This post answers what is Mars' gravity at its highest point (Olympus Mons) compared to the Earth's and Mars' standard, it's 0.3736 g (Mars standard is 0.3794 g). This also seems to be the lowest gravity anywhere on Mars. Mercury has a similar surface gravity to that of Mars, and I'm trying to figure out the gravity at Mercury's highest point (which also may be the lowest gravity anywhere on the planet).

Mercury's mass are 3.3011e+23 kg and Mercury's mean radius are 2439.7 km. This results in a surface gravity of 3.7014 m/s² or 0.3774 g. Mercury's highest elevation is 2.78 mi (4.48 km) above what is considered the sea level. So I add these 4.48 km to the mean radius which results in 2444.18 km, thus the gravity would be 3.688 m/s² or 0.3761 g. Since Mercury rotates extremely slowly, I guess any difference in latitudinal gravity is tiny enough so we can neglect it here as well as any equatorial bulge (the highest point is close to the equator). However, there may still be differences in mascons.

Did I make any mistake? Do we know whether any mascons are to be considered? If I'm right, Mars' lowest gravity is lower than Mercury's lowest one, despite Mars' average gravity being higher than that of Mercury.

  • $\begingroup$ "This also seems to be the lowest gravity anywhere on Mars." Are you sure about that? Unlike Mercury, Mars does have a large equatorial bulge (~40 km). If one assumes that diameter decreases linearly from the equator to the pole, it's more than 4 km every 10°. Arsia Mons is lower than Olympus Mons but is also ~10° lower in latitude... Ascraeus Mons could be a candidate as well, might be worth calculating. $\endgroup$ – Jean-Marie Prival Nov 9 '20 at 11:19
  • $\begingroup$ @Jean-MariePrival No, I ain't sure about it. But Olympus Mons still is 21.9 km above the "sea level" of Mars though I dunno whether that's the average radius or the average air pressure level or the triple point of water pressure level (there are multiple ideas on how to define the Martian MSL). Still, if you're right, Mars has a lower minimum gravity than Mercury, despite having a higher average gravity. $\endgroup$ – John Nov 9 '20 at 11:27
  • $\begingroup$ FWIW, Wikipedia has extensive info on the physical characteristics of Mercury. It's quite dense, with a lot of iron, and a relatively large core. So I expect the core gravity to dominate the effects of mascons. OTOH, it may have some very large mascons, eg the remnant of the impactor which created the Caloris Basin. $\endgroup$ – PM 2Ring Nov 9 '20 at 13:49
  • $\begingroup$ I have just asked: What is the highest point on Mercury? $\endgroup$ – Nilay Ghosh Nov 9 '20 at 14:56
  • $\begingroup$ @NilayGhosh "But Mercury doesn't have sea" Really? Whoa, I didn't know this. If I claimed it has sea I'd have written "sea level", not "what is considered the sea level". The highest point of Mercury is 4.48 km above it, because it's a plateau rather than a mountain. The highest mountain from bottom to peak is, as you correctly write, one of the Caloris montes. $\endgroup$ – John Nov 9 '20 at 15:07

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