December 10

The weather has not been very cooperative lately, but we have still managed to get observations on nearly every date. This entry continues the story up till and including December 4, but is not intended to be a complete account. As ever, I can only post and discuss here a small fraction of the observations received.

Albedo feature changes are often slow and subtle, and one such example has been the gradual fading of the so-called “Aetheria darkening”, which was first apparent in the late 1970s, when a broad, triangular shading developed at the NW corner of Elysium. It was sometimes contracted to a small dark spot, but basically remained in place till recently. In 2010 there existed a tenuous streaky extension to the south, but after 2018 and the global dust storm the dark shading gradually faded. Now it has all but disappeared. Other features in the region have also changed. Trivium Charontis and Cerberus were dark areas until the late 1980s, but have progressively narrowed and faded. Thus the whole area around Elysium has seen a net accumulation of dust fallout, hiding albedo markings. Here I show comparative images by Damian Peach (UK) from 2010 and 2024, with some annotations. These really show the change well.

Of the changeable features elsewhere that have remained dark, the Indus streak from Oxia Palus to SE Mare Acidalium remains dark, and the streaky Hydaspes to the west of it remains noticeable.

In terms of high resolution imaging, Tom Williams used his new 60 cm (24-inch) reflector to obtain an amazingly detailed image on December 2. Of course, technical skill in processing is also needed for such results! Note the parallel belts of faint white cloud near the NPC, and the intricate details (for example) around the W. end of Valles Marineris at Tithonius Lacus.

The north polar hood has largely cleared now, but streaks and patches are sometimes seen in the morning.

Cutting across the N. polar cap near the CM, a coloured streak of airborne dust could be seen in the fine images by Peach and Peter Tickner (UK) on December 4. The dust streak was darker than the cap and brighter than the dark border of the cap. (See the 2010 report for an account of a conspicuous dust storm over the NPC.) Another, much less prominent dust streak at the cap edge was captured by Gary Walker (USA) at a higher longitude (close to the CM of the image, 082o) on the same date.

The orographic clouds over the Tharsis Montes are well visible in the image of November 26 by C.Foster (Namibia) shown here, which also shows cloud at Alba near the CM in the north. Notice how a blue/violet filter increases their contrast. The Alba orographic is also beautifully shown in an image of November 30 by E.Sussenbach (Dutch Caribbean), where the tailing off of the cloud to the west can be well seen. On December 2 T.Akutsu (Philippines) imaged a slight terminator projection due to high cloud, located near +2o, 202o (NE Aeolis).

I include other typical images by M.Hood (USA): note the partial morning clouds off the edge of the NPC; T.Arakawa (Japan): note the fine details NE, N and NW of the Syrtis Major, including Nodus Alcyonius; and T.Kumamori (Japan): the region of Indus and Hydaspes.

Opposition is fast approaching, so naturally more observers are joining in. The list of contributors posted on the front page has been updated, and already contains 53 names. If you are reading this as a BAA member please note that to start contributing to the Section you must first get in touch with the Director.

Expect another update shortly after the date of opposition.

With the US Presidential election taking place recently, I felt that some sort of parallel counting operation should be done in the UK, so on October 27 I tallied up the observations sent in to date, and there were 256 drawings and 2,285 images. I will not comment upon whether there were more blue images than red ones, but you will recall that I always hope for more blue ones! This blog post is complete up to and including Oct 31.

We have had new observations showing evening cloud over Arsia Mons and Olympus Mons (perhaps the first sign of the latter cloud). See the image by Gary Walker (USA) for Oct 23 posted here. Seasonally this is to be expected. Naturally the eye is drawn to the variable N. polar hood and its environs. Several observers have paid attention to the lower latitude of the hood in the vicinity of Mare Acidalium as well as its partial transparency over the north of the latter, while at some longitudes we have seen east-west elongated strips of cloud detached from the S. edge of the polar region.

Occasionally, frontal systems have moved off the cap to the south, and sometimes they have generated obvious small dust storms. A recent example (posted here) is a little yellow patch of dust caught in images by Luigi Morrone and Raimondo Sedrani (Italy) on Oct 30. This lay over E. Cydonia, NW of Ismenius Lacus. Note the very white morning limb cloud adjacent to the cap. Other such dust clouds at the cap/hood boundary have been seen.

Earlier, an even more dramatic storm in the form of an east-west shaped arc of dust was seen on Oct 13 by Flanagan and Mike Hood (USA), rapdily fading the next day. It was located west of the N. end of Syrtis Major, between it and Elysium. With its long dusty arc, the Oct 13 sharpened image gives a slightly unusual appearance to the planet. See the Oct 12-14 collage posted here. On this occasion the dust storm coincided with enhanced activity at the edge of the polar region. David Basey (UK) on Oct 11 drew attention to what appeared to be two bright projections off the edge of the cap, while closer inspection showed these to have been due to the presence of a horizontal cloud band that was transparent in the middle, with a dark feature (corresponding to the classical Sithonius Lacus) showing through. Sedrani captured the same activity. Johan Warell (Sweden) made a similar comment about enhanced hood activity at this longitude upon his images of Oct 12. The dust storm is the second of two recent events to have occurred near the boundaries of Elysium, an area where we know there has been a net accumulation of dust for some years now. (This is evident from the progressive fading of Cerberus, Trivium Charontis and the Aetheria dark marking.)

The N. polar hood will persist for some time into northern spring, particularly on the morning side of the disk, and in certain longitudes. N. spring (Ls = 0o) begins on Mars on Nov 12.

In the December Journal I have a note about the closely similar 1898-99 apparition, one of the earliest to be followed by the Mars Section, and I am suggesting that observers might challenge themselves to obtain images at very similar times and longitudes to the drawings published in the article, in order to make a comparison of albedo changes over 126 years. Let me know if you succeed.

October 10

Since the large Regional dust storm, there has been smaller scale dust activity in the same area. The weather was less cooperative, resulting in lower coverage. Initial observations were made – and promptly reported – by Foster in Namibia and Haigh in the UK, on the morning of Sep 18, when there were two small, bright dust cores in southern Chryse, and another dust cloud curving around the N. and W. of Lunae Lacus at the SW border of Tempe. Nothing had been seen in high resolution images by Haigh on the 17th. The Director immediately posted the news on the BAA Forum. On Sep 19, images were made by Foster, Haigh and Peach. Now there was dust along Valles Marineris bordering Chryse-Xanthe. There was a large, lightish patch of dust over Chryse, and an E-W dust streak obscured parts of Nilokeras and cut across Mare Acidalium, disfiguring Niliacus Lacus. Haigh’s Sep 18 and 19 image sets are shown here.

On Sep 20, images by Foster and Peach (posted here) showed the dust clouds more diffuse, causing a wide loss of contrast. The Valles Marineris dust now extended slightly to the SW. The immediate impression was of a N-S belt of dust (with a brighter core in Chryse) stretching from Niliacus Lacus into Mare Erythraeum. On Sep 21, the only coverage was from Europe: Basey, J.Sussenbach and Tickner participated. A large, bright dust cloud persisted just east of Aurorae Sinus, overlapping a part of Valles Marineris and Mare Erythraeum, and the bright core persisted in Chryse, while Mare Acidalium was returning to normal. On Sep 22, Foster’s images (posted here) showed all cores subsiding, with a slight residual loss of contrast. The two dark spots located upon Nilokeras, Idaeus and Achilles Fons, adjacent to the site of one of the initial dust cores, were now large and dark again.

Sep 23: Sedrani (Italy) showed Mare Acidalium normal, but the storm area was close to the morning limb. Sep 24: E.Sussenbach (Dutch Caribbean) showed residual dust over part of Nilokeras and (again) Mare Acidalium, though the latter was close to the evening terminator.

As this event was clearly subsiding, another, much more local storm arose on Sep 25, when images by Arakawa and Inoue (Japan) showed a small dust cloud at the E. border of Elysium. This may have persisted a day or two, but quickly vanished. See Inoue’s Sep 25 image posted here.

The N. polar canopy persists in white light over Mare Acidalium. In this longitude it has often been possible to see the lower part of Acidalium as a dark patch (sometimes an E-W oriented slit), due to thinning of the cloud. This feature was dubbed “Dawes’ slit” by the late Masatsugu Minami in honour of the English astronomer W.R.Dawes, who had been the first to observe it clearly, back in 1864-65.

Again my thanks to our 39 observers for their splendid early morning efforts which have brought in over 230 drawings and over 1,900 images so far.

As you may have read from the alerts and follow-ups that I posted upon the BAA Forum, we have recently had a major Regional dust storm. I will cover this in some preliminary notes below which extend up to and including September 4. But first, to follow up upon the previous happenings….

The local dust storm described in the previous blog post lasted only a few days, but in late July and early August there was a slight resurgence of activity when a local dust cloud appeared in southern Chryse. This too lasted only briefly. On Aug 3 there was virtually no trace of it on the morning side to the Japan observers, while on the same date J.Warell (Sweden) caught the now inactive region at the evening terminator, proving that no activity had spread to the west.

It was to be in a similar location that more significant activity began on Aug 18, when images by Clyde Foster from 05:10 UT onwards showed very bright dust activity along eastern and central Valles Marineris, with two bright cores overlapping the southern deserts of Chryse/Xanthe. At Ls = 313.5 degrees, it had commenced at a point fractionally beyond the last moment for an encircling storm to have developed, but a large Regional event could not be ruled out at that stage, and indeed turned out to be the case. The eastern bright core was centred at -8.7, 034.4 degrees according to images at 00:23 UT taken by the MARCI instrument aboard the Mars Reconnaissance Orbiter (MRO), as provided by A.Sanchez-Lavega. (This location is close to Eos or Pyrrhae Region on the classic albedo maps.) Eric Sussenbach caught the western end of the event at 10:04 UT.

Next day, Aug 19, the storm expanded to the north over Chryse-Xanthe, and to the south over Mare Erythraeum. At this time I suggested that secondary dust cores would probably arise, perhaps over some or all of Meridiani Sinus, Margaritifer Sinus and Argyre, as they have done in similar events in the past.

By Aug 20 the storm had definitely reached Regional status (its long axis extending over 2000 km, or 34 angular degrees). Foster’s images (from Namibia) and Nick Haigh’s (UK) show that it had reached and faded E. Meridiani Sinus on the eastern front, while Peter Tickner’s full daylight IR image (from the UK) timed at 08.45 UT showed dust surrounding a still dark Aurorae Sinus to the west, and still expanding south west, with apparently one discrete cloud near Solis Lacus. Dust continued to occupy Chryse and Xanthe, with Mare Acidalium to the north largely unaffected. Although UK observers were now losing the emergence site over the morning limb at dawn, the eastern end would remain in view.

Further secondary cores now emerged, and I cannot mention all of them here. The dust core located near Solis Lacus became large and extremely bright on Aug 22 according to images by Gary Walker, Frank Melillo and others. Gregory Terrance, using a 50 cm aperture, showed that this new core was in fact highly condensed. However, little further development on the western side occurred. On Aug 21, Haigh caught a bright dust core between Meridiani Sinus and Margaritifer Sinus which lasted a few days, while to the south, dust was invading western Noachis.

A new (or resonant) core formed in Hellas: it is shown on the Aug 19 and 21 MARCI maps that have been forwarded by colleagues in the USA. Dust remained within the basin. On Aug 25 however, Haigh and Peach showed a bright yellow cloud in the NW corner of the basin spilling out of it into Iapigia, which was confirmed by Foster next day. The core was small and bright in early September, but by then dust was confined to the basin. An image by Walker dated Sep 4 shows this aspect. Furthermore, a new dark patch had developed adjacent to it on the west, as often happens as a result of events here. (Larger events cause a broadening and darkening of all of Mare Serpenis-Yaonis Fretum, bordering Hellas.)

Dust had covered Mare Erythraeum and Argyre and environs in the form of several parallel E-W belts. Within days these bright areas would become static, indicating that fallout was occurring. Sussenbach’s images on Aug 23 and 24 show daily changes.

On Aug 25 I posted the following at the Forum: “As of today this event seems to be ending. The eastern secondary core at Meridiani Sinus and more prominent western ones at or near Solis L. did not last long; for a time there was a bit of atmospheric dust raised in Hellas. The area around Argyre is still bright, but its lack of daily movement suggests it is now dust fallout from the storm. This area is larger than Argyre, as was the case with the similar event in 2022. Compared with the 2020 and 2022 regional storms at similar seasonal dates, the present one was less energetic and less extensive.”

There were a few final flourishes. Mike Hood and Walker on Aug 29 recorded a new bright dust cloud in SE Chryse more or less following the line of Oxia Palus-Indus. It did not develop, and more recent images show that the emergence site has returned to normal, in spite of the strong activity that had taken place there, while the Oxia Palus-Indus dark feature and other halftone streaks crossing Chryse are well seen again.

Several Japanese observers were very active as usual, but could hardly watch the storm. However, their work showed that the evening orographic cloud at Arsia Mons remained bright throughout its course, showing that dust did not significantly warm the atmosphere beyond the confines of the event. Great storms warm the entire atmosphere, causing all white crystal clouds to disappear.

In the north, although the polar hood presently persists (and should continue to do so for a long time) we have witnessed the first signs of the ground cap. Around Aug 9 the polar region had become brighter and sharply defined in red images (and to a lesser extent in IR images), at Ls = 309 degrees, though the larger overlying hood was visible in blue light. Makoto Adachi and myself consider that the ground cap was captured on this date by S.Ito and S.Watanabe, while Adachi may have seen it visually on Aug 7. (In 2012 BAA data showed the ground cap was first sighted at Ls = 312 degrees.) It is usual for the polar region to be changeable at this Ls, and indeed the hood is often more prevalent than the ground cap in the longitude of Mare Acidalium. We did not see the hood recede during the current Regional dust storm, confirming that dust was obviously not penetrating very far north of the equator.

Posted here are several daily compilations showing different stages of the Regional dust storm. This is in no way intended to be a complete account. I would like to thank all those who responded to the Forum posts and to personal email alerts. We now have over 36 observers sending or posting data, and the list of them on the front page has been updated.

Front page teaser image – Eastern End of Dust Storm, Clyde Foster. Western End of Dust Storm, Eric Sussenbach.

Previous Post – 5 August 2024

This is a summary of observations up till July 31.

By early July a trace of bluish-white N. polar hood along the limb had been discernible for some time. It had never been prominent. Tomio Akutsu’s images of June 27-28 and Clyde Foster’s images of July 9-10 clearly show how some cloud had moved south to cover the N. end of Mare Acidalium, as is often the case. The hood will become very prominent over the next few months. A nice image of it was secured by Damian Peach on July 28.

O.Inoue on Jul 20 imaged an evening cloud at Arsia Mons at Ls = 297 deg. It was clearly confirmed by MacNeill’s work two days later. These may be the first images of it this apparition.

Indus continues to be easily visible. It is now quite clear that Sinus Gomer (at the northern edge of Mare Cimmerium) has faded greatly since 2022. This had been suspected some months ago, but we could not be certain with such a tiny disk diameter back then. See the July 28 image of Peach. I also suspect that Lunae Lacus may now be somewhat darker than it has been for some time. East of Syrtis Major there is a hint of the southern part of Nepenthes being weakly imaged, while to the north, Nodus Alcyonius remains small and weak compared with a decade ago. And Solis Lacus may be a little smaller, particularly in the N-S sense.

During July 27-29, imaging and visual observations from Japan revealed a small dust storm upon the western edge of Margaritifer Sinus, in the eastern part of Valles Marineris. See the July 28 image by Inoue. As of today it does not appear to be expanding, and is now fading out. This continues the trend of recent years with, Hellas less active in producing storms and Valles Marineris (upon the border of Chryse-Xanthe) exhibiting greater activity.

I am posting Foster’s image of July 10 here, plus others from Casely (June 23), Haigh (June 17), Inoue (July 28), Ito (July 6), Akutsu (June 27) and Peach (July 28).

At July 31 we are at Ls = 303 degrees. A large planet-encircling storm might yet commence within the next 10 degrees in Ls, so please keep watching intensively

Front page teaser: Another dust storm and some small albedo changes. Image by O Inoue

Previous Post – 5 July 2024