[Herra Tohtori]

http://www.bbc.co.uk/news/science-environment-16040655


AAAAAAAAAAA

[The E]

Sweet. Gonna book myself some tickets.

[Dragon]

The question is, what is the mass of this planet. I guess that with 2.4 times the diameter of Earth, G on Kepler 22 b has a lot higher value of G.

[MP-Ryan]

Why hello Goldilocks.... how you doin'?

[Nuke]

yay! lets go nuke it!

The question is, what is the mass of this planet. I guess that with 2.4 times the diameter of Earth, G on Kepler 22 b has a lot higher value of G.

depends on its density. if it has a large iron core, forget it. we might be able to land but i dont think were going to be getting out of that gravity well, let alone function well. of course if it has a less dense composition, it could just as easily be close to our gravity. large planet of course means more surface area and better access to resources, so provided gravity is not insane it might be valuable.

[Dragon]

That's why I' concerned about the G value, this planet is 4,5 times as large as Earth. If it's as dense as the Earth, then it's completely uninhabitable (nobody except fighter pilots is exposed to 4.5G too frequently).
I guess it's mass should be measurable somehow, so I'm eagerly awaiting news on that.

[The E]

I guess it's mass should be measurable somehow, so I'm eagerly awaiting news on that.

Nope. I mean, you could estimate it, but that would require knowing what else is floating around in that system, and where it is. And the mass of the sun in that system. And having equipment sensitive enough to detect their orbits. Not really possible with current equipment for a small target like that.

[Nuke]

is it currently possible to do spectroscopy on exoplanets?

[Dragon]

Nope. I mean, you could estimate it, but that would require knowing what else is floating around in that system, and where it is. And the mass of the sun in that system. And having equipment sensitive enough to detect their orbits. Not really possible with current equipment for a small target like that.

Well, with current equipment, maybe. But telescopes are getting bigger and more precise. I hope we'll have a rough idea of it's G in the near future.
Anyway, we should have the technology to know it's mass well before somebody thinks of sending a Sleeper Ship onto it. 
In general, it's an interesting discovery. It could be especially valuable to our search for extraterrestrial life forms. 600LY is relatively close, maybe close enough for detecting possible emissions from them, or for them to detect ours. But we'll see about that in 1200 years, because that's how long we'll wait for any possible answer to our signals.

is it currently possible to do spectroscopy on exoplanets?

It won't do much good here, I don't think you can look inside the planet using it.

[Mongoose]

These things are such cockteases.  I mean, it's awesome that we're finding them, but then you think about the fact that we won't be able to get even a closer look at them, much less go to them, for a very long time.

[Nuke]

is it currently possible to do spectroscopy on exoplanets?

It won't do much good here, I don't think you can look inside the planet using it.

granted it would only be a surface scan. but you could tell if the planet had a thick atmosphere, or a solid surface, or water. it wont give you an accurate picture of the planets density though.

[LordPomposity]

Space thread, paging FlamingCobra.

[Herra Tohtori]

Well.

The only way to determine a planet's mass is to look at the effect it has on the central star. Planet and star both orbit the same centre of gravity, so the heavier the planet, the more the star is displaced from its exact centre.

If the planet is massive enough, and its orbital period short enough, that can give the central star's light a detectable doppler shift variation as the star's radial velocity cyclically changes in conjunction with the planet's orbital period. If - and only if - you have accurate enough spectrometre to detect this shift of spectral lines, then you can determine the mass of the planet (within error bars of course).

If the planet doesn't cause detectable weave in the star's velocity, that gives use a crude upper limit for the planet's mass: Below observation threshold.


The problem here is that the planet is quite far from the star so orbital period is rather long, which reduces the radial velocity changes (and their frequency), and the planet is also likely quite small, which further reduces the amplitude of the velocity change.

I'm afraid we don't have sufficiently accurate means of observation to detect the mass of such a small orbiting body.




Of course, if we simply bruteforce our way through a few generations of telescope sizes, and the planet happens to have a moon of detectable size orbiting it... then it would make determining the mass and therefore surface gravity of the planet much easier and more accurate.



Spectroscopy of the planet itself would be incredibly awesome as it would gives us overall idea of its atmospheric composition, and even possible surface composition if you get lucky.

[The E]

In general, it's an interesting discovery. It could be especially valuable to our search for extraterrestrial life forms. 600LY is relatively close, maybe close enough for detecting possible emissions from them, or for them to detect ours. But we'll see about that in 1200 years, because that's how long we'll wait for any possible answer to our signals.

Wrong. You are suffering from the same misconceptions that the original SETI people suffered from. Let me explain.

When SETI was founded, people thought that we would be pumping out as many radio emmissions or more than we did at the time. Remember, back then, there were lots of very very big radar installations, and TV and radio stations had to broadcast with high energy levels to be receivable.
However, if anything, the amount of RF energy generated by our civilization has dropped off sharply, given that we've laid a lot of cable, and our emmitters and receivers have become smaller, more efficient over time.
There's a corollary to the famous saying "Sufficiently advanced technology is indistinguishable from magic", called "sufficiently advanced technology is indistiniguishable from nature". Meaning that as our technology matures, it will get more eficient, less disturbing, and thus less detectable, especially over distances of several light years. If we take our technological development as an example, there's about a 100 to 200 year window where we put out enough energy to be visible over interstellar distances. Before and after that window, there simply isn't anything you really can detect from space.

This means that the chances of catching a civilization in that developmental stage are astronomically low, and establishing two-way communications is practically impossible.

Oh, and of course that is all predicated on having an alien species that follows the same path of technological discovery we did.

[watsisname]

The surface gravity of a planet is given by g=GM/r².  For Earth, that's (6.67x10^-8erg*cm*g^-2(5.97x10²⁷g)/(6.37x10⁸cm), which gives us 981cm/s². 

We don't know the mass of Kepler 22 b, though we could find out by using the Radial Velocity method.  However, if we assume that the planet is composed of roughly the same materials as Earth, and thus has a similar average mass density ρ as Earth (5.51g/cm³), then its mass is just ρ*4/3*п*(2.4R_E)³ = 8.25x10²⁸g, or about 13.8x more massive than Earth.

Then the surface gravity of Kepler 22 b would be (G*ρ*4/3*п*(2.4R_E)³)/(2.4R_E)².  The (2.4R_E)² downstairs cancels two of the same upstairs, and we get a result of ~2353cm/s², or about 2.4 Earth gravity.  Wait, holy ****, was that a coincidence that it scaled exactly with the planet radius?  Let's see... duh, of course!  Replace M_E with volume times density, and everything but the 2.4 cancels out.  So it turns out the surface gravity of a planet scales exactly with the planet radius, if the average mass density is held constant.  You learn something new every day.

[Herra Tohtori]

Then the surface gravity of Kepler 22 b would be (G*ρ*4/3*п*(2.4R_E)³)/(2.4R_E)².  The (2.4R_E)² downstairs cancels two of the same upstairs, and we get a result of ~2353cm/s², or about 2.4 Earth gravity.  Wait, holy ****, was that a coincidence that it scaled exactly with the planet radius?  Let's see... duh, of course!  Replace M_E with volume times density, and everything but the 2.4 cancels out.  So it turns out the surface gravity of a planet scales exactly with the planet radius, if the average mass density is held constant.  You learn something new every day.

The gravitational effects of a sphere, outside the sphere's surface radius, are identical to that of a singularity positioned at the sphere's centre.

So, yes, if you increase radius by a factor of k, mass increases by a factor of k³, and effect of gravity is inversely proportional to square of radius... you end up with


g₁ = GM / r²

g₂ = G k³M / (kr)² =  G k³M / k² r² =  k³/k² * GM / r²

g₂ = k * g₁

QED.


Of course, if density is not the same as Earth's, we get deviation from this equation. Which is what needs to be determined.



I just have to say, I'm incredibly thankful this thing is not orbiting a gas giant. Would be too close to Pandora for comfort.

I would not be opposed to finding out the planet is inhabited by blue aliens, though. I'd be ok with that.

[LordPomposity]

In general, it's an interesting discovery. It could be especially valuable to our search for extraterrestrial life forms. 600LY is relatively close, maybe close enough for detecting possible emissions from them, or for them to detect ours. But we'll see about that in 1200 years, because that's how long we'll wait for any possible answer to our signals.

Wrong. You are suffering from the same misconceptions that the original SETI people suffered from. Let me explain.

When SETI was founded, people thought that we would be pumping out as many radio emmissions or more than we did at the time. Remember, back then, there were lots of very very big radar installations, and TV and radio stations had to broadcast with high energy levels to be receivable.
However, if anything, the amount of RF energy generated by our civilization has dropped off sharply, given that we've laid a lot of cable, and our emmitters and receivers have become smaller, more efficient over time.
There's a corollary to the famous saying "Sufficiently advanced technology is indistinguishable from magic", called "sufficiently advanced technology is indistiniguishable from nature". Meaning that as our technology matures, it will get more eficient, less disturbing, and thus less detectable, especially over distances of several light years. If we take our technological development as an example, there's about a 100 to 200 year window where we put out enough energy to be visible over interstellar distances. Before and after that window, there simply isn't anything you really can detect from space.

This means that the chances of catching a civilization in that developmental stage are astronomically low, and establishing two-way communications is practically impossible.

Oh, and of course that is all predicated on having an alien species that follows the same path of technological discovery we did.

Correct insofar as the odds of both of us detecting one another's stray emissions are insignificant. However, if they're past the point where they're putting out stray emissions, they could still detect ours in another 600 years--and then they could choose to respond with a powerful radio signal* if they wanted to.

*or relativistic weapon

[Firstdragon34]

Gah! Its 600 Light Years away! But I'm renaming it Alpha Pacifica.

It almost seems that Gliese 581 disappeared from the headlines that system seemed the most promising since it was only 20 light years away. It had four to six planets around a Red Dwarf Star.

[achtung]

981cm

Why?

I'm also proud to say I understand what you did there. Thank you physics course.

[redsniper]

Because **** decimals.