What is the legacy of Venus Express?
What are the significant discoveries made by Venus Express during the past 8 years?
ESA's Venus Express mission has been hugely successful, greatly surpassing its design lifetime. With over 200 directly enabled published papers it has solidly anchored Europe as the world leader in Venus science.
A quick recap of these great years, adapted from ESA's own Venus Express top 8 Science Highlights:
- Measurements of sulphur dioxide in the upper atmosphere have greatly varied during the 8 year mission span
Sulphur dioxide is one of the main gases released in the atmosphere by volcanic eruptions. At this altitude, the gaz is easily destroyed by energetic UV rays from the sun. Its detection means it was thrust upwards very recently, possibly by the strength of a volcanic eruption. Although not definitive, it is a clear indication de planet might still be geologically active today. The competing hypothesis is that unknown atmospheric circulation disturbances could mix the higher altitude gas with the sulphur rich lower altitude one to produce a similar effect.
E. Marcq et al. (2012) Evidence for Secular Variations of SO2 above Venus’ Clouds Top, Nature Geoscience.
- Numerous lava flows less than 2.5 million years have been reported
A better constraint of the type and rate of resurfacing has significant implications on the understanding of climate and interior dynamics of terrestrial planets. Using the atmospheric window at 1.02 micrometre, the VIRTIS instrument aboard Venus Express was able to measure surface emissivity as a means for remote mineralogical mapping.
The spectral emissivity is the ratio of the radiance measured from the surface to the radiance that a black body at the same temperature would emit. Variations in emissivity relate to variations in chemical composition and/or amount of weathering. This in turn can be used to determine if the volcanic flows in the hot spot regions are consistent with relatively recent volcanic lava flows. From the available data it is highly unlikely that the heat of actual lava flows or volcanic eruptions are the source of the emissivity anomalies rather consistent with equivalent 20 degrees surface temperature variations. However, for Idunn Mons in the Imdr Regio area (pictured above) they point towards an age most likely comprised between a few thousand to a few ten thousand years, with additional very large model uncertainties at both extremes.
Furthermore, atmospheric scattering limits the spatial resolution to 50km per pixel at best. EnVision will improve these measurements by orders of magnitude with the dedicated instrument Venus Emissivity Mapper. Measurements from the radar payload will also complement them with data acquired at completely different wavelength.
The Venus Monitoring Camera has also detected some bright, transient features, including an apparent hot spot in the Ganiki Chasma region. The localised region of higher-than-expected temperature may have been a volcanic eruption or fresh lava flow, although this interpretation of the images is by no means certain. EnVision aims to find out.
Smrekar, S., Stofan, E., Mueller, N., Treiman, A., Elkins-Tanton, L., Helbert, J., Piccioni, G. and Drossart, P. (2010). Recent hotspot volcanism on Venus from VIRTIS emissivity data. Science, 328(5978), pp.605--608.
- The rotation period of Venus is changing
Surface feature tracking by VIRTIS during the nominal mission duration uncovered discrepancies between predictions based on Magellan data and assumption of a constant rotation periods. Our neighbour seems to be spinning slower by at approximately 6 minutes as revealed by surface features as far as 20km away from their expected locations.
These discrepancies could be explained by angular momentum exchange between the planet and its atmosphere. Decadal weather cycles have shown to be a possibility and such sinusoidal variations could fit the data from Magellan, VIRTIS and other Earth based radar observation. Other contributors to the observed variations could include the torque exercised by the gravitational pull of the Sun or even a differentially rotating solid inner core in resonance with Earth showing that this question also relates to science investigation on Venus’ puzzling atmosphere and its inner structure.
Not only will EnVision provide meter scale surface feature tracking but the first ever InSAR coverage of Venus North pole will yield precise insight into short and long term variations in spin rate and spin axis direction.
Mueller, N., Helbert, J., Erard, S., Piccioni, G. and Drossart, P. (2012). Rotation period of Venus estimated from Venus Express VIRTIS images and Magellan altimetry. Icarus, 217(2), pp.474--483.
- And many other game changing scientific discoveries including Shape-shifting polar vortices, Snow on Venus, Ozone layer characterization, New insights into water loss, a Magnetic surprise...
Previous Venus Missions, is this the first exploration of Venus?
Is the Timing right? EnVision as an enabler of future exploration
What world-wide firsts will EnVision accomplish during its mission?