Astronomers See Evidence for Youngest Planet
By Robert Roy Britt
Senior Science Writer
posted: 02:45 pm ET
27 May 2004
Astronomers have found evidence for what could be the youngest planet ever detected, a world no more than a million years old circling a distant star.
The finding was part of a trio of discoveries from the Spitzer Space Telescope announced at a NASA press conference today.
The orbiting observatory also spotted the raw materials for life — water and other prebiotic chemistry — in planetary construction zones around five young, Sun-like stars in the constellation Taurus, 420 light-years from Earth.
"We’ve seen the building blocks of habitable planets for the first time unambiguously" in stars that will turn out like our Sun, said Dan Watson, professor of physics and astronomy at the University of Rochester in New York.
And Spitzer uncovered a stellar nursery where at least two developing stars, called protostars, contain the gas and dust needed to form planets. The study suggests up to 300 of the stars in the cluster may be similarly equipped.
The three discoveries are seen as related, all pointing to the possibility that planet formation is common and that even Earth-like planets, which might support life, may not be rare.
Behind the veil
Spitzer records infrared light, which allows it to peer through the planet-forming envelopes of dust that surround newborn stars. Our own solar system, now 4.6 billion years old, was once shrouded in a similar cocoon, astronomers believe.
"By seeing what’s behind the dust, Spitzer has shown us star and planet formation is a very active process in our galaxy," said Ed Churchwell, an astronomy professor at the University of Wisconsin, Madison.
The candidate for youngest known planet is not visible and so must be confirmed by future observations, but the infrared view showed there’s a clear hole in a disk of dust circling a young star named CoKu Tau 4. Theorists say such a hole — this one is 10 times the size of Earth’s orbit around the Sun — would most likely be created by a newborn planet that acted as a cosmic broom. Similar holes have signaled planets around other stars, but none so young.
The star’s age is fairly easy to determine, and it’s set at 1 million years. The planet would have had to form within a million years, too.
"That probably makes it the youngest planet we’ve ever seen," Watson said.
It also puts yet another thorn in the side of the standard model for planet formation, which says ice and dust stick together and collide with ever-larger rocks until a giant core is formed, then gas can be drawn into the mix. That process takes some 4 million years, however, said Alan Boss, a theorist at the Carnegie Institution of Washington who was not involved in the observations.
The other way
Boss argues that planets — especially gas giant planets like Jupiter — form instead when instabilities in the disk of leftover material circling a star collapse. His method can build the guts of a planet in 1,000 years.
The new observations fit neatly with his scheme.
That’s important because in dense star-formation regions, where most Sun-like stars form, a giant, outer planet may have just 100,000 years to get going before radiation from nearby massive stars strips all the raw material away.
Boss was also excited to learn of Spitzer’s observations of water ice, methanol and carbon dioxide collecting on the dust in disks around the five young, Sun-like stars. These are the ingredients of comets, which theorists figure helped prepare Earth for life by filling its oceans and adding the right organic chemistry.
Other searches have found organic chemicals around stars, but this is the first time the goods were clearly in a disk of material that could form planets.
"If our assumptions are correct" about the Spitzer observations, the work has "profound implications" for the number of planets that probably exist, Boss said. "It may very well be that solar systems like our own are not rare in our galaxy."