Mars Section Circular No. 6

1999 April 16–May 31

General

This Circular summarises the period 1999 April 16 to May 31 (Ls 130 to 147 deg). The planet was at opposition on April 24 (Ls 129 deg., D 16 arcsec, lat. of centre of disk 18 deg. N, decl. –12 deg.). By May 31, D had decreased to 14.2 arcsec, and at the time of mailing this Circular, D has fallen to just over 12 arcsec.

The UK weather has remained unhelpful on the whole: compare the number of clear nights in 1999 with the splendid weather near opposition in 1997, when Comet Hale–Bopp was well-placed. Personally I have managed only 40 drawings with my 22-cm reflector. But this is the busiest time of the academic year for me, and although I am grateful for having received a deluge of post and e-mail, it has not always been possible to reply at once: most of my time has been spent in merely filing away the data to look at later! In addition to those observers listed in Circular No. 5, I am grateful to Paul Abel, Tom Cave, Antonio Cidadao, Maurizio Di Sciullo, Colin Ebdon, David Fisher, Maurice Gavin, Michael Hendrie, Henk Munsterman (via Wim Cuppens), Terry Platt (via Maurice Gavin), Elisabeth Siegel, David Storey and Myron Wasiuta for sending me observations. Apologies to anyone I have forgotten. Michael Hendrie’s sketches (15-cm OG) are very good representations of the planet’s features, and Johan Warell made excellent use of a 16-cm apochromat. Australian planetary coordinator Bary Adcock sent excellent CCD images by Stefan Buda and Bratislav Curcic (25-cm Dall–Kirkham). Antonio Cidadao (Oeiras, Portugal, 25-cm reflector) and Maurizio Di Sciullo (Coconut Creek, Florida, USA, 25-cm reflector) have sent amazing colour CCD images, and Maurizio’s can be seen in the July issue of Sky and Telescope, p.124. Jean Dijon’s monochrome ones, secured from his observatory in France, are superb too, but most other European images have evidently been limited by less favourable seeing conditions.

Antonio Cidadao’s images seemed so good that I asked him if he enjoyed excellent seeing. In fact, he does not; but he does have extensive experience in image processing, so here follow his remarks which may be helpful to others.

Image processing : Antonio Cidadão

I began to obtain CCD images in 1994, but the only camera I had at that time – an ST6, with large pixels – was not the best for obtaining planetary photographs. Nevertheless, I did obtain some images for pictorial purposes, and to optimise a technique that would allow me to get the best resolution possible. You can take a look at a first version of that technique (I still use it now) on my web site:

www.geocities.com/CapeCanaveral/5409/planet_index.html.

I later discovered that such a manual ‘super-resolution’ approach from under-sampled images was nearly identical to that applied by Tim Parker from the JPL to process the Pathfinder lander camera images. Since then I have been in contact with him. So, I must tell you that I do not have ‘super’ seeing conditions – I wish I had. In fact, I work from a ‘roof-top’ window observatory that heats up considerably during the day and is surrounded by some 3 or 4 ‘active’ fireplace chimneys. Believe me, I can tell the difference when people start to use them during the winter. What happens is that I try to fight a lot to get the best possible resolution by averaging a lot of registered frames. For instance, for each final filtered component of my Mars images I average some 30–50 original images (about 15 for Jupiter, as it rotates faster). That is a lot of processing – but it does seems to work.

MTO-II in Icarus

Mars Telescopic Observations – II. This was the course the Director attended in Tucson, Arizona, in 1997. Some papers from the proceedings have now been formally published in Icarus, 138 (1), 1999 March. I would appreciate reprints from any authors reading this Circular!

New global topographic maps of Mars

John Rogers reports that some excellent coloured maps have appeared in Science (284, 1495) in June, and have also been placed on the Mare Global Surveyor web site.

News from the Hubble Space Telescope

In a recent Marswatch electronic newsletter there was some reference to the HST work. As has been noted previously in these Circulars, Hubble has been taking very few images this apparition. Here is the relevant extract:

‘HST Mars Observations: April 27 through May 7. All of the planned Hubble Space Telescope (HST) observations of Mars for this opposition have now been scheduled. HST will observe Mars at four central meridian longitudes (for full global coverage) between April 27 and May 7 (hopefully the recent failure of one of the HST gyros will not hinder this!). The exact times when HST will be observing Mars are indicated in the table below (times are given in Greenwich Mean Time or Universal Time, which is currently four hours ahead of U.S. Eastern Daylight Time). I am organizing these observations, and I am especially interested in obtaining supporting ground-based CCD images from amateurs and professionals during the times when the STIS instrument (Space Telescope Imaging Spectrograph) will be observing Mars. For the times when STIS is observing, we need high quality CCD images especially in the blue, so that we can determine where clouds, hazes, and fogs are most likely interfering with our spectroscopic measurements. If you are able to observe Mars in the blue at these times, we would greatly appreciate receiving copies of your images and their descriptions! We will be posting the HST images onto a web site as soon as we get them processed.’

Visit 1 2 4 7 8 5 6 3

Instrument WFPC2 STIS WFPC2 WFPC2 STIS WFPC2 STIS STIS

Start Time (GMT) 1999 Apr 27 17:55:38 1999 Apr 27 19:32:20 1999 Apr 28 00:22:25 1999 May 1 13:47:34 1999 May 1 15:24:53 1999 May 6 11:28:10 1999 May 6 13:04:18 1999 May 7 06:52:54

End Time (GMT) 1999 Apr 27 18:51:12 1999 Apr 27 23:23:27 1999 Apr 28 01:17:59 1999 May 1 14:43:08 1999 May 1 19:14:14 1999 May 6 12:22:14 1999 May 6 16:51:20 1999 May 7 10:55:14

As BAA data cover every date during April and May, no doubt at least some of our observations will coincide with the HST images. Members having CCD images close to the above times are invited to send Dr Bell duplicate copies, if they have not already done so.

News from Mars Global Surveyor

MGS is very active, and plenty of new images have been posted on the web. The Marswatch newsletter also contained a paragraph about the status of MGS:

‘Update on the Mars Global Surveyor Antenna Glitch. On April 15 the Mars Global Surveyor spacecraft experienced an ‘anomaly’ (a glitch) with its main high-gain antenna. Apparently one of the hinges on the high gain antenna got stuck, meaning that the antenna can only swing in one direction instead of in two directions. JPL engineers are troubleshooting the problem, and mapping has been put on hold. The plan is to continue mapping next week, because high-speed communications with Earth can still work for now even if the antenna can only move along one axis.’

Check the April 23 and earlier updates for many more details: mars.jpl.nasa.gov/mgs/mgs-readme.html; also, check out some of the spectacular early mapping data at: www.msss.com/mars_images.

BAA , HST and MGS observations, April 16 to May 31

I have sometimes gone a little way into June in order to continue the narrative.

1.1 Surface features

Fine surface details have been imaged and sketched throughout the period under review, but as mentioned earlier, these details are closely similar to 1997, even at the resolution of the HST. Gray caught the dark patch inside the Huygens crater, which lies in W. Iapigia. With the better resolution near opposition some observers were able to detect the little feature Gallinaria Silva, the ‘oasis’ following Solis Lacus which I use as a sort of indicator for secular change in the region. It was inconspicuous. During the last opposition it appeared from Parker’s CCD images that part of the following (W. areographic) side of Solis Lacus was fading a little. This fade has not continued during the current apparition, and Solis Lacus therefore remains unusually large and dark.

A few observers noted the apparent martian colours. Amongst them was P.Devadas (Madras, India, 36-cm refl.) who on April 20 found M. Acidalium grey compared with the bluish-green tint of the S. markings under CML 57 deg. This difference in apparent colour between the N. and S. markings has been remarked upon before. On May 23 Frassati found Propontis (I) to be dark brown. (This was also Masatsugu Minami’s finding, in April.)

1.2 White clouds

Equatorial Cloud Banding seemed progressively less prominent during the period reviewed, though traces of it were still present in the longitudes E. of Syrtis Major in early June. On mid-disk the bluish ‘Syrtis cloud’ has been seen in the evening and morning, though smaller by late May than in April or earlier, and not lasting as long into the martian day. With the decline of equatorial white cloud generally, Syrtis Major was easier to see in violet light. Ophir–Candor often showed up as a bright streak on mid-disk.

The SPH has seemed bright, progressively becoming more or less continuous across the S. limb, enveloping Phaethontis, Electris, Eridania, Ausonia, Hellas, southern Noachis, Argyre and southern Thaumasia/Mare Australe. Hellas itself was not as bright as earlier in the apparition according to the OAA. The OAA commented on the diurnal behaviour of the Thaumasia cloud, as seen on April 16: Minami found brightness S. of Solis Lacus at CML 68 deg; the bright cloud passed the CM during CML about 78 to 87 deg; under CML 98 deg. the cloud was seen to be occupying Daedalia; under CML 109 deg. the W. end of the cloud passed the CM. In Parker’s early June CCD images the polar hood was constant in latitude across southern Thaumasia and environs at these longitudes.

Morning and evening clouds appeared over Libya–Isidis (related to the Syrtis cloud). Chryse–Xanthe remained bright in a.m. or p.m., though by early June this activity had declined. Small morning and evening clouds were imaged over Tempe in April and May. The diurnal clouds over Elysium continued to appear, though they were much less prominent towards the end of the period reviewed. (On June 10 Parker drew attention to the decline of the orographics in an e-mail.) A set of observations was made by Minami in the first half of May to show the daily changes in thick morning mist over Utopia.

Many observers do not send comments with their CCD images. As an example of what might be written, here are Di Sciullo’s notes, in part, for his May 3 images, which relate chiefly to the large number of white clouds then imaged:

‘Equipment: Excelsior Optics E-258 10’ (25 cm) f/8 Newtonian using eyepiece projection @ f/47 Starlight Xpress HX-516 CCD camera, True Technologies Dichroic Filters + IR block. No dark frame, flat fielding or bias correction applied. Camera operated in ‘binned’ (low-res) mode. Seeing: Mediocre–Fair; 4–5/10. Low humidity (~60%), north wind at 3–6 knots. Integration Times: 610 – 720 nm: 0.20s; 490 – 590 nm: 0.14s; 400 – 510 nm: 0.19s. All images acquired with 700 – 1200+ nm block filter in line with eyepiece projection unit. Significant activity in 400–510 nm band. Heavy evening haze over Xanthe Terra, south to Margaritifer Sinus. Northern extent of haze appears to be southern limit of Mare Acidalium, or approximately Chryse Planitia area, at roughly same parallel as Viking 1 landing site. Haze is triangular in shape, coming to a point at an area between Ascraeus Mons, and Hebes Chasma. Spot cloud observed at this location, north of Valles Marineris and Syria. Second area of pronounced limb haze showing over Aonia, arcing to eastern Mare Sirenum. 400 – 510 nm band also showing cloud bank over Tempe Terra / Acidalia region, along with another bright cloud over extreme northern Acidalia. Persistent cloud or detached ice cap still present at perimeter of Olympia Planitia, at extreme northern latitude. Other spot clouds showing over Alba Patera, a pair over Ascraeus Mons, and a faint spot over caldera of Olympus Mons. Shield of volcano showing as ‘bull’s eye’ just west of meridian, demarcated by slight circular darkening in 400 – 590 nm range, punctuated by central bright spot in mentioned bands. Final faint hint of morning haze present over Orcus Patera. Odd cloud, dusky blue–green in color observed near 52 north latitude, 202 longitude, just north-west of Propontis Complex, and due north of Elysium Mons. Not likely to be a processing artefact, as careful attention was paid to correct color balance.’

1.3 Yellow clouds (dust storms)

MGS returned further interesting observations, including some signs of dust in W. Valles Marineris, near Melas Lacus: see section 3 below for complete details. Part of southern Chryse was definitely light in red light on a number of occasions, and sometimes Chryse was visually yellowish (e.g., to Warell, May 5, 6 on the morning side of the disk). Although there was no large event there, small-scale dust activity, perhaps persisting from earlier in the apparition, seems the inevitable conclusion. In red light (W25 filter) Cidadao imaged a small bright cloud close to the NPC over Mare Boreum on June 2 (near the CM, with CML 92 deg.). Invisible in the blue images, it had become more extended to the SE (areographic; e.g., Sp.) towards Baltia by June 3, and may have persisted a few more days. Nothing of the sort had been imaged by Cidadao on June 1, albeit under poorer conditions. Observing on June 3 McKim confirmed the light detached area imaged by Cidadao. It is provisionally concluded that there was a small dust cloud over Mare Boreum; it was smaller than the ‘HST polar cyclone’ (due to white cloud; see below), and closer to the polar cap. (Without proper filtration, the situation about the cap can easily become confused by the bright areas of white cloud sometimes surrounding the NPC, these being parts of the newly forming N polar hood. These latter areas are brighter in blue light.)

The OAA Communications In Mars Observations No.217 (1999 May 10) reported still another yellow streak associated with Valles Marineris. On April 16, under CML 48–58 deg. in good seeing, Minami (20-cm OG, Fukui City Observatory, Japan) found a light (but not brilliant) yellowish slit streak which separated Margaritifer Sinus from Mare Erythraeum. After a hiatus caused by bad weather, OAA observer Akutsu imaged a faint segment between Erythraeum and Eos on April 20.

I also received yellow cloud alerts for Tempe (more than one observer), Arcadia and Cydonia, and am still assessing the data to see if the timecourses of any phenomena may be detailed. At the same time I get the distinct impression that too many observers are trying too hard to discover dust storms!

1.4 North polar region

The NPC remained static in size, as far as could be seen without making precise measurements. Hyperboreus Lacus was large and dark. Chasma Boreale was seen visually by Tom Cave, Warell and others, and Olympia was widely reported or imaged throughout the period under review. Around the cap the amount of polar haze increased, so that sometimes the NPC had a more diffuse whitish surround. This was especially noticed by Walter Haas, Mario Frassati and the Director. At other times and longitudes discrete bright spots of polar cloud were seen, and MGS images were released in both static and movie format showing the motions of some wispy streaks about the NPC remnant. The HST imaged what the Space Telescope Institute Press Release termed a ‘polar cyclone’ on April 27 (see section 2 for details). There was also a smaller dust cloud near the NPC (see section 1.3).

2. Hubble’s ‘polar cyclone’, April 27

HST observations of the so-called ‘polar cyclone’ were obtained on April 27, and were described by the following Press Release (STScI-PRC99-220) dated May 19 (figure references are to pictures on the web site):

‘Hubble Views Colossal Polar Cyclone on Mars. [Left]: Here is the discovery image of the Martian polar storm as seen in blue light (410 nm). The storm is located near 65 deg. N latitude and 85 deg. W longitude, and is more than 1000 miles (1600 km) across. The residual north polar water ice cap is at the top of the image. A belt of clouds like that seen in previous telescopic observations during this Martian season can also be seen in the planet’s equatorial regions and northern mid-latitudes, as well as in the southern polar regions. The volcano Ascraeus Mons can be seen as a dark spot poking above the cloud deck near the western (morning) limb. This extinct volcano towers nearly 16 miles (25 km) above the surrounding plains and is about 250 miles (400 km) across. [Upper right]: This is a color polar view of the north polar region, showing the location of the storm relative to the classical bright and dark features in this area. The color composite data (410, 502, and 673 nm) indicate that the storm is fairly dust-free and therefore likely composed mostly of water ice clouds. The bright surface region beneath the eye of the storm can be seen clearly. This map covers the region north of 45 degrees latitude and is oriented with 0 degrees longitude at the bottom. [Lower right]: This is an enhanced orthographic view of the storm centred on 65 deg. N latitude, 85 deg. W longitude. The image has been processed to bring out additional detail in the storm’s spiral cloud structures. The pictures were taken on April 27, 1999, with the NASA Hubble Space Telescope’s Wide Field and Planetary Camera 2. Credit: Jim Bell (Cornell U.), Steve Lee (U. Colorado), Mike Wolff (SSI), and NASA.’

This event was also the subject of a strange note in BAA Circular 771, in which it was unfortunately described as a dust storm. The note did not originate from the Director, who had not been consulted about it. So what did the ground-based observers actually see?

I received several images and sketches which showed this phenomenon, including one by myself on April 27, when I found Iaxartes invisible, and the area between Hyperboreus L. and M. Acidalium to be light. The same day, Cliff Meredith caught the cloud on a (low resolution) CCD image. The best ground-based image I have received is due to Cidadao, who caught the cloud on April 28 under a CML of 88 deg., when it had become a less impressive E–W whitish streak. Remnants of what may have been the same cloud showed up on his May 3 image (CML about 119 deg.), though by then the identity of the white patches had become questionable. This longitude band was not observable from the USA at the critical time, but the Japanese observers could catch the E. end of the phenomenon on the morning side of the disk. OAA observers established that morning cloud over Baltia, between M. Acidalium and Hyperboreus Lacus, developed from April 25 onwards; they were able to follow the phenomenon until April 29.

Such polar clouds have been known for many years of course; ground-based observations of identical features were made in 1997, for example. What was exceptional in the present case was the resolution achieved in the HST images.

3. MGS views dust in Valles Marineris

Amongst the more breathtaking images released onto the web site by MGS, there has been an image dated May 16 showing atmospheric dust in the Valles Marineris. It will be recalled that this site has been active twice already this apparition (see earlier Mars Section Circulars). Given the chance viewing of any single site by the MGS cameras, it seems unlikely that it would catch a storm at its onset. Perhaps more likely is that the billowing dust was raised from the latter of the two previous events, and was imaged slowly settling rather than rising. MGS only shot one image on one date, so no more can be concluded. None of this small-scale detail could be seen by the BAA team, so the activity was too small to be viewed from Earth: though Don Parker and others turned in fine detailed CCD shots of the albedo features and large-scale diurnal clouds around the Valles Marineris, these do not show any fine-scale tonal differences in the canyon system during May. In particular, Don’s images revealed no changes there during May 3 to 14. After May 14 our colleague from Florida lost the area at the morning terminator. Nothing was reported by any ground-based astronomers. Here is the full text from the MGS web site:

‘May 1999 Dust Storm in Valles Marineris: MGS MOC Release No. MOC2-130, 27 May 1999. Mars Global Surveyor’s (MGS) Mars Orbiter Camera (MOC) captured this view of a dust storm within the Ius and Melas Chasms of the Valles Marineris trough system on May 16, 1999. The dust storm is seen in the lower 1/3 of the image. It occurs at the junction between eastern Ius Chasma and western Melas Chasma. The apparent motion of the storm is approximately from the south (bottom of image) toward the north. The dust cloud forms a sharp front along its northern margin, which is seen along the north wall of Ius and Melas Chasms – in fact, at the time the image was taken, the dust had advanced up over the north wall of Melas Chasma (upper portion of lower right third of image) and was advancing across the upland that separates this chasm from western Candor Chasma. For a clear-atmosphere view of western Candor and Melas Chasms, see ‘Western Melas and Candor Chasms, Valles Marineris, MOC2-105, 25 March 1999’. For scale, note that the large crater south of Hebes Chasma, Perrotin, is about 95 kilometres (59 miles) across. Bluish-white clouds in the image are interpreted to consist of water ice. The pink/red clouds of the dust storm occur closer to the ground, at a lower altitude than the water ice clouds. One of the most interesting aspects of this dust storm is that Valles Marineris was observed to have a dust storm at exactly the same time of year, one Martian year ago. During its approach to Mars, MOC obtained a picture of the planet on July 2, 1997, just prior to the Mars Pathfinder landing. At the time, it was winter in the southern hemisphere, and dust clouds were observed within Valles Marineris. The picture is seen in ‘Mars Orbiter Camera Views Mars Pathfinder Landing Site, MOC2-1, 3 July 1997’. It will be interesting to see if similar storms occur within the Valles Marineris 1 and 2 Mars years hence. The next times will be in early April 2001 and mid-February 2003.’

The BAA martian dust storm Memoir I am now busy correcting the first proofs, and the printers hope to publish by early August 1999. An advertisement will appear in the BAA Journal. I am very pleased with the appearance of the text and colour cover. (For details, see Memoir.) An old drawing by E.M. Antoniadi Peter Hingley has published one of Antoniadi’s coloured Mars drawings in the RAS magazine, Astronomy and Geophysics. This drawing is in the RAS archives (see the 1999 June issue, p.7, where, oddly, north is uppermost). I published a black-and-white version of the same drawing (dated 1909 September 20) in my biographical study of Antoniadi, to which Peter refers. Antoniadi published some of his 1909 drawings in colour during his lifetime, but such reference sources are not readily available today.

Pages from Pathfinder (and MGS!)

In the same issue of Astronomy and Geophysics., p.6, the Editor notes the availability of a special section (576 pp.) of the 1999 April 25 issue of Journal of Geophysical Research devoted to the Pathfinder results. The principal scientific results include discoveries of:

· The spin pole and precession rate of Mars since Viking, 20 years ago; results require a central metallic core of radius between 1,400 and 2,200 kilometres.

· Evidence of warmer and wetter times in the past.

· A dusty lower atmosphere where ‘dust devils’ are common.

· Ice clouds common in the early morning, and morning near-surface temperatures changing abruptly with time and height.

On p.4, ibid., the magazine’s Editor briefly discusses the ‘magnetic stripes’ discovered by MGS on parts of the martian surface, and the possible implication of past tectonic activity by analogy with the stripes on Earth’s ocean floors, caused by crustal spreading.

BAA Exhibition Meeting

UK members may wish to know that I will be displaying some of the Section’s work at the BAA Exhibition Meeting later this month. This is the first time I have been able to attend in person since my term as BAA president (1993–95), so I am looking forward to meeting old and new friends.

The next Circular

Please report June observations by July 10, so that the next Circular can be issued by mid-July. Good observing!

Richard McKim, Director

1999 June 20