First Pictures of Alien Planet System Revealed
for National Geographic News
|November 13, 2008|
Astronomers today unvieled unprecedented glimpses of alien planets, including the first ever images of another multiplanet system and the first visible-light images of a planet outside the solar system.
The discoveries represent major advances in our planet-finding abilities and raise hopes for perhaps the ultimate astronomical milestone: the first picture of an Earthlike planet.
Planets outside our solar system—called exoplanets—are usually detected only indirectly, without any kind of visual confirmation of the planets.
Their gravitational fields can induce detectable "wobbles" in their host stars, for example. Or when a planet crosses in front of its star, the planet can "bend" the starlight, tipping off scientists.
Actual imaging of an extrasolar planet, though, is nearly unheard of. (See "First Picture of Alien Planet Orbiting Sunlike Star?" [September 15, 2008]).
"It's something that people have understood for a long time, but this is the first time you can actually see a picture of planets going around a star," NASA researcher Mark Marley said.
"It's like you know that there's somebody in the next room, but now you open the door and you see what they look like," said Marley, who was not involved with either of two exoplanet studies published today on the Web site of the journal Science.
Alien Star System
Earth-based telescopes captured the multiplanet system, which orbits the star HR 8799, in a frame-by-frame movie, according to one of the new studies.
The relatively new infrared technology used by Hawaii's Gemini North telescope and the W.M. Keck Observatory had previously captured a single exoplanet in 2004 (see picture). Infrared light is invisible to the naked eye.
With the new direct-imaging technique, astronomers were able to confirm the planets' presence by observing the system for less an hour total, though over the course of several months, said HR 8799 study leader Christian Marois of Canada's Herzberg Institute of Astrophysics.
By contrast, indirect methods of verifying an exoplanet require many different types of information and sometimes waiting for a suspected planet to make a complete orbit of its star—which in the case of the HR 8799 system would have taken about 450 years.
60 Million Years Young
About 130 light-years from Earth, HR 8799 is visible in autumn from the Northern Hemisphere with binoculars shortly after sunset, Marois said.
Unlike our solar system, which is believed to have formed about 4.6 billion years ago, HR 8799 and the planets around it are probably about 60 million years old, Marois said.
The three planets are giant—probably around seven times the mass of Jupiter, Marois said.
"The next step is to do spectroscopy"—the study of the light wavelengths emanating from the planets—"to be able to study their composition and the details of the atmosphere," Marois said.
The second big exoplanet discovery this week is Fomalhaut b, the first exoplanet to be captured in a visible-light photograph, according to study leader Paul Kalas of the University of California, Berkeley. The work isbased on pictures taken by the Hubble Space Telescope.
Fomalhaut b is no more than three times the mass of Jupiter, Kalas said.
The planet takes 872 years to orbit its star, Fomalhaut, one of our closest neighbors at 25-light years from Earth. Sky-watchers in the Northern Hemisphere can see this bright star in the summer as part of the constellation Piscus Austrinus (Southern Fish), the astronomer said.
Astronomers have suspected a planet orbits Fomalhaut since 2005, when Hubble sent back pictures of a ring or dust belt around the star.
Signs of a planet's gravitational pull were visible in the dust belt's sharply defined inner edge and in the ring's off-center arrangement. (See the telltale 2005 image.)
"We're really excited, because not only do we have a planet, we can see how it interacts with this vast belt of comets and asteroids," Kalas said.
Marc Kuchner, a NASA researcher who specializes exoplanets, said the photographs of Fomalhaut b could herald a new era of planet detection.
"There are many other rings around stars like Fomalhaut that are probably pointing the way to planets," said Kuchner, who was not involved with the studies published today.
"It suggests that there's going to be a whole series of discoveries like this."
The Next Earth?
The exoplanets reported today are gaseous, like Jupiter. The next step will be to find rocky planets like Earth—planets that could potentially harbor life as we know it.
Kuchner said such detection will require instruments that are one thousand to ten thousand times stronger than those in use today—which is no reason to be discouraged, he said.
"When there are exciting discoveries like the ones [announced today], you never know what that will do to make things go faster, to inspire people to come up with new ideas and find new resources," Kuchner said.
Still, most scientists expect the discovery of another Earth will take some time.
"I think everybody is dreaming the dream of taking a picture of a terrestrial planet orbiting a star," the Herzberg Institute's Marois said. "But I think that's going to take a while."
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