New Venus Express Map Hints at Venus' Wet, Volcanic Past

http://www.esa.int/SPECIALS/Venus_Ex...QCLXOWF_0.html

New map hints at Venus' wet, volcanic past
European Space Agency
14 July 2009

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 Muller at the Joint Planetary Interior Physics Research Group of
the University Münster 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' 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 Muller.

Müller 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 3â20°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 around, Müller 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.


*Notes for editors:*

Venus surface thermal emission at 1 micron in VIRTIS imaging
observations: Evidence for variation of crust and mantle
differentiation
conditions by N. Müller, J. Helbert, G. L. Hashimoto, C. C. C. Tsang,
S.
Erard, G. Piccioni, and P. Drossart was published in The Journal of
Geophysical Research in December 2008.


*For more information:*

Joern Helbert, DLR Institure of Planetary Research, Berlin-Adlershof
Email: Joern.Helbert @ dlr.de

Giuseppe Piccioni, VIRTIS co-Principal Investigator,
IASF-INAF, Rome, Italy
Email: Giuseppe.Piccioni @ iasf-roma.inaf.it

HÃ¥kan Svedhem, ESA Venus Express Project Scientist
Email: Hakan.Svedhem @ esa.int