Andrew Yee[_1_]
March 12th 08, 05:38 AM
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 fur Weltraumforschung
(IWF), Osterreiche 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 ]
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 fur Weltraumforschung
(IWF), Osterreiche 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 ]