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MESSENGER's new view of Caloris

MESSENGER's new view of Caloris
MESSENGER's new view of Caloris During its first flyby of Mercury MESSENGER finally got a look at the western half of the Caloris basin, a giant impact structure only partially revealed by Mariner 10. One of the first lessons learned from the MESSENGER image is that Caloris is larger than initially thought; the diameter estimated from MESSENGER data (blue dashed line) is 1,550 kilometers, compared to the 1,300 kilometers estimated from the Mariner 10 images (yellow dashed line). Very close to the geographic center of the basin (blue dot) is an enigmatic feature that the science team refers to as the "spider." Throughout the Caloris basin, small craters have unusual appearances, with dark interiors or rims, hinting at compositional differences among the materials hidden beneath the basin. NASA / JHUAPL / CIW