Category: Extrasolar Planets

Penn State’s Alex Wolszczan, the discoverer in 1992 of the first planets ever found outside our solar system, now has discovered with Caltech’s Maciej Konacki the smallest planet yet detected,in that same far-away planetary system. Immersed in an extended cloud of ionized gas, the new planet orbits a rapidly spinning neutron star called a pulsar. The discovery, to be announced during a press conference at a meeting concerning planetary formation and detection in Aspen, Colorado, on 7 February, yields an astonishingly complete description of the pulsar planetary system and confirms that it is remarkably like a half-size version of our own solar system ? even though the star these planets orbit is quite different from our Sun.

“Despite the extreme conditions that must have existed at the time these planets were forming, Nature has managed to create a planetary system that looks like a scaled-down copy of our own inner solar system,” Wolszczan reports. The star at the center of this system is a pulsar named PSR B1257+12 ? the extremely dense and compact neutron star left over from a massive star that died in a violent explosion 1,500 light years away in the constellation Virgo.

Wolszczan and his colleagues earlier had discovered three terrestrial planets around the pulsar, with their orbits in an almost exact proportion to the spacings between Mercury, Venus, and Earth. The newly discovered fourth planet has an orbit approximately six times larger than that of the third planet in the system, which Konacki says is amazingly close to the average distance from our Sun to our solar system’s asteroid belt, located between the orbits of Mars and Jupiter.

“Because our observations practically rule out a possible presence of an even more distant, massive planet or planets around the pulsar, it is quite possible that the tiny fourth planet is the largest member of a cloud of interplanetary debris at the outer edge of the pulsar’s planetary system, a remnant of the original protoplanetary disk that created the three inner planets,” Wolszczan explains. The small planet, about one-fifth of the mass of Pluto, may occupy the same outer-boundary position in its planetary system as Pluto does in our solar system. “Surprisingly, the planetary system around this pulsar resembles our own solar system more than any extrasolar planetary system discovered around a Sun-like star,” Konacki says.

Fifteen years ago, before Wolszczan’s discovery of the first extrasolar planets, astronomers did not seriously entertain the idea that planets could survive around pulsars because they would have been blasted with the unimaginable force of the radiation and remnants of their exploding parent star. Since then, Wolszczan, Konacki, and colleagues have gradually been unraveling the mysteries of this system of pulsar planets, using the Arecibo radio telescope in Puerto Rico to collect and analyze pulsar-timing data. “We feel now, with this discovery, that the basic inventory of this planetary system has been completed,” Wolszczan says.

These discoveries have been possible because pulsars, especially those with the fastest spin, behave like very accurate clocks. “The stability of the repetition rate of the pulsar pulses compares favorably with the precision of the best atomic clocks constructed by humans,” Konacki explains. Measurements of the pulse arrival times, called pulsar timing, give astronomers an extremely precise method for studying the physics of pulsars and for detecting the phenomena that occur in a pulsar’s environment.

“A pulsar wobble due to orbiting planets manifests itself by variations in the pulse arrival times, just like a stellar wobble is detectable with the well-known Doppler effect so successfully used by optical astronomers to identify planets around nearby stars by the shifts of their spectral lines,” Wolszczan explains. “An important advantage of the fantastic stability of the pulsar clocks, which achieve precisions better than one millionth of a second, is that this method allows us to detect planets with masses all the way down to those of large asteroids.”

The very existence of the pulsar planets may represent convincing evidence that Earth-mass planets form just as easily as do the gas giants that are known to exist around more than 5 percent of the nearby Sun-like stars. However, Wolszczan says, “the message carried by the pulsar planets may equally well be that the formation of Earth-like planets requires special conditions, making such planets a rarity. For example, there is growing evidence that a nearby supernova explosion may have played an important role in our solar system’s formation.” Future space observatories, including the Kepler and the Space Interferometry Missions, and the Terrestrial Planet Finder, will play a decisive role in making a distinction between these fundamental alternatives.

Unique follow up observations carried out with NASA’s Hubble Space Telescope are providing important supporting evidence for the existence of a candidate planetary companion to a relatively bright young brown dwarf star located 225 light-years away in the southern constellation Hydra.

Astronomers at the European Southern Observatory’s Very Large Telescope (VLT) in Chile detected the planet candidate in April 2004 with infrared observations using adaptive optics to sharpen their view. The VLT astronomers spotted a faint companion object to the brown dwarf star 2MASSWJ 1207334-393254 (aka 2M1207). The object is a candidate planet because it is only one-seven-hundredth the brightness of the brown dwarf (at the longer-than-Hubble wavelengths observed with the VLT) and glimmers at barely 1800 degrees Fahrenheit, which is cooler than a light bulb filament.

Because an extrasolar planet has never been directly imaged before, this remarkable observation required Hubble’s unique abilities to do follow-up observations to test and validate if it is indeed a planet. Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) camera conducted complementary observations taken at shorter infrared wavelength observations unobtainable from the ground. This wavelength coverage is important because it is needed to characterize the object’s physical nature.

Very high precision measurements of the relative position between the dwarf and companion were obtained with NICMOS in August 2004. The Hubble images were compared to the earlier VLT observations to try and see if the two objects are really gravitationally bound and hence move across the sky together. Despite the four months between the VLT and NICMOS observations, astronomers say they can almost rule out the probability that the suspected planet is really a background object, because there was no noticeable change in its position relative to the dwarf.

If the two objects are indeed gravitationally bound together they are at least 5 billion miles apart, about 30 percent farther apart than Pluto is from the Sun. Given the mass of 2M1207, inferred from its spectrum, the companion object would take a sluggish 2,500 years to complete one orbit. Therefore, any relative motion seen between the two on much shorter time scales would reveal the candidate planet to be a background interloper and not a gravitationally bound planet.

“The NICMOS photometry supports the conjecture that the planet candidate is about five times the mass of Jupiter if it indeed orbits the brown dwarf,” says Glenn Schneider of the University of Arizona. “The NICMOS position measurements, relative to VLT’s, indicate the object is a true (and thus orbiting) companion at a 99 percent level of confidence — but further planned Hubble observations are required to eliminate the 1 percent chance that it is a coincidental background object which is not orbiting the dwarf.”

Schneider is presenting these latest Hubble observations today at the meeting of the American Astronomical Society in San Diego, Calif.

The candidate planet and dwarf are in the nearby TW Hydrae association of young stars that are estimated to be no older than 8 million years. The Hubble NICMOS observations found the object to be extremely red and relatively much brighter at longer wavelengths. The colors match theoretical expectations for an approximately 8 million-year-old object that is about five times as massive as Jupiter.

Further Hubble observations by the NICMOS team are planned in April 2005.

Original Source: Hubble News Release

Astronomers say a dusty disc swirling around the nearby star Vega is bigger than earlier thought. It was probably caused by collisions of objects, perhaps as big as the planet Pluto, up to 2,000 kilometers (about 1,200 miles) in diameter.

NASA’s Spitzer Space Telescope has seen the dusty aftermath of this “run-in.” Astronomers think embryonic planets smashed together, shattered into pieces and repeatedly crashed into other fragments to create ever-finer debris. Vega’s light heats the debris, and Spitzer’s infrared telescope detects the radiation.

Vega, located 25 light-years away in the constellation Lyra, is the fifth brightest star in the night sky. It is 60 times brighter than our sun. Observations of Vega in 1984, with the Infrared Astronomical Satellite, provided the first evidence for dust particles around a typical star. Because of Vega’s proximity and because its pole faces Earth, it provides a great opportunity for detailed study of the dust cloud around it.

“Vega’s debris disc is another piece of evidence demonstrating the evolution of planetary systems is a pretty chaotic process,” said lead author of the study, Dr. Kate Su of the University of Arizona, Tucson, Ariz. The findings were presented today at the 205th meeting of the American Astronomical Society in San Diego.

Like a drop of ink spreading out in a glass of water, the particles in Vega’s dust cloud don’t stay close to the star long. “The dust we are seeing in the Spitzer images is being blown out by intense light from the star,” Su said. “We are witnessing the aftermath of a relatively recent collision, probably within the last million years,” she explained.

Scientists say this disc event is short-lived. The majority of the detected material is only a few microns in size, 100 times smaller than a grain of Earth sand. These tiny dust grains leave the system and dissipate into interstellar space on a time scale less than 1,000 years. “But there are so many tiny grains,” Su said. “They add up to a total mass equal to one third of the weight of our moon,” she said.

The mass of these short-lived grains implies a high dust-production rate. The Vega disc would have to have an improbably massive reservoir of planet-building material and collisions to maintain this amount of dust production throughout the star’s life (350 million years, 13 times younger than our sun). “We think a transient disc phenomenon is more likely,” Su said.

Su and her colleagues were struck by other characteristics of Vega’s debris disc, including its physical size. It has a radius of at least 815 astronomical units, roughly 20 times larger than our solar system. One astronomical unit is the distance from Earth to the sun, which is 150 million kilometers (93 million miles). A study of the disc’s surface brightness indicates the presence of an inner hole at a radius of 86 astronomical units (twice the distance between Pluto and the sun). Large embryonic planets at the edge of this inner hole may have collided to make the rest of the debris around Vega.

“Spitzer has obtained the first high spatial-resolution infrared images of Vega’s disc,” said Dr. Michael Werner, co-author and project scientist for Spitzer at NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif. “Its sensitive infrared detectors have allowed us to see that Vega is surrounded by an enormous disc of debris,” he said.

JPL manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology (Caltech) in Pasadena. JPL is a division of Caltech. The multi-band imaging photometer for Spitzer, which made the new disc observations, was built by Ball Aerospace Corporation, Boulder, Colo.; the University of Arizona; and Boeing North American, Canoga Park, Calif.

Imagery and additional information about the Spitzer Space Telescope is available on the Internet, at:

http://www.spitzer.caltech.edu/Media

Original Source: NASA News Release

Two of NASA’s Great Observatories, the Spitzer Space Telescope and the Hubble Space Telescope, have provided astronomers an unprecedented look at dusty planetary debris around stars the size of our sun.

Spitzer has discovered for the first time dusty discs around mature, sun-like stars known to have planets. Hubble captured the most detailed image ever of a brighter disc circling a much younger sun-like star. The findings offer “snapshots” of the process by which our own solar system evolved, from its dusty and chaotic beginnings to its more settled present-day state.

“Young stars have huge reservoirs of planet-building materials, while older ones have only leftover piles of rubble. Hubble saw the reservoirs and Spitzer, the rubble,” said Dr. Charles Beichman of NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif. He is lead author of the Spitzer study. “This demonstrates how the two telescopes complement each other,” he added.

The young star observed by Hubble is 50 to 250 million years old. This is old enough to theoretically have gas planets, but young enough that rocky planets like Earth may still be forming. The six older stars studied by Spitzer average 4 billion years old, nearly the same age as the sun. They are known to have gas planets, and rocky planets may also be present. Prior to the findings, rings of planetary debris, or “debris discs,” around stars the size of the sun had rarely been observed, because they are fainter and more difficult to see than those around more massive stars.

“The new Hubble image gives us the best look so far at reflected light from a disc around a star the mass of the sun,” said Hubble study lead author, Dr. David Ardila of the Johns Hopkins University, Baltimore. “Basically, it shows one of the possible pasts of our own solar system,” he said.

Debris discs around older stars the same size and age as our sun, including those hosting known planets, are even harder to detect. These discs are 10 to 100 times thinner than the ones around young stars. Spitzer’s highly sensitive infrared detectors were able to sense their warm glow for the first time.

“Spitzer has established the first direct link between planets and discs,” Beichman said. “Now, we can study the relationship between the two.” These studies will help future planet-hunting missions, including NASA’s Terrestrial Planet Finder and the Space Interferometry Mission, predict which stars have planets. Finding and studying planets around other stars is a key goal of NASA’s exploration mission.

Rocky planets arise out of large clouds of dust that envelop young stars. Dust particles collide and stick together, until a planet eventually forms. Sometimes the accumulating bodies crash together and shatter. Debris from these collisions collects into giant doughnut-shaped discs, the centers of which may be carved out by orbiting planets. With time, the discs fade and a smaller, stable debris disc, like the comet-filled Kuiper Belt in our own solar system, is all that is left.

The debris disc imaged by Hubble surrounds the sun-like star called HD 107146, located 88 light-years away. John Krist, a JPL astronomer, also used Hubble to capture another disc around a smaller star, a red dwarf called AU Microscopii, located 32 light-years away and only 12 million years old. The Hubble view reveals a gap in the disc, where planets may have swept up dust and cleared a path. The disc around HD 107146 also has an inner gap.

Beichman and his colleagues at JPL and the University of Arizona, Tucson, used Spitzer to scan 26 older sun-like stars with known planets, and found six with Kuiper Belt-like debris discs. The stars range from 50 to 160 light-years away. Their discs are about 100 times fainter than those recently imaged by Hubble, and about 100 times brighter than the debris disc around the sun. These discs are also punctuated by holes at their centers.

Both Hubble images were taken with the advanced camera for surveys. They will be published in the Astronomical Journal and the Astrophysical Journal Letters. The Spitzer observations are from the multiband imaging photometer and will appear in the Astrophysical Journal.

The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).

Original Source: Hubble News Release

One of the currently hottest astrophysical topics – the hunt for Earth-like planets around other stars – has just received an important impetus from new spectral observations with the MIDI instrument at the ESO VLT Interferometer (VLTI).

An international team of astronomers [2] has obtained unique infrared spectra of the dust in the innermost regions of the proto-planetary discs around three young stars – now in a state possibly very similar to that of our solar system in the making, some 4,500 million years ago.

Reporting in this week’s issue of the science journal Nature, and thanks to the unequalled, sharp and penetrating view of interferometry, they show that in all three, the right ingredients are present in the right place to start formation of rocky planets at these stars.

“Sand” in the inner regions of stellar discs
The Sun was born about 4,500 million years ago from a cold and massive cloud of interstellar gas and dust that collapsed under its own gravitational pull. A dusty disc was present around the young star, in which the Earth and other planets, as well as comets and asteroids were later formed.

This epoch is long gone, but we may still witness that same process by observing the infrared emission from very young stars and the dusty protoplanetary discs around them. So far, however, the available instrumentation did not allow a study of the distribution of the different components of the dust in such discs; even the closest known are too far away for the best single telescopes to resolve them. But now, as Francesco Paresce, Project Scientist for the VLT Interferometer and a member of the team from ESO explains, “With the VLTI we can combine the light from two well-separated large telescopes to obtain unprecedented angular resolution. This has allowed us, for the first time, to peer directly into the innermost region of the discs around some nearby young stars, right in the place where we expect planets like our Earth are forming or will soon form”.

Specifically, new interferometric observations of three young stars by an international team [2], using the combined power of two 8.2-m VLT telescopes a hundred metres apart, has achieved sufficient image sharpness (about 0.02 arcsec) to measure the infrared emission from the inner region of the discs around three stars (corresponding approximately to the size of the Earth’s orbit around the Sun) and the emission from the outer part of those discs. The corresponding infrared spectra have provided crucial information about the chemical composition of the dust in the discs and also about the average grain size.

These trailblazing observations show that the inner part of the discs is very rich in crystalline silicate grains (“sand”) with an average diameter of about 0.001 mm. They are formed by coagulation of much smaller, amorphous dust grains that were omnipresent in the interstellar cloud that gave birth to the stars and their discs.

Model calculations show that crystalline grains should be abundantly present in the inner part of the disc at the time of formation of the Earth. In fact, the meteorites in our own solar system are mainly composed of this kind of silicate.

Dutch astronomer Rens Waters, a member of the team from the Astronomical Institute of University of Amsterdam, is enthusiastic: “With all the ingredients in place and the formation of larger grains from dust already started, the formation of bigger and bigger chunks of stone and, finally, Earth-like planets from these discs is almost unavoidable!”

Transforming the grains
It has been known for some time that most of the dust in discs around newborn stars is made up of silicates. In the natal cloud this dust is amorphous, i.e. the atoms and molecules that make up a dust grain are put together in a chaotic way, and the grains are fluffy and very small, typically about 0.0001 mm in size. However, near the young star where the temperature and density are highest, the dust particles in the circumstellar disc tend to stick together so that the grains become larger. Moreover, the dust is heated by stellar radiation and this causes the molecules in the grains to re-arrange themselves in geometric (crystalline) patterns.

Accordingly, the dust in the disc regions that are closest to the star is soon transformed from “pristine” (small and amorphous) to “processed” (larger and crystalline) grains.

Spectral observations of silicate grains in the mid-infrared wavelength region (around 10 ?m) will tell whether they are “pristine” or “processed”. Earlier observations of discs around young stars have shown a mixture of pristine and processed material to be present, but it was so far impossible to tell where the different grains resided in the disc.

Thanks to a hundred-fold increase in angular resolution with the VLTI and the highly sensitive MIDI instrument, detailed infrared spectra of the various regions of the protoplanetary discs around three newborn stars, only a few million years old, now show that the dust close to the star is much more processed than the dust in the outer disc regions. In two stars (HD 144432 and HD 163296) the dust in the inner disc is fairly processed whereas the dust in the outer disc is nearly pristine. In the third star (HD 142527) the dust is processed in the entire disc. In the central region of this disc, it is extremely processed, consistent with completely crystalline dust.

An important conclusion from the VLTI observations is therefore that the building blocks for Earth-like planets are present in circumstellar discs from the very start. This is of great importance as it indicates that planets of the terrestrial (rocky) type like the Earth are most probably quite common in planetary systems, also outside the solar system.

The pristine comets
The present observations also have implications for the study of comets. Some – perhaps all – comets in the solar system do contain both pristine (amorphous) and processed (crystalline) dust. Comets were definitely formed at large distances from the Sun, in the outer regions of the solar system where it has always been very cold. It is therefore not clear how processed dust grains may end up in comets.

In one theory, processed dust is transported outwards from the young Sun by turbulence in the rather dense circumsolar disc. Other theories claim that the processed dust in comets was produced locally in the cold regions over a much longer time, perhaps by shock waves or lightning bolts in the disc, or by frequent collisions between bigger fragments.

The present team of astronomers now conclude that the first theory is the most likely explanation for the presence of processed dust in comets. This also implies that the long-period comets that sometimes visit us from the outer reaches of our solar system are truly pristine bodies, dating back to an era when the Earth and the other planets had not yet been formed.

Studies of such comets, especially when performed in-situ, will therefore provide direct access to the original material from which the solar system was formed.

More information
The results reported in this ESO PR are presented in more detail in a research paper “The building blocks of planets within the “terrestrial” region of protoplanetary disks”, by Roy van Boekel and co-authors (Nature, November 25, 2004). The observations were made in the course of ESO’s early science demonstration programme.

Notes

[1]: This ESO press release is issued in collaboration with the Astronomical Institute of the University of Amsterdam, The Netherlands (NOVA PR) and the Max-Planck-Institut f?r Astronomie (Heidelberg, Germany (MPG PR).

[2]: The team consists of Roy van Boekel, Michiel Min, Rens Waters, Carsten Dominik and Alex de Koter (Astronomical Institute, University of Amsterdam, The Netherlands), Christoph Leinert, Olivier Chesneau, Uwe Graser, Thomas Henning, Rainer K?hler and Frank Przygodda (Max-Planck-Institut f?r Astronomie, Heidelberg, Germany), Andrea Richichi, Sebastien Morel, Francesco Paresce, Markus Sch?ller and Markus Wittkowski (ESO), Walter Jaffe and Jeroen de Jong (Leiden Observatory, The Netherlands), Anne Dutrey and Fabien Malbet (Observatoire de Bordeaux, France), Bruno Lopez (Observatoire de la Cote d’Azur, Nice, France), Guy Perrin (LESIA, Observatoire de Paris, France) and Thomas Preibisch (Max-Planck-Institut f?r Radioastronomie, Bonn, Germany).

[3]: The MIDI instrument is the result of a collaboration between German, Dutch and French institutes. See ESO PR 17/03 and ESO PR 25/02 for more information.

Original Source: ESO News Release

Image credit: NASA/JPL
In June, researchers from the University of Rochester announced they had located a potential planet around another star so young that it defied theorists’ explanations. Now a new team of Rochester planet-formation specialists are backing up the original conclusions, saying they’ve confirmed that the hole formed in the star’s dusty disk could very well have been formed by a new planet. The findings have implications for gaining insight into how our own solar system came to be, as well as finding other possibly habitable planetary systems throughout our galaxy.

“The data suggests there’s a young planet out there, but until now none of our theories made sense with the data for a planet so young,” says Adam Frank, professor of physics and astronomy at the University of Rochester. “On the one hand, it’s frustrating; but on the other, it’s very cool because Mother Nature has just handed us the planet and we’ve got to figure out how it must have been created.”

Intriguingly, working from the original team’s data, Frank, Alice Quillen, Eric Blackman, and Peggy Varniere revealed that the planet was likely smaller than most extra-solar planets discovered thus far – about the size of Neptune. The data also suggested that this planet is about the same distance from its parent star as our own Neptune is from the Sun. Most extra-solar planets discovered to date are much larger and orbit extremely close to their parent star.

The original Rochester team, led by Dan Watson, professor of physics and astronomy, used NASA’s new Spitzer Space Telescope to detect a gap in the dust surrounding a fledgling star. The critical infrared “eyes” of the infrared telescope were designed in part by physics and astronomy professors Judith Pipher, William Forrest, and Watson, a team that has been among the world leaders in opening the infrared window to the universe. It was Forrest and Pipher who were the first U.S. astronomers to turn an infrared array toward the skies: In 1983, they mounted a prototype infrared detector onto the University telescope in the small observatory on top of the Wilmot Building on campus, taking the first-ever telescopic pictures of the moon in the infrared, a wavelength range of light that is invisible to the naked eye as well as to most telescopes.

The discovered gap strongly signaled the presence of a planet. The dust in the disk is hotter in the center near the star and so radiates most of its light at shorter wavelengths than the cooler outer reaches of the disk. The research team found that there was an abrupt dearth of light radiating at all short infrared wavelengths, strongly suggesting that the central part of the disk was absent. Scientists know of only one phenomenon that can tunnel such a distinct “hole” in the disk during the short lifetime of the star – a planet at least 100,000 years old.

This possibility of a planet on the order of only 100,000 to half a million years old was met with skepticism by many astronomers because neither of the leading planetary formation models seemed to allow for a planet of this age. Two models represent the leading theories of planetary formation: core accretion and gravitational instability. Core accretion suggests that the dust from which the star and system form begins to clump together into granules, and those granules clump into rocks, asteroids, and planetoids until whole planets are formed. But the theory says it should take about 10 million years for a planet to evolve this way – far too long to account for the half-million-year-old planet found by Watson.

Conversely, the other leading theory of planetary formation, gravitational instability, suggests that whole planets could form essentially in one swoop as the original cloud of gas is pulled together by its own gravity and becomes a planet. But while this model suggests that planetary formation could happen much faster – on the order of centuries – the density of the dust disk surrounding the star seems to be too sparse to support this model either.

“Even though it doesn’t fit either model, we’ve crunched the numbers and shown that yes, in fact, that hole in that dust disk could have been formed by a planet,” says Frank. “Now we have to look at our models and figure out how that planet got there. At the end of it all, we hope we have a new model, and a new understanding of how planets come to be.”

This research was funded by the National Science Foundation.

Original Source: University of Rochester News Release

A research paper by an international team of astronomers [2] provides sound arguments in favour, but the definitive answer is now awaiting further observations.

On several occasions during the past years, astronomical images revealed faint objects, seen near much brighter stars. Some of these have been thought to be those of orbiting exoplanets, but after further study, none of them could stand up to the real test. Some turned out to be faint stellar companions, others were entirely unrelated background stars. This one may well be different.

In April of this year, the team of European and American astronomers detected a faint and very red point of light very near (at 0.8 arcsec angular distance) a brown-dwarf object, designated 2MASSWJ1207334-393254. Also known as “2M1207”, this is a “failed star”, i.e. a body too small for major nuclear fusion processes to have ignited in its interior and now producing energy by contraction. It is a member of the TW Hydrae stellar association located at a distance of about 230 light-years. The discovery was made with the adaptive-optics supported NACO facility [3] at the 8.2-m VLT Yepun telescope at the ESO Paranal Observatory (Chile).

The feeble object is more than 100 times fainter than 2M1207 and its near-infrared spectrum was obtained with great efforts in June 2004 by NACO, at the technical limit of the powerful facility. This spectrum shows the signatures of water molecules and confirms that the object must be comparatively small and light.

None of the available observations contradict that it may be an exoplanet in orbit around 2M1207. Taking into account the infrared colours and the spectral data, evolutionary model calculations point to a 5 jupiter-mass planet in orbit around 2M1207. Still, they do not yet allow a clear-cut decision about the real nature of this intriguing object. Thus, the astronomers refer to it as a “Giant Planet Candidate Companion (GPCC)” [4].

Observations will now be made to ascertain whether the motion in the sky of GPCC is compatible with that of a planet orbiting 2M1207. This should become evident within 1-2 years at the most.

Just a speck of light
Since 1998, a team of European and American astronomers [2] is studying the environment of young, nearby “stellar associations”, i.e., large conglomerates of mostly young stars and the dust and gas clouds from which they were recently formed.

The stars in these associations are ideal targets for the direct imaging of sub-stellar companions (planets or brown dwarf objects). The leader of the team, ESO astronomer Gael Chauvin notes that “whatever their nature, sub-stellar objects are much hotter and brighter when young – tens of millions of years – and therefore can be more easily detected than older objects of similar mass”.

The team especially focused on the study of the TW Hydrae Association. It is located in the direction of the constellation Hydra (The Water-Snake) deep down in the southern sky, at a distance of about 230 light-years. For this, they used the NACO facility [3] at the 8.2-m VLT Yepun telescope, one of the four giant telescopes at the ESO Paranal Observatory in northern Chile. The instrument’s adaptive optics (AO) overcome the distortion induced by atmospheric turbulence, producing extremely sharp near-infrared images. The infrared wavefront sensor was an essential component of the AO system for the success of these observations. This unique instrument senses the deformation of the near-infrared image, i.e. in a wavelength region where objects like 2M1207 (see below) are much brighter than in the visible range.

The TW Hydrae Association contains a star with an orbiting brown dwarf companion, approximately 20 times the mass of Jupiter, and four stars surrounded by dusty proto-planetary disks. Brown dwarf objects are “failed stars”, i.e. bodies too small for nuclear processes to have ignited in their interior and now producing energy by contraction. They emit almost no visible light. Like the Sun and the giant planets in the solar system, they are composed mainly of hydrogen gas, perhaps with swirling cloud belts.

On a series of exposures made through different optical filters, the astronomers discovered a tiny red speck of light, only 0.8 arcsec from the TW Hydrae Association brown-dwarf object 2MASSWJ1207334-393254, or just “2M1207”, cf. PR Photo 26a/04. The feeble image is more than 100 times fainter than that of 2M1207. “If these images had been obtained without adaptive optics, that object would not have been seen,” says Gael Chauvin.

Christophe Dumas, another member of the team, is enthusiastic: “The thrill of seeing this faint source of light in real-time on the instrument display was unbelievable. Although it is surely much bigger than a terrestrial-size object, it is a strange feeling that it may indeed be the first planetary system beyond our own ever imaged.”

Exoplanet or Brown Dwarf?
What is the nature of this faint object [4]? Could it be an exoplanet in orbit around that young brown dwarf object at a projected distance of about 8,250 million km (about twice the distance between the Sun and Neptune)?

“If the candidate companion of 2M1207 is really a planet, this would be the first time that a gravitationally bound exoplanet has been imaged around a star or a brown dwarf” says Benjamin Zuckerman of UCLA, a member of the team and also of NASA’s Astrobiology Institute.

Using high-angular-resolution spectroscopy with the NACO facility, the team has confirmed the substellar status of this object – now referred to as the “Giant Planet Candidate Companion (GPCC)” – by identifying broad water-band absorptions in its atmosphere, cf. PR Photo 26b/04.

The spectrum of a young and hot planet – as the GPCC may well be – will have strong similarities with an older and more massive object such as a brown dwarf. However, when it cools down after a few tens of millions of years, such an object will show the spectral signatures of a giant gaseous planet like those in our own solar system.

Although the spectrum of GPCC is quite “noisy” because of its faintness, the team was able to assign to it a spectral characterization that excludes a possible contamination by extra-galactic objects or late-type cool stars with abnormal infrared excess, located beyond the brown dwarf.

After a very careful study of all options, the team found that, although this is statistically very improbable, the possibility that this object could be an older and more massive, foreground or background, cool brown dwarf cannot be completely excluded. The related detailed analysis is available in the resulting research paper that has been accepted for publication in the European journal Astronomy & Astrophysics (see below).

Implications

The brown dwarf 2M1207 has approximately 25 times the mass of Jupiter and is thus about 42 times lighter than the Sun. As a member of the TW Hydrae Association, it is about eight million years old.

Because our solar system is 4,600 million years old, there is no way to directly measure how the Earth and other planets formed during the first tens of millions of years following the formation of the Sun. But, if astronomers can study the vicinity of young stars which are now only tens of millions of years old, then by witnessing a variety of planetary systems that are now forming, they will be able to understand much more accurately our own distant origins.

Anne-Marie Lagrange, a member of the team from the Grenoble Observatory (France), looks towards the future: “Our discovery represents a first step towards opening a whole new field in astrophysics: the imaging and spectroscopic study of planetary systems. Such studies will enable astronomers to characterize the physical structure and chemical composition of giant and, eventually, terrestrial-like planets.”

Follow-up observations
Taking into account the infrared colours and the spectral data available for GPCC, evolutionary model calculations point to a 5 jupiter-mass planet, about 55 times more distant from 2M1207 than the Earth is from the Sun (55 AU). The surface temperature appears to be about 10 times hotter than Jupiter, about 1000 ?C; this is easily explained by the amount of energy that must be liberated during the current rate of contraction of this young object (indeed, the much older giant planet Jupiter is still producing energy in its interior).

The astronomers will now continue their research to confirm or deny whether they have in fact discovered an exoplanet. Over the next few years, they expect to establish beyond doubt whether the object is indeed a planet in orbit around the brown dwarf 2M1207 by watching how the two objects move through space and to learn whether or not they move together. They will also measure the brightness of the GPCC at multiple wavelengths and more spectral observations may be attempted.

There is no doubt that future programmes to image exoplanets around nearby stars, either from the ground with extremely large telescopes equipped with specially designed adaptive optics, or from space with special planet-finder telescopes, will greatly profit from current technological achievements.

More information
The results presented in this ESO Press Release are based on a research paper (“A Giant Planet Candidate near a Young Brown Dwarf” by G. Chauvin et al.) that has been accepted for publication and will soon appear in the leading research journal “Astronomy and Astrophysics”. A preprint is available here.

Notes
[1]: This press release is issued simultaneously by ESO and CNRS (in French) .

[2]: The team consists of Gael Chauvin and Christophe Dumas (ESO-Chile), Anne-Marie Lagrange and Jean-Luc Beuzit (LAOG, Grenoble, France), Benjamin Zuckerman and Inseok Song (UCLA, Los Angeles, USA), David Mouillet (LAOMP, Tarbes, France) and Patrick Lowrance (IPAC, Pasadena, USA). The American members of the team acknowledge funding in part by NASA’s Astrobiology Institute.

[3]: The NACO facility (from NAOS/Nasmyth Adaptive Optics System and CONICA/Near-Infrared Imager and Spectrograph) at the 8.2-m VLT Yepun telescope on Paranal offers the capability to produce diffraction-limited near-infrared images of astronomical objects. It senses the radiation in this wavelength region with the N90C10 dichroic; 90 percent of the flux is transmitted to the wavefront sensor and 10 percent to the near-infrared camera CONICA. This mode is particularly useful for sharp imaging of red and very-low-mass stellar or substellar objects. The adaptive optics corrector (NAOS) was built, under an ESO contract, by Office National d’Etudes et de Recherches A?rospatiales (ONERA), Laboratoire d’Astrophysique de Grenoble (LAOG) and the LESIA and GEPI laboratories of the Observatoire de Paris in France, in collaboration with ESO. The CONICA camera was built, under an ESO contract, by the Max-Planck-Institut f?r Astronomie (MPIA) (Heidelberg) and the Max-Planck Institut f?r extraterrestrische Physik (MPE) (Garching) in Germany, in collaboration with ESO.

[4]: What is the difference between a small brown dwarf and an exoplanet ? The border line between the two is still being investigated but it appears that a brown dwarf object is formed in the same way as stars, i.e. by contraction in an interstellar cloud while planets are formed within stable circumstellar disks via collision/accretion of planetesimals or disk instabilities. This implies that brown dwarfs are formed faster (less than 1 million years) than planets (~10 million years). Another way of separating the two kinds of objects is by 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. Unfortunately, the first definition cannot be used in practice, e.g., when detecting a faint companion as in the present case, since the observations do not provide information about the way the object was formed. On the contrary, the above mass criterion is useful in the sense that spectroscopy and astrometry of a faint object, together with the appropriate evolutionary models, may reveal the mass and hence the nature of the object.

Original Source: ESO News Release

Astronomers announced today the first discovery of a new class of planets beyond our solar system about 10 to 20 times the size of Earth – far smaller than any previously detected. The planets make up a new class of Neptune-sized extrasolar planets.

In addition, one of the new planets joins three others around the nearby star 55 Cancri to form the first known four-planet system.

The discoveries consist of two new planets. They were discovered by the world renowned planet-hunting team of Drs. Paul Butler and Geoffrey Marcy of the Carnegie Institute of Washington and University of California, Berkeley, respectively; and Barbara McArthur of the University of Texas, Austin. Both findings were peer- reviewed and accepted for future publication in the Astrophysical Journal. NASA and the National Science Foundation funded the research.

“NASA, along with our partner NSF, is extremely proud of this significant planetary discovery,” said Al Diaz, Associate Administrator of NASA’s Science Mission Directorate. “The outcome of the tremendous work of the project scientists is a shining example of the value of space exploration.”

“These Neptune-sized planets prove that Jupiter-sized, gas giants aren’t the only planets out there,” Marcy said. Butler added, “We are beginning to see smaller and smaller planets. Earth-like planets are the next destination.”

Future NASA planet-hunting missions, including Kepler, the Space Interferometry Mission and the Terrestrial Planet Finder, will seek such Earth-like planets. Nearly 140 extrasolar planets have been discovered.

Both of the new planets stick very close to their parent stars, whipping around them in a matter of days. The first planet, discovered by Marcy and Butler, circles a small star called Gliese 436 about every two-and-one-half days at just a small fraction of the distance between Earth and the Sun, or 4.1 million kilometers (2.6 million miles). This planet is only the second known to orbit an M dwarf, a type of low-mass star four-tenths the size of our own sun. Gliese 436 is located in our galactic backyard, 30 light-years away in the constellation Leo.

The second planet, found by McArthur, speeds around 55 Cancri in just under three days, also at a fraction of the distance between Earth and the sun, at approximately 5.6 million kilometers (3.5 million miles). Three larger planets also revolve around the star every 15, 44 and 4,520 days, respectively. Marcy and Butler discovered the outermost of these in 2002. It is still the only known Jupiter-like gas giant to reside as far away from its star as our own Jupiter. The 55 Cancri is about 5 billion years old, a bit lighter than the sun, and is located 41 light-years away in the constellation Cancer. “55 Cancri is a premier laboratory for the study of planetary system formation and evolution,” McArthur said.

Because the new planets are smaller than Jupiter, it is possible they are made of rock, or rock and ice, rather than gas. According to the scientists, the planets may have, like Earth, formed through gradual accumulation of rocky bodies. “A planet of Neptune’s size may not have enough mass to hold onto gas, but at this point we don’t know,” Butler said.

Both discoveries were made using the “radial velocity” technique, in which a planet’s gravitational tug is detected by the wobble it produces in the parent star. Butler, Marcy and collaborators, including Dr. Deborah Fischer of San Francisco State University and Dr. Steven Vogt of the University of California, Santa Cruz, discovered their “Neptune” after careful observation of 950 nearby stars with the W.M. Keck Observatory in Mauna Kea, Hawaii. They were able to spot such a relatively small planet, because the star it tugs on is small and more susceptible to wobbling.

McArthur and collaborators Drs. Michael Endl, William Cochran and Fritz Benedict of the University of Texas discovered their “Neptune” after obtaining over 100 observations of 55 Cancri from the Hobby- Eberly Telescope at McDonald Observatory in West Texas. Combining this data with past data from Marcy, Fischer and Butler from the Lick Observatory in California, and archival data from NASA’s Hubble Space Telescope, the team was able to model the orbit of 55 Cancri’s outer planet. This, in turn, allowed them to clearly see the orbits of the other three inner planets, including the new Neptune-sized one.

Original Source: NASA News Release

A European team of astronomers [1] has discovered the lightest known planet orbiting a star other than the sun (an “exoplanet”).

The new exoplanet orbits the bright star mu Arae located in the southern Altar constellation. It is the second planet discovered around this star and completes a full revolution in 9.5 days.

With a mass of only 14 times the mass of the Earth, the new planet lies at the threshold of the largest possible rocky planets, making it a possible super Earth-like object. Uranus, the smallest of the giant planets of the Solar System has a similar mass. However Uranus and the new exoplanet differ so much by their distance from the host star that their formation and structure are likely to be very different.

This discovery was made possible by the unprecedented accuracy of the HARPS spectrograph on ESO’s 3.6-m telescope at La Silla, which allows radial velocities to be measured with a precision better than 1 m/s. It is another clear demonstration of the European leadership in the field of exoplanet research.

A unique planet hunting machine
Since the first detection in 1995 of a planet around the star 51 Peg by Michel Mayor and Didier Queloz from the Geneva Observatory (Switzerland), astronomers have learned that our Solar System is not unique, as more than 120 giant planets orbiting other stars were discovered mostly by radial-velocity surveys (cf. ESO PR 13/00, ESO PR 07/01, and ESO PR 03/03).

This fundamental observational method is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. The evaluation of the measured velocity variations allows to deduce the planet’s orbit, in particular the period and the distance from the star, as well as a minimum mass [2].

The continued quest for exoplanets requires better and better instrumentation. In this context, ESO undoubtedly took the leadership with the new HARPS spectrograph (High Accuracy Radial Velocity Planet Searcher) of the 3.6-m telescope at the ESO La Silla Observatory (see ESO PR 06/03). Offered in October 2003 to the research community in the ESO member countries, this unique instrument is optimized to detect planets in orbit around other stars (“exoplanets”) by means of accurate (radial) velocity measurements with an unequalled precision of 1 metre per second.

HARPS was built by a European Consortium [3] in collaboration with ESO. Already from the beginning of its operation, it has demonstrated its very high efficiency. By comparison with CORALIE, another well known planet-hunting optimized spectrograph installed on the Swiss-Euler 1.2-m telescope at La Silla (cf ESO PR 18/98, 12/99, 13/00), the typical observation times have been reduced by a factor one hundred and the accuracy of the measurements has been increased by a factor ten.

These improvements have opened new perspectives in the search for extra-solar planets and have set new standards in terms of instrumental precision.

The planetary system around mu Arae
The star mu Arae is about 50 light years away. This solar-like star is located in the southern constellation Ara (the Altar) and is bright enough (5th magnitude) to be observed with the unaided eye.

Mu Arae was already known to harbour a Jupiter-sized planet with a 650 days orbital period. Previous observations also hinted at the presence of another companion (a planet or a star) much further away.

The new measurements obtained by the astronomers on this object, combined with data from other teams confirm this picture. But as Fran?ois Bouchy, member of the team, states: “Not only did the new HARPS measurements confirm what we previously believed to know about this star but they also showed that an additional planet on short orbit was present. And this new planet appears to be the smallest yet discovered around a star other than the sun. This makes mu Arae a very exciting planetary system.”

During 8 nights in June 2004, mu Arae was repeatedly observed and its radial velocity measured by HARPS to obtain information on the interior of the star. This so-called astero-seismology technique (see ESO PR 15/01) studies the small acoustic waves which make the surface of the star periodically pulsate in and out. By knowing the internal structure of the star, the astronomers aimed at understanding the origin of the unusual amount of heavy elements observed in its stellar atmosphere. This unusual chemical composition could provide unique information to the planet formation history.

Says Nuno Santos, another member of the team: “To our surprise, the analysis of the new measurements revealed a radial velocity variation with a period of 9.5 days on top of the acoustic oscillation signal!”

This discovery has been made possible thanks to the large number of measurements obtained during the astero-seimology campaign.

From this date, the star, that was also part of the HARPS consortium survey programme, was regularly monitored with a careful observation strategy to reduce the “seismic noise” of the star.

These new data confirmed both the amplitude and the periodicity of the radial velocity variations found during the 8 nights in June. The astronomers were left with only one convincing explanation to this periodic signal: a second planet orbits mu Arae and accomplishes a full revolution in 9.5 days.

But this was not the only surprise: from the radial velocity amplitude, that is the size of the wobble induced by the gravitational pull of the planet on the star, the astronomers derived a mass for the planet of only 14 times the mass of the Earth! This is about the mass of Uranus, the smallest of the giant planets in the solar system.

The newly found exoplanet therefore sets a new record in the smallest planet discovered around a solar type star.

At the boundary
The mass of this planet places it at the boundary between the very large earth-like (rocky) planets and giant planets.

As current planetary formation models are still far from being able to account for all the amazing diversity observed amongst the extrasolar planets discovered, astronomers can only speculate on the true nature of the present object. In the current paradigm of giant planet formation, a core is formed first through the accretion of solid “planetesimals”. Once this core reaches a critical mass, gas accumulates in a “runaway” fashion and the mass of the planet increases rapidly. In the present case, this later phase is unlikely to have happened for otherwise the planet would have become much more massive. Furthermore, recent models having shown that migration shortens the formation time, it is unlikely that the present object has migrated over large distances and remained of such small mass.

This object is therefore likely to be a planet with a rocky (not an icy) core surrounded by a small (of the order of a tenth of the total mass) gaseous envelope and would therefore qualify as a “super-Earth”.

Further Prospects
The HARPS consortium, led by Michel Mayor (Geneva Observatory, Switzerland), has been granted 100 observing nights per year during a 5-year period at the ESO 3.6-m telescope to perform one of the most ambitious systematic searches for exoplanets so far implemented worldwide. To this aim, the consortium repeatedly measures velocities of hundreds of stars that may harbour planetary systems.

The detection of this new light planet after less than 1 year of operation demonstrates the outstanding potential of HARPS for detecting rocky planets on short orbits. Further analysis shows that performances achieved with HARPS make possible the detection of big “telluric” planets with only a few times the mass of the Earth. Such a capability is a major improvement compared to past planet surveys. Detection of such rocky objects strengthens the interest of future transit detections from space with missions like COROT, Eddington and KEPLER that shall be able to measure their radius.

More information
The research described in this Press release has been submitted for publication to the leading astrophysical journal “Astronomy and Astrophysics”. A preprint is available as a postscript file at http://www.oal.ul.pt/~nuno/.

Notes
[1]: The team is composed of Nuno Santos (Centro de Astronomia e Astrofisica da Universidade de Lisboa, Portugal), Fran?ois Bouchy and Jean-Pierre Sivan (Laboratoire d’astrophysique de Marseille, France), Michel Mayor, Francesco Pepe, Didier Queloz, St?phane Udry, and Christophe Lovis (Observatoire de l’Universit? de Gen?ve, Switzerland), Sylvie Vauclair, Michael Bazot (Toulouse, France), Gaspare Lo Curto and Dominique Naef (ESO), Xavier Delfosse (LAOG, Grenoble, France), Willy Benz and Christoph Mordasini (Physikalisches Institut der Universit?t Bern, Switzerland), and Jean-Louis Bertaux (Service d’A?ronomie de Verri?re-le-Buisson, Paris, France).

[2] A fundamental limitation of the radial-velocity method is the unknown of the inclination of the planetary orbit that only allows the determination of a lower mass limit for the planet. However, statistical considerations indicate that in most cases, the true mass will not be much higher than this value. The mass units for the exoplanets used in this text are 1 Jupiter mass = 22 Uranus masses = 318 Earth masses; 1 Uranus mass = 14.5 Earth masses.

[3] HARPS has been designed and built by an international consortium of research institutes, led by the Observatoire de Gen?ve (Switzerland) and including Observatoire de Haute-Provence (France), Physikalisches Institut der Universit?t Bern (Switzerland), the Service d’Aeronomie (CNRS, France), as well as ESO La Silla and ESO Garching.

Original Source: ESO News Release

Fifteen years ago, the largest telescopes in the world had yet to locate a planet orbiting another star. Today telescopes no larger than those available in department stores are proving capable of spotting previously unknown worlds. A newfound planet detected by a small, 4-inch-diameter telescope demonstrates that we are at the cusp of a new age of planet discovery. Soon, new worlds may be located at an accelerating pace, bringing the detection of the first Earth-sized world one step closer.

“This discovery demonstrates that even humble telescopes can make huge contributions to planet searches,” says Guillermo Torres of the Harvard-Smithsonian Center for Astrophysics (CfA), a co-author on the study.

This research study will be posted online at http://arxiv.org/abs/astro-ph/0408421 and will appear in an upcoming issue of The Astrophysical Journal Letters.

This is the very first extrasolar planet discovery made by a dedicated survey of many thousands of relatively bright stars in large regions of the sky. It was made using the Trans-Atlantic Exoplanet Survey (TrES), a network of small, relatively inexpensive telescopes designed to look specifically for planets orbiting bright stars. A team of scientists co-led by David Charbonneau (CfA/Caltech), Timothy Brown of the National Center for Atmospheric Research (NCAR) and Edward Dunham of Lowell Observatory developed the TrES network. Initial support for the TrES network came from NASA’s Jet Propulsion Laboratory and the California Institute of Technology.

“It took several Ph.D. scientists working full-time to develop the data analysis methods for this search program, but the equipment itself uses simple, off-the-shelf components,” says Charbonneau.

Although the small telescopes of the TrES network made the initial discovery, follow-up observations at other facilities were required. Observations at the W.M. Keck Observatory which, for the University of California, Caltech, and NASA, operates the world’s two largest telescopes in Hawaii, were particularly crucial in confirming the planet’s existence.

Planet Shadows
The newfound planet is a Jupiter-sized gas giant orbiting a star located about 500 light-years from the Earth in the constellation Lyra. This world circles its star every 3.03 days at a distance of only 4 million miles, much closer and faster than the planet Mercury in our solar system.

Astronomers used an innovative technique to discover this new world. It was found by the “transit method,” which looks for a dip in a star’s brightness when a planet crosses directly in front of the star and casts a shadow. A Jupiter-sized planet blocks only about 1/100th of the light from a Sun-like star, but that is enough to make it detectable.

To be successful, transit searches must examine many stars because we only see a transit if a planetary system is located nearly edge-on to our line of sight. A number of different transit searches currently are underway. Most examine limited areas of the sky and focus on fainter stars because they are more common, thereby increasing the chances of finding a transiting system. However the TrES network concentrates on searching brighter stars in larger swaths of the sky because planets orbiting bright stars are easier to study directly.

“All that we have to work with is the light that comes from the star,” says Brown. “It’s much harder to learn anything when the stars are faint.”

“It’s almost paradoxical that small telescopes are more efficient than the largest ones if you use the transit method, since we live in a time when astronomers already are planning 100-meter-diameter telescopes,” says lead author Roi Alonso of the Astrophysical Institute of the Canaries (IAC), who discovered the new planet.

Most known extrasolar planets were found using the “Doppler method,” which detects a planet’s gravitational effect on its star spectroscopically by breaking the star’s light into its component colors. However, the information that can be gleaned about a planet using the Doppler method is limited. For example, only a lower limit to the mass can be determined because the angle at which we view the system is unknown. A high-mass brown dwarf whose orbit is highly inclined to our line of sight produces the same signal as a low-mass planet that is nearly edge-on.

“When astronomers find a transiting planet, we know that its orbit is essentially edge-on, so we can calculate its exact mass. From the amount of light it blocks, we learn its physical size. In one instance, we’ve even been able to detect and study a giant planet’s atmosphere,” says Charbonneau.

Sorting Suspects
The TrES survey examined approximately 12,000 stars in 36 square degrees of the sky (an area half the size of the bowl of the Big Dipper). Roi Alonso, a graduate student of Brown’s, identified 16 possible candidates for planet transits. “The TrES survey gave us our initial line-up of suspects. Then, we had to make a lot of follow-up observations to eliminate the imposters,” says co-author Alessandro Sozzetti (University of Pittsburgh/CfA).

After compiling the list of candidates in late April, the researchers used telescopes at CfA’s Whipple Observatory in Arizona and Oak Ridge Observatory in Massachusetts to obtain additional photometric (brightness) observations, as well as spectroscopic observations that eliminated eclipsing binary stars.

In a matter of two month’s time, the team had zeroed in on the most promising candidate. High-resolution spectroscopic observations by Torres and Sozzetti using time provided by NASA on the 10-meter-diameter Keck I telescope in Hawaii clinched the case.

“Without this follow-up work the photometric surveys can’t tell which of their candidates are actually planets. The proof of the pudding is an orbit for the parent star, and we got that using the Doppler method. That’s why the Keck observations of this star were so important in proving that we had found a true planetary system,” says co-author David Latham (CfA).

Remarkably Normal
The planet, called TrES-1, is much like Jupiter in mass and size (diameter). It is likely to be a gas giant composed primarily of hydrogen and helium, the most common elements in the Universe. But unlike Jupiter, it orbits very close to its star, giving it a temperature of around 1500 degrees F.

Astronomers are particularly interested in TrES-1 because its structure agrees so well with theory, in contrast to the first discovered transiting planet, HD 209458b. The latter world contains about the same mass as TrES-1, yet is around 30% larger in size. Even its proximity to its star and the accompanying heat don’t explain such a large size.

“Finding TrES-1 and seeing how normal it is makes us suspect that HD 209458b is an `oddball’ planet,” says Charbonneau.

TrES-1 orbits its star every 72 hours, placing it among a group of similar planets known as “hot Jupiters.” Such worlds likely formed much further away from their stars and then migrated inward, sweeping away any other planets in the process. The many planetary systems found to contain hot Jupiters indicate that our solar system may be unusual for its relatively quiet history.

Both the close orbit of TrES-1 and its migration history make it unlikely to possess any moons or rings. Nevertheless, astronomers will continue to examine this system closely because precise photometric observations may detect moons or rings if they exist. In addition, detailed spectroscopic observations may give clues to the presence and composition of the planet’s atmosphere.

The paper describing these results is authored by: Roi Alonso (IAC); Timothy M. Brown (NCAR); Guillermo Torres and David W. Latham (CfA); Alessandro Sozzetti (University of Pittsburgh/CfA); Georgi Mandushev (Lowell), Juan A. Belmonte (IAC); David Charbonneau (CfA/Caltech); Hans J. Deeg (IAC); Edward W. Dunham (Lowell); Francis T. O’Donovan (Caltech); and Robert Stefanik (CfA).

This joint announcement is being issued simultaneously by CfA, IAC, NCAR, the University of Pittsburgh, and Lowell Observatory.

The W.M. Keck Observatory is operated by the California Association for Research in Astronomy, a scientific partnership of the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release