An amateur astronomer may have found the first crater ever spotted on Jupiter鈥檚 moon Io. Io is so volcanically active that eruptions tend to wipe away any impact craters, so we have never seen one until now.
Jesper Sandberg, an amateur astronomer in Sweden, spotted this apparent crater while combing through archival images from the Galileo spacecraft, which orbited Jupiter from 1995 to 2003. It is relatively small, just about 100 metres across, and located on a broad, flat plain of sulphur dioxide frost spewed out by Io鈥檚 many volcanoes.
鈥淲e can鈥檛 be 100 per cent sure that this is an impact crater because it鈥檚 a very small one and the image is not very high-resolution, but it certainly looks like one,鈥� says at NASA鈥檚 Jet Propulsion Laboratory in California, who is part of a team working to analyse the crater further. 鈥淭here鈥檚 nothing else around it and it鈥檚 very circular.鈥� The team presented its preliminary results on 13 December at a meeting of the American Geophysical Union in California.
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If the feature were the top of a lava tube, for example, it would be on a lava flow, not by itself in the middle of the frost plains. If it were the result of volcanism, we wouldn鈥檛 expect it to appear so perfectly circular, whereas impact craters are almost always round because of the way a collision blasts away material in all directions.
Neither the Juno mission, which has been orbiting Jupiter since 2016, nor the JUICE mission, which is on its way there, has the equipment to take high-resolution images and check whether this really is an impact crater 鈥� so we may never know for sure. 鈥淚o changes on a rapid scale, and that can be kind of frustrating,鈥� says Lopes. 鈥淲hen we go there with another mission, maybe years from now, this crater might not be there anymore.鈥�
