Comments on: Super Earth habitable? https://habitablezone.com/2011/09/01/super-earth-habitable/ Mon, 06 Apr 2026 09:05:36 -0700 hourly 1 http://wordpress.org/?v=3.3.1 By: hank https://habitablezone.com/2011/09/01/super-earth-habitable/#comment-5420 hank Tue, 06 Sep 2011 01:54:00 +0000 http://habitablezone.com/?p=3377#comment-5420 The gravitational acceleration 'A' at a planet's surface depends on its mass and its size, since the mass acts as if it was all concentrated at the very center. The equation is A = KM / R**2 where M is the mass, R the Radius, and K a constant that makes it all come out in the right units. So the earth's gravitational acceleration is Ae = K Me/Re**2, and the planet's gravitational acceleration is Ap = K Mp/Rp**2. If we set Me = 1 (one earth mass), and Re = 1 (one earth radius), the ratio of the gravitational accelerations of the two planets at their respective surfaces is Ap/Ae = ( K Mp/Rp**2) / (K Me/Re**2). We know from the article that Mp = 3.6 Me, so if we substitute, cancel and simplify Ap/Ae = (K 3.6 Me/Rp**2) / (K Me /Re**2) = Ap/Ae = 3.6/Rp**2. So the gravitational acceleration at the surface of the planet is Ap = 3.6Ae/Rp**2, where Rp is in terms of Re. so for the planet to have the same surface gravity as earth, it's radius would have to be almost 1.9 times as large as earth's. Conversely, it the planet were the same size as earth, it's surface gravity would be 3.6 times as large as earth's. We know Ae from measurement to be 9.8 m/s**2. The gravitational acceleration ‘A’ at a planet’s surface depends on its mass and its size, since the mass acts as if it was all concentrated at the very center. The equation is A = KM / R**2 where M is the mass, R the Radius, and K a constant that makes it all come out in the right units.

So the earth’s gravitational acceleration is Ae = K Me/Re**2,
and the planet’s gravitational acceleration is Ap = K Mp/Rp**2.

If we set Me = 1 (one earth mass), and Re = 1 (one earth radius), the ratio of the gravitational accelerations of the two planets at their respective surfaces is Ap/Ae = ( K Mp/Rp**2) / (K Me/Re**2).

We know from the article that Mp = 3.6 Me, so if we substitute, cancel and simplify

Ap/Ae = (K 3.6 Me/Rp**2) / (K Me /Re**2) = Ap/Ae = 3.6/Rp**2.

So the gravitational acceleration at the surface of the planet is

Ap = 3.6Ae/Rp**2, where Rp is in terms of Re.

so for the planet to have the same surface gravity as earth, it’s radius would have to be almost 1.9 times as large as earth’s. Conversely, it the planet were the same size as earth, it’s surface gravity would be 3.6 times as large as earth’s.

We know Ae from measurement to be 9.8 m/s**2.

]]> By: Eri https://habitablezone.com/2011/09/01/super-earth-habitable/#comment-5271 Eri Thu, 01 Sep 2011 19:13:18 +0000 http://habitablezone.com/?p=3377#comment-5271 Thanks for the clear, concise summary of what this planet could be and why. Very interesting. Thanks for the clear, concise summary of what this planet could be and why. Very interesting.

]]> By: hank https://habitablezone.com/2011/09/01/super-earth-habitable/#comment-5267 hank Thu, 01 Sep 2011 13:38:44 +0000 http://habitablezone.com/?p=3377#comment-5267 If its habitable, its only marginally so. The planet is very massive, so unless it has a correspondingly large radius, the gravitational acceleration at the surface is probably crushingly high. (As a rule, planetary accretion models suggest radii do not normally expand to keep up with mass, so massive rocky worlds most likely have crushing surface gravities). The planet also revolves very close to a very small star, so it it probably gravitationally locked to it so the same side always faces the star. Even if it is in the habitable zone, it probably has very weird weather, and horrific wind storms as the atmosphere circulates heat from the sunny side to the shady one. If the atmosphere is too thin, one side will be frozen snow and ice and the other baked, dry and airless. Also, the primary is a red dwarf, prone to flares, so the surface is probably periodic doused by radiation. We've been finding a lot of worlds like this, but not because they are necessarily very common. They just are easier to detect with our technology, so there still may be a lot more hospitable planets out there we just can't see. If its habitable, its only marginally so.
The planet is very massive, so unless it has a correspondingly large radius, the gravitational acceleration at the surface is probably crushingly high. (As a rule, planetary accretion models suggest radii do not normally expand to keep up with mass, so massive rocky worlds most likely have crushing surface gravities).

The planet also revolves very close to a very small star, so it it probably gravitationally locked to it so the same side always faces the star. Even if it is in the habitable zone, it probably has very weird weather, and horrific wind storms as the atmosphere circulates heat from the sunny side to the shady one. If the atmosphere is too thin, one side will be frozen snow and ice and the other baked, dry and airless. Also, the primary is a red dwarf, prone to flares, so the surface is probably periodic doused by radiation.

We’ve been finding a lot of worlds like this, but not because they are necessarily very common. They just are easier to detect with our technology, so there still may be a lot more hospitable planets out there we just can’t see.

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