Comunicato stampa ESA che, al solito, non ho il tempo di tradurre…
Mars Express and the story of water on Mars
European Space Agency
16 October 2006
For a number of decades now, astronomers have wondered about water on
Mars. Thanks to ESA’s Mars Express, much of the speculation has been
replaced with facts. Launched on 2 June 2003, Mars Express has changed
the way we think of Mars.
Since the Viking missions of the 1970s, planetary scientists have
changed their perception of water on Mars several times, passing from
the picture of a dry planet to that of a warmer and wetter one. Mars
Express’s data are now shading a new light on the complex issue of the
evolution of water on the Red Planet.
“We are re-writing the history of Mars,” says Gerhard Neukum, Freie
Universitaet Berlin, Germany, and the Principal Investigator on Mars
Express’s High Resolution Stereo Camera (HRSC). “The big picture of a
warm wet Mars is not completely correct. Any warm wet period lasted
a few hundred million years. By four thousand million years ago, it was
over,” he adds.
Three instruments on Mars Express have been at the centre of this
revolution in thought. One is the Mars Advanced Radar for Subsurface
Ionospheric Sounding (MARSIS). Since July 2005, MARSIS has probed
beneath the surface of Mars to depths of thousands of metres. This is
the first time such investigations have taken place.
“MARSIS has shown that many of the upper layers of Mars contain water
ice,” says Jeffrey Plaut of the Jet Propulsion Laboratory, Pasadena,
is the co-Principal Investigator on the MARSIS experiment.
The scientists detected abundant water ice in the Martian polar regions
and also received a surprise from some of the very first results that
MARSIS returned. When the radar passed over the mid northern latitudes
of Chryse Planitia, the signals showed a buried impact crater, below
surface. Inside this impact structure was a thick layer of possibly
water-ice-rich material. “We are finding reservoirs of ice that have
never been seen before,” says Plaut, “But we are still puzzling out
and where the water on Mars was liquid.”
“The last MARSIS observations have been done on the South Pole,” adds
Giovanni Picardi, MARSIS Principal Investigator, from the University of
Rome “La Sapienza”. “The quality of the preliminary results of the
advanced analysis we are still performing are really exciting and
promising, with respect to the main scientific objectives of our
experiment.” The objectives include the detection of subsurface water.
The OMEGA Visible and Infrared Mineralogical Mapping Spectrometer has
taken giant steps towards answering that question. OMEGA detects
minerals on the surface of Mars. Three in particular reveal the history
of Martian water. “We have demonstrated that water could have been
stable on Mars’s surface but not for very long,” says Jean-Pierre
Bibring, Institut d’Astrophysique Spatiale, Orsay, France, and OMEGA’s
OMEGA detected clay-like minerals that form during long-term exposure
water, but only in the oldest regions of Mars. That suggested water
flowed during the first few hundred million years of the planet’s
history only. When these bodies of water were lost, water then
occasionally burst from inside the planet but quickly evaporated.
During the evaporation they made sulphates, the second mineral that
OMEGA detected. When even this stopped and the remaining water on Mars
became permanently frozen, then the atmosphere gradually turned the
red by creating the third mineral OMEGA detected, ferric oxide.
Mars has been like this for thousands of millions of years. “It is
remarkable that, for the first time, we have identified where and when
liquid water might have been present on Mars. It is not where one
thought of before,” says Bibring.
The images from the High Resolution Stereo Camera (HRSC) point towards
the same conclusions. They show the Martian surface in the most
exquisite detail, revealing features just 10 metres across. They
show extremely old Martian regions that have been eroded by flowing
water. The pictures also show a huge valley, Kasei Valles, carved by a
gigantic Martian glacier that persisted for a thousand million years
during the time when the temperature of Mars had dropped too low for
liquid water to flow across the surface.
“We see a clear link between volcanic regions and water flows,” says
Neukum. Wherever there has been volcanic activity on Mars, it has
water inside Mars and let it flow to the surface. Some of these flows
are recent - geologically speaking. “At the foot of Olympus Mons, HRSC
sees evidence for water flows that have happened within the last 30
million years,” says Neukum.
NASA’s latest spacecraft, the Mars Reconnaisance Orbiter (MRO), carries
instruments that lead on from those of Mars Express. Many scientists
from the teams at work on MARSIS are now working on the ASI’s Shallow
Radar (SHARAD) on board MRO. This is tuned to focus on the shallower
layers of Mars, whereas MARSIS looks deeper. OMEGA’s sister instrument
on MRO is the Compact Reconnaissance Imaging Spectrometer for Mars
(CRISM). This will look in more detail at minerals on the Martian
surface. However, the instrument only has a small field of view, so it
will need guidance. “They will target primarily the areas that OMEGA
shown to be interesting,” says Bibring.
“Mars Express has provided unprecedented evidence on the history of
water on Mars. Now, we look forward to new investigations that will
build on this legacy,” says Augustin Chicarro, Mars Express?s Project
Scientist at ESA.
Note to editors
Mars Express data is still streaming down from HRSC, MARSIS, Omega but
also the probe’s other instruments, PFS, SPICAM, ASPERA, and MaRS. They
are probing all aspects of the Martian environment - studying
atmospheric gases, searching for eventual biological processes,
detecting high altitude clouds and hidden volcanoes and digging into
scavenging effects of the solar wind.
For more information
Agustin Chicarro, ESA Mars Express Project Scientist
Email: agustin.chicarro @ esa.int
Gerhard Neukum, HRSC Principal Investigator, Freie Universitaet Berlin,
Email: gneukum @ zedat.fu-berlin.de
Jean-Pierre Bibring, OMEGA Principal Investigator, Institut
d?Astrophysique Spatiale - IAS, Orsay, France
Email: jean-pierre.bibring @ ias.u-psud.fr
Giovanni Picardi, MARSIS Principal Investigator Univ. di Roma ‘La
Email: picar @ infocom.uniroma1.it
Jeffrey Plaut, MARSIS Co-Principal Investigator, NASA/JPL, USA
Email: plaut @ jpl.nasa.gov