Masses of known plutoids, compared to the mass of Luna, earth’s moon.

Masses of various plutoids.

From "The Big Bang Theory" -- Neil deGrasse Tyson plays himself, confronted by Sheldon Cooper over the "demotion" of Pluto

Link goes to YouTube — embedding of this was disabled, unfortunately.

These are called “transNeptunians” — objects which orbit outside Neptune’s orbit.  Some are dwarf planets, others are not, and many have yet to be officially classified.   This shows their relative sizes, to the extent of current knowledge, as well as their colors and albedos.

Snow White, the dwarf planet, covered in ice.

(Source: cbar)

microbatdynamo:

Astronomers find ice and possibly methane on Snow White, a distant dwarf planet

Astronomers at the California Institute of Technology (Caltech) have discovered that the dwarf planet 2007 OR10—nicknamed Snow White—is an icy world, with about half its surface covered in water ice that once flowed from ancient, slush-spewing volcanoes. The new findings also suggest that the red-tinged dwarf planet may be covered in a thin layer of methane, the remnants of an atmosphere that’s slowly being lost into space.

“You get to see this nice picture of what once was an active little world with water volcanoes and an atmosphere, and it’s now just frozen, dead, with an atmosphere that’s slowly slipping away,” says Mike Brown, the Richard and Barbara Rosenberg Professor and professor of planetary astronomy, who is the lead author on a paper to be published in the Astrophysical Journal Letters describing the findings. The paper is now in press.

Snow White—which was discovered in 2007 as part of the PhD thesis of Brown’s former graduate student Meg Schwamb—orbits the sun at the edge of the solar system and is about half the size of Pluto, making it the fifth largest dwarf planet. At the time, Brown had guessed incorrectly that it was an icy body that had broken off from another dwarf planet named Haumea; he nicknamed it Snow White for its presumed white color.

Soon, however, follow-up observations revealed that Snow White is actually one of the reddest objects in the solar system. A few other dwarf planets at the edge of the solar system are also red. These distant dwarf planets are themselves part of a larger group of icy bodies called Kuiper Belt Objects (KBOs). As far as the researchers could tell, Snow White, though relatively large, was unremarkable—just one out of more than 400 potential dwarf planets that are among hundreds of thousands of KBOs.

(via PhysOrg.com)

todeeinhistory:

july 29th, 2005 - A dwarf planet, Eris is discovered. 

whitefox83:

How could you NOT love National Geographic??

An illustration of a planet-like body in the Kuiper belt.

Rachel Kaufman

for National Geographic News

Published August 11, 2011

Three relatively bright space rocks recently found in Pluto’s neighborhood may be new members of the dwarf planet family, astronomers say.

The objects were discovered in a little studied section of the Kuiper belt, a region of the solar system that starts beyond the orbit of Neptune and extends 5.1 billion miles (8.2 billion kilometers) from the sun.

Astronomer Scott Sheppard, of the Carnegie Institute of Washington, and colleagues found the bodies using the 1.3-meter Warsaw University Telescope at Las Campanas in Chile.

The region of the Kuiper belt visible from Earth’s Northern Hemisphere has been fairly well studied. But until recently, a lack of instruments prohibited searches from the Southern Hemisphere.

The latest survey turned up 14 new Kuiper belt objects, three of which are probably big enough to join Pluto, Eris, Ceres, Haumea, and Makemake in dwarf-planet status, the study authors say. (Related: “Pluto Gets 14 New Neighbors.”)

“I’m glad someone finally did it. It needed to happen,” Mike Brown, a Caltech astronomer who was not involved in the study, said of the southern-sky survey.

New Bodies Are Planetary Pipsqueaks

The International Astronomical Union defines a dwarf planet as something orbiting the sun that’s so massive its own gravity molds the object into a rough sphere. Such worlds also haven’t cleared their neighborhoods of other small, planet-like bodies.

(Related: “New Moon Discovered Orbiting Pluto.”)

By estimating the objects’ reflectivity, Sheppard and colleagues could derive their sizes: The largest object is likely 384 miles (620 kilometers) across. The worlds are massive enough to be round, but they’re still pipsqueaks, even by dwarf-planet standards.

By contrast, Pluto and Eris are both 1,450 miles (2,333 kilometers) or so wide. Ceres, the smallest of the confirmed dwarfs, is about 303 miles (487 kilometers) across.

(Related: “NASA’s Dawn Spacecraft to Reach Asteroid This Weekend.”)

Because the newfound objects are so small and so far away, astronomers can’t yet say for sure whether they are in fact spherical and therefore worthy of being named dwarf planets.

Pluto Has No Southern Twins?

The Kuiper belt is full of objects about the size—or at least the brightness—of the three new bodies, Brown added. In fact, there are 37 other objects in the Kuiper belt at least as bright as the newly discovered candidate dwarfs.

Still, the new work does help fill in gaps in the known population of the solar system.

“By determining how many large objects are in the Kuiper belt, we now know how much stuff is there,” study leader Sheppard said. “The point was to complete [our knowledge of] the Kuiper belt.”

For instance, the study closes the possibility of finding a larger, Pluto-size object in the southern skies.

But it’s always possible that “we will find more objects out in the next region [beyond the Kuiper belt], where Sedna is,” Caltech’s Brown said, referring to another candidate dwarf planet, which orbits at an average of 8.9 billion miles (14.3 billion kilometers) from the sun.

The paper describing the three possible new dwarfs has been accepted for publication in the Astronomical Journal.

unknownskywalker:

Distant Eris

This illustration of our solar system shows Eris in its highly tilted orbit beyond Pluto.

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