Popular Astronomy

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Thu, 19 Jan 2017 - Interesting weather on the planets!

A number of interesting things are happening on the planets of our solar system at the moment. New cloud features have been discovered on Venus, we need to observe for planet-wide dust storms on Mars and enormous white storms are appearing in the South Equatorial belt of Jupiter.

Starting with Venus, instruments aboard the Japanese Akatsuki probe, currently orbiting Venus, have seen a strange wave of cloud in the upper atmosphere that resembles a ‘bow-shock’ and which spans some 4000 miles in size. The atmosphere of Venus ‘super-rotates’, that is it moves very much faster than the surface of the planet as it rotates; however this new cloud, which has been dubbed a “gravity wave”, stays stationary with regard to topographic features at ground level. It is thought that the Venusian atmosphere, while very dense, is much too thick for effects caused by the uplift of gas, as it is pushed up over high mountains, to be visible at the top of cloud-deck, however scientists believe that some form of phase-transition is taking place in gas forced very high in this way. This causes a rapid rise in density and the material then becomes more susceptible to the effects of gravity and sinks rapidly. The resulting atmospheric disturbance can be visible all the way through to the cloud tops.

So far the effect has only been seen by one space ship observing deep into the infra-red and the ultra violet, well outside the wavelengths accessible to instruments on the Earth’s surface, but amateurs are speculating that they may be visible here when large surface features such as Venus’s Mount Aphrodite are on view. These gravity waves are a meteorological feature and should not be confused with gravitational waves; distortions in space-time.  Amateurs regularly observe and image cloud detail on Venus using ultra-violet pass filters and these often form in ‘V’ or ‘Y’ shaped patterns and are not thought to be associated with these newly discovered gravity waves. Drop this link into your web-browser to see the original article published in Nature Magazine.

There are also major changes in the cloud patterns of Jupiter, though these are changes that have been observed before and may follow a predictable pattern. A white plume of gas has risen to the surface of a previously smooth and settles part of the South Equatorial Belt (SEB) indicating what may be the start of a large and impressive outbreak of convective storms within the belt. The first indication of this was seen by Phil Miles, observing from Australia, in late December and since then the convective region has grown. We would expect it to be joined soon by other white storms in roughly the same area and it will be an area of interest for the Juno probe to observe as it swings in its long elliptical orbits around the planet. Amateurs can expect to observe the outbreak for several weeks, even months, and should look around longitude 208 degrees using the L2 system, that is currently some 60 degrees ahead of the Great Red Spot. Amateur images from section members would be very welcome in the next few weeks.

Mars has reached the season in the southern hemisphere when massive dust storms have been known to kick-off and spread around the planet. Although not regular occurrences, planet wide storms can be seen in late summer for the southern hemisphere and have been seen starting as yellow streaks rising from known features such as the Hellas basin. Mars is very small and distant at the moment and is being ignored by many observers, however if you should spend part of the early evening looking at the crescent shape of Venus, please then switch to Mars, which remains nearby for the next couple of months and is visible for some hours after sunset; you may just be one of the first to catch one of these planet wide storms commencing.


Added by: Alan Clitherow