------------------------------------------------------------------- THE ASTRONOMER Electronic Circular No 1036 1996 Jan 20 15.45UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP,England. Telephone/FAX(0256)471074 Int:+44256471074 INTERNET: GUY@TAHQ.DEMON.CO.UK GMH at AST.STAR.RL.AC.UK WORLD WIDE WEB http://www.demon.co.uk/astronomer ------------------------------------------------------------------- MARS Ron Baalke reports via Astronet details of a possible Global Dust Storm on Mars as follows: "Todd Clancy (CU/LASP) reports that observations from Kitt Peak indicate that a large-scale dust storm is occurring on Mars. He is observing Mars with the 12-m NRAO telescope, measuring atmospheric CO absorption lines at millimeter wavelengths. Normally, under clear atmospheric conditions, there is a large enough temperature difference between the Martian surface and atmosphere to result in the formation of absorption features having high contrast. However, under dusty conditions, the surface-atmospheric temperature difference is smaller, and the absorption feature constrast is substantially decreased. He reports that observations from Kitt Peak this week (at Ls=222) reveal lower CO absorption band contrast than usual, indicating an estimated >=20K elevation in the atmospheric temperature above the 10-20 km level. This amount of atmospheric heating is consistent with a global-scale dust storm event, similar in nature though not as large as the events reported by Clancy and colleagues Grossman and Muhleman during April 1994 and April 1992. Todd Clancy notes that since this storm has apparently just begun (atmospheric heating was not detected in this year's observations prior to Ls=222), it is probably only in the early to mid stages of the dust build-up. Additional millimeter observations are planned for this weekend and later in January in order to confirm the storm and to more accurately quantify the dust opacity. It would be highly desirable to obtain visual confirmation of this dust event, both in order to scrutinize the storm itself as well as to "practice" obtaining the types of groundbased support observations that are needed by the upcoming Mars Pathfinder mission. However, this is a difficult and challenging task, as Mars is currently only 4.0 arcsec in apparent diameter and only 13 degrees from the Sun (and approaching conjunction). Both professional and amateur observers who can observe Mars now are encouraged to do so to try to provide visual verification and additional information about the character of the dust storm. Unfortunately, the Hubble Space Telescope will not be able to observe Mars until September because of solar phase angle limitations. EDITOR'S RETURN I am grateful to Martin Mobberley and Nick James for deputising for me during the last few days and can confirm that I am once again available to deal with TA queries and possible discoveries. Guy M Hurst