A colossal ring of gas has been revealed around Jupiter by NASA鈥檚 Cassini space probe.
The cloud is composed of water and lies along the orbit of Jupiter鈥檚 icy moon Europa, 670,000 kilometres from the planet. Researcher think the cloud is generated by radiation from Jupiter bombarding the surface of Europa.
Physicists from Johns Hopkins University, Maryland, studied measurements taken by Cassini as it flew past Jupiter in late 2000 and early 2001.
Advertisement
They conclude that the gas cloud both generates and attracts charged radiation particles and thus helps to maintain Jupiter鈥檚 magnetosphere 鈥� the region influenced by the planet鈥檚 magnetic field.
鈥淪urprisingly, Europa鈥檚 gas cloud compares to that generated by the volcanically active satellite Io,鈥� says Barry Mauk, at Johns Hopkins. 鈥淏ut where Io鈥檚 volcanoes are constantly spewing out gas, Europa is a comparatively quiet moon. The water gas we see is a direct consequence of its icy surface being bombarded so intensely.鈥�
The data were captured with a camera on Cassini that uses a technique known as energetic neutral atom imaging. 鈥淭his makes visible the three-dimensional structure of planetary space environments, which, until recently, were invisible to remote imaging techniques,鈥� says Mauk.
Cassini is on course to arrive at Saturn in July 2004, when it will deploy a smaller spacecraft called Huygens to study that planet.
Journal reference: Nature (vol 421, p 920)