Scientists don't know how much water might once have existed on Mars, but they
suspect there might have been periods when the planet had lakes and oceans.
If so, where did the water go?
One theory is that asteroid impacts early in the history of Mars, depicted
above, might be to blame. Climate change
may also be responsible. Whatever the causes, recent observations show there
is plenty
left, frozen at the poles and in the soil at other latitudes.
The big question, of course, is whether there ever was or is life on the red
planet.
The European Space Agency's Mars Express orbiter, with its Beagle 2 lander,
is taking a long-shot approach at answering that question.
"Meteorites from Mars that have landed on Earth show clear evidence that conditions
appropriate to life did exist on the planet, including in the recent past,"
says Colin Pillinger, consortium leader for Beagle 2 at the Open University
in the UK. "However, features in the meteorites which have been described as
nanofossils are highly controversial. Unfortunately, we cannot be sure that
organic matter found in the meteorites is the remnant of organisms that lived
on Mars and not due to contamination on Earth. We need to repeat the experiments
on rocks that never left the Red Planet."
Beagle 2 will measure the ratio of two types of carbon in Mars rocks. Biological
processes on Earth create more of a certain isotope, carbon-12, compared to
carbon-13. So a preponderance of carbon-12 is taken as evidence of life. On
Earth, the testing has been used to suggest past life even in rocks that are
billions of years old.
If the same process has occurred on Mars, Beagle 2 could suggest one of the
most important discoveries in the history of exploration. Many scientists, however,
doubt that finding evidence for life on Mars will be easy. So if Beagle 2 comes
up dry, or if it finds only suggestive evidence, the search for cosmic neighbors
is sure to continue. [Mission coverage]
