Mysteries of Jupiter

That second most important object in the Solar System, Jupiter, has had its ups and downs recently.

Several months ago its Southern Equatorial Belt vanished. Jupiter is of course a gas giant world with no surface as we know it. When we look at Jupiter through a telescope or binoculars (what do you mean you've never seen it? Look east in the early morning sky, it's the big bright thing!) we are looking at the top of a cloudscape. The planet's rapid spin forces the clouds into a series of bands running parallel to the planet's equator. Dark coloured bands are called belts, light ones zones, each has its own characteristics and is semi-permanent. The zones' pale colours are those of frigid wisps of frozen ammonia crystals, the belts are coloured by darker (possibly organic) material dredged from the planet's mysterious depths.

The Southern Equatorial Belt is usually the most distinct and dramatic belt, unsurprisingly the Great Red Spot is to be found there. Occasionally, though it fades away leaving a pale emptiness, obscured by cold clouds of ammonia, only to emerge again. We do not know why yet, the whole planet's atmosphere is a complex system of convectional upflows and downdrafts driven by titanic interplays of heat from the Sun and Jupiter's interior shaped by the mighty Coriolis forces of the planet's spin. We cannot yet accurately model the atmosphere of a tiny world like our own, never mind that of a behemoth like Jupiter. Presumably in the next few months the Southern Equatorial Belt will reappear, until then I cannot look at Jupiter without thinking that something is missing.

Then on 3 June 2010 amateur astronomers Anthony Wesley (in Australia) and Chris Go (in the Philipines) simultaneously observed a flash of light on the disc of Jupiter. This is not Wesley's first discovery of something hitting Jupiter, he was already celebrated for drawing the world's attention to the July 2009 impact on the planet which left a black smudge almost the size of the Earth on the planet. Similar wounds were observed following the 1994 impacts of the Shoemaker-Levy 9 cometary bodies and are thought to be clouds of dark and sooty debris from the impacting body.

Yet no such marks have appeared this time. Even the Hubble Space telescope's very sensitive Wide Field Camera 3 has failed to find any Jovian bruises. The impact location is circled in the HST image above, nothing can be seen there. Why was this event's aftermath so different? The previous impactors are believed to have penetrated deep into the planet's gargantuan atmosphere before exploding. In the latest case, the object was probably a giant meteor (giant by our standard, tiny compared to the previous impacting bodies) which burnt up at a high altitude above Jupiter's cloud tops, failing to leave behind a debris cloud, as seen in previous Jupiter collisions.

Wesley and Go were lucky enough to observe a fleeting glimpse of a flash of energy bright enough to be seen here on Earth, across 770 million kilometres of space. Take a moment to imagine what a similar impact would do to our fragile world. It is a frightening thought.

Image credit: NASA, ESA, M. H. Wong (University of California, Berkeley, USA), H. B. Hammel (Space Science Institute, Boulder, Colorado, USA), A. A. Simon-Miller (Goddard Space Flight Center, Greenbelt, Maryland, USA) and the Jupiter Impact Science Team.