[meteorite-list] Dustiest Star Could Harbor a Young Earth

[Ron Baalke]

Gemini Observatory
Hilo, Hawaii

Media Contact:
Peter Michaud
Gemini Observatory, Hilo HI
(808) 974-2510 (Office)

Science Contact:
Inseok Song
Gemini Observatory, Hilo HI
(808) 974-2609 (Office)

For Embargoed Release at 1:00pm (ET)/7:00am (HST) on July 20, 2005

Dustiest Star Could Harbor a Young Earth

A relatively young star located about 300 light-years away is greatly 
improving our understanding of the formation of Earth-like planets.

The star, going by the unassuming name of BD +20 307, is shrouded by the 
dustiest environment ever seen so close to a Sun-like star well after its 
formation. The warm dust is believed to be from recent collisions of rocky 
bodies at distances from the star comparable to that of the Earth from the 
Sun. The results were based on observations done at the Gemini and W.M. 
Keck Observatories, and were published in the July 21 issue of the British 
science journal Nature.

This finding supports the idea that comparable collisions of rocky bodies 
occurred early in our solar system's formation about 4.5 billion years 
ago.  Additionally, this work could lead to more discoveries of this sort 
which would indicate that the rocky planets and moons of our inner solar 
system are not as rare as some astronomers suspect.

"We were lucky. This set of observations is like finding the proverbial 
needle in the haystack," said Inseok Song, the Gemini Observatory 
astronomer who led the U.S.-based research team. "The dust we detected is 
exactly what we would expect from collisions of rocky asteroids or even 
planet-sized objects, and to find this dust so close to a star like our 
Sun bumps the significance way up. However, I can't help but think that 
astronomers will now find more average stars where collisions like these 
have occurred."

For years, astronomers have patiently studied hundreds of thousands of 
stars in the hopes of finding one with an infrared dust signature (the 
characteristics of the starlight absorbed, heated up and reemitted by the 
dust) as strong as this one at Earth-to-Sun distances from the star. "The 
amount of warm dust near BD+20 307 is so unprecedented I wouldn't be 
surprised if it was the result of a massive collision between planet-size 
objects, for example, a collision like the one which many scientists 
believe formed Earth's moon," said Benjamin Zuckerman, UCLA professor of 
physics and astronomy, member of NASA's Astrobiology Institute, and a 
co-author on the paper. The research team also included Eric Becklin of 
UCLA and Alycia Weinberger formerly at UCLA and now at the Carnegie 
Institution.

BD +20 307 is slightly more massive than our Sun and lies in the 
constellation Aries. The large dust disk that surrounds the star has been 
known since astronomers detected an excess of infrared radiation with the 
Infrared Astronomical Satellite (IRAS) in 1983. The Gemini and Keck 
observations provide a strong correlation between the observed emissions 
and dust particles of the size and temperatures expected by the collision 
of two or more rocky bodies close to a star. 

Because the star is estimated to be about 300 million years old, any large 
planets that might orbit BD +20 307 must have already formed. However, the 
dynamics of rocky remnants from the planetary formantion process might be 
dictated by the planets in the system, as Jupiter did in our early solar 
system.  The collisions responsible for the observed dust must have been 
between bodies at least as large as the largest asteroids present today in 
our solar system (about 300 kilometers across). "Whatever massive 
collision ocurred, it managed to totally pulverize a lot of rock," said 
team member Alycia Weinberger.

Given the properties of this dust, the team estimates that the collisions 
could not have occurred more than about 1,000 years ago. A longer history 
would give the fine dust (about the size of cigarette smoke particles) 
enough time to be dragged into the central star.

The dusty environment around BD +20 307 is thought to be quite similar, 
but much more tenuous than what remains from the formation of our solar 
system. "What is so amazing is that the amount of dust around this star is 
approximately one million time greater than the dust around the Sun," said 
UCLA team member Eric Becklin.  In our solar system the remaining dust 
scatters sunlight to create an extremely faint glow called the zodiacal 
light (see image above). It can be seen under ideal conditions with the 
naked eye for a few hours after evening or before morning twilight.

The team's observations were obtained using Michelle, a mid-infrared 
spectrograph/imager built by the UK Astronomy Technology Centre, on the 
Frederick C. Gillette Gemini North Telescope, and the Long Wavelength 
Spectrograph (LWS) at the W.M. Keck Observatory on Keck I.

For a wide assortment of astronomical images and other publication quality 
images of the Gemini telescopes see the Gemini Observatory Image Gallery,
     http://www.gemini.edu/images

[NOTE: Images supporting this release are available at
http://www.gemini.edu/index.php?option=content&task=view&id=138&Itemid=0&limit=1&limitstart=1 
]