Worlds collide, and astronomers at TSU discover it

An artist's conception shows the planetary collision in the BD+ 20-307 binary system that was confirmed by TSU researchers.

Two Tennessee State University astronomers have made a discovery that is causing a bang in the most prestigious astronomy circles — and that could give humans pause about Earth's fate.

Gregory Henry and Francis Frekel, part of a team of researchers from around the country, revealed that in a faraway solar system about as old as Earth's, two planets collided and annihilated each other.

Nothing was left but a dense cloud of warm dust. If life existed on either of the planets, it would have been wiped out.

While astronomers say that could happen on Earth, it's not likely.

Still, scientists have "a sense of awe because of what it could be," Henry said. "Could our own system become destabilized somehow, with a planet like Mercury or Venus coming up and colliding with the Earth?"

The findings will be published in the December issue of the Astrophysical Journal.

Astronomers say collisions are common in systems where planets and stars are just beginning to form.

And on our own planet, an asteroid slammed into Earth
65 million years ago. Scientists believe it killed off the dinosaurs.

But a crash in a fully mature solar system is a new thing.

"It is something we all thought was a very rare phenomenon," said Joel Tohline, an astronomy professor at Louisiana State University. "We ought to keep our eyes open as to whether this has happened more frequently than we are thinking. It is very interesting what they have found."

Team demoted Pluto

Henry, Frekel and scientists from the California Institute of Technology and the University of California, Los Angeles, first made their discovery in 2005, but they didn't realize what their finding meant until this summer.

The news comes two years after Frekel helped shake up Earth's solar system.

In August 2006, he voted with about 300 other astronomers worldwide to change the definition of a planet.

Doing so demoted Pluto, previously the ninth planet in our solar system, to one of dozens of dwarf planets.

In the recently revealed event, planets the size of Earth and its moon collided more than 100,000 years ago near a star dubbed BD+ 20-307, in a constellation named Aries that is 300 light years away. One light year is about 5.88 trillion miles.

The system has two sunlike stars and is 6 billion to 7 billion years old. Earth's system, which orbits one sun, is about 5 billion years old.

"It was a fully mature planetary system," Henry said. "Something destabilized it and caused the planets to collide.

"We didn't even think systems formed around a binary star. It's unusual the fact that we find so many unique things about this system."

Tohline, the LSU astronomy professor, points out that a binary system is usually unstable compared with one where planets orbit around one sun. So, he doesn't worry that a collision is inevitable for Earth anytime soon.

Contact Christina E. Sanchez at 615-726-5961 or cesanchez@tennessean.com.