Astronomical Society of Coonabarabran

Aussies on the Moon: We Search For Mawson

by Harry Roberts

In an earlier piece I suggested there are craters on the moon named after Australians, and we looked at crater Tebbutt and its impressive surroundings near Mare Crisium. We've also paid a visit to hard-to-see Gum. My next 'aussie' is Douglas Mawson, geologist and south polar explorer.

But wait! Mawson was born in UK and emigrated at the age of two, izzie an 'aussie'? Given that he grew up here, led Australian expeditions to Antarctica, gained his degree in Sydney I feel bound to class him an Australian. So where's his crater?

If you have an older map of the Moon's south polar region you may find it there, in addition to Shackleton and Scott, but in Rükl's "Atlas of the Moon" there's no trace of Mawson!

Fate robbed Mawson of the crater provisionally named for him. It happened like this: in 1997 when Gene Shoemaker died in an out-back crash his colleagues executed a remarkable plan to honour his work in astrogeology, they put some of his ashes aboard the Lunar Prospector probe and (when its work was done) crashed it into crater Mawson! The crater that now held Shoemaker's ashes was then named Shoemaker by the IAU, so ending Mawson's chances of a crater name.

Mawson is however honoured by a prominent mare ridge network (a dorsa) in Mare Fecunditatis. This is a marvellous feature, and when the lighting is right looks very like one of the ice ridges Mawson laboured over in searching for the Earth's south pole, and we may imagine him dangling down a crevice held only by his harness to the sled above.

After a long wait I finally had good lighting on Mawson's ridge on 2007 September 15, with the terminator only four degrees west of the landform. The dorsa casts little shadow even under low altitude lighting, and can only be a few hundred meters high. Even so it looked impressive. Giant crater Langrenus loomed at the east end, and the dorsa arose near a trio of smaller craters, the largest being Bilharz. At the west end of Dorsa Mawson a "ghost" crater with only the letter name U cuts through a branch of the dorsa. Another "ghost" is north of U, there are several of these partly submerged craters in the area, and the lava that flooded Mare Fecunditatis must be shallow in places. Perhaps Dorsa Mawson is the source of these flows.

Several fresh small craters punctuate the field, all shadow filled. Messier G (or Lindbergh) is labelled G. Below right of it is Ibn Battuta. Dorsa Mawson "disappears" as soon as the Sun rises over the site. Best views are 3 or 4 days after New Moon, or 3 days after Full Moon. The Dorsa is 180km long and about 22 wide.

Has Mawson's claim to a south polar crater lapsed for good, or will it be reconsidered? His claim to joining the other great polar explorers, ill-fated Scott, Shackleton, Amundsen et al, is a strong one. Wait and see. At least Dorsa Mawson is easy to find, whereas crater Shoemaker is almost impossible to view.