8.6 Dwarf Planets

Ceres

Ceres is the most massive object in the asteroid belt. Before 2006, Ceres was considered the largest of the asteroids, with only about 1.3 percent of the mass of the Earth’s Moon. However, unlike the asteroids, Ceres has enough mass that its gravity causes it to be shaped like a sphere. Like Pluto, Ceres is rocky. Ceres orbits the Sun, is round, and is not a moon. As part of the asteroid belt, its orbit is full of other smaller bodies, so Ceres fails the fourth criterion for being a planet.

Ceres’ Internal Structure

This artist's concept summarizes our understanding of how the inside of Ceres could be structured, based on the data returned by the NASA's Dawn mission.
Figure 8.28. Informed by NASA’s Dawn mission data, researchers inferred that Ceres possesses discrete layers. The inner “mantle” consists of hydrated rocks, whereas the outer crust, approximately 40 kilometres thick, contains ice, salts, and minerals. Interposed is a layer with potential brine, extending down 100 kilometres. Details further below this depth remain undisclosed.
PIA22660: Ceres’ Internal Structure (Artist’s Concept) by NASA/JPL-Caltech/UCLA/MPS/DLR/IDA, NASA Media Licence.

Makemake

Makemake is the third largest and second brightest dwarf planet we have discovered so far. With a diameter estimated to be between 1,300 and 1,900 km, it is about three-quarters the size of Pluto. Makemake orbits the Sun in 310 years at a distance between 38.5 to 53 AU. It is thought to be made of methane, ethane, and nitrogen ices.

Eris

Eris is the most widely-known dwarf planet in the solar system, which is roughly 27 percent more massive than Pluto. The object was not discovered until 2003 because it is about three times farther from the Sun than Pluto, and almost 100 times farther from the Sun than Earth is. For a short time, Eris was considered the “tenth planet” in the solar system, but its discovery helped to prompt astronomers to better define planets and dwarf planets in 2006. Eris also has a small moon, Dysnomia, that orbits it once about every 16 days.

Astronomers know there may be other dwarf planets in the outer reaches of the solar system. Haumea was made a dwarf planet in 2008, and so now the total is five. Quaoar, Varuna, and Orcus may be added to the list of dwarf planets in the future. We still have a lot to discover and explore.

Attribution

“2.7 Other Objects in the Solar System” from Physical Geography and Natural Disasters by R. Adam Dastrup, MA, GISP is licensed under a Creative Commons Attribution Non-Commerical Share-Alike 4.0 International License, except where otherwise noted.

License

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Fanshawe College Astronomy Copyright © 2023 by Dr. Iftekhar Haque is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.