Artist's rendering of a possible exoplanetary system with a gas-giant
planet orbiting close to his parent star which is more massive than our
sun.
Artwork by Lynette Cook
Credit: Gemini Observatory/AURA. Full Resolution TIFF (6MB) | Full Resolution JPEG (2MB) | Medium Resolution JPEG (296KB)
Gemini Observatory’s Planet-Finding Campaign finds that, around many types of stars, distant gas-giant planets are rare and prefer to cling close to their parent stars. The impact on theories of planetary formation could be significant.
Finding extrasolar planets has become so commonplace that it seems
astronomers merely have to look up and another world is discovered.
However, results from Gemini Observatory’s recently completed
Planet-Finding Campaign – the deepest, most extensive direct imaging
survey to date – show the vast outlying orbital space around many types
of stars is largely devoid of gas-giant planets, which apparently tend
to dwell close to their parent stars.
“It seems that gas-giant exoplanets are like clinging offspring,” says
Michael Liu of the University of Hawaii’s Institute for Astronomy and
leader of the Gemini Planet-Finding Campaign. “Most tend to shun orbital
zones far from their parents. In our search, we could have found gas
giants beyond orbital distances corresponding to Uranus and Neptune in
our own Solar System, but we didn’t find any.” The Campaign was
conducted at the Gemini South telescope in Chile, with funding support
for the team from the National Science Foundation and NASA. The
Campaign’s results, Liu says, will help scientists better understand how
gas-giant planets form, as the orbital distances of planets are a key
signature that astronomers use to test exoplanet formation theories.
Eric Nielsen of the University of Hawaii, who leads a new paper
about the Campaign’s search for planets around stars more massive than
the Sun, adds that the findings have implications beyond the specific
stars imaged by the team. "The two largest planets in our Solar System,
Jupiter and Saturn, are huddled close to our Sun, within 10 times the
distance between the Earth and Sun,” he points out. “We found that this
lack of gas-giant planets in more distant orbits is typical for nearby
stars over a wide range of masses."
Two additional papers from the Campaign will be published soon and
reveal similar tendencies around other classes of stars. However, not
all gas-giant exoplanets snuggle so close to home. In 2008, astronomers
using the Gemini North telescope and W.M. Keck Observatory on Hawaii’s
Mauna Kea took the first-ever direct images
of a family of planets around the star HR 8799, finding gas-giant
planets at large orbital separations (about 25-70 times the Earth-Sun
distance). This discovery came after examining only a few stars,
suggesting such large-separation gas giants could be common. The latest
Gemini results, from a much more extensive imaging search, show that
gas-giant planets at such distances are in fact uncommon.
Liu sums up the situation this way: “We’ve known for nearly 20 years
that gas-giant planets exist around other stars, at least orbiting
close-in. Thanks to leaps in direct imaging methods, we can now learn
how far away planets can typically reside. The answer is that they
usually avoid significant areas of real estate around their host stars.
The early findings, like HR 8799, probably skewed our perceptions.”
The team’s second new paper explores systems where dust disks around
young stars show holes, which astronomers have long suspected are
cleared by the gravitational force of orbiting planets. “It makes sense
that where you see debris cleared away that a planet would be
responsible, but we did not know what types of planets might be causing
this. It appears that instead of massive planets, smaller planets that
we can’t detect directly could be responsible,” said Zahed Wahhaj of the
European Southern Observatory and lead author on the survey’s paper on
dusty disk stars. Finally, the third new paper from the team looks at
the very youngest stars close to Earth. “A younger system should have
brighter, easier to detect planets,” according to the lead author Beth
Biller of the Max Planck Institute for Astronomy.
“Around other stars, NASA's Kepler telescope has shown that planets
larger than the Earth and within the orbit of Mercury are plentiful,”
explains Biller. “The NICI Campaign demonstrates that gas-giant planets
beyond the distance of the orbit of Neptune are rare.” The
soon-to-be-delivered Gemini Planet Imager will begin to bridge this gap
likely revealing, for the first time, how common giant planets are in
orbits similar to the gas-giant planets of our own Solar System.
The observations for the Campaign were obtained with the Gemini
instrument known as NICI, the Near-Infrared Coronagraphic Imager, which
was the first instrument for an 8-10 meter-class telescope designed
specifically for finding faint companions around bright stars. NICI was
built by Doug Toomey (Mauna Kea Infrared), Christ Ftaclas, and Mark Chun
(University of Hawai‘i), with funding from NASA.
The first two papers from the Campaign have been accepted for publication in The Astrophysical Journal (Nielsen et al. and Wahhaj et al.), and the third paper (Biller et al.) will be published later this summer.
The NICI Campaign team is composed of PI Michael Liu, co-PI Mark Chun
(University of Hawaii), co-PI Laird Close (University of Arizona), Doug
Toomey (Mauna Kea Infrared), Christ Ftaclas (University of Hawaii),
Zahed Wahhaj (European Southern Observatory), Beth Biller (Max Planck
Institute for Astronomy), Eric Nielsen (University of Hawaii), Evgenya
Shkolnik (DTM, Carnegie Institution of Washington), Adam Burrows
(Princeton University), Neill Reid (Space Telescope Science Institute),
Niranjan Thatte, Matthias Tecza, Fraser Clarke (University of Oxford),
Jane Gregorio Hetem, Elisabete De Gouveia Dal Pino (University of Sao
Paolo), Silvia Alencar (University of Minas Gerais), Pawel Artymowicz
(University of Toronto), Doug Lin (University of California Santa Cruz),
Shigeru Ida (Tokyo Institute of Technology), Alan Boss (DTM, Carnegie
Institution of Washington), and Mark Kuchner (NASA Goddard), Tom Hayward
and Markus Hartung (Gemini Observatory), Jared Males, and Andy Skemer
(University of Arizona).
Media Contacts:
- Peter Michaud
Gemini Observatory
Hilo, HI 96720
Office: +1 (808) 974-2510
Cell: +1 (808) 936-6643
pmichaud@gemini.edu
- Roy Gal
Institute for Astronomy
University of Hawaii at Manoa
Honolulu, HI 96822
Office: +1 (808) 956-6235
rgal@ifa.hawaii.edu
Science Contacts:
- Michael Liu
Institute for Astronomy
University of Hawaii at Manoa
Honolulu, HI 96822
Office: +1 (808) 956-6666
mliu@ifa.hawaii.edu
- Eric Nielsen
Institute for Astronomy
University of Hawaii at Manoa
Honolulu, HI 96822
Office: +1 (808) 956-9841
Cell: 408 394-4582
enielsen@ifa.hawaii.edu
Source: Gemini Observatory
