Seasons of Dusts on Mars

Forthcoming 2007/2008 Mars
(7)

The Seasons of Dusts

CMO #331 (25 May 2007)

Masatsugu MINAMI

n the coming 1^st day of June 2007, the Martian season reaches λ=249°Ls. It was at λ=250°Ls that the Noachis great dust storm spectacularly broke out in 1956, and so we should say the season of great dust storms has arrived. Note however that since then no Noachis dust storm has been seen at the same season, and if there arose a great dust storm it has chosen quite a different time (so if we borrow Don PARKER (DPk)’s words, it is quite natural for Mars to foil us). Even then we have been obliged to watch the place at the season and this time also we can not help watching. We cannot say it has meaningless to check whether it will occur or not. The dust activity must be a kind of catastrophe which arises when a consistence of a certain income and outgo is broken, but its catastrophe and feedback must not simply follow the solar calendar since Mars is not dead as the Moon. However the season of Mars is not irregular as Jupiter’s, and so it does not make any wrong if we say the season of dusts has set in.

　On the other hand, this apparition proceeds very slowly until the opposition time, and on 1 June the apparent diameter δ is only 5.7". One may be afraid that, in addition to the low altitude of the planet in the morning sky, such a small diameter will make it impossible to find and chase the dust cloud. However the fact that such images as were obtained by BUDA (SBd) and HEFFNER (RHf) from 23 April (λ=225°Ls) to 30 April (λ=229°Ls) when δ=5.2"~5.3" clearly show the dark area of M Serpentis tells us easily that such a bar-like dust as observed in 1956 and 1971 cannot be missed to be recorded even when δ=5.7". By naked eyes it may be hard in general to detect the dust disturbance if the diameter δ is under 10", but ANTONIADI once detected the disappearance of S Meridiani because of the dust covering when δ=7.5". This was of course made by the use of the Grande Lunette at Meudon, but it must be doubtless such an outstanding case will be caught by the present-day ccd technique, and even by the naked eyes it may be possible since the place is very characteristic if used a medium sized telescope. This discovery was just said made in January 1925 in his book: La Planète Mars, p92, but at p126 he describes that the Lunette showed him as if S Margaritifer was protruding from the terminator due to an orange cloud mass over there on 18 Jan 1925, and so the cloud on Meridiani S must have been related with this. Then the season must have been around λ=335°Ls. In 2007 this comes at the end of October with δ=11.4". In 2005, S Meridiani was nearly covered by a dust cloud on 30 Oct 2005 (λ=315°Ls). In 2007 the season will come on 17 Sept with δ=8.9"

The reason why we should not disregard the dust appearance even when the angular diameter is tiny is because the early dust disturbance may cause or have a relation with the further big disturbance later. It is well known that in 1971, the big 1971b great dust storm followed the preceding small 1971a dust. More serious case was in 1973: In 1973 the great dust storm occurred at λ=300°Ls and it is believed that this dust was given rise to by the temporary large dark marking at Daedalia which was extraordinary and appeared in early 1973 or before. Apparently this temporary dark albedo marking must have been caused by another preceding dust disturbance. Unfortunately this dust disturbance was not identified. In the case of Shotaro MIYAMOTO, Kwasan Observatory, Kyoto, he noticed this secular change on 1 July 1973 (λ=235°Ls) when δ=10.4", but not its original dust. MIYAMOTO started the year from the time when δ=7.1" (λ=195°Ls), and this was too late (unfortunately too late, because he otherwise started in 1969 and 1971 from δ=4.6").

　The rare example which we witnessed when the dark marking was produced by the dust disturbance is the case at M Serpentis in July 2003 (λ=215°Ls): The dark marking readily showed up as the dust subsided. In the case of Daedalia in 1973, we can suppose a much brighter dust must have occurred around there, and so it could not have been missed even if the diameter was smaller. By the same token, at present the area of M Serpentis is a live spot to be watched as well as Deucalionis R.

So we here, in order to give a guiding table, pick out some of data accumulated by the forerunners as a function of the coming season.

In ANTONIADI’s book, there is shown a figure showing his observations in 1909 on 23, ~27 August by the use of a 22cm spec (p40): The figure shows a vast yellow cloud which covers the northern hemisphere from the area of Trivium Charontis to the morning side. The season was around λ=258°Ls~260°Ls. This corresponds to mid-June 2007. ANTONIADI also writes that M Cimmerium is covered often by the yellow clouds which deform its shape or make it disappear, and among several examples, he picked out the case on 22, & 23 Aug 1909 when it was considerably pale (p174), and so this must have been an influence of the dust cloud just mentioned. He also writes that in August 1909 he certified (with QUÉNISSET) that Syrtis Mj was also virtually invisible near the CM covered by the lemon yellow cloud (p86) by the use of a 24 cm at Juvisy. (It was from 20 September 1909 that ANTONIADI used the 83cm refractor at Meudon.) At the beginning of September 1909, he also certified that Solis L disappeared because of dust covering (p142), and this was also the influence of the same dust event: This must have been just before λ=270°Ls. In 2007, the period λ=260°Ls~270°Ls corresponds to the term from the end of June to the beginning of July.

　The moment λ=260°Ls was the one the great dust storm was entrained at Noachis in 1971 (1971b). This case also has never repeated since then, but as the dust season it is well matured. In 2007 it occurs in mid-June. λ=260°Ls is realised on 18 June, and can be seen in Europe to the US in the morning. The area will come into sight from Oceania-Orient around from 4 July (λ=270°Ls). Instead in mid July, the area of M Cimmerium will face towards us.

When the planet Mars was most approaching the Earth in 1924, ANTONIADI observed consecutively five days from 10 to 14 October 1924 at Meudon, and made several observing notes. Among them, he observed on 12 October (with QUÉNISSET) that the coming Syrtis Mj was not perceived since it was covered by a greyish yellow cloud mass (p86). The season might have been around λ=277°Ls, and so we should a bit remember this in mid-July 2007.

The aforementioned ANTONIADI’s description of the yellow clouds at M Cimmerium was mainly concerned with the case during the period from 10 Oct to 31 Oct in 1894: Since it was seen at the opposition time, there were joined a lot of observers including FLAMMARION. BARNARD at Mt Hamilton was another. BARNARD suspected a presence of the dust from September, and he reported it continued until 28 Oct on which day M Cimmerium quite recovered. His drawing on 22 October shows a queer aspect of the region. Here we employ the date 10 Oct according to ANTONIADI, while in the Tome II of FLAMMARION’s book: The Planète Mars, there is shown a fine drawing by QUÉNISSET made on 20 September 1894 in which a dust core is shown to the south of the faint M Sirenum and this might have been related with the Oct dust. This was made by a use of 17cm refractor, but amazingly QUÉNISSET detected the spc to have been split into two (this was observed by BARNARD on 7 October by the big Lick refractor). The season was around λ=285°Ls. The period 10 Oct ~ 28 Oct might have been corresponded to λ=298°Ls ~ 308°Ls, and in 2007 the period will be realised from 19 Aug (δ=7.6") ~ 5 Sept (δ=8.5").

　Incidentally this 1894 Oct cloud was also observed by LOWELL: In Chap III of his book “Mars” (1896), he noted “Toward the end of October, a strange,…, a distressing phenomenon took place.” However his conclusion is much stranger: “This was not a case of obscuration; for in the first place it was general, and in the second place the coast-lines were not obliterated. The change, therefore, was not due to clouds or mist” (p120/p121). LOWELL started earlier from the time when the δ was 8.4", but his observations were made just intermittently, and for example, from September to October he was away from Flagstaff but in Boston. So he must have been late in grasping the concept of the yellow cloud. On the other hand it should be noted that he described “the coast-lines were not obliterated.” This implies we are given a warning not to process excessively any ccd image to describe the yellow clouds.

As mentioned, the great dust storm in 1973 occurred at λ=300°Ls. This 2007 year the season will visit around 23 August with δ=7.8". Because Daedalia has been bright ever since except for a presence of Phasis, no serious dust has been observed, but in 1973, there were known several small dusts since the time MIYAMOTO started till λ=300°Ls, and also in 2005 there occurred a Solis L active dust on 21 Oct 2005 at λ=310°Ls, we should be careful.

After λ=300°Ls, we must be attentive to the so-called cross-equatorial dusts which originate from the northern hemisphere. As noted in CMO #289,

http://www.kwasan.kyoto-u.ac.jp/~cmo/cmomn3/289Note02_03/index.htm

the second period of the north originated dusts is around λ=300°Ls~350°Ls (while the first one is around λ=210°Ls~230°Ls), and it is possible for some of the dusts to propagate to the southern hemisphere. The October 2005 Solis L dust at λ=310°Ls belongs to this kind, as well as the December 2003 dust detected by DPk at λ=315°Ls. So after λ=300°Ls, that is, after mid August in 2007, we should be careful to the dust from the area of M Acidalium as well as from the area of Utopia.

Now there is known a great dust storm in 1924 which was similar to the Noachis dust storms in 1956 and 1971: It was Dr McKIM (RMk) who unearthed some drawings of Rev PHILLIPS and others on 9~10 December 1924 showing a dust germ which broke Hellespontus near the CM. The season was around λ=313°Ls with a diameter of 10", and it developed to a great dust storm. In ANTONIADI’s book there is shown a drawing on 31 December 1924 where the surface was vastly covered by the dust except for the shadowy crest of Olympus Mons. This was at λ=325°Ls, and so it lasted long. In 2007, at λ=310°Ls δ is under 8", and as stated comes around 8 September. On the other hand λ=325°Ls implies the beginning of October 2007.

In ANTONIADI’s book at p41, there is a chart where it is shown there was a large dust storm on the southern hemisphere in 1911 from 3 November to 23 December (à). The season was around from λ=325°Ls ~ 355°Ls with the diameter around 17" before opposition. The dust on 3 November was already large and so it started earlier but not trapped because of no observation in Asia (the systematic Mars observation in Japan was after 1920). The season corresponds in 2007 to the period from the beginning of October to the end of November. The diameter is large enough and so cannot be missed.

　Incidentally the present writer (Mn) is of the opinion that the southern hemisphere in 1879 was also largely covered by the big yellow cloud as in 1911. This belief is based on the fact that SCHIAPARELLI faintly drew the southern hemisphere compared with the northern coasts of the central dark markings on his Albedo Map in 1879 (see the Tome I of FLAMMARION’s book at p332-p333), and there is also at least one drawing where the southern hemisphere is made very blank. In 1879 the planet was at opposition on 12 November (quite similar to the 2005 case: On 11 November, he spotted the shining Olympus Mons before noon), and the season he observed from September 1879 to March 1880, and produced the Map based on 30 complete drawings and 104 numbers of partial sketches. Here a part of the Map is copied from the Mimesis Edition of “La Vita sul Pianeta Marte” of SCHIAPARELLI (which book was given to Nj at Brera). Click the lhs Figure to see a larger one. The strange shape of the S Sabaeus and the dusty Deucalionis R must have been based on his drawing on 28 November, and so the dust phenomenon was going on at the season λ=335°Ls and so the situation was quite similar to the case in 1911 (including the fact that the date of the start is unknown). 1911 = 1879 +15+17.

　We have thus picked out some of interesting dust phenomena on the southern hemisphere, and eventually the season of dust is revealed to last without a break this year. However, as we have stated first, any dust occurrence don’t necessarily follow the rut left by the preceding dusts, and so a list is a list, and there are naturally Martian years where no big dust disturbance does not occur. Originally the dusts frequently occur when the balance of income and outgo is broken, but when the energy-balance is kept long, the big catastrophe is difficult to occur (as around in 1990). But recently there seem to be observed occasional changes in global albedo, and so the balance of energy looks a bit excessively in the red or black. So we should be careful this year.

　To sum up, here is a Table which shows possible period of dust seasons in 2007, but not perfect.

λ=250°Ls

λ=258°Ls

λ=260°Ls

λ=277°Ls

λ=285°Ls

λ=298°Ls

λ=300°Ls

λ=310°Ls

λ=313°Ls

λ=315°Ls

λ=325°Ls

λ=330°Ls

λ=335°Ls

Noachis

Elysium

Noachis

Syrtis Mj

Phaethontis

M Cimmerium

Solis L

Noachis

Chryse

Southern H

S Meridiani

Aug 1956

Aug 1909

Sept 1971

Oct 1924

Sept 1894

Oct 1894

Oct 1973

Oct 2005

Dec 1924

Dec 2003

Nov 1911

Nov 1879

Jan 1925

b. June

m. June

18 June

m. July

29 July

Aug-Sept

23 Aug

b. Sept

13 Sept

m. Sept

Oct-Nov

e. Oct

E,A

All

A: The season when the dust started

B: The area where the dust started

C: The period when the dust started

D: Corresponding period in 2007

E: Possible terrestrial region where the corresponding area can be seen

Abbreviation: b.=beginning, m.=mid, e.=end of the month

AO: Asia-Oceania, E: Europe, A: American continents

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