Look for brilliant Venus high in the west at sunset to pass close to Uranus on February 10th. A telescope will be needed to see faint Uranus – it is just at the limits of naked eye visibility, but even at low power, both planets will be in the same field of view. Venus is un-mistakable – it has been climbing higher and higher since the end of last year and now shines brightly in the evening sky. Its brilliance is due to how reflective its atmosphere is – the same atmosphere that makes Venus uninhabitable.
The atmosphere consists mainly of carbon dioxide, droplets of sulphuric acid and virtually no water vapour – not a great place for people or plants! In addition, the thick atmosphere allows the Sun’s heat in but does not allow it to escape, resulting in surface temperatures over 450 C, even hotter than the surface of the planet Mercury, which is closer to the Sun. The high density of the atmosphere results in a surface pressure 90 times that of Earth, which is why probes that have landed on Venus have only survived a maximum of two hours before being destroyed.
Venus is generally taken as an example of a planet where no life could exist – it is just too hot, but recent modelling of land planets (as compared to water planets like Earth) have suggested that Venus might have gone through a period where it was a dry but habitable planet. Some astro-biologists have argued that life might exist in the clouds of Venus, even now – high enough up from the surface where the temperature and pressure drop, providing a less imposing set of environmental conditions. They argue that the early Venus may have had liquid water, back before the runaway greenhouse effect kicked in. Any life that developed at that time may have been able to migrate to the clouds as they thickened and became permanent. They point to the unusual Y and C cloud features that absorb ultra violet radiation as a possible indicator of micro-organisms that use u-v to power life processes.
Artist's impression of Venus Express orbit insertion Credits: ESA - AOES Medialab
The Venerean atmosphere has another unexplained feature – a thick layer of sulphur dioxide. This was discovered in 2008 by ESA’s Venus Express and recent simulations have shown that it may have been produced by the evaporation of sulphuric acid droplets. This shows that the atmospheric sulphur cycle is much more complicated than was thought. It also casts doubts on some earth-bound ideas of injecting sulphuric acid into our atmosphere to slow the effect of climate change.
If you miss Venus and Uranus this month – look out for Venus near Jupiter on March 15th, in a spectacular planetary conjunction which is easily the best of Venus’ 2012 appearance.
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