Extrasolar Planets - Astronomy News

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Posts: 131433

Date: Oct 12 06:58 2006

On the formation of terrestrial planets in hot-Jupiter systems	Permalink

Title: On the formation of terrestrial planets in hot-Jupiter systems Authors: Martyn J. Fogg, Richard P. Nelson We present a series of calculations aimed at examining how an inner system of planetesimals/protoplanets, undergoing terrestrial planet formation, evolves under the influence of a giant planet undergoing inward type II migration through the region bounded between 5 - 0.1 AU. We find that > 60% of the solids disk survives by being scattered by the giant planet into external orbits. Planetesimals are scattered outward almost as efficiently as protoplanets, resulting in the regeneration of a solids disk where dynamical friction is strong and terrestrial planet formation is able to resume. A simulation extended for a few Myr after the migration of the giant planet halted at 0.1 AU, resulted in an apparently stable planet of ~ 2 Earth masses forming in the habitable zone. Migration-induced mixing of volatile-rich material from beyond the `snowline' into the inner disk regions means that terrestrial planets that form there are likely to be water-rich. We predict that hot--Jupiter systems are likely to harbour water-rich terrestrial planets in their habitable zones. These planets may be detected by future planet search missions. Read more (440kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Oct 11 12:27 2006

The Habitable Zone	Permalink

“35% of the Giant Planets Could Form Planets Like the Earth in the Habitable Zone” When planets were first found around other stars, the planets that were found—at least around stars like the sun - were giant planets; they were more like Jupiter than Earth, so they were many hundreds of times more massive than the Earth. instead of being rocky planets they were big balls of gas like Jupiter. They were found very close to their stars, maybe 10% or even less of the Earth’s Sun distance, and because of this they were called “hot Jupiters” because they were gas-like planets. When a few of these were found, people tried to study exactly how these planets would form. All of the models require them to form much further away from the star: it’s thought that they can’t form that close to the star, they actually form much further out, and then somehow they move in. Read more __________________

Blobrana

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Posts: 131433

Date: Oct 9 19:33 2006

Epsilon Eridani	Permalink

NASA's Hubble Space Telescope, in collaboration with ground-based observations, has provided definitive evidence for the existence of the nearest extrasolar planet to our solar system. The Jupiter-sized world orbits the Sun-like star Epsilon Eridani, which is only 10.5 light-years away. The results are being presented today at the 38th Annual Division of Planetary Sciences Meeting in Pasadena, Calif. and will appear in the November issue of the Astronomical Journal. This is an artist's concept of a Jupiter-mass planet orbiting the nearby star Epsilon Eridani. Expand (199kb, 800 x 600) Position (2000): R.A. 03h 32m 55s.84 Dec. -09° 27' 29".7 Read more __________________

Blobrana

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Posts: 131433

Date: Oct 9 17:50 2006

RE: Extrasolar Planets	Permalink

Title: The Extrasolar Planet Epsilon Eridani b - Orbit and Mass Authors: G. Fritz Benedict, Barbara E. McArthur, George Gatewood, Edmund Nelan, William D. Cochran, Artie Hatzes, Michael Endl, Robert Wittenmyer, Sallie L. Baliunas, Gordon A. H. Walker, Stephenson Yang, Martin K¨urster, Sebastian Els, and Diane B. Paulson Hubble Space Telescope (HST ) observations of the nearby (3.22 pc), K2 V star Epsilon Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model the astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Because of the long period of the companion, Epsilon Eri b, we extend our astrometric coverage to a total of 14.94 years (including the three year span of the HST data) by including lower-precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocities now span 1980.8 – 2006.3. We obtain a perturbation period, P = 6.85 ± 0.03 yr, semi-major axis á = 1.88±0.20 mas, and inclination i = 30°.1 ± 3°.8. This inclination is consistent with a previously measured dust disk inclination, suggesting coplanarity. Assuming a primary mass M* = 0.83solarMasses, we obtain a companion mass M = 1.55 ± 0.24 MJup. Given the relatively young age of Epsilon Eri (~800 Myr), this accurate exoplanet mass and orbit can usefully inform future direct imaging attempts. We predict the next periastron at 2007.3 with a total separation, ñ = 0.“3 at position angle, p.a. = 27°. Orbit orientation and geometry dictate that Epsilon Eri b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 years indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 years, possibly responsible for one feature of the dust morphology, the inner cavity. Read more (PDF) __________________

Blobrana

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Posts: 131433

Date: Oct 9 17:37 2006

Epsilon Eridani	Permalink

Astronomers at The University of Texas at Austin have gone a long way toward proving that planets are born from disks of dust and gas that swirl around their home stars, confirming a theory posed by philosopher Emmanuel Kant more than two centuries ago. G. Fritz Benedict and Barbara E. McArthur have used NASA’s Hubble Space Telescope, in collaboration with ground-based observatories, to demonstrate that Kant and scientists were correct in predicting the source of planet formation. The results are being presented today in Pasadena, California at a meeting of the American Astronomical Society’s Division of Planetary Sciences, and will be published in the November issue of the Astronomical Journal. Read more Epsilon Eridani b Discovered in 2000 Mass 1.55 (± 0.24) MJ Semi major axis 3.39 (± 0.36) AU Orbital period 2502 (± 10) days Eccentricity 0.702 (± 0.039) Omega 47 (± 3) deg. Tperi 54207 (± 7) JD 2.400.000 Inclination 30.1 (± 3.8) deg. __________________

Blobrana

L

Posts: 131433

Date: Oct 9 09:37 2006

M Dwarf GJ849	Permalink

Title: A Long-Period Jupiter-Mass Planet Orbiting the Nearby M Dwarf GJ849 Authors: R. Paul Butler, John A. Johnson, Geoffrey W. Marcy, Jason T. Wright, Steven S. Vogt, Debra A. Fischer We report precise Doppler measurements of GJ849 (M3.5V) that reveal the presence of a planet with a minimum mass of 0.82 Mjup in a 5.16 year orbit. At a = 2.35 AU, GJ849b is the first planet discovered around an M dwarf to orbit beyond 0.21 AU, and is only the second Jupiter mass planet discovered around a star less massive than 0.5 Msun. This detection brings to 4 the number of M stars known to harbor planets. Based on the results of our survey of 1300 FGKM main--sequence stars we find that giant planets within 2.5 AU are ~3 times more common around GK stars than around M stars. Due to the GJ849's proximity of 8.8 pc, the planet's angular separation is 0."27, making this system a prime target for high--resolution imaging using adaptive optics and future space--borne missions such as the Space Interferometry Mission. We also find evidence of a linear trend in the velocity time series, which may be indicative of an additional planetary companion. Read more (68kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Oct 5 11:19 2006

Ultra-short-period planets (USPPs)	Permalink

Title: Transiting extrasolar planetary candidates in the Galactic bulge Authors: Kailash C. Sahu, Stefano Casertano, Howard E. Bond, Jeff Valenti, T. Ed Smith, Dante Minniti, Manuela Zoccali, Mario Livio, Nino Panagia, Nikolai Piskunov, Thomas M. Brown, Timothy Brown, Alvio Renzini, R. Michael Rich, Will Clarkson, Stephen Lubow More than 200 extrasolar planets have been discovered around relatively nearby stars, primarily through the Doppler line shifts owing to the reflex motions of their host stars, and more recently through transits of some planets across the face of the host stars. The detection of planets with the shortest known periods, 1.2 to 2.5 days, has mainly resulted from transit surveys which have generally targeted stars more massive than 0.75 M_sun. Here we report the results from a planetary transit search performed in a rich stellar field towards the Galactic bulge. We discovered 16 candidates with orbital periods between 0.4 and 4.2 days, five of which orbit stars of 0.44 to 0.75 M_sun. In two cases, radial-velocity measurements support the planetary nature of the companions. Five candidates have orbital periods below 1.0 day, constituting a new class of ultra-short-period planets (USPPs), which occur only around stars of less than 0.88 M_sun. This indicates that those orbiting very close to more luminous stars might be evaporatively destroyed, or that jovian planets around lower-mass stars might migrate to smaller radii. Read more (603kb, PDF) __________________

Blobrana

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Posts: 131433

Date: Oct 4 18:20 2006

HUBBLE FINDS EXTRASOLAR PLANETS FAR ACROSS OUR GALAXY	Permalink

NASA's Hubble Space Telescope has discovered 16 extrasolar planet candidates orbiting a variety of distant stars in the central region of our Milky Way galaxy. The planet bonanza was uncovered during a Hubble survey, called the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). Hubble looked farther than has ever successfully been searched for extrasolar planets. Hubble peered at 180,000 stars in the crowded central bulge of our galaxy 26,000 light-years away. That is one-quarter the diameter of the Milky Way's spiral disk. The results will appear in the Oct. 5 issue of the journal Nature. Read more __________________

Blobrana

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Posts: 131433

Date: Oct 4 18:16 2006

New Extrasolar Planets Class	Permalink

Astronomers have discovered a new class of planets that take less than a day to whiz round their parent stars. Observations with the Hubble Space Telescope revealed the existence of the planets, which orbit closer to their stars than any previously known. Dr Kailash Sahu and colleagues report finding the planets in a faint, crowded star field in a region of the Milky Way known as the Galactic bulge. Read more __________________

Blobrana

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Posts: 131433

Date: Sep 29 09:33 2006

HD97048	Permalink

Astronomers reported on Thursday that a huge dust disc around a star more massive than our Sun appeared to be a precursor of planets, and provided a rare opportunity to witness the conditions of planet formation. Writing in the Sept. 28 online edition of the journal Science, the astronomers said the young star HD 97048, which is 600 light years away from Earth, belonged to the Chameleon I dark cloud. The star is 40 times more luminous than our Sun and is 2.5 times as massive. The researchers used the very large telescope of the European Southern Observatory to map the disc surrounding the young star in an infrared spectrum. They found that the dust disc was at least 12 times more extended than the orbit of Neptune. The observations suggest the disc to be flared. Planets form in massive, gaseous and dusty proto-planetary discs that surround nascent stars, according to a well-accepted theory. This process must be rather ubiquitous, but very little is known about these discs, especially those around stars more massive than the Sun. It is the first time such a structure, predicted by some theoretical models, has been observed around a massive star, according to the astronomers. The geometry of the dust disc can only be explained if it contains a large amount of gas, in this case, at least as much as 10 times the mass of Jupiter. It should also contain more than 50 Earth masses in dust, they said. The dust mass derived here is more than a thousand times larger than what is observed in debris discs and Kuiper belt-like structures found around older stars such as Vega. HD 97048's disc is most likely to be a precursor of debris discs observed around older stars, and planetary embryos may be present in the inner part of the disc, the researchers concluded. Source Xinhua __________________

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