Rice University
Rice Magazine| The Magazine of Rice University | No. 1 | 2008
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The Universe in a Grain of Sand

By Jade Boyd

Imagine trying to glean useful information from processes that take millions of years or from objects so far away they can’t be seen. Welcome to the world — or, rather, the universe — of the astronomer. Sometimes, though, ingenuity can help bridge even interstellar distances and shed light on the unknown.

Universe“Precisely how and when planets form is an open question,” said Rice astronomer Christopher Johns-Krull.

“One theory is that the disc-shaped clouds of dust around newly formed stars condense into microscopic grains of sand that eventually clump into pebbles, boulders and whole planets.”

Johns-Krull is a member of an international team that analyzed a binary star system using data collected during the past 12 years from a dozen observatories around the world. The team’s findings may help explain how Earthlike planets form.

The researchers looked at a pair of stars called KH-15D in the Cone Nebula (image at left). The stars are about 2,400 light-years from Earth, and they are only about 3 million years old, compared to the sun’s 4.5 billion years. But the stars’ youth wasn’t their only important feature.

“We were attracted to this system because it appears bright and dim at different times, which is odd,” Johns-Krull said.

Nature article: tinyurl.com/5ojsvf

Animation of KH-15D: tinyurl.com/6c5aaf

This hinted at a situation that might allow the researchers to directly observe processes taking place near the stars, which normally is difficult because glare from a star obscures its nearby region. Until now, astronomers have used infrared heat signals, instead of direct observation, to identify microscopic dust particles around distant stars, but the method isn’t precise enough to tell astronomers just how big the particles become and how closely they orbit their star. KH-15D offered a solution.

The researchers found that the Earth has a nearly edge-on view of KH-15D. From this perspective, the disc of dust surrounding the system blocks one of the stars from view, but its twin has an eccentric orbit that causes it to rise above the disc at regular intervals. When it rises above the disc, its light reflects off the dust, allowing the researchers to take photometric and spectrographic readings to determine the dust’s composition and chemical makeup.

The results were the first measured evidence of small, sandy particles orbiting a newborn solar system at about the same distance as the Earth orbits the sun.

“One theory is that the disc-shaped clouds of dust around newly formed stars condense into microscopic grains of sand that eventually clump into pebbles, boulders and whole planets.” —Christopher Johns-Krull

The research was funded by NASA and the Keck Foundation, and the report was published online in the journal Nature.