Is there life on Mars?
UH team tackles the question
Co-investigators in front of a thermal-image mural of the Mars equator. Click for larger version.
Bring astronomers, chemists, computer scientists, geologists and oceanographers together, and Mars is the limit...or, rather, the beginning. An interdisciplinary University of Hawaiʻi at Mānoa group commissioned by NASA’s Astrobiology Institute is one of 16 astrobiology lead teams in the nation seeking extraterrestrial life.
The UH group, which has a five-year, $5 million research budget, is unique in two ways—it is the only team with all members on one campus, and it coalesces around the theme of water.
It’s the water
Karen Meech captured the image of target comet Tempel 1, inset on NASA’s depiction of the impactor departing the flyby craft. Click for larger version.
In the laboratory (top), co-investigator Ralf Kaiser’s group simulates the conditions in space and on planets to identify environments that can form the molecules necessary for life.
In the field, scientists investigate the extraterrestrial-like conditions of extreme Earth environments from mountain top lakes to seafloor vents. Above, a drill rig was used to sample bacteria living under Iceland’s Grimsvötn glacier during a 2002 expedition led by astrobiology co-investigator Eric Gaidos.
"Water is the medium of life and the major component of cells," explains the Institute of Astronomy’s Karen Meech, UH team leader. Liquid at a wide range of temperatures, it sustains life functions, regulates geologic activity and creates favorable environmental conditions, she says. Water interacts in the rising, cooling and sinking of Earth’s crust, keeping it from getting stiff. Thermal currents in the ocean buffer the continents, keeping land habitats suitable for life.
So the search for life is the search for water. And there is evidence that there is, or was, water on Mars. It is certainly present in the polar ice caps. Elsewhere on the red planet, evidence is circumstantial.
Mapping by orbital surveyors depicts gullies and moraines like those associated with glaciers on Earth. In computer models, tectonic activity alone cannot fully explain the formation of Valles Marineris, a feature six times the depth of the Grand Canyon and the length of the United States. Gamma ray analysis indicates there is more hydrogen-the H in H2O-on Mars than expected, perhaps as permafrost in the upper layers of soil, says planetary geophysicist and astrobiology team member Scott Anderson. Thermal emission spectrometry detected an area the size of Connecticut strewn with microscopic pebbles of hematite called blueberries.
"There are many ways to form hematite, and many of them involve water," says geologist Victoria Hamilton, one of several UH faculty members pursuing Mars research outside of the astrobiology effort. Hawaiʻi Institute of Geophysics and Planetology colleague Peter Mouginis-Mark, who is following the progress of the Mars rovers Spirit and Opportunity, says jarosite also appears to be present, a mineral that forms over long periods of time in water. Ripples and sedimentary layers recorded by the rovers’ cameras may also be signs of a once-shallow sea on a now dusty Martian plain.
Where did the water come from? It is found in the interstellar medium and the denser molecular clouds that give rise to star-forming regions. It was present in our universe when grains clumped together to form planetary bodies. The Institute for Astronomy’s Bo Reipurth is examining the interstellar medium while Meech and David Jewitt pursue the evidence preserved in the comets. Since the planets formed a few billion years ago, these "big dirty snowballs" have held the "leftover junk" in cold storage, says Meech. Under the cosmically weathered surface, the pristine interior holds a chemical record of our early planet. NASA’s Deep Impact mission, set to launch Jan. 8 and collide with comet Tempel 1 in July, aims to give scientists a peek. Meech is a co-investigator on the mission.
There’s more to life
Water, alone, is insufficient for life. An energy source is a must, and the sun isn’t always available. Life may have originated near high-temperature water-rock interactions, now occurring in places like Yellowstone geysers and undersea vents near Lōʻihi. James Cowen, David Karl and Michael Mottl from the School of Ocean and Earth Science and Technology are studying the microbiology and geochemistry of seafloor thermal vents to understand the life-forms there and on early Earth.
Mars and Jupiter’s satellite Europa, the other habitats in the Solar System where life might exist, are cold and icy, however. "In the search for analogous environments on Earth, what you’re looking for is ice and volcanoes," says SOEST geobiologist Eric Gaidos.
He finds both in Iceland. The island is ideally situated—on the arctic circle and above the mid-Atlantic ridge. It is home to Vatnajökull, the largest ice sheet in Europe, which lies atop Grimsvötn, one of the most active volcanoes in the world. Eruptions beneath the aptly named "water glacier" melt large amounts of ice, creating subglacial lakes that occasionally burst from under the ice in massive floods.
Grimsvötn is a plausible small-scale analog for Mars, and it harbors life. In 2002, Gaidos and his U.S. and Icelandic colleagues drilled through the ice. They found a microbial community in the water and sediment below. DNA studies show a microbe population distinct from that of nearby snow, ice and hot springs.
"They’re not contamination from another source, they actually grow there," says Gaidos, a physicist with a bent for biology. The lake isn’t completely sealed from the outside world—surface snow is compacted and buried, eventually cycling down and melting. Still, the ice acts as a bottleneck through which microbes must pass to colonize this extreme environment. So the focus isn’t on how life originates or evolves, but how it colonizes, how it survives and, ultimately, what "footprints" it leaves behind. These become the signs to look for in exploring extraterrestrial environments for life.
If there’s life on Mars, it’s not going to jump up and introduce itself," says Gaidos. "The signature may be very subtle."
A carbon copy
Life also requires a source of carbon and potential nutrients. These too can be found in comets, suggesting their presence in the pre-planet solar nebula. They may also have been delivered to Earth, and possibly Venus and Mars, via meteorite. Klaus Keil and others at UH are slicing and examining meteorites to identify when and where they formed and how much material they delivered to earth. The National Science foundation and NASA fund an annual meteorite hunt in Antarctica; Joseph Boyce is the latest UH participant, spending Christmas 2004 on the ice.
Most meteorites are very old, Hamilton says, but the 32 known Martian meteorites are relatively young, at age 1 billion or so. Zagami, whose fall was documented in Nigeria in the 1800s, provides evidence of Mars’ volcanic activity and gas bubbles that yield samples of the Mars atmosphere. Hamilton uses thermal emission spectrometry to determine the fingerprint for earthly and meteoritic minerals and rocks. Her spectra of Martian meteorites helped identify similar spectra on Mars, and she hopes to use the complete catalog as a basis for comparison with spectra readings from throughout the solar system.
Anderson uses similar technology to sample for complex organic compounds such as hopanes, isoprenoids and steranes, common building blocks of cell walls on Earth. During three weeks on the Arctic ice in fall 2001, he and colleagues successfully tested Cryobot, a self-contained drilling robot that melts its way through the ice to sample what's below. The team is now working to miniaturize a mass spectrometer and the electronics to run it, capable of running on solar energy and surviving a drop onto Mars.
Why not fly samples back to existing Earth-based labs, ? la moon rocks? Anderson, who helped operate the Odyssey orbiter at NASA's Jet Propulsion Laboratory before coming to UH, says a return spacecraft would probably increase costs five-fold. (Relatively cheap one-way missions cost taxpayers about 15 cents a year.) Until we know more about what’s there, he adds, we don’t know the "right" rock to bring back.
It takes chemistry
Excitement mounted when carbon was found in a meteorite a few years ago and methane detected on Mars more recently. Neither was proof of life. Both elements could have originated in either biologic or standard chemical processes, says Ralf Kaiser, an astrochemist inspired by the popularity of Star Trek in his native Germany.
The cold clouds of space contain 130 different molecules. Many, including sugars and amino acids, are important to life. Kaiser’s Reaction Dynamics group in the Department of Chemistry uses laboratory equipment to simulate conditions of space, planets or even combustible flames. They can condense H2O and CO2 ice, create temperatures from 10 to a few hundred degrees Kelvin and duplicate the particle-charging effect of solar wind.
The group seeks to answer questions such as whether H2CO3, an acid that is unstable under standard conditions on Earth, might influence the pH balance on other planets, affecting the geochemistry by dissolving different minerals. Radiation is an important factor too, given the thin atmosphere on planets like Mars.
"When you understand which environment can form the molecules necessary for life, then you can predict where they might form," Kaiser says. "To be 100 percent sure life is present, you have to find life".
Looking beyond Mars, Gaidos studies Jupiter’s moon Europa, and Anderson is interested in Venus. Kaiser eagerly awaits results from the Huygens probe, due to drop from the Cassini orbiter Jan. 14, 2005, parachute through the thick atmosphere of Saturn’s moon Titan and look for molecules and chemical interactions similar to what took place on early pre-biotic Earth.
"The next generation will reap the rewards of our work. We’ll tell them where to go." says Gaidos. Among the up-and-comers are eight postdoctoral researchers Meech calls "the glue that holds it all together."
Manned missions will come in time, and new targets. There are 110 known planets outside our solar system, so far identified only by the gravitational tug they exert, Meech points out. Mars is just the beginning.