Saturday, November 17, 2007

Dusty stars: images of our past?

Something familiar but still strange is happening around star HD 23514 in the Makali'i, the star cluster otherwise known as the Pleiades, Seven Sisters, or Subaru.

(Photo credit: Inseok Song/Digital Sky Survey, inset: Gemini Observatory/Lynette Cook. The larger image was created by combining B, R and I band images from individual second generation Digital Sky Survey images into blue, green and red image layers, respectively. HD 23514 is shown by the yellow arrow.)

What's strange, according to astronomers who used Hawai'i's Gemini Observatory, atop Mauna Kea, along with the Spitzer Space Telescope, is that they have identified what appears to be the formation of rocky planets, like Earth, around a star in Makali'i.

It's interesting, in part, because life like ours could not survive on many planets, even ones in our own solar system.

Researchers, writing in the Astrophysical Journal, say the planet formation in the Pleiades “may well be the first observational evidence that terrestrial planets like those in our solar system are quite common," said UCLA astronomer Joseph Rhee.

They studied a star called HD 23514 in the Makali'i. It's slightly brighter than our sun and is surrounded by lots of hot dust. The astronomers figure the dust is the result of massive collisions between planets or the embryos of planets.

The dust forms the “building blocks of planets” and can clump together with other dust to form small objects the size of asteroids, and continue to clump up to eventually create objects the size of planets, said Inseok Song, a former Gemini staffer who now works with NASA's Spitzer Science Center at the California Institute of Technology.

“In the process of creating rocky, terrestrial planets, some objects collide and grow into planets, while others shatter into dust; We are seeing that dust,” Song said in a Gemini/UCLA press release.

Also interesting about what the astronomers are seeing is that the dust is collected in the right zone. The news release on the research said: “The emission appears to originate from dust located in the terrestrial planet zone between about 1/4 to two astronomical units (AUs) from the parent star HD 23514, a region corresponding to the orbits of Mercury and Mars in our solar system.”

An AU is the distance from Earth to our Sun.

The activity at HD 23514, which is much younger than our Sun, may mimic what happened when our own solar system was younger. Astronomers believe our Moon was created by the collision between a young Earth and a planet the size of Mars. Another collision, between an asteroid and Earth, is believed to have been the cause of the extinction of dinosaurs.

The scientists earlier found another dusty star about 300 light years away in the constellation Aries, which may also be indicative of planet-formation.

Any hope of finding intelligent life on HD 23514? We may have a while to wait. Our sun is on the order of 4.5 billion years old, but HD 23514 is only about 400 million. It's just in the process of building its solar system.

But the good news, for those interested in the possibility of extraterrestrial life or at least planets capable of sustaining it, is that planets like ours may not be that rare.

“Our observations indicate that terrestrial planets similar to those in our solar system are probably quite common, said Benjamin Zuckerman, a professor of physics and astronomy at UCLA.

So the dusty evidence of planet formation, while it seems strange to us now, many not be so strange at all.

A little more about the Makali'i. When you take a close look, the Seven Sisters may only appear to have six members visible to the naked or binocular-assisted eye. But if you take a really, really close look, the cluster has something like 1,400 stars.

Makali'i is among the closest groups of stars to the Earth, about 400 light years away, meaning that if you had a space ship that could go the speed of light, which is really fast, you still would take four centuries to get there.

Some folks might have been surprised at the start of this article to learn that the Makali'i are known in Japan as Subaru. Yep, those stars on the front of the Japanese car represent the Makali'i, that little clutch of stars in the northern sky that are distinctive because they are all gathered together like coins in a purse. They swing across the sky between Taurus the bull and Perseus the warrior.

The Makali'i are not hard to find. If you go out at this time of year, on a clear night in the early evening, they're right there.

© 2007 Jan W. TenBruggencate

For more information, see the Gemini release at

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