by Eric Jaffe
Grant, no longer a kid in stature if still in spirit, now plays a substantial role in setting those odds.
The geologist at the Center for Earth and Planetary Studies, part of
the National Air and Space Museum, is one of a half dozen scientists
in charge of creating itineraries for Spirit and Opportunity, the
two NASA rovers that since early 2004 have explored Mars for signs
of life, past or present.
They lack the equipment to analyze organic compounds or examine fossils. (The mission's running joke, says Grant, is that a rover will spot a dinosaur bone and be unable to retrieve it.)
These tasks are reserved for the Mars Science Laboratory mission, scheduled for 2010.
The search for life in the universe, however, isn't confined to the rovers' path.
For that matter, it's no longer limited to Mars, or even the Earth's solar system. More and more, astronomers at labs and observatories around the world are finding evidence for the foundations of life - foremost, water - in our planet cluster and beyond.
That column received another check in mid June, when a group of scientists revived the idea that a vast ocean once existed on the northern hemisphere of Mars.
decades ago, scientists analyzed images of this region and found
what seemed to be a shoreline. But an ocean shoreline has a uniform
elevation, and later topographical tests revealed great variation - in
some places, more than a mile separated the terrain's peaks and
Whether scientists can dig into the planet's surface and find evidence of water - and with it signatures of life - remains to be seen.
Whether they can identity those signatures accurately is even another question. Still, the new work invites a fresh topic to a conversation that has focused on the rovers' images, writes Maria Zuber of the Massachusetts Institute of Technology, who was not associated with the study, in an accompanying commentary.
Europa circles Jupiter every few days, and this rapid orbit
generates friction that heats up the moon's interior. For that
reason, some feel that an enormous salty ocean still exists beneath
Europa's frozen surface, containing perhaps twice as much liquid as
all the Earth's oceans combined.
Algae, bacteria and even animals exist in similar conditions in Antarctica, often living under ice shelves.
Because Europa is bombarded by radiation, Earth-like organisms could not live on the surface.
they might exist just several feet below in visible cracks. In
recent papers and talks, Jere Lipps of the University of California,
Berkeley, has outlined several ways in which life on Europa, or its
remains, might be exposed to the surface - and likewise to rovers or
orbiters sent to study the moon. These include places where ice has
cracked and refrozen with life trapped inside; blocks of ice that
have broken off, flipped over and now face the surface; and debris
lodged in ridges or deep crevices.
While Europa and other sites near Earth, such as Saturn's moon Titan, remain promising places to find water, some scientists have set their sights far beyond this solar system.
Recently, Travis Barman of Lowell Observatory in Flagstaff, Arizona,
detected water in the atmosphere of a planet some 150 light years
away - the first such evidence for a planet outside Earth's cluster.
When he compared his models to images of HD 209458b from the Hubble telescope, those that included water in the atmosphere proved accurate, he reports in the June 1 Astrophysical Letters.
An artist's impression shows an extended ellipsoidal envelope of oxygen and carbon discovered around the extrasolar planet HD 209458b.
Credit: European Space Agency and Alfred Vidal-Madjar
(Institut d'Astrophysique de Paris, CNRS, France)
A couple weeks later, a team of European researchers announced another breakthrough outside this solar system: the discovery of a planet incredibly similar to Earth.
The planet, some 20 light years
away and five times the mass of Earth, circles the
star Gliese 581.
Several years ago, scientists found another planet - this one similar
to Venus - orbiting this same star.
But because Gliese is smaller than the Sun, the temperature on this planet's surface could be amenable to liquid water, the researchers report in an upcoming issue of Astronomy & Astrophysics.
In the end, though, watery conditions, or even water itself, can only tell so much of the story of life beyond Earth.
The conclusion must wait until more powerful tools or more precise explorations turn mere suggestion into solid proof.