A possible super-Earth or Brown Dwarf in our Solar System

[|Glitch|]

A super-Earth in our solar system? Not so fast.

Astronomers quietly submitted a research paper claiming they may have found a large planet on the far fringes of our solar system.

Astronomers working with the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered what they claim could be another large planet on the fringes of our solar system.

Source: Astronomy Magazine

Below is the arXiv free reprint being referenced by the above magazine article. Ironically, they were using ALMA in order to attempt to confirm the exoplanet previously found orbiting Alpha Centauri B when this object was discovered.

Curiously, when we examined a total of 766,925 known solar-system objects for being within 15' around α Cen at the time of observation, we found no source down to the limiting V-magnitude of 26.0.

The brighter the object the more likely it would have been discovered previously. In order to be roughly the same distance as the Alpha Centauri system, 1.34 parsecs away, the object would have to be an M2 star. Which seems very unlikely that it would remain undiscovered until now.

What confuses me is why this object would need to be as large as a "super-Earth" or Brown Dwarf? Could it not also be considerably smaller, say on the order of a Pluto-sized object for example, and be much closer? In order to be the size of a Brown Dwarf it would have to have an orbit of ≈20,000 AU according to the temperature-distance diagram they provided in their paper (referenced below), which seems to be a bit extreme. To be a "super-Earth" the object would need to have an orbit of ≈300 AU. My question is, could not the object be considerably smaller, and therefore much closer - similar to Sedna or Pluto in size and at distance of ≈100 AU?

This is certainly going to feed the Nemesis believers if it is confirmed that this object is as large as they suspect.

Source:
A new submm source within a few arcseconds of α Centauri: ALMA discovers the most distant object of the solar system - arXiv 1512.02652v1

 

[jimgraber]

Indeed, the authors do seem to consider a TNO or ETNO similar to what you describe as a third possibility. However, at some point, as the new object gets dimmer and closer, it is so close that its orbital transverse motion is expected to exceed the observed transverse motion. Thanks for pointing out a very interesting paper.

 

[MTd2]

There was someone claiming that 200 000 objets would just destroy the solar system. I don't think this is the case, if these are grouped in resonant orbits, like many asteroids of the asteroid belt. Not even gravitationally, since if they have a radial distribution, by gauss law (considering 200k a continuous distribuition), they'd cancel the overall effect.

 

[baudrunner]

We permit ourselves to infer the presence of a rather odd planet X type body in the Vega star system with an eccentric orbit estimated to be about 2,200 Sol years, and an asteroid belt there as well, and nobody accuses their discoverers of heresy, but we are still skeptical of inferring a Planet X type body in our own solar system to account for the behavior of Neptune and Uranus, which mystery factor has been a thorn in the side of astronomers for a long time. Yet we continue finding things here that we didn't know were there. I think that in the interest of truth, we would be better off making those observations from Vega.

 

[Ernest S Walton]

The field of view of ALMA is very narrow so the probability of finding a planet-sized body in just that position is extremely low. On the other hand its brightness indicates that it's a significant object. Something's not adding up here.

 

[jimgraber]

Yes, this seems like a very low probability coincidence. And if it is truly, not part of the Alpha Centauri system, then smaller and nearer is more likely. So I'm betting my $.02 ( not more) on a KBO.

 

[|Glitch|]

Apparently there appears to be evidence that another "planet," or at least a large trans-Neptunian object (TNO), with a semi-major axis greater than 150 AU and a mass

10 M_⊕ with between 2 and 4 R_⊕ may exist.

Evidence for a Distant Giant Planet in the Solar System - Published 2016 January 20 • The Astronomical Journal, Volume 151, Number 2. (free article)

 

[ohwilleke]

Probably not the same thing. The Astronomical Journal article by Brown (based upon analysis of the dynamics of KBOs) is supposed to be at about 600 AU distance. The ALMA object is either a dwarf planet at ca. 15-25 AU or is a true planet at 4000+ AU according to one of a couple of preprints on the subject. Neither hypothesis for the ALMA object fits the planet that Brown has nicknamed Planet Nine at 600ish AU.

It would be possible to map out the approximate orbital plane of Brown's Planet Nine from the paper which is described there (I don't have the means to do that easily at hand), and see if the ALMA object is within that plane, but I suspect that it is not.

 

[|Glitch|]

Probably not the same thing. The Astronomical Journal article by Brown (based upon analysis of the dynamics of KBOs) is supposed to be at about 600 AU distance. The ALMA object is either a dwarf planet at ca. 15-25 AU or is a true planet at 4000+ AU according to one of a couple of preprints on the subject. Neither hypothesis for the ALMA object fits the planet that Brown has nicknamed Planet Nine at 600ish AU.

It would be possible to map out the approximate orbital plane of Brown's Planet Nine from the paper which is described there (I don't have the means to do that easily at hand), and see if the ALMA object is within that plane, but I suspect that it is not.

They are definitely not the same object. They know the Right Ascension and Declination of the Liseau et. al. object mentioned in the original post, but not its distance. It may, or may not, be a TNO. However, it does seem likely that the Liseau et. al. object is a TNO considering that it would have to be a previously undiscovered star if it is not in our solar system, which seems highly unlikely. Whereas the location of the Batygin and Brown TNO is unknown, but is certainly a TNO. However, both objects could be more massive with a larger diameter than Earth.

 

[fizzy]

The Batygin & Brown paper is very interesting, though they only consider mass <= 10 Earth masses.

This seems to be on the grounds that this is the minimum for the calculated orbits to stabalise in the known age of the solar system.

I don't see any discussion of larger masses, which would also satisfy this condition. It seems like ten Earth masses is the minimum rather than a best estimation.

 

[tony873004]

If it were much larger, the WISE survey would have detected it.

 

[Dotini]

This article hints that the evidence for Planet X from Brown and Batygin may be statistically weak.

http://www.sciencemag.org/news/2016/01/feature-astronomers-say-neptune-sized-planet-lurks-unseen-solar-system

(DATA) JPL; BATYGIN AND BROWN/CALTECH; (DIAGRAM) A. CUADRA/SCIENCE

 

[mfb]

The ALMA astronomers took their preprint down, by the way: the significance of the second observation is too weak. With just one observation, the nature of the observed object is unclear.