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Giovanna Tinetti, lead author of a study published today in Nature, reports presence of water in the atmosphere of an extra-solar planet.

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A scorching-hot gas planet beyond our solar system is steaming up with water vapour, according to new observations from NASA's Spitzer Space Telescope.
The planet, called HD 189733b, swelters as it zips closely around its star every two days or so. Astronomers had predicted that planets of this class, termed "hot Jupiters," would contain water vapour in their atmospheres. Yet finding solid evidence for this has been slippery. These latest data are the most convincing yet that hot Jupiters are "wet."

"We're thrilled to have identified clear signs of water on a planet that is trillions of miles away"  -  Giovanna Tinetti, a European Space Agency fellow at the Institute d'Astrophysique de Paris in France.  

Tinetti is lead author of a paper on HD 189733b appearing today in Nature.

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For the first time, astronomers have succeeded in mapping the way heat is spread through the atmosphere of a planet orbiting a distant star.
The fast-orbiting "Hot Jupiter" planet known as HD189733b was observed for 33 hours by the Spitzer Space Telescope, which is specially suited to measure heat in the form of infrared light. Those hours garnered 278,528 images covering more than half of the planets orbit around its star.
With that data the astronomers were able to piece together a map from the heat of the planet. The resulting map implies that there are strong winds there, which spread the heat around.

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Title: A map of the day-night contrast of the extrasolar planet HD 189733b
Authors: Heather A. Knutson, David Charbonneau, Lori E. Allen, Jonathan J. Fortney, Eric Agol, Nicolas B. Cowan, Adam P. Showman, Curtis S. Cooper, S. Thomas Megeath

"Hot Jupiter" extrasolar planets are expected to be tidally locked because they are close (<0.05 astronomical units, where 1 AU is the average Sun-Earth distance) to their parent stars, resulting in permanent daysides and nightsides. By observing systems where the planet and star periodically eclipse each other, several groups have been able to estimate the temperatures of the daysides of these planets. A key question is whether the atmosphere is able to transport the energy incident upon the dayside to the nightside, which will determine the temperature at different points on the planet's surface. Here we report observations of HD 189733, the closest of these eclipsing planetary systems, over half an orbital period, from which we can construct a 'map' of the distribution of temperatures. We detected the increase in brightness as the dayside of the planet rotated into view. We estimate a minimum brightness temperature of 973 ± 33 K and a maximum brightness temperature of 1212 ± 11 K at a wavelength of 8 microns, indicating that energy from the irradiated dayside is efficiently redistributed throughout the atmosphere, in contrast to a recent claim for another hot Jupiter. Our data indicate that the peak hemisphere-integrated brightness occurs 16 ±6 degrees before opposition, corresponding to a hot spot shifted east of the substellar point. The secondary eclipse (when the planet moves behind the star) occurs 120 ± 24 s later than predicted, which may indicate a slightly eccentric orbit.




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-- Edited by Blobrana at 11:52, 2007-05-09

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The CHARA Array has been used to, for the first time, directly determine the diameter of an extrasolar planet. The planet circles the star HD 189733 every 2.2 days.
HD189733HD 189733 _003
Credit NASA

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Astronomers using the Spitzer Space Telescope have detected a strong flow of heat radiation from a planet orbiting the nearby star HD 189733b. The findings allowed the team to "take the temperature" of the planet.

"This is the closest extrasolar planet to Earth that has ever been detected directly, and it presents the strongest heat emission ever seen from an exoplanet" - Drake Deming, NASA's Goddard Space Flight Centre, Greenbelt, US.

Deming is the lead author of a paper on this observation to be published in the Astrophysical Journal on June 10.

The planet "HD 189733b" orbits a star that is a near cosmic neighbour to our sun, at a distance of 63 light years in the direction of the Dumbbell Nebula. It orbits the star very closely, just slightly more than three percent of the distance between Earth and the sun. Such close proximity keeps the planet roasting at about 844 Celsius, according to the team's measurement.

The planet was discovered last year by François Bouchy of the Marseille Astrophysics Laboratory, France, and his team. The discovery observations allowed Bouchy's team to determine the planet's size (about 1.26 times Jupiter's diameter), mass (1.15 times Jupiter), and density (about 0.75 grams per cubic centimetre). The low density indicates the planet is a gas giant like Jupiter.
The observations also revealed the orbital period (2.219 days) and the distance from the parent star. From this distance and the temperature of the parent star, Bouchy's team estimated the planet's temperature was at least several hundred degrees Celsius, but they were not able to measure heat or light emitted directly from the planet.

"Our direct measurement confirms this estimate" - Drake Deming .

This temperature is too high for liquid water to exist on the planet or any moons it might have. Since known forms of life require liquid water, it is unlikely to have emerged there.
Last year, Deming's team and another group based at the Harvard-Smithsonian Centre for Astrophysics used Spitzer to make the first direct detection of light from alien worlds, by observing the warm infrared glows of two other previously detected "Hot Jupiter" planets, designated HD 209458b and TrES-1.

Infrared light is invisible to the human eye, but detectable by special instruments. Some infrared light is perceived as heat. Hot Jupiter planets are alien gas giants that zip closely around their parent stars, like HD 189733b. From their close orbits, they soak up ample starlight and shine brightly in infrared wavelengths.
Deming's team used the same method to observe HD 189733b. To distinguish the planet's glow from its hot parent star, the astronomers used an elegant method. First, they used Spitzer to collect the total infrared light from both the star and its planet. Then, when the planet dipped behind the star as part of its regular orbit, the astronomers measured the infrared light coming from just the star. This pinpointed exactly how much infrared light belonged to the planet. Under optimal circumstances this same method can be used to make a crude temperature map of the planet itself.

"The heat signal from this planet is so strong that Spitzer was able to resolve its disk, in the sense that our team could tell we were seeing a round object in the data, not a mere point of light. The current Spitzer observations cannot yet make a temperature map of this world, but more observations by Spitzer or future infrared telescopes in space may be able to do that"- Drake Deming.

Deming's team includes Joseph Harrington, Cornell University, Ithaca, N.Y.; Sara Seager, Carnegie Institution of Washington; and Jeremy Richardson, NASA Postdoctoral Fellow at Goddard, in the Exoplanets and Stellar Astrophysics Laboratory.

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Title: Strong Infrared Emission from the Extrasolar Planet HD189733b
Authors: Drake Deming, Joseph Harrington, Sara Seager, L. Jeremy Richardson

We report detection of strong infrared thermal emission from the nearby (d=19 pc) transiting extrasolar planet HD189733b, by measuring the flux decrement during its prominent secondary eclipse. A 6-hour photometric sequence using Spitzer's infrared spectrograph in peak-up imaging mode at 16-microns shows the secondary eclipse depth to be 0.551 ±0.030%, with accuracy limited by instrumental baseline uncertainties, but with 32-sigma precision (0.017%) on the detection. The 16-micron brightness temperature of this planet (1117±42K) is very similar to the Spitzer detections of TrES-1 and HD209458b, but the observed planetary flux (660 micro-Jy) is an order of magnitude greater. This large signal will allow a detailed characterisation of this planet in the infrared. Our photometry has sufficient signal-to-noise (~400 per point) to motivate a search for structure in the ingress/egress portions of the eclipse curve, caused by putative thermal structure on the disk of the planet. We show that by binning our 6-second sampling down to 6-minute resolution, we detect the modulation in the intensity derivative during ingress/egress due to the overall shape of the planet, but our sensitivity is not yet sufficient to distinguish between realistic models of the temperature distribution across the planet's disk. We point out the potential for extending Spitzer secondary eclipse detections down to the regime of transiting hot Neptunes, if such systems are discovered among nearby lower main sequence stars.


Upper Panel: Baseline-removed aperture photometry of the HD189733 secondary eclipse. Points are individual 6-second measurements, with error bars suppressed for clarity, but showing the eclipse curve having the best-fit amplitude (0.551 ± 0.03%) and central phase. Lower Panel: Data from the upper panel averaged in bins of width 0.001 in phase (~ 3 minutes), with error bars and the best-fit eclipse curve.


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An international team of astronomers led by François Bouchy has announced the discovery of a new transiting extra-solar planet.
The planet HD189733b, in the constellation Vulpecula, was detected and studied by the combination of two different methods, radial velocities and photometric transits, using the telescopes at Haute-Provence Observatory (OHP). It is one of the few extra-solar planets for which scientists have been able to accurately determine both its radius (1.26 Jupiter radii) and mass (1.15 Jupiter masses). Thus, and also due to its nearness, about 60 light-years from Earth, the extra-solar planet HD 189733b offers exciting new possibilities for follow-up studies.



The new extra-solar planet was found by the Haute-Provence Observatory on September 15, 2005 by an international team of astronomers from the Laboratoire d'Astrophysique de Marseille (LAM), the Observatoire de Haute-Provence (OHP) and Observatoire de Genève.
This discovery was made, using the Doppler method, with the ELODIE spectrograph at the 1.93-m telescope, the same one used ten years earlier to find the very first extra-solar planet 51 Peg b. Simultaneously, the CCD camera at the 1m20 telescope was used to detect the transit of the extra-solar planet across the disk of the star. This phenomenon can be explained by the favourable orientation of the system as seen from the Earth: the orbital plane is seen edge-on and the extra-solar planet crosses the disk of the star, occulting it partially. The scientific team has thus been able to derive both the exact mass and radius of the planet, concluding that it is a large "hot Jupiter".


Position(2000): RA = 20 00 43.71 Dec = +22 42 39.1

The planetary system in HD189733 is particularly interesting for several reasons:

• This new extra-solar planet joins the very exclusive group of planets outside our solar system that scientists have been able to measure precisely. Even if 160 extra-solar planets are presently known, accurate values for masses and radii are known only for 9 systems. HD189733b has a mass 365 times that of the Earth and a radius 14 times larger. Its density is comparable to that of Saturn. This extra-solar planet is located nearby, only 63 light-years away. The star HD189733 can be seen using binoculars (visual magnitude 7.7) in the constellation Vulpecula (The Fox). It just happens to be located by in the vicinity of the famous M27 "Dumbell" planetary nebula, well known to amateur astronomers.
• Its orbital period is one of the shortest known (only 2.2 days), nearly 2000 times faster than Jupiter, which takes 12 years to make a trip around the Sun. Due to the favourable orientation of its orbital plane, the planet HD189733b occults the central star every 2.2 days, producing a photometric transit (analogous to the Venus transit of the Sun seen in June 2004), a small decrease of flux lasting 2 hours.
• The transit of HD 189733b produces a decrease in luminosity of 3% which makes this system the one with the deepest partial occultation of the nine known transiting systems. This is due to the small size of the star (3/4 the size of the Sun) and the large size of the planet (1.26 times the size of Jupiter).
• The central star of this new planetary system is bright (V=7.7); most ground-based and space-borne telescopes will soon try to measure other interesting parameters, in particular its atmosphere. The small distance separating the planet from its star (only 3/100 of the Earth-Sun distance) implies that its atmosphere must be very hot, several hundred degrees. Attempts will be made to measure the reflectivity of its atmosphere, its chemical composition and the rate of evaporation. The light emitted by the planet itself may even be within reach of interferometry.

The extra-solar planet HD189733b will transit its host star on Wednesday, October 5, 2005 at 20h40 UT and every 53 hours thereafter. The members of the team will not miss this date and will try to obtain more data on this planet. Observations of this type made from a ground-based observatory (for example from OHP) allow the discovery of giant planets around other stars, but the transit method from space will make possible the discovery of even smaller planets: this is the aim of the COROT space mission to be launched in 2006.

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