Earth-sized exoplanet ‘habitable zone’ • Hacker News Board

Re: Earth-sized exoplanet ‘habitable zone’

#11

Post by hcrisp » Wed, Jan 08, 2020, 7:35 PM UTC

saagarjha wrote: post #7

jcims wrote: post #4

> Astronomers have discovered a world only a little bit bigger than Earth, whirling around a bright star about 31 parsecs from our planet. Parsec is one of those units that is difficult to remember if you just look at the conversion (1 parsec = 3.26 light years). If you remember how it's defined, however, it somehow becomes easier (for me anyway). One parsec is the distance at which one astronomical unit (AU, mean di…

I’m not sure if the definition helped.

How about a picture?

https://socratic.org/questions/how-do-you-convert-parsecs-to...

Re: Earth-sized exoplanet ‘habitable zone’

#12

Post by skykooler » Wed, Jan 08, 2020, 7:37 PM UTC

jcims wrote: post #4

> Astronomers have discovered a world only a little bit bigger than Earth, whirling around a bright star about 31 parsecs from our planet. Parsec is one of those units that is difficult to remember if you just look at the conversion (1 parsec = 3.26 light years). If you remember how it's defined, however, it somehow becomes easier (for me anyway). One parsec is the distance at which one astronomical unit (AU, mean di…

Of course, that definition is confusing, because it's an inverse thing - from the name you'd expect something 31 parsecs away to have a parallax of 31 arcseconds, but instead it's 1/31 of an arcsecond.

Re: Earth-sized exoplanet ‘habitable zone’

#13

Post by saagarjha » Wed, Jan 08, 2020, 7:40 PM UTC

hcrisp wrote: post #11

saagarjha wrote: post #7

Earlier quoted context omitted.

I’m not sure if the definition helped.

How about a picture? https://socratic.org/questions/how-do-you-convert-parsecs-to...

I mean, that helps explain the definition. But in practical use I just know to multiply by three to get lightyears and I couldn't really care less about the projection of an arc subtended by a certain angle at a certain distance.

Re: Earth-sized exoplanet ‘habitable zone’

#14

Post by LeifCarrotson » Wed, Jan 08, 2020, 7:43 PM UTC

Pfhreak wrote: post #5

baxtr wrote: post #3

Earlier quoted context omitted.

I imagine that there is a small area where life would be possible?

These types of planets are known as 'Eyeball planets'. [1] They are hypothesized to have a hot side and a cold side, and potentially a ring around the periphery that is 'just right' where liquid water could form and sustain life. Not sure if this particular planet would meet those criteria. [1] https://en.wikipedia.org/wiki/Eyeball_planet

Seems that it be more likely to produce habitable eyeball planets than habitable Earth-like rotating planets - an Earth that was 50 degrees warmer might only be habitable at the poles, while an Earth that was on average 50 degrees colder might be a frozen wasteland all the way the equator - not to mention that seasonal swings in climate for temperate latitudes further decrease your options.

With an eyeball planet the acceptable distance from the star, heat flux, and other variables could produce a ring of acceptable climate even if the average global temperature was +/- 100C relative to Earth.

Re: Earth-sized exoplanet ‘habitable zone’

#15

Post by dmurray » Wed, Jan 08, 2020, 7:43 PM UTC

jcims wrote: post #4

> Astronomers have discovered a world only a little bit bigger than Earth, whirling around a bright star about 31 parsecs from our planet. Parsec is one of those units that is difficult to remember if you just look at the conversion (1 parsec = 3.26 light years). If you remember how it's defined, however, it somehow becomes easier (for me anyway). One parsec is the distance at which one astronomical unit (AU, mean di…

I just remember that a parsec is the same as a light year. By astronomical standards of precision, that's about right.

Re: Earth-sized exoplanet ‘habitable zone’

#16

Post by ppeetteerr » Wed, Jan 08, 2020, 7:45 PM UTC

I've been pondering this for a while: once we have artificial gravity in space (from rotation, for instance), would we ever want to shackle ourselves to the gravity of a foreign planet? It would be so much easier just to create the ideal environment in a large, rotating cylinder instead of having adjust a planet's environment to our needs.

Take this new discovery for instance. Imagine that this planet is 400m years younger than earth. Would it have the necessary composition in its atmosphere to make it breathable? Does it share our gravity? Does it deflect enough stellar radiation?

I doubt we'll find earth 2, but we can recreate a comfortable environment in our own solar system. We just have to let go of the notion that we will colonize another planet for more than just curiosity-sake

To give some idea of what I mean by rotating cylinder, check out the O'Neill Cylinder https://en.wikipedia.org/wiki/O'Neill_cylinder

Re: Earth-sized exoplanet ‘habitable zone’

#17

Post by dcminter » Wed, Jan 08, 2020, 7:45 PM UTC

saagarjha wrote: post #7

jcims wrote: post #4

> Astronomers have discovered a world only a little bit bigger than Earth, whirling around a bright star about 31 parsecs from our planet. Parsec is one of those units that is difficult to remember if you just look at the conversion (1 parsec = 3.26 light years). If you remember how it's defined, however, it somehow becomes easier (for me anyway). One parsec is the distance at which one astronomical unit (AU, mean di…

I’m not sure if the definition helped.

The point of a parsec is that if you're stuck on earth a very long way from the stars and you're trying to work out where they are relative to each other, you can take advantage of the fact that the earth itself moves around the sun. So if you take a photo of a star in summer and then take another photo of it in winter, your vantage point has conveniently moved 2AU because during that time you've moved to the other side of the sun (and 1AU is by definition your distance from the sun).

So then if the star appears to move against the stars so far away that they didn't appear to move, you can do a spot of geometry and work out how much the subject star has moved in "arcseconds".

A star that is exactly far enough away to "move" 2 arcseconds over this 2AU distance (or, if you prefer, one which has "moved" 1 arcsecond when we move 1AU) is one parsec away. By definition.

When discussing relative distances from earth for stars, it's therefore a useful unit (we can't just compare arcseconds because further stars move less against the background, not more).

As with so many puzzling units the key is to find out why they're used. This one was used by astronomers who didn't have a better way to determine how far away stars were.

The wikipedia article, incidentally, is much better than that old Encyclopaedia Britannica article that I read in high school. I envy kids today.

https://en.wikipedia.org/wiki/Parsec

Oh and the actual distance is kind of irrelevant and I don't even try to remember it :)

Re: Earth-sized exoplanet ‘habitable zone’

#18

Post by lxe » Wed, Jan 08, 2020, 7:47 PM UTC

dmurray wrote: post #15

jcims wrote: post #4

> Astronomers have discovered a world only a little bit bigger than Earth, whirling around a bright star about 31 parsecs from our planet. Parsec is one of those units that is difficult to remember if you just look at the conversion (1 parsec = 3.26 light years). If you remember how it's defined, however, it somehow becomes easier (for me anyway). One parsec is the distance at which one astronomical unit (AU, mean di…

I just remember that a parsec is the same as a light year. By astronomical standards of precision, that's about right.

If you're measuring galactic distances (nearest galaxy is 2 million light years away) then that's fair, but for "nearby" objects, a 3x the distance means a lot.

Re: Earth-sized exoplanet ‘habitable zone’

#19

Post by giarc » Wed, Jan 08, 2020, 7:48 PM UTC

pushpop wrote: post #6

CWuestefeld wrote: post #2

According to this [1] it's probably tidally locked, which means that despite being in the goldilocks zone, the environment is likely problematic for life. [1] https://www.sciencealert.com/nasa-found-a-tatooine-like-plan...

People keep saying that for extreme climates on Earth and are then constantly surprised by the variety and abundance of life - admittedly sometimes just microbiology - found in those locations. So I wouldn’t write off a planet just for tidal lock.

Probably best to say "unlikely to contain multicellular life" or maybe even complex life. As we know from here on Earth, microorganisms exist in almost every extreme location on Earth.

Re: Earth-sized exoplanet ‘habitable zone’

#20

Post by Diederich » Wed, Jan 08, 2020, 7:52 PM UTC

jcims wrote: post #4

> Astronomers have discovered a world only a little bit bigger than Earth, whirling around a bright star about 31 parsecs from our planet. Parsec is one of those units that is difficult to remember if you just look at the conversion (1 parsec = 3.26 light years). If you remember how it's defined, however, it somehow becomes easier (for me anyway). One parsec is the distance at which one astronomical unit (AU, mean di…

> 1 parsec = 3.26 light years

I mentally just estimate 1 parsec as equal to π light years.