Planet
Trawling
Summary (May 24,
2006): An international team of professional and amateur
astronomers, using simple off-the-shelf equipment to trawl the
skies for planets outside our solar system, has hauled in its
first "catch."
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Planet Trawling
based on a HUBBLESITE
release
 |
This artist's impression shows a
dramatic close-up of the extrasolar planet, called
XO-1b, passing in front of a Sun-like star 600
light-years from Earth. The Jupiter-sized planet is in a
tight four-day orbit around the star.
Credit:
NASA, ESA, and P. McCullough (STScI)
|
An international team of
professional and amateur astronomers, using simple
off-the-shelf equipment to trawl the skies for planets outside
our solar system, has hauled in its first "catch."
The
astronomers discovered a Jupiter-sized planet orbiting a
Sun-like star 600 light-years from Earth in the constellation
Corona Borealis. The team, led by Peter McCullough of the
Space Telescope Science Institute in Baltimore, Md., includes
four amateur astronomers from North America and
Europe.
Using modest telescopes to search for
extrasolar planets allows for a productive collaboration
between professional and amateur astronomers that could
accelerate the planet quest.
"This discovery suggests
that a fleet of modest telescopes and the help of amateur
astronomers can search for transiting extrasolar planets many
times faster than we are now," McCullough said. The finding
has been accepted for publication in the Astrophysical
Journal.
McCullough deployed a relatively inexpensive
telescope made from commercial equipment to scan the skies for
extrasolar planets. Called the XO telescope, it consists of
two 200-millimeter telephoto camera lenses and looks like a
pair of binoculars. The telescope is on the summit of the
Haleakala volcano, in Hawaii.
"To replicate the XO
prototype telescope would cost $60,000," McCullough explained.
"We have spent far more than that on software, in particular
on designing and operating the system and extracting this
planet from the data."
McCullough's team found the
planet, dubbed X0-1b, by noticing slight dips in the star's
light output when the planet passed in front of the star,
called a transit. The light from the star, called XO-1, dips
by approximately 2 percent when the planet XO-1b passes in
front of it. The observation also revealed that X0-1b is in a
tight four-day orbit around its parent star.
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| Astronomers used this inexpensive
telescope to find an extrasolar planet. The telescope,
which looks like a pair of binoculars, consists of two
200-millimeter telephoto camera lenses. The lenses are
attached to electronic devices that measured slight dips
in light output from the star, indicating that an object
was crossing in front of it. The telescope is on the
summit of the Haleakala volcano in Hawaii. Credit:
NASA, ESA, and J. Stys (STScI)
|
Although astronomers have
detected more than 180 extrasolar planets, X0-1b is only the
tenth planet discovered using the transit method. It is the
second planet found using telephoto lenses. The first, dubbed
TrES-1, was reported in 2004. The transit method allows
astronomers to determine a planet's mass and size. Astronomers
use this information to deduce the planet's characteristics,
such as its density.
The team confirmed the planet's
existence by using the Harlan J. Smith Telescope and the
Hobby-Eberly Telescope at the University of Texas's McDonald
Observatory to measure the slight wobble induced by the planet
on its parent star. This so-called radial-velocity method
allowed the team to calculate a precise mass for the planet,
which is slightly less than that of Jupiter (about 0.9 Jupiter
masses). The planet also is much larger than its mass would
suggest. "Of the planets that pass in front of their stars,
XO-1b is the most similar to Jupiter yet known, and the star
XO-1 is the most similar to the Sun," McCullough said,
although he was quick to add, "but XO-1b is much, much closer
to its star than Jupiter is to the Sun."
The
astronomer's innovative technique of using relatively
inexpensive telescopes to look for eclipsing planets favors
finding planets orbiting close to their parent stars. The
planet also must be large enough to produce a measurable dip
in starlight.
The planet is the first discovered in
McCullough's three-year search for transiting extrasolar
planets. The planet quest is underwritten by a grant from
NASA's Origins program.
McCullough's planet-finding
technique involves nightly sweeps of the sky using the XO
telescope in Hawaii to note the brightness of the stars it
encounters. A computer software program sifts through many
thousands of stars every two months looking for tiny dips in
the stars' light, the signature of a possible planetary
transit. The computer comes up with a few hundred
possibilities. From those candidates, McCullough and his team
select a few dozen promising leads. He passes these stars on
to the four amateur astronomers to study the possible transits
more carefully.
From September 2003 to September 2005,
the XO telescope observed tens of thousands of bright stars.
In that time, his team of amateur astronomers studied a few
dozen promising candidate stars identified by McCullough and
his team. The star X0-1 was pegged as a promising candidate in
June 2005. The amateur astronomers observed it in June and
July 2005, confirming that a planet-sized object was eclipsing
the star.
McCullough's team then turned to the McDonald
Observatory in Texas to obtain the object's mass and verify it
as a planet. He received the news of the telescope's
observation at 12:06 a.m. Feb. 16, 2006, from Chris
Johns-Krull, a friend and colleague at Rice
University.
"It was a wonderful feeling because the
team had worked for three years to find this one planet,"
McCullough explained. "The discovery represents a few bytes
out of nearly a terabyte of data: It's like trying to distill
gold out of seawater."
 |
Spitzer Space Telescope, the fourth
and final element in NASA's family of Great
Observatories.
Credit: Ball Aerospace &
Technologies Corp., 2003 |
The
discovery also has special familial significance for the
astronomer. "My father's mentor was Harlan J. Smith, the man
whose ambition and hard work produced the telescope that we
used to acquire the verifying data."
McCullough
believes the newly found planet is a perfect candidate for
study by the Hubble and Spitzer space telescopes. Hubble can
measure precisely the star's distance and the planet's size.
Spitzer can actually see the infrared radiation from the
planet. By timing the disappearance of the planet behind the
star, Spitzer also can measure the "ellipticity," or
"out-of-roundness," of the planet's orbit.
If the orbit
is elliptical, then the varying gravitational force would
result in extra heating of the planet, expanding its
atmosphere and perhaps explaining why the object's diameter
seems especially large for a body of its calculated
mass.
"By timing the planet's passages across the star,
both amateur and professional astronomers might be lucky
enough to detect the presence of another planet in the XO-1
system by its gravitational tugs on XO-1b," McCullough said.
"It's even possible that such a planet could be similar to
Earth."
Related Web Pages
The
Search for More Earths ET: The
Exoplanet TrackerTrio of
Neptunes McDonald ObservatoryAstrobiology
Magazine New Planets Rice University Extrasolar
Planets Encyclopedia
Planet Quest
(JPL)
Boston
UniversityDarwin Mission University
of Hawaii's IfA Note:
New
Planets
Display Options: Wednesday, May 24, 2006
