New Planet First Magnetic Roaster
"We are witnessing the birth of a new observational science: the discovery and characterization of extrasolar planetary systems." --G. Marcy, UC Berkeley
Canadian astronomers announced today the first evidence of a magnetic field on a planet outside of our solar system which is also the first observation of a planet heating its star. In our own solar system, if Jupiter was just ten times bigger, it would have sufficient critical mass to ignite as a second star. Because of their enormous sizes, most such gas giants have appeared in early planet discovery surveys, just because such 'hot Jupiters' have a significant pull on their own stars to aid terrestrial detection.
|Interaction between the sun's magnetic field and the Earth's magnetosphere. Solar wind distorts the earth's magnetic field. Banner image shows artist conception of the magnetic heating of the star and its new planet discovered.
Credit:NASA; Banner Credit: Erno, UBC
The report was presented Thursday at at the meeting of the American Astronomical Society in Atlanta, Georgia. Ph.D. candidate Evgenya Shkolnik, Dr. Gordon Walker, both of the University of British Columbia, Vancouver, BC and Dr. David Bohlender of the National Research Council of Canada / Herzberg Institute for Astrophysics, Victoria, BC suggested that the result may offer clues about the structure and formation of the giant planet.
Unlike a Jupiter that might ignite to a star using nuclear fusion, the marriage between the new planet and its star has more to do not with fusion, but with their magnetic entanglements. The team presented evidence that the star is being heated by its planet through magnetic interactions.
The trio observed the sun-like star HD179949 with the 3.6-meter (142-in) Canada-France-Hawaii Telescope atop Mauna Kea, Hawaii (a 14,000-ft. dormant volcano) using its high-resolution spectrograph called Gecko. HD179949 is 90 light years away in the direction of the southern constellation of Sagittarius (the Archer) but it is too faint to be seen without a telescope. It was first reported to have a close-in planet by Tinney, Butler, Marcy and others in the first results of the Anglo-Australian planet search in 2000.
The planet is at least 270 times more massive than the Earth, almost as big as Jupiter, and orbits the star every 3.093 days at 350,000 mph. A year on the planet is only three terrestrial days. One reason for this rapidly turning calendar page is its close orbit, which is around four percent of the Sun-Earth distance (or 0.045 Astronomical Units, AU).
Such tightly orbiting "roasters" or "hot jupiters" make up 20% of all known extrasolar planets. For most all of the 119 or so known planets, all that scientists can surmize about their size is the minimum mass needed to cause its parent star to wobble. That wobbling motion is the primary way the planet reveals its presence to terrestrial telescopes.
|Sun's chromosphere seen in ultraviolet. Hotspots are the result of giant magnetic storms, and are visible as bright patches of the light emitted by singly ionized calcium. Inset lower left shows the predicted orbital effects of the new planet as it orbits its magnetically tied parent star.Credit: National Solar Orbservatory
The star's chromosphere, a thin, hot layer just above the visible photosphere, was observed in the ultraviolet light emitted by singly-ionized Calcium atoms. Giant magnetic storms produce hot spots which are visible as bright patches in this light. Such a persistent hotspot is observed on HD 179949 keeping pace with the planet in its 3-day orbit for more than a year (or 100 orbits)!
The hotspot appears to be moving across the surface of the star slightly ahead of, but keeping pace with the planet. Most evidence suggests the star is rotating too slowly to carry the spot around so quickly.
The best explanation for this traveling hot spot is an interaction between the planet's magnetic field and the star's chromosphere, something predicted by Steve Saar of the Harvard-Smithsonian Center for Astrophysics and Manfred Cuntz of the University of Texas at Arlington in 2000. If so, this is the first ever glimpse of a magnetic field on a planet outside of our solar system, and may provide clues about the planet's structure and formation.
"If we are indeed witnessing the entanglement of the magnetic field of a star with that of its planet it gives us an entirely new insight into the nature of closely bound planets," said Dr. Gordon Walker.
Magnetic fields are thought to play an important role in whether an atmosphere, or eventually life, has a shot of evolving on most planets. Mars, for instance, is thought to have lost its magnetic field early in its lifecycle, and this has dramatically changed both its seasons, its orbital tilt, and finally its environmental resistance to maintaining any liquid water.
More observations are needed to test if the magnetic interaction is a transient event or something longer lasting. Also, observations from the 8-meter Gemini-South Telescope in Chile of this stellar system are underway in the infrared light emitted by Helium which would map hotspots at higher levels of the chromosphere.
Scientists hope to launch six new space-borne missions over the next few years to search for terrestrial planets.
They include France's small-scale COROT, NASA's more-ambitious Kepler mission, the European Space Agency's (ESA) Eddington and NASA's Space Interferometry Mission (SIM).
The French COROT mission, approved and due for launch in late 2004, will study asteroseismology, or oscillations within stars, and likely will be the first orbiting telescope to search for extrasolar planets.It will look at 50,000 to 60,000 stars and should find a few dozen terrestrial planets and several hundred close-in gas-giant planets during a two- to three-year mission, says Pierre Barge, an astronomer at the Laboratory of Astrophysics in Marseille and leader of COROT's exoplanets group. COROT - for Convection, Rotation and Planetary Transits - is a mission of CNES, the French National Center for Space Studies, in partnership with ESA, Italy, Belgium and Germany. When searching for extrasolar planets, COROT's 27-centimeter (10.6-inch) telescope will use a method called photometry, in which sensitive light detectors look for a slight drop in a star's brightness as a small planet "transits" the star (crosses the face of the star as viewed from COROT).
|SIM, scheduled for launch in 2009, will determine the positions and distances of stars several hundred times more accurately than any previous program.
Credit: NASA / JPL
The Kepler mission is scheduled for launch into solar orbit in October 2006. Kepler will simultaneously observe 100,000 stars in our galactic "neighborhood," looking for Earth-sized or larger planets within the "habitable zone" around each star - the not-too-hot, not-too-cold zone where liquid water might exist on a planet. To highlight the difficulty of detecting an Earth-sized planet orbiting a distant star, Borucki, Kepler's principal investigator, points out it would take 10,000 Earths to cover the Sun's disk. One NASA estimate says Kepler should discover 50 terrestrial planets if most of those found are about Earth's size, 185 planets if most are 30 percent larger than Earth and 640 if most are 2.2 times Earth's size. In addition, Kepler is expected to find almost 900 giant planets close to their stars and about 30 giants orbiting at Jupiter-like distances from their parent stars. Because most of the gas giant planets found so far orbit much closer to their stars than Jupiter does to the Sun, Borucki believes that during the four- to six-year mission, Kepler will find a large proportion of planets quite close to stars. If that proves true, he says, "We expect to find thousands of planets."
Due for launch in 2009 is the almost $1 billion NASA-ESA Next Generation Space Telescope, or NGST [James Webb Space Telescope], a near-infrared telescope that will succeed the Hubble Space Telescope. Planet hunting will be a minor part of its job. Like Hubble, NGST will be a general-purpose telescope with an emphasis on cosmology. But it will investigate stars with dusty disks - the early stage of planet formation - and may also be able to study Jupiter-size planets.
Several new astrometric satellites are now being planned to measure star distances, which will improve the selection criteria for habitability.
The most ambitious planned star cataloguing projects are NASA's Space Interferometry Mission [SIM] and ESA's Galactic Census Project, or GAIA mission, which may yield large numbers of parallaxes with precisions better than ~ 10 micro-arcseconds. SIM is scheduled to operate from 2006 to 2011 while GAIA, if accepted by ESA, could launch in 2009 with a 5 year lifetime.
SIM would provide astrometric measurements of 10,000 stars and GAIA would measure around 10 billion positions.
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