NASA

• A new animation shows the orbits of hundreds of dwarf
  planets beyond Pluto.
• The astronomer who compiled the data says it may only
  capture a small fraction of dwarf planets in the solar
  system.
• A new definition of “planet” may recategorize 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 100- or even 1,000-fold:

However, if a small group of astronomers gets its way, many of
these worlds may become fully 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 Sandbox²,
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 all belong to dwarf planets.

In response to the Reddit post, Dixon said the orbits are based
on a constantly updated
list of candidate worlds maintained by Mike Brown, an
astronomer at Caltech.

“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.”

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 bonafide 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–t”). The public also didn’t take it well:
Brown has since received a torrent of hate mail from school
children.

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-out 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 other objects 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’ again?

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!”

Brown doesn’t think
nuclear-powered spacecraft like New Horizons (which is

now exploring the Kuiper Belt) will discover most of those
missing worlds, however.

“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 of 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 worlds as planets, dwarf planets, and
moons — terms based on their orbits around the sun and one
another — the team wants to simplify the system: As long as 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.