In 1971 the former Soviet Union launched the Mars 2 and Mars 3 missions to Mars. Each consisted of an orbiter plus a lander. Both orbiter missions were successful, although the surface of Mars was obscured by a planet-encircling dust storm. The Mars 2 lander crashed but Mars 3 became the first successful soft landing on the Red Planet. Unfortunately, after just 14.5 seconds transmission from the lander stopped, for unknown reasons.
The predicted landing site was at latitude 45 degrees south, longitude 202 degree east, in Ptolemaeus Crater. MRO's HiRISE camera acquired a large image at this location in November 2007. This image, PSP_006154_1345, contains 1.8 billion pixels of data, so about 2,500 typical computer screens would be needed to view the entire image at full resolution. Promising candidates for the hardware from Mars 3 were found only very recently.
Vitali Erogov from Russia is the founder and administrator of the largest Russian Internet community about MSL Curiosity. Subscribers of this community did the preliminary search for Mars 3 via crowdsourcing. Expected hardware included the parachute, the heat shield, the terminal retrorocket, and the actual lander. Erogov made scale models of what each piece should look like at the HiRISE image scale (25.3 cm/pixel), and carefully searched the many small features in this large image, finding what appear to be viable candidates in the southern part of the scene. Each candidate has a size and shape consistent with the expected hardware, and they are arranged on the surface as expected from the entry, descent, and landing sequence.
One of their advisors was Dr. Alexander "Sasha" Basilevsky, who is well known to the international science community. Basilevsky contacted Alfred McEwen, principal investigator for HiRISE, suggesting a follow-up image. MRO acquired this image on 10 March 2013. The image was targeted to cover some of the hardware candidates in color and to get a second look with different illumination angles, to provide more information. No color anomalies are seen in the images, which is understandable after more than 40 years of dust deposition. Meanwhile, Basilevsky and Erogov contacted Russian engineers and scientists who worked on Mars 3 for some more information.
The candidate parachute is the most distinctive and unusual feature in the images. It is an especially bright spot for this region, about 7.5 meters in diameter. The parachute would have a diameter of about 11 meters if fully spread out over the surface, so this is consistent. In the second HiRISE image the parachute appears to have brightened over much of its surface, probably due to its better illumination over the sloping surface, but it is also possible that the parachute brightened in the intervening years because dust was removed. HiRISE recently showed that the MSL parachute has shifted in the wind, which might also kick off dust. Since the parachute from Viking Lander 1 (1976) can still be seen as a bright area, it is reasonable that a slightly older parachute would also remain visible, perhaps because dust is kicked off. The bright spot is definitely an unusual feature--there is no similar feature anywhere else on these images, which we would expect if it was a natural bright spot of some sort. In the second image with more overhead illumination, it is clearly the brightest spot here. It differs from the parachutes from U.S. Mars landers because it isn't elongated due to the lateral velocity of the backshell attached to the parachute. The Soviet design resulted in a vertical descent that is expected to leave a more circular parachute on the ground.
The descent module or retrorocket was attached to the lander container by a chain, and the candidate feature has the right size and even shows a linear extension that could be a chain. Erogov was later informed that the length of the chain was 4.5 meters, which is a good match to the image line (4.8 meters), which might have resulted from dragging the chain and disturbing the surface. Nearby the candidate descent module is a feature with the right size and shape to be the actual lander, with four open petals.
The image of the candidate heat shield matches a shield-shaped object with the right size, that is partly buried.
Together, this set of features and their layout on the ground provide a remarkable match to what is expected from the Mars 3 landing, but alternative explanations for the features cannot be ruled out. Further analysis of the data and future images to better understand the 3-dimensional shapes may help to confirm this interpretation.
Written by: Alfred McEwen (11 April 2013)