|Texture of landing sites. Upper left, the moon; upper right, Venus; middle left, Pathfinder 1997 Mars; middle right, Viking 1977 Mars; lower left, airbag imprint in Eagle Crater, Meridiani Planum 2004; lower right, airbag drag mark, Meridiani Planum, 2004 Opportunity site. The 1997 Sojourner rover never was able to travel far from its lander but in any case, the nearly twenty percent coverage of the ground by large rocks would have made its traverse challenging if not impossible. The two Viking landers from 1976-77 had no roving capabilities but lasted in place for nearly a decade using nuclear powered generators. This current generation of rovers is more limited in their expected lifetimes, owing to dust coverage of their solar panels and slow mechanical breaks.
Six years ago, then NASA Associate Administrator Wesley Huntress, Jr., stated , "Wherever liquid water and chemical energy are found, there is life. There is no exception." Few opportune years like 2004 have presented astrobiology with as many remarkable vistas and fresh perspectives on this fundamental triad of water, chemical energy and life.
Consider this year’s accomplishments of those dedicated to searching for life in the universe.
Landing on Mars not once, but twice. Then finding evidence for water on opposite sides of the red planet. Picking up what appears to be methane signals in the martian atmosphere, one of the residues that might prove one day to be the product of underground biology. Scientists began to discuss seriously what colonization strategies make sense.
Flying through the tail of a comet and heading home after collecting the first extraterrestrial samples from such dusty iceballs. Launching the Deep Impact probe to smash into a comet and watch how the dust and ice get kicked up.
Filling the astronomy catalogs with well over a hundred new planets, including what may prove to be the first visible exoplanet. Finding some nearby candidates that might occupy temperate locations or safely orbit Sun-like stars.
The editors of Astrobiology Magazine revisit the highlights of the year and where possible point to one of the strongest lineups ever for beginning a new turn of the calendar. Between the marathon still being run by the twin Mars rovers and the expected descent to Saturn’s moon, Titan, next year promises no letdowns.
Number one on the countdown of 2004 highlights was the Opportunity mission to Mars.
On January 25, Opportunity landed on Mars. The landing site, Meridiani Planum, was the flattest location scouted in the history of Mars exploration. Meridiani also offered some of the most unique geochemistry seen on the red planet, so scientists set their sights on finding water–or at least, the remnant evidence that water once existed on what today is a dust bowl.
|The spherules, blueberries and naming have become important to clues on an alien landscape.
The Opportunity exploration team was not to be disappointed in 2004.
The rover’s story, as detailed in the eleven Science papers published in December, is mainly one about water and salt.
Sedimentary rocks Opportunity examined, "clearly preserve a record of environmental conditions different from any on Mars today," report 50 rover-team scientists led by Dr. Steve Squyres of Cornell University, Ithaca, N.Y. and Dr. Ray Arvidson of Washington University, St. Louis, Mo.
"Liquid water was once intermittently present at the Martian surface at Meridiani, and at times it saturated the subsurface. Because liquid water is a key prerequisite for life, we infer conditions at Meridiani may have been habitable for some period of time in Martian history," according to Squires, Arvidson and other co-authors.
One type of evidence that Meridiani was wet is the composition of rocks there. The rocks have a high and variable ratio of bromine to chlorine; indicating "the past presence of large amounts of water," write Dr. Rudi Rieder and Dr. Ralf Gellert of Max-Planck-Institute for Chemistry, Mainz, Germany, and co-authors.
|Cover of Science Magazine devoted to Opportunity rover initial results.
Their paper and another by Dr. Phil Christensen of Arizona State University, Tempe, and collaborators report an abundance of sulfur-rich minerals in the rocks, another clue to a watery past. Clinching the case is identification of a hydrated iron-sulfate salt called jarosite in the rocks, as reported by Dr. Goestar Klingelhoefer of the University of Mainz, and Dr. Richard Morris of NASA’s Johnson Space Center, Houston, and co-authors.
If life ever did exist at Meridiani, the type of rocks found there could be good preservers of fossils, according to Squyres, Dr. John Grotzinger of the Massachusetts Institute of Technology, Cambridge, and co-authors.
What does this synopsis say about martian habitability? One thing the Viking probes found in the 1970’s was Mars is rusting. Indeed the soil was considered highly reactive and oxidizing with the corrosive strength of hydrogen peroxides. The challenge for life at Meridiani is daunting. To survive requires tolerance for extreme conditions: supercold, salty and acidic. While individually not outside the bounds of Earth organisms, the biological hurdle is a challenging one.
A supercold world of acidic brines may have once been the best description of Mars.
– Mars Reconnaissance Orbiter (MRO) launch, Mars Orbiter to collect high-resolution, 1-meter, images in stereo-view of Mars
– European Venus Express, Venus Orbiter for two-year nominal mapping life [486 days, two Venus year]
– New Horizons, Pluto and moon Charon flyby, mapping to outer solar system cometary fields and Kuiper Belt
– Dawn, Asteroid Ceres and Vesta rendezvous and orbiter, including investigations of asteroid water and influence on meteors
– Kepler, Extrasolar Terrestrial Planet Detection Mission, designed to look for transiting or earth-size planets that eclipse their parent stars [survey 100,000 stars]
– Europa Orbiter, planned Orbiter of Jupiters ice-covered moon, Europa, uses a radar sounder to bounce radio waves through the ice
– Japanese SELENE Lunar Orbiter and Lander, to probe the origin and evolution of the moon
– Japanese Planet-C Venus Orbiter, to study the Venusian atmosphere, lightning, and volcanoes.
– Mars Scout mission, final selections August 2003 from four Scouts: SCIM, ARES, MARVEL and Phoenix
– French Mars Remote Sensing Orbiter and four small Netlanders, linked by Italian communications orbiter
– BepiColumbo, European Mercury Orbiters and Lander, including Japanese collaborators, lander to operate for one week on surface
– Mars 2009, proposed long-range rover to demonstrate hazard avoidance and accurate landing dynamics
Related Web Pages
2003: Year in Review
Solar System Exploration Survey
Mars Opportunity Rover
Mars Spirit Rover
Planet Ten: Beyond Pluto?