astralavista

In science, as in life, things aren't always what they seem. Take planetary formation.

Back in April 1984, American planetary scientists Bradford Smith and Richard Terrile observed a nearby star called Beta Pictoris and made a startling discovery: for the first time they saw a huge disk of orbiting dust spreading from the star like the swirling skirt of a Russian peasant bride. "I was very, very excited," Terrile told astronomer Ken Croswell, who tells the story in his book Planet Quest. "You look at the fundamental questions of astronomy - the origin of the universe, the origin of life: those are the things that we really, deep down in our souls, want to know, the things that keeps us up at night. Here's a direct link to that," said Terrile.
"Everybody had this feeling that we understood how planets formed, from a flattened disk of material," he told Croswell. "But there was no real hard physical evidence - no picture that you can see. And suddenly, in this blazing, obvious thing, is this picture which is an absolutely classic example of exactly what we thought happened when stars and planets formed. It was a slap in the face that said: Wake up, don't you see what's going on all around you."

Now it looks like we'll need to take another one on the jaw before we figure out how planets form. For Terrile's giddy conjecture about their formation may have been a tad too optimistic. New evidence shows that some disks may just be barren pancakes of dust that will never give birth to any new world.

Scientists from the Harvard-Smithsonian Center for Astrophysics have just discovered a dust disk that is 25 million years old and shows no signs of planet formation. The finding contradicts accepted theory, which says that most protoplanetray disks last only a few million years and rarely longer than 10 million years. "Finding this disk is as unexpected as locating a 200-year-old person," the Center's Lee Hartmann said in a press release. "We don't know why this disk has lasted so long, because we don't know what makes the planetary process start," said his colleague Nuria Calvet.

The disk, which is almost 600 million miles wide, orbits two red dwarf stars located some 350 light years away in the constellation Taurus.

"The disk looks a lot different than most other disks we've seen. This disk looks a lot more evolved than those around younger stars," said Hartmann. "Most stars, by the age of 10 million years, have done whatever they're going to do. If it hasn't made planets by now, it probably never will."

While Hartmann remains pessimistic about the disks chances every bearing a planet, Calvet still gives it a fighting chance. "This disk still has a lot of gas in it, so it may still form giant planets," he said.

Hartmann and Calvet said they want to search for more old disks and find out why some disks survive so much longer than most others.

Said Calvet: "It's important to find more objects like this because they give us clues about the conditions that influence the formation of planets."


Hartmann and Calvet's research will be published in The Astrophysical Journal Letters