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Titan up close
Scientists reveal stunning pictures of Saturn's moon Titan and other results during this news conference from July 3. (38min 17sec file)
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Saturn ring pictures
Cassini's stunning close-up images of the rings around Saturn, taken just after the craft entered orbit Thursday morning, are presented with expert narration by Carolyn Porco, the mission imaging team leader. (8min 39sec file)
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Burn ignition!
Mission control erupts in applause as communications from Cassini confirm the orbit insertion burn has begun. (60sec file)
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Burn completed
Signals from Cassini announce the conclusion of the Saturn orbit insertion burn, confirming the spacecraft has arrived at the ringed planet. (2min 15sec file)
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Post-arrival briefing
Mission officials hold a post-orbit insertion burn news conference at 1 a.m. EDT July 1 to discuss Cassini's successful arrival at Saturn. (25min 27sec file)
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International cooperation
Officials from the U.S., European and Italian space agencies discuss the international cooperation in the Cassini mission and future exploration projects during this news conference from 2 p.m. EDT June 30. (19min 35sec file)
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'Ring-side' chat
This informal "ring-side chat" from 5 p.m. EDT June 30 discusses the Cassini mission to Saturn and the future of space exploration. (49min 20sec file)
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How to fail at being a star
HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS NEWS RELEASE
Posted: July 9, 2004

At the 13th Cambridge Workshop on "Cool Stars, Stellar Systems, and the Sun," Dr. Kevin L. Luhman (Harvard-Smithsonian Center for Astrophysics) announced the discovery of a unique pair of newborn brown dwarfs in orbit around each other. Brown dwarfs are a relatively new class of objects discovered in the mid-1990s that are too small to ignite hydrogen fusion and shine as stars, yet too big to be considered planets. "Are brown dwarfs miniature failed stars, or super-sized planets, or are they altogether different from either stars or planets?" asks Luhman. The unique nature of this new brown dwarf pair has brought astronomers a step closer to the answer.


Newly discovered young brown dwarfs with masses of 50 and 25 times the mass of Jupiter orbit each other at a distance of about 20 billion miles (six times the distance of Pluto from the Sun). Credit: K. Luhman (Harvard-Smithsonian Center for Astrophysics)
 
One possible explanation for the origin of brown dwarfs is that they are born in the same way as stars. Stars form in huge interstellar clouds in which gravity causes clumps of gas and dust to collapse into "seeds," which then steadily pull in more and more material until they grow to become stars. However, when this process is studied in detail by computer, many simulations fail to produce brown dwarfs. Instead, all the seeds grow into full-fledged stars. This result led some astronomers to wonder if brown dwarfs and stars are created in different ways.

"In one alternative that has been proposed recently," explains Luhman, "the seeds in an interstellar cloud pull on each other through their gravity, causing a slingshot effect and ejecting some of the seeds from the cloud before they have a chance to grow into stars. These small bodies are what we see as brown dwarfs, according to that hypothesis."

Testing these ideas for the birth of brown dwarfs is hampered by the fact that brown dwarfs are normally extremely faint and hard to detect in the sky. For most of their lives, they are not hot enough to ignite hydrogen fusion, so they do not shine brightly like stars, and instead are relatively dim like planets. However, for a short time immediately following their birth, brown dwarfs are relatively bright due to the leftover heat from their formation. As a result, brown dwarfs are easiest to find and study at an age of around 1 million years, which is newborn compared to the 4.5 billion year age of our Sun.

Taking advantage of this fact, Luhman searched for newborn brown dwarfs in a cluster of young stars located 540 light-years away in the southern constellation of Chamaeleon. Luhman conducted his search using one of the two 6.5-meter-diameter Magellan telescopes at Las Campanas Observatory in Chile, which are among the largest telescopes in the world.

Of the two dozen new brown dwarfs found, most were isolated and floating in space by themselves. However, Luhman discovered one pair of brown dwarfs orbiting each other at a remarkably wide separation. All previously known pairs of brown dwarfs are relatively close to each other, less than half the distance of Pluto from the Sun. But the brown dwarfs in this new pair are much farther apart, about six times the distance of Pluto from the Sun.

Because these brown dwarfs are so far apart, they are very weakly bound to each other by gravity, and the slightest tug would permanently separate them. Therefore, Luhman concludes, "The mere existence of this extremely fragile pair indicates that these brown dwarfs were never subjected to the kind of violent gravitational pulls that they would undergo if they had formed as ejected seeds. Instead, it is likely that these baby brown dwarfs formed in the same way as stars, in a relatively gentle and undisturbed manner."

Dr. Alan P. Boss (Carnegie Institution) agrees, stating, "Luhman's discovery strengthens the case for the formation mechanism of brown dwarfs being similar to that of stars like the Sun, and hence for brown dwarfs being worthy of being termed 'stars,' even if they are too low in mass to be able to undergo sustained nuclear fusion."

The discovery of this binary brown dwarf will be published in an upcoming issue of The Astrophysical Journal. The discovery paper currently is online in PDF format at http://cfa-www.harvard.edu/~kluhman/paper.pdf

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

The Magellan telescopes are operated by the Carnegie Institution of Washington, the University of Arizona, Harvard University, the University of Michigan, and the Massachusetts Institute of Technology.

Las Campanas Observatory is operated by the Carnegie Observatories, which was founded in 1904 by George Ellery Hale. It is one of six departments of the private, nonprofit Carnegie Institution of Washington, a pioneering force in basic scientific research since 1902.

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