Thousands of worlds may lurk beyond Pluto — and a stunning new animation shows the ones we've found
(NASA)
A new animation shows the orbits of hundreds of dwarf planets beyond Pluto.
The astronomer who compiled the data says it may capture only a small fraction of dwarf planets in the solar system.
A new definition of "planet" may categorize many dwarf planets and moons as planets.
You may be familiar with our solar system's eight planets — Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. There's also their famous dwarf-planet companion, Pluto.
But this icy world may just be an appetizer to what lurks in a region beyond Pluto called the Kuiper Belt.
As this stunning animation suggests, dwarf planets may outnumber regular planets hundredfold or even thousandfold:
However, if a small group of astronomers gets its way, many of these objects will become full-fledged planets and drop the "dwarf" label.
Where the animation comes from
We first saw the animation in a Reddit post by user Nobilitie. It's actually a recording of a physics-based simulator game called "Universe Sandbox 2," according to Dan Dixon, the creator and director of the software.
Each ring represents an object's orbit, and the mess of rings beyond the inner eight rings belong to dwarf planets.
In response to the Reddit post, Dixon said the orbits were based on a constantly updated list of candidate objects. The list is maintained by Mike Brown, an astronomer at the California Institute of Technology.
"It's a nice illustration of what is out there," Brown wrote in an email to Business Insider. "The striking difference between the orderly giant planets and the randomness of the dwarf planets is quite apparent."
(An artist's impression of the dwarf planet Eris.ESO/L. Calçada and Nick Risinger (skysurvey.org))
Brown discovered Eris, a 10th solar system object that's about 27% more massive than Pluto. His find eventually "killed" Pluto as a bona fide planet — in 2006, thousands of astronomers voted on new celestial terminology, categorizing Pluto as a dwarf planet alongside Eris.
Some astronomers disagreed with the decision (one called it "bulls---"). The public also didn't take it well — Brown said he has since received a torrent of hate mail from schoolchildren.
Definitions aside, the list kept by Brown sorts objects detected in deep space based on the likelihood of their existence. Larger, inner objects tend to be more certain, while farther objects are less certain.
Pluto, Eris, Ceres, Makemake, Haumea, and five others meet Brown's "near certainty" criteria — in other words, they're definitely dwarf planets and not comets or other astronomical objects. Thirty are "highly likely" to be dwarf planets, 75 are "likely," and nearly 850 are "probably" or "possibly" dwarf planets.
Brown guessed that about half of the dwarf-planet candidates have yet to be detected, bringing their numbers close to 2,000 or more.
Redefining 'planet'?
(An illustration of Pluto's orbit is shown in yellow. The dots beyond it are Kuiper Belt objects.NASA)
Even Brown's best estimate may be low, though.
"As you can see from the illustration, some of them are on exceedingly elliptical orbits. Those guys are going to spend most of their time at the outer edge of their orbit, so they're hard to see," Brown said. "There might be a factor of ~5 more of those objects that we don't know about."
But Brown says he doesn't think nuclear-powered spacecraft like New Horizons — which is now exploring the Kuiper Belt — will discover most of those missing worlds.
"The fact that there are so many of these things out there really shows that the future of their exploration is going to mostly rely on telescopes," he said.
A twist in all this is that astronomers are once again wondering what to call floating orbs of rock, metal, and ice in space, according to a poster that seven researchers are presenting this week at the 48th Lunar & Planetary Science Conference.
Instead of categorizing objects as planets, dwarf planets, and moons — terms based on their orbits of the sun and one another — the team wants to simplify the system: If an object is big enough to be mostly round and isn't fusing hot gases (like the sun), it should be deemed a planet.
If enough astronomers agree with them, in time the solar system may be said to contain 110 official planets — and perhaps hundreds or even thousands more if Brown's list of candidates pans out.
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