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Published online: 7 September 2005; | doi:10.1038/news050905-10
Martian methane probe in trouble
Device may be unable to settle debate over indications of life
One of the best chances for solving Mars's methane mystery may
have been lost. The Planetary Fourier Spectrometer (PFS) on board
the Mars Express orbiter seems to be broken, perhaps for good.
The instrument's failure would be a blow for scientists who want
to find out how the red planet is producing the methane that has
been detected in recent years.
Almost all the methane on Earth comes from some sort of
biological source. As a methane molecule typically survives for
only a few hundred years in the martian atmosphere, something
must have been spewing it out recently, scientists reason. And
this has fuelled hopes for discovering life on Mars.
But scientists have recorded very different methane levels with
different techniques. In 2004, the PFS found that methane
averaged abut 10 parts per billion in Mars's atmosphere,
suggesting that more than 100 tonnes of the gas is released from
the surface each year. That same year, Mike Mumma of NASA's
Goddard Space Flight Centre in Maryland spotted levels of 250
parts per billion using a telescope in Hawaii. This week he told
an American Astronomical Society meeting in Cambridge that he had
spotted levels of 44-63 parts per billion from a different part
of the planet.
To pin down the source of the gas, these disagreements need to be
sorted out. One explanation might be that methane is venting
intermittently from specific points on the surface. To check,
researchers hope to take simultaneous readings of exactly the
same place using both orbiting and earth-based instruments.
But the chance to do this may now be lost, says Thérèse Encrenaz,
of the Paris Observatory in France, who is part of the PFS team.
She says that the spectrometer has been in trouble for two
months, and various attempts to fix it have proven fruitless.
"There's still a chance it could be fixed," she told
at the Cambridge meeting. "But if it cannot be
fixed then the experiment will be stopped."
Ludmilla Zasova of the Space Research Institute in Moscow, says
the instrument stopped working some time in July. "It's a problem
with the vibration of the spacecraft," says Zasova, who leads the
Russian contingent of scientists working with the PFS. These
vibrations have shown up in PFS data for the duration of the
mission, although scientists have been able to filter out the
effects to generate clean results. Zasova thinks the vibrations
are affecting a pendulum inside the instrument that helps to
control the way it collects light.
But team members are unclear about the severity of the problem.
Vittorio Formisano of the Institute of Physics and Interplanetary
Science in Rome, Italy, would not confirm that it is broken.
Formisano is in charge of the instrument and says he is being
kept busy working on it.
This isn't the first trouble that Mars Express has had. The
European Space Agency's craft had difficulty opening some radar
booms needed for its water detection experiment in May, although
these are now working well (see 'Mars Express radar on hold' ).
And there have been controversies surrounding interpretation of
data from the spectrometer. In February of this year, Formisano
said that the PFS had found large quantities of formaldehyde
around Mars (see 'Formaldehyde claim inflames martian debate').
This implied that millions of tonnes of methane were being
released by the planet each year: much, much more than thought.
Encrenaz says most scientists now agree that these claims about
formaldehyde were incorrect.
Without nailing the methane numbers, it will be hard for all
scientists to agree on a source for the gas. For now, many say it
is probably due to heating of water and carbon dioxide with a
mineral called olivine, rather than life, says Sushil Atreya, a
member of the PFS team from the University of Michigan in Ann
If the Mars Express methane instrument fails to provide further
data, the next opportunity will be NASA's Mars Science
Laboratory, due to blast off in 2009. This will not only measure
trace levels of methane, but also check its isotopic make-up for
signs of biological activity.