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
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
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
Astronomers have suspected a planet orbits Fomalhaut since
2005, when Hubble sent back pictures of a ring or dust belt around the
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
Marc Kuchner, a NASA researcher who specializes exoplanets,
said the photographs of Fomalhaut b could herald a new era of planet
"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,"
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."
Copyright: National Geographic News