Far-Out Space Rock Is Weirdly Bright, Clean, & Shiny

By Andrew Moseman | June 17, 2010 10:00 am

KBOWater, water (or ice) everywhere—that’s the refrain this year. This week we covered the study declaring that the moon was home to perhaps 100 times more water than previously thought, and it was just two months ago that sky-watchers spotted the first frosty asteroid out in the Asteroid Belt. Now, in a study in Nature, a team of astronomers says they’ve found another icy surprise in our solar system: a bright shiny object way out in the Kuiper Belt.

The Kuiper Belt is that mess of objects orbiting the sun out beyond Neptune, but not as far as the Oort Cloud (once-proud Pluto is a Kuiper Belt object). There are plenty of icy bodies out there, including Pluto. But what doesn’t make sense about this one, KBO 55636, is how it stayed so pristine after a billion years of floating alone. MIT’s James Elliot, who led the study, says the object’s albedo, or reflectivity, is striking:

“That turned out to be very high, almost 90 percent… That’s consistent with it having a very highly reflective surface like water ice.” The finding was surprising because such old, distant bodies tend to have weathered, dull surfaces. “Objects orbiting that far out in space get generally darkened by accumulating dust… We don’t have an explanation for how it could stay so pristine” [Space.com].

To study the object, Elliot’s team relied on a method called stellar occultation—when an object passes in front of a star and obscures its light. It’s something like the way exoplanet hunters find new worlds by employing the transit method: watching a star dim as its planets pass in front of it. In this case, Elliot knew about KBO 55636 already. He’d been tracking it for years, waiting for it to make this pass so his team could figure out its true size (89 miles across) and brightness.

He wasn’t expecting the tiny rock to be a shiny enigma.

Bigger objects, such as Pluto or Saturn’s moon Enceladus, are able to brighten their surfaces with a fresh supply of ice from processes such as cryovolcanism which sees ice – not lava – spew from the interior of the objects. This explanation did not really apply to the KBO due to its tiny size and the time it had spent floating in space, said the professor [BBC News].

Related Content:
DISCOVER: Beyond the Nine Planets
DISCOVER: Pluto Explored, on the New Horizons mission
80beats: Moon May Have 100 Times More Water Than We Thought. How’d We Miss It?
80beats: Frost-Covered Asteroid Suggests Extraterrestrial Origin for Earth’s Oceans

Image: NASA

  • JMW

    Perhaps the side presented to Elliot’s team is relatively new, if KBO 55636 collided with something and broke apart?

  • http://laurele.livejournal.com Laurel Kornfeld

    Pluto is BOTH a planet and a Kuiper Belt Object. Why is this so hard for some to understand? Dwarf planets are planets too, in spite of the controversial IAU definition, adopted by only four percent of its membership. It is New Horizons Principal Investigator Dr. Alan Stern who coined the term dwarf planet in the first place to mean a third class of planets in addition to terrestrials and jovians. He never intended for dwarf planets to not be considered planets at all. Notably, only four percent of the IAU voted on the demotion, and most are not planetary scientists. Hundreds of professional astronomers led by Stern immediately rejected the IAU decision in a formal petition. This debate is very much ongoing, and referring to Pluto as a planet is a perfectly acceptable scientific position. It is a disservice to readers to present one side of the ongoing planet debate as fact when it is really only one interpretation.

  • http://discovermagazine.com Andrew Moseman


    I appreciate your passion on Pluto’s behalf. I just wanted to remind readers who might not know that Pluto is a resident of the Kuiper Belt; it wasn’t my intention to suggest that it’s not a dwarf planet. Indeed, it’s both.

  • Richard Fidler

    Is it certain the thing is made of water ice? Could it be made of something else? Don’t want to suggest it could be the Death Star….

  • Julian Strong

    I like the idea JMW had, but if it had recently broken apart or collided with another object in space wouldn’t the surface of the object appear to be marred or irregular in it’s luster? Unless the object is made of the same material all the way through it would show very detectable changes in not only the texture of the object but there would be obvious fracture lines where the inside of the object may or may not be a different material then on the outside. Unless the object broke apart many many years ago. Perhaps the object had recently left a warm spot in our solar system only recently cooling to the point of forming ice around it’s body.

  • XPT

    It would be amazing if New Horizon could visit this object after Pluto!

    If this is the same KBO: http://en.wikipedia.org/wiki/(55636)_2002_TX300 there is an interesting spectral analysis: “As suggested by Licandro et al. 2006, this lack of irradiated mantle suggest either a recent collision or comet activity.”


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