Dwarf Planets You May Not Have Heard Of
- Eris, hailed as “Planet X” when it was discovered, is slightly larger than Pluto in size and 130% of its mass. Eris and its moon Dysnomia were originally known as Xena and Gabrielle, but the IAU insists on names taken from traditional mythology, not modern fantasy.
- Haumea (artist’s concept, NASA) and its moons Hi’aka and Namaka are named after Hawaiian deities. Making a complete turn every 4 hours, Haumea is the fastest-spinning large body in the solar system. It’s not that much smaller than Pluto, but the rapid spin means it solidified as an egg rather than a sphere, very unusual for a body that large. Haumea has a mysterious reddish patch.
- Makemake is another dwarf planet a little larger than Haumea. No moons detected so far. Then again, all but one of Pluto’s moons have been discovered within the past few years, thanks to intense observations from Hubble in preparation for the New Horizon spacecraft’s flyby in July 2015. I’m sure we’ll find more moons around other dwarf planets, too.
- Quaoar, classified as an asteroid when it was first discovered and likely to be added to the dwarf planet roster, is larger than Ceres and has at least one moon, Weywot.
- Sedna is the second-farthest object in the solar system discovered so far, 8 billion miles away. It’s slightly larger than Ceres, at about 1000 km in diameter; that’s a little less than half the size of Pluto. There are believed to be other Sednas out there, including the newly-discovered 2012 VP113, which may be another dwarf planet. 2012 VP113 is even farther away than Sedna.
- Ceres was the first dwarf planet to be discovered, back in 1801. At first, it was classified as a planet. However, when Vesta and several other large bodies were discovered a few years later in a belt between Mars and Jupiter, Ceres was demoted from planet to asteroid. The IAU has now recognized Ceres as a dwarf planet, with water ice, a differentiated crust and core, and signs of planetary evolution. The Dawn Spacecraft reaches Ceres in April! Ceres is the closest dwarf planet to Earth, and it’s a likely site of human exploration and mining.
- Vesta is not a proper dwarf planet, but is sometimes called a protoplanet, since it has a crust, core and mantle like Ceres, although it’s not quite big enough for gravity to have pulled it into a spheroid.
- 2007OR10 is still waiting for an official name; at the moment it’s going by the nickname “Snow White.” It appears to be covered in ice spewed out of slush volcanoes. Larger than Makemake and slightly smaller than Haumea, it was discovered by Mike Brown’s graduate student Meg Schwamb.
- Orcus is a Kuiper Belt Object like Pluto, about half its size, with at least one moon named Vanth. Named after the Etruscan equivalent of Pluto, Orcus is known as the “Anti-Pluto.” Its tipped orbit is essentially a mirror image of Pluto’s, and they seem to be moving in resonance with one another. When Pluto is close to the sun, Orcus is at the far side of its orbit, and vice versa.
- The bottom photos are Hubble’s clearest images of Pluto. Can’t wait for the New Horizons spacecraft to give us better ones during its July 2015 flyby!
Mike Brown’s Palomar Observatory team has so far discovered “seven dwarfs”: Quaoar, Sedna, Haumea, Orcus, Makemake, Eris, and “Snow White.”
Other fun facts: There are 7 moons larger than Eris & Pluto. In order of size (largest to smallest: Ganymede, Titan, Callisto, Io, the Moon, Europa and Triton.
While about 10 dwarf planets have been discovered so far, there may be hundreds.