by Robert Roy Britt
Senior Science Writer
01 April 2005
After a few close calls, astronomers
have finally obtained the first photograph of a planet beyond our
solar system, SPACE.com has learned.
this time they say theyíre sure. Though some doubt lingers about the
mass of the object. The planet is thought to be one to two times as
massive as Jupiter, according to the scientists who imaged it. It
orbits a star similar to a young version of our Sun.
The young star
GQ Lupi (A), and its fainter planetary companion (b). Image
The star, GQ Lupi, (click image
right) has been observed by a team of European astronomers
since 1999. They have made three images using the Very Large
Telescope (VLT) of the European Southern
Observatory (ESO) in Chile. The Hubble Space
Telescope and the Japanese Subaru Telescope
each contributed an image, too.
The work was led by Ralph Neuhaeuser of the Astrophysical
Institute & University Observatory (AIU).
"The detection of the faint object
near the bright star is certain," Neuhaeuser told
SPACE.com on Friday.
The system is young, so the planet is
rather warm, like a bun fresh out of the oven. That warmth made it
comparatively easier to see in the glare of its host star compared
with more mature planets. Also, the planet is very far from the star
-- about 100 times the distance between Earth and the Sun, another
factor in helping to separate the light between the two objects.
The discovery will be detailed in an upcoming issue of the
journal Astronomy & Astrophysics. Neuhaeuserís co-authors
include Ph.D. student Markus Mugrauer, who performed the
observations, and Guenther Wuchterl.
The object appears to be "the first directly imaged and confirmed
companion to a Sun-like star, and as such [would mark] the dawn of a
new era in planet detection," said Ray Jayawardhana, a
University of Toronto researcher who was not involved in the
discovery but has seen the scientific paper.
Jayawardhana added, though, that some models used to estimate
the objectís heft show it could be tens of times as massive as
Jupiter, in which case it might cross over into the territory,
bulk-wise, of a failed type of star known as a brown dwarf.
Other recent milestones
Over the past decade, astronomers have found about 150 extrasolar
planets. The vast majority have only been detected indirectly,
by noting wobbles that the planets induce in their stars.
Earlier this month, astronomers announced the detection of a
planetís infrared light using the
Spitzer Space Telescope.
But that observation did not involve a photograph. Instead, the
systemís total light was seen to drop when the planet was eclipsed
by the star.
Late last year, another European team announced what
might have been
the first photograph of an extrasolar planet. That
planet candidate has
yet to be confirmed, however, because itís not
yet clear whether it is orbiting the star or if it might be an
object in the distant background. And even if it is a planet,
it is an unusually large one -- several times the mass of
Jupiter -- and it orbits a failed star known as a
The object around GQ Lupi is clearly linked to the
"The separation between star and
planet has not changed from 1999 to 2004, which means that they
move together on the sky," Neuhaeuser said. "In our case,
we do have a normal plain image showing the bright star and the
faint planet a little bit west of the star. The planet is only
156 times fainter than the star, because the planet is still
very young and hence still forming, still contracting."
This object "appears to pass" the
observational tests "for being a very low mass companion to its
parent star," Jayawardhana said.
Familiar yet different
picture of GQ Lupi and its planet is exciting to
astronomers because the system resembles in some respects our own
solar system in its formation years.
The planet is about 3,140 degrees Fahrenheit (2000 Kelvin) -- not
the sort of place that would be expected to support life.
Neuhaeuserís team has also detected water in the planetís
atmosphere. The world is expected to be gaseous, like
Jupiter. It is about twice the diameter of Jupiter.
The mass estimate -- one to two times that of Jupiter
-- is "somewhat uncertain," Neuhaeuser said.
The planet is three times farther from GQ Lupi than
Neptune is from our Sun.
"We should expect that the planet
orbits around the star, but at its large separation one orbital
period [a year] is roughly 1,200 years, so that orbital motion
is not yet detected."
Itís not known why it is so far out.
"It is unlikely, but not impossible,
that the planet formed at that large separation, because
circumstellar disks around other stars often are that large or
even larger," Neuhaeuser said.
Or perhaps the planet had a close brush
with another developing world. The interaction could have thrown the
newly discovered planet outward while tossing the other one, which
has not been detected, in toward the star. Itís also possible the
newfound planet has a highly elliptical orbit and is currently near
its outer bounds.
The star GQ Lupi is part of a star-forming region
about 400 light-years away. At 70 percent the mass of the Sun, it is
"quite similar to our Sun," Neuhaeuser said. But
GQ Lupi is only about 1 million years old. The Sun is
middle-aged, at 4.6 billion years old.
"Whatís most intriguing about this discovery is that it raises a
plethora of new questions regarding the origin of a this object so
far out from its parent star," Jayawardhana, who is an expert
on the disks around young stars from which planets form, said in a
Jayawardhana wonders whether it formed in a protoplanetary
disk much closer in, roughly where Jupiter is in our
solar system, and then get flung out. Or, perhaps more likely, if it
was born almost at the same time as its star, fragmenting out of a
contracting protostellar cloud as a brown dwarf companion.
"One way or another, this object
must have formed pretty quickly" given the starís age, he said.
Knots of gas and dust have been detected
around other young stars in setups that astronomers believe are
solar systems in the making. Theorists believe our solar system
formed when the Sunís leftovers developed into a
thin disk of
orbiting material. Rocky planets like Earth formed when chunks stuck
do not agree, however, how gas giants are
Alan Boss, a planet formation theorist at Carnegie
Institution of Washington, called the image "really exciting."
But he said there is "one little nagging doubt" in that the objectís
mass is only an estimate.
Christophe Dumas, who worked on the European team that
announced a possible photo of an extrasolar planet last year,
said of the new image: "There is still a large uncertainty on what
the mass of this object is."
Weighing it precisely would involve noting the gravitational wobble
the apparent planet induces on the star, but this object is too far
from the star to produce a meaningful wobble. Yet even if the object
is four times the mass of Jupiter it would still be considered a
planet, Boss said in a telephone interview.
"I think thereís a really good
chance that this is an historic photo," Boss said.