Photos of distant planets put astronomers in orbit
Reaching a milestone in the search for Earth-like planets in the universe, two teams of astronomers say they have parted the curtains of space to take the first pictures of planets beyond our solar system.
The first team, led by UC Berkeley researchers, used the Hubble Space Telescope to take a picture of a giant planet orbiting the star Fomalhaut, 25 light-years away.
“It’s almost science fiction,” said Berkeley astronomer Eugene Chiang. “I didn’t think this day would occur until years from now.”
Paul Kalas, the lead astronomer for the Berkeley team, said he “nearly had a heart attack” when he found the new planet, tentatively named Fomalhaut b. “It’s a profound and overwhelming experience to lay eyes on a planet never before seen.”
The other effort relied on the giant Keck and Gemini telescopes in Hawaii to take images of three planets surrounding the young star HR8799, 130 light-years -- about 800 trillion miles -- away.
Scientists compared the imaging of these so-called exoplanets to taking a picture from Los Angeles of a firefly buzzing around a searchlight in New York.
“We’ve been trying to image planets for eight years with no luck and now we have pictures of three planets at once,” said Bruce MacIntosh, an astrophysicist at Lawrence Livermore National Laboratory and one of the leaders of the effort.
Both discoveries were released Thursday by the journal Science and presented at a news conference at NASA headquarters in Washington.
“These two papers will represent a milestone in the field that people will look back on years from now,” said Benjamin Zuckerman, an astronomer at UCLA and a member of the Keck-Gemini team.
Finding Earth-like planets has been a dream of scientists and authors for centuries. Over the last decade, astronomers have found more than 300 exoplanets, but they have all been detected indirectly -- by the slight wobble their gravity causes in their parent stars.
The big challenge to actually seeing planets is that their faint reflected light is easily overwhelmed by the glow of their parent stars.
The two teams used different techniques to solve that problem. To tease out Fomalhaut b, Berkeley’s Kalas relied on Hubble’s Advanced Camera for Surveys, fitted with a coronagraph to screen out the star’s light.
The planet’s existence had been suspected since 2005, when Kalas studied a picture of a dust ring around the star. He noticed the inner edge of the ring was sharply defined, raising his suspicions that there was something hiding there with a lot of gravity. Planets tend to sweep their orbits clean, either by ejecting pretenders or smashing them to dust.
When he studied a new picture, taken in 2006, he found an object in the dust belt. Comparing the two pictures, he determined that it was indeed orbiting the star.
“The gravity of Fomalhaut b is the key reason that the vast dust belt surrounding Fomalhaut is cleanly sculpted into a ring and offset from the star,” Kalas said. “We predicted this in 2005, and now we have the direct proof.”
The planet would not be capable of supporting life as we know it. At 11 billion miles from its star, about three times as far from its sun as Pluto is from ours, it would be too frigid.
Fomalhaut b, at between one and three Jupiter masses, is the lowest-mass planet yet found outside our solar system, Chiang said, and its discovery brings the day closer when researchers might be able to find Earth-like planets.
The planet has some surprising characteristics. For one thing, it is bluish, rather than the redder hue scientists expected.
“Both discoveries are causing us to re-question what a planet is,” Sara Seager, a planetary scientist at the Massachusetts Institute of Technology, said at the news conference.
The second team, which included researchers from Lawrence Livermore, UCLA and the NRC Herzberg Institute of Astrophysics in Canada, took its photographs in infrared light.
Two breakthroughs made this discovery possible. First was the use of adaptive optics -- a set of optical techniques that correct for the interference of Earth’s atmosphere, which bends and twists incoming light. In recent years, adaptive optics has become so sophisticated that ground telescopes can take pictures nearly as eye-popping as those from Hubble. Because the mirrors of Gemini and Keck are so large, 26 and 32 feet across, they can gather even more light.
Scientists estimated the three planets were seven to 10 times the size of Jupiter, just under the 13-Jupiter-mass-limit that scientists believe separates planets from brown dwarfs, which are failed stars. Like Fomalhaut b, they are far from their parent star, ranging from 24 to 67 astronomical units. An astronomical unit is the distance from Earth to the sun, about 93 million miles.
But this time it wasn’t their distance from HR8799 that enabled the researchers to spot them. It was their youth. They are only about 60 million years old. Researchers realized young planets would still be glowing from their formation, generating enough heat to be seen in the infrared spectrum.
“Seeing these planets directly -- separating their light from the star -- lets us study them as individuals, and use spectroscopy to study their properties, like temperature or composition,” said MacIntosh.
It appears all three planets have complex atmospheres, with dusty clouds that trap radiating heat, scientists said.
Not everyone was ready to pop champagne corks. Alan Boss, a physicist with the Carnegie Institution in Washington, said he still needed more evidence to be convinced. “Only time will tell,” he said.
European planet-hunters using the Very Large Telescope in Chile made claims a couple of years ago that they had imaged exoplanets, but those claims were disputed by scientists who believed the planets were actually brown dwarfs.
The twin discoveries mean researchers have found alien planets whose orbits are close to (seen using the wobble technique) and far away from (via direct imaging studies) stars outside our solar system. That still leaves a vast area in between, where any Earth-like planets are likely to reside.
Probing that territory awaits at least one leap forward in technology. The first is a new and improved adaptive optics system called the Gemini Planet Imager. Expected to be 100 times more sensitive than current instruments, it should be able to find planets the size of Jupiter around other stars.
It is expected to be in operation on the Gemini South telescope in Chile in 2011.
HR8799 will be a key target.
“I think there’s a very high probability that there are more planets in the system that we can’t detect yet,” MacIntosh said.
Finding the next Earth could require a leap beyond that, perhaps with a space mission such as the Terrestrial Planet Finder. Proposed by NASA several years ago, it would include a suite of space-based observatories outfitted to search for Earth-like planets in our neighborhood of space.
That mission has been deferred for budgetary reasons.