We've all heard the on-again, off-again theories of another massive object in the vast reaches of the outer solar system. Some potential evidence to support the possibility are its affects on smaller dwarf planet bodies, with their distorted orbits.

I think most propose it to be a very large gas giant, if anything. I have also heard people propose a red dwarf star, though we would have surely seen this with our current telescopes.

What I'd like to know is, if a brown dwarf (something more massive and hotter than most gas giants) were the culprit, could it elude detection by our current means of observing the universe? They are hot objects, many of which produce some amount of light.

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    $\begingroup$ We may not have "surely seen" a dwarf star in the outer solar system. astronomy.stackexchange.com/q/1179/26216 It's likely trickier than we might think. But we are very close. Also, I feel like this is two questions disguised as one. You should publish the second question separately. $\endgroup$
    – BMF
    May 4, 2019 at 11:41
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    $\begingroup$ Well, I meant if it were a red dwarf we'd have surely seen it. Also, I wasn't trying to disguise anything but I'll omit the last part if I made a faux pas. Sorry. $\endgroup$
    – Cereza
    May 4, 2019 at 12:06
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    $\begingroup$ +1 I meant no disrespect by "disguised," I think this is a great question! $\endgroup$
    – BMF
    May 4, 2019 at 12:09
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    $\begingroup$ Obligatory XKCD... which does a surprisingly good job of talking about this, despite being a comic and making fun of the whole process! $\endgroup$
    – Cort Ammon
    May 4, 2019 at 16:15
  • $\begingroup$ @Cereza, I believe you should accept Mark's answer and not mine. Not that either of us really needs the rep ... $\endgroup$
    – o.m.
    May 5, 2019 at 10:51

2 Answers 2


There's no chance of it.

In 2010, the WISE infrared telescope photographed the entire night sky, half of it twice or more. Any brown dwarf within about 10 light-years of the Sun would have been imaged (it found three of them); super-Jupiters within a third of a light-year would have been found, as would Saturn-sized or larger gas giants within a sixth of a light-year.

In short, we can fairly conclusively say that there are no large surprises lurking in the Solar System. Any new planets are likely to be Earth-sized or smaller.


No, unless it is extremely far out.

The outer planets were detected by analyzing perturbations in the orbit of planets further in. Something on the scale of a brown dwarf, several times the mass of Jupiter, should have been detected indirectly by modern astronomy, not remain speculation.

Brown dwarfs radiate in the infrared spectrum and a telescope could be pointed at predicted locations.

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    $\begingroup$ It's not just gravitational effects. The WISE telescope survey has eliminated the possibility of a super-Jupiter less than a third of a light-year out, and a brown dwarf less than about 10 light-years out. $\endgroup$
    – Mark
    May 4, 2019 at 18:28
  • $\begingroup$ I kind of figured this would be the case, especially due to WISE, but I couldn't seem to find a conclusive bit of documentation on just how potent something had to be for WISE to spot it. We've gotten pretty good at spotting "invisible" objects by their secondary effects if nothing more. So it would seem that if I want to put a big object out there, I'd have to work some handwavium to explain away it being hidden, which I'd rather avoid. Dwarf planet it is then! $\endgroup$
    – Cereza
    May 5, 2019 at 1:05
  • $\begingroup$ @Mark, make that an answer and you get my upvote. $\endgroup$
    – o.m.
    May 5, 2019 at 3:59

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