The changing faces of the planets

With Saturn’s rings just past being edge on to us, the familiar disc and hoop appearance of the planet has turned more to a disc and line (such as in Christopher Go‘s photos, which I mentioned in an earlier post). However, Saturn (a true colour video of which has come from Cassini) isn’t the only planet looking a little bit different at the moment. Jupiter has lost its southern equatorial band.

Looking at the giant planet through small telescopes, it normally appears as a big disc with two dark bands crossing it. Now one of them has vanished, the one normally overlaying the big red spot. Before and after photos of the event, which happens every 3-15 years, can be seen here. The band is expected to return, but not for a while.

Mars is well known for changing its appearance at the eyepiece. As dust storms rage on the Red Planet, they can obscure details on the surface. But even further back in time, volcanic ash once filled the air along with the dust. Meridiani Planum is a dark feature on Mars, coloured by volcanic ash and lying between the Tharsis volcanic Region and the Hellas Planitia impact basin. It is the Greenwich Meridian of the Martian Geographic System used by those who study the planet. Studies of the region with the High Resolution Stereo Camera of the Mars Express satellite have been used to determine the prevailing wind system in the region, noting that ash seems to have been picked up and deposited preferentially in one direction. With such a dynamic landscape and changing views, Mars became the perfect model for the A Moment in Time project of the New York Times Lens Blog. The idea was that at 15:00 UTC on May 2nd, people around the world would take shots. As it happened, people around the world and one off-world rover – Opportunity – ended up participating. Universe Today carries that picture.

Venus and Mercury may not have any discernible surface features (beyond a few clouds edging on the UV side for Venus, visible to some), but they both undergo phases. Venus shines brightly in the evening for those with a good western horizon at the moment and Mercury will be popping up low on the eastern horizon in the mornings.

But it isn’t just physics and chemistry altering the faces of planets, biology does it too. Every time you breath in, you take oxygen out of the atmosphere and pump carbon dioxide into it. So what is the cumulative effect of every creature that ever walked, slithered or in other ways interacted with the atmosphere on the atmosphere of the Earth? According to Discovery, it was to turn the sky from orange to blue, taking out the methane and promoting the oxygen-nitrogen atmosphere we see today. Algae trying out the latest thing – photosynthesis – and a glut of phosphorous rich rocks exposed by geological changes fed the change.

But one little rock in the sky that hasn’t got a ‘biosphere’ to make such a change is Titan. Saturn’s largest moon has surprised researchers recently, who have noticed a methane-ethane based weather system moving slowly over the surface of the frozen world. Now, according to data from Cassini, the gentle rains have a new added feature – flash flooding. Deposits of ‘pebbles’ made of rock solid water ice and smoothed to spheres by liquid flowing through river channels have been seen in reflected microwave data. It is now hoped that as the seasons at Titan are on the change, some view of the actual rivers flowing might be caught, to be pinned up on the Cassini team fridge along with such gems as light glinting off the surface of lakes on the tiny satellite.


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