Where Are All the Kuiper Belt Objects?

By Nancy Atkinson - October 03, 2008 08:20 AM UTC | Planetary Science

[/caption] A group of astronomers spent two years photographing portions of the sky to look for small chunks of rock and ice orbiting beyond Neptune, in the Kuiper Belt region of our Solar System. The survey targeted Kuiper Belt objects (KBOs) with sizes between 2 miles (3 km) and 17 miles (28 km). The researchers are surprised, as well as a little disappointed with the results. They came up empty. Nada. Not a single KBO within those parameters was spotted. But these researchers from the Taiwanese-American Occultation Survey (TAOS) are 'glass-half-full' types, and say that defeat can provide as much information as a successful search, so they are making the most of their data. What this means is that there are less KBOs out there than previously thought.

Since the KBO's this group searched for are too small to see directly, the survey watched for stars to dim as KBOs passed in front of and occulted them. After accumulating more than 200 hours of data watching for stellar flickers lasting a second or less, TAOS did not spot any occultations.

Here's a movie that illustrates their search.

The Kuiper Belt contains objects in a range of sizes: a few very large ones (like the dwarf planets Pluto, Eris, Makemake and Haumea) and many more smaller ones. The commonness of a given size tells us information about the history of planet formation and dynamics. In particular, the size distribution of KBOs reflects a history of agglomeration, in which colliding objects tended to stick together, followed by destructive collisions, where collisional velocities were high enough to shatter the rocks involved.

Astronomers questioned whether they would find more and more objects as sizes decreased further, or whether the distribution leveled out. The fact that no occultations were seen sets a stringent upper limit on the number density of KBOs between 2 and 17 miles in diameter. The outer solar system, therefore, appears not as crowded as some theories suggest, perhaps because small KBOs have already stuck together to form larger bodies or frequent collisions have ground down small KBOs into even smaller bits below the threshold of the survey.

The paper announcing this result, co-authored by CfA director Charles Alcock, was published in the October 1 issue of the Astrophysical Journal Letters.

Sources:

TAOS

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CfA

Nancy Atkinson

Nancy Atkinson

Nancy Atkinson is a space journalist and author with a passion for telling the stories of people involved in space exploration and astronomy. She is currently retired from daily writing, but worked at Universe Today for 20 years as a writer and editor. She also contributed articles to The Planetary Society, Ad Astra (National Space Society), New Scientist and many other online outlets.

Her 2019 book, "Eight Years to the Moon: The History of the Apollo Missions,” shares the untold stories of engineers and scientists who worked behind the scenes to make the Apollo program so successful, despite the daunting odds against it. Her first book “Incredible Stories From Space: A Behind-the-Scenes Look at the Missions Changing Our View of the Cosmos” (2016) tells the stories of 37 scientists and engineers that work on several current NASA robotic missions to explore the solar system and beyond.

Nancy is also a NASA/JPL Solar System Ambassador, and through this program, she has the opportunity to share her passion of space and astronomy with children and adults through presentations and programs. Nancy's personal website is nancyatkinson.com