Lunar Gullies – slip sliding away….
Running water on Earth carves into soils causing gullies. These are particularly well seen on hillsides and steep slopes, often resembling ditches and small valleys. Similar features have been spotted on photographs of Mars (Fig. 1), but there is much scientific debate about whether such gullies are caused by running water, periodic release of snow or underground ice or frozen carbon dioxide or if they are formed in slope or debris collapses that do not have to involved water at all (e.g. landslides).
Fig. 1. Gullies on Mars.
In both cases the start of the gully is at the top of the image and material has flowed towards the bottom of the image. LEFT: Gullies in Nirgal Vallis. MGS MOC Release No. MOC2-535.This is a Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) narrow angle image of gullies carved into debris on the south-facing wall of Nirgal Vallis, an ancient martian valley. Scaled image width: ~3 km. RIGHT: MOC image S09-01005. Crater Wall in Noachis Terra. Scaled image width: ~1 km. Here the gullies are well developed with deep upper cut regions and fan like debris deposits at the bottom of the slope.
In 2006 Gwen Bart, a US planetary scientist searched through available images of the Moon that were collected by 1960’s Lunar Orbiter mission to see if she could find examples of gullies on the Moon. She suggested that if gullies could be seen on the slopes of lunar craters, and as the Moon typically has very very little water, it may provide evidence that gullies on Mars don’t have to have formed in the presence of water or ice. Her preliminary results are presented here and there is a nice summary of the implications of her study here.
As Moon Zoo users well know – the new images by the LRO LROC NAC are knocking the spots off the older Moon photos! For example, now we have these amazing new NAC images they are showing that gullies really are found all over the Moon…
Montage of LROC NAC image M127009259 (not map projected) showing view of Gambert C crater which is located on the nearside of the Moon near Copernicus crater.
Close up images of gullies in Gambert C crater shown in wider view above. Several gully networks can be seen in each image. In all cases the source of the gullies is at the top of the image and they flow down towards the base on the image. Flows and gullies show lobate tracks and channels, often with blocky rubble material having been pushed to the sides and end of the main channel.
Left: Montage of LROC NAC image M105185599E (not map projected) and close up section shown at right. Bright, elongate gully tracks can been seen in the photo eminating from bright rubbley regions on the crater wall. The gullies start in the bottom left hand corner and flowed towards the top right.
And Moon Zoo users have already done a great job in spotting some really nice examples of landslides, gullies and channels on slopes. Check out the examples in Birt crater, Proclus crater and in other places on the Moon here and here.
So – we would like to issue a renewed challenge to keep a close eye out for gullies and landslides on the Moon. Hopefully your discoveries will help to provide a good database that scientists can use to address the diversity, shape and form of gullies on the Moon compared with those seen on Mars, the Earth and other planets.
Please remember, as well as posting examples on the Moon Zoo Forum under the landslides and gullies topic, if you find examples in the Moon Zoo user interface to flag these features as linear features so that we also have a record noted in our database!
Thanks for your help,
Moon Zoo Team
(Thanks to Allan Treiman and Amanda Nahm at LPI for drawing our attention to this interesting lunar science and Martian science topic).