98/99 Mars CMO Note (8)

1998/99 Mars CMO Note
- 08 -
from CMO #231


  @ Many visual observers can detect a conspicuous fragment called Olympia detached from the north polar cap (npc) centered near at longitude=200°W as the npc recedes down to its minimal state. The observations in 1997 were reported in CMO #202 p2259 and supplemented in #204 p2288: Olympia was visually observed even by a 15 cm class telescope. The HST image taken on 10 Mar 1997 (089°Ls) near at LCM=210°W shows clearly a detailed aspect of Olympia, and was cited in #202 as well as in #189 p2076.

  @ An existence of another white detachment preceding Olympia was also suggested on the partial sketch shown right at p2259 of #202 which was taken on 20 Mar 1997 (093°Ls) at LCM=137°W by the present writer (Mn).
  Similar observations by Mn were made on 24 Mar 1997 (095°Ls) at LCM=112°W (Mn-427D/1997), on 25 Mar 1997 (095°Ls) at LCM=108°W (Mn-437D)~LCM=128°W (Mn-439D/1997), and on 27 Mar 1997 (096°Ls) at LCM=115°W (Mn-447D)~LCM=135°W (Mn-449D/1997) etc.

  @ It is much harder to detect this smaller detachment than to see Olympia, but fortunately this apparition in 1999 we succeeded in watching clearly the detachment on 16 May 1999 (140°Ls) under good seeing condition at Fukui (by the use of a 20 cm refractor). We started from 10:20 GMT just after twilight at LCM=099°W (Mn-572D/1999). The detachment was already seen at the morning side, but from 12:40 GMT, the white fragment became constantly and clearly visible, and thus quite evident on the drawings made at LCM=138°W(13:50 GMT, Mn-572D)~LCM=157°W (Mn-574 D).

  From 15:00 GMT, the seeing condition turned to be poorer, and no more than Olympia was detected. That night we watched up until 17:00 GMT at LCM=196°W (Mn-578D).

  On 17 May 1999 (140°Ls) we also narrowly observed it under a worse seeing condition at LCM=109°W (Mn-583D) and also at LCM=119°W (Mn-584D). It was still possible to see it 21 May 1999 (142°Ls) at LCM=130°W (Mn-596D), and on 22 May 1999 (142°Ls) at LCM=092°W (Mn-604D): The later case the detachment was quite in the morning side.
  @ The observations on 16 May showed us that a deeply dark area lay between this detachment and Olympia adjacent to the npc. This was judged to be Deucalidonius L. From the lake, a canal Magnes is said to run southwards: This was not detected but it consisted a boundary of the reddish dark region to Propontis II, while the eastern preceding side appeared less reddish and less darkish.

  @ Soon we learned that Nicolas BIVER (NBv) at Hawaii clearly detected the white detachment on the preceding day 15 May 1999 (139°Ls) at LCM=103°W. The time was at 10:00 GMT, when it was still bright at Fukui. NBv used 510x 26cm spec. This was reported in #218 p2523 (unfortunately the day 15 May was misprinted as 5 May). Partially here cited the drawing: As to the original refer to NBv's Web-Site (cf. #210 p2377).

  @ A bird's eye view of the npc at a minimal state observed by Audouin DOLLFUS (ADl) in 1946~1952 was published in Icarus 18 (1973)142, and cited in our CMO #183 (25 Jan 1997) at p1083. Here we reproduced his map at 108°Ls (from an original copy; by courtesy of A DOLLFUS). 180°W is up. Note that Ierne is evident as well as Olympia, and Deucalidonius L is dark between them.

  @ ADl observed the north polar region thirty years later in 1984 by the use of 1000x 200 cm telescope at l'Observatoire du Pic-du-Midi. Here cited is the one reproduced from the juillet-août 1987 issue of l'Astronomie. This drawing was obtained on 12 Apr 1984 (132°Ls) at around 4:00 GMT. The LCM was so nearLCM=139°W, and the drawing can be thought to show the same detachment in addition to Olympia. The planet was at opposition on 11 May 1984.

  @ As far as we know, the detachment is said to have not so often observed through smaller/medium sized telescopes. Toshihiko OSAWA in 1982 (opposition on 31 March) however clearly dissolved this fragment further to two pieces. We here cite his observation on 21 May 1982 (125°Ls) at LCM=134°W by the use of a 31 spec. Here the picture is reproduced from the article by J DRAGESCO, La Planète Mars en 1981-1982, l'Astronomie, juillet-août 1986 p327.

  @ The HST in 1997 (opposition on 17 Mar) of course depicted the fragment in addition to Olympia. See the one cited in CMO #191 p2102, which was taken on 30 Mar 1997 (097°Ls) at around LCM=094°W. From the HST images in 1999, we here show the one taken through 502 nm wavelength on 28 Apr 1999 (131°Ls): The LCM lies between 111°W~124°W: The detachment proves to consist of several smaller ingredients. The circular cloud on the preceding side is the famous cyclone which has been weakened in the afternoon (#227 p2666).

  @ The detachment in question is usually called Ierne. The map of E M ANTONIADI (Calotte polaire boralé) does show this white fragment, but it is not named. Olympia was named by him in 1903 and clearly made entry to the map. The nomenclature Ierne (SCHIAPARELLI in 1886) is used for the area bounded south at the central latitude=65°N by Illisus (1888). The position of the fragment in question is around the central latitude=80°N, and so it is a white patch quite inside the larger region Ierne. According to ANTONIADI (La Planète Mars, 1930, p 219), G V SCHIAPARELLI observed in 1888 (at opposition on 11 April) a light detachment adjacent to the npc inside Ierne, and one round after in 1903 P LOWELL and P B MOLESWORTH detected it (Mars at opposition on 29 March 1903). Olympia was regarded at that time as a part of Lemuria.
  @ The nomenclature of Magnes/Deucalidonius L was given by SCHIAPARELLI in 1888. Ierne is after the holy Ireland, and Deucalidionius L after the northern Scotland Caledonia.

  @ The light detachment Ierne seems to be constantly visible indifferent to minor meteorological conditions at the npr, and so we consider paradoxically it is not so important to detect the fragment. However, it is a standard marking when one refers to a possible existence of the dust cloud near the npc as well as the minor markings inside the npc. For example, it is absurd to allude to such an illusionary marking as Rima Tenius without detecting Ierne. The images by CCD also should convey a trace of Ierne (for example it is difficult to see it explicitly on the images taken at Pic du Midi on 24 Mar 1999 (114°Ls) at LCM=059°W~LCM=132°W as far as we see them through the URL: (http://www.bdl.fr/s2p/mars/ma23399a.gif) ).