2025 January 8

Mars Opposition Blog 8 January 2025

Richard Mckim

2025 January 8

Opposition (January 16) is now just days away. As of today, the Mars Section has 64 active observers (see the updated list on the front page), and by December 31 these individuals had contributed no fewer than 3,611 images and 353 drawings. The following notes are complete up till January 3, and are necessarily highly selective.

A large number of images have shown details within the N. polar cap. Since late last year there have been some records of the high latitude annular rift within the cap (the feature that marks the outline of the permanent summer cap remnant), and this is normal, while at other times the area N. of the rift up to the N. pole has also looked dark. It seems that the latter darkening could be due to dust dispersed from the several small storms that have appeared at the edge of the seasonal cap from time to time. For example, observing visually on the evening of January 2, the Director noticed the relative darkness of the N. part of the cap, N. of the circumpolar rift, and this appearance was confirmed by the receipt, a few hours later, by an image by Mark Radice.

We have seen several active bright spots – white clouds – just north of the boundary of the cap. Frontal weather systems which move southward from the cap edge sometimes raise local dust storms in the N. hemisphere, as recent blog postings have shown.

There have been several bright orange patches – local dust storms – seen at the cap edge, and (as described and illustrated in the last posting) on occasions festoons of dust emanating from them have impinged upon the cap, the dust having a lower albedo than the latter. As the dust begins to settle (subsequently being dispersed by winds), parts of the cap briefly take on a warm tint. For example, on December 17 Foster’s images showed the morning side of the cap to be dull, and he remarked upon a warm tint there. On December 17 and 20 Gary Walker and Bill Flanagan respectively showed a complex dark dusty feature crossing the cap obliquely near the CM. Such features are darkest (and hence best seen) in blue or violet light. Particularly striking are the observations by Tiziano Olivetti and Tomio Akutsu on December 30 and 31 respectively, in which a prominent orange tendrill of suspended dust is seen cutting across the edge of the cap around longitude 300 degrees. Each successive storm lasts several days.

Since early December, Argyre has looked bright at the S. limb, particularly in the morning and evening, and its greater brightness in blue light indicates the presence of white cloud. (The southern basins do not become covered with ground frost until later in the martian year.)

Also since December, orographic clouds have been reported over all three of the Tharsis Montes. These are now quite striking near the evening limb. Alba Patera in the north also sports such an afternoon cloud, as do Elysium Mons and the great Olympus Mons. A good illustration of these clouds is to be found in Frank Melillo’s image of December 31, while on the same date Tom Williams captured the clouds earlier in the martian afternoon. As we near opposition there will be a bright patch marking the locations of the volcanoes even when they are not clouded. Such a situation is visible upon Damian Peach’s image of December 20, in which Elysium Mons and Hecates Tholus show up as very small bright spots. E-W belts of white cloud were sometimes to be seen near the edge of the NPC: for example, Flanagan on December 12 shows such a feature in N. Tempe, and Peter Tickner’s UV image on December 17 (posted here) shows another such cloud west of Casius-Utopia.

For those in Scotland, there will be a grazing occultation of Mars by the Moon on February 9 (see pages 45-46 of the 2025 Handbook). Those of us at lower latitudes will have had to make do with the lunar occultation of Saturn on January 4….

Good observing! The images are posted in chronological order here, with the earliest ones at the bottom of the page.