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TOPIC: Extrasolar Planets


L

Posts: 131433
Date:
OGLE-2005-BLG-169lb
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OGLE-2005-BLG-169lb
Astronomers on Monday announced the discovery of a newfound cold extrasolar planet, OGLE-2005-BLG-169lb, 13 times heavier than Earth , orbiting a small red dwarf star roughly 9,000 light-years away.

The finding alters astronomers' perceptions of solar system formation and the distribution of planets in the galaxy, suggesting that large rock-ice worlds might outnumber gas giants like Jupiter.

The planet has an icy and rocky but barren terrestrial surface, and is one of the coldest planets ever discovered outside of our solar system.

It orbits 400 million kilometres away from a red dwarf star, which is cooler than and about half the size of our sun. The orbital distance about the same as our solar system's asteroid belt is from the sun.
The planet is similar in rocky structure to Earth, and it is described a "super-Earth."
But being so far away from a red dwarf means that its surface temperature is at -201 degrees Celsius, about the same as Uranus. Too cold for liquid water.

Further analysis of the system revealed the absence of Jupiter-like gas giants, and scientists suspect the system literally ran out of gas and failed to form any. This may have starved the planet of the raw materials it needed to turn into a gas giant itself.

"This icy super-Earth dominates the region around its star that in our solar system is populated by the gas-giant planets, Jupiter and Saturn. We've never seen a system like this before, because we've never had the means to find them" - study author Andrew Gould, Ohio State University and leader of the MicroFUN planet-searching team.

Planet formation theory predicts that small, cold planets should form more easily than larger ones around big stars. A previous study suggests that about two-thirds of all star systems in the galaxy are red dwarf stars, so solar systems filled with super-Earths might be three times more common than those with giant Jupiters.

"These icy super-earths are pretty common," Gould said. "Roughly 35 percent of all stars have them" - Andrew Gould.

While this is one of the coldest exoplanets ever discovered, it is not the smallest. Earlier this year astronomers announced the discovery of an exoplanet just 5.5 times Earth's mass. The previous record holder weighed in at 7.5 Earth masses.

"Our discovery suggests that different types of solar systems form around different types of stars. Sunlike stars form Jupiters, while red dwarf stars form super-Earths. Larger A-type stars may even form brown dwarfs in their disks" - Scott Gaudi, Harvard-Smithsonian Centre for Astrophysics.

Brown dwarfs are dim, failed stars that straddle the mass range between gas planets and real stars.
Astronomers discovered the planet using a technique called microlensing, an effect where the gravity of a foreground star makes a more distant star appear brighter. If the foreground star is orbited by a planet, the planet's gravity can periodically warp the brightness of the background star by tiny amounts.
This shift is a telltale indicator of a planet, but is so brief that scientists must monitor the star closely and make multiple observations to confirm the planet's existence. In this case, the scientists were concerned that the warp wasn't caused by a planet, so they wrote a special computer program to speed up their models and confirm the existence of the Neptune-sized object.
The planet's existence was determined by researchers from the MicroFUN, OGLE (Optical Gravitational Lensing Experiment) projects and the MDM Observatory in Arizona. The group has submitted their findings for publication in the journal Astrophysical Journal Letters.

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Posts: 131433
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RE: Extrasolar Planets
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Astronomers are hoping to use the Terrestrial Planet Finder (TPF), now planned for launch between 2014 and 2020, and the ESA's Darwin planned groups of observatories to search for a rocky inner planet in the so-called "habitable zone" (HZ) around nearby stars.



Turnbull's list for the SETI search includes:

* Beta Canum Venaticorum, Turnbull's top prospect. It's a sunlike star about 26 light-years away in the northern constellation Canes Venatici. Astronomers have been looking for planets around the star but have found none to date.
* HD 10307, another sunlike star about 42 light-years away. It has nearly the same mass, temperature and metal content as our sun — plus a companion star.
* HD 211415, which has about half the metal content of the sun and is a bit cooler.
* 18 Scorpii, a popular target for proposed planet searches. The star is almost an identical twin of the sun, Turnbull says.
* 51 Pegasus, which was the first normal star beyond our solar system known to have a planet. The Jupiterlike planet was detected in 1995, and Turnbull believes 51 Pegasus could harbour Earthlike planets as well.


The top five Terrestrial Planet Finder mission targets were:

* Epsilon Indi A, about 11.8 light-years from Earth, leads Turnbull's list. It's a star somewhat cooler and smaller than our sun, and was recently found to have a brown-dwarf companion. "Star Trek" fans consider it the home of the Andorian race. In the original "Star Trek" series, it was the base of operations for an evil entity called "Gorkon."
* Epsilon Eridani, 10.5 light-years away, is a star somewhat smaller and cooler than our sun, and is already known to have at least one planet. By some science-fiction accounts, Epsilon Eridani is the parent star for Vulcan, Mr. Spock's home planet on "Star Trek." However, Trekkers have come to favour another star in the same constellation....
* Omicron 2 Eridani, also known as 40 Eridani, is now cited in most "Star Trek" literature as Mr. Spock's home turf. It's a yellow-orange star about 16 light-years away, and is roughly the same age as our sun.
* Alpha Centauri B is part of the triple-star system closest to our own sun, just 4.35 light-years away. It's long been considered one of the places in the Milky Way that might offer terrestrial conditions.
* Tau Ceti is in the same brightness category as our sun. It's metal-poor, compared to the sun, but long-lived enough for life forms to evolve.

Source MSNBC

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L

Posts: 131433
Date:
Terrestrial Planet Finder
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Astronomers are hoping to use the Terrestrial Planet Finder (TPF), now planned for launch between 2014 and 2020, and the ESA's Darwin planned groups of observatories to search for a rocky inner planet in the so-called "habitable zone" (HZ) around nearby stars.

It is planned for the TPF to include two complementary observatory groups: a visible-light coronagraph to launch around 2014; and a "formation-flying" infrared interferometer to launch before 2020, while Darwin will launch a flotilla of three mid-infrared telescopes and a fourth communications hub beginning around 2015.

Astronomer Margaret Turnbull at the Carnegie Institution in Washington DC has been working on identifying the best stars for the TPF to target its observatories.
She looked at criteria such as the star's age and the amount of iron in its atmosphere.

"Sigma Draconis is one of our best TPF-C targets, and the 4th easiest star in the universe to detect terrestrial planets" - Margaret Turnbull

Another top candidate was beta CVn, a Sun-like star 26 light-years away.

Sigma Draconis is a main-sequence orange-red dwarf star of spectral and luminosity type K0 V. The star has about 89 percent of Sol's mass (RECONS), 79 percent of its diameter, and 39 percent of its luminosity. Although the star may only be about 3.3 billion years old, it appears to be less enriched than Sol in elements heavier than hydrogen ("metals") with only about 56 to 59 percent of Sol's abundance of iron.
It has the Catalogue and New Suspected Variable designations of CSV 101868 and NSV 12176.

See more

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L

Posts: 131433
Date:
OGLE-2005-BLG-390Lb
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The new planet was found using the ‘microlensing’ technique, described by the leader of the RoboNet microlensing planet search, Prof. Keith Horne of the University of St. Andrews in Scotland, as the "fastest way to find small cool planets down to the mass of the Earth...".

Flash movie

"If we can deploy robotic telescopes at additional sites in the southern hemisphere we can expect to find several more cool planets every year, which could include the first detection of extra-solar Earths. This is a very important discovery. It is the first planet which is likely to be ‘rocky’ i.e. similar to the composition of the Earth, Venus and Mars, as opposed to gas giants of the Jupiter type. Planets of the terrestrial type are of course the ‘holy grail’ for those who search for life in the Universe” - Malcolm Fridlund, study scientist for ESA’s Darwin mission.

ESA is also involved in the Corot mission to be launched later this year that will search for planets occulting their parental stars. A planet like OGLE-2005-BLG-390Lb found closer to its star would be easy for Corot to pick up and this discovery makes it even more probable.
ESA’s Darwin is intended to search for Earth-like planets, the most likely places for life to develop; it will survey 1000 of the closest stars, looking for small rocky planets. Darwin will be a flotilla of four free-flying spacecraft that will search for such Earth-like planets around other stars and analyse their atmospheres for the chemical signature of life.

Corot, due for launch at the end of this year, will be the first mission capable of detecting rocky planets, several times larger than Earth, around nearby stars. Corot is led by the French space agency CNES. ESA joined the mission in October 2000 by agreeing to provide the optics for the telescope and to test the payload. As a result of the collaboration, scientists from ESA’s Member States will be given access to the satellite’s data.

Source ESA

-- Edited by Blobrana at 15:21, 2006-01-26

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Posts: 131433
Date:
RE: Extrasolar Planets
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Position (J2000): R.A. 17h 54 m 19s.2 Dec. -30° 22' 38 "
Constellation: Sagittarius
This artist's illustration shows an icy/rocky planet orbiting a dim star.
Credit: NASA, ESA and G. Bacon (STScI)

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Posts: 131433
Date:
New Planet
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When OGLE detected the July 11 lensing, its early warning system alerted fellow astronomers across the globe to microlensing event OGLE-2005-BLG-390 (for the 390th galactic bulge OGLE discovered in 2005). At that point, though, no one knew a planet would emerge.

"The only way to realize the full scientific benefit of our observations is to share the data with our competition" - co-author Bohdan Paczynski of Princeton University, who along with Andrzej Udalski of Warsaw University Observatory and their colleagues co-founded OGLE in 1997.

The telescopes of PLANET (Probing Lensing Anomalies NETwork) and RoboNet tracked the July 11 episode to completion, providing the data that confirmed the presence of a previously unknown planet. These telescopes collect observations more frequently in an attempt to detect the microlensing signature of planets.

Read More


Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing*

In the favoured core-accretion model of formation of planetary systems, solid planetesimals accumulate to build up planetary cores, which then accrete nebular gas if they are sufficiently massive. Around M-dwarf stars (the most common stars in our Galaxy), this model favours the formation of Earth-mass (M.) to Neptune-mass planets with orbital radii of 1 to 10 astronomical units (AU), which is consistent with the small number of gas giant planets known to orbit Mdwarf host stars 1-4. More than 170 extrasolar planets have been discovered with a wide range of masses and orbital periods, but planets of Neptune’s mass or less have not hitherto been detected at separations of more than 0.15 AU from normal stars. Here we report the discovery of a 5.5 2.7 +5.5 M. planetary companion at a separation of 2.6 0. 0.6 +1. 1.5 AU from a 0.22 0.11 +0.21 solar mass (M.) M-dwarf star. star, where M. refers to a solar mass. (We propose to name it OGLE-2005-BLG-390Lb, indicating a planetary mass companion to the lens star of the microlensing event.)
The mass is lower than that of GJ876d, although the error bars overlap. Our detection suggests that such cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory.

Read More (PDF)

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Posts: 131433
Date:
OGLE-2005-BLG-390Lb
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"This planet is actually the first and only planet that has been discovered so far that is in agreement with the theories for how our Solar System formed" - Uffe Gråe Jørgensen (Niels Bohr Institute, Copenhagen, Denmark), member of the team.

The favoured theoretical explanation for the formation of planetary systems proposes that solid 'planetesimals' accumulate to build up planetary cores, which then accrete nebular gas - to form giant planets - if they are sufficiently massive. Around red dwarfs, the most common stars of our Galaxy, this model favours the formation of Earth- to Neptune-mass planets being between 1 and 10 times the Earth-Sun distance away from their host.


Position(2000): RA = 17:54:19.19 Dec = -30:22:38.3.
Mass: 0.018 (± 0.01) MJ
Orbit: 2.6 AU

"OGLE-2005-BLG-390Lb is only the third extra-solar planet discovered so far through microlensing searches. While the other two microlensing planets have masses of a few times that of Jupiter, the discovery of a 5 Earth mass planet - though much harder to detect than more massive ones - is a strong hint that these lower-mass objects are very common" - Jean-Philippe Beaulieu (Institut d'Astrophysique de Paris, France), the lead author.

The OGLE (Optical Gravitational Lensing Experiment) search team (led by A. Udalski, Warsaw University Observatory, Poland) discovered the event OGLE-2005-BLG-390 on 11 July 2005, triggering the PLANET telescopes to start taking data. A light curve consistent with a single lens star peaking at an amplification of about 3 on 31 July 2005 was observed, until 10 August when PLANET member Pascal Fouqué, observing at the Danish 1.54m at ESO La Silla, noticed a planetary deviation. An OGLE point from the same night showed the same trend, while the last half of the planetary deviation, lasting about a day, had been covered by images from Perth Observatory. The MOA (Microlensing Observations in Astrophysics) collaboration was later able to identify the source star on its images and confirmed the deviation.


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(333kb, 1053 x 800)
Data obtained by PLANET/RoboNet, OGLE, and MOA on the microlensing event OGLE-2005-BLG-390 together with a model light curve, showing the planetary deviation on its falling part, lasting about a day. Also shown are best-fitting models with a single lens and a binary source (long-dashed) and a single-source-single-lens light curve (short-dashed). Each point represents the brightness in a single image and the data are colour-coded in order to indicate the telescope: Danish 1.54m at ESO La Silla (Chile), Perth 0.6m (Bickley, Western Australia), Canopus 1.0m (Hobart, Tasmania, Australia), Faulkes North 2.0m (Haleakela, Hawaii, USA), OGLE 1.3m (Las Campanas, Chile), and MOA 1.8m at Mt John Observatory (New Zealand). The regular cycle of colours shows how observing is taken over by the next telescope in turn as the night ends at each site. An enlargement of the planetary deviation is shown as inset in the top right.


No other interpretation than the presented sub-Neptune mass planet with its quoted parameters appeared to fit the extensive data set. This discovery brings a fresh look at the field of planetary science.
In particular, astronomers now think that such frozen worlds are much more common than their larger, Jupiter-like brethren.

"Indeed if Jupiter-like planets were as widespread, the microlensing method should have found dozens of them by now" - David Bennett (University of Notre Dame, USA), another PLANET team member.

The microlensing technique is most probably the only method currently capable of detecting planets similar to Earth.

"The search for a second Earth is the driving force behind our research and this discovery constitutes a major leap forward since it is the most Earth-like planet we know of so far" - co-author Daniel Kubas, ESO.

Read More

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L

Posts: 131433
Date:
RE: Extrasolar Planets
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DISCOVERY OF A ROCKY/ICY 5 EARTH-MASS EXOPLANET
M Dominik (for the PLANET and RoboNet collaborations)
School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Scotland.

We report the discovery of exoplanet OGLE 2005-BLG-390Lb, which orbits its parent star, a Solar analogue with 0.2 Solar masses located near the centre of the Milky Way, at an orbital radius of 3 AU with a period of 11 years. With a mass of about 5 times that of Earth, is probably the least massive exoplanet around an ordinary star discovered so far (with some statisticical overlap to GJ876d), and with a surface temperature of about 50 K certainly the coolest, so that it is undoubtedly of rocky/icy rather than gaseous nature. The planet revealed its existence by its gravitational field affecting the light of an observed background star in the Galactic bulge. This phenomenon is known as gravitational lensing, discussed by Einstein in 1936. Over a time-span of about one day, a significant deviation to the brightening caused by its parent star alone was observed with two telescopes participating in the PLANET/RoboNet campaign, capable of quasi-continuous round-the-clock monitor!

This deviation was confirmed by a few additional data points from the OGLE and MOA surveys, providing daily sampling with a single telescope. Results of simulations of planet formation and migration based on core-accretion models match the observed distribution of about 150 exoplanets discovered so far remarkably well, while these predict a large abundance of planets less massive than 10 Earth masses and orbital semi-major axes between 0.1 and 10 AU. Such separations coincide with the favoured sensitivity range of microlensing, making it the ideal method for detecting these low-mass planets. In particular, it is the only technique currently able to detect planets of Earth mass. Our recent discovery provides a strong observational hint for Earth-like planets being common and indicates that an intensive microlensing campaign, possible with the deployment of UK-built robotic telescopes in the southern hemisphere, will detect several of these within a few years.


The PLANET microlensing campaign: Implications for planets around galactic disk and bulge stars

Abstract:
With round-the-clock monitoring of galactic bulge microlensing events, the PLANET experiment constrains the abundance and can yield the discovery of planets down to the mass of earth around galactic disk and bulge stars. Data taken until 1999 imply that less than 1/3 of bulge M-dwarfs are surrounded by jupiter-mass companions at orbital radii between 1 and 4 AU. The current rate of microlensing alerts allows 15–25 jupiters and 1–3 earths to be probed per year.


Read more (PDF)

-- Edited by Blobrana at 18:57, 2006-01-25

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Posts: 131433
Date:
OGLE-2005-BLG-390Lb
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The planet, named OGLE-2005-BLG-390Lb, is estimated to be about 5.5 times as massive as Earth and thought to be rocky. It orbits a red dwarf star, orbiting at 2.5 AU from a star 25,000 light years away, close to the centre of the Milky Way

It may have a frozen ocean on a rocky core, the surface temperature is at - 220 degrees zero.
The new planet takes about 10 years to orbit its parent star
Prior to this discovery, the smallest extrasolar planet found around a normal star was about 7.5 Earth masses.

A microlensing technique was used to discover the planet. light from the distant star was bent and magnified by the gravitational field of a foreground star. The presence of a planet around the foreground star causes light from the distant star to become momentarily brighter.

The microlensing event was detected July 11 by telescopes in the OGLE (Optical Gravitational Lensing Experiment) project.

-- Edited by Blobrana at 18:37, 2006-01-25

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Posts: 131433
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RE: Extrasolar Planets
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Webcast

A New Path to New Earths
Media Briefing
1/25/2006 1:00:00 PM - 60 minutes

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