“Snow White” or “Rose Red” (2007 OR10)

Discovered in 2007 by former graduate student Meg Schwamb, dwarf planet Snow White orbits at the edge of the Solar System. Roughly half the size of Pluto, its color was nicknamed erroneously. At one time it was surmised the diminutive planet was a white, icy world broken away from a larger planet, but further studies show it may be the most red of all.

Astronomers at the California Institute of Technology (Caltech) have been taking a much closer look at dwarf planet 2007 OR10. This Kuiper Belt Object is a frozen world, covered in water ice which may have originated volcanically. While the slush covered rock could be assumed to be white, a more rosy hue is in order. Why? According to the new research, Snow White may have a thin atmosphere of methane that’s methodically dissipating.

“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. “With all of the dwarf planets that are this big, there’s something interesting about them—they always tell us something,” Brown says. “This one frustrated us for years because we didn’t know what it was telling us.”

When dwarf planet 2007 OR10 was first discovered, the best instrument at the time for study was the Near Infrared Camera (NIRC) at the Keck Observatory. But, it wouldn’t be long until Adam Burgasser, a former graduate student of Brown’s and now a professor at UC San Diego, helped design a new instrument called the Folded-port Infrared Echellette (FIRE) to study Kuiper Belt Objects. Last fall, Brown, Burgasser, and postdoctoral scholar Wesley Fraser put FIRE to the test with the 6.5-meter Magellan Baade Telescope in Chile to take a closer look at Snow White. As they had surmised, the little planet was red – but what they weren’t expecting was the presence of water ice. “That was a big shock,” Brown says. “Water ice is not red.”

Is Snow White alone in its rose garden? The answer is no. A few years earlier Brown also discovered another dwarf planet – Quaoar – which had both a red spectrum and water ice. Because of its small size, Quaoar couldn’t hold on to an atmosphere. Over its evolutionary period, the volatile compounds were lost to space, leaving only methane which appears red. Because the spectrum of both small planets are similar, the conclusion is they both share similar properties. “That combination—red and water—says to me, ‘methane,'” Brown explains. “We’re basically looking at the last gasp of Snow White. For four and a half billion years, Snow White has been sitting out there, slowly losing its atmosphere, and now there’s just a little bit left.”

But the team is being cautious for now. While findings point to water ice, the presence of methane isn’t yet documented and will need further studies with larger telescopes like Keck. If their hypothesis turns out to be true, Snow White will join Quaoar as one of two dwarfs capable of keeping their volatile natures intact. Next up for the team is renaming 2007 OR10 since “white” no longer describes it. Before the discovery of water ice and the possibility of methane, “2007 OR10” might have sufficed for the astronomy community, since it didn’t seem noteworthy enough to warrant an official name. “We didn’t know Snow White was interesting,” Brown says. “Now we know it’s worth studying.”

Original Story Source: Caltech News Release. For further reading: Mike Brown’s Planets.

What is a Plutoid?

About Dwarf Planets


Pluto, we hardly knew ya! Don’t worry, she’s not going anywhere. However, this once happy planet will no longer be listed amongst the “planets” in our solar system. According to International Astronomical Union (IAU), which began meeting in August of 2006, the term Plutoid now applies to Pluto, as well as any other small stellar body that exist beyond the range of Neptune. Arriving at this working definition in 2008, two years after first meeting, the IAU defines the term Plutoids thusly: “Plutoids are celestial bodies in orbit around the Sun at a semimajor axis greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit.”

The reason the IAU began meeting in the first place was to iron out some ambiguities that exist in the terminology of astronomy. For example, thought some might find it shocking, astronomers had never actually come up with a definition of “planet”. Originally, a planet meant a “wandering star” – ie. a star that appeared to move from constellation to constellation. This was the definition used by ancient astronomers, and it applied to the sun and moon as well. However, Copernicus’s heliocentric model changed all that; now it was clear that the Earth was a planet itself and moved around the Sun with the rest of them. In addition, more and planets were being discovered beyond Jupiter, such as Uranus and Neptune, and then between Jupiter and Mars. This included Ceres, Pallas, Vesta, and Juno, but astronomers soon realized that these bodies were far too small to fit with the rest of the planets.

Then came Pluto’s discovery. At the time, scientists thought it to be several times larger than it actually was; accordingly they placed it on the list of planets. Eventually, its true size was realized and other bodies similar to Pluto in size and composition were found far beyond Neptune, in what is known as the Kuiper Belt. Pluto was to these stellar objects what Ceres was to large objects in the asteroid belt – that is to say, comparable in size. Astronomers proposed several names for these objects, but matters did not come to a head until Eris was discovered. This dwarf planet was actually larger than Pluto, 2500 km in diameter, making it twenty-seven percent larger than Pluto.

In the end, the IAU could only resolve this matter by removing Pluto from the list of planets and devising a new category for dwarf planets that could no longer be considered true planets. Plutoid was the result, and now applies to the trans-Neptunian objects of Pluto, Haumea, Makemake, and Eris.

We have written many articles about Plutoid for Universe Today. Here are some facts about Pluto, and here’s an article about why Pluto is no longer a planet.

If you’d like more info on Pluto, check out Hubblesite’s News Releases about Pluto, and here’s a link to NASA’s Solar System Exploration Guide to Pluto.

We’ve also recorded an episode of Astronomy Cast dedicated to Pluto. Listen here, Episode 64: Pluto and the Icy Outer Solar System.


Pluto Fact Sheet

The following Pluto fact sheet is based on NASA’s excellent planetary fact sheets. Pluto is no longer a planet, but a dwarf planet.

Mass: 0.0125 x 1024 kg
Volume: 0.715 x 1010 km3
Average radius: 1,195 km
Average diameter: 2,390 km
Mean density: 1.750 g/cm3
Escape velocity: 1.2 km/s
Surface gravity: 0.58 m/s2
Natural satellites: 3
Rings? – No
Semimajor axis: 5,906,380,000 km
Orbit period: 90,465 days
Perihelion: 4,436,820,000 km
Aphelion: 7,375,930,000 km
Mean orbital velocity: 4.72 km/s
Orbit inclination: 17.16°
Orbit eccentricity: 0.2488
Sidereal rotation period: 153.2928 hours
Length of day: 153.2820 hours
Axial tilt: 122.53°
Discovery: 18 February 1930
Minimum distance from Earth: 4,284,700,000 km
Maximum distance from Earth: 7,528,000,000 km
Maximum apparent diameter from Earth: 0.11 arc seconds
Minimum apparent diameter from Earth: 0.06 arc seconds
Maximum visual magnitude: 13.65

We’ve written many articles about Pluto for Universe Today. Here’s an article about why Pluto isn’t a planet any more, and here’s an article about the distance to Pluto.

If you’d like more info on Pluto, check out Hubblesite’s News Releases about Pluto, and here’s a link to NASA’s Solar System Exploration Guide to Pluto.

We’ve also recorded an entire episode of Astronomy Cast just about Pluto. Listen here, Episode 64: Pluto.

2003 ub313


In 2003, a celestial object was discovered, but little did astronomers know that this object, which was designated 2003ub313, was going to change astronomy forever. Although the object was first photographed in 2003 by Mike Brown and other astronomers, it was not until 2005 that astronomers announced their discovery. You may better know 2003 ub 313, which was its designation given when it was believed to be a minor planet, as Eris. Eris made such a fuss because it is larger than Pluto – 27% more massive. Some people labeled it as the tenth planet while others did not think it should join the ranks of the nine planets we had. Finally, the International Astronomical Union (IAU) met to decide on a definition of a planet. Eventually, they decided on a definition in 2006, and 2003ub313 was not classified as a planet but rather a dwarf planet.  In addition to Eris, Pluto was reclassified as a dwarf planet, and several other celestial bodies – including Ceres, Haumea, and Makemake – were classified as dwarf planets. Astronomers are evaluating dozens more celestial bodies to see whether they fall under the classification of dwarf planets.

Eris is the ninth largest celestial body in our Solar System that orbits the Sun and the most distant object orbiting the Sun. It takes the dwarf planet 556.7 years to orbit our star. Eris is located in the scattered disc, which is a region beyond the Kuiper Belt. In addition to being a dwarf planet, Eris is also classified as a Trans-Neptunian Object (TNO). The surface of the dwarf planet is grey, and astronomers believe that the surface is covered with methane ice, which is what causes it to appear grey.  Methane is the same substance that makes Uranus and Neptune blue. Scientists think that Eris’ composition is similar to that of Pluto. Eris also has a very eccentric orbit, and it is also highly inclined. At some point in its orbit, Eris will actually be closer to the Sun than Pluto will be.

Like most celestial bodies, Eris was named after a figure in mythology. Eris was the Greek goddess of strife and discourse. Many believe this is a very fitting name for the dwarf planet, which caused so much division over the definition of a planet and the fate of Pluto.  The dwarf planet Eris also has a moon, which was named Dysnomia. Dysnomia was Eris’ daughter in Greek mythology and the demon of lawlessness.

Universe Today has articles on Eris including dwarf planet Eris and plutoid Eris is changing.

For more information, check out the discovery of Eris and former 10th planet officially named Eris.

Astronomy Cast has an episode on Pluto’s planetary crisis you will want to hear.

Source: NASA

How Big is Pluto?

Pluto used to be the smallest planet in the Solar System, but now it isn’t a planet any more, thanks to a recent decision from the International Astronomical Union. But now it’s one of the largest dwarf planets, so that’s a good thing. How big is Pluto?

The diameter of Pluto is only 2,390 km across. Just for comparison, that’s about 70% the diameter of the Moon. And it’s a fraction of the size of the Earth; about 18% of the Earth’s diameter.

In terms of volume, Pluto only has 6.39 x 109 km3. That sounds like a huge number, but it’s only 0.59% of the volume of the Earth. In other words, you could put almost 170 objects the size of Pluto inside the Earth.

The mass of Pluto is 1.3 x 1022 kg, which is only 0.2% the mass of the Earth, or 18% the mass of the Moon. Needless to say, Pluto doesn’t have very much mass at all.

The surface area of Pluto is 1.67 x 107 square kilometers. That’s only 3.3% the surface area of Earth, and about the same surface area as Russia.

If you could stand on the surface of Pluto, you would experience only 6.7% the gravity you enjoy on Earth.

We have written many article about Pluto for Universe Today. Here’s an article that explains why Pluto isn’t a planet any more, and here are some interesting facts about Pluto.

Want more information on Pluto? Here’s Hubblesite’s News Releases about Pluto, and here’s a link to NASA’s Solar System Exploration Guide to Pluto.

We’ve recorded an entire episode of Astronomy Cast about Pluto and the rest of the icy outer Solar System. You can find it here.