A Dwarf Planet Beyond Sedna (and Its Implications)

by Paul Gilster on March 26, 2014

Most Centauri Dreams readers are hardly going to be surprised by the idea that a large number of objects exist well outside the orbit of Pluto and, indeed, outside the Kuiper Belt itself. The search for unknown planets or even a brown dwarf that might perturb cometary orbits in the Oort Cloud has occupied us for some time, with the latest analysis of WISE findings showing that nothing larger than Jupiter exists out to a distance of 26,000 AU. Objects of Saturn size or larger are ruled out within 10,000 AU, according to the work of Kevin Luhman (Penn State) and team, whose study probed deeply into the Wide-field Infrared Survey Explorer’s results. For more on all this, see WISE: New Stars and Brown Dwarfs.

But the evidence for objects big enough to perturb the local neighborhood does persist, even if we have to scale down our expectations as to its size. A new paper in Nature reports the discovery of 2012 VP113, a dwarf planet that joins Sedna in orbiting entirely beyond the Kuiper Belt’s outer edge, which is normally defined at 50 AU. The object at perihelion does not approach closer than 80 AU, making it more distant than Sedna itself. The work of Scott Sheppard and Chadwick Trujillo (Carnegie Institution for Science, Washington), the paper goes on to suggest a larger inner Oort Cloud population and the possibility of perturbed orbits there. Are the orbits of objects like 2012 VP113 and Sedna telling us something about larger bodies in this region?

The researchers used the NOAO 4-meter telescope in Chile in conjunction with the Dark Energy Camera (DECam), a high-performance, wide-field CCD imager, a combination that offers a wide field of view in the search for faint objects in large areas of sky. They also used the Magellan 6.5-meter instrument at Las Campanas Observatory to help determine the orbit of the newfound object. As with Sedna, we find that the orbit of 2012 VP113 takes it well outside the Kuiper Belt. In fact, given that their orbits extend at aphelion out to hundreds of AU, it is only the fact that both are currently near their closest approach to the Sun that has made them detectable.

Kuiper_oort

Image: Artist’s rendering of the Oort cloud and the Kuiper belt. Credit: NASA.

Sedna, it appears, is not unique, and we can continue to infer from this the existence of the so-called inner Oort Cloud, extending out to about 1500 AU, where numerous objects with sizes larger than 1000 kilometers may exist. Sheppard and Trujillo, basing their estimate on the amount of sky searched, believe that 900 objects in this category may be found there, with a total inner Oort Cloud population probably larger than both the Kuiper Belt and the main asteroid belt.

The problem of distance is such that most would not be visible with current technology. However, says Sheppard, “Some of these inner Oort cloud objects could rival the size of Mars or even Earth. The search for these distant… objects beyond Sedna and 2012 VP113 should continue, as they could tell us a lot about how our solar system formed and evolved.”

2012 VP113’s orbit brings it to as close as 80 AU, outside Sedna’s perihelion. Interestingly, this finding indicates at least the possibility of a much larger planet, perhaps ten times the size of the Earth, orbiting in the inner Oort and influencing the orbits of both Sedna and the newfound object. The possibility remains that a ‘super-Earth’ or somewhat larger object at hundreds of AU, and thus well within the inner Oort, could be influencing the orbital configurations of objects like 2012 VP113 and Sedna. And based on Kevin Luhman’s WISE data studies, the existence of such a planet would not be inconsistent with what WISE is capable of telling us. If this unseen world is just several Earth masses in size, it’s going to be tricky to find, although locating more small objects being gravitationally influenced by it could eventually help us pin its orbit down.

Sheppard

Image: This is an orbit diagram for the outer solar system. The Sun and Terrestrial planets are at the center. The orbits of the four giant planets, Jupiter, Saturn, Uranus and Neptune, are shown by purple solid circles. The Kuiper Belt, including Pluto, is shown by the dotted light blue region just beyond the giant planets. Sedna’s orbit is shown in orange while 2012 VP113′s orbit is shown in red. Both objects are currently near their closest approach to the Sun (perihelion). They would be too faint to detect when in the outer parts of their orbits. Notice that both orbits have similar perihelion locations on the sky and both are far away from the giant planet and Kuiper Belt regions. Credit: Scott Sheppard / Carnegie Institution for Science.

Meanwhile, the inner edge of the Oort Cloud seems to be fairly well defined. From the paper:

Although our survey was sensitive to objects from 50 AU to beyond 300 AU, no objects were found with perihelion distances between 50 AU and 75 AU, where objects are brightest and easiest to detect. This was true for the original survey that found Sedna and the deeper follow-up survey… If the inner Oort cloud objects had a minimum perihelion of 50 AU and followed a size distribution like that of the large end of all known small-body reservoir distributions…, there would be only a 1% chance of finding 2012 VP113 and Sedna with perihelion greater than 75 AU and no objects with perihelion less than 75 AU. Therefore, we conclude that there are few (although probably not zero) inner Oort cloud objects in the 50-75 AU region. Some stellar encounter models that include the capture of extrasolar material predict a strong inner edge to the perihelion distribution of objects, which is consistent with our observations.

A few words about this: Sheppard and Trujillo distinguish between the inner Oort out to 1500 AU and an outer Oort Cloud, assuming that beyond 1500 AU objects are more subject to interstellar influences. One theory of inner Oort Cloud object formation is that Sedna and its ilk are captured extrasolar planetesimals lost in encounters with stars in the Sun’s birth cluster. Primordial close encounters with other stars may be implicated, but only further discovery of other inner Oort Cloud objects will provide the information needed to make this call about our system’s evolution.

The paper is Sheppard and Trujillo, “A Sedna-like body with a perihelion of 80 astronomical units,” Nature 507 (27 March, 2014), 471-474..

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{ 21 comments… read them below or add one }

Leon March 26, 2014 at 15:32

So does that mean that if a planet Mars size or larger is found in these outer reaches of the solar system, we will again have 9 planets in our solar system?

JoeP March 26, 2014 at 16:16

Most of these objects, even if they were as massive as Earth, probably have not “not cleared the neighborhood” around their orbits, so would be classified as dwarf planets according to the current criteria. (“Dwarf” isn’t such a good name then and a bad term to use if such large objects are found.)

But how interesting if such large objects exist!!

ljk March 26, 2014 at 17:08

To quote from the main article:

The problem of distance is such that most would not be visible with current technology. However, says Sheppard, “Some of these inner Oort cloud objects could rival the size of Mars or even Earth. The search for these distant… objects beyond Sedna and 2012 VP113 should continue, as they could tell us a lot about how our solar system formed and evolved.”

If astronomers do detect Oort Cloud objects as large as our planet, you know at least some media outlets will declare that “another Earth has been found beyond Pluto!”

At least we might be able to get funding for a probe mission to such a world that way.

How ironic that the revamped Cosmos series on Fox television just discussed the Oort Cloud and its “discoverer” in its third episode last Sunday.

ljk March 26, 2014 at 17:10

Speaking of Cosmos Mark 2, not everyone believes in the existence of the Oort Cloud, however:

http://www.motherjones.com/environment/2014/03/neil-tyson-cosmos-comets-creationists

Oy.

Gerry March 26, 2014 at 18:38

Another possible target for an interstellar-precursor mission someday. There was a presentation I saw not long ago from one of the interstellar conferences about the idea of establishing a sort of beam propulsion highway over interstellar distances, using relays to deal with the challenge of keeping tight enough focus on a target. The relay lenses/generators would be spaced many AU’s apart so a trip to something “only” in the Kuiper or inner Oort might make for a good dry run of the technology.

Wojciech J March 26, 2014 at 20:15

Implications are obvious-lot’s and lot’s of resources and place out there for exploitation and settlement(if it would be needed at all). Secondly-a good and gentle reminder how little we know about space, even in our own Solar System(the ringed asteroid Chariklo was also discovered today)…I am sure there are plenty surprises still in store of us…

Paul Gilster March 26, 2014 at 20:21

Gerry writes:

There was a presentation I saw not long ago from one of the interstellar conferences about the idea of establishing a sort of beam propulsion highway over interstellar distances, using relays to deal with the challenge of keeping tight enough focus on a target.

I think you’re talking about Charles Quarra’s ideas. Very interesting stuff! More here:

http://www.centauri-dreams.org/?p=28727

Michael Spencer MLA ASLA March 27, 2014 at 7:05

We will be living out there one day.

swage March 27, 2014 at 10:29

Hmm… not quite “nemesis theory”, but still… probably there is something massive out there – not quite as massive as a neutron star, however. Good find.

ljk March 27, 2014 at 12:03

Would we be able to detect brown dwarfs or rogue planets (ones that have been drifting through the galaxy) in the very outer Sol system?

Doug M. March 27, 2014 at 12:11

I have seen the dark universe yawning
Where the black planets roll without aim
Where they roll in their horror unheeded,
Without knowledge or luster or name.

– H.P. Lovecraft

The two current models IIUC are “there’s a perturbing body (or two) out there somewhere)” and “the Sun used to be in a more densely populated stellar neighborhood, like an open cluster”.

Doug M.

Astronist March 27, 2014 at 13:13

Sorry to be picky, but 2012 VP113 does not seem to be “beyond Sedna” in any sense. The diagram shows it currently closer to the Sun than Sedna. Its semi-major axis of 263 AU is less than the 519 AU of Sedna, which therefore remains the outermost known Solar System body. Also, although the caption to the diagram states that the perihelia of the two planets have similar locations on the sky, the diagram itself shows those perihelia to be separated by around 70 degrees of longitude (plus a bit more if the orbits are not coplanar).

But certainly an interesting story, and fascinating to learn more about the dim outer reaches of our Solar System.

Stephen A.

Adam March 27, 2014 at 21:47

Patryk Lykawka has posited the Mars-Earth sized “planetoid” not far beyond the Kuiper Belt for some years based on the Kuiper Belt cutoff radius highlighted in the news. In parallel Lorenzo Iorio has studied the perturbations of the planets to narrow down the possible radii. Combining the two approaches with this new data might allow a narrowing of where the telescopes should be looking…

A. A. Jackson March 28, 2014 at 9:33

The inner Oort cloud has been an object of much research since it could play a role in possible comet showers due to passage of a star , far from the Sun but inside the classical ‘Oort shell’ , which may have a boundary of almost a light year.
Oort cloud formation and dynamics.Dones, L.; Weissman, P. R.; Levison, H. F.; Duncan, M. J.,Comets II, M. C. Festou, H. U. Keller, and H. A. Weaver (eds.), University of Arizona Press, Tucson, 745 pp., p.153-174

One has to be careful about the ‘inner edge’ of the ‘inner Oort cloud’ because any Planet X there has to be either far enough away or have a mass small enough so as not to break the 3 to 2 resonance between Neptune and Pluto.
Outer-wise Pluto would have been ejected from the Solar System.
A. A. Jackson and R. M. Killen; Killen (1988). “Planet X and the stability of resonances in the Neptune-Pluto system”. Monthly Notices Royal Astronomical Society 235: 593–601.

andy March 28, 2014 at 15:12

For a rather sobering take on how much evidence 2012 VP113 actually provides for “Planet X”, it’s worth reading Emily Lakdawalla’s blog post on the subject. The case for “Planet X” is not all that strong.

Lionel March 29, 2014 at 0:26

Cool news.

Note that even if we find a super-earth or Neptune size gas giant in the Oort Cloud, according to the IAU’s definition it won’t be a planet because it hasn’t clear it’s orbit! The orbit-clearing definition will not stand the test of time and has got to go.

As I’m concerned 2012VP113 is the 2nd Oort Cloud planet. Great that we’ve now found more than one.

sedjak March 29, 2014 at 13:22

Do current theories of solar system formation take into account dark matter? Since the peculiar orbital mechanics of stars far outside in their respective galaxies gave rise to the theorization of dark matter, could it not be possible that the same phenomenon is at work in solar systems. If it is in ours, then we could have a richer Oort cloud or Kuiper belt teeming with larger and more numerous “dwarf” planets. We might be able to rule out dark matter in the nearby solar system, but I do not know about the far unexamined darker reaches.

kzb March 31, 2014 at 7:45

sedjack, I believe that the amount of non-baryonic dark matter within the solar system amounts to only about one asteriod of mass. And it is diffuse.

Laurel Kornfeld March 31, 2014 at 12:52

@Leon Our solar system already has more than 9 planets, at least according to the geophysical planet definition, which does not require an object to “clear the neighborhood of its orbit” to be a planet. The possibility of a large planet out in the Oort Cloud shows just how ridiculous the IAU planet definition is. If an Earth-sized object is discovered out there, it would not be considered a planet according to the IAU definition because it would not “clear” that orbit of multitudes of tiny comets. Yet an object of the same size, the Earth is classed as a planet. A definition that takes two objects of the same size and makes one a planet and one not a planet makes absolutely no sense. That is why the many astronomers who reject the IAU definition and consider dwarf planets a subclass of planets already view our solar system as having at minimum 14 planets and counting.

andy March 31, 2014 at 14:16

@Laurel Kornfield: if the IAU definition is ridiculous then it is only because it is poorly worded. As written, it is a zeroth-order approximation to the concept of dynamical dominance which has effectively served as a criterion ever since the main belt asteroids were de-planetified in the 19th century. In other words: is it a member of a belt population, if so then it is not a planet.

A definition of the planetary boundaries based on intrinsic properties leads to a needlessly confusing description of the solar system. Incidentally when looking at exoplanets, the same goes for distinguishing planets and brown dwarfs based on the intrinsic property of whether the object is/was capable of undergoing deuterium fusion.

Lionel April 1, 2014 at 4:06

I agree with Laurel Kornfield’s view and disagree with Andy’s – the IAU’s top-down nomenclature is needlessly confusing and counter-intuitive.
A bottom-up nomenclature – advocated by many, including New Horizons mission Director Alan Stern – is the way to go. This says:

-a planet is any body with enough mass to have become more or less spherical and not enough mass to start nuclear fusion. Simple!

—If this round body orbits a star, then great, it’s a classical planet.

—If this round body another planet, then hey, it’s a satellite-planet.

—If it doesn’t orbit anything, then it’s a rogue-planet.

—If it hasn’t dominated it’s orbit, then yes it’s a dwarf-planet or detatched-planet

Crucially, this system counts dwarf planets and rogue planets as types of planet. It’s terribly confusing that the IAU currently says dwarf-*planets* and rogue-planets are NOT types of planet.

It is bizarre that if Earth and Eris were to swap locations then the former stops being a planet planet and the latter becomes one. Equally bizarre, if Earth were flung into interstellar space then it stop being a planet. Or, in a sci-fi story where we move to Mars’s location to Earth’s L4 or L5, then ooops, Earth and Mars aren’t planets any more. We may make the thrilling discovery of a gas giant or super-earth in the Oort cloud – but Planet X couldn’t be a planet either as things stand.

This all goes against the grain of intuition and what the public expects, making space inaccessible and a lot less interesting.

Sedna should be a household name – it’s a fascinating place – and it’s largely the IAU’s current denial of its planethood that took the bang out of it’s incredible discovery. Likewise, next year’s visits to Pluto and Ceres historic interplanetary voyages that are open for all of humanity to marvel at… but the media will leave the public with a confused and underwhelming message about what these places actually are because the 2006 nomenclature is inaccessible and counterintuitive.

What other nomenclature system features a dwarf-[whatever] or rogue-[whatever] is not a type of –[whatever]? Is a dwarf elephant not an elephant, a rogue agent not an agent?

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