Discovery Hints at a Quadrillion Space Rocks Beyond Neptune

Dozens ofrocky bodies that are part of a sea of small rocky fragments never observedbefore have been spotted in the suburbs of our solar system beyond planetNeptune, thanks to a novel technique.

These newlydetected chunks of dust and rock coined Trans-Neptunian Objects (TNO) are smallerthan 330 feet (100 meters) across. They are leftovers from the formationof planets.

Scientistshad previously detected TNOs larger than 31 miles (50 kilometer) across such asthe Kuiper Belt Objects (KBO), a subset of TNOs. They suspected that there maybe distant objects beyond Neptune since the 1940's, but it wasn't until 1992that the first KBO was discovered.

Since then,they've found so many large objects in the outskirts of the solar system thatthey had to come up with crazy names,like Plutinos, Centaurs, and Cubewanos, to keep them in order. And althoughresearchers suspected the presence of smaller objects, they didn't have a wayto detect the sea of debris.

"Thesearches for Kuiper Belt Objects usually look for reflected light from the Sunand the small motion relative to fixed background stars," said AsanthaCooray, assistant professor of Physics and Astronomy at the University ofCalifornia, Irvine. The amount of reflected light from a small body, however,is so extremely dim that not even the largest telescopes, or much largertelescopes one could imagine building either on Earth or space, could see it.

But scientists didn't lookfor the reflected light this time. Examining data from NASA's Rossi X-ray Timing Explorer, theymonitored the light from a background star,Scorpius X-1, as small objects moved in front of it in what are calledoccultations. They found obvious dips in the light.

Other thanthe Sun, Scorpius X-1 is the brightestX-ray source in the sky, said study leader Hsiang-Kuang Chang, AssociateProfessor of Physics & Institute of Astronomy at the National Tsing HuaUniversity, Taiwan.

"Wediscussed various possibilities for causing these dips and concluded thatoccultation by small TNOs are the most likely one," he told SPACE.comin an email interview.

Alltogether,Chang and colleagues identified 58 definite dips. Their findings are detailedin the Aug. 10 issue of the journal Nature.

Observingoccultations is a widely known method for studying foreground objects bymonitoring the light of background stars. The rings of Uranus were firstdiscovered during an occultation of a star by Uranus. But never have such smallobjects been detected this way.

"Theinteresting thing here is that instead of monitoring optical stars, theseauthors monitor light from an X-ray source since X-ray detectors can recordlight at small time intervals compared to optical detectors," Cooray told SPACE.com. "A 100-meter body only occults a background source for about 10milliseconds and optical detectors cannot record light continuously at suchsmall time intervals."

Based onthis finding, the researchers estimate that the number of TNOs reaches around aquadrillion, rather than the mere billions to a trillion as previously thought.

This showsan extremely dense disk of material at the outer edges of the solar systemmostly populated by smaller bodies, Cooray said. "Since these are leftovermaterial from the solar system formation process, it says that the originaldisk from which the planets formed was more massive at distances around Neptunethan previously suggested and in strong conflict with some of the early modelsfor the formation of Kuiper Belt Objects."

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