What’s the closest earth like planet or moon to earth we have discovered in our galaxy?

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    $\begingroup$ Earth itself would be the trivial answer. Assuming you are excluding that, what criteria do you want to use for "Earth-like"? $\endgroup$ – user24157 Jan 28 '19 at 8:29
  • $\begingroup$ Up to the person answering to define what they consider to be earth like. $\endgroup$ – Tikkaty Jan 28 '19 at 8:34
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    $\begingroup$ Agreed, this needs clarification. It can be Earth-like radius (easiest to measure), Earth-like mass (much harder) or average temperature (often impossible to determine in detail, as it needs details of the atmosphere) $\endgroup$ – astrosnapper Jan 29 '19 at 0:16
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    $\begingroup$ @Tikkaty "Up to the person answering to define what they consider to be earth like." That's not how Stack Exchange works. The question should be clear about it. It's okay to leave some flexibility in the details, but earth-like is the core concept in your one-sentence question. You can't ask for the answer to define the question. I'm voting to close as unclear what you're asking as well. Why not find an accepted definition for Earth-like, add the definition to your question and include a link. That way if an answer is posted, it will be unambiguous and clear to voters if it's right or wrong. $\endgroup$ – uhoh Jan 30 '19 at 5:50

Well, this really does depend on what is considered an Earth-like planet. For instance, one could conclude that Venus is an Earth-like planet based off of them being similar in mass and also in regards to the similarities in radius. As for Earth-like moon, Titan would be a great candidate if located inside the so-called Goldilocks zone.

Counting planets outside our solar system, the nearest planet I could find was about 4.243 light-years away. Astronomers found it on August 24, 2016. It is a rocky planet in the habitable zone of its parent star Proxima Centauri, the closest star to Earth. The name of the planet is Proxima b, this planet is approximately 1.3 times the mass of Earth and possesses an orbital period of roughly 11.2 Earth days.

However, since Proxima Centauri is classified as a red dwarf this casts reasonable doubts on whether Proxima b is habitable. To be habitable Proxima b would have to deal with low stellar flux, which causes a high probability of tidal locking, and high stellar variation.

List of nearest planets

List of possible habitable moons

  • $\begingroup$ Did you mean 12 light years away or was that a typo. The distance to Proxima Centauri is about 4.2 light years. en.wikipedia.org/wiki/Proxima_Centauri $\endgroup$ – irchans Jan 29 '19 at 18:55
  • $\begingroup$ Your right, don't know what I was thinking. Thank you for letting me know about that!!! $\endgroup$ – Kolby L Jan 29 '19 at 18:56
  • $\begingroup$ One thing to note is that we only know the minimum mass for Proxima b thanks to the mass-inclination degeneracy in the radial velocity method. If the orbit is nearly face-on (geometrically less likely, but not ruled out), it could be significantly more massive than 1.3 Earths and be Neptune-like rather than terrestrial. $\endgroup$ – user24157 Jan 29 '19 at 22:56

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