Mars is the most earth-like planet in the solar system. However, there are significant differences between the two planets. Mars is a small world, about half the size of the Earth, and in the billions of years since its formation, most of its atmosphere leaked into space, leaving a relatively thin atmosphere predominantly of carbon dioxide. In its ancient past Mars certainly had shallow oceans, but now what little water is left exists seasonally in the two polar caps and what appears to be a planet-wide layer of frozen water beneath the Martian surface. A day on Mars is very close to 24 hours. The temperatures on this little world are far colder because Mars orbits further from the Sun than our own planet.
Mars is at the center of my personal fascination with planetary imaging and it is a very challenging subject. Getting sharp images of the surface of Mars is best done at opposition – the point of closest approach to Earth. Images don’t have to be obtained right at opposition, so, depending on the size of your telescope, useful images can usually be obtained for up to several months centered on the time of opposition. The Outer gas Giants of the solar system (Jupiter and Saturn) travel slowly in their orbits compared to the Earth, such that earth is in opposition with each of them on an almost annual basis. Mars is close enough to the earth that it actually takes the earth approximately two years to catch up with the planet between oppositions. What this means is that Jupiter and Saturn can generally be imaged for several months approximately once a year. In contrast Mars can only be imaged for a few months every two years. The planet is relatively small but it is bright. Because of its small size it is often desirable to apply use auxiliary lenses to increase the magnification of the telescope but this can be touchy if you don’t have really good seeing. Click on Mars on [NASA Solar System Exploration] page for a lot more information on the “Red Planet”.
Shown below are images from both the 2014 and 2016 oppositions. Different telescopes were used for each opposition and there has not been a Mars opposition since the addition of the OMC 200 telescope to the Observatory. In June and July 2018 it should be possible to try our luck with the new telescope, but the older images are included here to give you a sense of what can be accomplished.
During the 2014 apparition, the primary telescope at the Observatory was the very popular Celestron 8-inch (203 mm) Schmidt Cassegrain (SCT).The C8 had a native focal ration of f/10, which is too low a value for a reaslonable image scale. For this session the instrument was equipped with a 2.5X PowerMate for a working focal ratio of f/26.
Only one session produced really nice images, one of which is shown here. The small North Polar Cap, the low-albedo circumpolar ring is quite prominent, as are numerous surface features, including Syrtis Major toward the SW limb. The large white area to the extreme south is NOT the South Polar Cap. Note that it is offset from the Northern Polar Cap is is actually the Hellas Basin, a huge depression several kilometers below the average surface elevation. Hellas is often filled with clouds (as it is here). A very subtle feature can be seen along the western limb. What looks like a bluish-white haze is just that – high ice clouds typical of the night side of Mars (where temperatures commonly drop to more than 100 degrees below zero (Centigrade). The clouds here are still present after local sunrise but will disappear quickly as the surface warms to a balmy 50-60 degrees below zero!
Mars had an apparent diameter of 15.1 arc-sec. at opposition on 08 April that year. This image was obtained late in the month and the apparent diameter had dropped to just under 141arc-sec. The planet was at an elevation of 43 degrees – reasonably good conditions!
22 May was the date of opposition in 2016 and on 30 May the Earth made is closest approach to the Red Planet. Four days later, on the 3rd of June, I got the best image of the apparition. The 180 mm Maksutov (f/17) was used with a 1.6X Barlow lens on the camera to achieve a working focal ratio of f/28. This normally would have been too high a focal ratio, but for this session had exceptionally good seeing for a change. This image does not look as good as the one from 2014, but that is only because itg happened to cover a relatively “dull” area of Mars. In fact, surface detail is excellent for an instrument with an aperture of 180 mm/7 inches!
While the image on the third of June benefited from the use of an accessory Barlow to increase the image scale, this is not always the case. Above are two images from the 7th and 9th of June. The images on the left were obtained at the native or “prime focus” (f/17) of the 180 mm Maksutov, the images on the right were captured using the 1.6X Barlow, proving an effective focal ratio of f/28. While the f/28 images are larger, they have lower contrast and show less actual detail than the smaller f/17 images. On both 07 and 09 June, the seeing simply would not support the use of the higher focal ratio. Not only was the use of the Barlow a waste of time, it actually degraded the images compared to those captured at f/17! Additional magnification is of no use unless the seeing will support the magnification that is employed.
New Images will be posted here as Mars approaches the current opposition on 27 July 2018.
So why no new Mars images? Here is the main reason! As Mars began its close-in approach to opposition in May, a planet-wide dust-storm, something that occurs every six years or so, kicked up and the entire surface was obscured by a veil of atmospheric dust that completely obscured surface detail. This image, taken on 11 July 2018 is typical. Hints of some of the darker surface features, as well as traces of the polar caps, are faintly visible through the dust, but this is far from satisfactory when you have been waiting two years for what was supposed to be the best opposition in a long time!
What was shaping up to be a disastrous apparition (there was no reasonable hope that the storm would clear sufficiently for detailed color imaging prior to late September) was saved by the prospect of imaging the planet in the near infra-red (IR). Using a grayscale camera (ASI120MM) and a Baader far-red to Near-IR filter, it was possible to see through the obscuring dust veil in the atmosphere and actually image surface features!
Note that the image of 05 August is shown at twice the diameter of its neighbors. This is the most detailed of the Near-IR images (seeing was very good) and it has been enlarged to show some of the details. Note the three Tharsis volcanoes arranged in a straight line tending NE and SW, located in the NW quadrant of the disc. The three volcanoes are close enough to the sunrise terminator that each casts a small, but distinctive shadow, giving them a distinctly three-dimensional appearance.
With the exception of the 2X enlargement of the image from the 5th of August, the image sequence starts with Mars appearing relatively large and the average size shrinks into September. Mars was at opposition on 27 July with an apparent diameter of over 23 arc-sec. From that point on, the distance between the Earth and Mars increases steadily, and the diameter of the disc decreases to about 17.1 arc-sec by mid September. Although the dust storm is beginning to wind down, by the time the planet’s sky is clear, Mars will be too distant to image in any detail.
The opposition of 2020 (the next one) will be a good one, with the elevation of Mars exceeding 50 degrees (compared to around 20 or so degrees this summer), so the next time we get a good look, it should present some nice full-color views.
Anyone needed more precise observational data for any of these images can simply email be for the details and indicated the date of the image in question.