Second Most Earth-Like Planet to Date Found

[Centauri5921]

Kepler has recently discovered the exoplanet Kepler-452b, which is, after Kepler-438b, the most Earth-like exoplanet discovered. It orbits its parent star in just 385 days, meaning it's in Kepler-452's habitable zone. It has a mass roughly five times that of Earth, and is thought to have twice our planet's gravity. It's 1,400 lightyears away, meaning that at New Horizons' speed, it would take more than 25 million years to get there ;o

Here's the article http://www.nature.com/news/nasa-spies-ea...ar-1.18048

[stevebowers]

5 Earth masses and two gees? That's not particularly Earth-like. Compared to that, Venus is a much more Earth-like world.

[Cray]

5 Earth masses and two gees? That's not particularly Earth-like. Compared to that, Venus is a much more Earth-like world.

By itself, 2Gs isn't that bad compared to 900F at 90 bars. But if Kepler 452b has gone into a runaway greenhouse...yeah. Less so than Venus.

[radtech497]

By itself, 2Gs isn't that bad compared to 900F at 90 bars. But if Kepler 452b has gone into a runaway greenhouse...yeah. Less so than Venus.

According to this paper, Kepler 452b has a radius 1.63 times that of Earth (10,396.303 km) and a mass between 3.0 and 7.0 times that of Earth (1.792e+25 to 4.182e+25 kg), giving a bulk density between 3807.431 and 8884.005 kg/m^3 (indicating a solid, rocky planet). At the low end of the mass scale, Kepler 452b has a mean surface gravity of 1.128 g, while at the high end, it is 2.633 g.

Kepler 452, the planet's host star, is 1.037 times as massive as Sol, has a radius 1.11 times that of Sol, and has an effective temperature of 5757 Kelvin; this gives a luminosity 1.216 times Sol's.

Kepler 452b orbits Kepler 452 at a semi-major axis of 1.046 AU, with an orbital eccentricity of 0.03, once every 384.843 days. At this distance, the planet receives 11.128% more insolation than does Earth. With an equilibrium temperature of 260.821 Kelvin (assuming an Earth-like albedo of 0.306) and, if an Earth-like amount of atmospheric radiative forcing is assumed, a mean surface temperature of 294.945 Kelvin, then the planet is eminently habitable and has been for most of its six billion year history.

Radtech497

[Cray]

According to this paper, Kepler 452b has a radius 1.63 times that of Earth (10,396.303 km) and a mass between 3.0 and 7.0 times that of Earth (1.792e+25 to 4.182e+25 kg), giving a bulk density between 3807.431 and 8884.005 kg/m^3 (indicating a solid, rocky planet). At the low end of the mass scale, Kepler 452b has a mean surface gravity of 1.128 g, while at the high end, it is 2.633 g.

Kepler 452, the planet's host star, is 1.037 times as massive as Sol, has a radius 1.11 times that of Sol, and has an effective temperature of 5757 Kelvin; this gives a luminosity 1.216 times Sol's.

Kepler 452b orbits Kepler 452 at a semi-major axis of 1.046 AU, with an orbital eccentricity of 0.03, once every 384.843 days. At this distance, the planet receives 11.128% more insolation than does Earth. With an equilibrium temperature of 260.821 Kelvin (assuming an Earth-like albedo of 0.306) and, if an Earth-like amount of atmospheric radiative forcing is assumed, a mean surface temperature of 294.945 Kelvin, then the planet is eminently habitable and has been for most of its six billion year history.

Such...awesome...crunchy...math...

Radtech, some of that mass range gets into the "lots of internal heat and surface vulcanism ranges." What ranges of density and mass give the most Earth-like surface conditions for a 6-billion year old star and planet?

[radtech497]

Such...awesome...crunchy...math...

Radtech, some of that mass range gets into the "lots of internal heat and surface vulcanism ranges." What ranges of density and mass give the most Earth-like surface conditions for a 6-billion year old star and planet?

The most obvious (and flippant) answer is 5515 kg/m^3 and 5.9736e+24 kg, which describes Earth. But I'm pretty sure you are referring to Kepler-452b and not just any planet. From this paper, the lowest mass and density figures give a planet that is 0.77 times as tectonically active as present-day Earth; the high end of the mass range gives a world that is 1.22 times as tectonically active. The crust is noticeably thinner than is Earth's (0.89x to 0.38x). With a mantle mass ranging between 2.025 and 4.725 Earth-masses, the mantle temperatures are very similar (between 2273 and 2323 K at its current age of 6.0 Gyr). So it is likely that surface conditions on Kepler-452b are, geologically at least, fairly similar to those found on Earth throughout the mass range. The constituents of the atmosphere, of course, is largely dependent on volcanic outgassing (most, if not all, of the planet's primary atmosphere of hydrogen and helium will long ago have been lost to space), though the Earth-like insolation implies a nitrogen-dominant atmosphere (if photosynthetic life is present, there may be a significant O2 fraction; if not, CO2 levels may be significant enough to induce a "runaway greenhouse" similar to what happened on Venus). If the planet has been dessicated a`la Venus, then it is likely that the planet is in a "stagnant-lid mode" in which tectonism has ceased and volcanism is restricted to periodic (several million years or more between events) lava flows which resurface significant portions of the surface, rather than discrete eruptions. So it really depends on whether life has emerged on Kepler-452b.

Hope this helps,

Radtech497

[stevebowers]

The lowest density figures would give a waterworld, which could conceivably have an abiotic oxygen atmosphere. Although I wouldn't expect advanced life on a waterworld, it could support an ocean-going colony.

Trouble is, most rocky planets heavier than Earth are likely to be denser, with high gravity and thicker atmospheres. This doesn't rule out life, but it does rule out anything like Earth life.

[radtech497]

The lowest density figure, 3807.431 kg/m^3, is 461.031 kg/m^3 more than the density of Luna (3346.4 kg/m^3), so it is more likely to give a Selenian-type planet than a water world.

Radtech497

[stevebowers]

I don't think that a super-selenian is necessarily the most likely case, since there would probably be some core material present. A more likely case is a planet with an iron core and a smaller radius at the rocky surface covered by a thick hydrosphere and/or atmosphere to fill the planet out to the observed radius.

Alternately it could be a carbon planet; these are dry, so no hydrosphere would be present but with a minimal iron core you could get the same density. So there are lots of possibilities that fill the smallest mass case. Life might be possible on a carbon planet, but it would not not very similar to Earth-life.

[stevebowers]

Here's Andrew le Page, with his usual 'habitability reality check';
http://www.drewexmachina.com/2015/07/24/...pler-452b/

Unfortunately, with a radius of 1.6 RE, Kepler 452b has maybe no more than a 40% chance of being a rocky planet given what we have seen of earlier Kepler finds. It seems a bit more likely that Kepler 452b is a mini-Neptune instead with poor prospects of being habitable in the conventional sense. We will have to wait to get more data for a more definitive determination of the true nature of this newly discovered world.
Despite the outstanding issue of the nature of Kepler 452b, it still has very real prospects of be potentially habitable.

This is actually a much better result than almost every other planet LePage has examined, so we might be starting to see some potential life-bearing worlds here.