55 Cancri
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NOS Teletekst van vrijdag 14 juni 2002:
NASA Science News for June 13, 2002
Extraterrestrial Jupiter
Today astronomers announced the discovery of more than a dozen new planets
orbiting distant stars. One of those planetary systems harbors a
Jupiter-like world that reminds researchers of our own solar system.
NASA Headquarters, Washington
Jet Propulsion Laboratory, Pasadena, Calif.
University of California, Berkeley
June 13, 2002
NEWFOUND PLANETARY SYSTEM HAS "HOMETOWN" LOOK
After 15 years of observation and a lot of patience,
the world's premier planet-hunting team has finally found a
planetary system that reminds them of our own home solar
system.
Dr. Geoffrey Marcy, astronomy professor at the University of California, Berkeley, and astronomer Dr. Paul Butler of the Carnegie Institution of Washington, Washington, D.C., today announced the discovery of a Jupiter-like planet orbiting a Sun-like star at nearly the same distance as the Jovian system orbits our Sun.
"All other extrasolar planets discovered up to now orbit closer to the parent star, and most of them have had elongated, eccentric orbits. This new planet orbits as far from its star as our own Jupiter orbits the Sun,'' said Marcy. NASA and the National Science Foundation fund the planet-hunting team.
The star, 55 Cancri in the constellation Cancer, was already known to have one planet, announced by Butler and Marcy in 1996. That planet is a gas giant slightly smaller than the mass of Jupiter and whips around the star in 14.6 days at a distance only one-tenth that from Earth to the Sun.
Using as a yardstick the 93-million mile Earth-Sun distance, called an astronomical unit or AU, the newfound planet orbits at 5.5 AU, comparable to Jupiter's distance from our Sun of 5.2 AU (or about 512 million miles). Its slightly elongated orbit takes it around the star in about 13 years, comparable to Jupiter's orbital period of 11.86 years. It is 3.5 to 5 times the mass of Jupiter.
"We haven't yet found an exact solar system analog, which would have a circular orbit and a mass closer to that of Jupiter. But this shows we are getting close, we are at the point of finding planets at distances greater than 4 AU from the host star," said Butler. "I think we will be finding more of them among the 1,200 stars we are now monitoring."
The team shared its data with Dr. Greg Laughlin, assistant professor of astronomy and astrophysics at the University of California, Santa Cruz. His dynamical calculations show that an Earth-sized planet could survive in a stable orbit between the two gas giants. For the foreseeable future, existence of any such planet around 55 Cancri will remain speculative.
"The existence of analogs to our solar system adds urgency to missions capable of detecting Earth-sized planets - first the Space Interferometry Mission and then the Terrestrial Planet Finder," said Dr. Charles Beichman, NASA's Origins Program chief scientist at the agency's Jet Propulsion Laboratory, Pasadena, Calif.
"This planetary system will be the best candidate for direct pictures when the Terrestrial Planet Finder is launched later this decade," said UC Berkeley astronomer Dr. Debra A. Fischer. Marcy, Butler, Fischer and their team also announced a total of 13 new planets today, including the smallest ever detected: a planet circling the star HD49674 in the constellation Auriga at a distance of .05 AU, one-twentieth the distance from Earth to the Sun. Its mass is about 15 percent that of Jupiter and 40 times that of Earth. This brings the total number of known planets outside our solar system to more than 90.
Discovery of a second planet orbiting 55 Cancri culminates 15 years of observations with the 3-meter (118-inch) telescope at Lick Observatory, owned and operated by the University of California. The team also includes Dr. Steve Vogt, UC Santa Cruz; Dr. Greg Henry, Tennessee State University, Nashville; and Dr. Dimitri Pourbaix, the Institut d'Astronomie et d'Astrophysique, Universite Libre de Bruxelles.
The star 55 Cancri is 41 light years from Earth and is about 5-billion years old. Further data are needed to determine whether yet another planet is orbiting it, because the two known planets do not explain all the observed Doppler wobbling. One possible explanation is a Saturn-mass planet orbiting about .24 AU from the star.
JPL manages the Terrestrial Planet Finder and Space Interferometry Mission for NASA. JPL is a division of the California Institute of Technology in Pasadena. More information, including artist concept and animations, can be found on the Internet at:
http://www.jpl.nasa.gov/images/newplanets
http://exoplanets.org
http://planetquest.jpl.nasa.gov
University of Arizona
UA SCIENTISTS ARE FIRST TO DISCOVER DEBRIS DISK AROUND STAR ORBITED BY A PLANET
Planetary scientists have discovered the first circumstellar disk
ever seen around a star like our sun, a star known to be orbited
by a planet. The system is more like our solar system than any
yet found.
The disk of material is around 55 Cancri, a sun-like star, barely visible to the human eye, about 40 light years away in the constellation Cancer. The disk of material around the star looks similar in many ways to our solar system's Kuiper belt, a ring of comets and dusty debris left over from the formation of the planets, the scientists say.
"And, for all we know, there could be other similarities in this system yet to be discovered," said David E. Trilling of the Lunar and Planetary Laboratory at The University of Arizona in Tucson. Trilling and UA planetary sciences Professor Robert H. Brown report on their discovery in the current (Oct. 22) issue of the journal Nature.
San Francisco State University astronomers two years ago discovered a planet orbiting 55 Cancri. They used the radial velocity technique for their observations, a technique that detects gravity-induced wobble in the movement of stars. The technique does not show how the orbital plane of the system is inclined to the Earth, so the astronomers could only calculate a minimum mass for the stellar companion. The mass of the companion object, 55 Cancri b, was determined to be from about the mass of Jupiter to 100 or more Jupiter masses -- in which case the object would be a star, not a planet.
55 Cancri b is ten times closer to its star than the Earth is to the sun. Direct imaging of a planet so close to a star is not yet possible.
Trilling and Brown used NASA's Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, with "Co Co" or the Cold Coronagraph, an instrument that Brown designed, developed and built for this specific telescope. A coronagraph blocks light from the central star so observers can image the region near the star at high sensitivity. Co Co is superb at masking starlight.
The Arizona scientists viewed 55 Cancri at infrared wavelengths 1.5 microns to 2.4 microns -- and discovered the circumstellar disk. The inner edge of the disk is probably closer than 27 astronomical units (AU) from the star -- at which point the coronagraph mask cut off their view -- and probably extends farther than 44 AU, Trilling said. (One astronomical unit is the distance from Earth to the sun. Jupiter is five AU from the sun; Pluto is 40 AU from the sun. Scientists usually consider the inner edge of the Kuiper belt to begin at about 50 AU. How far it extends is unknown. Estimates are that the outer edge of the Kuiper belt extends from between 100 AU to l,000 AU.)
"The disk we have found is similar in extent to our solar system's Kuiper belt, and has a spectral signature similar to some Kuiper Belt Objects, suggesting similar compositions," Trilling said. He and Brown compared spectra from the 55 Cancri disk to spectra from Pluto, the largest and closest of the 60 known Kuiper Belt Objects. Their data are consistent with the presence of methane ice, a hydrocarbon found on Pluto and in the icy, organic-rich Kuiper belt, Trilling said.
"Further, by directly imaging this dust disk, we have determined the inclination of the 55 Cancri system relative to observers on Earth. Given this inclination, we constrain the mass of the planet to be around 1.9 times the mass of Jupiter.
"By determining that the companion is a planet and not a star, we have extended the idea that the 55 Cancri system is, in many ways, a near analog for our solar system. This detection is the first time that a circumstellar disk has been found around a star with a known planetary companion; both are expected to be present in mature planet-bearing solar systems."
Trilling, a planetary sciences graduate student, won the 1998 Kuiper Award for his work on the formation and evolution of planetary systems. Brown's theoretical and observational research recently has focused on searches for and studies of planets orbiting nearby stars, as well as the icy surfaces in the outer solar system, particularly Triton, Pluto and the Kuiper belt.
The researchers were not surprised that 55 Cancri b - a planet about twice the size of Jupiter - is so close to its star. The planet is about 50 times closer than Jupiter is to the sun.
Their search for dust disks around solar-type stars orbited by planets has been guided by a powerful UA theory group studying ideas of extra-solar planet formation. The group includes Trilling, Jonathan Lunine and William Hubbard of the UA Lunar and Planetary Laboratory (LPL); Adam Burrows of the UA Steward Observatory; Tristan Guillot and Didier Saumon, formerly post-doctoral researchers at the LPL; and Willy Benz, formerly of the UA Steward Observatory, now with the University of Bern, Switzerland.
The theory explains why planets migrate inward toward their central stars after they form, and it predicts that the migration process creates a circumstellar disk that should be relatively bright and massive enough to detect.
The discovery of a Kuiper belt-like disk around 55 Cancri and its known planet strengthens the idea that our galaxy holds many other solar systems like our own, Trilling said.
"To know that there is this analog for our solar system of course implies that there are others, that this isn’t the only one," he said.
"The more analogs we find, the more data we can interpret for better theories and then the more we can observe and figure out how planets and solar systems form.
"Can we learn what governs planet formation, including the question of how did Earth form? That's the question," Trilling said.
The color image released today can be viewed at http://irtf.ifa.hawaii.edu/Science/GalleryOfImages/55cancri.html.
CAPTION:
This is an infrared image of the circumstellar disk around 55 Cancri, a star known to be orbited by a planet. The disk is similar in extent and implied composition to our solar system’s Kuiper belt,. The round, red circle in the middle of this image is the mask of the coronagraph, used to block out light from the star. The horizontal and vertical lines crossing the frame are artifacts introduced by the telescope's superstructure.
The disk extends from the central star to the northeast (upper left) and southwest (lower right). The detectable extent of the disk is approximately 27 AU to 45 AU. This image represents several hours of telescope time, and the observations were made in the near infrared at around 1.6 microns. The observations were carried out with CoCo, the Cold Coronagraph, mounted on NASA's Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, in February 1998.
CREDIT: David E. Trilling and Robert H. Brown, The University of Arizona.
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