Forthcoming 2005 Mars
(9)

Watch the North Polar Region from λ=310°Ls to λ=350°Ls

Masatsugu MINAMI

 T

his time we feature the period when the north polar region is attentively observed, though not easy to observe.

It is quite natural to refer to the situation of Mars in 1990 as we did in order to seek a guide in observing the coming 2005 Mars since a cycle of 15 years gives an easy recurrence of the similar Mars (season, diameter, and so on).

As to the recurrence periods, the present writer once gave an idea in The Heavens (OAA Journal, in Japanese) vol 65 (1984) p185, and repeated it in English in CMO #106 (15 June 1991) p910 (see Web Page). Essential point is this: Let m and n be integers. Then if we can choose m and n in such a way that the rational number n/m is akin to an irrational number 7.390..., the combination 2n+m gives a good recurrence period. Proof of this proposition was given in CMO #106 p910 and here reproduced in its Web page. One of best approximations is given by the choice n=133 and m=18, so that n/m=7.388 which is quite near 7.390 and 2n+m gives 2×133+18=285. The recurrence period of 285 years looks therefore the best if we seek years in hundreds. The period of 15 = 2×7 + 1 years is given by the approximation 7/1=7.000, and the period of 17 = 2×8 + 1 years by 8/1=8.000: Thus any possible recurrence years are fallen between 7 and 8, and the more plausible ones are the nearer ones to 7.390. The well-known 79 year period is given by 37/5=7.400 and so we should say this is one of better approximations (note however 7.400 - 7.390 = 0.01, while 7.390 - 7.388 = 0.002).

This time, though slightly inferior to the above examples, we pick out the case 66/9 = 7.333 . (7.390-7.333 = 0.057). The recurrence period then gives 141 which implies we choose 1864 = 2005 - 141 as a plausible year as a guide for the 2005 case. In 1864, the planet was closet to the Earth on 23 November, and the maximal angular diameter was 17.5 arcsecs. Since in 2005, the very day occurs on 30 October, it looks slightly far. In fact another opposite choice of 67/9=7.444 (7.444-7.390 =0.054) gives a recurrence in 143 years, and hence the next 2007 apparition is also similar to the 1864 one (in 2007, Mars is closest on 18 December). That is, the 1864 apparition is ambivalently approximate both to the 2005 and 2007 apparitions. In other words, what we are to describe about 1864 is also applicable in the next apparition. On the other hand, we can prove the 1864 apparition was more akin to the 1990 one, since 1990-1864 =126, whose recurrence is given by the rational number 59/8=7.375 and 7.39-7.375 is only 0.015. It is needless to say the 1864 apparition was more akin to the 1943 case.

Remark that 66/9 which gives 141 recurrence year is equal to 22/3, and so it is no more than a repeating of 2×22+3 = 47 yrs recurrence. 47 = 15+17+15, and so the case of 1864 is not so different from the rough approximation which we meet if we use the 1958 apparition (in 1958, the planet was closest on 8 November with the maximal δ 19.2"). Incidentally, the Lowell and Barnard year 1984 is given from 2005 by the 111 year recurrence of 52/7=7.428 (7.428 - 7.390 = 0.038), and not so bad.

The season when the planet Mars was closest to the Earth was respectively λ=299°Ls in 1894, λ=315°Ls in 2005, λ=320°Ls in 1958, λ=336°Ls in 1990 and λ=341°Ls in 1864. These apparitions more showed the southern hemisphere and therefore were not so pertinent to the watching of the high latitude region of the northern hemisphere, while they provide large disks of Mars in the season after λ=300°Ls.

Recently it has been recognised to be important to pay attention to the north polar region in the periods (A) from λ=210°Ls to λ=230°Ls, and also (B) from λ=310°Ls to λ=350°Ls because there seem to arise some dust disturbances at the northern high latitude areas in these periods and some of them develop into the so-called cross-equatorial dust storms. We learned from Christophe PELLIER, private communication, that the dust storm detected by Don PARKER in December 2003 was one of the cross-equatorial dusts, and PELLIER also speculates other two storms observed in 2003 (including the interesting June/July one) were originated from the northern hemisphere. Note that the December storm was detected at λ=315°Ls, and so belonged to the period (B). In 2003, the angular diameter at the season was only 9.9 arcsecs, while in 2005 the season visits when the diameter is maximal.

We should call attention of the readers to the MGS Weekly News in 2002 (from January to September) in

where we can find several images of dust occurrences at the northern high latitude areas; for example at Xanthe at λ=315°Ls, at Chryse at λ=328°Ls, at Utopia at λ=342°Ls, at Chryse at λ=350°Ls and so on.

In 2005, the season λ=310°Ls of (B) comes on 21 October with a large diameter of δ=19.9", and the final season λ=350°Ls will visit at the beginning of the next year when δ keeps still 12" ; and hence the 2005 apparition provides a good opportunity to do the watching during the period (B). We should especially choose the periods when M Acidalium or Utopia is visible.

 W

e are now in a position to state the reason why we pick out the 1864 apparition: It is because the north polar hood was attentively observed in 1864 maybe for the first time. According to the list made by C FLAMMARION, in 1864 such observers as GREEN, BANKS, WILLIAMS, KAISER, DAWES, SECCHI and others were active (also in 1864 HUGGINS and others made spectroscopic observations to detect water vapour on Mars). ANTONIADI reports that F KAISER made an observation in which M Acidalium was completely covered by the white cloud (north polar hood=nph). Among them William R DAWES (1799-1868) produced some impressive observations of the north polar region. DAWES's observation in 1864 had really a good reputation, and no other than KAISER's could rank with his. DAWES used in 1864 a 20 cm Cooke refractor with a magnification 258×: It seems to be quite low from our view-point and when the seeing was poor, he even used 155×. DAWES however was said to have the keen eyes though he used a thick eyeglasses (W SHEEHAN, The Planet Mars, 1966, p53f).

The BAA inherited all of 16 drawings of DAWES made in 1864, and in 1988 Richard J McKIM and Robert A MARRIOTT published them in a beautiful printing set in JBAA 95 (1988) No 6 p294: Until then a set of 8 drawings were known in a lithograph form, but in the article all (including other 8 unpublished drawings) were reproduced from DAWES's original drawings in a photograph form (for the first time).

The DAWES drawings are important in several respects, but among them they are important since they depict clearly the variation or activity of the nph. On 20 November and 26 November (λ=343°Ls), the wavy nph was caught to the north of Syrtis Mj, and on 13 November and 15 November (λ=337°Ls, δ17.3", φ=4°S) the nph was interestingly depicted at the angles where M Acidalium stayed. By courtesy of Dr R McKIM, we can here show the photographic copy of the original drawing on 15 November at 00:00 GMT (new GMT system): Its lithograph was already cited in CMO #106: Compare with the drawing in  the Web Page

DAWES himself described that a short and rather thick dark line" which was observed on 14 November (12h) had not been visible on 12 November (old GMT system) and as also suggested by R McKIM and R A MARRIONETT this drawing shows the phenomenon which must have shown a popping out of the southern part of M Acidalium from a window of the thick nph. This kind of nph activity is common in this season, and also since belongs to the period (B) must be related with the dust onsets near the npr if any.

Note also that the DAWES drawing shows, in addition to the clear detection of Aryn Fastigium (Dawes' forked bay) a strange canal called Hydaspes and Sinus Hydaspis which ran from Margaritifer S to Niliacus L: This was a temporary dark marking which was apparent from 1851 to 1871: It was first detected by Angelo SECCHI, and observed in 1862 by J N LOCKYER, and in 1864 by KAISER and DAWES. Sinus Hydaspis (named by ANTONIADI) was a kind of the river mouth of Hydaspes (named by SCHIAPARELLI).

Hitherto the relation of several secular changes of the dark markings on the northern hemisphere and the activity of dusts has not fully been discussed (nor observed), but it was quite possible for the strange secular change (appearance and fading) to have been caused by the activity of the northern dusts which were switched by the atmospheric activities at the npr. Unfortunately such detections were not made those times because the observations were scarce and the tilt of the north pole was quite away from the Earth.

As frequently remarked, the area from Tempe or M Acidalium to Chryse is important, while if we look back on the past data, the secular change around the area of Utopia has also been intensive, and though not yet discussed was the explicit relation with the dust movements, the changes must have been caused by the northern dust activities. The appearance of N Laocoontis was given rise to in 1946, but it is possible it was formed by the dust disturbance in 1943: However the year 1943 was the year when the situation was not favourable for the observations. The aspect of the withered area of Utopia and Cebrenia as seen at present has been settled from the 1980s, but we should say any decisive beginning of this secular change was not pinned down. In the 1973 season the area was not observable because of the spread of the vast dust.

The northern tail of Syrtis Mj, or Nilosyrtis, is also not the same at present as the one SECCHI called Syrtis Mj Scorpion (or blue Scorpion in the morning). DAWES' drawing on 26 November describes Nilosyrtis in connection with the nph expansion.

We already discussed the activity of the nph in the 1990 apparition in (6): Finally we cite here an observation made by the present writer on 22 October 1990 on which day the nph kept a bit away from a part of M Acidalium, as shown in the diagram shown in

and the very drawing shows the moment when the part was seen dark as a segment as was quite the same case as in DAWES'. The geometrical situation was similar since δ=16.1" and φ=4°S on the day, while the season was λ=321°Ls and earlier than DAWES's case, though still inside the period (B). So such an activity lasts long. As reported in (6), just after the interesting activity of the nph, a second dust storm was observed from 2 November (λ=326°Ls): This is also inside the period of (B), but unfortunately the accumulation of observational data was few before the detection (because of lack of data in the Asia to Middle-East), and no one can say whether it was a cross-equatorial dust storm or not, but very possible. Fortunately no explicit secular change occurred.

In 2005, the situation will be slightly poorer since the tilt will not decline more than φ=15°S during the period (B) so that it may be rather difficult to observe the northern limb, but since the diameter still remain large as pointed, there may be a little possibility to be able to witness a new secular change of the dark markings in the northern hemisphere due to a rise of the northern dust associate with the activity of the nph, if we thickly observe during the period.