[meteorite-list] Venus, if you will

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Tue, 14 Jul 2009 18:07:32 -0500
Message-ID: <ho3q55pqq66o9i6n8h6theetmk8mbr4s3u_at_4ax.com>

http://spacefellowship.com/2009/07/14/new-map-hints-at-venus-wet-volcanic-past/

New map hints at Venus? wet, volcanic past
By
Rob Goldsmith
Published: 14 July 2009 10:42 AM UTC

Venus Express has charted the first map of Venus? southern hemisphere at
infrared wavelengths. The new map hints that our neighbouring world may once
have been more Earth-like, with a plate tectonics system and an ocean of water.

The map comprises over a thousand individual images, recorded between May 2006
and December 2007. Because Venus is covered in clouds, normal cameras cannot see
the surface, but Venus Express used a particular infrared wavelength that can
see through them.

Although radar systems have been used in the past to provide high-resolution
maps of Venus? surface, Venus Express is the first orbiting spacecraft to
produce a map that hints at the chemical composition of the rocks. The new data
are consistent with suspicions that the highland plateaus of Venus are ancient
continents, once surrounded by ocean and produced by past volcanic activity.

?This is not proof, but it is consistent. All we can really say at the moment is
that the plateau rocks look different from elsewhere,? says Nils M?ller at the
Joint Planetary Interior Physics Research Group of the University M?nster and
DLR Berlin, who headed the mapping efforts.

The rocks look different because of the amount of infrared light they radiate
into space, similar to the way a brick wall heats up during the day and gives
off its heat at night. Besides, different surfaces radiate different amounts of
heat at infrared wavelengths owing to a material characteristic known as
emissivity. The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS)
instrument captured this infrared radiation during Venus Express?s night-time
orbits around the planet?s southern hemisphere.

The eight Russian landers of the 1970s and 1980s touched down away from the
highlands and found only basalt-like rock beneath their landing pads. The new
map shows that the rocks on the Phoebe and Alpha Regio plateaus are lighter in
colour and look old compared to the majority of the planet. On Earth, such
light-coloured rocks are usually granite and form continents.

Granite is formed when ancient rocks, made of basalt, are driven down into the
planet by shifting continents, a process known as plate tectonics. The water
combines with the basalt to form granite and the mixture is reborn through
volcanic eruptions.

?If there is granite on Venus, there must have been an ocean and plate tectonics
in the past,? says M?ller.

M?ller points out that the only way to know for sure whether the highland
plateaus are continents is to send a lander there. Over time, Venus? water has
been lost to space, but there might still be volcanic activity. The infrared
observations are very sensitive to temperature. But in all images they saw
variations of only 3?20?C, instead of the kind of temperature difference they
would expect from active lava flows.

Although Venus Express did not see any evidence of ongoing volcanic activity
this time this time around, M?ller does not rule it out. ?Venus is a big planet,
being heated by radioactive elements in its interior. It should have as much
volcanic activity as Earth,? he says. Indeed, some areas do appear to be
composed of darker rock, which hints at relatively recent volcanic flows.

The new map gives astronomers another tool in their quest to understand why
Venus is so similar in size to Earth and yet has evolved so differently.
Received on Tue 14 Jul 2009 07:07:32 PM PDT