For my story, I'm trying to figure out where to send a probe that might have a chance at finding an alien civilization similar to ours. What is the closest star system to ours that might have a chance at supporting life?

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    $\begingroup$ This is a risky topic for a short story, because whatever you choose, it may well soon be invalidated by new scientific research. $\endgroup$
    – Mike Scott
    Commented Apr 10, 2017 at 5:42
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    $\begingroup$ @MikeScott Yeah, and aspiring writers should know that nothing burns me up more than reading a story that was invalidated by events that came after it was written! ;-) $\endgroup$
    – Michael
    Commented Apr 10, 2017 at 15:29
  • $\begingroup$ Your question and title don't match up. We may choose to send probes to a (relatively) accessible system we assume is dead for the purpose of other scientific inquiry. $\endgroup$
    – Kys
    Commented Apr 12, 2017 at 16:29

4 Answers 4


Question being answered: "What is the closest star system to ours that might have a chance at supporting life?" the answer is Proxima Centauri

"Proxima Centauri" - https://en.wikipedia.org/wiki/Proxima_Centauri -

In 2016, the European Southern Observatory announced the discovery of Proxima b, a planet orbiting the star at a distance of roughly 0.05 AU (7,500,000 km) with an orbital period of approximately 11.2 Earth days. Its estimated mass is at least 1.3 times that of the Earth. The equilibrium temperature of Proxima b is estimated to be within the range where water could exist as liquid on its surface, thus placing it within the habitable zone of Proxima Centauri, although because Proxima Centauri is a red dwarf and a flare star, whether it could support life is disputed. Previous searches for orbiting companions had ruled out the presence of brown dwarfs and supermassive planets.

The Breakthrough Starshot initiative has plans to send a probe there - http://www.space.com/33844-proxima-b-exoplanet-interstellar-mission.html-

The founders of the Breakthrough Starshot initiative want to send wafer-thin probes to Proxima Centauri at very high speeds. The plan calls for equipping these probes with thin sails, which would capture the energy imparted by a powerful Earth-based laser.

This laser would accelerate the probes to 20 percent the speed of light (about 134.12 million mph, or 215.85 million km/h), according to the program scientists. At that rate, the probes could reach Proxima Centauri in 20 to 25 years.

An updated approach is this "Studying Proxima b: Tiny Sailing Probes Could Orbit Nearby Exoplanet" http://www.space.com/35549-proxima-centauri-mission-solar-sail.html

The original Starshot plan calls for missions to this planet (known as Proxima b), or to any other destination, to be flyby affairs; the nanoprobes would snap photos and collect other data as they hurtle by at breakneck speed. But it doesn't have to be this way, according to the new study, which was led by René Heller of the Max Planck Institute for Solar System Research in Göttingen, Germany.

Heller and co-author Michael Hippke, an IT specialist, performed computer simulations showing that Starshot-like probes could slow down enough at Alpha Centauri to be captured into orbit there. This deceleration would come courtesy of the binary's starlight pressure — which would push back on the nanoprobes' sails, just as outgoing photons would have pushed the spacecraft forward at the beginning of its trek — and the gravitational pull of the Alpha Centauri stars.

This has been proposed well before any of the new knowledge existed by Larry Niven & Jerry Pournelle in "Footfall" https://en.wikipedia.org/wiki/Footfall

Footfall is a 1985 science fiction novel by American writers Larry Niven and Jerry Pournelle. It was nominated for both the Hugo and Locus Awards in 1986, and was a No. 1 New York Times Bestseller. The book depicts the arrival of members of an alien species called the Fithp that have traveled to our solar system from Alpha Centauri in a large spacecraft driven by a Bussard ramjet. Their intent is conquest of the planet Earth.

I have seen more than a few ask about this "Bussard ramjet" well the Book gives a good description on how it works. The Book also uses "Herd mentality" which of course could open a few questions here.

I do not know the legal requirements or etiquette but ... I will inlcude this in case it spurs some creativity

They possess more advanced technology than humans, but have developed none of it on their own. In the distant past on their planet, another species was dominant. This predecessor species badly damaged the environment, rendering themselves and many other species extinct, but left behind their knowledge inscribed on large stone cubes, from which the Fithp have gained their technology. Facing possible extinction due to the long-term effects of biological weapons, a group of high-ranking Fithp were selected to escape to the stars

  • $\begingroup$ The catch is, that close into the star runs the risk of it being sterilized by radiation from it. $\endgroup$ Commented Apr 10, 2017 at 6:03
  • $\begingroup$ @JoeKissling Shrug I concede your point but I object to the "sterilized from it" There is a short series (3 or 4 episodes) where Proxima b class environment is looked at in terms of "Life", as 1 one hour episode. There are apparently numerous ways life could survive such events. The point being until we get there it may not be as impossible as some would think. I am hesitant to link this because of the "climate change reference" but here goes OUR SUN (SOL LOL) "Solar Dynamics Observatory: The 'Variable Sun' Mission" - science.nasa.gov/science-news/science-at-nasa/2010/05feb_sdo $\endgroup$ Commented Apr 10, 2017 at 14:23
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    $\begingroup$ 1+ It should be noted that the OP asks about a civilization like our own. While Proxima Centauri might have life supporting planets, any radio emissions like those produced by humans would have probably reached us by now, since it's "only" ~5 light years away. We should actually be able to watch their TV shows (with a 5 year delay), shouldn't we? :) $\endgroup$
    – r41n
    Commented Apr 10, 2017 at 14:43
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    $\begingroup$ @r41n I'm sure that experts are right about being able to read any signals from other star systems. However, I think it might also be possible that, considering we have never received artificial signals from other star systems before, that there might be something that we have yet to discover that would either prevent signals from reaching us or, perhaps, the signal is in some way obscured using a different or more advanced technology. I'm no expert, just thinking out loud (I realize I need to address this argument in the book). $\endgroup$
    – Brian
    Commented Apr 10, 2017 at 23:56
  • $\begingroup$ @Brian, that's right. Alien civilizations might be much more advanced than we are, or already extinct, for what we know. On the other hand however, and this is what seems most plausible to me, space is unfathomably huge. While there might be thousand civilizations out there, they might just be scattered too far apart. While the nearest star is obviously the first choice for exploration, it doesn't make it the most probable location to actually encounter another civilization. $\endgroup$
    – r41n
    Commented Apr 11, 2017 at 6:28

Your Probes Better Have Good Range

If there were a civilization as advanced as us nearby we would almost certainly know about them. Radar from earth could be picked up at a distance of 15 light years with current SETI technology and up to 250 light years with proposed systems. Other forms of highly directional broadcasts may reach even further than that.

As far as possibly supporting life look no further than the Kepler Mission, its catalog has hundreds of rocky worlds that are the goldilocks zone. These are not sure fire things, but they are the very best bets for life as we understand it.

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    $\begingroup$ Meh. Not really. Don't forget that the original Drake's equations forgot to take into account how fast a civilization would give up uncompressed, single-band data transmission and the difficulties in detecting any civilization using a radically different time scale. $\endgroup$ Commented Apr 10, 2017 at 5:36
  • $\begingroup$ Giving up single band transmission is done so that you can transmit more data... at least the way our species is doing it, more multiband means a noisier, more easy-to-detect civilization, not a harder one. @CharlesMerriam $\endgroup$
    – SRM
    Commented Apr 10, 2017 at 5:47
  • $\begingroup$ @CharlesMerriam All SETI is looking for are radio signals that have some order to them and are not cause by the background of the universe. All that matters is that they are broadcasting. $\endgroup$ Commented Apr 10, 2017 at 6:01
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    $\begingroup$ this assumes there is nothing new to discover in physics that might allow communication from A to B to be performed without it passing through the physical space between. If there is then any advanced civilisation would not be bleeding their communications out into space. $\endgroup$ Commented Apr 10, 2017 at 8:59
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    $\begingroup$ The ubiquitous relavent xkcd: what-if.xkcd.com/47 $\endgroup$
    – Baldrickk
    Commented Apr 10, 2017 at 10:24

For finding intelligent life at our own tech level in another star system: we probably won't, ever. It would be like finding a needle in a haystack made out of more haystacks. And the needles are radioactive and keep decaying into hay. And that's ignoring the time component. Ie a civilization as advanced as our own, existing at the same time as our own has a virtually zero probability of occurring.

For example, if you imagine the history of the universe compressed down to the length of your arm, if you took a nail file to your middle finger, oops, there went all life on earth. If the history of all life on earth were the length of your arm instead, the same nail file would have removed all human history. If instead all of human history were the length of your arm, the nail file would have removed everything since the industrial revolution.

We've been searching the skies for alien radio for 50-odd years now, and not a blip.

Getting a prove to another star system would take as much time as the length of your fingernail in this last comparison. Roughly. I'm not in a position to do a precise calculation at the moment, but it gives you an idea of just the shear scale of the problem.

Realistically we'd send probes out to every system with an earth sized rocky planet in the habitable zone nearer than 100 light years. We MIGHT get lucky and find something. For your story, we do. Problem solved. The thing is, they wouldn't be aimed, they'd be scatter shot. Unless they were von neuman in design (see: We are Legion (We are Bob).)

  • $\begingroup$ Rather than snark the question, fix the question. I've edited it to remove the "solar system" phrasing and so make it technically accurate. Likewise, I'm editing this answer to remove the now-disconnected comments about the "solar system". $\endgroup$
    – SRM
    Commented Apr 10, 2017 at 5:44
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    $\begingroup$ @SRM, I didn't take that first comment to be snarky. It's an accurate comment about the wording used in the OP. It was the first thought I had when I read the title. If the question had been asked on astronomy or space exploration SE it would have had the exact same comment made... in a much less friendly manner. That it was asked here on worldbuilding, friendly readers often answer the intended question behind the often incorrect phrasing. But it's always helpful to know what you have wrong so that it doesn't make it into your story...then you would get an even worse reaction from readers! $\endgroup$ Commented Apr 10, 2017 at 6:15
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    $\begingroup$ "if you imagine the history of the universe compressed down to the length of your arm, if you took a nail file to your middle finger, oops, there went all life on earth" - The universe is 13.8 billion years old and life first appeared on Earth over 4 billion years ago. Maybe you have really short stumpy arms, but unless you want to be chopping off you hand, wrist, and a good portion of your forearm, I think you may want to drop this analogy. $\endgroup$ Commented Apr 10, 2017 at 10:01
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    $\begingroup$ @ScottWhitlock I was posting from a hotel on a tablet at midnight after having gotten up at 7am and driven from Philadelphia to Chicago; I knew my analogy wasn't 100% and didn't have the energy to correct it. Ditto any snark (I was trying to be gently joshing). $\endgroup$ Commented Apr 10, 2017 at 12:07
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    $\begingroup$ And my answer is: remotely anything vaguely in the neighborhood. Don't sort, send a probe to all of them. We have no ability to sort priority beyond "is it in the habitable zone, small, rocky, with an atmosphere." The question is like asking which square millimeter in Africa we should send a drone to first in order to locate an elephant based on the soil pH. $\endgroup$ Commented Apr 10, 2017 at 14:22

I would say your best chance of a nearby life-sustaining planet would be a planet whose life has not explored the communication options presented by radio - it is nearby, but simply hasn't been detected with conventional means.

There are two main candidates that are relatively well-known - Proxima Centauri's planet Proxima b (described in detail by other comments), and the furthest out planet of the newly discovered TRAPPIST-1 system (39 light years away).

The reason that despite being proclaimed as 'having several planets in the habitable zone' only the furthest out is habitable is that the solar wind has the impact of moving the habitable zone further out.

TRAPPIST-1h (the furthest out planet) orbits its parent star every 18.7 days, it orbits at an average of 0.06 AU, its radius is 0.76 times that of earth and its mass is unknown. It is most likely a rocky planet as no traces of hydrogen have been found in its atmosphere.

One of the other pros of the TRAPPIST-1 system is that the other planets are easily visible in the sky ('No Man's Sky proportions') and are only kept from destabilisation by orbital resonance.

Because of this, a physical probe like one in the starshot/starwisp program has a good chance of catching several of them in one photo by simply aiming for the star and expecting to miss slightly.

All that would be needed to confirm life would be a photo showing clear evidence - an artificial structure like a large dam, or (from a photo that can be further away) flora with a clear identifiable colour.

  • $\begingroup$ TBF, we don't know much about the TRAPPIST-1 system's planets yet. Other than "rocky" and "at the distance for liquid water," based on the s star's output energy. Given the orbital distance though, is highly likely that the planets are tidally locked, which would be a death knell for life there. Same issue with the solar wind: probably stripping the planets of their atmosphere. Point is, its really to early to talk about the potential yet. The only photograph we have of the system makes the 1970's photo of Pluto like like HD: barely more than 1 pixel for the star itself. $\endgroup$ Commented Apr 10, 2017 at 12:13
  • $\begingroup$ @Draco18s It may be to early to talk about potential, in terms of "reality", it certainly isn't to early to talk about the "what if" aspect of such a system. Imagine if we could survive there and all those planets would be closer than Mars or Venus .... :) How could that not spur Space Travel by magnitudes? $\endgroup$ Commented Apr 10, 2017 at 14:51
  • $\begingroup$ Also, since we are talking about aliens native to the system, the easy visibility of the other planets would make them more inviting - I think we would have not got far past Low Earth Orbit (LEO) if all we could see was ourselves, the sun, and a few distant coloured dots (planets). The moon was a handy challenge that (I hope) will act as a stepping stone to the rest of the solar system. $\endgroup$
    – Harmless
    Commented Apr 10, 2017 at 19:20

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