CfA Press Release
Release No.: 04-27|
For Release: 11:00 a.m. EDT, Tuesday, August 24, 2004
Note to editors: High-resolution artwork of the newly discovered planet
TrES-1 will be posted online at
Tiny "David" Telescope Finds "Goliath" Planet
Cambridge, MA--Fifteen years ago, the largest telescopes in the world
yet to locate a planet orbiting another star. Today telescopes no larger
than those available in department stores are proving capable of
previously unknown worlds. A newfound planet detected by a small,
4-inch-diameter telescope demonstrates that we are at the cusp of a new
of planet discovery. Soon, new worlds may be located at an accelerating
pace, bringing the detection of the first Earth-sized world one step
"This discovery demonstrates that even humble telescopes can make huge
contributions to planet searches," says Guillermo Torres of the
Harvard-Smithsonian Center for Astrophysics (CfA), a co-author on the
This research study will be posted online at
http://arxiv.org/abs/astro-ph/0408421 and will appear in an upcoming
of The Astrophysical Journal Letters.
This is the very first extrasolar planet discovery made by a dedicated
survey of many thousands of relatively bright stars in large regions of
sky. It was made using the Trans-Atlantic Exoplanet Survey (TrES), a
of small, relatively inexpensive telescopes designed to look
for planets orbiting bright stars. A team of scientists co-led by David
Charbonneau (CfA/Caltech), Timothy Brown of the National Center for
Atmospheric Research (NCAR) and Edward Dunham of Lowell Observatory
developed the TrES network. Initial support for the TrES network came from NASA's Jet Propulsion Laboratory and the California Institute of Technology.
"It took several Ph.D. scientists working full-time to develop the data
analysis methods for this search program, but the equipment itself uses
simple, off-the-shelf components," says Charbonneau.
Although the small telescopes of the TrES network made the initial
discovery, follow-up observations at other facilities were required.
Observations at the W.M. Keck Observatory which, for the University of
California, Caltech, and NASA, operates the world's two largest
in Hawaii, were particularly crucial in confirming the planet's
The newfound planet is a Jupiter-sized gas giant orbiting a star located
about 500 light-years from the Earth in the constellation Lyra. This
circles its star every 3.03 days at a distance of only 4 million miles,
closer and faster than the planet Mercury in our solar system.
Astronomers used an innovative technique to discover this new world. It was found by the "transit method," which looks for a dip in a star's brightness when a planet crosses directly in front of the star and casts a shadow. A Jupiter-sized planet blocks only about 1/100th of the light from a Sun-like star, but that is enough to make it detectable.
To be successful, transit searches must examine many stars because we
see a transit if a planetary system is located nearly edge-on to our line
sight. A number of different transit searches currently are underway.
examine limited areas of the sky and focus on fainter stars because they
more common, thereby increasing the chances of finding a transiting
However the TrES network concentrates on searching brighter stars in
swaths of the sky because planets orbiting bright stars are easier to
"All that we have to work with is the light that comes from the star,"
Brown. "It's much harder to learn anything when the stars are faint."
"It's almost paradoxical that small telescopes are more efficient than the largest ones if you use the transit method, since we live in a time when astronomers already are planning 100-meter-diameter telescopes," says lead author Roi Alonso of the Astrophysical Institute of the Canaries (IAC), who discovered the new planet.
Most known extrasolar planets were found using the "Doppler method,"
detects a planet's gravitational effect on its star spectroscopically by
breaking the star's light into its component colors. However, the
information that can be gleaned about a planet using the Doppler method
limited. For example, only a lower limit to the mass can be determined
because the angle at which we view the system is unknown. A high-mass
dwarf whose orbit is highly inclined to our line of sight produces the
signal as a low-mass planet that is nearly edge-on.
"When astronomers find a transiting planet, we know that its orbit is
essentially edge-on, so we can calculate its exact mass. From the amount
light it blocks, we learn its physical size. In one instance, we've even
been able to detect and study a giant planet's atmosphere," says
The TrES survey examined approximately 12,000 stars in 36 square degrees
the sky (an area half the size of the bowl of the Big Dipper). Roi Alonso,
graduate student of Brown's, identified 16 possible candidates for
transits. "The TrES survey gave us our initial line-up of suspects. Then,
had to make a lot of follow-up observations to eliminate the imposters,"
says co-author Alessandro Sozzetti (University of Pittsburgh/CfA).
After compiling the list of candidates in late April, the researchers
telescopes at CfA's Whipple Observatory in Arizona and Oak Ridge
in Massachusetts to obtain additional photometric (brightness)
as well as spectroscopic observations that eliminated eclipsing binary
In a matter of two month's time, the team had zeroed in on the most
promising candidate. High-resolution spectroscopic observations by
and Sozzetti using time provided by NASA on the 10-meter-diameter Keck I
telescope in Hawaii clinched the case.
"Without this follow-up work the photometric surveys can't tell which of
their candidates are actually planets. The proof of the pudding is an
for the parent star, and we got that using the Doppler method. That's
the Keck observations of this star were so important in proving that we
found a true planetary system," says co-author David Latham (CfA).
The planet, called TrES-1, is much like Jupiter in mass and size
It is likely to be a gas giant composed primarily of hydrogen and
the most common elements in the Universe. But unlike Jupiter, it orbits
close to its star, giving it a temperature of around 1500 degrees F.
Astronomers are particularly interested in TrES-1 because its structure
agrees so well with theory, in contrast to the first discovered
planet, HD 209458b. The latter world contains about the same mass as
yet is around 30% larger in size. Even its proximity to its star and the
accompanying heat don't explain such a large size.
"Finding TrES-1 and seeing how normal it is makes us suspect that HD
is an `oddball' planet," says Charbonneau.
TrES-1 orbits its star every 72 hours, placing it among a group of
planets known as "hot Jupiters." Such worlds likely formed much further
from their stars and then migrated inward, sweeping away any other
in the process. The many planetary systems found to contain hot Jupiters
indicate that our solar system may be unusual for its relatively quiet
Both the close orbit of TrES-1 and its migration history make it unlikely
possess any moons or rings. Nevertheless, astronomers will continue to
examine this system closely because precise photometric observations may
detect moons or rings if they exist. In addition, detailed spectroscopic
observations may give clues to the presence and composition of the
The paper describing these results is authored by: Roi Alonso (IAC);
M. Brown (NCAR); Guillermo Torres and David W. Latham (CfA); Alessandro
Sozzetti (University of Pittsburgh/CfA); Georgi Mandushev (Lowell), Juan
Belmonte (IAC); David Charbonneau (CfA/Caltech); Hans J. Deeg (IAC);
W. Dunham (Lowell); Francis T. O'Donovan (Caltech); and Robert Stefanik
This joint announcement is being issued simultaneously by CfA, IAC, NCAR, the University of Pittsburgh, and Lowell Observatory.
The W.M. Keck Observatory is operated by the California Association for
Research in Astronomy, a scientific partnership of the California
of Technology, the University of California, and the National
and Space Administration.
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.
National Center for Atmospheric Research press release
Astrophysical Institute of the Canaries press release
Lowell Observatory press release
For more information, contact:
David Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7462 Fax: 617-495-7468
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016