratory, the halophiles displayed significant growth to 30 degrees Fahrenheit (minus 1 degree Celsius). The methanogens were active to 28 degrees Fahrenheit (minus 2 degrees Celsius).

"We have extended the lower temperature limits for these species by several degrees," said Shiladitya DasSarma, a professor and a leader of the team at the Center of Marine Biotechnology, University of Maryland Biotechnology Institute. "We had a limited amount of time to grow the organisms in culture, on the order of months. If we could extend the growth time, I think we could lower the temperatures at which they can survive even more. The brine culture in which they grow in the laboratory can remain in liquid form to minus 18 degrees Fahrenheit (minus 28 degrees Celsius), so the potential is there for significantly lower growth temperatures."

The scientists also were surprised to find that the halophiles and methanogens protected themselves from frigid temperatures. Some arctic bacteria show similar behavior.

"These organisms are highly adaptable, and at low temperatures they formed cellular aggregates," DasSarma explained. "This was a striking result, which suggests that cells may ‘stick together' when temperatures become too cold for growth, providing ways of survival as a population. This is the first detection of this phenomenon in Antarctic species of extremophiles at cold temperatures."

The scientists selected these extremophiles for the laboratory study because they are potentially relevant to life on cold, dry Mars. Halophiles could thrive in salty water underneath Mars's surface, which can remain liquid at temperatures well below 32 degrees Fahrenheit (0 degrees Celsius). Methanogens could survive on a planet without oxygen, such as Mars. In fact, some scientists have proposed that methanogens produced the methane detected in Mars's atmosphere.

"This finding demonstrates that rigorous scientific studies on known extremophiles on Earth can provide clues to how life may survive elsewhere in the universe," DasSarma said.

The researchers next plan to map the complete genetic blueprint for each extremophile. By inventorying all of the genes, scientists will be able to determine the functions of each gene, such as pinpointing the genes that protect an organism from the cold.

Many extremophiles are evolutionary relics called Archaea, which may have been among the first homesteaders on Earth 3.5 billion years ago. These robust extremophiles may be able to survive in many places in the universe, including some of the roughly 200 worlds around stars outside our solar system that astronomers have found over the past decade. These planets are in a wide range of environments, from so-called "hot Jupiters," which orbit close to their stars and where temperatures exceed 1,800 degrees Fahrenheit (1,000 degrees Celsius), to gas giants in Jupiter-like orbits, where temperatures are around minus 238 degrees Fahrenheit (minus 150 degrees Celsius).

The discovery of planets with huge temperature disparities has scientists wondering what environments could be hospitable to life. A key factor in an organism's survival is determining the upper and lower temperature limits at which it can live.

Although Martian weather conditions are extreme, the planet does share some similarities with the most extreme cold regions of Earth, such as Antarctica. Long regarded as essentially barren of life, recent investigations of Antarctic environments have revealed considerable microbial activity. "The Archaea and bacteria that have adapted to these extreme conditions are some of the best candidates for terrestrial analogues of potential extraterrestrial life; understanding their adaptive strategy, and its limitations, will provide deeper insight into fundamental constraints on the range of hospitable environments," DasSarma said.

The team's research was supported through grants from the Space Telescope Science Institute's Director's Discretionary Research Fund, a National Science Foundation, and the Australian Research Council.

The Space Telescope Science Institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington.

One of five centers forming the University of Maryland Biotechnology Institute (UMBI) the Center of Marine Biotechnology, located in Baltimore's Inner Harbor, employs researchers who apply the tools of modern biology and biotechnology to study, protect, and enhance marine and estuarine resources.

Deep down, Mars is a softie

photo: This artistic depiction of the martian interior shows a large, hot, molten core with a radius that's about half as large as the planet's. The core is mostly iron but contains some lighter elements as well. The mantle is the darker material between the core and the thin crust. JPL / NASA

Date: March 12, 2003

Mars may be the god of war, but its namesake planet apparently has a soft heart. Information from the orbiting Mars Global Surveyor spacecraft suggests the martian core is at least partially fluid.

In a paper published online by Science on March 7, a team of scientists from the Jet Propulsion Laboratory (JPL) and California Institute of Technology report on their analysis of more than three years of orbital data from Mars Global Surveyor."Mars is influenced by the gravitational pull of the sun," explains lead author and JPL planetary scientist Charles Yoder. "This causes a solid body tide with a bulge toward and away from the sun." This is similar to the ocean tides our moon causes on Earth. However, the tidal changes on Mars measure less than a centimeter — tiny compared to Earth's tides.

"The tidal bulge is a very small but detectable force on the spacecraft," says JPL co-author Alex Konopliv. "It causes a drift in the tilt of the spacecraft's orbit around Mars of one-thousandth of a degree over a month."

"By measuring this bulge in the Mars gravity field we can determine how flexible Mars is," Yoder adds. "The size of the measured tide is large enough to indicate the core of Mars can not be solid iron but must be at least partially liquid."

The martian core may be entirely molten, or it may be like Earth's — solid on the inside with a liquid outer core.

Yoder and his colleagues partnered the orbital data from Global Surveyor with earlier data about Mars's precession from the Mars Pathfinder and Viking landers to learn more about the Red Planet's core. (For instance, a faster precession rate is indicative of a larger dense core.) From this, the team determined that the size of the core is about half that of the planet's size — like the cores of Venus and Earth. Additionally, this size suggests the martian core isn't completely iron but contains a significant amount of a lighter element such as sulfur or hydrogen, the team reports.

An Icy Discovery on Mars, but Where’s the Water?

Photo: A layer of water frost is seen near the Phoenix Mars lander, but the frost was gone after 6 a.m. (NASA/JPL-Caltech)

After a much ballyhooed discovery two months ago of water ice in the northern plains of Mars, scientists are now perplexed by the water that NASA’s Phoenix Mars lander has not found.A few years ago, the Mars Odyssey spacecraft found, from orbit, signs of vast quantities of water ice a few inches below the planet’s surface. In July, mission scientists confirmed that patches of white seen in the soil near the lander were indeed ice. Phoenix’s weather station has also detected wisps of water vapor in the thin Martian air, and scientists expected that as the nighttime temperature plunged to minus-110 degrees Fahrenheit from minus-20 — and with it the amount of moisture that the Martian air can hold — minuscule specks of moisture would glom onto dust particles at the surface. The presence of water would show up in electrical measurements by a probe stuck into the soil. Except Mars has not cooperated.“We’re seeing nothing,” said Aaron Zent of the NASA Ames Research Center at Moffett Field, Calif., the lead scientist for Phoenix’s thermal and electroconductivity probe. “Big fat nothing.”Actually, the first measurement did yield the expected readings. “A lovely signal,” Dr. Zent said. “But we never saw it again.”Every subsequent measurement, taken at almost all hours of the day, indicated dry soil.

On Earth, dropping moisture level in the air leads to the condensation of morning dew; on Mars, because the water layer on the dust particles would be only a couple of molecules thick, it would not freeze into the crystal structure of ice, but instead remain more liquidlike, with molecules able to move along the surface of the grains.The moisture in the air during the day has to go somewhere at night, and that somewhere seems almost certain to be the soil. “It has to,” Dr. Zent said. “There’s no other place for it to go. The soil is sucking it up at night. We certainly expect that we should be able to see some of this.”

Dr. Zent said that perhaps the signal was more subtle than expected. It is possible that the water layer is somehow thick enough to freeze into ice, which would not show the expected electrical behavior. (Photographs of the landscape do show frost on the ground in the morning.) Or the water layer is so thin that the molecules bind tightly to the dirt; that, too, would suppress the electrical signal.The next step is for Phoenix to jam its electroconductivity probe deeper into the soil, closer to the ice layer. Maybe then, Phoenix will once again discover water.