SpaceX has downselected 7 potential Mars landing sites for Starship

On September 2019 it was revealed SpaceX has selected several Starship candidate landing sites on Mars. The candidate sites were located in Southern Arcadia Planitia East of Erebus Montes and one in Phlegra Montes.

Since then SpaceX has conducted several workshops with the Mars science community to evaluate and narrow the list of candidate landing sites. All the sites must fit several criteria:

1. close to significant deposits of water/ice, a required resource for in situ propellant production and a consumable to support habitation;
2. elevation below -2 km (with respect to the MOLA geoid) that can support the delivery of large payloads, with -3 km preferred;
3. latitude must be <40° for solar power and thermal management, and closer to the equator is desirable;
4. multiple separate landing locations spaced within a few km of each other, to support the multiple missions needed to grow an outpost;
5. slopes should be <5° over a 10 m length scale and the chance of impacting a rock greater than 0.5 m high (1 m diameter) should be <5%;
6. landing site must be radar reflective to enable measurement of the distance to the surface, and it must be load bearing to support the spacecraft at touchdown.

Recently an abstract with the conclusions has been published (the results of the study will be presented in two weeks, at the 52nd Lunar and Planetary Science Conference), pointing out 4 prime and 3 secondary potential Starship landing sites selected for further study and located in Phlegra Montes, Erebus Montes and Southern Arcadia Planitia:

• PM-1 has the lowest latitude and elevation of the Phlegra Montes sites, a clear association with LDAs (local ice deposits expressed as lobate debris aprons), well developed polygons (one of the indicators of ice-related morphologies), and has the highest SWIM (Subsurface Water Ice Mapping) score for geomorphic indicators of ice;
• AP-1 (Arcadia Planitia) appears to be one of the safest sites and has a moderate combined SWIM score for ice;
• AP-9 has the thickest ice from radar returns (of the Arcadia Planitia sites) and geomorphology indicating shallow ice. It has the highest combined SWIM score for ice, but appears slightly rocky and rough;
• EM-16 has a clear association with an LDA with nearby brain terrain and the strongest radar return for shallow ice and the highest combined SWIM score of the Erebus Montes sites;
• AP-8 (Arcadia Planitia) appears to be one of the safest sites and has the highest neutron and combined SWIM scores for ice;
• EM-15 (Erebus Montes) is associated with a prominent but less extensive LDA, has well developed polygons, nearby brain terrain and appears smooth;
• PM-7 is adjacent to lineated valley fill (attributed to glacial flow) and appears to be the safest of the Phlegra sites.

We highlighted selected ★ prime and ★ secondary sites on the map:

Candidate sites for SpaceX Starship Mars landings revealed

[on September 2 info & map updated with additional two possible landing sites]

Robert Zimmerman from BehindTheBlack.com has found several images labelled as "Candidate Landing Site for SpaceX Starship [..]" in the latest data release from University of Arizona's HiRISE camera (aboard NASA's Mars Reconnaissance Orbiter). It means that with help from NASA SpaceX is already quietly evaluating the best place where to land first Starships on Mars. Here are direct links to HiRISE image of: Site 1, Site 2, Site 3, Site 4, Site 5 (in Arcadia Planitia) & Site 6 (in Phlegra Montes).

For several years it hasn't been a secret SpaceX is considering four Martian regions for landings: Deuteronilus Mensae, Phlegra Montes, Utopia Planitia and southern Arcadia Planitia. But even in 2017 southern Arcadia Planitia looked "more promising", according to Paul Wooster, Principal Mars Development Engineer at SpaceX. So by now SpaceX may very well be down to evaluating more precise landing sites in that region.

All the candidate landing sites (except #6 in Phlegra Montes) are located on the border between Amazonis Planitia and Arcadia Planitia. According to latest data, Arcadia Planitia is one of the few regions where abundant shallow ice is present at relatively low latitudes. There is strong evidence that this location holds buried ice glaciers. So it has two critical elements looked by SpaceX for its Mars Base Alpha: solar energy and water. Those are critical not only for life support but also for refueling Starships. It's also in low altitude meaning a bit higher air pressure than in higher areas on Mars; that is beneficial for radiation protection and creates more atmospheric drag during the landing.

We made a map of all of the candidate sites: