Mars and Venus are surprisingly similar (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Wed, 12 Mar 2008 06:41:52 GMT
ESA News
http://www.esa.int
5 March 2008
Mars and Venus are surprisingly similar
Using two ESA spacecraft, planetary scientists are watching the
atmospheres of Mars and Venus being stripped away into space. The
simultaneous observations by Mars Express and Venus Express give
scientists the data they need to investigate the evolution of the two
planets' atmospheres.
Scientists call this work comparative planetology. Mars Express and Venus
Express are so good at it because they carry very similar science
instruments. In the case of the Analyser of Space Plasmas and Energetic
Atoms (ASPERA), they are virtually identical. This allows scientists to
make direct comparisons between the two planets.
The new results probe directly into the magnetic regions behind the
planets, which are the predominant channels through which
electrically-charged particles escape. They also present the first
detection of whole atoms escaping from the atmosphere of Venus, and show
that the rate of escape rose by ten times on Mars when a solar storm
struck in December 2006.
By observing the current rates of loss of the two atmospheres, planetary
scientists hope that they will be able to turn back the clock and
understand what they were like in the past. "These results give us the
potential to measure the evolution of planetary climates," says David
Brain, Supporting Investigator for plasma physics for Venus Express and
Co-Investigator for ASPERA on Mars and Venus Express at the University of
California, Berkeley.
The new observations show that, despite the differences in size and
distance from the Sun, Mars and Venus are surprisingly similar. Both
planets have beams of electrically charged particles flowing out of their
atmospheres. The particles are being accelerated away by interactions with
the solar wind, a constant stream of electrically charged particles
released by the Sun.
At Earth, the solar wind does not directly interact with the atmosphere.
It is diverted by Earth's natural cloak of magnetism. Neither Mars nor
Venus have appreciable magnetic fields generated inside the planet, so
each planet's atmosphere suffers the full impact of the solar wind.
Interestingly, this full-on interaction does create a weak magnetic field
that drapes itself around each planet and stretches out behind the
night-side in a long tail. Venus' atmosphere is thick and dense, whereas
that of Mars is light and tenuous. Despite the differences, the
magnetometer instruments have discovered that the structure of the
magnetic fields of both planets are alike.
"This is because the density of the ionosphere at 250 km altitude is
surprisingly similar," says Tielong Zhang, Principal Investigator for the
Venus Express magnetometer instrument at Institut für Weltraumforschung
(IWF), Österreiche Akademie der Wissenschaften, Austria. The ionosphere is
the surrounding shell of electrically-charged particles created by the
impact of sunlight on the planet's upper atmosphere.
The proximity of Venus to the Sun does create an important difference,
however. The solar wind thins out as it moves through space so the closer
to the Sun it is encountered, the more concentrated is its force. This
creates a stronger magnetic field, making the escaping atmospheric
particles move collectively like a fluid.
At Mars, the weaker field means that the escaping particles act as
individuals. "This is a fundamental difference between the two planets,"
says Stas Barabash, ASPERA Principal Investigator on both Mars Express and
Venus Express, Swedish Institute of Space Physics.
Another illuminating difference between Mars and Venus is that Mars
displays strong small-scale magnetic fields locked into the crust of the
planet. In some regions, these pockets protect the atmosphere, in others
they actually help funnel the atmosphere into space.
The complexity of the different processes revealed at Venus and Mars means
that planetary scientists do not yet have the full picture. "There will be
many more results to come," says Barabash.
There is a lot to do because there are many different mechanisms that may
cause the atmospheric particles to escape. Untangling it all will take
time. "The longer the spacecraft work together, the longer we can watch
and see what really happens," says Brain.
Notes for Editors:
These new results are presented in 19 papers to be published in a special
issue of the journal Planetary and Space Science. Some out of these have
been available online from 19 January 2008.
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaSC/SEMMAGK26DF_index_1.html ]
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