A Habitable Exoplanet - for real this time • Hacker News Board

Re: A Habitable Exoplanet - for real this time

#11

Post by ugh » Thu, Sep 30, 2010, 12:48 AM UTC

aaronbrethorst wrote: post #3

hugh3 wrote: post #2

Borderline habitable, anyway. Rocky planet, two Earth masses, looks promising, but so close to its (small, dim) star that it's probably tidally locked, meaning the same side will always point towards its sun. This means that the vast majority of its surface will either be too hot or too cold for life. But a certain ring will have constant perfect weather!

FTA: "That means the planet has...a band of eternal sunrise or sunset where water — and perhaps life — could subsist comfortably."

That would be awesome as premise for a science fiction short story or novel!

Re: A Habitable Exoplanet - for real this time

#12

Post by phreeza » Thu, Sep 30, 2010, 1:08 AM UTC

Link to the actual paper: http://arxiv.org/abs/1009.5733

Re: A Habitable Exoplanet - for real this time

#13

Post by grackle » Thu, Sep 30, 2010, 1:21 AM UTC

patio11 wrote: post #6

anigbrowl wrote: post #4

20 lightyears is a long way, but not that long. What we're 'seeing' via our instruments was taking place around 1990.

So if we had pointed Voyager at it back in the 1970s, we would only have 19.997 lightyears left to travel! Space is big. We are slow. Everything cool about scifi is fiction. None of this will change in our lifetimes.

I would argue that this falls into the "cool" part of what, until now, has been entirely scifi - and that I'm absolutely ridiculously excited about seeing more and more of these discoveries in the years to come.

No, there's no hope of ever visiting this place in our respective lifetimes (sans cryogenics), but I'd put money on the prediction that we will certainly see real imagery of exoplanets within 50 years. And that's cool. Really cool. So cool that we'll look back and laugh at the original question of "are all exoplanets bigger than Jupiter and closer to their suns than Mercury?"

Re: A Habitable Exoplanet - for real this time

#14

Post by imp » Thu, Sep 30, 2010, 1:48 AM UTC

tocomment wrote: post #8

kqr2 wrote: post #7

Earlier quoted context omitted.

According to http://news.yahoo.com/s/afp/20100929/sc_afp/usastronomyplane... , surface gravity might only be slightly higher than earth's.

How is that possible?

It's more massive, but the radius is bigger as well. It could be as low as 1.5 Gs. Modifying the gravitational formula (http://en.wikipedia.org/wiki/Earths_gravity), it's m/r^2, so 3/(1.4^2) = 1.53 Gs. That's neglecting any local variations.

Re: A Habitable Exoplanet - for real this time

#15

Post by hugh3 » Thu, Sep 30, 2010, 1:49 AM UTC

cryptoz wrote: post #10

tocomment wrote: post #8

Earlier quoted context omitted.

How is that possible?

Density of a planet's interior is not uniform, and gravity tapers exponentially with distance. So, a planet with a dense core and a less-dense middle area could easily have less gravitational force than you might expect since the surface is so far away from the dense core.

Surprisingly not so.

If you have a body with a spherically symmetric mass distribution, from the outside it always has exactly the same gravitational field as a point mass at the centre.

Proof: http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/sphshel...

Re: A Habitable Exoplanet - for real this time

#16

Post by cma » Thu, Sep 30, 2010, 3:33 AM UTC

patio11 wrote: post #6

anigbrowl wrote: post #4

20 lightyears is a long way, but not that long. What we're 'seeing' via our instruments was taking place around 1990.

So if we had pointed Voyager at it back in the 1970s, we would only have 19.997 lightyears left to travel! Space is big. We are slow. Everything cool about scifi is fiction. None of this will change in our lifetimes.

With an Orion-type ship we could make it to this thing in a decade (from the time-perspective of the travellers).

Re: A Habitable Exoplanet - for real this time

#17

Post by eru » Thu, Sep 30, 2010, 4:05 AM UTC

cryptoz wrote: post #10

tocomment wrote: post #8

Earlier quoted context omitted.

How is that possible?

Density of a planet's interior is not uniform, and gravity tapers exponentially with distance. So, a planet with a dense core and a less-dense middle area could easily have less gravitational force than you might expect since the surface is so far away from the dense core.

> and gravity tapers exponentially with distance.

Inverse square law.

Re: A Habitable Exoplanet - for real this time

#18

Post by anigbrowl » Thu, Sep 30, 2010, 7:32 AM UTC

patio11 wrote: post #6

anigbrowl wrote: post #4

20 lightyears is a long way, but not that long. What we're 'seeing' via our instruments was taking place around 1990.

So if we had pointed Voyager at it back in the 1970s, we would only have 19.997 lightyears left to travel! Space is big. We are slow. Everything cool about scifi is fiction. None of this will change in our lifetimes.

I was thinking more of spectroscopic interferometry. We probably can't make laser strong enough now, but a 40 year round trip for a light probe to start feeding data is enough for one person to consider making it a lifetime endeavour.

Re: A Habitable Exoplanet - for real this time

#19

Post by cryptoz » Thu, Sep 30, 2010, 12:49 PM UTC

hugh3 wrote: post #15

cryptoz wrote: post #10

Earlier quoted context omitted.

Density of a planet's interior is not uniform, and gravity tapers exponentially with distance. So, a planet with a dense core and a less-dense middle area could easily have less gravitational force than you might expect since the surface is so far away from the dense core.

Surprisingly not so. If you have a body with a spherically symmetric mass distribution, from the outside it always has exactly the same gravitational field as a point mass at the centre. Proof: http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/sphshel...

Wait, but didn't I specifically say I was referring to a body without a spherically symmetric mass distribution? Maybe I'm incorrect in my understanding of symmetric, but I was definitely referring to a non-symmetric case in my text.

Re: A Habitable Exoplanet - for real this time

#20

Post by hugh3 » Thu, Sep 30, 2010, 3:01 PM UTC

cryptoz wrote: post #19

hugh3 wrote: post #15

Earlier quoted context omitted.

Surprisingly not so. If you have a body with a spherically symmetric mass distribution, from the outside it always has exactly the same gravitational field as a point mass at the centre. Proof: http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/sphshel...

Wait, but didn't I specifically say I was referring to a body without a spherically symmetric mass distribution? Maybe I'm incorrect in my understanding of symmetric, but I was definitely referring to a non-symmetric case in my text.

Spherically symmetric means that it looks the same no matter which way you rotate it. You talked about a dense core, less dense middle-region planet, which is spherically symmetric.

If the planet had an ultra-dense region off to one side then it wouldn't be spherically symmetric and it would have gravity slightly stronger on one side than on the other... it's hard to imagine such a planet existing though.