Astronomers find a "giant Earth"

[puskas78]

The planet is very hot, and the gravity must be horrible
http://www.cfa.harvard.edu/news/2014-14
Reddit discussion: http://www.reddit.com/r/science/comment ... lanet_the/
http://www.eurekalert.org/pub_releases/ ... 053014.php
Reddit discussion: http://www.reddit.com/r/science/comment ... lanet_the/
http://phys.org/news/2014-06-astronomer ... earth.html
Reddit discussion: http://www.reddit.com/r/science/comment ... lanet_the/

[Channel72]

Why do they call it "mega-earth"? It's a "mega" solid planet, that's it. Calling it "earth" misleadingly suggests this planet could potentially support life, which Kepler-10c can't.

[puskas78]

(Posted here because I'm not allowed to edit to main post anymore )
If the diameter is 30000 km and the mass is 17 Earth masses, then the surface gravity is about 30.52 m·s−2, (3.1 times the gravity of Earth) and the density is about 7280 kg/m3. This is higher than Earth's density, but I'm not sure what that means. Does it have a large iron core, like Earth, or is it all rock compressed by internal pressure?

[Guardsman Bass]

It's probably rocky with a very large iron core for its size.

Considering the age of the system (11 billion years) and the close orbit, my guess is that it's a former gas giant that spiraled inward and lost most of its atmosphere over time. Although since they seem pretty surprised by that, maybe that's wrong.

[LaCroix]

And again, I'm picturing a astronomy professor, entering the lecture with the words: "Collegues, forget what I told you yesterday, now it's like this..."

This thing is almost the size of Neptune, but solid - really exiting times for them...

[Guardsman Bass]

Reasonably solid. Someone pointed out over at Centauri Dreams that the model they use in the research paper predicts volatiles somewhere between 5-20% of its mass. It's still a giant rock/iron ball, but it probably has a dense, hot hydrogen-helium atmosphere as well even if it's not a full-blown gas giant.

[Borgholio]

Something that big, it would have so much latent heat due to it's size...would it even be possible for stable (solid) crust to form?

[puskas78]

Something that big, it would have so much latent heat due to it's size...would it even be possible for stable (solid) crust to form?

What if the solid crust is very thin and the planet is more like a super-Io than a super-Earth?
http://en.wikipedia.org/wiki/Super-Eart ... c_activity
http://en.wikipedia.org/wiki/Io_%28moon%29#Volcanism

[Guardsman Bass]

I take back what I said earlier, having looked at the Arvix paper. Apparently it's too small and too hot to hold on to either outgassed hydrogen or an accreted hydrogen-helium envelope, so it is indeed a rocky planet with an atmosphere made up of heavy volatiles (aka water) and whatever it outgassed over its planetary history.

[Irbis]

Why do they call it "mega-earth"? It's a "mega" solid planet, that's it. Calling it "earth" misleadingly suggests this planet could potentially support life, which Kepler-10c can't.

Um, and why you believe this to be the case? There is nothing prohibiting life from emerging there, it's not that close to the sun and 3G gravity is less than even some terrestrial organisms might tolerate.

Something that big, it would have so much latent heat due to it's size...would it even be possible for stable (solid) crust to form?

Um, I beg your pardon? Why not?

[Borgholio]

Um, I beg your pardon? Why not?

An object that big is going to be very hot. I was asking the question, "Would it be so hot that a solid crust would be unable to form?" Our own planet was a lava planet for quite a while before it cooled enough to solidify.

[Irbis]

An object that big is going to be very hot. I was asking the question, "Would it be so hot that a solid crust would be unable to form?" Our own planet was a lava planet for quite a while before it cooled enough to solidify.

Very hot objects also cool faster due to greater temperature difference. Then, there is the fact that the system is 11 billion years old, it would need to be really hot at start to not develop solid crust over that long period.

In fact, I'd bet that if that thing was in the solar system, it would be next most habitable planet after Earth. It has water/oxygen atmosphere, and while it might be hot, it's much less so than Venus and I can imagine a few scenarios of building viable habitat.

[Guardsman Bass]

It has a 45 day orbit and an estimated equilibrium temperature without taking the atmosphere into account of 584 degrees Kelvin, or 310 degrees Celsius. There's no way the surface of that thing is habitable for any life that we would recognize, not even extremophiles. If it has an atmosphere (which I suspect it would), it's going to be even hotter than that.

[Irbis]

It has a 45 day orbit and an estimated equilibrium temperature without taking the atmosphere into account of 584 degrees Kelvin, or 310 degrees Celsius. There's no way the surface of that thing is habitable for any life that we would recognize, not even extremophiles. If it has an atmosphere (which I suspect it would), it's going to be even hotter than that.

It does? I saw estimates 150-210 degrees Celsius. Anyway, what if the planet would be tidally locked? Then the dark side could be cool enough for earthlike life given the planet size, though I'd need to run the numbers to be sure.

If it had dense atmosphere, life could potentially survive in the higher, less hot parts. There were plans of making flying habitats on Venus keeping them at earthlike pressure, on this planet we wouldn't have problems with sulphuric acid clouds and the height would alleviate both temperature and gravity problems to some degree.

[ArmorPierce]

45 day orbit? Could it be that due to the proximity to the sun that the sun simply solar winds any gas preventing it from becoming a gas giant?

[Irbis]

45 day orbit? Could it be that due to the proximity to the sun that the sun simply solar winds any gas preventing it from becoming a gas giant?

45 is not that little. There is whole category of planets, Hot Jupiters and puffy planets, that orbit close enough to have orbits measured in days. Like Bellerophon with its 4 day orbit and 1400 degree surface temperature. Of course, most of them are larger and in younger systems, but then again Kepler-10 is relatively inactive star and I don't really see puffy planets having that strong hold on their atmosphere.

[Sky Captain]

Assuming a civilization develops on similar planet that is in the habitable zone would it be possible to achieve spaceflight on planet with 3x more gravity than on Earth? Not only gravity but velocity to establish stable orbit also would be much higher and possibly a thick atmosphere that would make rocket based launch systems really inefficient. A rocket on a 3G world would have to be built much stronger to not collapse under its own weight, would need more powerful and thus heavier engines so the mass ratio would be worse than possible on Earth. Is it possible that civilization on such planet is chained forever to the ground never to reach space and spread out into their star system and beyond?

[Borgholio]

I don't know the actual numbers, but in principle I'd have to say yes. There is a finite amount of thrust you can get from chemical fuels. If the gravity exceeds the amount of thrust, then the rocket is stuck and won't go anywhere. I would think they'd have to use alternate methods to get to space. As an example, with higher gravity comes a thicker atmosphere. Thicker atmosphere means easier to achieve lift with a winged flying machine. So they might be forced to do a variation of the "Launch rocket from the back of a high-flying jump jet" thing.

[Guardsman Bass]

Astronaut Don Pettit touched on that in an essay about the tyranny of the rocket equation:

If the radius of our planet were larger, there could be a point at which an Earth escaping rocket could not be built. Let us assume that building a rocket at 96% propellant (4% rocket), currently the limit for just the Shuttle External Tank, is the practical limit for launch vehicle engineering. Let us also choose hydrogen-oxygen, the most energetic chemical propellant known and currently capable of use in a human rated rocket engine. By plugging these numbers into the rocket equation, we can transform the calculated escape velocity into its equivalent planetary radius. That radius would be about 9680 kilometers (Earth is 6670 km). If our planet was 50% larger in diameter, we would not be able to venture into space, at least using rockets for transport.

I think that's assuming the same Earth-level gravity as well. Factor in the higher gravity and it's even more impossible - you might simply be unable to get off the planet without weird stuff like laser-propulsion launches.

45 day orbit? Could it be that due to the proximity to the sun that the sun simply solar winds any gas preventing it from becoming a gas giant?

The research paper I linked to seemed to think so. They think it was basically too small and too hot to become a gas giant at that distance (it needed to be at least three Earth radii).

[Sky Captain]

Yeah, not only there is more delta V required to get into orbit, but also thrust to weight ratio must be 3 times better to achieve liftoff. According to this calculator a mega Earth would have delta v to low orbit ~20 km/s. No human space vehicle has ever attained that much delta v. A 4 or 5 stage chemical rocket may be able to do it, but 3 G gravity would be a killer. A Saturn V would need not 5 but 15 engines to be able to liftoff with all the increases of dry mass it would bring. If you need 3000 ton rocket to launch a few kg sattellite then I would consider practical spaceflight pretty much impossible.

In theory a nuclear pulse propulsion may allow enough thrust and delta v to go to orbit (energy and power is there), but engineering challenges to build a rocket that can survive thousands of nuclear explosions would be enormous if possible at all.

[Elheru Aran]

In theory a nuclear pulse propulsion may allow enough thrust and delta v to go to orbit (energy and power is there), but engineering challenges to build a rocket that can survive thousands of nuclear explosions would be enormous if possible at all.

Not really. Project Orion was a theoretical possibility as far back as the 60s. For obvious reasons it's almost always been posited as used in space, but if you didn't care about the impact upon the planet, you could certainly use it as a surface-to-orbit booster. The specific mechanics of that would be very different than using it in space, though, and I don't know if that was ever worked out. I suspect the acceleration would be ridiculous and possibly render occupants to chunky salsa...

[agent009]

Thicker atmosphere means easier to achieve lift with a winged flying machine. So they might be forced to do a variation of the "Launch rocket from the back of a high-flying jump jet" thing.

Yes, a denser atmosphere certainly could somewhat offset the effects of gravity. Apart from giving better performance to winged aircraft, atmospheric density also gives you more aerostatic lift which is not affected by gravity (for gases, it is merely a function of molar masses and pressure). So, a hydrogen or helium filled balloon could easily serve as a launching platform for a rocket if average molar mass and pressure of atmospheric air were high enough.

[Sky Captain]

Yes, a denser atmosphere certainly could somewhat offset the effects of gravity. Apart from giving better performance to winged aircraft, atmospheric density also gives you more aerostatic lift which is not affected by gravity (for gases, it is merely a function of molar masses and pressure). So, a hydrogen or helium filled balloon could easily serve as a launching platform for a rocket if average molar mass and pressure of atmospheric air were high enough.

High altitude launching platform would help, depending on atmospheric pressure and density you may be able to cut off few km/s of delta V. However any orbital launcher capable of 20 km/s deltaV and 3 G+ thrust would be very large and heavy. A balloon platform even in atmosphere giving it order of magnitude advantage compared to Earth would still be enormous to lift several thousand ton rocket.

Not really. Project Orion was a theoretical possibility as far back as the 60s. For obvious reasons it's almost always been posited as used in space, but if you didn't care about the impact upon the planet, you could certainly use it as a surface-to-orbit booster. The specific mechanics of that would be very different than using it in space, though, and I don't know if that was ever worked out. I suspect the acceleration would be ridiculous and possibly render occupants to chunky salsa...

Yeah if used in space only you could get away with low acceleration reducing the structural loads. IIRC during the Project Orion feasibility study it was deemed it would be possible to build an Orion rocket capable of enough acceleration and delta V to lift off from Earth, fly to Mars and back as SSTO. But you need only around 1.2 - 1.5 G acceleration to launch from Earth. A mega Earth planet would need ~3.5 G to lift off and sustain that kind of acceleration for first ~10 km/s, after that you probably could reduce thrust to 2G or less and still maintain positive acceleration and climb rate. While nuclear explosions could give you that kind of thrust and delta V engineering the rocket to not break apart from extreme stresses would be much harder than on Earth where only 1.5 G is plenty for liftoff.

[agent009]

High altitude launching platform would help, depending on atmospheric pressure and density you may be able to cut off few km/s of delta V. However any orbital launcher capable of 20 km/s deltaV and 3 G+ thrust would be very large and heavy. A balloon platform even in atmosphere giving it order of magnitude advantage compared to Earth would still be enormous to lift several thousand ton rocket.

This could work pretty well in a denser atmosphere:

http://en.wikipedia.org/wiki/SpaceShaft

[Sky Captain]

High altitude launching platform would help, depending on atmospheric pressure and density you may be able to cut off few km/s of delta V. However any orbital launcher capable of 20 km/s deltaV and 3 G+ thrust would be very large and heavy. A balloon platform even in atmosphere giving it order of magnitude advantage compared to Earth would still be enormous to lift several thousand ton rocket.

This could work pretty well in a denser atmosphere:

http://en.wikipedia.org/wiki/SpaceShaft

Launching from above most of the atmosphere would eliminate looses from drag and engine inefficiency and depending on density of atmosphere may reduce delta v requirements by few km/s. Another advantage of launchpad above the atmosphere if using some sort of radiation spewing nuclear engine is fallout would take long time to reach ground most of the really nasty stuff would decay and there would be little if any increase of background radiation.

The engineering difficulties designing an engine that could push multi thousand ton rocket at 3+ G without exploding would remain though.