Category: Extrasolar Planets

Until a decade ago, astronomers weren’t even sure there were any planets outside the Solar System. You’d be hard-pressed to find anyone who believed we had the only planets in the entire Universe, but we still didn’t have any direct evidence they existed. That all changed in October 5, 1995 when Michel Mayor and Didier Queloz announced they had discovered a planet half the mass of Jupiter orbiting furiously around a star called 51 Pegasi. The discoveries came fast; at last count, there are 122 confirmed extrasolar planets.

But these extrasolar systems generally look nothing like our own Solar System. Many contain massive planets which orbit extremely close to their parent star; no chance for life there. Planets roughly the size and orbit of Jupiter have been uncovered, but it’s impossible for the current technology to see anything the size of our own Earth.

Fortunately, there’s a series of ground and space-based observatories in the works that should be capable of detecting Earth-sized planets around other stars. NASA and the ESA are working towards the goal of being able to directly photograph these planets and measure the composition of their atmospheres. Find large amounts of oxygen, and you’ve found life.

Corot – 2006
The European Space Agency will be the first off the mark in the hunt for rocky planets with the launch of Corot in 2006. It’ll carefully monitor the brightness of stars, watching for a slight dimming that happens in regular intervals. These dimmings are called “transits”, and happen when a planet passes in between the Earth and a distant star. The concept of a “transit” should be fresh in your mind – Venus performed one recently on June 8, 2004. Corot will be sensitive enough to detect rocky planets as small as 10 times the size of the Earth.

A follow on mission, Eddington, was originally scheduled for launch in 2007, would have been able to spot planets half the size of the Earth. But it was recently canceled, unfortunately.

Kepler – 2007
The first space observatory designed to find Earth-sized planets in orbit around other stars will be Kepler, named after the German astronomer who devised the laws of planetary motion. It’s scheduled to launch in 2007, and will also use the transit method to detect planets.

Kepler has an extremely sensitive photometer hooked up to its one-metre telescope. It’ll monitor the brightness of hundreds of thousands of stars in a chunk of sky about the same size as your outstretched hand, and watch for that telltale periodic “dimming”.

Over the course of its four year mission, Kepler should discover plenty of objects orbiting other stars, and its photometer is just sensitive enough that it should notice an Earth-sized planet as it crosses in front of a star for a few hours.

Space Interferometry Mission – 2009
Next up will be the Space Interferometry Mission, due for launch in 2009. Once in space, the SIM will take up a position in orbit that trails the Earth as it goes around the Sun, slowly drifting further and further away – this’ll give it a good, stable view of the heavens, without having the Earth around to block the view.

The observatory is designed to measure the distance to stars with incredible precision. It’s so precise, that it should be able to spot a star being moved through the gravitational interaction with its planets. For example, if you looked at the position of our own Sun from a distant point, it would look like it’s wobbling around thanks to the gravity of Jupiter, Saturn, and even the Earth. SIM will be able to detect a star’s interactions with planets down to the size of a few times the mass of the Earth. That’s precise.

Terrestrial Planet Finder – 2012-2015
Unlike the previous missions, which will detect Earth-sized planets indirectly, the Terrestrial Planet Finder (TPF) will “see” them. It’s scheduled for launch in 2012 and will nullify the light from distant stars by a factor of 100,000 times, revealing their planets. The final design is still in the works, but it could end up being a group of spacecraft flying in close formation, merging their light together to form a much larger virtual space telescope.

The TPF will pick up where SIM leaves off, surveying the habitable zone of stars 50 light years away from the Earth. Not only will it be able to see Earth-sized planets in these zones, it’ll be able to analyze the composition of their atmospheres. Here’s the key: the TPF will be able to spot the presence of oxygen, water vapour, methane and carbon dioxide in Earth-sized planets in the habitable zone of other stars. If could find the fingerprint for life in the atmospheres of these planets.

Find life on other planets, and you can assume that it’s probably common throughout our Milky Way galaxy, and maybe even the entire Universe.

Darwin – 2014
Shortly after the TPF gets to work, the European Space Agency is planning to launch Darwin; a flotilla of 8 spacecraft working together to find Earth-sized planets and search for the chemical signatures of life. Darwin will be the most powerful space-based observatory, providing images 10-times more detailed than even the James Webb Space Telescope (due for launch 2009).

Stars are billions of times brighter than the planets that orbit them, so Darwin will solve this problem by observing in the infrared spectrum, where this difference is much smaller. It’ll also be capable of canceling out starlight to reveal the much dimmer planets.

Darwin is similar enough to the Terrestrial Planet Finder, that the two agencies are considering combining their designs into a single mission funded by both groups.

Maybe we aren’t alone after all.
In just a decade, and less than 20 years after the discovery of the first planets orbiting other stars, astronomers should be able to supply us with an answer to one of the most fundamental questions humans have asked themselves… are we alone? If the Terrestrial Planet Finder hasn’t turned up evidence of life yet, then the answer will still be, “not yet”. But there’s a chance that in 10 years, you’ll be reading news that that life has been discovered orbiting another star.

But that won’t be the end of it. The scientists will press on, with new equipment, observatories and techniques to search even deeper into space. And the philosophers and theologians will get to work considering our place in a very crowded Universe.

McDonald Observatory astronomers Bill Cochran, Michael Endl, and Barbara McArthur have exploited the Hobby-Eberly Telescope’s (HET’s) capabilities to rapidly find and confirm, with great precision, the giant telescope’s first planet outside our solar system. The event serves as proof-of-concept that HET, combined with its High Resolution Spectrograph instrument, is on track to become a major player in the hunt for other worlds. The research has been accepted for publication in an upcoming edition of Astrophysical Journal Letters.

With a mass 2.84 times that of Jupiter, the newly discovered planet orbits the star HD 37605 every 54.23 days. HD 37605 is a little smaller and little cooler than the Sun. The star, which is of a type called “K0” or “K-zero,” is rich in heavy chemical elements compared to the Sun.

Of the approximately 120 extrasolar planets found to date, this new planet has the third most eccentric orbit bringing it in close in to its parent star like a “hot Jupiter,” and swinging it back out. The planet’s average distance from its star is 0.26 Astronomical Units (AU). One AU is the Earth-Sun distance.

The team used the “radial velocity” technique, a common planet-search method, to find the planet. By measuring changes in the star’s velocity toward and away from Earth –its wobble– they deduced that HD 37605 is orbiting the center of mass of a star-planet system.

“In 100 days of observations –less than two full orbits– we were able to get a very good solution for this planet’s orbit,” Cochran said. The quick results were due to HET’s “queue scheduling” system. Astronomers do not travel to the observatory to operate the telescope themselves. Rather, a telescope operator at McDonald Observatory has a list of all HET research projects and selects the ones best suited to any given night’s weather conditions and Moon phase. This way, many targets for different research projects can be observed each night, and any particular target can be observed dozens of nights in a row. According to Cochran, “queue scheduling is the ideal way to do planet searching. If the HET had a normal scheduling system, it would have taken us a year or two to confirm this planet.”

Endl added that “with the queue scheduling mode, we can put every candidate star BACK into the queue at a high priority to secure follow-up telescope observations immediately.”

Cochran added that the high precision of the team’s radial velocity measurements “proves that the HET and the High Resolution Spectrograph have met their design specs.” He explained that the total error (called “root-mean-square deviation”) in the team’s velocity measurements was 3 meters per second — state of the art for planet searching. Many of the team’s measurements had even lower errors. The High Resolution Spectrograph that made this research possible was built by Phillip MacQueen, Robert Tull, and John Good of The University of Texas at Austin.

The Hobby-Eberly Telescope is a joint project of The University of Texas at Austin, The Pennsylvania State University (Penn State), Stanford University, Ludwig-Maximilians-Universitat Muenchen, and Georg-August- Universitat Goettingen.

This planet detection research is supported by the National Aeronautics and Space Administration.”

Original Source: University of Texas at Austin News Release

Image credit: David A. Hardy
Astronomers studying the Tau Ceti system have discovered that it contains ten times as much material in the form of asteroids and comets as our own solar system.

Tau Ceti, only 12 light years away, is the nearest sun-like star and is easily visible without a telescope. It is the first star to be found to have a disk of dust and comets around it similar in size and shape to the disk of comets and asteroids that orbits the Sun.

The astronomers’ discovery, being published in Monthly Notices of the Royal Astronomical Society, suggests that even though Tau Ceti is the nearest Sun-like star, any planets that may orbit it would not support life as we know it due to the inevitable large number of devastating collisions. It also suggests that the tranquil space environment around the Earth may be more unusual than previously realized.

Though the star Tau Ceti is similar to the Sun, any planets it has are unlikely to be havens for life, say a team of UK astronomers. Using submillimeter images of the disk of material surrounding Tau Ceti, they found that it must contain more than ten times as many comets and asteroids than there are in the Solar System.

With so many more space rocks hurtling around the star, devastating collisions of the sort that could lead to the destruction of life would be much more likely in the Tau Ceti system than in our own planetary system.

Publication of the result in Monthly Notices of the Royal Astronomical Society coincides with an exhibit ‘Hunting for Planets in Stardust’ at the Royal Society Summer Exhibition by the same science team from the UK Astronomy Technology Centre in Edinburgh and the University of St. Andrews.

The similarity between Tau Ceti and our own sun ends with their comparable sizes and luminosities, explains Jane Greaves, Royal Astronomical Society Norman Lockyer Fellow and lead scientist: ‘Tau Ceti has more than ten times the number of comets and asteroids that there are in our Solar System. We don’t yet know whether there are any planets orbiting Tau Ceti, but if there are, it is likely that they will experience constant bombardment from asteroids of the kind that is believed to have wiped out the dinosaurs. It is likely that with so many large impacts life would not have the opportunity to evolve.’

The discovery means that scientists are going to have to rethink where they look for civilizations outside our Solar System.

Jane Greaves continues, ‘We will have to look for stars which are even more like the Sun, in other words, ones which have only a small number of comets and asteroids. It may be that hostile systems like Tau Ceti are just as common as suitable ones like the Sun.’

The reason for the larger number of comets is not fully understood explains Mark Wyatt, another member of the team: ‘It could be that the Sun passed relatively close to another star at some point in its history and that the close encounter stripped most of the comets and asteroids from around the Sun.’

The new results are based on observations taken with the world’s most sensitive submillimetre camera, SCUBA. The camera, built by the Royal Observatory, Edinburgh, is operated on the James Clerk Maxwell Telescope in Hawaii. The SCUBA image shows a disk of very cold dust (-210 degrees C) in orbit around the star. The dust is produced by collisions between larger comets and asteroids that break them down into smaller and smaller pieces.

Original Source: NASA Astrobiology Story

Image credit: NASA/JPL
NASA has announced new findings from the Spitzer Space Telescope, including the discovery of significant amounts of icy organic materials sprinkled throughout several “planetary construction zones,” or dusty planet-forming discs, which circle infant stars.

These materials, icy dust particles coated with water, methanol and carbon dioxide, may help explain the origin of icy planetoids like comets. Scientists believe these comets may have endowed Earth with some of its water and many of its biogenic, life-enabling materials.

Drs. Dan Watson and William Forrest of the University of Rochester, N.Y, identified the ices. They surveyed five very young stars in the constellation Taurus, 420 light-years from Earth. Previous studies identified similar organic materials in space, but this is the first time they were seen unambiguously in the dust making up planet- forming discs.

In another finding, Spitzer surveyed a group of young stars and found intriguing evidence that one of them may have the youngest planet detected. The observatory found a clearing in the disc around the star CoKu Tau 4. This might indicate an orbiting planet swept away the disc material, like a vacuum leaving a cleared trail on a dirty carpet. The new findings reveal the structure of the gap more clearly than ever before. Because CoKu Tau 4 is about one million years old, the possible planet would be even younger. As a comparison, Earth is approximately 4.5-billion years old.

“These early results show Spitzer will dramatically expand our understanding of how stars and planets form, which ultimately helps us understand our origins,” said Dr. Michael Werner, Spitzer project scientist at NASA’s Jet Propulsion Laboratory , Pasadena, Calif., which manages the mission.

Spitzer also discovered two of the farthest and faintest planet- forming discs ever observed. These discs surround two of more than 300 newborn stars uncovered for the first time in a stunning new image of the dusty stellar nursery called RCW 49. It is approximately 13,700 light-years from Earth in the constellation Centaurus.

“Preliminary data suggest that all 300 or more stars harbor discs, but so far we’ve only looked closely at two. Both were found to have discs,” said Dr. Ed Churchwell of the University of Wisconsin, Madison, Wis., principal investigator of the RCW 49 research, with Dr. Barbara Whitney of Space Science Institute, Boulder, Colo.

Planet-forming, or “protoplanetary,” discs are a natural phase in a star’s life. A star is born inside a dense envelope of gas and dust. Within this envelope, and circling the star, is a flat, dusty disc, where planets are born.

“By seeing what’s behind the dust, Spitzer has shown us star and planet formation is a very active process in our galaxy,” Churchwell said.

Spitzer’s exquisitely sensitive infrared eyes can see planet-forming discs in great detail. “Previously, scientists could study only a small sample of discs, but Spitzer is already on its way toward analyzing thousands of discs,” Werner said.

Spitzer’s infrared spectrograph instrument, which breaks apart infrared light to see the signatures of various chemicals, was used to observe the organic ices and the clearing within CoKu Tau 4’s disc. Spitzer’s infrared array camera found the new stars in RCW 49. Papers on the research will appear in the September 1 issue of the journal Astrophysical Journal Supplements. For images and information about the research on the Internet, visit: http://www.spitzer.caltech.edu/ and http://photojournal.jpl.nasa.gov .

Original Source: NASA News Release

Image credit: NASA/JPL
Included in the nation’s new vision for space is a plan for NASA to “conduct advanced telescope searches for Earth-like planets and habitable environments around other stars.” To meet this challenge, NASA has chosen to fly two separate missions with distinct and complementary architectures to achieve the goal of the Terrestrial Planet Finder. The purpose will be to take family portraits of stars and their orbiting planets, and to study those planets to see which, if any, might be habitable, or might even have life. Both missions would launch within the next 10 to 15 years.

The two missions are:

* Terrestrial Planet Finder-C: a moderate-sized visible-light telescope, similar to the 4- by 6-meter (13.1- by 19.6-foot) version currently under study, to launch around 2014. Onboard coronagraph instrumentation will use a central disc and other specialized techniques to block the glare of a star, allowing detection and characterization of dimmer planets around it.

* Terrestrial Planet Finder-I: multiple spacecraft carrying 3 to 4 meter (9 to 13 foot) infrared telescopes flying in precise formation, to launch before 2020, and to be conducted jointly with the European Space Agency. Combining the infrared, or heat radiation gathered by the multiple telescopes, using a technique called interferometry, will simulate a much larger telescope. This will enable the mission to detect and study individual planets orbiting a parent star observed by TPF-C and also new ones beyond the reach of TPF-C.

Observing extra-solar planets in both visible and infrared light allows scientists to obtain a rich set of data to understand what chemical processes may be going on at various levels in a planet’s atmosphere and surface. That leads to understanding of whether a planet ever could or actually does harbor life. A review of these two plans will be conducted over the summer by NASA and the National Academy of Sciences Committee on Astronomy and Astrophysics. Two other architectures that were studied, the large visible coronagraph and the structurally connected infrared interferometer, will be documented and further studies concluded this summer.

Terrestrial Planet Finder is managed by NASA’s Jet Propulsion Laboratory, Pasadena, Calif., for NASA’s Office of Space Science, Washington, D.C. It is part of NASA’s Origins program, a series of missions and studies designed to answer the questions: Where did we come from? Are we alone?

Original Source: NASA/JPL News Release

Image credit: ESO
A European team of astronomers [1] are announcing the discovery and study of two new extra-solar planets (exoplanets). They belong to the OGLE transit candidate objects and could be characterized in detail. This trebles the number of exoplanets discovered by the transit method; three such objects are now known.

The observations were performed in March 2004 with the FLAMES multi-fiber spectrograph on the 8.2-m VLT Kueyen telescope at the ESO Paranal Observatory (Chile). They enabled the astronomers to measure accurate radial velocities for forty-one stars for which a temporary brightness “dip” had been detected by the OGLE survey. This effect might be the signature of the transit in front of the star of an orbiting planet, but may also be caused by a small stellar companion.

For two of the stars (OGLE-TR-113 and OGLE-TR-132), the measured velocity changes revealed the presence of planetary-mass companions in extremely short-period orbits.

This result confirms the existence of a new class of giant planets, designated “very hot Jupiters” because of their size and very high surface temperature. They are extremely close to their host stars, orbiting them in less than 2 (Earth) days.

The transit method for detecting exoplanets will be “demonstrated” for a wide public on June 8, 2004, when planet Venus passes in front of the solar disc, cf. the VT-2004 programme.

Discovering other Worlds
During the past decade, astronomers have learned that our Solar System is not unique, as more than 120 giant planets orbiting other stars were discovered by radial-velocity surveys (cf. ESO PR 13/00, ESO PR 07/01, and ESO PR 03/03).

However, the radial-velocity technique is not the only tool for the detection of exoplanets. When a planet happens to pass in front of its parent star (as seen from the Earth), it blocks a small fraction of the star’s light from our view. The larger the planet is, relative to the star, the larger is the fraction of the light that is blocked.

It is exactly the same effect when Venus transits the Solar disc on June 8, 2004, cf. ESO PR 03/04 and the VT-2004 programme website. In the past centuries such events were used to estimate the Sun-Earth distance, with extremely useful implications for astrophysics and celestial mechanics.

Nowadays, planetary transits are gaining renewed importance. Several surveys are attempting to find the faint signatures of other worlds, by means of stellar photometric measurements, searching for the periodic dimming of a star as a planet passes in front of its disc.

One of these, the OGLE survey, was originally devised to detect microlensing events by monitoring the brightness of a very large number of stars at regular intervals. For the past four years, it has also included a search for periodical shallow “dips” of the brightness of stars, caused by the regular transit of small orbiting objects (small stars, brown dwarfs or Jupiter-size planets). The OGLE team has since announced 137 “planetary transit candidates” from their survey of about 155,000 stars in two southern sky fields, one in the direction of the Galactic Centre, the other within the Carina constellation.

Resolving the nature of the OGLE transits
The OGLE transit candidates were detected by the presence of a periodic decrease of a few percent in brightness of the observed stars. The radius of a Jupiter-size planet is about 10 times smaller than that of a solar-type star [2], i.e. it covers about 1/100 of the surface of that star and hence it blocks about 1 % of the stellar light during the transit.

The presence of a transit event alone, however, does not reveal the nature of the transiting body. This is because a low-mass star or a brown dwarf, as well as the variable brightness of a background eclipsing binary system seen in the same direction, may result in brightness variations that simulate the ones produced by an orbiting giant planet.

However, the nature of the transiting object may be established by radial-velocity observations of the parent star. The size of the velocity variations (the amplitude) are directly related to the mass of the companion object and therefore allow to discriminate between stars and planets as the cause of the observed brightness “dip”.

In this way, photometric transit searches and radial-velocity measurements combine to become a very powerful technique to detect new exoplanets. Moreover, it is particularly useful for elucidating their characteristics. While the detection of a planet by the radial velocity method only yields a lower estimate of its mass, the measurement of the transit makes it possible to determine the exact mass, radius, and density of the planet.

The follow-up radial-velocity observations of the 137 OGLE transit candidates is not an easy task as the stars are comparatively faint (visual magnitudes around 16). This can only be done by using a telescope in the 8-10m class with a high-resolution spectrograph.

The nature of the two new exoplanets
A European team of astronomers [1] therefore made use of the 8.2-m VLT Kueyen telescope. In March 2004, they followed 41 OGLE “top transit candidate stars” during 8 half-nights. They profited from the multiplex capacity of the FLAMES/UVES fiber link facility that permits to obtain high-resolution spectra of 8 objects simultaneously and measures stellar velocities with an accuracy of about 50 m/s.

While the vast majority of OGLE transit candidates turned out to be binary stars (mostly small, cool stars transiting in front of solar-type stars), two of the objects, known as OGLE-TR-113 and OGLE-TR-132, were found to exhibit small velocity variations. When all available observations – light variations, the stellar spectrum and radial-velocity changes – were combined, the astronomers were able to determine that for these two stars, the transiting objects have masses compatible with those of a giant planet like Jupiter.

Interestingly, both new planets were detected around rather remote stars in the Milky Way galaxy, in the direction of the southern constellation Carina. For OGLE-TR-113, the parent star is of F-type (slightly hotter and more massive than the Sun) and is located at a distance of about 6000 light-years. The orbiting planet is about 35% heavier and its diameter is 10% larger than that of Jupiter, the largest planet in the solar system. It orbits the star once every 1.43 days at a distance of only 3.4 million km (0.0228 AU). In the solar system, Mercury is 17 times farther away from the Sun. The surface temperature of that planet, which like Jupiter is a gaseous giant, is correspondingly higher, probably above 1800 ?C.

The distance to the OGLE-TR-132 system is about 1200 light-years. This planet is about as heavy as Jupiter and about 15% larger (its size is still somewhat uncertain). It orbits a K-dwarf star (cooler and less massive than the Sun) once every 1.69 days at a distance of 4.6 million km (0.0306 AU). Also this planet must be very hot.

A new class of exoplanets
With the previously found planetary transit object OGLE-TR-56 [3], the two new OGLE objects define a new class of exoplanets, still not detected by current radial velocity surveys: planets with extremely short periods and correspondingly small orbits. The distribution of orbital periods for “hot Jupiters” detected from radial velocity surveys seems to drop off below 3 days, and no planet had previously been found with an orbital period shorter than about 2.5 days.

The existence of the three OGLE planets now shows that “very hot Jupiters” do exist, even though they may be quite rare; probably about one such object for every 2500 to 7000 stars. Astronomers are truly puzzled how planetary objects manage to end up in such small orbits, so near their central stars.

Contrary to the radial velocity method which is responsible for the large majority of planet detections around normal stars, the combination of transit and radial-velocity observations makes it possible to determine the true mass, radius and thus the mean density of these planets.

Great expectations
The two new objects double the number of exoplanets with known mass and radius (the three OGLE objects plus HD209458b, which was detected by the radial velocity surveys but for which a photometric transit was later observed). The new information about the exact masses and radii is essential for understanding the internal physics of these planets.

The complementarity of the transit and radial velocity techniques now opens the door towards a detailed study of the true characteristics of exoplanets. Space-based searches for planetary transits – like the COROT and KEPLER missions – together with ground-based radial velocity follow-up observations will in the future lead to the characterization of other worlds as small as our Earth.

Original Source: ESO News Release

Image credit: NASA/JPL
Like Sherlock Holmes holding a magnifying glass to unveil hidden clues, modern day astronomers used cosmic magnifying effects to reveal a planet orbiting a distant star.

This marks the first discovery of a planet around a star beyond Earth’s solar system using gravitational microlensing. A star or planet can act as a cosmic lens to magnify and brighten a more distant star lined up behind it. The gravitational field of the foreground star bends and focuses light, like a glass lens bending and focusing starlight in a telescope. Albert Einstein predicted this effect in his theory of general relativity and confirmed it with our Sun.

“The real strength of microlensing is its ability to detect low-mass planets,” said Dr. Ian Bond of the Institute for Astronomy in Edinburgh, Scotland, lead author of a paper appearing in the May 10 Astrophysical Journal Letters. The discovery was made possible through cooperation between two international research teams: Microlensing Observations in Astrophysics (Moa) and Optical Gravitational Lensing Experiment (Ogle). Well-equipped amateur astronomers might use this technique to follow up future discoveries and help confirm planets around other stars.

The newly discovered star-planet system is 17,000 light years away, in the constellation Sagittarius. The planet, orbiting a red dwarf parent star, is most likely one-and-a-half times bigger than Jupiter. The planet and star are three times farther apart than Earth and the Sun. Together, they magnify a farther, background star some 24,000 light years away, near the Milky Way center.

In most prior microlensing observations, scientists saw a typical brightening pattern, or light curve, indicating a star’s gravitational pull was affecting light from an object behind it. The latest observations revealed extra spikes of brightness, indicating the existence of two massive objects. By analyzing the precise shape of the light curve, Bond and his team determined one smaller object is only 0.4 percent the mass of a second, larger object. They concluded the smaller object must be a planet orbiting its parent star.

Dr. Bohdan Paczynski of Princeton University, Princeton, N.J., an OGLE team member, first proposed using gravitational microlensing to detect dark matter in 1986. In 1991, Paczynski and his student, Shude Mao, proposed using microlensing to detect extrasolar planets. Two years later, three groups reported the first detection of gravitational microlensing by stars. Earlier claims of planet discoveries with microlensing are not regarded as definitive, since they had too few observations of the apparent planetary brightness variations.

“I’m thrilled to see the prediction come true with this first definite planet detection through gravitational microlensing,” Paczynski said. He and his colleagues believe observations over the next few years may lead to the discovery of Neptune-sized, and even Earth-sized planets around distant stars.

Microlensing can easily detect extrasolar planets, because a planet dramatically affects the brightness of a background star. Because the effect works only in rare instances, when two stars are perfectly aligned, millions of stars must be monitored. Recent advances in cameras and image analysis have made this task manageable. Such developments include the new large field-of-view Ogle-III camera, the Moa-II 1.8 meter (70.8 inch) telescope, being built, and cooperation between microlensing teams.

“It’s time-critical to catch stars while they are aligned, so we must share our data as quickly as possible,” said Ogle team-leader Dr. Andrzej Udalski of Poland’s Warsaw University Observatory. Udalski in Poland and Paczynski in the U.S lead the Polish/American project. It operates at Las Campanas Observatory in Chile, run by the Carnegie Institution of Washington, and includes the world’s largest microlensing survey on the 1.3 meter (51-inch) Warsaw Telescope.

NASA and the National Science Foundation fund the Optical Gravitational Lensing Experiment in the U.S. The Polish State Committee for Scientific Research and Foundation for Polish Science funds it in Poland. Microlensing Observations in Astrophysics is primarily a New Zealand/Japanese group, with collaborators in the United Kingdom and U.S. New Zealand’s Marsden Fund, NASA and National Science Foundation, Japan’s Ministry of Education, Culture, Sports, Science, and Technology, and the Japan Society for the Promotion of Science support it.

Images and information about the latest research are available on the Internet at http://www.jpl.nasa.gov/releases/2004/103a.cfm. More information on NASA’s planet-hunting efforts is at http://planetquest.jpl.nasa.gov.

Original Source: NASA/JPL News Release

Image credit: NASA
More than 100 planetary systems have already been discovered around distant stars. Unfortunately, the limitations of current technology mean that only giant planets (like Jupiter) have so far been detected, and smaller, rocky planets similar to Earth remain out of sight.

How many of the known exoplanetary systems might contain habitable Earth-type planets? Perhaps half of them, according to a team from the Open University, led by Professor Barrie Jones, who will be describing their results today at the RAS National Astronomy Meeting in Milton Keynes.

By using computer modelling of the known exoplanetary systems, the group has been able to calculate the likelihood of any ‘Earths’ existing in the so-called habitable zone – the range of distances from each central star where life as we know it could survive. Popularly known as the “Goldilocks” zone, this region would be neither too hot for liquid water, nor too cold.

By launching ‘Earths’ (with masses between 0.1 and 10 times that of our Earth) into a variety of orbits in the habitable zone and following their progress with the computer model, the small planets have been found to suffer a variety of fates. In some systems the proximity of one or more Jupiter-like planets results in gravitational ejection of the ‘Earth’ from anywhere in the habitable zone. However, in other cases there are safe havens in parts of the habitable zone, and in the remainder the entire zone is a safe haven.

Nine of the known exoplanetary systems have been investigated in detail using this technique, enabling the team to derive the basic rules that determine the habitability of the remaining ninety or so systems.

The analysis shows that about half of the known exoplanetary systems could have an ‘Earth’ which is currently orbiting in at least part of the habitable zone, and which has been in this zone for at least one billion years. This period of time has been selected since it is thought to be the minimum required for life to arise and establish itself.

Furthermore, the models show that life could develop at some time in about two thirds of the systems, since the habitable zone moves outwards as the central star ages and becomes more active.

Habitable Moons
A different aspect of this problem is being studied by PhD student David Underwood, who is investigating the possibility that Earth-sized moons orbiting giant planets could support life. A poster setting out the possibilities will be presented during the RAS National Astronomy Meeting.

All of the planets discovered so far are of similar mass to Jupiter, the largest planet in our Solar System. Just as Jupiter has four planet-sized moons, so giant planets around other stars may also have extensive satellite systems, possibly with moons similar in size and mass to Earth.

Life as we know it cannot evolve on a gaseous, giant planet. However, it could survive on Earth-sized satellites orbiting such a planet if the giant is located in the habitable zone.

In order to determine which of the gas giants located within habitable zones could possess a life-friendly moon, the computer models search for systems where the orbits of Earth-sized satellites would be stable and confined within the habitable zone for at least the one billion years needed for life to emerge.

The OU team’s method of determining whether any putative ‘Earths’ or Earth-sized satellites in habitable zones can offer suitable conditions for life to evolve can be applied rapidly to any planetary systems that are newly announced. Future searches for ‘Earths’ and extraterrestrial life should also be assisted by identifying in advance the systems most likely to house habitable worlds.

The predictions made by the simulations will have a practical value in years to come when next-generation instruments will be able to search for the atmospheric signatures of life, such as large amounts of oxygen, on ‘Earths’ and Earth-sized satellites.

Background
There are currently 105 known planetary systems other than our own, with 120 Jupiter-like planets orbiting them. Two of these systems contain three known planets, 11 contain two and the remaining 92 each have one. All but one of these planets has been discovered by their effect on their parent stars’ motion in the sky, causing them to wobble regularly. The extent of these wobbles can be determined from information within the light received from the stars. The remaining planet was discovered as the result of a slight dimming of starlight caused by its regular passage across the disk of its parent star.

Future discoveries are likely to contain a higher proportion of systems that resemble our Solar System, where the giant planets orbit at a safe distance beyond the habitable zone. The proportion of systems that could have habitable ‘Earths’ is, therefore, likely to rise. By the middle of the next decade, space telescopes should be capable of seeing any ‘Earths’ and investigating them to see if they are habitable, and, indeed, whether they actually support life.

Original Source: RAS News Release

Image credit: NASA
If alien astronomers around a distant star had studied the young Sun four-and-a-half billion years ago, could they have seen signs of a newly-formed Earth orbiting this innocuous yellow star? The answer is yes, according to Scott Kenyon (Smithsonian Astrophysical Observatory) and Benjamin Bromley (University of Utah). Moreover, their computer model says that we can use the same signs to locate places where Earth-size planets currently are forming-young worlds that, one day, may host life of their own.

The key to locating newborn Earths, say Kenyon and Bromley, is to look not for the planet itself, but for a ring of dust orbiting the star that is a fingerprint of terrestrial (rocky) planet formation.

“Chances are, if there’s a ring of dust, there’s a planet,” says Kenyon.

Good Planets Are Hard To Find

Our solar system formed from a swirling disk of gas and dust, called a protoplanetary disk, orbiting the young Sun. The same materials are found throughout our galaxy, so the laws of physics predict that other star systems will form planets in a similar manner.

Although planets may be common, they are difficult to detect because they are too faint and located too close to a much brighter star. Therefore, astronomers seek planets by looking for indirect evidence of their existence. In young planetary systems, that evidence may be present in the disk itself, and in how the planet affects the dusty disk from which it forms.

Large, Jupiter-sized planets possess strong gravity. That gravity strongly affects the dusty disk. A single Jupiter can clear a ring-shaped gap in the disk, warp the disk, or create concentrated swaths of dust that leave a pattern in the disk like a wake from a boat. The presence of a giant planet may explain the wake-like pattern seen in the disk around the 350 million-year-old star Vega.

Small, Earth-sized worlds, on the other hand, possess weaker gravity. They affect the disk more weakly, leaving more subtle signs of their presence. Rather than looking for warps or wakes, Kenyon and Bromley recommend looking to see how bright the star system is at infrared (IR) wavelengths of light. (Infrared light, which we perceive as heat, is light with longer wavelengths and less energy than visible light.)

Stars with dusty disks are brighter in the IR than stars without disks. The more dust a star system holds, the brighter it is in the IR. Kenyon and Bromley have shown that astronomers can use IR brightnesses not only to detect a disk, but also to tell when an Earth-sized planet is forming within that disk.

“We were the first to calculate the expected levels of dust production and associated infrared excesses, and the first to demonstrate that terrestrial planet formation produces observable amounts of dust,” says Bromley.

Building Planets From The Ground Up
The most prevalent theory of planet formation calls for building planets “from the ground up.” According to the coagulation theory, small bits of rocky material in a protoplanetary disk collide and stick together. Over thousands of years, small clumps grow into larger and larger clumps, like building a snowman one handful of snow at a time. Eventually, the rocky clumps grow so large that they become full-fledged planets.

Kenyon and Bromley model the planet formation process using a complex computer program. They “seed” a protoplanetary disk with a billion planetesimals 0.6 miles (1 kilometer) in size, all orbiting a central star, and step the system forward in time to see how planets evolve from those basic ingredients.

“We made the simulation as realistic as we could and still complete the calculations in a reasonable amount of time,” says Bromley.

They found the planet formation process to be remarkably efficient. Initially, collisions between planetesimals occur at low velocities, so colliding objects tend to merge and grow. At a typical Earth-Sun distance, it takes only about 1000 years for 1-kilometer objects to grow into 100-kilometer (60-mile) objects. Another 10,000 years produces 600-mile-diameter protoplanets, which grow over an additional 10,000 years to become 1200-mile-diameter protoplanets. Hence, Moon-sized objects can form in as little as 20,000 years.

As planetesimals within the disk grow larger and more massive, their gravity grows stronger. Once a few of the objects reach a size of 600 miles, they begin “stirring up” the remaining smaller objects. Gravity slingshots the smaller, asteroid-sized chunks of rock to higher and higher speeds. They travel so fast that when they collide, they don’t merge-they pulverize, smashing each other apart violently. While the largest protoplanets continue to grow, the rest of the rocky planetesimals grind each other into dust.

“The dust forms right where the planet is forming, at the same distance from its star,” says Kenyon. As a result, the temperature of the dust indicates where the planet is forming. Dust in a Venus-like orbit will be hotter than dust in an Earth-like orbit, giving a clue to the infant planet’s distance from its star.

The size of the largest objects in the disk determines the dust production rate. The amount of dust peaks when 600-mile protoplanets have formed.

“The Spitzer Space Telescope should be able to detect such dust peaks,” says Bromley.

Currently, Kenyon and Bromley’s terrestrial planet formation model covers only a fraction of the solar system, from the orbit of Venus to a distance about halfway between Earth and Mars. In the future, they plan to extend the model to encompass orbits as close to the Sun as Mercury and as distant as Mars.

They also have modeled the formation of the Kuiper Belt-a region of small, icy and rocky objects beyond the orbit of Neptune. The next logical step is to model the formation of gas giants like Jupiter and Saturn.

“We’re starting at the edges of the solar system and working inward,” Kenyon says with a grin. “We’re also working out way up in mass. The Earth is 1000 times more massive than a Kuiper Belt object, and Jupiter is 1000 times more massive than the Earth.”

“Our ultimate goal is to model and understand the formation of our entire solar system.” Kenyon estimates that their goal is attainable within a decade, as computer speed continues to increase, enabling the simulation of an entire solar system.

This research was published in the February 20, 2004, issue of The Astrophysical Journal Letters. Additional information and animations are available online at http://cfa-www.harvard.edu/~kenyon/.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics 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: CfA News Release

Image credit: UBC

Astronomers from the University of British Columbia have discovered that a Jupiter-sized planet is interacting with its star, causing magnetic storms. The sun-like star, HD170049, is located approximately 90 light-years away in the constellation of Sagittarius, and was found to have a planet back in 2000 by another group of astronomers. These new observations using the Canada-France-Hawaii telescope on Mauna Kea have tracked a bright spot that goes around the star keeping pace with its planet – it’s been doing this for more than 100 orbits of the planet.

Canadian astronomers announced today the first evidence of a magnetic field on a planet outside of our solar system which is also the first observation of a planet heating its star. The report was presented this morning by Ph.D. candidate Evgenya Shkolnik, Dr. Gordon Walker, both of the University of British Columbia, Vancouver, BC and Dr. David Bohlender of the National Research Council of Canada / Herzberg Institute for Astrophysics, Victoria, BC at the meeting of the American Astronomical Society in Atlanta, Georgia. The result may offer clues about the structure and formation of the giant planet.

The trio observed the sun-like star HD179949 with the 3.6-meter (142-in) Canada-France-Hawaii Telescope atop Mauna Kea, Hawaii (a 14,000-ft. dormant volcano) using its high-resolution spectrograph called Gecko. HD179949 is 90 light years away in the direction of the southern constellation of Sagittarius (the Archer) but it is too faint to be seen without a telescope. It was first reported to have a close-in planet by Tinney, Butler, Marcy and others in the first results of the Anglo-Australian planet search in 2000. The planet is at least 270 times more massive than the Earth, almost as big as Jupiter, and orbits the star every 3.093 days at 350,000 mph. Such tightly orbiting ?roasters? or ?hot jupiters? make up 20% of all known extrasolar planets.

The star?s chromosphere, a thin, hot layer just above the visible photosphere, was observed in the ultraviolet light emitted by singly-ionized Calcium atoms. Giant magnetic storms produce hot spots which are visible as bright patches in this light. Such a persistent hotspot is observed on HD 179949 keeping pace with the planet in its 3-day orbit for more than a year (or 100 orbits)! The hotspot appears to be moving across the surface of the star slightly ahead of, but keeping pace with the planet. Most evidence suggests the star is rotating too slowly to carry the spot around so quickly.

The best explanation for this traveling hot spot is an interaction between the planet?s magnetic field and the star?s chromosphere, something predicted by Steve Saar of the Center for Astrophysics and Manfred Cuntz of the University of Texas at Arlington in 2000. If so, this is the first ever glimpse of a magnetic field on a planet outside of our solar system, and may provide clues about the planet?s structure and formation.

?If we are indeed witnessing the entanglement of the magnetic field of a star with that of its planet it gives us an entirely new insight into the nature of closely bound planets.? — Dr. Gordon Walker

Obviously, more observations are needed to test if the magnetic interaction is a transient event or something longer lasting. Also, observations from the 8-meter Gemini-South Telescope in Chile of this stellar system are underway in the infrared light emitted by Helium which would map hotspots at higher levels of the chromosphere.

This work was supported by the Canadian Natural Science and Engineering Research Council and the National Research Council of Canada.

Original Source: UBC News Release