|
Benchmark Survey Shows that Giant Outer Extrasolar Planets Are Rare
July 12, 2007Astronomers who used powerful telescopes in Arizona and Chile in a survey for planets around nearby stars have discovered that extrasolar planets more massive than Jupiter are extremely rare in other outer solar systems.
University of Arizona astronomers and their collaborators from the European Southern Observatory, the Max Planck Institute for Astronomy in Heidelberg, Italy's Arcetri Observatory, the W.M. Keck Observatory and the Harvard-Smithsonian Center for Astrophysics just concluded a benchmark three-year survey using direct detection techniques sensitive to planets farther from their stars. The survey looked at 54 young, nearby stars that were among the best candidates for having detectable giant Jupiter-like planets at distances beyond five astronomical units (AU), or the distance between Jupiter and the sun. One AU is the distance between Earth and the sun.
Since 1995, astronomers have found more than 230 "super Jupiters" orbiting very close to their parent stars using the radial velocity method. This indirect planet-detecting technique measures the slight back-and-forth motion of the star as it is tugged by an unseen planet's gravity. Scientists have written more than 2,000 scholarly papers about these giant Jupiter-like planets within a few Earth-to-sun distances of their stars.
However, the radial velocity method presently used is most sensitive to planets close to their stars. The technique reveals little about extrasolar planets farther out in nearby solar systems.
Astronomers need other techniques to map extrasolar planets beyond five AU so they can determine what the "average" planetary system looks like - and whether ours is a typical solar system.
The three-year survey didn't turn up even one giant extrasolar planet in the outer part of any nearby solar system.
"We certainly had the ability to detect outer super Jupiter planets at 10 AU, and farther out, around young sun-like stars," said UA astronomy Professor Laird Close. Close, along with Rainer Lenzen of the Max Planck Institute for Astronomy and Don McCarthy of The University of Arizona, designed the unique, methane-planet sensitive imagers used on two powerful telescopes for the survey.
"The odds are extremely slight that planets larger than four to five Jupiter masses exist at distances greater than 20 AU from these stars," concluded graduating doctoral student Beth Biller of the UA Steward Observatory. Biller is lead author on the first scholarly paper reporting direct-imaging results for farther-out massive Jupiters from this survey, the most sensitive to date.
"There is no 'planet oasis' between 20 and 100 AU," doctoral student Eric Nielsen of Steward Observatory agreed. "We achieved contrasts high enough to find these super Jupiters, but didn't." Twenty AU is the orbital distance of the planet Uranus in our own solar system.
Astronomers were surprised in the early days of planet finding to discover a population of planets more massive than Jupiter, within the orbit of Mercury, taking only a few days to orbit their host star, Biller said. "Now that we know there aren't large numbers of giant planets lurking at large distances from their stars, astronomers have a more complete picture, and can better constrain how planets are formed," she said.
The team used Close's novel Simultaneous Differential Imager (SDI) for observations made with the European Southern Observatory's (ESO) 8.2-meter Very Large Telescope's (VLT) in Chile and with the 6.5-meter, UA/Smithsonian MMT Observatory on Mount Hopkins, Ariz.
One SDI instrument was used with Lenzen's CONICA adaptive optics camera on the VLT, and another SDI instrument was used with McCarthy's ARIES adaptive optics camera on the MMT. The SDI devices made the highest contrast astronomical images ever made from ground or space of methane-rich companions within an arc second of their stars. (An arc second is the diameter of a dime seen from two miles away). A related previous news release about SDI is online at http://uanews.org/spots/sci-12395.html.
The survey was funded by NASA and the National Science Foundation. It is being published in the Astrophysical Journal. Preprints are online at http://arxiv.org/abs/0705.0066 and http://arxiv.org/abs/0706.4331
University of Arizona
However, the radial velocity method presently used is most sensitive to planets close to their stars. The technique reveals little about extrasolar planets farther out in nearby solar systems.
Astronomers need other techniques to map extrasolar planets beyond five AU so they can determine what the "average" planetary system looks like - and whether ours is a typical solar system.
The three-year survey didn't turn up even one giant extrasolar planet in the outer part of any nearby solar system.
"We certainly had the ability to detect outer super Jupiter planets at 10 AU, and farther out, around young sun-like stars," said UA astronomy Professor Laird Close. Close, along with Rainer Lenzen of the Max Planck Institute for Astronomy and Don McCarthy of The University of Arizona, designed the unique, methane-planet sensitive imagers used on two powerful telescopes for the survey.
"The odds are extremely slight that planets larger than four to five Jupiter masses exist at distances greater than 20 AU from these stars," concluded graduating doctoral student Beth Biller of the UA Steward Observatory. Biller is lead author on the first scholarly paper reporting direct-imaging results for farther-out massive Jupiters from this survey, the most sensitive to date.
"There is no 'planet oasis' between 20 and 100 AU," doctoral student Eric Nielsen of Steward Observatory agreed. "We achieved contrasts high enough to find these super Jupiters, but didn't." Twenty AU is the orbital distance of the planet Uranus in our own solar system.
Astronomers were surprised in the early days of planet finding to discover a population of planets more massive than Jupiter, within the orbit of Mercury, taking only a few days to orbit their host star, Biller said. "Now that we know there aren't large numbers of giant planets lurking at large distances from their stars, astronomers have a more complete picture, and can better constrain how planets are formed," she said.
The team used Close's novel Simultaneous Differential Imager (SDI) for observations made with the European Southern Observatory's (ESO) 8.2-meter Very Large Telescope's (VLT) in Chile and with the 6.5-meter, UA/Smithsonian MMT Observatory on Mount Hopkins, Ariz.
One SDI instrument was used with Lenzen's CONICA adaptive optics camera on the VLT, and another SDI instrument was used with McCarthy's ARIES adaptive optics camera on the MMT. The SDI devices made the highest contrast astronomical images ever made from ground or space of methane-rich companions within an arc second of their stars. (An arc second is the diameter of a dime seen from two miles away). A related previous news release about SDI is online at http://uanews.org/spots/sci-12395.html.
The survey was funded by NASA and the National Science Foundation. It is being published in the Astrophysical Journal. Preprints are online at http://arxiv.org/abs/0705.0066 and http://arxiv.org/abs/0706.4331
University of Arizona
Extrasolar Planets News and Current Extrasolar Planets Events RSSDeep Impact extended mission heads for comet Hartley 2
NASA has given a University of Maryland-led team of scientists the green light to fly the Deep Impact spacecraft to Comet Hartley 2 on a two-part extended mission known as EPOXI. The spacecraft will fly by Earth on New Year's Eve at the beginning of a more than two-and-a-half-year journey to Hartley 2.
Hazy red sunset on extrasolar planet
A team of astronomers have used the NASA/ESA Hubble Space Telescope to detect, for the first time, strong evidence of hazes in the atmosphere of a planet orbiting a distant star. The discovery comes after extensive observations made recently with Hubble's Advanced Camera for Surveys (ACS).
Astronomers discover record 5th planet around nearby star 55 Cancri
A team of American astronomers announced today (Tuesday, Nov. 6) the discovery of a record-breaking fifth planet around the nearby star 55 Cancri, making it the only star aside from the sun known to have five planets.
Scientists ponder plant life on extrasolar Earthlike planets
When we think of extrasolar Earth-like planets, the first tendency is to imagine weird creatures like Jar Jar Binks, Chewbacca, and, if those are not bizarre enough, maybe even the pointy-eared Vulcan, Spock, of Star Trek fame.
Massive Transiting Planet with 31-hour Year Found Around Distant Star
An international team of astronomers with the Trans-atlantic Exoplanet Survey today announce the discovery of their third planet, TrES-3.
XO-3b: Supersized planet or oasis in the 'brown dwarf desert'?
The latest find from an international planet-hunting team of amateur and professional astronomers is one of the oddest extrasolar planets ever cataloged -- a mammoth orb more than 13 times the mass of Jupiter that orbits its star in less than four days.
UCF professor finds that hottest measured extrasolar planet is 3700 degrees
"HD 149026b is simply the most exotic, bizarre planet," Harrington said. "It's pretty small, really dense, and now we find that it's extremely hot."
NASA predicts nongreen plants on other planets
NASA scientists believe they have found a way to predict the color of plants on planets in other solar systems.
NASA Scientists Detect Spectrum of Planets Orbiting Other Stars
For the first time, scientists at Goddard have obtained a spectrum, or molecular fingerprint, of a planet orbiting another star. Using spectroscopy, scientists were able to identify silicon dust in clouds on a gas-giant planet called HD 209458b. That planet is located 150 light years from Earth.
Cold climate produced by algae contributed to onset of multicellular life
The rise of multicellular animals about 540 million years ago was a turning point in the history of life. A group of Finnish scientists suggests a new climate-biosphere interaction mechanism for the underlying processes in a new study.
More Extrasolar Planets News Articles
| © 2008 BrightSurf.com |