Nearest potential earthlike planets

I was having a discussion tonight with some friends and we were speculating about extra-solar exploration. The question was, which stars near enough to earth to make travel possible potentially COULD have earth like planets? I realize that this is more pure speculation than a factual question, so if this is in the wrong place (and if the question is actually intersting to get a few posts) then the mods are free to move to the right forum.

Some parameters. Lets assume that humans are able to develop a continuous propulsion system that can, say, achieve max speeds of .5c. Obviously there is going to be acceleration and negative acceleration times, so figure that in to potential destinations. In addition, lets assume that humans come up with a method to suspend life in status for some period of time so that the crew neither ages nor requires food/water, etc…or that nutrients are otherwise fed to the crew.

So, are there any stars close enough to actually get to (with the above assumptions) that MIGHT have earth like planets?


A planet orbiting Alpha Centauri A at approximately our distance-from-the-Sun would be stable, albeit the orbit would likely be somewhat eccentric owing to the presence of B in the system. Since the A. Cent. system is the closest other than the Sun, it’s the closest possible answer. A. Cent A is a “G2” star, very slightly dimmer than the Sun (a “G0”).

The only other star in the 50 closest stars (within 16 light years) that is a “G” star is Tau Ceti, a G8 at 11.8 LY.

Procyon, a F5 star somewhat brighter than the Sun, is 11.38 LY away, but has a white dwarf companion.

Those three constitute the only stars in the approximate H/R range of the Sun within the 50.

There are a number of K stars, significantly redder and dimmer than the Sun. The problem with them is that the annulus in which a habitable planet may be found is so much smaller than the Sun’s that the statistical chance of having a planet within the “life zone” is much much smaller than for F and G stars.

K stars include Alpha Centauri B (a K0, which means that you could theoretically have two planets at the “perfect” distance within the same stellar system), Epsilon Eridani, Epsilon Indi, the two stars in the 61 Cygni system (A and B again), and Groombridge 1618.

Finally, and questionable for other reasons that a good astrophysicist should explain, there is Sirius, a bright A0 star with a white dwarf companion that is only 8.5 LY away.

This is of course not saying that any of these stars do have planets, much less Earthlike planets at the proper distance to be habitable. What it is saying is that they are stars sufficiently like the Sun to be good candidates, and near enough to make finding out worthwhile.

As you know, the smallest exoplanets discovered so far are about the size of neptune so there’s not much to go on yet as to what types of systems would hold earth-like planets. However, the 136 known exoplanets (see link above) do tend to cluster around heavy metal (AKA iron) rich stars. Maybe earth type planets follow the same pattern, in which case there should be a lot of them ‘nearby’.

Wow…thanks guys. I love this board.


Polycarp, I thought the Sun was a G2 as well. At least that’s how most references list it these days. When I first learned about spectral classifications back in the 70s, the sun was thought to be a G0, but sometime since then they reclassified it as G2.

A couple links may be useful. Sol Station is very nice. Click on the link for Stars on the left hand side to get a number of pages on many nearby stars. There’s some discussions on their specific likelyhood of inhabitable planets.

For those who want the most up-to-date list of nearby stars, RECONS is the place to go. Somewhere on that page is a link to a list of the 100 nearest systems known as of July 1. Note that the data there is oriented towards the professional astronomer. For instance, there’s no column for the distance in either lightyears or parsecs. Instead, there’s the parallax and if you want distance, you have to convert it yourself (a trivial operation: divide the parallax into 1 to get parsecs and multiply the parsecs by 3.26 to get lightyears).

You’re no doubt right, then – I gave the Sun’s H/R class based on memory, and when I learned it was back then too.