New Object Offers Hint of “Planet X”

The discovery of 2012 VP113, a sizable object roughly twice Pluto's distance from the Sun, has dynamicists wondering whether a super-Earth-size perturber lies undiscovered even farther out.

Discovery of 2012 VP<sub>113</sub>
This animation shows the motion of object 2012 VP 113 over 5 hours as recorded in its discovery images. The field of view is about 1 arc-minute wide. This object is currently about 83 astronomical units (7.7 billion miles) from the Sun — nearly as close as it ever gets.
S. Sheppard / Carnegie Inst. of Science
This week's issue of Nature features an interesting announcement by Chadwick Trujillo (Gemini Observatory) and Scott Sheppard (Carnegie Institution for Science). These two observers have found an object orbiting the Sun, designated 2012 VP113, that they first spotted 17 months ago with the 4-m Blanco Telescope on Cerro Tololo in Chile and then followed up last year with the 6.5-m Magellan-Baade reflector at nearby Las Campanas Observatory.

With an estimated diameter of roughly 280 miles (450 km), this 23rd-magnitude blip hardly ranks as one of the giants of the outermost solar system. More interesting is 2012 VP113's distant, highly elongated orbit, which brings it 80 astronomical units from the Sun at its closest and a whopping 472 a.u. away at its farthest. It takes 4,600 years to loop around the Sun. Another such object, 90377 Sedna, is likewise distantly adrift. Both lie well outside the Kuiper Belt, which extends outward only to about 50 a.u.

Sedna caused quite a stir after its discovery in 2003, because it resides in a kind of orbital "no man's land". Its perihelion (closest point to the Sun) is 76 a.u. — too far away to have been flung out there by a close pass with an outer planet. Dynamicists have speculated that a star passed very close to our solar system in primordial times, drawing objects out of the Kuiper Belt and into Sedna-like orbits before moving on. It's easy to think that 2012 VP113 had the same fate.

Orbits of 2012 VP<sub>113</sub> and Sedna
Both 2012 VP113 and Sedna are currently nearly as close as they can come to the Sun. Notice that both orbits have similar perihelion locations on the sky and both are much more distant than the outer planets and the Kuiper Belt. Click here for a larger version.
S. Sheppard / Carnegie Inst. of Science
However, what's got dynamicists buzzing about this new find is not so much its distance, but instead what it has in common with Sedna's orbit. Both have perihelia near the plane of the ecliptic. So do several other far-out objects, 12 in all, whose distance from the Sun averages at least 150 a.u.

This isn't due to some kind of observational bias, note Trujillo and Sheppard, and it's statistically unlikely to be mere coincidence. Importantly, this kind of orbital alignment means there was no close-passing star at the dawn of solar-system history, because the orbits' orientations would have become randomized in the eons since by gravitational nudges from the outer planets.

Instead, the observers suggest, this might be the handiwork of a super-Earth-size planet roughly 250 a.u. from the Sun, in what's considered the inner Oort Cloud of comets. This rogue world would have enough mass to perturb objects like 2012 VP113 and Sedna inward.

Notably, Trujillo and Sheppard aren't saying this "Planet X" is the real deal. But their computer simulations suggest that it would indeed push objects into these otherwise unexplained orbits. "This is at the suggestive stage," Trujillo cautions. "There are many possible configurations of perturber(s) that could cause the effect."

"If you're asking me whether they've found a planet, the answer is no," comment dynamicist Hal Levison (Southwest Research Institute). "But I'm uncertain about what it means" because the observational data look sound to him.

Levison explains that big primordial objects, Earth-size or bigger, could easily have been thrown into the Oort Cloud after encountering the growing cores of what became to outer planets. For example, some have speculated that Uranus got knocked over into its sideways spin after colliding with an Earth-mass object. However, he cautions, the chance of ending up in the Inner Oort Cloud is small, only about 2%. So lots of objects must have been tossed around to get one to "stick".

Interestingly, way back in 1991, Alan Stern (then at the University of Colorado) postulated that the Kuiper Belt and Oort cloud should contain roughly 1,000 objects the size of Pluto, numerous Mars-sized objects, and potentially a few biggies potentially with masses of up to several times Earth's.

So, can this modern-day "Planet X" be found? Not directly, it seems. Something that far out and having a dark surface (which is most likely) would be too faint to sweep up by any deep telescopic survey now under way.

What about NASA's Wide-Field Infrared Survey Explorer (WISE)? It's especially good at detecting the heat given off by dark objects. But 250 a.u. is too far away to get much warmth from the Sun. A recent analysis of WISE observations rules out anything larger than Jupiter or Saturn in extremely distant solar orbits. Kevin Luhman (Penn State University), who published his assessment last January, thinks WISE would not spot anything as small as Uranus or Neptune closer in.

"This is too faint for WISE," notes project scientist Ned Wright (University of California, Los Angeles). "Earth has a small internal heat output, about 10,000 times less than Jupiter, so a super-Earth would probably heat itself to about 40 K, too cold for WISE to detect."

"We just have circumstantial evidence, so we need to find more of these Sedna-type objects," explains Sheppard. "We do have several more candidates in our ongoing outer-solar-system survey."

Meanwhile, Levison is eager to start digging deeper into the intriguing orbital alignments of 2012 VP113, Sedna, and their kin — either to uncover alternate perturbation schemes or to strengthen the theoretical case for a distant planet-mass instigator.

For more information, you can read Carnegie's press release or, better still, Sheppard's website devoted to the Inner Oort Cloud. And check out the special interactive app by Ron Baalke (Jet Propulsion Laboratory) for displaying the orbits of Sedna and 2012 VP113 together.

Reference:
C. Trujillo and S. Sheppard, "A Sedna-like body with a perihelion of 80 astronomical units" Nature, March 27, 2014.

16 thoughts on “New Object Offers Hint of “Planet X”

  1. dusanmal

    Occasions like this are perfect opportunity to underline consequences of current definition of the planet. Object 10 times size of Earth at suggested range of orbits would be classified as … Dwarf Planet X. At that distance even a gas giant of Jupiter proportions would be … a dwarf planet. It is a time for a simpler truly scientific definition of a planet…

  2. kdconodKC

    We’ve heard this story from dynamicsists before yet we still come up empty. I dunno I find it hard to believe that all these infrared surveys and telescopes have missed something as a big as Uranus.

    Re: definition of a planet I find that argument a red herring. Find a Jupiter in the Kuiper belt first – then propose a new definition for a planet.

  3. Anthony Barreiro

    Well if we can’t find Planet X with an infrared space telescope, I guess we’ll just have to send Bruce Willis. Might as well give him a thermonuclear bomb, just in case Planet X proves dangerous.

  4. Karl

    An "astronomical Unit" is basically the average distance between Earth and our Sun, or roughly 93 million miles.

    Let’s not get into parsecs just yet. LOL

    Karl

  5. G. H. Martin

    Scooter, look it up! Any dictionary, or if you prefer, Google.
    (I agree with Karl about parsecs. Use of that unit of measure for distance should be banned. A light year can be easily understood; not so a parsec. If you don’t agree, then define "parsec" in 25 words or less in terms that could be understood by a 7th grader. Struggle with that for a while, and I’m sure you will get my point.)

  6. Martin

    Peter, you just provided the best argument for not using the parsec.

    What brings the size of our universe and our understanding, or lack thereof, in perspective, is that we can detect a galaxy millions of light-years away, but a planet "only" 250 AU or ~33 light-days away can only be seen if it happens to occult a distant bright object, unless it has some internal heat source that will make it visible in infrared.

  7. G. H. Martin

    Yes, Peter, but we have a different idea of what makes sense to a typical seventh-grader. By the time we explain what an arc-second of sky is, we’re way over 25 words. My point is that a light year is a much easier concept to grasp, so for the sake of helping the public understand astronomy, we should use light-years rather than parsecs.

  8. Mike W. Herberich

    http://en.wikipedia.org/wiki/Parsec — I second Scooter in general for his reserve towards terms and their abbreviations and acronyms. Too often and too much one uses them thoughtlessly, instead of only when and where it certainly is an alleviation of any sort, be it for the writer/ speaker and/ or the reader/ listener. Not so in this case: Kelly Beatty uses the full words "astronomical unit" a good three times which is very laudable and thoughtful. — As for the Parsec itself: 2 reasons for it to be and probably remain a little confusing: 1. Why does one need it at all, having the "astronomical unit" AND the "light year" (plus intrinsically the "light month", "light week", "light day", …!) already? 2. As opposed to all other distance measurings we know of, one has to send one’s mind roaming away from earth and look back from THAT far at the "astronomical unit" which makes it look like an arc-second. That does not only sound complicated and takes certainly MORE words (even if not more than 25) than to picture and explain any other pure and simple distance measure, but the concept per se takes more than one level of thinking: an extra meta-level. Although both questions (might) have perfect answers to them, that additional complexity level remains and will not go away: it is the very definition of the parsec.

  9. stargeezer15601

    I was taught that a parsec was the distance at which an object would have an annual parallax of 1 arc second or about 3.26 light years. The legacy probably originates from using triangulation to measure distances to nearby stars. Triangulation works well within a galaxy, but fails at extragalactic measure when such things as Cepheid variables and type Ia supernova. Otherwise it is an inconvenient unit as mentioned by others.
    What I find interesting about the article is what chaos theory has to say about planets and their orbital evolution. I suggest reading "CHAOS AND HARMONY" by Trinh Xuan Thuan. Herein is a great discourse on why the planets, both near and far, are where they are. Planetary distances are not random. Gravity is a stern taskmaster.
    Doc John-stargeezer 15601

  10. Rick Littleton

    Would it not be a feasible idea for us to send a Voyager-type probe out to the Oort Cloud region in order to search for Planet X and other "residents" of that area?

    The results would not be immediate, but might be very informative.

    Would it hasten any results if the probe were to orbit against the direction of orbit of the other bodies out there?

    R.L.

  11. Anthony Barreiro

    The light year has already become the most commonly used and widely understood unit for measuring distances beyond our solar system. So beating up on the parsec seems like kicking a unit of measure when it’s already down. Still, anybody interested in the history of astronomy, i.e. anybody who wants to understand *how* we’ve measured the universe, needs to understand the parsec. Parallax measurements are the first step on our cosmic distance scale, and the parsec unit has the great advantage of being a directly observed quantity, not an inference. The Gaia satellite will be measuring parallax in arcseconds!

  12. Anthony Barreiro

    Rick — The Voyager probes are currently travelling at roughly 3 AU’s per year. The Oort cloud is believed to lie about 50,000 AU’s from the Sun. So a craft traveling at 5 AU per year would take over 10,000 years just to get to the edge of the Oort cloud. Then, if it were able to start traveling around the circumference at the same speed, another 70,000 years or so to complete one survey. I still think we should send Bruce Willis.

  13. Bruce Mayfield

    Anthony, that’s downright COLD man. What have you got against Bruce!? He’d be downright cold too by the time he got there.
    The League of Extraordinary Bruces

COMMENT