"surprise discovery" in the outer Solar System Options

[alan]

http://www.nature.com/news/asteroids-can-h...ngs-too-1.14937

http://www.nature.com/news/dwarf-planet-st...-s-edge-1.14921

ETA

The newfound object's official name is 2012 VP113, but the discovery team calls it VP for short, or just 'Biden' — after US Vice-President Joe Biden.

[Lucas]

I entered the orbital elements into Celestia and rendered the orbits of Eris, Sedna & 2012 VP113. It's hard to display all of them simultaneously because of the different inclinations, but I think this gives a good perspective.

Edit: I added another view with a different orientation (far above the ecliptic plane). In the first one it seems like 2012 VP113 has a larger semimajor axis than Sedna, but that was just due to the perspective.

Attached thumbnail(s)

 

[elakdawalla]

That's a nice diagram, thanks; I will use it! I had forgotten about the Small-body browser -- thanks for the reminder. I made an animated diagram.

[Holder of the Tw...]

But the other options are still in play, I think (passing star... )

There has been precious little mention of how much disruption to the Oort cloud could be caused by another star coming close, but here is one online article from four years ago:
Close encounters of the stellar kind

WISE has eliminated things bigger than Saturn, but there's plenty of room for a Neptune or smaller ...

From the diagrams and previous discussions I've seen, I believe IIRC that the closest a Neptune could be, given the WISE data, is 3000 AU. Could one a little further out than this be a suitable perturber then? Or maybe the Neptune analog itself could be in an elongated orbit that brings it closer in?

[Phil Stooke]

I'm surprised that the trajectories of the Pioneers and Voyagers don't indicate where and how massive a local massive object might be, given how carefully they were monitored to study the 'pioneer anomaly'. Also really surprised that IR surveys don't pick up something as big as is being suggested here. But I'm not an astronomer so I don't really know anything about this stuff. I just thought I did!

Phil

[siravan]

I think Voyagers cannot detect small gravitational anomalies as Pioneers were because they are 3-axis stabilized and frequent spin desaturation complicates things.

[Gerald]

Could one a little further out than this be a suitable perturber then?

This depends much on the composition. A rocky Neptune-sized planet can obtain almost any mass up to a Brown Dwarf (> 13 Jupiter masses). Such a heavy object probably didn't form in the protoplanetary disk of the sun due to lack of enough "metal"; but it might have been captured - although unlikely - after being ejected from the planetary system of a heavy star.
(For water ice it wouldn't need to be much larger than Neptune to be able to obtain almost any mass.)

If it would be composed mainly of hydrogen and helium (more likely in our solar system), a Neptune-sized planet would be of at most 5 Earth masses with a rather restricted effect regarding the vast volume of the outer Oort cloud. The excerted acceleration decreases with the square of the distance, and is proportional to the mass. The Hill radius with respect to the sun would hence be about (1/3x66,000)^(1/3) = 1/100 of the distance to the sun.

Long-term resonances could lead to perturbations over long distances. But with a semi-major axis of 3,000 a.u. we get orbital periods of more than 100,000 years.

(Edit: Fixed Hill radius.)

[nprev]

Gotta say that I much favor the close stellar approach hypothesis on the basis of what we've been able to determine already; it can take literally millions of years for the effects to be noticeable.

At the same time, though, I wouldn't be too surprised if something Mars-mass or above is lurking out there at a few thousand AU. The sheer volume of space we're talking about is SO vast, and it's a bit chilly out there; a gas giant would emit at least some IR above the background, but a solid object might radiate very, very little.

If an object like that exists it might be literally generations before we find it.

[0101Morpheus]

I am also intrigued by how close the new object is to Sedna. But it might just be a coincidence just as much as indicating something. That is the problem when we have only two examples of an object.

[Phil Stooke]

http://sci.esa.int/cluster/43018-beamed-ra...ion-from-earth/

Hmmm... would an Earth-mass object that far out emit radio like our auroras do? OK, so Venus doesn't, presumably. But people are talking now about possible detection of extra-solar planet radio emissions, so something at 5000 AU should be detectable.

I'm just a bit concerned about people saying 'it would be too faint for us to detect' when gravity and radio are added to the arsenal. We're pretty good at detecting things.

Phil

[ngunn]

The upper limit of the perihelion of any putative super-earth would be set by the lowest aphelion distance among the Sedna-class objects, so this new object constrains that more than Sedna does. The perihelion of the perturber cannot be higher than about 400 AU. It's aphelion distance can be anything you want, including infinity.

Of course there could be more than one perturbing body. Favouring the most parsimonious hypothesis is not necessarily a good guiding principle in the outer outer Solar System.

[Holder of the Tw...]

A rocky Neptune-sized planet can obtain almost any mass up to a Brown Dwarf ...

Yes, but with a corresponding increase in both accretion energy and radioactive material picked up. I not sure what the overall effect the rocky composition would have on its heat signature and radius, but I'm sure the first two effects would try to boost its infrared, probably making it detectable further out.

[Gerald]

... would an Earth-mass object that far out emit radio like our auroras do? ... But people are talking now about possible detection of extra-solar planet radio emissions, so something at 5000 AU should be detectable.

Not that straightforward. Earth's aurora is caused a good part by solar wind interacting with the atmosphere after being focussed by Earth's magnetic field.
Outside about 200 a.u. we're in the interstellar medium.

Might be by gravitational lensing detectable by Gaia tiny (tiniest) shifts of stellar positions could provide a hint of where to look closer. But that's really tricky.

@Holder of the Two Leashes: Yes fully agreed, those massive planets should possess enough primordial (adiabatic) compression heat plus radioactive decay heat to be detectable in infrared.

[elakdawalla]

So after talking to Hal Levison, I have to dial back my enthusiasm about planet X, sadly. Still a cool discovery.

[alan]

The the extended data tables and figures in the Nature article (scroll to the end) describes how the arguments of perihelion cluster for the the most distant objects, those with perihelion above 30 AU and semi-major axis above 150 AU. As an illustration (while noting that this solution is not unique) they show how 2012 VP113's argument of perihelion would oscillate within the cluster's range if a 5 Earth mass planet was orbiting at 210 AU.