The best evidence yet for active volcanism on Venus: Venus Express observations show changes in surface temperatures, over the course of several days, in tectonic rift areas on the flank of a volcano. The discovery was made using data from the Venus Monitoring Camera (VMC), by a team of researchers led by Eugene Shalygin of the Max-Planck Society of Solar System Research. The paper describing this research is being published in Geophysical Research Letters and can be found here: dx.doi.org
An ESA press release about this finding can be found on the ESA Venus Express website: www.esa.int
This detection is very much at the limits of what can be done with Venus Express. This detection is based on observations of infrared radiation at a wavelength of 1 micron, thermally emitted from the surface, which escapes to space where it is observed by the spacecraft. On its way from the surface to space, however, the infrared light is reflected dozens of times from cloud droplets. Luckily, the cloud droplets are highly reflective, which is why measurable amounts of infrared radiation reach space - but this bouncing of the light from cloud droplets blurs the image considerably. The cloud layer extends from 50 to 70 km above the surface, so the blurring occurs on length scales at least this large. No matter how high the resolution of the imager, any images of the surface still appear blurred out over this scale.
The hot regions in the images are spread over an area typically 100 km across, as expected from the blurring function due to clouds; this is consistent with what would be observed if the hot region were much smaller in size. The researchers calculate that the hot regions would have to be up to 550 degrees centigrade, if they are 1 square kilometre in size; however, they could equally be hotter and cover a smaller area, or not quite so hot and covering a larger area.
Although it is not possible to conclude exactly how hot these hot patches are, or over what area they extend, the fact remains that they have found to vary in time, appearing over the course of a couple of days and then disappearing again before the next visit of the spacecraft some months later. It has been shown that the features do not move – as would be the case if they were cloud features; they persist at the same geographic co-ordinates – unlike artefacts in the camera system, or artefacts due to solar energetic particles or cosmic rays.
This result offers exciting possibilities for future observation. One approach is to repeat the same experiment - imaging at 1 micron wavelength from an orbiter - but with a more sensitive camera, in a low circular orbiter which would get many more repeated observations of the same regions. An instrument like this has been proposed by Joern Helbert at DLR Berlin along with several colleagues, for possible inclusion on a NASA-led or ESA-led Venus orbiter.
Another approach for future observation is to monitor the thermal emission from the surface at radio frequencies. An orbital Venus radar mapper might be able to do this, depending on its design. This kind of radiometry was, for example, demonstrated by the Magellan radar orbiter; some of these results yielded hints of possible thermal anomalies at the surface (see for example Bondarenko et al GRL 2010 - dx.doi.org
) - but not enough repeat observations had been obtained on that occasion to enable detection of temporal changes. Radiometry at these radar wavelengths may also achieve higher spatial resolution than is achievable using the infrared observations, and it probes temperatures a few cm below the surface, which is complementary to the near-infrared observations.
The team of researchers behind this work includes researchers from Russia, Ukraine, Germany, and the USA - a demonstration that our nations' scientists continue to collaborate successfully, even though our governments may be in conflict.