Forthcoming 2007/2008 Mars
(9)
The
Second Bright Dust at Deucalionis R in 1956
CMO #333 (10 July 2007)
Masatsugu MINAMI
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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=246°Ls))
began to subside around from 10 September (λ=259°Ls), 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=274°Ls) as
described in Tsuneo SAHEKI’s 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. SAHEKI’s 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=260°W. On 4
Oct at 12h GMT (21h JST) it read ω=268°W, 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=249°W~),
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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