Laurel Astronomer Helps Find Proof of High-Speed Collision Between Two Planets

Carey Lisse, a Johns Hopkins University Applied Physics Laboratory astronomer, helped find proof of planets colliding.
Carey Lisse, a Johns Hopkins University Applied Physics Laboratory astronomer, helped find proof of planets colliding. (By Greg Dohler -- The Gazette)
By Tiffany March
Gazette Staff Writer
Thursday, August 20, 2009

An astronomer at a Laurel lab helped find proof for the first time of a high-speed impact between two planets in a solar system similar to ours, supporting the theory that an object the size of Mars collided with Earth and formed the moon.

Carey Lisse was the lead author of the paper describing the collision published this month in the Astrophysical Journal. He works at the Johns Hopkins University Applied Physics Lab in Laurel and said he is excited to share the results from his two years of research.

Using information from NASA's Spitzer Space Telescope collected at the Spitzer Science Center at the California Institute of Technology in Pasadena, Lisse and other astronomers say that two young planets slammed into each other at more than 22,000 miles per hour, colliding sometime within the past few millennia. The planets that collided were probably 12 million years old and about 100 light-years away in the direction of the far southern constellation Pavo. In comparison, Earth's solar system is estimated to be 4.5 billion years old.

Scientists previously suspected that high-speed impacts led to many unique features of our solar system but had only theorized on the subject until now. Planetary experts across the country say they are gratified by the discovery, after years of speculation.

"Since we don't have time machines, we look at other young stars that are nearby and see what they're doing," said Lisse of Silver Spring, who earned his PhD in physics at the University of Maryland at College Park.

Collisions in the early years of our solar system might also have tipped Uranus on its side, sheared layers of rock off the surface of Mercury, caused Venus to spin backward and wiped out the craters on half of Mars, Lisse said.

Christine Chen, from the Space Telescope Science Institute in Baltimore, collaborated with Lisse.

"What's critical about this system is that it's young, in this epoch where it's forming terrestrial planets, like the moon-Earth thing," Chen said.

Using an instrument on the Spitzer telescope called a spectrograph, which analyzes the light wavelengths of elements to show the chemical composition of matter floating in space, Lisse noticed unusual substances that turned out to be vaporized debris from the collision.

Two of the substances, amorphous silica, which is basically melted glass, and silicon monoxide gas, were especially important.

Chen said it was the first time that they were found together, which is "the best evidence so far for a large collision."

Jay Melosh, a professor at Purdue University in Indiana, said he expected that scientists would find silicon monoxide gas after a planet collision because he has seen it in supernova explosions.

"I'm really glad that they found it and that it's not just speculation anymore," he said.

Joseph Nuth, who works in the Solar System Exploration Division at NASA in Greenbelt, said technological improvements would reveal other impacts in forming solar systems.

"This discovery may be the first of many reports of such impacts," he said.

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