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There are many galaxies in the universe. Is there any other Earth-like planet out there?

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  • $\begingroup$ I think, the criteries are these: 1. planet with Earth mass 2. orbiting a star with Sun mass 3. on a near-circular orbit 4. roughly 1AU away. | And now, 7 years later, I think the answer is still no (mostly because extrasolar planets with these parameters are hard to discover). $\endgroup$
    – peterh
    Nov 17, 2020 at 12:22

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YES

Ok, it is easy to say yes but the basic idea is statistics. There are more and more planets discovered outside of our solar system virtually every day. With better instruments, ever smaller planets can be discovered. Besides, it depends on your definition of 'earth-like'. If you restrict this to size, the distance to its star (with respect to the 'habitable zone') and an potential atmosphere (thus ignoring the questions of atmosphere chemistry and life), it is a rather clear yes.

News (all referring to a discovery published December 2011):

A paper:

Further reading:

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  • $\begingroup$ Of course, even if they did get the unique "aminoacid presoup" climate sometime in their history, that doesn't mean the aminoacids combined into anything self-replicable, and no life = no oxygen. $\endgroup$
    – SF.
    Aug 24, 2013 at 19:53
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    $\begingroup$ 'Alien Earth' is among eight new far-off planets $\endgroup$
    – James Jenkins
    Jan 7, 2015 at 15:15
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The answer is strongly defined by how one defines "Earth Like."

The working definition has yet to be established for the scientific purposes that I've seen.

The common minimum: terrestrial, within the liquid water zone, and not more than about 4 Earth masses; a lower bound of about 1/2000th Earth mass (large enough to be self rounding). In which case, there's one about 1 light second away... Luna.

Over a dozen extrasolar worlds fit that very broad definition.

Let us narrow it to worlds which have an atmosphere; this sets the mass to between 2 Earth masses and 1/4 Earth mass. There are several detected in the same range, but all are over Earth mass, and as far as I know, outside the Goldilocks zone. Gliese 581 has 3 candidate worlds (581 c, 581 d, and 581 e) that are within the correct mass and potentially have atmospheres. Kepler-452b is 1.6 earth diameters, and in the ecosphere of it's parent star; its atmosphere isn't yet detected.

If we narrow it further, to free atmospheric oxygen on such a world, only one so far is known, and we are on it. Until the Terrestrial Planet Finder mission (presuming it isn't cancelled before then; as of Jul 2015, it's indefinitely postponed), it's unlikely to be detected, as the current instruments are not optimized for that.

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We are in eternal pursuit of a solution to a vast equation on the likelihood of life elsewhere in the universe. With the extremophiles that we have found here on Earth, it is extremely unlikely that life itself is missing or even rare out there. That presumed, the next question is about intelligence. The factor that seems most important for us is the geological history of Earth with the various extinctions timed such that successor forms of life become dominant. It is certainly possible that at least the dinosaurs could have evolved to significant intelligence and sufficient manipulation capability to make and use tools. The timing of extinction events and the ecosystems of the intervals certainly could determine the overall outcome. With basic intelligence achieved, can intelligence and concomitant technology occur with sufficient speed for the intelligent species to survive a major extinction event and move on to a level detectible across space to us. There are so many ways for intelligence to wipe itself out or to be destroyed by external factors.

Without building truly massive long base line instruments, we may never know except by random chance. That is a very unsatisfying answer, but I fear that it is the only one that we shall ever have. Every day, I awake with the hope that I am wrong.

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It's July 2015. NASA Claims that they have discovered Earth 2.0 , Approx 1400 Light years.

https://en.wikipedia.org/wiki/Kepler-452b

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    $\begingroup$ The data on Keppler-452b is way too little to actually declare it "Earth-Like"... It's the first low-mass (≤2 Earth-masses) in the liquid water zone, but that doesn't mean it has liquid water, and it's a bit far to get good spectroscopy of it separate from its parent star. $\endgroup$
    – aramis
    Jul 24, 2015 at 12:57
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    $\begingroup$ This got to be the 5th or so NASA press release "We discovered a second Earth!" in the past decades. It usually means "We discovered a new exoplanet which appears to be slightly more similar to Earth than the others in one of the many relevant metrics". It usually is accompanied by an "artist impression" 3d render, even though all that is known about the planet are some rough numbers which are often only known with a very, very low precision. $\endgroup$
    – Philipp
    Jul 24, 2015 at 13:50

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