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Hot stuff on Venus! Venus Express sees right down to the hell-hot surface 
Thanks to ESA’s Venus Express data, scientists obtained the first large-area temperature maps of the southern hemisphere of the inhospitable, lead-melting surface of Venus. The new data may help with searching and identifying ‘hot spots’ on the surface, considered to be possible signs of active volcanism on the planet. The results, presented today at the American Geophysical Union (AGU) assembly in San Francisco, USA, were obtained thanks to VIRTIS, the Visible and Infrared Thermal Imaging Spectrometer on board Venus Express.
To obtain this fundamental information about the surface temperature, VIRTIS made use of the so-called infrared spectral 'windows’ present in the Venusian atmosphere. Through these ‘windows’ thermal radiation at specific wavelengths can leak from the deepest atmospheric layers, pass through the dense cloud curtain situated at about 60 kilometres altitude, and then escape to space, where it can be detected by instruments like VIRTIS. In this way VIRTIS succeeded in looking through the thick carbon dioxide curtain surrounding Venus and detected the heat directly emitted by the hot rocks on the ground.
"We are very excited about these results, as they represent a very important item in the list of Venus Express' and VIRTIS' scientific objectives at Venus", says Giuseppe Piccioni, one of the Principal Investigators of the VIRTIS experiment, from the Istituto di Astrofisica Spaziale e Fisica Cosmica in Rome, Italy.
On Venus there are no day and night variations of the surface temperature. The heat is globally 'trapped' under the carbon-dioxide atmosphere, with pressure 90 times higher than on Earth. Instead, the main temperature variation is due to topography. Just like on Earth, mountain tops are colder, whereas the lowlands are warmer. The 'only' difference is that on Venus 'cold' means 447º Celsius, while 'warm' means 477º Celsius. Such high temperatures are caused by the strongest greenhouse effect found in the Solar System.
"The VIRTIS results represent a major step forward in our attempt to identify specific surface features on the surface of Venus", said Jörn Helbert from the German Aerospace Center's (DLR) Institute of Planetary Research in Berlin, Germany, and a member of the VIRTIS team. "By 'peeling' off the atmospheric layers from the VIRTIS data, we can finally measure the surface temperature," Helbert added.
Eventually, the VIRTIS team hopes to identify 'hot spots' on the surface of Venus, possibly stemming from active volcanoes. In the Solar System, besides Earth, active volcanoes have been observed only on Io, a satellite of Jupiter, on Neptune's satellite Triton, and on Saturn's moon Enceladus (in the form of the so-called 'cryo-volcanism'). Venus is the most likely planet to host other active volcanoes.
This direct interdependence between temperature and topography will enable scientists to derive new topography maps of the Venusian surface from temperature measurements. This will help in complementing the Magellan maps.
"Actually, when comparing our temperature map with topographical data from Magellan, we are not only obtaining quite a good agreement, but we can even fill gaps that the Magellan and Venera 15 radar data sets left open", concluded Pierre Drossart, the other Principal Investigator of the VIRTIS experiment, from the Observatoire de Paris Meudon, France.
Note to editors Even though Venus is the brightest planet in the night sky other than Earth's moon, and it is the closest planet to Earth, it is extremely difficult to obtain detailed information about its surface from Earth. Even if some evidence of surface thermal emission has been obtained from ground-based telescopes working in the near-infrared since 1990, the spatial resolution of such observations remain very limited.
Venus Express is instead making use of the 'infrared windows', known to scientists from the middle of the 1980s. In 1990, during the flyby of Venus, NASA's Galileo spacecraft on its way to Jupiter made a first attempt to make use of these 'windows'.
For more information Jörn Helbert, VIRTIS team, German Aerospace Center's (DLR) Institute of Planetary Research in Berlin, Germany Email: joern.helbert @ dlr.de
Giuseppe Piccioni, VIRTIS co-Principal Investigator, IASF-INAF, Rome, Italy
Pierre Drossart, VIRTIS co-Principal Investigator, Observatoire de Paris, France
Hakan Svedhem, ESA Venus Express Project Scientist
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ESA astronaut C. Nicollier on voyaging to Venus (mms://esamultimedia.esa.int/multimedia/audio/cn_venus.mp3)