The latest set of photos beamed back by NASA’s Messenger probe have revealed more interesting features from Mercury. Earlier this month photos from Messenger showed huge cliffs, now the mission has found a strange ‘spider’ feature and been forced to increase estimates of the size of a massive basin on the planet.
“This flyby allowed us to see a part of the planet never before viewed by spacecraft, and our little craft has returned a gold mine of exciting data. From the perspectives of spacecraft performance and manoeuvre accuracy, this encounter was near-perfect, and we are delighted that all of the science data are now on the ground,” says Sean Solomon, principal investigator for the mission (press release).
The Spider
This feature – of a type not seen before on Mercury or on the Moon – consists of over a hundred narrow trenches radiating out from a central point. An impact crater in the middle may explain this feature, which NASA says resulted from the breaking apart of materials that filled the Caloris Basin (where the feature resides) after its formation.
But it may not. “The Spider has a crater near its centre, but whether that crater is related to the original formation or came later is not clear at this time,” says James Head, science team co-investigator at Brown University, Providence. Infuriatingly there are no other explanations at this time.
Caloris Basin
As well as being home to the Spider the basin itself has surprised scientists. Data from the last Mercury mission in 1975 led to the belief that the basin was around 1,300 kilometres across. Now it looks like this estimate will be revised upwards by up to 250 km.
“Understanding the formation of this giant basin will provide insight into the early history of major impacts in the inner Solar System, with implications not just for Mercury, but for all the planets, including Earth,” says Robert Strom, of the University of Arizona.
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Photo and presentation details from the NASA team
Images: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Brown University