Click for full image.
In just over a month, on February 18, 2021, the American rover Perseverance will come screaming through the thin atmosphere of Mars at a speed of over 12,000 miles per hour to hopefully land successfully in Jezero Crater.
The map to the right, cropped and reduced to post here, was released last week by the Perseverance science team and shows the landing ellipse in that crater. It also shows the much larger landing ellipses of previous landers/rovers. As they noted,
As landing technology improves and these landing ellipses shrink, missions can aim for more precise landings, opening up new areas of Mars to explore.
Perseverance takes it two steps further than previous missions. First, it uses a new algorithm to time its parachute deployment based on distance to its target rather than vehicle velocity. This shrinks the landing ellipse to 4.8 miles by 4.1 miles (7.7 kilometers by 6.6 kilometers). Second, the rover uses maps stored in its memory to avoid landing hazards within that smaller ellipse during its propulsive descent phase. This allows Perseverance to target safe landing locations within Jezero Crater. The rover is set to land on Feb. 18, 2021.
Improvements in interplanetary navigation tightened the landing ellipse of Mars Pathfinder in comparison with missions before it. It landed by bouncing on the surface with airbags, and has the largest ellipse in this image, measuring 124.3 miles by 43.5 miles (200 by 70 kilometers). The Phoenix and InSight landers used retrorockets to land on three legs, but still had large possible landing areas about 80.8 miles (130 kilometers) long.
In 2012, the Curiosity team developed guided entry technology, shrinking its landing ellipse further. The spacecraft used small rockets to steer itself through the atmosphere as it headed toward Gale Crater.
In the image to the right I have focused on the landing ellipse itself, cropped at full resolution. This improvement in landing technology has clearly allowed Perseverance’s engineers to take a lot more risks than previous missions. The ellipse is centered right on the edge of the gigantic delta of material that at sometime in the past poured through a western break in the crater’s rim. In fact, the very steep and rough edge of that delta is in the dead center of the landing ellipse.
I also think they have made a change in their target ellipse. In two earlier articles about the geology of the Jezero Crater landing site on March 22, 2019 and July 30, 2020 I included the second overview map to the right.
With this older map the ellipse was placed by me using data from other research. In the old map almost none of the delta is within the ellipse. In the new map above the ellipse has shifted to the west and north, putting almost all of the delta within it.
If this new placement is correct, it appears they are now trying to land as close as they can to the edge of the delta. To land on the crater floor just to the east of the delta makes great sense, as they can then quickly start climbing onto it, gathering data.
The map above however also suggests they are willing to land right on the delta. To do this however makes less sense, as for research purposes you want to work your way up to study the delta’s history, which is going to be revealed by the lower layers. Landing on top prevents you from doing that research.
I therefore wonder if the placement of the ellipse in the new image is wrong. I cannot find my source for my initial placement of this ellipse, but I know I would have taken it from a legitimate source.
Jezero Crater delta
There is another possibility. They want to land on the delta to speed their journey west into the crater rim gap and out into the canyon from which that delta flowed. This would mean the science target has shifted from the delta to the drainages to the west. That would make sense, considering all.
Either way, we will find out in only a few weeks. To the right is the beautiful color Mars Reconnaissance Orbiter photo of that delta, as indicated by the white box in the second overview map. This is amazing terrain. Wherever Perseverance goes it will see wonderful things.