Kepler finds planet in habital zone, temperature 72f!

[Neil]

If you know the mass and know the size you can figure out the density. Saturn is huge but it's density is so low it would float.

If the density is low it's made of gas, if heavier then mostly water, if heavier still rock.

Yes, I am familiar with density. But that doesn't tell you if there's liquid on it currently. I mean - if it's x heavy, it could be anywhere from all rock to a mix of liquid and heavier rock. I wasn't really talking about high-school level chemistry and physics. I was wondering if there's a way we can actually *tell* something useful about the planet's composition from this far away.

Astronomers have done spectral analysis of  the atmospheres of hot jupiters, but I don't think it's yet possible for earth sized planets. It's theoretically possible with better equipment though.

It's not like it's just a matter of better equipment.  What you're talking about is a ridiculously difficult task, not just because of technology, but also because of physics.

There are space telescopes that are planned which will be capable of that.

We'll see.  I have my doubts.  SDI was supposed to work too, but it turns out that it doesn't.

[Ideologue]

For real.  Nucleosynthesis-wise, it's like a planet made out of fluorine, except even dumber, and that's before even getting in to its instability.

I was thinking of the decay.  Even if you started with a whole cloud of plutonium, by the time that the planetary formation process ran through, it would be be mostly decay products.

Yeah, I meant nuclear instability--even plutonium-244 would be mostly gone by now.

[Neil]

For real.  Nucleosynthesis-wise, it's like a planet made out of fluorine, except even dumber, and that's before even getting in to its instability.

I was thinking of the decay.  Even if you started with a whole cloud of plutonium, by the time that the planetary formation process ran through, it would be be mostly decay products.

Yeah, I meant nuclear instability--even plutonium-244 would be mostly gone by now.

Oh.  I thought you were thinking that a planetary mass of plutonium would most certainly be supercritical.

[Ideologue]

I dunno enough about fission reactions to know whether or not that would be the case--I don't think Pu-244 can sustain a nuclear chain reaction--although I expect that we can imagine the planet of 244 being created ex nihilo being staying molten for much longer than a comparable iron-nickel planet like Earth.  (Though maybe not, since Earth's heating was generated by a uniformly distributed body suddenly experiencing massive frictional heating through the fall of iron and nickel into the core.  An entirely plutonium globe might not differentiate like that.)

Now I keep using Pu-244, but that's because non-244 plutonium wouldn't last long enough to condense, let alone blow up.

It does make me wonder, though, that the Earth must have been significantly more radioactive in the past than at present.

[Neil]

I dunno enough about fission reactions to know whether or not that would be the case--I don't think Pu-244 can sustain a nuclear chain reaction--although I expect that we can imagine the planet of 244 being created ex nihilo being staying molten for much longer than a comparable iron-nickel planet like Earth.  (Though maybe not, since Earth's heating was generated by a uniformly distributed body suddenly experiencing massive frictional heating through the fall of iron and nickel into the core.  An entirely plutonium globe might not differentiate like that.)

Now I keep using Pu-244, but that's because non-244 plutonium wouldn't last long enough to condense, let alone blow up.

It does make me wonder, though, that the Earth must have been significantly more radioactive in the past than at present.

Radioactivity to be sure, but even more important is the heat.

[The Brain]

It does make me wonder, though, that the Earth must have been significantly more radioactive in the past than at present.

We used to have natural nuclear reactors.

[Ideologue]

It does make me wonder, though, that the Earth must have been significantly more radioactive in the past than at present.

We used to have natural nuclear reactors.

I read about the one in Africa.  It was pretty cool.