Today the Red Planet is dry and barren, but
what about tomorrow? New data suggests that the long story of water
on Mars isn't over yet.
By Trudy E Bell and Dr Tony
When Orson Welles broadcast "The War of
the Worlds" in 1938, many listeners were ready to believe in Martians.
After all, astronomers had long debated markings on the Red Planet
that might be aquaducts or fields of vegetation. Why not warlike aliens
Among laypeople (and some scientists)
the notion that Mars was "Earth-Like" - warm, wet and
verdant - persisted for decades, until the first spacecraft visited
the Red Planet. The Mariner missions of the late 1960's revealed
the real Mars: heavily cratered, dotted with extinct volcanoes,
colder than Antarctica and drier than the Sahara desert. There were
no trees, no canals, no Martians - and very little atmosphere! "The
War of the Worlds" was a fantasy after all.
Subsequent missions mostly confirmed
a new paradigm: Mars was once wet, but now it is dry. Spacecraft
photos of Mars reveal signs of ancient rivers, lakes and maybe even
an ocean. They might have been filled with water billions of years
ago, but something happened - no one knows what - and the planet
became a global desert.
by artist Duane
Hilton is a fake! It shows a standing pool of water on
Mars - impossible today, but what of the future?
Wherever the moisture went, new data
suggest it might not be gone for good. Indeed, water
may have flowed on Mars literally as recently as "yesterday or last
year," declares James Garvin, Chief Scientist for Mars exploration
at NASA headquarters. Evidence is mounting that water lies
beneath the Martian terrain, he says. Furthermore,
every few centuries weather conditions might become clement enough
for that water to "come and go" on the surface as well.
The first hints of water
near Mars' surface came in 2000 when the Mars Orbiter Camera (MOC)
on board NASA's Mars Global Surveyor spacecraft spotted hundreds of
delicately filigreed gully systems. Individual gullies are just 10
metres wide (earlier missions couldn't photograph such small features)
and a whole system might cover only a dozen city blocks. Their sculpted
terrain, cut-bank patterns, and fan-shaped accumulations of debris
look hauntingly similar to flash-flood gully washes in deserts on
Dozens of the gully
systems appear on the shaded sides of hills facing the polar ice
caps. Their geometry suggests that "swimming-pool volumes of water
could be entombed underground until suddenly it's warm enough for
an ice plug to burst, letting all the water rush down the slopes,"
Many of the gully systems
look extraordinarily recent - sharply carved and crossing older,
wind-scoured features. Their appearance is so fresh, in fact, that
it has excited planetary geologists such as MOC designer Mike Malin
to think that Mars "may have experienced massive, short-term climate
changes, where water could come and go in hundreds of years." Indeed,
Garvin said, scientists wonder whether liquid water might exist
on Mars now, buried in some areas perhaps 500 metres underground,
and that "there might be a dynamic cycling of the atmosphere going
on even today."
MOC's findings are
corroborated by data from another instrument on the spacecraft,
the Mars Orbiter Laser Altimeter (MOLA). For 27 months - longer
than a Martian year (one Martian year is 687 Earth days) - MOLA
gauged the daily height of the Red Planet's polar icecaps, meticulously
recording how much frozen material accumulated in winter and eroded
(sublimed or evaporated) in summer in each hemisphere. MOLA documented
that each ice cap has a volume as great as the Greenland ice cap
accumulated debris (or "apron") from this gully on Mars covers
sand dunes that may have formed less than a century ago. [more]
Although the upper
crust of frost is clearly carbon dioxide, scientists are now convinced
that much of both caps' supporting mass must be frozen water-structurally,
"dry ice can't stand up two miles high," Garvin remarked.
MOLA and MOC measured
how the polar caps shrink in each hemisphere's summer. They shrink
so much, in fact, that if the observed trends were continued for
just a few centuries, nearly a third of each polar cap could evaporate
into Mars's atmosphere. That would pump the atmospheric pressure
up from 6 millibars to 30 or 40 mb (the Earth's atmospheric pressure
is about 1000 mb) - high enough pressure for liquid water to be
stable on the planet's surface under certain temperature conditions.
Thus, perhaps as recently as just a century or two ago, Mars might
have been "clement enough for ponds of water" to have dotted its
surface like desert oases, Garvin said - and current trends suggest
it might become so again.
All these observations
reopen a venerable question: was there - or is there - life on
"Following the water makes sense if you're
prospecting for biology," Garvin declared. "If we could find evidence
of preserved liquid water on Mars, that would be the Holy Grail."
Looking for water is
in fact a prime mission of the Mars Odyssey spacecraft, whose high-gain
antenna unfurled on February 6, 2002, and whose instruments began
mapping Mars at the end of that month. Odyssey's multispectral camera
is imaging Mars simultaneously at numerous infrared wavelengths
(from 8 to 20 micrometres) with unprecedented football-field resolution,
seeking thermal and mineral "fingerprints" hinting of seeps, volcanic
vents, or underground reservoirs.
Initial science data
released on March 1st 2002 is already tantalising scientists. Within
its first week, Odyssey's gamma-ray spectrometer had detected significant
amounts of hydrogen in Mars's south polar regions-possibly indicating
the presence of frozen water in the upper few feet of the Martian
this false-colour map of Mars, soil enriched in hydrogen is
indicated by deep blue. Source: the neutron spectrometer onboard
NASA's 2001 Mars Odyssey spacecraft. [more]
Odyssey observations are the 'tip of the iceberg'," Garvin concluded.
Perhaps he was speaking quite literally!