Infrared dwarf: Icy world of slushy volcanoes

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  • Published: Sep 1, 2011
  • Author: David Bradley
  • Channels: Infrared Spectroscopy
thumbnail image: Infrared dwarf: Icy world of slushy volcanoes

Dwarf Snow White is actually Rose Red

US astronomers have used infrared techniques to reveal that the dwarf planet, nicknamed Snow White, is an icy world half covered in water ice that once spewed from slush volcanoes. Their data also hints that the planet has an atmosphere of methane, that is gradually evaporating into space.

Astronomers at the California Institute of Technology (Caltech) studied the ruddy dwarf planet 2007 OR10, nicknamed in an apparent paradox given its colour, Snow White. Snow White was discovered in 2007 by Mike Brown's former graduate student Meg Schwamb, it 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 guessed incorrectly that it was an icy body that had broken off from another dwarf planet named Haumea. Unfortunately, Brown nicknamed the dwarf Snow White for its presumed white colour.

Follow-up observations revealed Snow White to be one of the reddest objects in the solar system lying with myriad neighbours in the so-called Kuiper Belt. Despite the inappropriate name, there seemed to be nothing else remarkable about Snow White, other than its relatively large size. It was just one dwarf planets among the hundreds of thousands of Kuiper Belt Objects. However, more recent infrared studies have revealed new insights about this big red dwarf known as Snow White.

Rose-tinted spectacles not needed

"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," explains Brown, who is lead author on a paper to be published in Astrophysical Journal Letters. "With all of the dwarf planets that are this big, there's something interesting about them - they always tell us something," Brown adds. "This one frustrated us for years because we didn't know what it was telling us."

Until recently, the Near Infrared Camera (NIRC) at the Keck Observatory, designed in the 1990s by Caltech physicist Tom Soifer, chief instrument scientist Keith Matthews and others was the best instrument astronomers had to study KBOs. NIRC was retired and details of Snow White's face remained veiled by interplanetary space. However, Adam Burgasser, a former graduate student of Brown's, now at the University of California San Diego helped design a new instrument, the Folded-port Infrared Echellette (FIRE) built at MIT, which was hooked up to the 6.5-meter Magellan Baade Telescope in Chile to allow the astronomers to get a better view of Snow White.

As expected, pointing the "camera" at Snow White revealed her to be blushing red. Surprisingly, however, the new spectroscopic observations also revealed that the surface was actually covered in water ice, a substance that is common throughout the outer solar system and is usually white. "That was a big shock," Brown says. "Water ice is not red."

Red, red ice?

There is, however, one other dwarf planet that's both red and covered with water ice: Quaoar, which Brown helped discover in 2002. Slightly smaller than Snow White, Quaoar is still big enough to have had an atmosphere and a surface covered with volcanoes that spewed an icy slush, which then froze solid as it flowed over the surface.

Quaoar unlike Pluto and Eris, is small and its weak gravitational field does not hold on to volatile compounds such as methane, carbon monoxide, or nitrogen for long, meaning it has little or no atmosphere. Consequently, within a mere two billion years of formation, Quaoar's atmosphere contains nothing more than a little methane. Cosmic radiation gradually converts exposed methane to long hydrocarbon chains, which give the surface a red colour.

The spectrum of 2007 OR10 looks similar to that of Quaoar, suggesting that what happened on Quaoar also happened on 2007 OR10, perhaps not surprisingly. "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."

Although Snow White's spectrum clearly shows the presence of water ice, Brown says, the evidence for methane is not yet definitive. To find out, the astronomers will have to use a big telescope at the Keck Observatory to take an even closer look. If it emerges that Snow White has a frozen coating containing methane, the astronomers can add her to the very short list of just two dwarf planets, along with Quaoar, that straddle the border between the big atmospheric objects and the smaller KBOs with no atmosphere.

A dwarf called Rosie

But, about that name. Thankfully, Snow White is not an official monicker, that is 2007 OR10, giving the dwarf an official, colloquial name could now become an important task, given that this KBO suddenly takes on special scientific interest thanks to its IR spectrum. Perhaps, they could call it "Rosie"?or "Rosea" to give it a classical ring?


The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

 US astronomers have used infrared techniques to reveal that the dwarf planet, nicknamed Snow White, is an icy world half covered in water ice that once spewed from slush volcanoes. Their data also hints that the planet has an atmosphere of methane, that is gradually evaporating into space.

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