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TOPIC: Extrasolar Planets


L

Posts: 131433
Date:
WASP-1b and WASP-2b
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Astronomers at the St Andrews University in Fife, Scotland, have discovered two new planets in the constellations of Andromeda and Delphinus. These planets are almost the size of Jupiter in the solar system.
Using a budget search technique which hunts for stars that "wink", the astronomers located the one of planets around a star more than 1000 light years away in the constellation of Andromeda, and the other 500 light years away in the constellation of Delphinus. These are among the hottest planets ever discovered.

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Title: WASP-1b and WASP-2b: Two new transiting exoplanets detected with SuperWASP and SOPHIE
Authors: A. Collier Cameron, F. Bouchy, G. Hebrard, P. Maxted, D. Pollacco, F. Pont, I. Skillen, B. Smalley, R. A. Street, R.G. West, D.M. Wilson, S. Aigrain, D.J. Christian, W.I. Clarkson, B. Enoch, A. Evans, A. Fitzsimmons, M. Gillon, C.A. Haswell, L. Hebb, C. Hellier, S.T. Hodgkin, K. Horne, J. Irwin, S.R. Kane, F.P. Keenan, B. Loeillet, T.A. Lister, M. Mayor, C. Moutou, A.J. Norton, J. Osborne, N. Parley, D. Queloz, R. Ryans, A.H.M.J. Triaud, S. Udry, P.J. Wheatley

We have detected radial-velocity variations in two objects that were identified as being likely host stars of transiting exoplanets in the 2004 SuperWASP wide-field transit survey. Using the newly-commissioned radial-velocity spectrograph SOPHIE at the Observatoire de Haute-Provence, we found that both objects exhibit reflex orbital radial-velocity variations with amplitudes characteristic of planetary-mass companions and in-phase with the photometric orbits. Line-bisector studies rule out faint blended binaries as the cause of either the radial-velocity variations or the transits. We perform preliminary spectral analyses of the host stars, which together with their radial-velocity variations and fits to the transit light curves, yield estimates of the planetary masses and radii. WASP-1b and WASP-2b have orbital periods of 2.52 and 2.15 days respectively. Given mass estimates for their F7V and K1V primaries we derive planet masses 0.80 to 0.98 and 0.81 to 0.95 times that of Jupiter respectively. WASP-1b appears to have an inflated radius of at least 1.33 R_Jup, whereas WASP-2b has a radius in the range 0.65 to 1.26 R_Jup.

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(revised v2): Sat, 7 Oct 2006 10:09:34 GMT

-- Edited by Blobrana at 10:44, 2006-10-10

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L

Posts: 131433
Date:
SuperWASP Planets
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A third planet that boasts extremely low density has been found, adding weight to the idea that these objects may be fairly common. The find is the first for a planet-finding survey called SuperWASP.

The planet was found by the characteristic dips in brightness created when it passes in front of its parent star. Only about a dozen extrasolar planets have been found with this method, called the transit technique. Most planets have been found by watching for the wobble that their gravity induces in their parent stars called the radial velocity method.
The planet, called WASP-1b, and another called WASP-2b, are the first to be discovered by a survey called the Super Wide Angle Search for Planets, led by Don Pollacco of Queen's University in Belfast, UK. The two "SuperWASP" telescopes can each capture an enormous 450-square-degree patch of sky in a single image, and can survey 10 to 15% of the sky each night.

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L

Posts: 131433
Date:
OGLE-2005-BLG-390Lb
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An international team of astronomers has found the smallest Earth-like planet yet outside our Solar System.

The new planet has five times the Earth's mass and can be found about 25,000 light-years away in the Milky Way, orbiting a red dwarf star.
The discovery, reported in the journal Nature, was made using a method called microlensing, which can detect far-off planets with an Earth-like mass.
The planet's cold temperatures make the chance of finding life very unlikely.
The planet, which goes by the name OGLE-2005-BLG-390Lb, takes about 10 years to orbit its parent star, a red dwarf which is cooler and smaller than Earth's Sun.
It is in the same galaxy as Earth, the Milky Way, but is found closer to the galactic centre.

The scientists say it probably has a rocky core and perhaps even a thin atmosphere, but its large orbit and cool parent star mean it is a very cold world.
Predicted surface temperatures are minus 220 degrees Celsius, meaning that its surface is likely to be layer of frozen liquid. It may therefore resemble a more massive version of Pluto.

"This is very exciting and important. This is the most Earth-like planet we have discovered to date, in terms of its mass and the distance from its parent star. Most of the other planets that have been discovered are either much more massive, much hotter or both" - Professor Michael Bode from Liverpool John Moores University, a principal investigator for the RoboNet project which collaborated on this research.

The microlensing technique used to find this planet was first predicted by Albert Einstein in 1912.
Microlensing occurs when a massive object in space, like a star, crosses in front of another more distant star.
As it passes, the gravity from the foreground object bends the light coming from the background star, temporarily making it look brighter. This usually lasts for about a month.
If the foreground star has a planet orbiting it, it will distort the light even more, and will make the star behind it look even brighter. But this effect lasts for a much shorter period, giving astronomers just hours or days to detect it.
Dr Martin Dominik from the University of St Andrews is a co-leader of the PLANET collaboration, one of the microlensing networks used to detect the new planet.

"We first saw the usual brightening reaching a peak magnification on 31 July 2005. On 10 August, however, there was a small 'flash' lasting about half a day. By succeeding in catching this anomaly with two of the telescopes of our network and with careful monitoring, we were able to conclude that the lens star is accompanied by a low-mass planet" - Dr Martin Dominik.

The discovery was the joint effort of three microlensing campaigns, PLANET/RoboNet, OGLE and MOA, and involved researchers from 12 countries.
So far, about 160 planets have been found outside our Solar System, but only three of them have been located using the microlensing technique.
Recent simulations of planet formation suggest that bodies with an Earth-like mass are abundant. Scientists are attempting to discover more new worlds using this technique and are looking for ways to refine it further.

"We could take this research forward by building a network of bigger telescopes around the world to make us more efficient at detecting these Earth-like planets" - Dr Nicholas Rattenbury, from Jodrell Bank Observatory in Cheshire, a member of the MOA microlensing collaboration.

If planets are found with conditions similar to our own planet, then the next step would be to begin the search for life, but this might not prove easy.

"To prove there is life on a far-off planet would be difficult. How can we prove there is life on a distant planet when we have problems seeing if there is life on Mars?" - Dr Martin Dominik.

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L

Posts: 131433
Date:
HAT-P-1b
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Title: HAT-P-1b: A Large-Radius, Low-Density Exoplanet Transiting one Member of a Stellar Binary
Authors: G. A. Bakos (1,2), R. W. Noyes (1), G. Kovacs (3), D. W. Latham (1), D. D. Sasselov (1), G. Torres (1), D. A. Fischer (6), R. P. Stefanik (1), B. Sato (7), J. A. Johnson (8), A. Pal (4,1), G. W. Marcy (8), R. P. Butler (9), G. A. Esquerdo (1), K. Z. Stanek (10), J. Lazar (5), I. Papp (5), P. Sari (5) B. Sipocz (4,1), ((1) CfA, (2) Hubble Fellow, (3) Konkoly Observatory, (4) Eotvos Lorand University, (5) Hungarian Astronomical Association, (6) San Francisco State University, (7) Okayama Astrophysical Observatory, (8) UC at Berkeley, (9) Carnegie, (10) Ohio State University)

Using small automated telescopes in Arizona and Hawaii, the HATNet project has detected an object transiting one member of the double star system ADS 16402 AB. This system is a pair of G0 main-sequence stars with age about 3 Gyr at a distance of ~139 pc and projected separation of ~1550 AU. The transit signal has a period of 4.46529 days and depth of 0.015 mag. From follow-up photometry and spectroscopy, we find that the object is a "hot Jupiter" planet with mass about 0.53 M_jup and radius ~1.36 R_jup travelling in an orbit with semimajor axis 0.055 AU and inclination about 85.9 deg, thus transiting the star at impact parameter 0.74 of the stellar radius. Based on a data set spanning three years, ephemerides for the transit centre are: T_C = 2453984.397 + N_tr * 4.46529. The planet, designated HAT-P-1b, appears to be at least as large in radius, and smaller in mean density, than any previously-known planet.

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L

Posts: 131433
Date:
RE: Extrasolar Planets
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It is only a matter of time before astronomers find an Earth-sized planet orbiting a distant star. When they do, the first questions people will ask are: Is it habitable? And even more importantly, is there life present on it already? For clues to the answers, scientists are looking to their home planet, Earth.
Astronomers Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics (CfA) and Wesley Traub of NASA's Jet Propulsion Laboratory and CfA, propose using Earth's atmospheric history to understand other planets.

"Good planets are hard to find. Our work provides the signposts astronomers will look for when examining truly Earth-like worlds" - Lisa Kaltenegger

Geologic records show that Earth's atmosphere has changed dramatically during the past 4.5 billion years, in part because of life forms developing on our planet. Mapping what gases comprised Earth's atmosphere during its history, Kaltenegger and Traub propose that by looking for similar atmospheric compositions on other worlds, scientists will be able to determine if that planet has life on it, and if so, that life's evolutionary stage.
To date, all extrasolar planets have been studied indirectly, for example by monitoring the way a host star wobbles as the planet's gravity tugs it. Only four extrasolar planets have been detected directly, and they are massive Jupiter-sized worlds. The atmosphere of one of these worlds was detected by another CfA scientist, David Charbonneau, using NASA's Spitzer Space Telescope. The next generation of space-based missions such as NASA's Terrestrial Planet Finder (TPF) and ESA's Darwin will be able to directly study nearby Earth-sized worlds.
Astronomers particularly want to observe the visible and infrared spectra of distant terrestrial planets to learn about their atmospheres. Particular gases leave signatures in a planet's spectrum, like fingerprints or DNA markers. By spotting those fingerprints, researchers can learn about an atmosphere's composition and even deduce the presence of clouds.
Today, Earth's atmosphere consists of about three-fourths nitrogen and one-fourth oxygen, with a small percentage of other gases like carbon dioxide and methane. But four billion years ago, no oxygen was present. Earth's atmosphere has evolved through six distinct epochs, each characterized by a particular mix of gases. Using a computer code developed by Traub and CfA colleague Ken Jucks, Kaltenegger and Traub modelled each of Earth's six epochs to determine what spectral fingerprints would be seen by a distant observer.

"By studying Earth's past, we can learn about the present state of other worlds. If an extrasolar planet is found with a spectrum similar to one of our models, we potentially could characterise that planet's geological state, its habitability, and the degree to which life has evolved on it" - Wesley Traub.

To better understand these time periods, or "epochs," and to put them into perspective, one can scale the Earth's 4.5-billion-year history down to one year, attaching dates beginning with January 1 - the date the Earth formed.

EPOCH 0 - February 12
At Epoch 0 (3.9 billion years ago), the young Earth possessed a turbulent, steamy atmosphere composed mostly of nitrogen, carbon dioxide and hydrogen sulphide. The days were shorter and the Sun was dimmer, shining as a red orb through our orange brick-coloured sky. The one ocean that covered our entire planet was a muddy brown that absorbed bombardment from incoming meteors and comets. Carbon dioxide helped warm our world since the infant Sun was a third less luminous than today. Although no fossils survived from this time period, isotopic signatures of life may have been left behind in Greenland rocks.

EPOCH 1 - March 17
About 3.5 billion years ago (Epoch 1), the planet landscape featured volcanic island chains poking out of the vast global ocean. The first life on Earth was anaerobic bacteria - bacteria that could live without oxygen. These bacteria pumped large amounts of methane into the planet's atmosphere, changing it in detectable ways. If similar bacteria exist on another planet, future missions like TPF and Darwin could detect their fingerprint in the atmosphere.

EPOCH 2 - June 5
About 2.4 billion years ago (Epoch 2), the atmosphere reached its maximum methane concentration. The dominant gases were nitrogen, carbon dioxide, and methane. Continental landmasses were beginning to form. Blue green algae began pumping large amounts of oxygen into the atmosphere. Big changes were about to happen.

"I'm sorry to say the first signs of E.T. probably won't be a radio or TV broadcasts; instead, it could be oxygen from algae" - Lisa Kaltenegger .

EPOCH 3 - July 16
Two billion years ago (Epoch 3), these first photosynthetic organisms shifted the atmosphere's balance permanently-they produced oxygen, a highly reactive gas that cleared out much of the methane and carbon dioxide, while also suffocating the anaerobic, methane-producing bacteria. In doing so, the planet's atmosphere gained its first free oxygen. The landscape now was flat and damp. With volcanoes smoking in the distance, brilliantly coloured pools of greenish-brown scum created a sheen on the stench-filled water. The oxygen revolution was fully underway.

"The introduction of oxygen was catastrophic to the dominant life on Earth at that time; it poisoned it. But at the same time, it made multicellular life, including human life, possible" - Wesley Traub.

EPOCH 4 - October 13
At 800 million years ago, the Earth entered Epoch 4, with continuing increases in oxygen levels. This time period coincides with what is now known as the "Cambrian Explosion." Beginning 550 to 500 million years ago, the Cambrian Period is a significant marker post in the history of life on Earth: It is the time most major animal groups first appear in the fossil records. The Earth was now covered with swamps, seas and a few active volcanoes. The oceans were teaming with life.

EPOCH 5 - November 8
Finally, 300 million years ago in Epoch 5, life had moved from the oceans onto land. The Earth's atmosphere had reached its current composition of primarily nitrogen and oxygen. This was the beginning of the Mesozoic period that included the dinosaurs. The scenery looked like Jurassic Park on a Sunday afternoon.

EPOCH 6 - December 31 (11:59:59)
The intriguing question that remains is: What would Epoch 6, the time period humans occupy today, look like? Could we detect the telltale signs of alien technologies on distant worlds?
As the general consensus builds among scientist that human activity has altered Earth's atmosphere by inputting carbon dioxide as well as gases like Freon, could we identify the spectral fingerprints of those byproducts on other worlds? Although Earth-orbiting satellites and balloon experiments can measure these changes here at home, detecting similar effects on a distant world are beyond even the capabilities of upcoming programs like Terrestrial Planet Finder and Darwin. It will take gigantic flotillas of future space-based infrared telescopes to be able to accomplish those measurements.

"As daunting as this challenge sounds. I do believe in the next few decades we will know whether or not our little blue world is all alone in the Universe or if there are neighbours out there waiting to meet us" - Lisa Kaltenegger.

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L

Posts: 131433
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Using a network of small, automated telescopes known as HAT, Smithsonian astronomers have discovered a planet unlike any other known world. This new planet, designated HAT-P-1, orbits one member of a pair of distant stars 450 light-years away in the constellation Lacerta.

"We could be looking at an entirely new class of planets" - Gaspar Bakos, a Hubble fellow at CfA. Bakos designed and built the HAT network and is lead author of a paper submitted to the Astrophysical Journal describing the discovery.

With a radius about 1.38 times Jupiter's, HAT-P-1 is the largest known planet. In spite of its huge size, its mass is only half that of Jupiter.
HAT-P-1's parent star is one member of a double-star system called ADS 16402 and is visible in binoculars. The two stars are separated by about 1500 times the Earth-Sun distance. The stars are similar to the Sun but slightly younger - about 3.6 billion years old compared to the Sun's age of 4.5 billion years.

ADS 16402
Position(2000): RA 22 57 46.83 Dec +38 40 29.8
magnitude 10.4
Size 14'1 x 14'1

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L

Posts: 131433
Date:
HAT-P-1
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Scientists have discovered an unusually large and light planet orbiting a star that could force them to re-examine theories about how planets are formed.

The planet, dubbed HAT-P-1, is roughly one-third larger than Jupiter but weighs only half as much, astronomers with the Harvard-Smithsonian Center for Astrophysics said Thursday.
The planet is about one-quarter the density of water.

"Its lighter than a giant ball of cork" - Gaspar Bakos, Harvard-Smithsonian fellow .

HAT-P-1 revolves around its parent star once every 4.5 Earth days in an orbit one-seventh of the distance from Mercury to the sun.

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Posts: 131433
Date:
TrES-2
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Title: TrES-2: The First Transiting Planet in the Kepler Field
Authors: Francis T. O'Donovan, David Charbonneau, Georgi Mandushev, Edward W. Dunham, David W. Latham, Guillermo Torres, Alessandro Sozzetti, Timothy M. Brown, John T. Trauger, Juan A. Belmonte, Markus Rabus, Jose M. Almenara, Roi Alonso, Hans J. Deeg, Gilbert A. Esquerdo, Emilio E. Falco, Lynne A. Hillenbrand, Anna Roussanova, Robert P. Stefanik, Joshua N. Winn

We announce the discovery of the second transiting hot Jupiter discovered by the Trans-atlantic Exoplanet Survey. The planet, which we dub TrES-2, orbits the nearby star GSC 03549-02811 every 2.47063 days. From high-resolution spectra, we determine that the star has T_eff = 5960 100 K and log(g) = 4.4 0.2, implying a spectral type of G0V and a mass of 1.08 +0.11/-0.05 M_sun. High-precision radial-velocity measurements confirm a sinusoidal variation with the period and phase predicted by the photometry, and rule out the presence of line-bisector variations that would indicate that the spectroscopic orbit is spurious. We estimate a planetary mass of 1.28 +0.09/-0.04 M_Jup. We model B, r, R, and I photometric timeseries of the 1.4%-deep transits and find a planetary radius of 1.24 +0.09/-0.06 R_Jup. This planet lies within the field of view of the NASA Kepler mission, ensuring that hundreds of upcoming transits will be monitored with exquisite precision and permitting a host of unprecedented investigations.

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L

Posts: 131433
Date:
RE: Extrasolar Planets
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Earthlike planets covered with deep oceans that could harbor life may be found in as many as a third of solar systems discovered outside of our own, U.S. researchers said on Thursday.

These solar systems feature gas giants known as "Hot Jupiters," which orbit extremely close to their parent stars -- even closer than Mercury to our sun, University of Colorado researcher Sean Raymond said.

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http://exoplanets.org/

Title: Predicting Planets in Known Extra-Solar Planetary Systems I: Test Particle Simulations
Authors: Rory Barnes, Sean N. Raymond

Recent work has suggested that many planetary systems lie near instability. If all systems are near instability, an additional planet must exist in stable regions of well-separated extra-solar planetary systems to push these systems to the edge of stability. We examine the known systems by placing massless test particles in between the planets and integrating for 1-10 million years. We find that some systems, HD168443 and HD74156, eject nearly all test particles within 2 million years. However we find that HD37124, HD38529, and 55Cnc have large contiguous regions in which particles survive for 10 million years. These three systems, therefore, seem the most likely candidates for additional companions. Furthermore HD74156 and HD168443 must be complete and therefore radial velocity surveys should only focus on detecting more distant companions. We also find that several systems show stable regions that only exist at nonzero eccentricities.

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Title: The Search for other Earths: limits on the giant planet orbits that allow habitable terrestrial planets to form
Authors: Sean N. Raymond

Gas giant planets are far easier than terrestrial planets to detect around other stars, and are thought to form much more quickly than terrestrial planets. Thus, in systems with giant planets, the late stages of terrestrial planet formation are strongly affected by the giant planets' dynamical presence. Observations of giant planet orbits may therefore constrain the systems that can harbour potentially habitable, Earth-like planets. We present results of 460 N-body simulations of terrestrial accretion from a disk of Moon- to Mars-sized planetary embryos. We systematically vary the orbital semimajor axis of a Jupiter-mass giant planet between 1.6 and 6 AU, and eccentricity between 0 and 0.4. We find that for Sun-like stars, giant planets inside roughly 2.5 AU inhibit the growth of 0.3 Earth-mass planets in the habitable zone. If planets accrete water from volatile-rich embryos past 2-2.5 AU, then water-rich habitable planets can only form in systems with giant planets beyond 3.5 AU. Giant planets with significant orbital eccentricities inhibit both accretion and water delivery. The majority of the current sample of extra-solar giant planets appears unlikely to form habitable planets.

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