Tales of the Occult[ation]: Who Cleaned Up the Back Yard?

Don’t feel too bad for poor demoted Pluto—it and its fellow dwarf planets in the Kuiper belt seem to have found a mysterious cosmic Snow White to help clean house.

A relatively recent project called the Taiwan-America Occultation Survey (TAOS) announced today that after about two years staring at the right parts of the sky, it didn’t see a single object in the Kuiper belt between 2 miles (3 kilometers) and 17 miles (28 kilometers) wide.

Normally you wouldn’t think a survey that found nothing is Big News. But it is kind of a big deal to astronomers, because they were expecting to see loads of icy litter in this region of the solar system.

The Kuiper belt, after all, is a swath of stuff extending from Neptune‘s orbit to about 4.6 billion miles (7.5 billion kilometers) away from the sun. It contains plenty of large planet-like objects, including three of the five official dwarf planets.


The presence of so many big things makes people think there should be lots of little things, as bodies must be jostling around up there, breaking off smaller chunks or joining up to make larger ones.

The problem is getting a good look at them, as tiny things at that distance aren’t easy to spot—in the last few years we’ve found objects in the Kuiper belt we hadn’t noticed before that are big enough to dub dwarf planets!

An artist’s impression of the New Horizons spacecraft looking back toward the sun from the Kuiper belt

—Image courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute (JHUAPL/SwRI)

In comes a technique called occultation: looking at distant stars and waiting to see if objects that pass between us and them make the stars dim momentarily.

Tying together observation resources from Taiwan, the U.S., and Korea, TAOS got busy looking for stellar flickerings that lasted a second or less. After collecting 200 hours’ worth of data, not a thing in the targeted size range showed up.

Fellow space blogger Phil Plait notes on Bad Astronomy that we can’t yet tell why the Kuiper belt is less crowded than we thought.

He also tosses out the tantalizing theory that there could be an even larger planet waaaaay out in the distant solar system that might be having some effect on the small stuff, but admits there’s simply no evidence to support that idea.

Most likely we won’t have a good picture of what’s out there until we, well, go out there and take some pictures. Maybe the New Horizons mission can help clear some of this up when it gets to Pluto in 2015?

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