Category: Extrasolar Planets

Artist illustration of the rocky planet around the M dwarf Gliese 876. Image credit: NSF. Click to enlarge.
In the land rush known as extrasolar planet hunting, the most prized real estate is advertised as “Earth-like.” On Monday, June 13, scientists raced to plant their flag on a burning hunk of rock orbiting a red star.

This newly discovered planet is about seven times the mass of Earth, and therefore the smallest extrasolar planet found to orbit a main sequence, or “dwarf” star (stars, like our sun, that burn hydrogen).

There are even smaller planets known to exist beyond our solar system, but they have the misfortune to encircle pulsars, those rapidly spinning husks of dying stars. Such planets aren’t thought to be remotely habitable, due to the intense radiation emitted by pulsars.

Planets that are ten Earth masses or less are thought to be rocky, while more massive planets are probably gaseous, since their stronger gravity means they collect and retain more gas during planetary formation. 155 extrasolar planets have been found so far, but most of them have masses that are more comparable to gaseous Jupiter than rocky Earth (Jupiter is 318 times the mass of Earth).

Although this new planet is advertised as Earth-like because of its relatively low mass, earthlings wouldn’t want to rent a house there any time soon. For one thing, the house would melt. The surface temperatures estimated for this planet – 200 to 400 degrees Celsius (400 to 750 degrees Fahrenheit) – are due to the planet’s kissing-close distance from its star.

The planet resides a mere 0.021 AU from the star Gliese 876 (1 AU is the distance between the Earth and the sun), and completes an orbit in less then two Earth days. The closest planet to the sun in our own solar system – blazing hot Mercury – is nearly 20 times further away, orbiting at about 0.4 AU.

“Because the planet is in a two-day orbit, it is heated to oven-like temperatures, so we do not expect life,” says science team member Paul Butler of the Carnegie Institution of Washington.

In our solar system, the habitable zone – the temperate region where water could exist as a liquid on a planet’s surface – is roughly 0.95 to 1.37 AU, or between the orbits of Venus and Mars. The star Gliese 876 is about 600 times less luminous than our sun, so the proposed habitable zone is much closer in, roughly between 0.06 and 0.22 AU.

At 0.021 AU, the new planet is too close to the star to be in the habitable zone, and it also is subjected to greater amounts of high energy radiation like ultraviolet light and X-rays. While red dwarfs like Gliese 876 emit lower levels of UV than stars like our sun, they do emit violent X-ray flares.

Another complication from such a close orbit is that the planet may be tidally locked, with the same side of the planet always facing the star. Unless there is a substantial atmosphere to distribute heat, one side of the planet will be overcooked while the other will remain cold.

Gliese 876 is thought to be about 11 billion years old, making it more than twice as old as our sun. But in a way, Gliese is a teenager to our sun’s middle-aged adult. G-class stars like our sun live about 10 billion years, while M-class red dwarfs are thought to live for 100 billion years (older than the age of the universe!).

Science team member Geoff Marcy of the University of California, Berkeley, says that M stars take a long time to cool off and shrink down to their main sequence size and luminosity. He says that if the planet migrated inwards to its present day close orbit, it probably made this move during the first few million years, and then was subjected to much more radiation than at present for hundreds of millions of years.

Gliese 876 is thought to be metal-poor (to an astronomer, any element heavier than hydrogen and helium is classified as a “metal”). The formation of planets may be related to the metallicity of the star, since both the star and the planets form from the same original material. So a rocky planet like the Earth, made out of elements such as silicates and iron, is expected to orbit a star that is metal-rich.

Despite being metal-poor, Gliese 876 is a multiple planet system. Two gas giant planets are known to orbit Gliese 876: the outermost planet is nearly twice the mass of Jupiter, and orbits at 0.21 AU; the middle planet is about half the mass of Jupiter, orbiting at 0.13 AU.

“The whole planetary system is sort of a miniature of our solar system,” says Marcy. “The star is small, the orbits are small, and in closer is the smallest of them, just as the architecture is in our own solar system, with the smallest planets orbiting inward of the giants.”

We have a lot more elbow room in our solar system. Mercury is further away from the sun than the distances of all these planets combined. The planets in the Gliese 876 system are so close together, they gravitationally interact with each other. This sort of gravitational tug of war was how the scientists were able to detect the planets in the first place.

Over the course of an orbit, planets will gravitationally pull on their star from different sides. Scientists measure the resulting shift in star light to determine the existence of orbiting planets.

To learn more about Gliese 876’s smallest planet, scientists would need to use another planet-hunting technique called transit photometry. This method looks at how a star’s light seems to dip when a planet passes in front of the star from our field of view. The eclipse of the orbiting planet allows astronomers to determine that planet’s mass and radius. Pinning down those numbers indicates the planet’s density, which then suggests what the planet is made of, and whether the planet is rocky or gaseous.

Transit photometry can’t be used to tell us anything about planets orbiting Gliese 876, however, because the system is inclined 50 degrees from our point of view. This angle means the planets won’t block any of the starlight that reaches Earth.

Red dwarfs are the most common type of star in our galaxy, comprising about 70 percent of all stars. Yet out of the 150 red dwarfs they have studied over the years, Marcy and Butler only have found planets orbiting two of them. Because most of the planets found so far are gas giants, this could mean that red dwarfs are less apt to harbor those kinds of worlds.

Marcy says they will continue to monitor Gliese 876 for any hints of a fourth or fifth planet. “This will definitely be one of our favorite stars from now on.”

A Race to the Finish Line
The research paper describing this discovery has been submitted to the Astrophysical Journal. The scientists say they received a favorable preliminary referee’s report, and they expect their paper will be accepted and then published in a few months. During Monday’s press conference, the scientists were asked why they decided to publicize their finding now, before the paper had been accepted for publication. Was it done to beat out other planet hunters who might be hot on their heels?

Marcy replied that they wanted to prevent news of their discovery from leaking out. “We knew about it three years ago, we’ve been following it quietly, carefully, guarding the secret while we double and triple checked. Then about a month ago I talked with Michael Turner here, people at NSF (National Science Foundation), and jointly we decided that this discovery was so extraordinary, maybe what you would call a milestone in planetary science, that it was difficult to imagine keeping the lid on this for very much longer. So we decided that rather than have it leak out to the news media, and be dribbled around, with one newspaper learning about it early and so on, that it would be better to quickly announce this.”

Marcy then launched into a defense for why he believed their finding is correct, and he was quickly backed by his fellow team members. However, the accuracy of their finding had not been questioned. Perhaps their early announcement, combined with the need for secrecy beforehand, is evidence of the intense competition that has marked planet hunting since the beginning.

The first extrasolar planet discovery was announced October 5, 1995 by Michel Mayor and Didier Queloz of the Geneva Observatory, and Marcy and Butler confirmed the observations the following week. A recent example of the competition to grab other extrasolar planet “firsts” occurred last summer, when on August 25, 2004, Mayor, Nuno Santos, and colleagues announced the discovery of the first extrasolar Neptune-mass planet — at the time the smallest extrasolar planet known to orbit a sun-like star. This announcement came less than a week before two other Neptune-mass planet discoveries were announced by Marcy and Butler.

Mayor and his colleagues also have studied Gliese 876. At an astronomy conference in June 1998, Mayor and Marcy each independently announced the detection of the more massive gas giant orbiting this star. Marcy and Butler were first to follow up on this finding, announcing the discovery of the star’s second gas giant planet in 2001.

The Kepler mission, due to launch in June 2008, will search for terrestrial planets orbiting distant stars. The mission defines an Earth-size planet as being between 0.5 and 2.0 Earth masses, or between 0.8 and 1.3 Earth’s diameter. Planets between 2 and 10 Earth masses, such as the planet announced on Monday, are defined as Large Terrestrial planets.

Original Source: NASA Astrobiology

Artist illustration of the rocky planet around the M dwarf Gliese 876. Image credit: NSF. Click to enlarge.
Taking a major step forward in the search for Earth-like planets beyond our own solar system, a team of astronomers has announced the discovery of the smallest extrasolar planet yet detected. About seven-and-a-half times as massive as Earth, with about twice the radius, it may be the first rocky planet ever found orbiting a normal star not much different from our Sun.

All of the nearly 150 other extrasolar planets discovered to date around normal stars have been larger than Uranus, an ice-giant about 15 times the mass of the Earth.

“We keep pushing the limits of what we can detect, and we’re getting closer and closer to finding Earths,” said team member Steven Vogt, a professor of astronomy and astrophysics at the University of California, Santa Cruz.

?Today’s results are an important step toward answering one of the most profound questions that mankind can ask: Are we alone in the universe?? said Michael Turner, head of the Mathematical and Physical Sciences Directorate at the National Science Foundation, which provided partial funding for the research.

The newly-discovered ?super-Earth? orbits the star Gliese 876, located just 15 light years away in the direction of the constellation Aquarius. This star also possesses two larger, Jupiter-size planets. The new planet whips around the star in a mere two days, and is so close to the star’s surface that its temperature probably tops 400 to 750 degrees Fahrenheit (200 to 400 degrees Celsius)?oven-like temperatures far too hot for life as we know it.

Nevertheless, the ability to detect the tiny wobble that the planet induces in the star gives astronomers confidence that they will be able to detect even smaller rocky planets in orbits more hospitable to life.

“This is the smallest extrasolar planet yet detected and the first of a new class of rocky terrestrial planets,” said team member Paul Butler of the Carnegie Institution of Washington. “It’s like Earth’s bigger cousin.”

The team measures a minimum mass for the planet of 5.9 Earth masses, orbiting Gliese 876 with a period of 1.94 days at a distance of 0.021 astronomical units (AU), or 2 million miles.

Though the team has no direct proof that the planet is rocky, its low mass precludes it from retaining gas like Jupiter. Three other purported rocky planets have been reported, but they orbit a pulsar, the flashing corpse of an exploded star.

“This planet answers an ancient question,” said team leader Geoffrey Marcy, professor of astronomy at the University of California, Berkeley. “Over 2,000 years ago, the Greek philosophers Aristotle and Epicurus argued about whether there were other Earth-like planets. Now, for the first time, we have evidence for a rocky planet around a normal star.”

Marcy, Butler, theoretical astronomer Jack Lissauer of NASA/Ames Research Center, and post-doctoral researcher Eugenio J. Rivera of the University of California Observatories/Lick Observatory at UC Santa Cruz presented their findings today (Monday, June 13) during a press conference at NSF in Arlington, Va.

Their research, conducted at the Keck Observatory in Hawaii, was supported by NSF, the National Aeronautics and Space Administration, the University of California and the Carnegie Institution of Washington.

A paper detailing the results has been submitted to The Astrophysical Journal. Coauthors on the paper are Steven Vogt and Gregory Laughlin of the Lick Observatory at the University of California, Santa Cruz; Debra Fischer of San Francisco State University; and Timothy M. Brown of NSF?s National Center for Atmospheric Research in Boulder, Colorado.

Gliese 876 (or GJ 876) is a small, red star known as an M dwarf ? the most common type of star in the galaxy. It is located in the Aquarius constellation, and, at about one-third the mass of the sun, is the smallest star around which planets have been discovered. Butler and Marcy detected the first planet there in 1998; it proved to be a gas giant about twice the mass of Jupiter. Then, in 2001, they reported a second planet, another gas giant about half the mass of Jupiter. The two are in resonant orbits, the outer planet taking 60 days to orbit the star, twice the period of the inner giant planet.

Lissauer and Rivera have been analyzing Keck data on the Gliese 876 system in order to model the unusual motions of the two known planets, and three years ago got an inkling that there might be a smaller, third planet orbiting the star. In fact, if they hadn’t taken account of the resonant interaction between the two known planets, they never would have seen the third planet.

“We had a model for the two planets interacting with one another, but when we looked at the difference between the two-planet model and the actual data, we found a signature that could be interpreted as a third planet,” Lissauer said.

A three-planet model consistently gave a better fit to the data, added Rivera. “But because the signal from this third planet was not very strong, we were very cautious about announcing a new planet until we had more data,” he said.

Recent improvements to the Keck Telescope’s high-resolution spectrometer (HIRES) provided crucial new data. Vogt, who designed and built HIRES, worked with the technical staff in the UC Observatories/Lick Observatory Laboratories at UC Santa Cruz to upgrade the spectrometer’s CCD (charge coupled device) detectors last August.

“It is the higher precision data from the upgraded HIRES that gives us confidence in this result,” Butler said.

The team now has convincing data for the planet orbiting very close to the star, at a distance of about 10 stellar radii. That’s less than one-tenth the size of Mercury’s orbit in our solar system.

“In a two-day orbit , it’s about 200 degrees Celsius too hot for liquid water,” Butler said. “That tends to lead us to the conclusion that the most probable composition of this thing is like the inner planets of this solar system ? a nickel-iron rock, a rocky planet, a terrestrial planet.”

“The planet’s mass could easily hold onto an atmosphere,” noted Laughlin, an assistant professor of astronomy at UC Santa Cruz. “It would still be considered a rocky planet, probably with an iron core and a silicon mantle. It could even have a dense steamy water layer. I think what we are seeing here is something that’s intermediate between a true terrestrial planet like the Earth and a hot version of the ice giants Uranus and Neptune.”

Combined with improved computer software, the new CCD (charge coupled device) detectors designed by this team for Keck’s HIRES spectrometer can now measure the Doppler velocity of a star to within one meter per second ? human walking speed ? instead of the previous precision of three meters per second. This improved sensitivity will allow the planet-hunting team to detect the gravitational effect of an Earth-like planet within the habitable zone of M dwarf stars like Gliese 876.

“We are pushing a whole new regime at Keck to achieve one meter per second precision, triple our old precision, that should also allow us to see Earth-mass planets around sun-like stars within the next few years,” Butler said.

“Our UC Santa Cruz and Lick Observatory team has done an enormous amount of optical and technical and detector work to make the Keck telescope a rocky planet hunter, the best one in the world,” Marcy added.

Lissauer also is excited by another feat reported in the paper submitted to the journal. For the first time, he, Rivera and Laughlin have determined the line-of-sight inclination of the orbit of the stellar system solely from the observed Doppler wobble of the star. Using dynamical models of how the two Jupiter-size planets interact, they were able to calculate the masses of the two giant planets from the observed shapes and precession rates of their oval orbits. Precession is the slow turning of the long axis of a planet’s elliptical orbit.

They showed that the orbital plane is tilted 40 degrees to our line of sight. This allowed the team to estimate the most likely mass of the third planet as seven and a half Earth masses.

“There’s more dynamical modeling involved in this study than any previous study, much more,” Lissauer said.

The team plans to continue to observe the star Gliese 876, but is eager to find other terrestrial planets among the 150 or more M dwarf planets they observe regularly with Keck.

“So far we find almost no Jupiter-mass planets among the M dwarf stars we’ve been observing, which suggests that, instead, there is going to be a large population of smaller mass planets,” Butler noted.

Original Source: Carnegie Institute News Release

Artist interpretation of an extrasolar planet. Image credit: NASA. Click to enlarge.
An international collaboration featuring Ohio State University astronomers has detected a planet in a solar system that, at roughly 15,000 light years from Earth, is one of the most distant ever discovered.
Andrew Gould

In a time when technology is starting to make such finds almost commonplace, this new planet — which is roughly three times the size of Jupiter — is special for several reasons, said Andrew Gould, professor of astronomy at Ohio State .

The technique that astronomers used to find the planet worked so well that he thinks it could be used to find much smaller planets — Earth-sized planets, even very distant ones.

And because two amateur astronomers in New Zealand helped detect the planet using only their backyard telescopes, the find suggests that anyone can become a planet hunter.

Gould and his colleagues have submitted a paper announcing the planet to Astrophysical Journal Letters, and have posted the paper on a publicly available Internet preprint server, http://arXiv.org . The team has secured use of NASA’s Hubble Space Telescope in late May to examine the star that the planet is orbiting.

The astronomers used a technique called gravitational microlensing, which occurs when a massive object in space, like a star or even a black hole, crosses in front of a star shining in the background. The object’s strong gravitational pull bends the light rays from the more distant star and magnifies them like a lens. Here on Earth, we see the star get brighter as the lens crosses in front of it, and then fade as the lens gets farther away.
Because the scientists were able to monitor the light signal with near-perfect precision, Gould thinks the technique could easily have revealed an even smaller planet. “If an Earth-mass planet was in the same position, we would have been able to detect it,” he said.

On March 17, 2005, Andrzej Udalski, professor of astronomy at Warsaw University and leader of the Optical Gravitational Lensing Experiment, or OGLE, noticed that a star located thousands of light years from Earth was starting to move in front of another star that was even farther away, near the center of our galaxy. A month later, when the more distant star had brightened a hundred-fold, astronomers from OGLE and from Gould’s collaboration (the Microlensing Follow Up Network, or MicroFUN) detected a new pattern in the signal — a rapid distortion of the brightening — that could only mean one thing.

“There’s absolutely no doubt that the star in front has a planet, which caused the deviation we saw,” Gould said.

Because the scientists were able to monitor the light signal with near-perfect precision, Gould thinks the technique could easily have revealed an even smaller planet.

“If an Earth-mass planet was in the same position, we would have been able to detect it,” he said.

OGLE finds more than 600 microlensing events per year using a dedicated 1.3-meter telescope at Las Campanas Observatory in Chile (operated by Carnegie Institution of Washington). MicroFUN is a collaboration of astronomers from the US, Korea, New Zealand, and Israel that picks out those events that are most likely to reveal planets and monitors them from telescopes around the world.

“That allows us to watch these events 24/7,” Gould said. “When the sun rises at one location, we continue to monitor from the next.”

Two of these telescopes belong to two avid New Zealand amateur astronomers who were recruited by the MicroFUN team. Grant Christie of Auckland used a 14-inch telescope, and Jennie McCormick of Pakuranga used a 10-inch telescope. Both share co-authorship on the paper submitted to Astrophysical Journal Letters.

Two other collaborations — the Probing Lensing Anomalies NETwork (PLANET) and Microlensing Observations in Astrophysics (MOA) — also followed the event and contributed to the journal paper.

Ohio State scientists on the project included Darren DePoy and Richard Pogge, both professors of astronomy, and Subo Dong, a graduate student. Other partners hail from Warsaw University in Poland, Princeton University, Harvard-Smithsonian Center for Astrophysics, Universidad de Concepci?n in Chile, University of Manchester, California Institute of Technology, American Museum of Natural History, Chungbuk National University in Korea, Korea Astronomy and Space Science Institute, Massy University in New Zealand, Nagoya University in Japan, and the University of Auckland in New Zealand.

This is the second planet that astronomers have detected using microlensing. The first one, found a year ago, is estimated to be at a similar distance.

Gould’s initial estimate is that the new planet is approximately 15,000 light years away, but he will need more data to refine that distance, he said. A light year is the distance light travels in a year — approximately six trillion miles.

The OGLE collaboration is funded by the Polish Ministry of Scientific Research and Information Technology, the Foundation for Polish Science, the National Science Foundation, and NASA. Some MicroFUN team members received funding from the National Science Foundation, Harvard College Observatory, the Korea Science and Engineering Foundation, and the Korea Astronomy and Space Science Institute.

Original Source: OSU News Release

ESO image of a completely different star, 2M1207, and its planet. Image credit: ESO. Click to enlarge.
Canadian astronomers using the MOST space telescope have observed a remarkable planetary system where a giant close-in planet is forcing its parent star to rotate in lock-step with the planet’s orbit. “This is truly a stellar story of `tail wags dog’,” according to Dr. Jaymie Matthews of the University of British Columbia, leader of the Canadian Space Agency’s MOST space telescope mission, in an announcement about the exoplanetary system tau Bootis made at the annual meeting of the Canadian Astronomical Society in Montreal today.

“The interactions between the star and the giant planet in the tau Bootis system are unlike anything astronomers have seen before,” elaborates Dr. Matthews. “And they would be undetectable by any instrument on Earth or in space other than MOST.”

The MOST (Microvariability & Oscillations of STars) satellite has revealed that the star tau Bootis is undergoing subtle variations in its light output that are in synch with the orbit of the planet – unimaginatively designated tau Bootis b – in a tight orbit around it. The best explanation is that the planet’s gravity has forced the outer envelope of the star to rotate so it always keeps the same face to the planet – despite the fact that the planet is probably under 1% of the star’s mass.

“It’s no surprise when a star or planet gravitationally forces its smaller companion to spin according to its orbital rhythm, like the Moon always keeping the same face to the Earth,” Dr. Matthews explains. “But for a planet to force a star to do this is very unusual.” In all likelihood, only the surface layers of gas in the star have succumbed to the planet’s influence, just as in the Earth-Moon system, where the Moon has succeeded in causing a bulge in the thin layer of water on the Earth’s surface which results in the ocean tides, but has not forced the massive solid Earth underneath to rotate in step.

The only reason why the planet can lead even part of the star in the tau Bootis system is because it orbits so closely – only 1/20th of the Earth-Sun distance – and because it’s quite big as planets go – at least 4 times the mass of Jupiter, the largest planet in our own Solar System. The planet was discovered in 1997 by American astronomers Paul Butler, Geoff Marcy and colleagues based on the wobbling motions induced in the star by the 3.3-day orbit of an unseen companion. With such a small orbit, you might expect other complicated interactions between the star and planet, and MOST has observed evidence for these as well. There are indirect indications of starspots, tidal distortion, and even magnetic activity on the surface of tau Boo a.

Last year, another team of Canadian scientists, led by Evgenya Shkolnik (an alumna of UBC now at the University of Hawaii) and Gordon Walker (an exoplanet pioneer and MOST Science Team member at UBC), presented evidence in a system similar to tau Boo, HD179949, for a planet heating up the gas in its parent star, which is also behaviour never seen before. This would probably be caused by the entanglement of a magnetic field of the planet with the star’s field. “We may be witnessing another example of this in tau Bootis,” notes Dr. Walker. “The nature of the light variations is different for each of the nine exoplanet orbits monitored by MOST in 2004 and 2005. The explanation for all the variability will have to include intrinsic stellar effects, like rotation, and planet-induced effects, like heating caused by tides and magnetic fields – a complex model, to be sure.”

The theories of the origins and evolution of planetary systems were shaken up a decade ago with the discovery of the first of these giant close-in exoplanets (dubbed “hot Jupiters”) around the Sun-like star, 51 Pegasi. The planet in the tau Bootis system is more massive and closer to its star than the one in 51 Pegasi, and represents a remote laboratory for planetary scientists to test new theories about planet formation that will eventually be applied to our own Solar System. The details revealed by MOST have already excited theorists, and certainly excited the observers on the MOST team. Dr. Rainer Kuschnig, MOST Instrument Scientist (UBC) can barely contain his enthusiasm: “It’s tremendous fun to watch the data on this system come in from the satellite and see something new every day. It’s so cool!”

MOST (Microvariability & Oscillations of STars) is a Canadian Space Agency mission. Dynacon Inc. of Mississauga, Ontario, is the prime contractor for the satellite and its operation, with the University of Toronto Institute for Aerospace Studies (UTIAS) as a major subcontractor. The University of British Columbia (UBC) is the main contractor for the instrument and scientific operations of the MOST mission. MOST is tracked and operated through a global network of ground stations located at UTIAS, UBC and the University of Vienna.

Animations of eta Boo and tau Boo are available at:

http://www.astro.umontreal.ca/~casca/PR/etaBoo2.wmv
http://www.astro.umontreal.ca/~casca/PR/tauBootis3.wmv

Original Source: MOST News Release

The suitcase-sized MOST space telescope. Image credit: MOST. Click to enlarge.
MOST, Canada’s first space telescope, has turned up an important clue about the atmosphere and cloud cover of a mysterious planet around another star, by playing a cosmic game of `hide and seek’ as that planet moves behind its parent star in its orbit.

The exoplanet, with a name only an astrophysicist could love, HD209458b (orbiting the star HD209458a), cannot be seen directly in images, so the scientists on the MOST (Microvariability & Oscillations of STars) Satellite Team have been using their space telescope to look for the dip in light when the planet disappears behind the star. “We can now say that this puzzling planet is less reflective than the gas giant Jupiter in our own Solar System,” MOST Mission Scientist Dr. Jaymie Matthews announced today at the annual meeting of the Canadian Astronomical Society in Montréal. “This is telling us about the nature of this exoplanet’s atmosphere, and even whether it has clouds.”

Many of the planets discovered around other stars, known as exoplanets or extrasolar planets, hug surprisingly close to their parent stars; HD209458b orbits at only 1/20th of the Earth-Sun distance (an Astronomical Unit or AU). It could never support life as we know it. But understanding HD209458b is a key piece in the puzzle of planet formation and evolution that is revising theories of our own Solar System, and estimates of how common are habitable worlds in our Galaxy. How a giant ball of gas that is larger than the planet Jupiter (which orbits 5 AU from our Sun) got so close to its star, and how its atmosphere responds to the powerful radiation and gravitation fields of that star, are still open questions to exoplanetary scientists.

“The way this planet reflects light back to us from the star is sensitive to its atmospheric composition and temperature,” describes Jason Rowe, a Ph.D. student at the University of British Columbia who processed the MOST data. “HD209458b is reflecting back to us less than 1/10,000th of the total visible light coming directly from the star. That means it reflects less than 30-40% of the light it receives from its star, which already eliminates many possible models for the exoplanetary atmosphere.” By comparison, the planet Jupiter would reflect about 50% of the light in the wavelength range seen by MOST.

“Imagine trying to see a mosquito buzzing around a 400-Watt streetlamp. But not at the street corner, or a few blocks away, but 1000 km away!” explains Dr. Matthews. “That’s equivalent to what we’re trying to do with MOST to detect the planet in the HD209458 system.”

The planet was detected directly earlier this year in the infrared by NASA’s US$720M Spitzer Space Observatory. At a wavelength of 24 micrometres, about 50,000 times longer than the light waves seen by human eyes, the exoplanet HD209458b is actually faintly glowing, with what physicists call “thermal emission.” MOST looks at the Universe in the same wavelength range as the eye. By combining the Spitzer far-infrared thermal result with the MOST visible light reflection limit, theoreticians are now able to develop a realistic model of the atmosphere of this so-called “hot Jupiter.”

And MOST has not given up on HD209458b. “It can orbit, but it can’t hide,” quips Dr. Matthews. “MOST will put this system under a 45-day stakeout at the end of the summer to continue to improve our detection limit. Eventually, the planet will emerge from the noise and we’ll have a clearer picture of the composition of the exoplanet atmosphere and even its weather – temperature, pressure and cloud cover.”

A scientific paper on these results will be submitted soon, by Jason Rowe and Dr. Jaymie Matthews (UBC), Dr. Sara Seager (Carnegie Institute of Washington), Dr. Dimitar Sasselov (Harvard-Smithsonian Center for Astrophysics), and the rest of the MOST Science Team, with members from UBC, the University of Toronto, Université de Montréal, St. Mary’s University, and the University of Vienna.

Dr. Seager, a world leader in the field of modelling exoplanet atmospheres, emphasises the challenge of this kind of science: “We’re like weather forecasters trying to understand winds and clouds on a world we can’t even see. It’s hard enough for meteorologists to tell you whether it will be cloudy tomorrow in your hometown here on Earth. Imagine what it’s like to try to forecast weather on a planet 150 light years away!”

Dr. Sasselov is also excited by MOST’s early findings: “This capability of MOST is paving the way to the great prize – the discovery of Earth-sized planets. The search for other worlds like home is now on.” Dr. Matthews can’t resist adding, “Not bad for a space telescope with a mirror the size of a pie plate and a price tag of Can$10M, eh?”

MOST (Microvariability & Oscillations of STars) is a Canadian Space Agency mission. Dynacon Inc. of Mississauga, Ontario, is the prime contractor for the satellite and its operation, with the University of Toronto Institute for Aerospace Studies (UTIAS) as a major subcontractor. The University of British Columbia (UBC) is the main contractor for the instrument and scientific operations of the MOST mission. MOST is tracked and operated through a global network of ground stations located at UTIAS, UBC and the University of Vienna.

Original Source: CASCA News Release

The brown dwarf 2M1207 and its planetary companion. Image credit: ESO/VLT/NACO. Click to enlarge.
An international team of astronomers reports today confirmation of the discovery of a giant planet, approximately five times the mass of Jupiter, that is gravitationally bound to a young brown dwarf. This puts an end to a year long discussion on the nature of this object, which started with the detection of a red object close to the brown dwarf.

In February and March of this year, the astronomers took new images of the young brown dwarf and its giant planet companion with the state-of-the-art NACO instrument on ESO’s Very Large Telescope in northern Chile. The planet is near the southern constellation of Hydra and approximately 200 light years from Earth.

“Our new images show convincingly that this really is a planet, the first planet that has ever been imaged outside of our solar system,” tells Gael Chauvin, astronomer at ESO and leader of the team of astronomers who conducted the study.

“The two objects – the giant planet and the young brown dwarf – are moving together; we have observed them for a year, and the new images essentially confirm our 2004 finding,” says Benjamin Zuckerman, UCLA professor of physics and astronomy, member of NASA’s Astrobiology Institute, and a member of the team. “I’m more than 99 percent confident.” The separation between the planet and the brown dwarf is 55 times the separation of the Earth and Sun.

Anne-Marie Lagrange, another member of the team from the Grenoble Observatory in France, looks towards the future: “Our discovery represents a first step towards one of the most important goals of modern astrophysics: to characterize the physical structure and chemical composition of giant and, eventually, terrestrial-like planets.”

Last September, the same team of astronomers reported a faint reddish speck of light in the close vicinity of a young brown dwarf (see ESO PR 23/04). The feeble object, now called 2M1207b, is more than 100 times fainter than the brown dwarf, 2M1207A. The spectrum of 2M1207b presents a strong signature of water molecules, thereby confirming that it must be cold. Based on the infrared colours and the spectral data, evolutionary model calculations led to the conclusion that 2M1207b is a 5 Jupiter-mass planet. Its mass can be estimated also by use of a different method of analysis, which focuses on the strength of its gravitational field; this technique suggests that the mass might be even less than 5 Jupiters.

At the time of its discovery in April 2004, it was impossible to prove that the faint source is not a background object (such as an unusual galaxy or a peculiar cool star with abnormal infrared colours), even though this appeared very unlikely. Observations with the Hubble Space Telescope, obtained in August 2004, corroborated the VLT/NACO observations, but were taken too soon after the NACO ones to conclusively demonstrate that the faint source is a planet.

The new observations show with high confidence that the two objects are moving together and hence are gravitationally bound.

“Given the rather unusual properties of the 2M1207 system, the giant planet most probably did not form like the planets in our solar system,” says Gael Chauvin. “Instead it must have formed the same way our Sun formed, by a one-step gravitational collapse of a cloud of gas and dust.”

The paper describing this research has been accepted for publication in Astronomy and Astrophysics.

The same European/American team has had another paper just accepted for publication in Astronomy & Astrophysics; this paper reports the imaging discovery with the same VLT/NACO instrumentation of a lightweight companion to AB Pictoris, a young star located about 150 light years from Earth. The estimated mass of the companion is between 13 and 14 times the mass of Jupiter, which places the companion right on the border line between massive planets and the lowest mass brown dwarfs.

Original Source: ESO News Release

Image credit: NWU
The peculiar orbits of three planets looping around a faraway star can be explained only if an unseen fourth planet blundered through and knocked them out of their circular orbits, according to a new study by researchers at the University of California, Berkeley, and Northwestern University.

The conclusion is based on computer extrapolations from 13 years of observations of planet motions around the star Upsilon Andromedae. It suggests that the non-circular and often highly elliptical orbits of many of the extrasolar planets discovered to date may be the result of planets scattering off one another. In such a scenario, the perturbing planet could be shot out of the system entirely or could be kicked into a far-off orbit, leaving the inner planets with eccentric orbits.

“This is probably one of the two or three extrasolar systems that have the best observations and tightest constraints, and it tells a unique story,” said Eric Ford, a Miller postdoctoral fellow at UC Berkeley. “Our explanation is that the outer planet’s original orbit was circular, but it got this sudden kick that permanently changed its orbit to being highly eccentric. To provide that kick, we’ve hypothesized that there was an additional planet that we don’t see now. We believe we now understand how this system works.”

If such a planet had caromed through our solar system early in its history, the researchers noted, the inner planets might not now have such nicely circular orbits, and, based on current assumptions about the origins of life, Earth’s climate might have fluctuated too much for life to have arisen.

“While the planets in our solar system remain stable for billions of years, that wasn’t the case for the planets orbiting Upsilon Andromedae,” Ford said. “While those planets might have formed similarly to Jupiter and Saturn, their current orbits were sculpted by a late phase of chaotic and violent interactions.”

According to Ford’s colleague, Frederic A. Rasio, associate professor of physics and astronomy at Northwestern, “Our results show that a simple mechanism, often called ‘planet-planet scattering’ – a sort of slingshot effect due to the sudden gravitational pull between two planets when they come very near each other – must be responsible for the highly eccentric orbits observed in the Upsilon Andromedae system. We believe planet-planet scattering occurred frequently in extrasolar planetary systems, not just this one, resulting from strong instabilities. So, while planetary systems around other stars may be common, the kinds of systems that could support life, which, like our solar system, presumably must remain stable over very long time scales, may not be so common.”

The computer simulations are reported in the April 14 issue of the journal Nature by Ford, Rasio and Verene Lystad, an undergraduate student majoring in physics at Northwestern. Ford was a student of Rasio’s at the Massachusetts Institute of Technology before pursuing graduate studies at Princeton University and arriving at UC Berkeley in 2004.

The planetary system around Upsilon Andromedae is one of the most studied of the 160-some systems with planets discovered so far outside our own solar system. The inner planet, a “hot Jupiter” so close to the star that its orbit is only a few days, was discovered in 1996 by UC Berkeley’s Geoff Marcy and his planet-hunting team. The two outer planets, with elongated orbits that perturb each other strongly, were discovered in 1999. These three, huge, Jupiter-like planets around Upsilon Andromedae comprised the first extrasolar multi-planet system discovered by Doppler spectroscopy.

Because of the unusual nature of the planetary orbits around Upsilon Andromedae, Marcy and his team have studied it intensely, making nearly 500 observations – 10 times more than for most other extrasolar planets that have been found. These observations, the wobbles in the star’s motion induced by the orbiting planets, allow a very precise charting of the planets’ motions around the star.

“The observations are so precise that we can watch and predict what will happen for tens of thousands of years in the future,” Ford said.

Today, while the innermost planet huddles close to the star, the two outer planets orbit in egg-shaped orbits. Computer simulations of past and future orbital changes showed, however, that the outer planets are engaged in a repetitive dance that, once every 7,000 years, brings the orbit of the middle planet to a circle.

“That property of returning to a very circular orbit is quite remarkable and generally doesn’t happen,” Ford said. “The natural explanation is that they were once both in circular orbits, and one got a big kick that caused it to become eccentric. Then, the subsequent evolution caused the other planet to grow its eccentricity, but because of the conservation of energy and angular momentum, it returns periodically to a very nearly circular orbit.”

Previously, astronomers had proposed two possible scenarios for the formation of Upsilon Andromedae’s planet system, but the observational data was not yet sufficient to distinguish the two models. Another astronomer, Renu Malhotra at the University of Arizona, had previously suggested that planet-planet scattering might have excited the eccentricities in Upsilon Andromedae. But an alternative explanation claimed that interactions among the planets and a gas disk surrounding the star could also have produced such eccentric orbits. By combining additional observational data with new computer models, Ford and his colleagues were able to show that interactions with a gas disk would not have produced the observed orbits, but that interactions with another planet would naturally produce them.

“The key distinguishing feature between those theories was that interactions with an outer disk would cause the orbits to change very slowly, and a strong interaction with a passing planet would cause the orbits to change very quickly compared to the 7,000-year time scale for the orbits to evolve,” Ford said. “Because the two hypotheses make different predictions for the evolution of the system, we can constrain the history of the system based on the current planetary orbits.”

Ford said that as the planets formed inside a disk of gas and dust, the drag on the planets would have kept their orbits circular. Once the dust and gas dissipated, however, only an interaction with a passing planet could have created the particular orbits of the two outer planets observed today. Perhaps, he noted, the perturbing planet was knocked into the inner planets by interactions with other planets far from the central star.

However it started, the resulting chaotic interactions would have created a very eccentric orbit for the third planet, which then also gradually perturbed the second planet’s orbit. Because the outer planet dominates the system, over time it perturbed the middle planet’s orbit enough to deform it slowly into an eccentric orbit as well, which is what is seen today, although every 7,000 years or so, the middle planet returns gradually to a circular orbit.

“This is what makes the system so peculiar,” said Rasio. “Ordinarily, the gravitational coupling between two elliptic orbits would never make one go back to a nearly perfect circle. A circle is very special.”

“Originally the main objective of our research was to simulate the Upsilon Andromedae planetary system, essentially in order to determine whether the outer two planets lie in the same plane like the planets in the solar system do,” said Lystad, who started working with Rasio when she was a sophomore and did many of the computer integrations as part of her senior thesis. “We were surprised to find that, for many of our simulations, it was difficult to tell whether the planets were in the same plane due to the fact that the middle planet’s orbit periodically became so very nearly circular. Once we noticed this strange behavior was present in all of our simulations, we recognized it as an earmark of a system that had undergone planet-planet scattering. We realized there was something much more interesting going on than anyone had found before.”

Understanding what happened during the formation and evolution of Upsilon Andromedae and other extrasolar planetary systems has major implications for our own solar system.

“Once you realize that most of the known extrasolar planets have highly eccentric orbits (like the planets in Upsilon Andromedae), you begin to wonder if there might be something special about our solar system,” Ford said. “Could violent planet-planet scattering be so common that few planetary systems remain calm and habitable? Fortunately, astronomers – led by Geoff Marcy, a professor of astronomy at UC Berkeley – are diligently making the observations that will eventually answer this exciting question.”

The research was supported by the National Science Foundation and UC Berkeley’s Miller Institute for Basic Research.

Original Source: Berkeley News Release

Illustration by: Jimmy Paillet
As of February 5, we know of 136 extrasolar planets. These have been discovered in four ways: The first – called pulsar timing – allowed us to detect Earth-sized and smaller planets by studying the variations in arrival time of radiation generated by a pulsar. The next – Doppler spectroscopy – allows ground-based telescopes to measure the “shift” in a star’s spectrum caused by the gravity of an orbiting planet. The third – astrometry – is used in much the same way – looking for the periodic “wobble” in position that a possible planet could cause on its parent star. And the last? Transit photometry allows for the study of the periodic dimming of a star as a body passes in front of it from a particular viewpoint – producing a light curve.

In April 2004, Luc F. A. Arnold, (Observatoire de Haute-Provence CNRS 04870 Saint-Michel – l’Observatoire, France) was working on a transit generated by a saturn-like planet when he had an idea. Could this same principle be applied to look for transiting bodies that were artificial in nature?

“I discussed the idea with several colleagues who found it interesting,” commented Arnold. A collection of artificial bodies would produce light curves easily distinguishable from natural ones. For example, a triangular object or something shaped like our own man-made satellites would show an entirely different signature. If multiple artificial objects were detected transiting – this could possibly be a form of signaling the presence of other intelligent life – one with an effectiveness equal to the range of the laser pulse method.

A cost-effective alternative to radio SETI or optical SETI is to look for artificial planet-size bodies which may exist around other stars. Since they would always pass in front of their parent star for a given remote observer, there is a strong possibility they can be detected and characterized using the transit photometry method. A planetary transit light curve contains fine features due to the object shape – such as planet oblateness, double planets or ringed planets. As Arnold explains, “The sphere is the equilibrium shape preferred for massive and planet-size bodies to adapt to their own gravity, (but) one can consider non-spherical bodies, especially if they are small and lightweight and orbit a dwarf star. Their transits in front of a star would produce a detectable signal.” Non-spherical artificial objects – like a triangle – would produce a specific transit light curve. If multiple objects should transit, a remarkable light curve would be created by their “on again – off again” nature of light. Such an observation would clearly claim an artificial nature. To visualize this, think of a flashlight moving behind a lowered window blind, and you’ll begin to get the idea!

The bulk of Luc Arnold’s work – just accepted for publication in the “Astrophysical Journal” – has been to prove through computer simulation the effects of different and multiples shapes and show these differing light curves. To help you better understand, the screen that you are now looking at is composed of pixels – a logical rather than a physical unit. If you were to place a triangle shape over your monitor’s screen, it would cover the pixels in a specific arrangement. During a simulation, the stellar flux is zeroed out in pixels and compared to the normal flux of the star. This simulated artificial body transit is then fitted against known planetary transit using a Powell algorithm.

“But most complex artificial objects’ light curve cannot be exactly superposed by a planetary transit, and the algorithm ends with non-zero residuals, i.e. a non-zero difference between the two light curves. This difference is the ‘personal’ signature of the artificial object. Should it rotate, the residual light curves will show additional modulation. When set against a gradient, such as the limb, an artificial object would also show sudden slope variations in the light curve during ingress or egress,” explains Arnold.

The equilateral triangle produces a transit light curve different than a sphere. In fact, its light curve resembles a ringed planet transit, so an ambiguity may remain in distinguishing these objects. But more complex objects, such as clusters of shapes, for example, create very specific signatures. For an artificial satellite-like object, its symmetrical structure would be apparent – as each area would impact the light curve at specific intervals. An elongated object, would produce undulation in its longer period of ingress and egress – in effect causing multiple “transits” making detection easier. The nature of these oscillations could very well be considered a sign of intelligent device. If several objects were spatially arranged in groups to ingress a star in a mathematically constant manner, these drops in the light curve could clearly represent a type of message – the language of science.

With the computer simulations perfected, Arnold knows what a natural or artificial transiting body should look like in a light curve – but has science observed a planetary transit? “Up to now, there is only one transit light curve obtained with a very good accuracy – the transit for HD 209 458b observed with the Hubble Space Telescope. T. Brown and colleagues found the light curve could be fitted with a spherical body to within the measurement accuracy.” This type of information provides Arnold with the model he needs. In June 2006, his vision may be realized. COROT (a space mission approved by the French Space Agency CNES, with a participation of Austria, Belgium, Brazil, Germany, Spain, ESA and ESTEC) will be dedicated to stellar seismology and the study of extrasolar planets – the first approved space mission solely devoted to these subjects. The spacecraft will consist of a ~ 30 cm telescope with an array of detectors to monitor the light curves of well chosen stars through CCD. The overall potential of COROT (COnvection, ROtation and planetary Transits) is to detect several tens of Earth sized planets and more upcoming programs such as the Terrestrial Planet Finder (TPF) and Space Interferometry Mission (SIM) will change the face of all we know about extrasolar planets.

What does this kind of new technology mean to researchers like Luc Arnold? “These space missions will give a (photometric) accuracy of down to 0.01% – but 1% could be sufficient if objects are big enough.” According to his research a single transit of an artificial body would require that kind of accuracy, but a multiple transit would be much more relaxed. “1% photometry is within the capability of thousands of amateur astronomers equipped with CCD.” Chances are far greater that a communicative civilization would favour a series of objects over a single non-spherical one for signaling their presence. Transits of opaque objects are achromatic, putting them within detectability of CCD over the entire spectrum.

As Luc points out, this type of research may well be within the realm of the contributing amateur astronomer. Currently the search for signs of extra-terrestrial intelligence are limited to radio and the search for laser pulse which demands specialized equipment. “For the moment, there is no project to apply this idea. If it the idea turns into a specific (SETI) observing program, a number of collaborations would be welcome!”

The search for planetary transits is already in operation, such as the Optical Gravitational Lensing Experiment (OGLE), “and the multiple transit case could be discovered within the course of these programs – maybe tomorrow!” While tomorrow might seem like an impossible dream, Arnold knows differently. His work has already been submitted to the SETI institute. For the rest of the citizens of planet Earth, we await the results. Will tomorrow show us a possible energy collection, communication or study device put into orbit by another sentient species? If we consider what we know of astronomy to be a basic “truth” throughout the Cosmos, then a discovery of this magnitude could be the biggest news of them all… “Assuming we are sure to have detected an alien artifact in a transit light curve, my opinion is that we should consider it as a clear ‘Hello world… We are here!’ addressed to the whole Galaxy!”

Written by Tammy Plotner

Since the discovery in 1995 of the first planet orbiting a normal star other than the Sun, there are now more than 150 candidates of these so-called exoplanets known. Most of them are detected by indirect methods, based either on variations of the radial velocity or the dimming of the star as the planet passes in front of it (see ESO PR 06/03, ESO PR 11/04 and ESO PR 22/04).

Astronomers would, however, prefer to obtain a direct image of an exoplanet, allowing them to better characterize the object’s physical nature. This is an exceedingly difficult task, as the planet is generally hidden in the “glare” of its host star.

To partly overcome this problem, astronomers study very young objects. Indeed, sub-stellar objects are much hotter and brighter when young and therefore can be more easily detected than older objects of similar mass.

Based on this approach, it might well be that last year’s detection of a feeble speck of light next to the young brown dwarf 2M1207 by an international team of astronomers using the ESO Very Large Telescope (ESO PR 23/04) is the long-sought bona-fide image of an exoplanet. A recent report based on data from the Hubble Space Telescope seems to confirm this result. The even more recent observations made with the Spitzer Space Telescope of the warm infrared glows of two previously detected “hot Jupiter” planets is another interesting result in this context. This wealth of new results, obtained in the time span of a few months, illustrates perfectly the dynamic of this field of research.

Tiny Companion
Now, a different team of astronomers [1] has possibly made another important breakthrough in this field by finding a tiny companion to a young star. Since several years these scientists have conducted a search for planets and low-mass objects, in particular around stars still in their formation process – so-called T-Tauri stars – using both the direct imaging and the radial velocity techniques. One of the objects on their list is GQ Lupi, a young T-Tauri star, located in the Lupus I (the Wolf) cloud, a region of star formation about 400 or 500 light-years away. The star GQ Lupi is apparently a very young object still surrounded by a disc, with an age between 100,000 and 2 million years.

The astronomers observed GQ Lupi on 25 June 2004 with the adaptive optics instrument NACO attached to Yepun, the fourth 8.2-m Unit Telescope of the Very Large Telescope located on top of Cerro Paranal (Chile). The instrument’s adaptive optics (AO) overcomes the distortion induced by atmospheric turbulence, producing extremely sharp near-infrared images.

As ESO PR Photo 10a/05 shows, the series of NACO exposures clearly reveal the presence of the tiny companion, located in the close vicinity of the star. This newly found object is only 0.7 arcsecond away, and would have been overlooked without the use of the adaptive optics capabilities of NACO.

At the distance of GQ Lupi, the separation between the star and its feeble companion is about 100 astronomical units (or 100 times the distance between the Sun and the Earth). This is roughly 2.5 times the distance between Pluto and the Sun.

The companion, called GQ Lupi B or GQ Lupi b [2], is roughly 250 times fainter than GQ Lupi A as seen in this series of image. Further images obtained with NACO in August and September confirmed the presence and the position of this companion.

Moving in the same direction
The astronomers then uncovered that the star had been previously observed by the Subaru telescope as well as by the Hubble Space Telescope. They retrieved the corresponding images from the data archives of these facilities for further analysis.

The older images, taken in July 2002 and April 1999, respectively, also showed the presence of the companion, giving the astronomers the possibility of precisely measuring the position of the two objects over a period of several years. This in turn allowed them to determine if the stars move together in the sky – as should be expected if they are gravitationally bound together – or if the smaller object is only a background object, just aligned by chance.

From their measurements, the astronomers found that the separation between the two objects did not change over the five-year period covered by the observations (see ESO PR Photo 10b/05). For the scientists this is a clear proof that both objects are moving in the same direction in the sky. “If the faint object would be a background object”, says Ralph Neuh?user of the University of Jena (Germany) and leader of the team, “we would see a change in separation as GQ Lup would be moving in the sky. From 1999 to 2004, the separation would have changed by 0.15 arcsec, while we are confident that the change is a least 20 times smaller.”

Exoplanet or brown dwarf?
To further probe the physical nature of the newly discovered object, the astronomers used NACO on the VLT to take a series of spectra. These showed the typical signature of a very cool object, in particular the presence of water and CO bands. Taking into account the infrared colours and the spectral data available, atmospheric model calculations point to a temperature between 1,600 and 2,500 degrees and a radius that is twice as large as Jupiter (see PR Photo 10c/05). According to this, GQ Lupi B is thus a cold and rather small object.

But what is the nature of this faint object? Is it a bona-fide exoplanet or is it a brown dwarf, those “failed” stars that are not massive enough to centrally produce major nuclear reactions? Although the borderline between the two is still a matter of debate, one way to distinguish between the two is by their mass (as this is also done between brown dwarfs and stars): (giant) planets are lighter than about 13 Jupiter-masses (the critical mass needed to ignite deuterium fusion), brown dwarfs are heavier.

What about GQ Lupi b?
Unfortunately, the new observations do not provide a direct estimate of the mass of the object. Thus the astronomers must rely on comparison with theoretical models of such objects. But this is not as easy as it sounds. If, as astronomers generally accept, GQ Lupi A and B formed simultaneously, the newly found object is very young. The problem is that for such very young objects, traditional theoretical models are probably not applicable. If they are used, however, they provide an estimate of the mass of the object that lies somewhere between 3 to 42 Jupiter-masses, i.e. encompassing both the planet and the brown dwarf domains.

These early phases in brown dwarf and planet formation are essentially unknown territory for models. It is very difficult to model the early collapse of the gas clouds given the conditions around the forming parent star. One set of models, specifically tailored to model the very young objects, provide masses as low as one to two Jupiter-masses. But as Ralph Neuh?user points out “these new models still need to be calibrated, before the mass of such companions can be determined confidently”.

The astronomers also stress that from the comparison between their VLT/NACO spectra and the theoretical models of co-author Peter Hauschildt from Hamburg University (Germany), they arrive at the conclusion that the best fit is obtained for an object having roughly 2 Jupiter radii and 2 Jupiter masses. If this result holds, GQ Lupi b would thus be the youngest and lightest exoplanet to have been imaged.

Further observations are still required to precisely determine the nature of GQ Lupi B. If the two objects are indeed bound, then the smallest object will need more than 1,000 years to complete an orbit around its host star. This is of course too long to wait but the effect of the orbital motion might possibly be detectable – as a tiny change in the separation between the two objects – in a few years. The team therefore plans to perform regular observations of this object using NACO on the VLT, in order to detect this motion. No doubt that in the mean time, further progress on the theoretical side will be achieved and that many sensational discoveries in this field will be made.

More information
The research presented in this ESO Press Release is published in a Letter to the Editor accepted for publication by Astronomy and Astrophysics (“Evidence for a co-moving sub-stellar companion of GQ Lup” by R. Neuh?user et al.) and available in PDF form at http://www.edpsciences.org/articles/aa/pdf/forthpdf/aagj061_forth.pdf.

Note
[1]: The team is composed of Ralph Neuh?user, G?nther Wuchterl, Markus Mugrauer, and Ana Bedalov (University of Jena, Germany), Eike Guenther (Th?ringer Landessternwarte Tautenburg, Germany), and Peter Hauschildt (Hamburger Sternwarte, Germany).

[2]: In the astronomical literature, the convention is to put capitals for stars member of multiple systems, but small letters for planets. If the companion to GQ Lupi A turns out to be a planet, it would be called GQ Lupi b, while if it is a brown dwarf, it would be identified as GQ lupi B. Given the present uncertainty, we have therefore used both denominations in this press release, as did the authors in the original scientific paper.

Original Source: ESO News Release