Students at CU-Boulder, who built a dust counter for the New Horizons mission to Pluto, have been eyeing the data for decade now. And the results are showing the solar system really is pretty barren if you put aside the planets, rings, moons, comets and asteroids.

The Student Dust Counter (SDC) found only a handful of dust grains, the building blocks of planets, when the spacecraft whipped by Pluto at 31,000 miles per hour last July. Data show the space environment around Pluto and its moons contains only about six dust particles per cubic mile, says Professor Fran Bagenal, who leads the New Horizons Particles and Plasma Team.

"The bottom line is that space is mostly empty," explains Bagenal, a faculty member at the Laboratory for Atmospheric and Space Physics (LASP). "Any debris created when Pluto's moons were captured or created during impacts has long since been removed by planetary processes."

Since its launch in 2006, SDC has identified a few thousand microscopic dust particles, the building blocks of both our solar system and the universe and which can give researchers clues about how the solar system was formed billions of years ago and how it works today.

"CU-Boulder is the only place in the world where students could have built an instrument that eventually flew off to another planet," says Bagenal.

A lot of dust is on the horizon for New Horizons, which is now on the edge of the Kuiper Belt, a vast region thought to span more than a billion miles beyond Neptune's orbit. the Kuiper Belt is believed to harbor at least 70,000 objects more than 60 miles in diameter and contain samples of ancient material created during the solar system's violent formation some 4.5 billion years ago.

"Now we are now starting to see seeing a slow but steady increase in the impact rate of larger particles, possibly indicating that we already have entered the inner edge of the Kuiper Belt," says physics Professor Mihaly Horanyi, the principal investigator for the SDC.

A new study involving Bagenal, Horanyi, CU-Boulder doctoral student Marcus Piquette and Southwest Research Institute (SwRI) postdoctoral researcher Jamey Szalay, who received his doctorate in physics from CU-Boulder last year, was just published in Science.

The CU-Boulder dust counter is a thin film resting on a honeycombed aluminum structure the size of a cake pan mounted on the spacecraft's exterior. A small electronic box functions as the instrument's "brain" to assess each individual dust particle that strikes the detector, allowing the students to infer the mass of each particle.

A revolving cast of more than 20 CU-Boulder students, primarily undergraduates, worked on designing and building the SDC for New Horizons between 2002 and 2005. Several students and researchers are now assessing data from the flyby.

"Our instrument has been soaring through our solar system's dust disk and gathering data since launch," said Szalay, who works at SwRI headquarters in San Antonio. "It's going to be very exciting to get into the Kuiper Belt and see what we find there."

New Horizons is traveling at a mind-blowing 750,000 miles a day. Images from closest approach were taken from roughly 7,700 miles above Pluto's surface. The spacecraft, about the size of a baby grand piano, carries six other instruments.

The next and final target of New Horizons is a 30-mile-in diameter Kuiper Belt object named 2014 MU69, which the spacecraft is expected to pass in January 2019.

Funding for student dust counter came primarily through the Johns Hopkins University Applied Physics Laboratory, which manages New Horizons, and SwRI. LASP also has contributed funds to help pay students working on SDC.