Gazing at Venus from Earth and from Space
April 03rd, 2016
This month sees the 10th anniversary of the arrival at Venus of Venus Express. On 11th April 2006, Venus Express started orbiting Venus, following a five-month cruise through space. It successfully operated in orbit around Venus far in excess of its nominal science mission of 500 days, finally running out of propellant in November 2014 and burning up in the atmosphere of Venus soon afterwards in January 2015.
This week sees some 140 scientists gathering for a major international conference on Venus science, held in Oxford, U.K. (venus2016.uk ). Most presentations are, directly or indirectly, dealing with results from Venus Express. While some of the most spectacular recent results from Venus Express, arguably, have been those hinting at recent volcanism (see for example www.esa.int ), the mission has produced a very wide range of further results dealing with atmospheric phenomena, from dynamics and temperature structure to chemistry and clouds, as well as many new observations of the interaction region between the atmosphere and space.
One highlight this week has been seeing how the scientific return from Venus Express has been augmented through co-ordinated observations with ground-based telescopes. Ground based telescopes have the advantage that they can be equipped with sophisticated spectrometers far too massive and complex to deploy on a spacecraft; these ground-based instruments can thus be sensitive to trace constituents or faint motions of the atmosphere in a way which is complimentary to spacecraft observations.
This was clearly demonstrated when it came to wind measurements on Venus. We can see, using images from spacecraft or from telescopes, that the cloud features on Venus are moving incredibly fast, at 300 – 400 km/h. However, there has always been a doubt regarding wind speeds obtained by tracking the movements of clouds: are these true wind speeds, or are they just the speeds of waves moving through the clouds (like foamy crests on ocean waves, for example)? Earth-based telescopes have enough spectral sensitivity that they can directly measure the actual velocity of cloud particles by measuring the Doppler shift of sunlight they reflect. Co-ordinated campaigns of observations with Venus Express confirmed that the velocities of individual cloud particles did indeed match up very accurately with the velocities calculated from cloud imagery. This provided a vital confirmation that decades of cloud tracking observations, dating back to the 1970s, were indeed representative of true wind speeds.
Another example of how ground-based observations are complementary to space-based ones is in the mapping of Sulphur Dioxide (SO2). SO2 is a volcanic gas – its only natural source on Earth is from volcanoes – so its high abundance on Venus is suggestive of active or recent volcanism. Venus Express has been recording the variable abundance of SO2 in the upper atmosphere for many years – but it can observe only one point, immediately below the spacecraft, at any one time. It was not possible to understand the global picture of how SO2 was distributed across the planet from these point measurements alone. Using NASA’s InfraRed Telescope Facility, it was possible to measure maps of SO2 and other abundances across the whole face of Venus. These maps – when combined with the vertical profiling capabilities of observations from Venus Express – give a much better understanding of how SO2 abundances vary in three dimensions and with time, helping to establish whether these variations are linked to active volcanism. Further observations of SO2 have been carried out from radio frequency telescopes and even from the Hubble Space telescope.
Another highlight this week has been seeing how the legacy of Venus Express is being passed to the next generation of Venus researchers. All scientific data from Venus Express are publically accessible from ESA’s Planetary Science Archive – <www.rssd.esa.int A special session at the conference saw the Principal Investigators of each of the Venus Express payloads summarise the scientific achievements of their instruments, but also summarise outstanding science questions which could be addressed using data in the PSA.
After the demise of the Venus Express orbiter in early 2015, the guardianship of Venus has now been passed to the Japanese Akatsuki orbiter – Akatsuki, like Venus Express, focusses mainly on the atmosphere of Venus, so this conference offered an excellent opportunity to exchange the latest atmospheric findings. Akatsuki arrived at Venus in Dec 2015 and is now starting its science mission following several months of on-orbit commissioning. The Akatsuki team will be presenting this week some of their first results from Venus: all the scientific payloads seem to be functioning well leading to hopes for a good science return from this mission. Major science goals to be addressed by Akatsuki include the super-rotating winds of Venus – Akatsuki will monitor how these evolve from its high near-equatorial orbit – and an optical search for lightning using a high speed camera, which will complement well the magnetic characterization of lightning performed by Venus Express. Akatsuki’s 1 µm cameras will also be able to map surface thermal emissions, to look for further signs of active or recent volcanism as hinted at from Venus Express results.
At the International Venus Science conference this week, The Akatsuki science team are meeting with many of the observers who collaborated with Venus Express, to discuss the next round of collaborative observations. The strong foundations laid over the past decade, then, are helping to maximise Venus scientific exploration in decades to come.
This week sees some 140 scientists gathering for a major international conference on Venus science, held in Oxford, U.K. (venus2016.uk ). Most presentations are, directly or indirectly, dealing with results from Venus Express. While some of the most spectacular recent results from Venus Express, arguably, have been those hinting at recent volcanism (see for example www.esa.int ), the mission has produced a very wide range of further results dealing with atmospheric phenomena, from dynamics and temperature structure to chemistry and clouds, as well as many new observations of the interaction region between the atmosphere and space.
One highlight this week has been seeing how the scientific return from Venus Express has been augmented through co-ordinated observations with ground-based telescopes. Ground based telescopes have the advantage that they can be equipped with sophisticated spectrometers far too massive and complex to deploy on a spacecraft; these ground-based instruments can thus be sensitive to trace constituents or faint motions of the atmosphere in a way which is complimentary to spacecraft observations.
This was clearly demonstrated when it came to wind measurements on Venus. We can see, using images from spacecraft or from telescopes, that the cloud features on Venus are moving incredibly fast, at 300 – 400 km/h. However, there has always been a doubt regarding wind speeds obtained by tracking the movements of clouds: are these true wind speeds, or are they just the speeds of waves moving through the clouds (like foamy crests on ocean waves, for example)? Earth-based telescopes have enough spectral sensitivity that they can directly measure the actual velocity of cloud particles by measuring the Doppler shift of sunlight they reflect. Co-ordinated campaigns of observations with Venus Express confirmed that the velocities of individual cloud particles did indeed match up very accurately with the velocities calculated from cloud imagery. This provided a vital confirmation that decades of cloud tracking observations, dating back to the 1970s, were indeed representative of true wind speeds.
Another example of how ground-based observations are complementary to space-based ones is in the mapping of Sulphur Dioxide (SO2). SO2 is a volcanic gas – its only natural source on Earth is from volcanoes – so its high abundance on Venus is suggestive of active or recent volcanism. Venus Express has been recording the variable abundance of SO2 in the upper atmosphere for many years – but it can observe only one point, immediately below the spacecraft, at any one time. It was not possible to understand the global picture of how SO2 was distributed across the planet from these point measurements alone. Using NASA’s InfraRed Telescope Facility, it was possible to measure maps of SO2 and other abundances across the whole face of Venus. These maps – when combined with the vertical profiling capabilities of observations from Venus Express – give a much better understanding of how SO2 abundances vary in three dimensions and with time, helping to establish whether these variations are linked to active volcanism. Further observations of SO2 have been carried out from radio frequency telescopes and even from the Hubble Space telescope.
Another highlight this week has been seeing how the legacy of Venus Express is being passed to the next generation of Venus researchers. All scientific data from Venus Express are publically accessible from ESA’s Planetary Science Archive – <www.rssd.esa.int A special session at the conference saw the Principal Investigators of each of the Venus Express payloads summarise the scientific achievements of their instruments, but also summarise outstanding science questions which could be addressed using data in the PSA.
After the demise of the Venus Express orbiter in early 2015, the guardianship of Venus has now been passed to the Japanese Akatsuki orbiter – Akatsuki, like Venus Express, focusses mainly on the atmosphere of Venus, so this conference offered an excellent opportunity to exchange the latest atmospheric findings. Akatsuki arrived at Venus in Dec 2015 and is now starting its science mission following several months of on-orbit commissioning. The Akatsuki team will be presenting this week some of their first results from Venus: all the scientific payloads seem to be functioning well leading to hopes for a good science return from this mission. Major science goals to be addressed by Akatsuki include the super-rotating winds of Venus – Akatsuki will monitor how these evolve from its high near-equatorial orbit – and an optical search for lightning using a high speed camera, which will complement well the magnetic characterization of lightning performed by Venus Express. Akatsuki’s 1 µm cameras will also be able to map surface thermal emissions, to look for further signs of active or recent volcanism as hinted at from Venus Express results.
At the International Venus Science conference this week, The Akatsuki science team are meeting with many of the observers who collaborated with Venus Express, to discuss the next round of collaborative observations. The strong foundations laid over the past decade, then, are helping to maximise Venus scientific exploration in decades to come.