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