In a First, Astronomers Report Viewing Planets of Other Suns
Friday, November 14, 2008
Staring at his computer screen in May, poking through images of the bright star Fomalhaut, astronomer Paul Kalas found himself staring at a tiny white dot. The dot appeared amid a great ring of dust circling the star. From one image to the next, the dot moved.
For four days, through the Memorial Day weekend, Kalas ransacked the possibilities before settling on a stunning conclusion: He was looking at a world, a giant planet circling Fomalhaut.
"At that point, I had a heart attack. I couldn't sleep. My heart was pounding out of my chest the whole night," Kalas, of the University of California at Berkeley, said this week.
Kalas's discovery was one of two announced yesterday that could be breakthroughs in the search for "extrasolar planets," or "exoplanets," those beyond our own solar system. The other, by Canadian astronomer Christian Marois and his colleagues, may be a triumph in triplicate, for the scientists say they have obtained images of three planets -- a scaled-up version of our solar system -- orbiting a distant star called HR 8799.
"I would have been happy with one planet, but finding three is absolutely amazing. I searched for these planets for eight years," Marois said.
Seeing an extrasolar planet directly was one of the last and most speculative goals of the Hubble Space Telescope when it was put in orbit in 1990, said Edward J. Weiler, associate administrator of NASA's science mission directorate, after a news conference yesterday at the agency's headquarters.
"I actually never thought it would happen," Weiler said. "This is kind of the last crumb on the plate of promises."
If the new claims, being published today in the journal Science, hold up to what is certain to be feverish scrutiny, they will represent significant progress in the census of planets in our galaxy. More than 300 extrasolar planets have been found in the past decade or so, but they have been detected indirectly through changes in starlight. Astronomers can tell they are there but have not been able to see them directly as distinct objects.
These planets are typically many millions or even billions of times fainter than the parent star and are washed out in the glare. But new astronomical instruments and techniques can subtract the starlight and make it possible to capture a planet's reflected light if it is far enough from the star.
The discovery of extrasolar planets is a critical step in the search for life beyond Earth. To date, life has been found only on Earth. There are hints that it might exist on Mars or on some of the moons in our solar system, but that remains speculative. Searches for signals from intelligent civilizations have turned up nothing compelling. But there has been tremendous progress in the hunt for extrasolar planets since the first one was detected in 1995.
Almost all the extrasolar planets identified since then, including those reported yesterday, have been "gas giants" such as Jupiter, in many cases much larger. At this point, the sensitivity of the technology is such that only the biggest planets reveal their presence through fluctuations in the starlight. European and American astronomers have ongoing efforts to drill deeper into the night sky in search of smaller, rocky, Earth-like planets that orbit stars in the "habitable zone" where water might exist in liquid form and life as we know it prosper.
Kalas, 41, began studying Fomalhaut 15 years ago. One of the brightest stars in the sky, it is 25 light-years from Earth, which is just down the block in the cosmic scheme of things. The star is about 200 million years old, quite young compared with the sun. Scientists said the key to finding the planet, called Fomalhaut b, was a new instrument that astronauts placed aboard the Hubble in 2002.
The images show only a small, nearly featureless dot. When asked what the planet would probably look like if seen up close, Kalas said: "I think it would look a lot like Neptune. Surrounded by a swirling disk of dust. In the background, you see Fomalhaut's dust belt, circling the star. A maelstrom of dust."
Marois, meanwhile, used two telescopes in Hawaii to study HR 8799, which is 128 light-years away, still in our same galactic Zip code. Marois, an astronomer with the Herzberg Institute of Astrophysics in Victoria, B.C., saw the first possible planet around HR 8799 this past spring. Then, on July 9, while taking the United flight from San Francisco to Hilo, Hawaii, he discovered what looked like a second planet lurking in the data on his laptop computer. That suggested he had found a planetary system and not just a single world.
"I wanted to yell, but I didn't say anything. I wanted to be in the rental car before actually expressing any emotion," Marois said.
Both Fomalhaut and HR 8799 are much younger and hotter than our sun. Any planets around them would be unlikely to harbor life. But recent advances in astronomy suggest that planets are common. The real estate in space is imponderably vast. Our galaxy is 100,000 light-years in diameter and has upward of 100 billion stars. There are many tens of billions of other visible galaxies.
Astronomers, however, often invoke the famous Carl Sagan rule that "extraordinary claims require extraordinary evidence." The newly discovered objects could be something other than the researchers perceive them to be. If, for example, the objects turn out to be much larger than currently estimated, they would probably be classified not as planets but as "brown dwarfs," objects capable of limited nuclear fusion but not quite big enough to shine like stars.
Astronomer Alan Boss, author of the forthcoming book "The Crowded Universe," said he's not ready to accept that the new objects are truly planets.
"Nothing's a done deal in this business, because we don't know exactly what the masses are," Boss said.
The three planets seen by the Marois team are estimated to be seven to 10 times the mass of Jupiter. That estimate is based on models for how stars and planets form. But Boss said such models have not been precisely calibrated. And Fomalhaut b has its own ambiguities. It is not clear whether the light is coming from a planet or from a disk of dust surrounding a planet.
NASA will launch a telescope called Kepler early next year that is designed to detect Earth-size planets that, in transiting the face of distant stars, dim the starlight. Astronomers hope one day to have space-based telescopes that could inspect planetary light for signs of oxygen, ozone, methane and other signatures of life.
"Is our solar system a freak? A stroke of luck? Will we find other planetary systems like ours?" asked William Borucki, principal scientist for the Kepler mission. "We certainly haven't seen any so far."
Seeing an Earth isn't easy across the depths of space, Borucki added. It is the equivalent of trying to detect a mosquito passing across a car headlight many miles away.