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The list of known rogue planets provided by Wikipedia is fairly short. Some are "candidates"; others "may be" red dwarfs. The two confirmed rogue planets are several times the size of Jupiter.

I understand that rogue planets can only be detected if they glow (which immediately brings the phrase "red dwarf" to mind) or if they cross the path of light emanating from a star. This makes detection extremely difficult.

The reason I ask is I'm not quite certain whether objects the size of Jupiter or smaller can even exist in interstellar space. Maybe dark matter grinds them to dust, or maybe they implode in the absence of any meaningful inertial frame - I don't know. Has anything Earth-sized been detected out there?

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    $\begingroup$ Suggest you edit or remove the penultimate sentence. It harms the quality of the question. $\endgroup$
    – James K
    Commented Nov 2, 2016 at 8:38
  • $\begingroup$ Interstellar space is fairly innocuous and terrestrial planets are mainly just rocks. There's really nothing that would prevent them from existing or anything strong enough to slowly destroy them over time. A rogue Earth-sized planet could potentially go floating through space for billions of years. $\endgroup$
    – zephyr
    Commented Nov 2, 2016 at 13:30
  • $\begingroup$ @zephyr: Theoretically, yes. But we can't say this for sure until we've seen one. $\endgroup$
    – Ricky
    Commented Nov 2, 2016 at 19:09
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    $\begingroup$ (Hypothetically, not theoretically - they're different). And yes, hypothetically a dragon could be flying around swallowing up Earth-sized rogue planets for all we know. But everything we know about space and astronomy indicates there's nothing to prevent it. While we haven't found one yet, the chances they exist are, I believe, extremely high, based on all current empirical evidence. $\endgroup$
    – zephyr
    Commented Nov 2, 2016 at 19:13
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    $\begingroup$ Astronomy is the oldest natural science known to man and to say our current empirical evidence is laughable shows extreme disregard for thousands of years worth of scientific progress. That's not to say we know everything, but I can assure your our current knowledge-base is far from laughable. I would suggest you delve deeper into it before dismissing it and claiming we "know next to nothing" and that it is "laughable". $\endgroup$
    – zephyr
    Commented Nov 2, 2016 at 20:05

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The list on Wikipedia looks current. It doesn't list planets that have only been detected as one-off microlensing events. This can detect Jupiter sized objects (with considerable uncertainty in mass). But observing a microlensing doesn't allow for study, so a microlensing is not considered to be enough evidence for naming or cataloging a known planet. So the short answer is no Earth sized rogue planets are known.

This is entirely due to the difficulty in detection. An Earth sized rogue planet would cool on its surface to a few degrees above absolute zero, and be undetectable with current telescopes. Microlensing events with small rogue planets would also be smaller and harder to detect above noise.

An Earth sized rogue planet has a perfectly good inertial frame, (it is the bound planets that are in a rotating, non-inertial frame), nor does a frame of reference have anything to do with implosions. Dark matter is doesn't grind anything since the main property of Dark matter is that it doesn't interact with regular matter.

In all likelihood, there are billions of rogue planets in the galaxy, and some are smaller, and some are Earth-sized and "rocky". They could have been formed around a star and then ejected.

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To add to the answer from James K, the ESA program "Gaia", amongst many other purposes, intends to capture hints predicting microlensing events. There is much to study in that domain, and the amateur astronomer community can help.

http://www.cosmos.esa.int/web/gaia/IoW_20161027

EDIT : forgot to mention the linked possible microlensing event is bound to happen the two first weeks of November 2016, which makes it quite current.

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