"We may have to revise some of the previous views," said Mars Express
investigator Gerhard Neukum of Freie Universität in Berlin. "It wasn't
so warm and not so wet in much of its time."
Neukum and several other Mar Express researchers announced the latest
findings at a European Space Agency/NASA press conference in
Paris, France, on Wednesday.
Among the evidence against Martian seas is the now-confirmed absence of
any telltale spectral signatures of the water-formed minerals known as
carbonates on Mars' surface.
Stranger, however, is the discovery that
even in Mars' water-carved canyons there is no sign of any water-made
minerals, said Mars Express investigator Jean-Pierre Bibring of the
Institut d'Astrophysique Spatiale in Orsay, France.
Instead, such minerals as clays, which require water to form, are found
on odd patches in the cratered landscape, where rocks from Mars' earliest
history may be exposed, said Bibring.
More importantly, it's in those clays, which come from the only
potentially Earth-like period of Mars' history, that we'd have the best
chances of finding evidence of early Martian life, he said.
High-resolution stereo imaging by Mars Express has also revealed far
more recently glaciated landscape and even what appears to be a lava
flow that ends in long, abrupt wall.
The wall appears to be where the
molten rock ran into now-evaporated glaciers just tens of millions of
years ago, said Neukum.
Mars Express has also begun looking under the Martian surface with
radar. Already, the ground-penetrating radar has revealed the first in
what may be a hidden population of buried ancient craters, possibly
soaked with frozen water.
The radar has also uncovered evidence that the
North Pole ice cap is made of more than a mile deep of nearly pure water
ice, said NASA's Jeffrey Plaut, a principal investigator for the
Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument
(MARSIS).
"We have no convincing evidence yet of subsurface liquid water," said
Plaut.
But that could change as the spacecraft gradually moves into a
better position to examine more of subsurface Mars.
"The search for
liquid water will begin in earnest next year," Plaut said.
The MARSIS instrument has bounced radio waves off the outer edge of
the Martian atmosphere — its charged ionosphere — and found it
remarkably bumpy, Plaut said.
The bumpiness seems to reflect how the
ionosphere responds to patchy remnants of magnetism in Mars crust. The
discovery could serve as a new way to map out the magnetism of Mars, he
said.
As for where that magnetism comes from, it's just faint mineralogical
memory of a once global magnetic field.
In fact, said Bibring, it's the
loss of that magnetic field that might have exposed Mars to more severe
solar radiation and triggered the climate change 3.5 million years ago that left it seemingly barren today.
