COMING 2001 MARS (07)

  To show how we did observe the south polar cap (spc) in 1986 in the appropriate season, we here cite a page from CMO #029 (25 March1987 issue) at p0225 where the locations of the spc's edge were plotted on a polar coordinate based on the observations of the present writer (Mn) during the season from 198°Ls (1 July 1986) to 216°Ls (31 July 1986). The period included the opposition on 10 July and the day 16 July when Mars most approached. The Figure was obtained by Le-Hsia CHANG at Taipei who measured the spc's depth d on Mn's drawings 140 times during the time Mn stayed at Taipei and calculated the latitudes of the edges based on the procedure introduced in CMO #003 (25 February 1986); one of the main formulae was given
        psi = - |phi| + cos^-1(1- (d/r)),
where psi is the half-width of the spc, phi the central latitude, and r the radius. CMO #003 also shows a Mariner 6 photograph of the spc on 30 July 1969 at 199°Ls (the season in 1969 when the planet was closest was 170°Ls however). The spiral does not show the contour of the spc at a fixed Ls, but the observations by Mn were performed every 40 minutes and hence locally the data were dense.

  The result proved that the spc was normal or was normally thawing in 1986 at the period; this was known if compared with the averaged results compiled by G E FISCHBACHER et al (Lowell Observatory, 1969) which were read from the Lowell Archives from 1905 to 1956. The second map in Fig 2 (which is cited from a page in P B JAMES et al, JGR 84 (1979) 2889) is the very map and shows the contours at 200°Ls and 210°Ls to be compared. The first map shows the data acquired by the Vikings .

  Later Kyosuke IWASAKI et al published their data on the 1986 spc boundary observations at Bosscha (K IWASAKI, Y SAITO, Y NAKAI, T AKABANE, E PANJAITAN, I RADIMAN & S WIRAMIHARDJA, Behavior of the Martian South Polar Cap 1986, Publ. Astron. Soc. Japan 41 (1989) 1083) and we cite here one of their results during the period from 205°Ls to 214°Ls. The circle is claimed as the best-fit circle and its center is located at (88.4°S, 10.8°W). No other earlier data in 1986 is there.

  We thus recommend the readers to observe the spr intensively this season also, if possible every forty minutes, to make the spiral polar coordinate map of the spc's edges and to compare the results with the data of the spc perimeters in Fig 2. The Viking observation began from 176°Ls, and hence no data before the period, but the data from the Lowell archives give the boundaries at earlier stages (maybe much affected by the south polar hood).

  Another but interesting observations may be made when the centre of the spc deviates from the south pole. As to the phenomenon, we touched in CMO #008 p0057: Referring to the observations also by A DOLLFUS in 1956, we called the readers' attention that they should concentrate on the spr from 230°Ls to 240°Ls. This year the season of 230°Ls will reach on 9 September 2001 and 250°Ls on 10 October 2001. The deviation was well observed in 1986 (cf CMO #018 p0145 (10 Oct 1986)), but more minutely in 1988:

  The last but not the least we make mention of the detachment phenomenon of Novus Mons (the Mountains of Mitchell): According to E C SLIPHER, Novus Mons begins to detach from the spc between 250°Ls and 252°Ls, but the Viking image shows that it was still a part of the spc as a peninsula even at 255°Ls. The peninsula is however to be checked around from 230°Ls, and hence the attention should be called from the beginning of September this year. Note also the Viking already found the shape of the brighter Novus Mons well inside the spc even at 183°Ls. All these are stated in CMO #007 p 0047 (25 April 1986).

  A report on the appearance of the early stage of the spc in 1986 and 1988 is found in CMO #115 p1004, and a report about the detachment of Novus Mons in the case of 1988 was given in CMO #111 p0963. The head page of CMO #116 shows a TP photo of MURAKAMI (Mk) by the use of a 10cm refractor on 29 Aug 1988 (at 262°Ls) at LCM=000°W where Novus Mons is clearly shot.

  We add that to compare the spc shown here in Fig 1 with the case this year, we should acquire the data of the spc perimeter at the beginning of August by taking account of the fact that the tilt of the central latitude is different. The following spiral data in 1986 was for example cited in CMO #040 p0335 where the season from 216°Ls to 235°Ls (during August 1986) was treated. There was observed no abnormality in the rate of thawing in 1986.