April 14, 2012
What Caused the Melting?
image from Chauhan and colleagues (2012)
In 1968, flush with the exhilaration of high-resolution Lunar Orbiter V images, Bob Strom and Gilbert Fielder interpreted flows and fractures within Tycho as evidence of volcanism. That was a reasonable interpretation for the time but by the mid-70s an understanding was developing of the wide distribution of flowage and splashing of impact-melted rocks. Impact melted and volcanic flows look similar but the very critical question is what caused the melting? If 100 m.y. old Tycho had extensive volcanism then the thermal history of the Moon was much different than widely believed. Surprisingly, scientists associated with the Indian Chandrayaan-1 lunar orbiter team have just published an article that could be Strom and Fielder, part 2. Using the wonderful high resolution images from Chandrayaan-1 and from LRO the team identifies morphological features like domes, fractures, lava ponds, lava channels, etc. They interpret these as being true volcanic landforms that erupted from an underlying plutonic (= unerupted volcanic) body, with the eruptions being triggered by release of pressure due to the impact removing billions of tons of overlying rocks. This theory goes against a huge body of understanding of impact melts, especially considering much new information from LRO. Looking at impact melts in hundreds of lunar craters it is clear that the flows and ponds in Tycho behaved exactly the way impact melts are manifest at large crater diameters. Building and launching a rocket to the Moon is a daunting challenge that requires engineers and scientists to learn from previous countries' experiences. No less is required of the scientists who interpret lunar data.
Rükl plate 64
Compositional and morphological analysis of high resolution remote sensing data over central peak of Tycho crater on the Moon: implications for understanding lunar interior (2012) Prakash Chauhan, Prabhjot Kaur, Neeraj Srivastava, Satadru Bhattacharya, Ajai, A. S. Kiran Kumar and J. N. Goswami. Current Science, Vol. 102, No. 7, 1041-1046.
Evidences of Multiphase Modification over the Central Peak of Tycho Crater on Moon from High Resolution Remote Sensing Data. P. Chauhan, N. Srivastava, P. Kaur, S. Bhattacharya, Ajai, A. S. Kiran Kumar, J. N. Goswami & R. R. Navalgund (2012) 42nd LPSC, 1341.
A more extensive, 1970 version of the Strom and Fielder work.
Yesterday's LPOD: A Tilting Tale
Tomorrow's LPOD: A Thick Pile of Debris