As our attention is drawn to the far distant parts of our planetary neighbourhood, it is worth reminding ourselves that there’s still much to learn in our local area of the solar system. Although most of my time I spend thinking about cooler planets and moons, there will always be a place in my heart for Venus.
It is Venus that is ever present in our sky, one of the first celestial objects that I learnt to identify. It was Venus that, as an undergrad in London, I chose a small part of to map. And it was thoughts about the extreme conditions found on our next-door neighbour that got me starting to wonder, how would materials respond to these? – leading me to a PhD in high pressure physics. Today Venus rushed back into my thoughts as I learnt that one of the biggest conundrums of our solar system, is this planet volcanically active, may have finally been solved.
Venus is, in many respects very similar to Earth. It is (roughly) made of the same stuff, about the same size as us, and to top it off has a sizable atmosphere. However, since we first started sending spacecraft to study it, it has been revealed to be a ‘hellish’ place. In the 1960’s the Russian space agency undertook the Venera program, a long term study that established much of what we know about Venus. Over 16 spacecraft they revealed the high temperature and pressure conditions on the surface, the high-winds that scream across it and began to map some its features.
With information from the Venera program, and the later NASA Magellan spacecraft, we obtained maps of the whole surface of the planet. Venus’ thick atmosphere is too thick to see through with visible light, instead these missions were equipped with synthetic aperture radar instruments. Sending radio waves through the atmosphere and bouncing back off the surface to the spacecraft, this built up a radar pictures of the surface charting differences in the texture of the surface.
I remember trawling though radar images of the surface taken by the Magellan spacecraft looking for a bit of Venus that had something interesting to map (and hadn’t been done before). I ended up picking a small piece of the Navka Platina, incorporating where the Venera 13 probe had landed (you can have a look through all the Magellan images with the USGS Map a Planet website).
I think one of the reasons I picked this bit was because it showed up all of the features of the Venusian surface I had learned about. Venus can be said to be a bit like a teenager – its surface is young and spotty. We know it is young because there are few impact craters on the surface, and where they are there they seem largely un-eroded. Also, the surface is ‘spotty’ in that it is littered with volcanic activity of all sizes. So given that the surface is young and there are many volcanoes – it’s rather odd that the surface seemed, from Magellan and Venera images, rather dormant.
Volcanic activity is a bit of a rarity in the solar system – only our own planet and Jupiter’s moon Io have been proved to be geologically active. Many people have believed that Venus belonged to this exclusive club – and the effort to show this was one of the aims of the European Space Agency’s Venus Express mission.
Arriving at Venus in 2006, the Venus Express spacecraft has since re-mapped the surface of Venus, with a similar radar instrument to that flown on Magellan, at least twice more. Scientists have been attempting a planetary ‘spot the difference’ between earlier and later images, to see if volcanic activity had changed any features. So far nothing concrete had been noticed.
However, Venus Express also carried an instrument known as the Venus Monitoring Camera. Though this instrument was designed mainly to look at the way Venus’s atmosphere behaved, it also could take advantage of ‘windows’ in the energy given off by the atmosphere to see right down to the surface. There it could detect extra heat on the surface.
The Venus Monitoring Camera (VMC) had already picked up areas of extra heat, further fuelling the idea that Venus was geologically active. However, even these signatures were seen to be stagnant, and we had yet to see one change. That is, until work published earlier this month.
The VMC took images over a region of Venus called Ganiki Chasma three times, twice in June 2008 and then later in October that year. In the June flybys it observed a significant heat signal (above that of the normal heat of Venus’ surface) which was absent in the later October image. Given that the heat signals were observed in an area already interpreted to be a rift zone (like the Great Rift Valley of East Africa), means this is the best evidence yet that Venus’ surface is actively changing.
With the question of Venus’ geological activity now probably laid to rest, researchers can now concentrate on the ways that Venus is different to Earth again. Much of this research centres round how Venus became the hostile place it is today, and if there is anything we can learn about the future of Earth’s climate from this.
Venus express met a fiery end in the atmosphere of Venus last year. Are there any plans to return to Venus any time soon? Not currently – though there is one mission that is going to have a second shot of getting there. The Japanese Space Agency (JAXA) Akatsuki mission missed Venus orbit on its first attempt in 2010. Since then it has been orbiting round the sun, biding its time for a second go. JAXA announced that they’ll try to get Akatsuki into Venusian orbit in November this year, and when it gets there will spend two years investigating the hostile climate of Venus.