General

This Circular summarises the period 1999 March 1–April 15. On Mar 1, Ls = 104 deg., D = 10 arcsec., lat. of centre of disk = 15 deg. N, with the planet’s declination at 13 deg. south. The planet will reach opposition on April 24 (Ls = 129 deg., D = 16 arcsec., lat. of centre of disk = 18 deg. N, decl. –12 deg.). The planet was becoming uncomfortably low for UK observers, but as can be seen, its declination will now be very slightly less southerly.

      The UK weather has been less than cooperative during opposition month, but nevertheless there have been a fair number of observers, including the usual contributions from overseas that are essential to maintain good longitudinal coverage. During the present apparition I have had observational data from the following individuals, and acknowledge it herewith if not already done so by letter or by e-mail: Leo Aerts, Sally Beaumont, Nicolas Biver, Ed Crandall, P.Devadas, Mario Frassati, Martin Gaskell, David Gray, Peter Grego, Walter Haas, Alan Heath, Carlos Hernandez, Frank Melillo, Cliff Meredith, Masatsugu Minami /OAA, Patrick Moore, Don Parker, Damian Peach, Tom Richards, Richard Schmude, David Strange, Paolo Tanga, Gerard Teichert, Rowland Topping, Dan Troiani/ALPO, Johan Warell, Sam Whitby and Jonathan Wojack.

      More than one observer has supplied unreadable CCD image files: I do not always have the software to decode compressed files, and it would sometimes save time to mail a disc. I would also kindly point out to observers that I do not always have time to look for images on their personal Websites, much as I would like to; if you want your images discussed in these reports, kindly send them along in a readable format!

      I am sorry that Dr Ebisawa’s health has not been very good, so that he has not been able to make his usual meticulous visual and polarimetric observations so far. Is anyone doing polarimetric work this apparition?

Observations

On Mars throughout March and April the N. polar cap remained small. A number of visual and CCD observations show haze around its S. perimeter. Despite this haze the outlying bright area of Olympia has been visible. Tanga saw it from Turin Observatory in fine seeing on April 18. White cloud activity remains quite high, but the Equatorial Cloud Band phenomenon (ECB) seemed much less conspicuous in April. The typical sites for white clouds have been active throughout the whole period, and a few observations will suffice to illustrate these locations and to describe some other features:

      McKim, April 13, 22-cm refl., 2318h UT, CML = 218 deg. Elysium on mid-disk whitish. Bright am cloud over Libya–Isidis (and Syrtis Major). Hellas a brighter spot within the light S. limb area. Cebrenia lightish on the CM, some haze S. of NPC, but cap edge sharp. Some pm cloud over Amazonis, but Nix Olympica would have rotated off the disk at an earlier hour. The Aetheria secular darkening remains extensive and dark, and extends somewhat to the SW as in the last few apparitions. Propontis (I) is dark, and the Phlegra/Styx–Trivium Charontis–Cerberus complex, though not dark, was easy to see.

      Meredith, April 14, 22-cm refl., 2355h UT, CML = 218 deg. CCD image much like McKim’s visual drawing above. (Cliff’s first really successful CCD work, well done to him.)

      Parker, March 7, 0.4-m refl., ca. 0735h UT, CM = 321 deg. Evening cloud dims Syrtis Major, extending across it from Libya to Aeria! The evening Hellas is bright. Morning cloud occupies Chryse and partly hides SW Mare Acidalium. Haze south of the NPC.

      Parker, March 12, ca. 0803h UT, CML = 282 deg. Hellas is very bright in white light. As Minami points out in the OAA’s CMO, the brightness sometimes extends outside the contours of the basin: Gray found a similar phenomenon with Argyre in January.) Hellas was large and bright in green (VG9 filter) and blue (BG12), but was smaller and paler in red (RG610).

      Parker April 3. This CCD image series even shows a little structure inside the Solis Lacus (which remains large and dark since the mid-’80s). The feature Gallinaria Silva, a small dark spot that was seen to the W. of the Solis Lacus in the apparitions immediately before the present one, seems to have nearly disappeared. This is therefore perhaps a small change since 1997. There is really fine structure in the Tithonius Lacus between Melas Lacus and Noctis Lacus! Aurorae Sinus appears detailed, with little northward projections including Baetis/ Juventae Fons, etc. Mare Acidalium and Niliacus Lacus are shown in fine detail. Hyperboreus Lacus is a dark spot adjacent to the small NPC.

      Teichert, April 10, 28-cm SCT, 0056h UT, CML = 277 deg. Hellas bright on the CM. Nepenthes is invisible. Moeris Lacus forms a small protrusion on the E. side of Syrtis Major.

      I do not intend a more complete analysis here. UK members may wish to know that I will be showing some illustrations of the Section’s work in my presentation at the BAA Northampton Meeting on Saturday April 24.

Pic du Midi web site

This is an excellent site (http://www.bdl.fr/s2p/mars.html), This Site No longer Exists and contains some medium- to high-resolution images of Mars (1988–99).

LPL Mars Water Group

Ann Sprague e-mailed with more details of her LPL Mars Water Group’s work at Catalina: see Rik Hill’s communication from the same group in the last Circular. Anne writes that they have been measuring water vapour in the martian atmosphere every two weeks since 1998 September. ‘We are measuring CO2 molecular absorption with the hopes of using radiative transfer to measure atmospheric dust… the depth of the water vapor absorption line in Mars’ Northern latitudes is much deeper than we have seen it in previous Northern summers.’

      February dust storm follow-up. Last time’s Circular detailed a Regional storm over the Mariner Valley, whose observation was mostly due to David Gray. Todd Clancy e-mailed on March 10 to report that this event (which had first been detected on February 21) had had no apparent effect upon the atmospheric temperature (as deduced from radio waveband work), but, interestingly: ‘the overall trend in temperatures over the past two months is 5–10 K warmer than at this time in the previous Mars year.’ For those wishing to see David Gray’s two sketches of the event, they may now do so thanks to Don Parker who scanned them and uploaded them to the Marwatch Website. Steve Lee e-mailed descriptions of the HST images of March 3 (CML 256, 280 deg.): these revealed ECB, but the CML was too high for them to show the Valles Marineris area.

      Note that the results of Ann Sprague’s spectroscopy and Todd Clancy’s work seem to fit nicely together! It will be interesting to see if this relates to the regression rate for the NPC.

Yet more dust over Valles Marineris!

A further event occurred during the Director’s absence on holiday abroad. Upon his return home on April 11, awaiting him was an e-mail and observation by Carlos Hernandez, dated March 31 (22cm refl., CML = 53 deg.), which revealed an already mature dust storm in progress, in the form of a bright streak running E–W along (the S. edge of?) Valles Marineris. At first sight I thought it might just have been residual dust (see my comments upon Don Parker’s March 3 CCD image in the last Circular), but Carlos had not noticed it earlier, and, moreover, it was too prominent, too well defined, and was bright through a W23A red filter. In his e-mail Carlos mentioned that a CCD image by Antonio Cidadao taken 1h earlier had also shown the bright streak. Carlos observed again a few days later on April 2, finding that the area had returned essentially to normal. So when did it begin? Several days later, David Strange e-mailed a good CCD image taken on March 27 at 0100h UT under CML = 43 deg. This showed a bright area in Ophir which interrupted the Agathodaemon (also known as Coprates, part of W. Valles Marineris: a classical ‘canal’ which runs between Aurorae Sinus (Planum) and Tithonius Lacus (Chasma)). This was most probably the initial cloud of the storm, and the event subsequently spread eastward along the canyon. Don Parker’s CCD images of April 1 show the area, but in very bad seeing; his work on April 2, 3 and 6 is high resolution, but apart from a possible faded appearance of Aurorae Sinus, the area seemed normal. Warell observed from Uppsala University Observatory, Sweden, with a 16-cm OG: on March 29, 30 and April 1 (CML = 23–34 deg.) he found a large am cloud over Tharsis and Thaumasia, etc., to appear distinctly yellowish. Johan’s seeing conditions were not good enough for him to see the dust actvity in the Valles Marineris, but the yellow tint could represent dust diffused from the minor storm then underway. Ditto April 5, under CML = 322 deg., when a yellow tint was evident in the Chryse–Xanthe am cloud. In any case, a short-lived event.

      Does anyone else have pertinent observations? If so, kindly let the Director know! Looking at the Pic du Midi website will reveal a March 24 image which does not show the storm, so we appear to have pinned it down quite well. The location of the 1984 June Regional storm fell in a similar location; in that case, dust also spread to the east over the same area, as well as dispersing generally over Mare Erythraeum. This storm was fully described in the writer’s published 1984 BAA apparition report.

      The Director looked up the work of the group that are analysing solar radio occultation data from MGS to determine atmospheric temperatures. There is a section on the MGS homepage. Joe Twicken of that group kindly (and rapidly) responded to a query from the Director with the following e-mail. ‘ We have not processed the raw data that we do have for the dates that you mention. We do have a lot of data from the February period, but very little from the March period. MGS did not begin normal mapping operations until this month. Precise reconstructions of the spacecraft orbit are required to process our raw data, and the orbit reconstructions from JPL for the February and March periods were not sufficiently accurate for us to retrieve meaningful atmospheric profiles. Other members of our Team are in the process of reconstructing the orbits, and we will process the data when we can. I will let you know if we see anything interesting. You should be aware that the spacecraft occultations during the periods you mention occurred at very high northern and southern latitudes, so we will not have any atmospheric data from the vicinity of Valles Marineris.’ Thus it seems that the only record of the March storm is again that of the ground-based observers. Keep up the good work, everybody! But for your observations, these two small but important events would have been completely missed!

Mars as seen through the eyes of the Global Surveyor

MGS has begun to image the planet from orbit again, after achieving final orbit about March 1. In the current (May) Sky & Telescope Jonathan McDowell’s Mission Update column mentions a dramatic incident at Mission Control which nearly interfered with the attainment of the final orbit…

      Since the release of the Aerobraking Image Set, the MGS website has been posting full-disk and closeup images from March and April. These show how successfully the craft is behaving, and whet the appetite for more! Polar dune fields, craters, clouds, Valles Marineris (including a fine shot of E. Tithonium Chasma, image MOC2-109)… But telescopic observers will be most interested in two full-disk ‘images’, reconstructed from a sequence of nine strip-maps obtained on successive orbits. These were obtained in March during the calibration phase of the mission. The Director has e-mailed for a more precise date in case the images can support the discussion of the latest Valles Marineris dust storm. The colours will not be perfect as the Martian Orbiter Camera (MOC) makes red and blue images, and averages them to make a ‘green’ image to combine with the others to make a colour composite. Another consequence of this process would seem to result in rather low albedo contrast compared with that telescopic observers can enjoy. (No matter, just try Adobe Photoshop or similar program on your PC, and you can make them look more like telescopic images – and put south at the top at the same time!!)

      MOC2-117 shows Syrtis Major central, partly covered by the bluish-white ‘Syrtis Cloud’. Iapigia shows the location of the large Huygens crater. Hellas is bright and looks mostly (but not entirely) frost-covered. The NPC shows fine rifts and the broad dark Chasma Boreale (Iaxartes). The fine albedo details around Utopia–Boreosyrtis–Propontis look to be very similar (if not identical) to 1997, as 1997 looked identical to 1995 in the HST images.

      MOC2-118 is an image of the Tharsis and Thaumasia regions. The morning clouds cover Olympus Mons, Alba Patera, Ascraeus Mons, but affect Pavonis and Arsia Mons less.
 
 
 

The BAA Martian dust storm Memoir
 

At last I can report that everything is finished and checked, and that I will be taking the text and figures to the printer, University Printing Services, Cambridge (the printers of the BAA Journal), in the next couple of days. It is to be hoped that it can be published in the next few months. The printed text will occupy about 168 pages, equivalent to three 56-page issues of the Journal! (For details, see Memoir.)

Reporting data to the Section

I am always happy to receive CCD images by e-mail. Any urgent and important drawing can be scanned and sent as an image file, but I do not want to receive routine drawings by e-mail, because the vast majority are sent to me as hard copies, and that is the form I like to compare (and archive) them in. I have to write that I am spending an enormous amount of time downloading files sent to me over the Internet, then decoding, analysing and refiling them in the Section’s records! Send mail to Cherry Tree Cottage, 16 Upper Main Street, Upper Benefield, Peterborough PE8 5AN, Great Britain;  home telephone 01832 205387; home

e-mail Rmckim5374@aol.com. (Do not use the former e-mail address for my place of work (mckim@oundle.northants.sch.uk).) Urgent faxes can be sent to my place of work on 01832 274052.

Reporting data to the Section

I am always happy to receive CCD images by e-mail. Any urgent and important drawing can be scanned and sent as an image file, but I do not want to receive routine drawings by e-mail, because the vast majority are sent to me as hard copies, and that is the form I like to compare (and archive) them in. I have to write that I am spending an enormous amount of time downloading files sent to me over the Internet, then decoding, analysing and refiling them in the Section’s records!

      Send mail to Cherry Tree Cottage, 16 Upper Main Street, Upper Benefield, Peterborough PE8 5AN, Great Britain; home telephone 01832 205387; home e-mail Rmckim5374@aol.com. (Do not use the former e-mail address for my place of work (mckim@oundle.northants.sch.uk).) Urgent faxes can be sent to my place of work on 01832 274052.

The next Circular

Please report observations April 16 to May 31 by June 7, so that the next Circular can be published in the second or third week of June. Good observing.
 

Richard McKim, Director

1999 April 23 – Opposition Day minus one!

Return to Mars Circulars for 1998-99

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