Space Is Full of Planets, and Most of Them Don't Even Have Stars • Hacker News Board

Re: Space Is Full of Planets, and Most of Them Don't Even Have Stars

#71

Post by richmarr » Wed, May 30, 2018, 8:00 AM UTC

zaarn wrote: post #57

lev99 wrote: post #32

Earlier quoted context omitted.

The article states that planets may outnumber stars 100,000 to 1. The Milky Way has 4E^11 stars. It has an upper estimate of 4E^16 planets. It has a lowest estimate diameter of 100kly. It has an estimated thickness of 2kly. It's lower estimate volume is 63,000 kly^2. ----------------------------- If planets are uniformly disrupted (they surely aren't), there are ~17 planets in every cubic light year. Sure, that's a h…

People tend to forget how big a cubic light year is. The earth itself is only 0.02 light seconds in diameter, yielding a cube of 8000 cubic lightmilliseconds. Compared to the 2.9 10^31 cubic light milliseconds in a cubic lightyear... It's a rounding error inside a rounding error. For light seconds, you're looking at 2.9 10^22 (if my math isn't wrong). That's the amount of cubes fitting between earth and moon to fill…

Just to bring the inevitable pedantry, you'd want to consider the cross-sectional surface area rather than the volume, and hitting the gravity well of a planet may turn out to be indirectly fatal too.

So while I agree it's still probably very small numbers I think you may be overcooking it.

Re: Space Is Full of Planets, and Most of Them Don't Even Have Stars

#72

Post by kamaal » Wed, May 30, 2018, 8:03 AM UTC

zaarn wrote: post #68

kamaal wrote: post #65

Earlier quoted context omitted.

If something doesn't shine already. The only way to detect its existence is to send radio waves and see if something bounces off(Like Radar). I guess the point people are trying to make here. If you can't see light coming off an object, then while traveling at interstellar speeds means it will be harder to spot objects until they get too close.

Not all black objects reflect radar, black holes don't reflect at all. I think if you were to encounter a black hole, esp an inactive one, in interstellar space, you'd probably just get sucked in if you didn't notice the black disk...

I thought black holes typically have accretion disk.

Re: Space Is Full of Planets, and Most of Them Don't Even Have Stars

#73

Post by zaarn » Wed, May 30, 2018, 8:14 AM UTC

kamaal wrote: post #72

zaarn wrote: post #68

Earlier quoted context omitted.

Not all black objects reflect radar, black holes don't reflect at all. I think if you were to encounter a black hole, esp an inactive one, in interstellar space, you'd probably just get sucked in if you didn't notice the black disk...

I thought black holes typically have accretion disk.

Only when active and sucking in matter.

If a black hole has been travelling without eating for long enough the accretion disk can disappear. If a black hole is large enough it won't form an accretion disk either as it swallows stars whole.

Re: Space Is Full of Planets, and Most of Them Don't Even Have Stars

#74

Post by akvadrako » Wed, May 30, 2018, 8:17 AM UTC

Fricken wrote: post #55

akvadrako wrote: post #54

Earlier quoted context omitted.

The author is not credible - he posts almost every day and he doesn't understand half of it. It's just fluff.

Ethan Siegel is trained as a theoretical astrophysicist.

And unable to make it as a scientist, he turns to journalism, where he can spout any bullshit without having to back it up with facts.

Re: Space Is Full of Planets, and Most of Them Don't Even Have Stars

#75

Post by hyperpallium » Wed, May 30, 2018, 8:25 AM UTC

perl4ever wrote: post #19

Based on the inverse correlation between star size and frequency, this doesn't surprise me at all. It seems like there is an obvious further inference to make - people have debated whether life originated on earth or not. Given that the vast majority of planets do not have a star, and given that we know there are chemotrophs even on Earth that prove it is possible to live without a sun, it seems overwhelmingly likely…

If you're a fan of Moore's Law and the Singularity, you'll love the reasoning of backtrapolating the exponentially increasing complexity of life over time... to get 0 well before the formation of the earth https://www.technologyreview.com/s/513781/moores-law-and-the...

Re: Space Is Full of Planets, and Most of Them Don't Even Have Stars

#76

Post by arethuza » Wed, May 30, 2018, 8:30 AM UTC

toong wrote: post #28

havemylife wrote: post #23

Earlier quoted context omitted.

I'm not discounting the possibility of life on Earth originating from somewhere other than Earth. However, why would the early conditions of Earth not be sufficient for life to begin over say any other object in space with the base elements for life? How life began is obviously still an unanswered question, but if the conditions for self replicating molecules were sufficient early on for Earth, I'm not sure why billi…

Earth needed ~ 2 billion years for life to start. Frequent solar winds - especially in the first few billion turbulent years of the universe - basically sterilize planets and the whole 2-billion-year counter gets reset to 0. Planets that exist without a solar system, but do retain sufficient heat, might have been out of solar winds harm ?

Life appears to have started on Earth remarkably soon after the creation of the planet and the subsequent formation of oceans - ~130 million years by some estimates:

https://en.wikipedia.org/wiki/Abiogenesis#Earliest_biologica...

Re: Space Is Full of Planets, and Most of Them Don't Even Have Stars

#77

Post by quietbritishjim » Wed, May 30, 2018, 8:35 AM UTC

perl4ever wrote: post #19

Based on the inverse correlation between star size and frequency, this doesn't surprise me at all. It seems like there is an obvious further inference to make - people have debated whether life originated on earth or not. Given that the vast majority of planets do not have a star, and given that we know there are chemotrophs even on Earth that prove it is possible to live without a sun, it seems overwhelmingly likely…

> life appeared so soon after the Earth became solid

It took hundreds of millions of years, possibly up to a billion years, for basic life to form on Earth. I would say that is not "soon"; it's a really long time.

The obvious response to that is, yes it seems like a long time, but it's not much on geological time scales. But it feels to me that there's an implicit circular argument here: the whole reason that geological time is measured in terms of such huge spans is because it took life such a vast amount of time to get to the point where humans exist to discuss it (understandably).

Re: Space Is Full of Planets, and Most of Them Don't Even Have Stars

#78

Post by hvidgaard » Wed, May 30, 2018, 8:38 AM UTC

zaarn wrote: post #73

kamaal wrote: post #72

Earlier quoted context omitted.

I thought black holes typically have accretion disk.

Only when active and sucking in matter. If a black hole has been travelling without eating for long enough the accretion disk can disappear. If a black hole is large enough it won't form an accretion disk either as it swallows stars whole.

That is actually scary. When you travel in interstellar space, you can only travel in directions where you can see light at all times.

Re: Space Is Full of Planets, and Most of Them Don't Even Have Stars

#79

Post by sundvor » Wed, May 30, 2018, 8:43 AM UTC

brazzy wrote: post #56

itronitron wrote: post #26

Interstellar travel now seems a lot more hazardous than it did before. To quote one of my TAs in college, "it's the stuff you can't see that gets you" ...

Quite the opposite, actually. At near lightspeed, a pea-sized rock will kill your spaceship just as dead as a planet. So you actually want your interstellar masses to be as concentrated as possible.

That's assuming we haven't figured out effective shielding by the time we have those near light speed engines.

Re: Space Is Full of Planets, and Most of Them Don't Even Have Stars

#80

Post by leonroy » Wed, May 30, 2018, 9:00 AM UTC

hvidgaard wrote: post #78

zaarn wrote: post #73

Earlier quoted context omitted.

Only when active and sucking in matter. If a black hole has been travelling without eating for long enough the accretion disk can disappear. If a black hole is large enough it won't form an accretion disk either as it swallows stars whole.

That is actually scary. When you travel in interstellar space, you can only travel in directions where you can see light at all times.

Which actually becomes a problem in the far future when stars have moved further away from each other in an ever expanding universe and their light output becomes increasingly dim to a space faring traveller...