Kuiper Belt Objects: Coordinated Stargazing

Coordinated Stargazing

The high albedo suggests that the KBO's surface is made of reflective water-ice particles, and that would support a theory about how the KBO formed.

Many researchers believe there was a collision that occurred one billion years ago between a dwarf planet in the Kuiper Belt known as Haumea and another object that caused Haumea's icy mantle to break into a dozen or so smaller bodies, including 55636.

Far beyond the orbit of Neptune in a region of the outer solar system known as the Kuiper Belt float thousands of icy, moon-sized bodies called Kuiper Belt objects (KBOs). Astronomers think they are the remnants of the bodies that slammed together to form the planets more than 4 billion years ago.

Unlike Earth, which has been continually eroded by wind and water since it was formed, KBOs haven't changed much over time and may hold clues about the early solar system and planet formation.

Until now, astronomers have used telescopes to find KBOs and obtain their spectra to determine what types of ices are on their surface. They have also used thermal-imaging techniques to get a rough idea of the size of KBOs, but other details have been difficult to glean.

While astronomers think there are about 70,000 KBOs that are larger than 100 kilometers in diameter, the objects' relatively small size and location make it hard to study them in detail.

One method that has been has been proposed for studying KBOs is to observe one as it passes briefly in front of a bright star; such events, known as stellar occultations, have yielded useful information about other planets in the solar system.

By monitoring the changes in starlight that occur during an occultation, astronomers can determine the object's size and temperature, whether it has any companion objects and if it has an atmosphere.

The trick is to know enough about the orbit of a KBO to be able to predict its path and observe it as it passes in front of a star.

This was done successfully for the first time last October when a team of 18 astronomy groups led by James Elliot, a professor of planetary astronomy in MIT's Department of Earth, Atmospheric and Planetary Sciences, observed an occultation by an object named "KBO 55636."

As Elliot and his colleagues report in a paper published in Nature, the occultation provided enough data to determine the KBO's size and albedo, or how strongly it reflects light.

The surface of 55636 turns out to be as reflective as snow and ice, which surprised the researchers because ancient objects in space usually have weathered, dull surfaces.