Press Release

Telescope Network Finds Far Away Planet

By SpaceRef Editor
August 24, 2004
Filed under , ,
Telescope Network Finds Far Away Planet

This is a joint announcement from the Astrophysical Institute of the
Canaries (IAC), National Center for
Atmospheric Research (NCAR), Harvard-Smithsonian Center for Astrophysics
(CfA), Lowell Observatory,
and California Institute of Technology.

Note to Editors: High-resolution artwork and animation of the newly
discovered planet TrES-1 is posted online at

Network of Small Telescopes Discovers Distant Planet

Flagstaff, AZ — Fifteen years ago, the largest telescopes in the world
had yet to locate a planet orbiting another star.
Today telescopes no larger than those available in department stores are
proving capable of spotting previously unknown
worlds. A newfound planet detected by a small, 4-inch-diameter telescope
demonstrates that we are at the cusp of a new
age of planet discovery. Soon, new worlds may be located at an
accelerating pace, bringing the detection of the first
Earth-sized world one step closer.

“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 study.

This is the first extrasolar planet discovery made by a dedicated survey
of many thousands of relatively bright stars
in large regions of the sky. It was made using the Trans-Atlantic
Exoplanet Survey (TrES), a network of small,
relatively inexpensive telescopes designed to look specifically for
planets orbiting bright stars. A team of scientists
co-led by Edward Dunham of Lowell Observatory, Timothy Brown of NCAR,
and David Charbonneau (CfA),
developed the TrES network. The network’s telescopes are located in
Palomar Observatory (California, USA),
Lowell Observatory (Arizona, USA), and the Canary Islands (Spain).

“The advantage of working as a network is that we can ‘stretch the
night’ and monitor our fields for a longer time,
increasing our chance of discovering a planet,” says Georgi Mandushev
(Lowell Observatory), a co-author of the paper.

This research study is posted online at and will appear in an upcoming
issue of
The Astrophysical Journal Letters.

“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
co-author David Charbonneau (CfA/Caltech).

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 operates the world’s two largest
telescopes in Hawaii for the University of California, Caltech, and
NASA, were particularly crucial in
confirming the planet’s existence.

Planet Shadows

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 world circles its star every 3.03 days at a
distance of only 4 million miles (6 million kilometers),
much closer and faster than the planet Mercury in our solar system.

Although such planets are relatively common, astronomers used an
uncommon technique to discover it. This world
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.

“This Jupiter-sized planet was observed doing the same thing that
happened in June when Venus moved across
(or transited) the face of our Sun,” says Mandushev. The difference is
that this planet is outside of our solar system,
roughly 500 light years away.”

To be successful, transit searches must examine many stars because we
only see a transit if a planetary system is
located nearly edge-on to our line of sight. A number of different
transit searches currently are underway. Most
examine limited areas of the sky and focus on fainter stars because they
are more common, thereby increasing
the chances of finding a transiting system. However the TrES network
concentrates on searching brighter stars in
larger swaths of the sky because planets orbiting bright stars are
easier to study directly.

“All that we have to work with is the light that comes from the star,”
says Tim Brown (NCAR), a study co-author.
“It’s much harder to learn anything when the stars are faint.”

Most known extrasolar planets were found using the “Doppler method,”
which detects a planet’s gravitational
effect on its star by looking for motions in the star’s spectrum, or
rainbow of colors. However, the information that
can be gleaned about a planet using the Doppler method is 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 brown dwarf whose orbit
is highly inclined to our line of sight produces the same 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 of 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 Charbonneau.

Sorting Suspects

The TrES survey examined approximately 12,000 stars in 36 square degrees
of the sky (about half of the size
of the bowl of the Big Dipper) in the constellation Lyra. Roi Alonso
(IAC), a graduate student of Brown’s,
identified 16 possible candidates for planet transits. “The TrES survey
gave us our initial line-up of suspects.
Then, we 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
used telescopes at CfA’s Whipple Observatory
in Arizona, Oak Ridge Observatory in Massachusetts, and Lowell
Observatory in Arizona to obtain additional
photometric (brightness) observations, as well as spectroscopic
observations that eliminated eclipsing binary stars.

In a matter of two month’s time, the team had zeroed in on the most
promising candidate. High-resolution
spectroscopic observations by Torres 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 a spectroscopic orbit for the parent star.
That’s why the Keck observations of this star
were so important in proving that we had found a true planetary system,”
says co-author David Latham (CfA).

Remarkably Normal

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 helium, the most common elements in the Universe. But
unlike Jupiter, it orbits very 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 transiting planet, HD 209458b. The latter world
contains about the same mass as TrES-1,
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
209458b is an ‘oddball’ planet,” says Charbonneau.

TrES-1 orbits its star every 72 hours, placing it among a group of
similar planets known as “hot Jupiters.” Such
worlds likely formed much further away from their stars and then
migrated inward, sweeping away any other planets
in the process. The many planetary systems found to contain hot Jupiters
indicate that our solar system may be
unusual for its relatively quiet history.

Both the close orbit of TrES-1 and its migration history make it
unlikely to 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 planet’s atmosphere.

The paper, “TrES-1: The Transiting Planet of a Bright K0V Star,”
describing these results is authored by:
Roi Alonso (IAC); Timothy M. Brown (NCAR); Guillermo Torres and David W.
Latham (CfA); Alessandro Sozzetti
(University of Pittsburgh/CfA); Georgi Mandushev (Lowell Observatory),
Juan A. Belmonte (IAC); David Charbonneau
(CfA/Caltech); Hans J. Deeg (IAC); Edward W. Dunham (Lowell
Observatory); Francis T. O’Donovan (Caltech); and
Robert Stefanik (CfA).

The W.M. Keck Observatory is operated by the California Association for
Research in Astronomy, a scientific
partnership of the California Institute of Technology, the University of
California, and the
National Aeronautics and Space Administration (NASA).

Funding for the research that led to this planet’s discovery was
provided by NASA’s Origins of Solar Systems Program.

Founded in 1894, Lowell Observatory pursues the study of astronomy,
conducts pure research in
astronomical phenomena, and maintains quality public education and
outreach programs.

For more information, contact:

Steele Wotkyns

Public Relations Manager

Lowell Observatory

(928) 233-3232

SpaceRef staff editor.