Two potentially life-friendly planets found orbiting a nearby star • Hacker News Board

Re: Two potentially life-friendly planets found orbiting a nearby star

#371

Post by soulofmischief » Wed, Jun 19, 2019, 1:05 PM UTC

Robotbeat wrote: post #369

xelxebar wrote: post #357

Earlier quoted context omitted.

> If it did, we wouldn’t be able to see stars at night from the Earth. Ha! I love straighforward sanity checks like this. My initial reaction was to ask myself about photon-photon collisions which are im fact possible, but your comment gives a nice Fermi bound on how rare such events actually are. Cool!

Photon-photon collisions are still technically possible... I remember a professor mentioning this as one question he got in grad school... draw out the Feynman diagram and you see a vanishingly small probability of photon-photon interaction. But yeah. Ionized particles like Galactic Cosmic Rays can be repelled by the local stellar magnetic field, but mostly the lower energy rays are deflected. Higher energy -to-charg…

Thank you for understanding my question before reaching for dismissal :)

I knew low-energy waves are partially deflected, I just wasn't sure about high-energy waves. Makes sense!

Re: Two potentially life-friendly planets found orbiting a nearby star

#372

Post by vageli » Wed, Jun 19, 2019, 1:09 PM UTC

EGreg wrote: post #146

metalchianti wrote: post #136

Earlier quoted context omitted.

Yes. How many people do you need in a room to be confident that one of them has the same birthday as you?

Assuming a uniform distribution, the probability is 1/365 for any person#. Those probabilities add up linearly if the people are guaranteed to have different birthdays (union/OR). Otherwise the probability of NOT having someone with the same birthday goes down exponentially as a an exponential power of the fraction 364/365 (intersection of complement/AND NOT) It’s exactly what you would expect from classical combinat…

> Assuming a uniform distribution, the probability is 1/365 for any person#. Those probabilities add up linearly if the people are guaranteed to have different birthdays (union/OR). Otherwise the probability of NOT having someone with the same birthday goes down exponentially as a an exponential power of the fraction 364/365 (intersection of complement/AND NOT)

Why would we assume a uniform distribution of birthdays? For example, birthdays occurring on the 31st of a month are probably less likely to occur on average given that every month does not have 31 days. This is just one example and doesn't even go into seasonality of conception cycles.

Re: Two potentially life-friendly planets found orbiting a nearby star

#373

Post by Robotbeat » Wed, Jun 19, 2019, 1:10 PM UTC

caymanjim wrote: post #190

XorNot wrote: post #107

The note that it's an old star makes me worry though. If they're older then us, and habitable, were they inhabited? Our current era is a few hundred years of real, directed technological development. A few thousands years either side of that and who knows what we'd be looking at, but you imagine that - hopefully - the general progression of technology is forward. So if they were inhabited, what happened to them? Are…

> So if they were inhabited, what happened to them? Are they exactly at our level of development? Earlier? Hopefully. Because later poses some real big questions - does technology top out about where we are now - no FTL travel, no really big radio transmitters or stellar engineering? No probes to nearby star systems? Did they even make it past the nuclear age, or avoid wrecking their climate? You get more than one ch…

I think there’s no technological barrier there, but cultural choice: if there’s no good economic reason to go to space (ie That has a high enough rate of return within a short enough period of time), we may just die out before doing any of that stuff. I think about that every time someone argues human spaceflight is worthless. I don’t think they’re wrong in the short-term, but the societal consequences are the same as if the entire species just decides to stop having children entirely because there’s no good economic reason to do so.

Especially thinking about this near the anniversary of Apollo. What if that was the greatest extent of human travel in space? To me, that’s so sad.

https://m.xkcd.com/893/ “The universe is probably littered with the one-planet graves of cultures which made the sensible economic decision that there's no good reason to go into space--each discovered, studied, and remembered by the ones who made the irrational decision.”

Re: Two potentially life-friendly planets found orbiting a nearby star

#374

Post by bradenb » Wed, Jun 19, 2019, 1:24 PM UTC

lelima wrote: post #360

petercooper wrote: post #20

"just 12 light-years away" I love the "just". I know it's nearby on galactic scales but it's practically about 450,000 Earth years away with current technology :-)

Time for the travelers will go slower, for earth time will be 450k years but for travelers will be less. Can someone explain this situation, what if the travelers reach almost speed light, they will reach on 12 years from earth perspective but for them how long will it take?

I believe the problem is that with current technology it isn't realistic to expect to accelerate continuously to a fraction of light speed where time dilation will be noticeable. We lack the ability to get a large enough amount of fuel off the planet and we obviously can't decelerate to harvest more fuel on the way there because then we lose the benefits of the continuous acceleration.

EDIT: I wonder how feasible it would be to gather a large enough store of fuel from asteroids or comets before even beginning acceleration. You'd likely have to do it both ways which may make it a one-way trip if the destination doesn't have the necessary resources.

The only way I'm aware of that we could power a long-running acceleration is via a nuclear-powered ion drive. But I don't believe the acceleration is great enough to make a dent in approaching the fraction of the speed of light we need for such a journey in a human lifetime.

Please someone correct me if I'm wrong. I'd love to be wrong.

Re: Two potentially life-friendly planets found orbiting a nearby star

#375

Post by zipwitch » Wed, Jun 19, 2019, 1:24 PM UTC

soulofmischief wrote: post #178

akiselev wrote: post #174

Earlier quoted context omitted.

It's not the density of the star but the density of stars. Dense clusters like those found in the center of our galaxy create a lot of secondary effects like bigger stars pulling matter away from smaller stars (creating lots of background radiation and matter floating around) and then stars plow through those interstellar clouds, creating deadly bursts capable of cooking entire planets, stripping away their atmospher…

I'm talking about the local solar density, not an individual star's density. Obviously that has little effect on the habitable zone of a planet. My question was about the ability of a system's star's own radiation to ward off extra-solar radiation and what kind of limitations we are aware of.

It sounds like you're thinking of the heliosphere, which is the bubble in the interstellar medium created by the solar wind. The solar wind, in turn, is created by outflowing plasma from the Sun, and is also responsible for auroras and comet tails. The details of how far from the sun the heliosphere extends are complex, but it encompasses all the known planets.

The heliosphere does provide us with a significant amount of protect from cosmic rays, which aren't actually electromagnetic radiation. Cosmic rays are extremely energetic particles, typically protons, coming in from outside the solar system. The Earth's atmosphere also does a good job stopping cosmic rays, which means their primarily a hazard to spacecraft, both manned an unmanned. (I don't know what effect cosmic rays would ultimately have on Earth if we didn't have the protection of both the heliosphere and our own atmosphere, but I know they have been investigated for links to mass extinctions.) They're a threat to space travel because they cause soft errors in electronics, and DNA and other radiation damage to human beings.

The Sun's magnetic field - aka the interplanetary magnetic field or heliospheric magnetic field - travels with the solar wind and fills the solar system. It is magnetically coupled to solar system bodies like the Earth and Jupiter. As an amateur astronomer, the heliospheric magnetic field doesn't have any significant effects on photons coming into the solar system.

Re: Two potentially life-friendly planets found orbiting a nearby star

#376

Post by CWuestefeld » Wed, Jun 19, 2019, 1:30 PM UTC

losvedir wrote: post #318

CWuestefeld wrote: post #197

Earlier quoted context omitted.

Over in the s-f subreddits, this novel gets so much love. So I feel left out that I - like you few here - really hated it. My big thing was that the science is just wrong . Most fundamentally, it's not a three-body problem, there are (at least) four bodies: the three suns and the planet. And the real world isn't going to follow any theoretical solution to TBP anyway. There is atmospheric drag, microscopic gravitation…

I don't understand your opposition to the name. The three body problem is so named precisely because it's intractable. In physics with two bodies you can perfectly model the evolution of a system, but as soon as you add a third it becomes chaotic and requires numerical simulation to approximate solutions.

I don't understand your opposition to the name. The three body problem is so named

Look at my first objection, that the problem described in the book has (at least) FOUR bodies. Yet the idea that it's a three-body problem is pervasive throughout the book.

Surely that in itself is enough to justify some aggravation.

Re: Two potentially life-friendly planets found orbiting a nearby star

#377

Post by dragonwriter » Wed, Jun 19, 2019, 1:48 PM UTC

lmm wrote: post #30

petercooper wrote: post #20

"just 12 light-years away" I love the "just". I know it's nearby on galactic scales but it's practically about 450,000 Earth years away with current technology :-)

> I know it's nearby on galactic scales but it's practically about 450,000 Earth years away with current technology :-) If we had the political will, the Orion design could get people there in, what, 200 years, and that's with '70s technology.

> If we had the political will, the Orion design could get people there in, what, 200 years, and that's with '70s technology.

No,the version of Orion that is mostly an integration challenge over 1970s tech would take almost 7 times that long to get to Alpha Centauri as a missile (i.e., without turnover to decelerate to relative rest.)

The even more speculative version was estimated to cut that by a factor for ten to only 133 years, but that's still to a target 1/3 the distance of this one, and still without deceleration.

Re: Two potentially life-friendly planets found orbiting a nearby star

#378

Post by LeifCarrotson » Wed, Jun 19, 2019, 2:00 PM UTC

zilian wrote: post #353

LeifCarrotson wrote: post #253

Earlier quoted context omitted.

...why the winky face?

Why not ? Maybe sentient / intelligent life is thriving everywhere but 99.9% of time, climate change or nuclear annihilation happens. Even in "easy mode" with several planets. I find it ironic and somehow poetic.

I believe (like many people) sentient/intelligent life to be intrinsically valuable, and the suffering or extinguishing of that life to be bad.

Our own species suffers and harms itself far too much already. I like to think that we're doing relatively well, solving problems and navigating bad Nash equilibria and local optimizations with social systems and technology to make the world a better place. In as little as the last century, we've made huge strides in solving problems of hunger, illness, education, freedom of expression, and more. Even with the huge efforts needed to escape our heavy planet's gravity well with chemical rockets, and the limited habitability of other planets in our system, we're exploring the possiblity of colonizing other planets.

To imagine that this is a hopeless fight, even at the best of odds - that sentient/intelligent life is not only unable to succeed but is actively continuously exterminating itself across the universe - is a ghastly, horrific, tragic nightmare.

Re: Two potentially life-friendly planets found orbiting a nearby star

#379

Post by soulofmischief » Wed, Jun 19, 2019, 2:20 PM UTC

zipwitch wrote: post #375

soulofmischief wrote: post #178

Earlier quoted context omitted.

I'm talking about the local solar density, not an individual star's density. Obviously that has little effect on the habitable zone of a planet. My question was about the ability of a system's star's own radiation to ward off extra-solar radiation and what kind of limitations we are aware of.

It sounds like you're thinking of the heliosphere , which is the bubble in the interstellar medium created by the solar wind. The solar wind, in turn, is created by outflowing plasma from the Sun, and is also responsible for auroras and comet tails. The details of how far from the sun the heliosphere extends are complex, but it encompasses all the known planets. The heliosphere does provide us with a significant amou…

That is incorrect. Energetic particles are radiation. Radiation isn't just photons.

I don't think you understood my question very well because none of what you presented is new to me nor is it what I asked about. Still, thank you for the time and effort.

Re: Two potentially life-friendly planets found orbiting a nearby star

#380

Post by dwaltrip » Wed, Jun 19, 2019, 2:39 PM UTC

isostatic wrote: post #367

dwaltrip wrote: post #336

Earlier quoted context omitted.

"Very unlikely" is a severe understatement. With only 100k people, the odds of no one else having your birthday is 10^-120. With a million people, it is 10^-1192. And with a billion people... apparently, there are over a million zeroes between the decimal place and the first non-zero number. That is a pretty damn small probability. Here is the code I used in python 3: from decimal import Decimal print((Decimal(364) /…

quite, hence "how confident" There's other things as play. Imagine you, born on July 15th, walked into a room with 1000 people. You'd be fairly confident someone will be born on July 15? What if I then told you it was the annual astrology get together of Capricorns?

Sure, but you did say "even distribution".