Planetary Section Report; October and November 2020. The Opposition of Mars

For the UK, early October saw one of the best oppositions of Mars for many a long year. Martian oppositions happen in a cycle with the relative positions of Earth and Mars returning to about the same place every 15th or 17th year and with a longer underlying cycle of 79 years that brings the planets back to very nearly exactly the same positions relative to the Sun and the background stars. On this occasion with Mars both close to us and high in the sky, perhaps not surprisingly, the majority of contributions received were of the red planet; there were some simply outstanding observations in this period. Happily other planets were not entirely neglected so I will deal with them first before returning to the meat of the section report.

Venus, Jupiter and Uranus Oct Nov 2020 annotated
Venus was well placed in the morning sky but received only a little attention; perhaps surprising given the recent discovery of Phosphine gas in its atmosphere. As this is a possible bio-signature I’m sure Venus will soon be receiving a great deal of professional attention and perhaps this will revive amateur interest. Dave Finnigan took a good image set in the early hours of the 17th of October combining infrared (IR) and ultraviolet (UV) light. IR detail is often illusive but Dave’s image shows subtle shading in the IR and more obvious dark patches in the UV; as has been previously noted dark UV features are often replaced by bright ones in the IR and the precise interaction between these different parts of the atmosphere is an active area of study.

Moving on, Larry Todd, Mark Beveridge Dave Finnigan and I all took images of Uranus in the period using both visible light and the near IR. No major bright storm features were visible and the planet continues placidly in its long lonely orbit, spinning on its side, its north pole currently tipped towards the Sun by, it is presumed, some long-ago calamitous collision; no doubt giving it some of the oddest weather in the solar system!

Jupiter and Saturn sat together in the early evening sky; drawing steadily closer towards their rare conjunction in late December. Larry Todd, observing from New Zealand, was able to get some detailed views showing the relative positions of Oval BA and the Great Red Spot (GRS) and the fragmented nature of the South Equatorial Belt. The Equatorial Zone is pale ochre in colour and the GRS has a dark spot at its heart while white storms disrupt the North Equatorial Belt. Mark Beveridge was able to capture a number of Jupiter images throughout November with the last, on the 28th, showing a similar view to Larry’s image from early October. The SEB now looks more settled but the NEB continues to be riven by storm activity, sending great plumes into the equatorial zone. Only one Saturn observation was received in the period so thanks again to Mark for sending that in.

Moving on to Mars, and I will begin by mentioning again the dark features seen within the Hellas impact basin by the membership during the last reporting period. Alan Heath, a tremendously experienced and highly regarded visual observer was aware of these markings from old maps and drawings made by others around the time of the 2003 opposition however he was good enough to confess that has never seen anything in that region himself. Given his extensive records and also the archive of images held by the SPA it seems probable that the winds associated with the dust storms that blew during the last opposition have uncovered these faint but visible dark surface albedo features for the first time since the 2003 opposition, and a number of observers caught them very clearly.

Hellas detail Oct Nov 2020 annotated
It would take up too much space to list each observation individually but I am indebted to James Martin, Ken’ Kennedy, Keith Johnson, Martin Lewis, Dave Tyler, Dave Finnigan, Alexei Pace, Steve Norrie, Mark Beveridge, Larry Todd, Lewis Parry, Alan Heath and Robert Steele for their many contributions. Alan and Robert sent in carefully drawn images of their observations at the eyepiece and Robert has compiled some of his drawings into a surface albedo map as seen with his 90 mm achromatic refractor.

cont73 mars7 map
One thing that has been noticeable absent throughout the observations in this period has been extensive cloud features. Cloud usually shows itself well when Mars is imaged through a blue filter and there are some areas where tell-tale banners of cloud quite frequently appear. The Tharsis bulge, and the huge shield-volcanoes rising up from that bulge, can have veils of cloud covering them as gas crossing the area is pushed up to high altitude, causing water or carbon-dioxide ice crystals to form. This period was notable for the near absence of any specific cloud structures. Early in the period there may have been some cloud around the shrinking south polar ice-cap but, otherwise, only thin blue hazes have appeared, particularly in the form of a ‘north-polar hood’.

Lack of cloud means the amount of visible surface detail has been impressive. The south polar cap itself is tiny and has taken on a slightly ‘tadpole’ shape in the most detailed of the images, with a dark lane cutting into the ice and creating the tail of the tadpole. A surrounding dark band is visible defining the disrupted ground where gas and water vapour erupts from the soil during the heat of mid-summer.

The major recognizable surface features have all been captured in considerable detail. As mentioned the Hellas Planitia contains a number of ‘long-lost’ features and, to the North of it, Syrtis Major is beautifully defined with small outlying ‘islands’ of dark material surrounding its northern extremities. Following west along the line of the equator Terra Meridiani shows a sharp northern perimeter and the cut-out of the crater Schaparelle is visible in a number of images along with the ‘fingers’ extending north from the Terra Meridiani and the Margaritifer Terra. This leads us into the Valles Marinaris, the Grand-Canyon of Mars, which is clearer in this apparition than in any previous one I can remember.

Just to the south of it sits the ‘Eye of Mars’ or the Solis Planum, also known as the Solis Lacus to many observers. This area was imaged by Martin Lewis in mid-November and in his one-shot-colour picture from the 18th and in a false-colour IR and blue light combination from the 19th a plume of dust is visible spreading eastwards from Solis Planum. This is a developing regional dust storm; several features, sharp in earlier images, are softened or partially obscured by this storm. With a solar longitude just approaching 320 degrees, this is very late in the season for a large dust event and shows how lucky we have been not to have such a storm closer to opposition in October. By the 22nd of November the dust is seen to cover the Argyle Planitia and by the 25th is softening the view of a large part of southern Mars. Recent reports suggest it has spread to interfere with views of Elysium and Arcadia Planitia in the north but further observations will be needed to confirm this.

Mars Nov 2020 dust event annotated
To the west of the Valles Meridiani sits the shield volcanoes of the Tharsis bulge and, while faintly visible, they have not really stood out apart from early in the period when both Dave Tyler and Dave Finnigan caught frost on Olympus Mons, causing it to shine brightly, particularly in IR images. Moving still further west, twin sharp projections to the north of Hesperia Planum are clearly visible; at the tip of the most eastern of these projections sits the Curiosity Rover; and no, I’m afraid you can’t quite make it out!
Throughout this period section members have observed consistently and produced impressive results. Conditions have ranged from dreadful to excellent, Steve Norrie describes one night as giving him his best mars image ever, and another as like trying to image through a bowl of Scotch broth, ‘though I’m not sure why he singled out that particular and most excellent soup. It is only a shame that it will take Mars quite so long to be so well placed again. At the next opposition The Red Planet will be higher in the sky but noticeably more distant so it will be interesting to see just what is visible around Christmas 2022.

Mars rotation Oct Nov 2020 annotated


Alan Clitherow