[BAA 00467] Mars Section: North polar cap

[Rick]

BAA electronic bulletin No. 00467 -- http://www.britastro.org/
Bulletin transmitted on Thu Jan 28 23:12:38 GMT 2010
(c) 2010 British Astronomical Association

Mars Section: North polar cap

Mars comes to opposition tomorrow. It is to be hoped that the recent extreme weather over the UK and Europe will not succeed in completely spoiling the moment for everyone.

Just now, there is an especially interesting feature visible within the large North polar cap, and observers should give it their attention. It is shown on many images, but visual observers often miss it: an annular rift is observable at all longitudes as a thin, dark line. When the seasonal carbon dioxide cap has sublimed away, this feature (a permanent dune field) will mark the boundary of the small cap remnant which persists throughout the summer. It is also known as the polar collar, and its thickness varies with longitude. The annular rift within the cap was well seen by Section members at the 1995 opposition, and it is also visible on amateur (and HST) images from other oppositions during the 1990s decade. However, historical observations have rarely shown it, suggesting that perhaps the thickness of the seasonal polar deposit may vary slightly from year to year. Historical data are reviewed in detail in our 1995 Section Report, which may be downloaded as a pdf file from the Mars Section website (http://www.britastro.org/mars).

Observers are also reporting brighter parts of the cap near its southern boundary: later on, irregularities and rifts will appear and portions of the cap will become detached. The best-known and largest of the detached portions is labelled Olympia on the telescopic maps. All of these details should be carefully recorded, and the data sent to the undersigned.

Further notes about the current opposition will appear in the February number of the BAA Journal.

Dr Richard McKim, Director, 2010 January 25