Taking Venus' temperature

Venus Express peers through Venus' dense clouds to map a large swath of surface temperatures.
Provided by ESA, Noordwijk, Netherlands

Published: December 14, 2006

The temperature maps of the venusian surface shown in this image were built thanks to direct measurements obtained by Venus Express' VIRTIS instruments (left), compared with surface-temperature predictions based on Magellan topographic data obtained in the early 1990s (right). VIRTIS, the Visible and Infrared Thermal Imaging Spectrometer aboard ESA's Venus Express, gathered the data combined into this mosaic on August 10, 2006, during a single orbit.

Photo by ESA/VIRTIS-VenusX Team

December 14, 2006
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.

The measurements, made in August 2006 over the Themis and Phoebe Regions in the southern hemisphere of Venus, reveal temperature variations of 30 degrees between lowlands and mountain tops, correlating well with existing topographical radar data from previous missions. The Themis Region is a highland plateau located at 270º East longitude and at about 37º South latitude. It is a region that has experienced strong volcanic activity, at least in the geologic past.

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.

In order to achieve this, the Venus Express scientists started comparing the maps of the Venusian topography obtained by NASA's Magellan orbiter in the early 1990s with the data gathered by VIRTIS. The Magellan topography maps allow for a rough prediction of the surface temperature, too. Comparing these predictions with the measurements made by VIRTIS allows searching for hot spots that show even higher temperatures than the oven-hot surface, possibly indicative of active volcanism.

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.

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DOUG COTTON said:

I'm afraid I don't agree that the reason for the surface temperature on Venus is entirely due to the composition of its atmosphere. The pressure (and thus height of the atmosphere) is sufficient in itself to provide considerably greater insulating effects than on Earth, and convection processes, for example, would take much longer regardless of the gas composition of the atmosphere.

I suggest that the absence of day/night variations does not lend support to the greenhouse hypothesis and cannot be brushed aside as planet-wide trapping.

My hypothesis ( as on http://climate-change-theory.com ) is that a planet's surface temperature is determined by a continuous temperature gradient from its centre to the top of its atmosphere, this gradient being set in place by the end temperatures (core and space) and the rates of thermal energy transfer above and below the surface. Obviously conduction plays a major role under the surface, but convection also plays a role above the surface, apart from radiation.

The base surface temperature itself is thus determined by the intersection of the temperature plot and the surface. On Earth there will be temporary thermal energy added during the day by solar insolation observed as heat flow into the surface and then out again at night. But the surface will not generally cool below the base temperature which it gets close to on a calm winter night.

Part of the reason Earth has considerable variation from equator to poles may be due to the heat generated by friction as the Moon stirs up the liquid core. Less friction would occur in polar regions and I would suspect the core could be a little cooler there. The core of Venus is far less volatile, so I presume the frictional component of core heat would be negligible. Now I know the variation is normally attributed to the angle and duration of solar insolation, but if so, then what variation do we see on Venus?

By the number of volcanoes and the lava coverage, it is obvious that considerable thermal energy is escaping from the core of Venus, and I suggest this would be quite sufficient to cause the observed temperatures when you consider the likely core temperature.

Submitted: 10/21/2011 6:22:30 PM (CST)