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The Second Bright Dust at Deucalionis R in 1956

CMO #333 (10 July 2007)

Masatsugu MINAMI


 

Japanese here


T

HE southern summer dust shows a tendency to encircle the Martian globe to the westward direction, generating several resonances of dusts. In1971, the 1971b Noachis dust storm completely circled the planet at mid-latitudes on 15th day, and it became impossible to trace the markings about after the 23rd day because the dust became thicker (J L MARTIN, Icarus 22 (1974) 175). The Noachis dust in 1956 was also of the southern summer type and encircled by about ten days, and (starting from 20 August 1956 (λ=246Ls)) began to subside around from 10 September (λ=259Ls), and so it was about for 20 days that the dust was furious. So the 1956 one was on a reduced scale, but showed an interesting aftermath.

If the dust grows thicker rapidly it may become difficult to detect a successive series of the resonant dusts, but if it shows the subsiding state early, some successive dust occurrences may be checked. In 1956, 45 days after the initial Noachis dust outbreak a second bright dust was onset in Deucalionis R on 3 October (λ=274Ls) as described in Tsuneo SAHEKIs book in 1968. From the end of September the area around S Meridiani and M Serpentis was disturbed (sometimes S Meridiani was cleaned up) and on the 1st and 2nd days of October, Deucalionis R showed an irregularity, but on 3 October 1956 the area suddenly brightened with a thick dust cloud, and it was observed by several (well-known) Japanese observers including Shotaro MIYAMOTO, Sanenobu FUKUI, Ichiro TASAKA and others. Among them there was named our colleague Takashi NAKAJIMA who was a beginner and only a high school boy at that time, using a 15cm refractor at the Fukui City Observatory. Here we shall show his drawing on the day. Since it was after opposition (at opposition on 10 September, closest on 7 September) the dust was new at the morning side. SAHEKIs book shows his own drawing on 4 October when the dust was also brilliant, and another made on 5 October which shows an eastward faint extension of the dust segment. (Unfortunately or strangely however, no record of the appearance of the dust on the morning terminator is described. The phase angle was about ι=20, and so Deucalionis R must have begun to show up at around ω=260W. On 4 Oct at 12h GMT (21h JST) it read ω=268W, and hence it was possible to catch and observe the early morning state of the dust reproduction.) It is reported that the last observations of the dust at Deucalionis R were made by MIYAMOTO and FUKUI on 6 October GMT and the dust was still existent. [MIYAMOTO observed on the day at 11:56GMT ~(ω=249W~), 14:55~(ω=292W), 17:13~(ω=326W): They may cover a vast interval of angles, but are never dense. Next observation was made on 14 October.] No further observation was in Japan. If it was possible to watch until 17h GMT (2h JST) it must have been possible to chase from Japan till 11 October. In addition to the weather conditions problem, we may say no definite observational method of the dust cloud was established at the time yet. Anyway the scene went to Europe. However no report of the dust on the European side is included in Richard McKIM, Memoirs of the BAA, 44 June 1999 issue (see p75), except for some comments on Henri CAMICHELs photo on 8 October at Pic. The dust stepped on brilliantly, but was forgotten. The apparent diameter on 10 October was still d=20.6".

To sum up, as in 1971 if the dust rapidly grows it may be hard to decipher each resonance, but if the optical depth of the dust continues to be shallow (or even if it begins to subside), we may be able to check and chase several sequences of dusts in the southern summer season.

 


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