Exactly- IIRC the problem with martian atmosphere is that its too thick to ignore (hello Mars Climate Orbiter) yet not thick enough for landing havy craft with parashutes or aero surfaces only. See the crazy sky crane system the latest Mars rovers use to work around it.
That they (at least on paper) have a solution for this problem good enough for a 60 metrr craft weighting 100+ tons makes the whole thing even mord remarkable! :)
Fortunately the force of gravity is much lower on both these bodies so I imagine the belly flop becomes less important.
On earth it's also about spreading the heat of reentry over a larger area. Fortunately on Mars (I believe that) the heat of reentry is even less of an issue than here on Earth.
Is that right... at orbital velocity I think Mars entry is a problem.
Are they planning on landing starships on earth? with Orbital refuelling couldn't they just land it like a Falcon 9
(I mean I guess that'd be super inefficient)
Yes, they plan to land "tanker" starships directly back on earth after they have transferred their fuel to another vessel.
They plan to land passenger ballistic re-entry starships which fly without a booster directly to another city on earth in <30 minutes. These are going relatively slowly.
They plan to land orbital starships, which is like landing the dragon capsule. These are going far faster than the falcon booster ever goes. The second stage (on top of the falcon) never lands, it's disposed of every mission. The StarShip (top half) is essentially a reusable second stage.
The Starship mars or moon editions will remain in orbit and never land on Earth again after initial launch. These do not need hardware for an Earth descent and will rely on refuelling. The Moon edition will have no heat-shield tiles (no need for atmospheric entry) and special thrusters half-way up.
You are correct that interplanetry velocities are very high, so yes... a Mars entry at Earth-Mars transfer velocities is likely to be quite ... exciting. I can't remember how exciting though.
The Falcon 9 booster is going relatively slowly, so retro propulsion into the atmosphere (re-entry burn), the grid fins, and the landing burn are sufficient to land it.
Starship is intended to re-enter from orbit, which is a lot faster. Using aero braking requires much less fuel, and avoids the need for a re-entry burn which may not even be feasible.
Of course, they'll have to land some other way on Mars or the Moon.