Category: Extrasolar Planets

Image credit: ESA

Planet hunters have found more than 30 stars with gas giants in a tight orbit. This orbit seems to be caused by a race between a young gas giant and the star’s planetary disk during early formation of the star system. It’s too hot for them to form in their tight orbit; instead it’s believed they’re formed further out and then slowly pushed into the star by material in the new star system. In some cases the planet is gobbled up by the star, while sometimes the planet consumes the early planetary disk of material and survives.

Of the first 100 stars found to harbor planets, more than 30 stars host a Jupiter-sized world in an orbit smaller than Mercury’s, whizzing around its star in a matter of days (as opposed to our solar system where Jupiter takes 12 years to orbit the Sun). Such close orbits result from a race between a nascent gas giant and a newborn star. In the October 10, 2003, issue of The Astrophysical Journal Letters, astronomers Myron Lecar and Dimitar Sasselov showed what influences this race. They found that planet formation is a contest, where a growing planet must fight for survival lest it be swallowed by the star that initially nurtured it.

“The endgame is a race between the star and its giant planet,” says Sasselov. “In some systems, the planet wins and survives, but in other systems, the planet loses the race and is eaten by the star.”

Although Jupiter-sized worlds have been found orbiting incredibly close to their parent stars, such giant planets could not have formed in their current locations. The oven-like heat of the nearby star and dearth of raw materials would have prevented any large planet from coalescing. “It’s a lousy neighborhood to form gas giants,” says Lecar. “But we find a lot of Jupiter-sized planets in such neighborhoods. Explaining how they got there is a challenge.”

Theorists calculate that so-called “hot Jupiters” must form farther out in the disk of gas and dust surrounding the new star and then migrate inward. A challenge is to halt the planet’s migration before it spirals into the star.

A Jupiter-like world’s migration is powered by the disk material outside the planet’s orbit. The outer protoplanetary disk inexorably pushes the planet inward, even as the planet grows by accreting that outer material. Lecar and Sasselov showed that a planet can win its race to avoid destruction by eating the outer disk before the star eats it.

Our solar system differs from the “hot Jupiter” systems in that the race must have ended quite early. Jupiter migrated for only a short distance before consuming the material between it and the infant Saturn, bringing the King of Planets to a halt. If the protoplanetary disk that birthed our solar system had contained more matter, Jupiter might have lost the race. Then it and the inner planets, including Earth, would have spiraled into the Sun.

“If Jupiter goes, they all go,” says Lecar.

“It’s too early to say that our solar system is rare, because it’s easier to find ‘hot Jupiter’ systems with current detection techniques,” says Sasselov. “But we certainly can say we’re fortunate that Jupiter’s migration stopped early. Otherwise, the Earth would have been destroyed, leaving a barren solar system devoid of life.”

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: Harvard CfA News Release

Image credit: NASA

According to a new simulation by a team of University of Washington astronomers, Earthlike worlds could be more common that previously believed. The team performed 44 computer simulations of planet formations near a star, and found that an Earth-sized world was created nearly every time – and a terrestrial planet was in the star’s habitable zone 25% of the time. The simulations also showed that the orbits of gas giants in a system might decide how much water remains on a terrestrial planet.

Astrobiologists disagree about whether advanced life is common or rare in our universe. But new research suggests that one thing is pretty certain ? if an Earthlike world with significant water is needed for advanced life to evolve, there could be many candidates.

In 44 computer simulations of planet formation near a sun, astronomers found that each simulation produced one to four Earthlike planets, including 11 so-called “habitable” planets about the same distance from their stars as Earth is from our sun.

“Our simulations show a tremendous variety of planets. You can have planets that are half the size of Earth and are very dry, like Mars, or you can have planets like Earth, or you can have planets three times bigger than Earth, with perhaps 10 times more water,” said Sean Raymond, a University of Washington doctoral student in astronomy.

Raymond is the lead author of a paper detailing the simulation results that has been accepted for publication in Icarus, the journal of the American Astronomical Society’s Division for Planetary Sciences. Co-authors are Thomas R. Quinn, a UW associate astronomy professor, and Jonathan Lunine, a professor of planetary science and physics at the University of Arizona.

The simulations show that the amount of water on terrestrial, or Earthlike, planets could be greatly influenced by outer gas giant planets like Jupiter.

“The more eccentric giant planet orbits result in drier terrestrial planets,” Raymond said. “Conversely, more circular giant planet orbits mean wetter terrestrial planets.”

In the case of our solar system, Jupiter’s orbit is slightly elliptical, which could explain why Earth is 80 percent covered by oceans rather than being bone dry or completely covered in water miles deep.

The findings are significant because of the discovery in recent years of a large number of giant planets such as Jupiter and Saturn orbiting other suns. The presence, and orbits, of those planets can be inferred from their gravitational interaction with their parent stars and their effect on light from those stars as seen from Earth.

It currently is impossible to detect Earthlike planets around other stars. However, if results from the models are correct, there could be planets such as ours around a number of other suns relatively close to our solar system. A significant number of those planets are likely to be in the “habitable zone,” the distance from a star at which the planet’s temperature will maintain liquid water on the surface. Liquid water is thought to be a requirement for life, so planets in a star’s habitable zone are ideal candidates for life. It is unclear, however, whether those planets could harbor more than simple microbial life.

The researchers note that their models represent the extremes of what is possible in forming Earthlike planets rather than what is typical of planets observed in our galaxy. For now, they said, it is unclear which approach is more realistic.

Their goal is to understand what a system’s terrestrial planets will look like if the characteristics of a system’s giant planets are known, Raymond said.

Quinn noted that all of the giant planets detected so far have orbits that carry them very close to their parent stars, so their orbits are completed in a relatively short time and it is easier to observe them. The giant planets observed close to their parent stars likely formed farther away and then, because of gravitational forces, migrated closer.

But Quinn expects that giant planets will begin to be discovered farther away from their suns as astronomers have more time to watch and are able to observe gravitational effects during their longer orbits. He doubts such planets will be found before they have completed whatever migration they make toward their suns, because their orbits would be too irregular to observe with any confidence.

“These simulations occur after their migration is over, after the orbits of the gas giants have stabilized,” he said.

The research is supported by the National Aeronautics and Space Administration’s Astrobiology Institute, its Planetary Atmospheres program, and Intel Corp.

Original Source: UW News Release

Image credit: PPARC

Astronomers from the Particle Physics and Astronomy Research Council believe they’ve discovered a planetary system around Vega, one of the brightest stars in the sky. Not only that, the star system seems remarkably similar to our own Solar System. So far, they’ve found evidence for a Neptune-sized planet in the same orbit as our own Neptune. This means there could be smaller, rocky planets closer in to the star.

Astronomers at the Particle Physics and Astronomy Research Councils UK Astronomy Technology Centre (ATC) at the Royal Observatory, Edinburgh have produced compelling new evidence that Vega, one of the brightest stars in the sky, has a planetary system around it which is more like our own Solar System than any other so far discovered.

All of the hundred or so planets that have been discovered around other stars have been very large gaseous (Jupiter-like) planets orbiting close to their star. This is very unlike our own Solar System. New computer modelling techniques have shown that observations of the structure of a faint dust disk around Vega can be best explained by a Neptune-like planet orbiting at a similar distance to Neptune in our own solar system and having similar mass. The wide orbit of the Neptune-like planet means that there is plenty of room inside it for small rocky planets similar to the Earth the Holy Grail for astronomers wanting to know whether we are alone in the Universe.

The modelling, which is described today (1 December 2003) in The Astrophysical Journal, is based on observations taken with the world’s most sensitive submillimetre camera, SCUBA. The camera, built at the ATC, is operated on the James Clerk Maxwell Telescope in Hawaii. The SCUBA image shows a disk of very cold dust (-180 degrees centigrade) in orbit around the star.

The irregular shape of the disk is the clue that it is likely to contain planets explains astronomer Mark Wyatt, the author of the paper. Although we cant directly observe the planets, they have created clumps in the disk of dust around the star.

The modelling suggests that the Neptune-like planet actually formed much closer to the star than its current position. As it moved out to its current wide orbit over about 56 million years, many comets were swept out with it, causing the dust disk to be clumpy.

Exactly the same process is thought to have happened in our Solar System, said Wyatt, Neptune was pushed away from the Sun because of the presence of Jupiter orbiting inside it. So it appears that as well as having a Neptune-like planet, Vega may also have a more massive Jupiter-like planet in a smaller orbit.

The model can be tested in two ways as Wayne Holland, who made the original observations, explains The model predicts that the clumps in the disk will rotate around the star once every three hundred years. If we take more observations after a gap of a few years we should see the movement of the clumps. Also the model predicts the finer detail of the disks clumpiness which can be confirmed using the next generation of telescopes and cameras.

Paradoxically the star barely appears in the SCUBA image because it is far too hot to be seen with this kind of detector. Vega is, however, easily seen with the naked eye. It is the third brightest star visible from Northern latitudes and is bluish-white in colour. Tonight you can see it in the west at around 7pm.

Facts about Vega
* Vega is the fifth brightest star in the sky and the third brightest visible in the Northern hemisphere.
* It is 25 light years away from the Sun (1AU is the distance between the Earth and Sun).
* It has a diameter three times bigger than the Sun.
* It is 58 times brighter than the Sun.
* Together with Deneb and Altair, Vega forms the summer triangle.
* Vega is the brightest star in the constellation Lyra, the Harp. The lyre, or harp, is supposed to have been invented by the Greek God Hermes who gave it to his half-brother Apollo. Apollo then gave it to his son Orpheus, the musician of the Argonaughts.
* Vega was the first star ever to be photographed. During the night of July 16-17 1850 the historic picture was taken at Harvard Observatory using a 15 inch refractor telescope during a 100 second exposure.

Original Source: PPARC News Release

Image credit: ESA

Astronomers from the University of Texas at Austin believe they’ve figured out an inexpensive way to search for extrasolar planets. After stars like our own Sun use up their fuel they eventually turn into red giant stars, and then shrink again to become white dwarfs. Although the process will likely destroy the inner planets, the outer planets will probably still remain in orbit around the star. These white dwarfs are known to pulsate at a specific rate, so the gravity of a planet moving around the star should affect this pulse rate by a minute amount that should be detectable by inexpensive Earth-based telescopes.

University of Texas at Austin astronomers have invented an inexpensive method to determine if other solar systems like our own exist.

Among the more than 100 stars now known to have planets, astronomers have found few systems similar to ours. It?s unknown if this is because of technological limitations or if our system is truly a rare configuration. The McDonald Observatory astronomers? novel search method uses a Depression-era telescope mated with today?s technology.

Astronomers Don Winget and Edward Nather, graduate students Fergal Mullally and Anjum Mukadem, and colleagues are looking for the “leftovers” of solar systems like ours. Their method searches for the pieces of such a solar system after its star has died, by exploiting a trait of ancient, burnt-out Suns called “white dwarfs.”

University of Texas astronomers Bill Cochran and Ted von Hippel are also involved, along with S.O. Kepler of Brazil?s Universidade Federal de Rio Grande dol Sul and Antonio Kanaan of Brazil?s Universidade Federal de Santa Catarina.

Astronomers know that as Sun-like stars use up their nuclear fuel, their outer layers will expand, and the star will become a “red giant” star. When this happens to the Sun, in about five billion years, they expect it will swallow Mercury and Venus, perhaps not quite reaching Earth. Then the Sun will blow off its outer layers and will exist for a few thousand years as a beautiful, wispy planetary nebula. The Sun?s leftover core will then be a white dwarf, a dense, dimming cinder about the size of Earth. And, most important, it likely will still be orbited by the outer planets of our solar system.

Once a Sun-like system reaches this state, Winget?s team may be able to find it. Their method is based on more than three decades of research on the variability (that is, changes in brightness) of white dwarfs. In the early 1980s, University of Texas astronomers discovered that some white dwarfs vary, or “pulsate,” in regular bursts. More recently, Winget and colleagues discovered that about one-third of these pulsating white dwarfs (PWDs) are more reliable timekeepers than atomic clocks and most millisecond pulsars.

These pulsations are the key to detecting planets. Planets orbiting a stable PWD star will affect observations of its timekeeping, appearing to cause periodic variations in the patterns of pulses coming from the star. That?s because the planet orbiting the PWD drags the star around as it moves. The change in distance between the star and Earth will change the amount of time taken for the light from the pulsations to reach Earth. Because the pulses are very stable, astronomers can calculate the difference between the observed and expected arrival time of the pulses and deduce the presence and properties of the planet. (This method is similar to that used in the discoveries of the so-called “pulsar planets.” The difference is, the pulsar companions are not thought to have formed with their stars, but only after those stars had exploded in supernovae.)

“This search will be sensitive to white dwarfs which were initially between one and four times as massive as the Sun, and should be able to detect planets within two to 20 AU from their parent star. This means we?ll be probing inside the habitable zone for some stars,” Winget said. (An AU, or astronomical unit, is the distance between Earth and the Sun.) “Basically, detecting Jupiter at Jupiter?s distance with this technique is easy. It?s duck soup,” he said.

Easy, but not quick. Outer planets, orbiting their stars at large distances, can take more than a decade to complete one orbit. Therefore, it can take many years of observations to definitively detect a planet orbiting a white dwarf.

“You need to look for a long time for a full orbit,” Winget said. “A half-orbit or a third of an orbit will tell us something?s going on there. But for a planet at Jupiter?s distance, a half-orbit is still six years.” Winget added that for this method, “detecting Jupiter at Uranus? distance is easier, but takes even longer.”

For the PWD planet search, Nather conceived a specialized new instrument for McDonald Observatory?s 2.1-meter Otto Struve Telescope. He and Mukadam designed and built the instrument, called Argos, to measure the amount of light coming from target stars. Specifically, Argos is a “CCD photometer” ? a photon counter that uses a charge-coupled device to record images. Located at the prime focus of the Struve Telescope, Argos has no optics other than the telescope?s 2.1-meter primary mirror. Copies of Argos are now being built at other observatories around the world.

Mullally continues the search for planets around white dwarfs with Argos on the Struve Telescope. He has 22 target stars, most of which were identified through the Sloan Digital Sky Survey. When the team finds promising planet candidates with Argos, they will follow up using the 9.2-meter Hobby-Eberly Telescope (HET) at McDonald Observatory.

“If we find large planets orbiting at large distances, that?s a good clue that there might be smaller planets closer in. In that case, what you do is pound away on that target with the largest telescope you have access to,” Winget said. The HET will enable more precise timing of the PWD?s pulses, and thus be able to pinpoint smaller planets.

This search will be able to study types of stars unable to be studied with the doppler spectroscopy method ? the most successful planet search method to date ? Winget said. Because of idiosyncrasies in the make-up of Sun-like stars, the doppler spectroscopy method is not very sensitive in looking for planets around stars twice as massive as the Sun. Roughly half of the stars in Winget?s study will be white dwarfs that were originally these types of stars. For this reason, the PWD study at McDonald can be instrumental in scouting and assessing targets and observing strategies for NASA space missions planned in the next two decades, specifically the Space Interferometry Mission, Terrestrial Planet Finder and Kepler spacecraft.

This research is funded by a NASA Origins grant, as well as an Advanced Research Project grant from the State of Texas. Through funding from the Texas Higher Education Agency, two secondary schoolteachers (Donna Slaughter of Stony Point High School in Round Rock, Texas, and Chris Cotter of Lanier High School in Austin) have been directly involved in this research. Plans are now underway to extend this involvement to other teachers, and the students in their classrooms by bringing the science, scientists and the Observatory directly into the classroom using the Internet. Cotter and his colleagues at Lanier High School are involved with Mullally in testing this concept.

Original Source: McDonald Observatory News Release

Image credit: ESA

The European Space Agency is working on a new mission that could be able to detect moons orbiting planets in other star systems. In 2008, the ESA will launch Eddington, which will detect the drop in light as planets as small as Mars pass in front of their parent stars. Astronomers should theoretically be able to detect moons going around those planets because of their gravity – if the planet dims the star a few minutes earlier or later than expected, it will have one or more moons.

ESA is now planning a mission that can detect moons around planets outside our Solar System, those orbiting other stars.

Everyone knows our Moon: lovers stare at it, wolves howl at it, and ESA recently sent SMART-1 to study it. But there are over a hundred other moons in our Solar System, each a world in its own right.

A moon is a natural body that travels around a planet. Moons are a by-product of planetary formation and can range in size from small asteroid-sized bodies of a few kilometres in diameter to several thousand kilometres, larger even than the planets Mercury and Pluto.

Landing on another moon
One such large moon is Titan, the target for ESA?s daring Huygens mission that in 2005 will become the first spacecraft ever to land on a moon of another planet. Titan is slightly bigger than the planet Mercury, and is only called a moon because it orbits the giant planet Saturn rather than the Sun.

Four other large moons can be found around another of our neighbours, Jupiter. These are Io, Europa, Ganymede and Callisto. Europa has captured attention because beneath its icy surface, scientists think that an ocean covers the entire moon. Some scientists have even speculated that microscopic life might be found in that ocean.

Habitable moons?
In 2008, ESA plans to launch its ?rocky planet? finder Eddington. By detecting the drop in light seen when a world passes in front of its parent star, Eddington will be capable of discovering planets the size of Jupiter, and also those smaller than Mars.

That means, if our own Solar System is anything to go by, it will be capable of detecting moons similar in size to Titan and the four large moons of Jupiter.

It would be particularly exciting if such combinations of planets and moons were found orbiting a star at Earth?s distance from the Sun. Perhaps then the surfaces of the moons would be warmed to habitable levels.

Orbital dancing
What about moons similar to our own? An equivalent of Earth?s moon would be too small to be detected directly by Eddington, but such a body would affect the way its planet moves and it is that movement which Eddington could detect.

The Earth and the Moon orbit the Sun like ballroom dancers who move around the floor, simultaneously twirling about one another. This means the Earth does not follow a strictly circular path through space, sometimes it will be leading the Moon and sometimes trailing.

This causes variations of up to five minutes from where the Earth would be if it did not possess a moon. By precisely timing when a rocky planet passes in front of its star, Eddington will be able to show if a moon is pulling its planet out of a strictly circular path around the star.

So, how many moons can Eddington expect to find circling planets around other stars? If we make an estimate based on our own Solar System, several thousands will be found ? however, no one knows for sure. That?s what makes the quest so exciting!

Original Source: ESA News Release

Image credit: NASA

A team of astronomers from Ohio State University believe that we should be seeking life on a wider range of planets than previously speculated. They calculated that NASA’s upcoming Space Interferometry Mission (SIM) should be able to detect habitable planets near stars which are much larger than the Sun. This opens up a whole new range of planets to look at. SIM was originally supposed to launch in 2009, but NASA is considering whether to use these funds to maintain Hubble past 2010 instead.

The search for life on other planets could soon extend to solar systems that are very different from our own, according to a new study by an Ohio State University astronomer and his colleagues.

In fact, finding a terrestrial planet in such a solar system would offer unique scientific opportunities to test evolution, said Andrew Gould, professor of astronomy here.

In a recent issue of Astrophysical Journal Letters, he and his coauthors calculated that NASA?s upcoming Space Interferometry Mission (SIM) would be able to detect habitable planets near stars significantly more massive than the sun.

Scientists have typically thought that the search for life should focus on finding planets like Earth that orbit stars like the sun, but this new finding shows that ?the field is wide open,? Gould said.

?Here?s a type of solar system that we never thought to look at,? he added, ?but now we?ll have the tools to do it.?

Gould is on the science team that is helping to plan the SIM mission, and he is working to define the capabilities of the satellite.

The satellite was set to launch in 2009, but its fate is now uncertain. NASA is considering whether to divert funds to maintain the Hubble Space Telescope beyond its scheduled retirement in 2010, Gould explained, and he has been asked to address the issue for an assembly of astronomers in Washington D.C. on Thursday, July 31.

SIM would help astronomers find habitable planets, Gould said. The key is detecting planets that circle a star at just the right distance to maintain a supply of liquid water. The range of most promising orbits depends on the type of the star, and is called the ?habitable zone.?

The earth resides directly in the habitable zone for our solar system, some 93 million miles from the sun. The nearest planets, Venus and Mars, barely lie within the edges of the habitable zone.

Hotter, more massive stars have always been considered less likely to harbor life, though not because they would be too hot. Planets could still enjoy temperate climates, just at orbits farther away from the star.

The problem is one of time, not temperature, Gould said.
Hotter stars tend to ?burn out? faster — perhaps too fast for life to develop there.

Our sun is approximately 4.5 billion years old; in contrast, one of the stars examined in the study is 1.5 times more massive than the sun, and would probably only generate life-sustaining energy for about two billion years.

Given the billions of years required for evolution of life on earth, scientists could question whether life would stand a chance in a shorter-lived solar system.

?We have no idea how evolution would proceed on any planet other than our own,? Gould said. ?If we find a planet around a shorter-lived star, we may be able to test what would happen to evolution under those circumstances.?

SIM will use Interferometry — a technique that involves the interference of light waves — to very accurately measure the position of stars in the sky. The satellite would notice, for instance, if a point of light on the surface of the moon moved the width of a dime.

In the case of distant stars, SIM will pick up on the tiny wobble in the position of a star caused by the gravity of its orbiting planets.

That?s what will make SIM ideal for studying hotter, massive stars, Gould said. Planets that orbit far from a star — as the habitable planets around a hot star would have to do — create a larger wobble.

He and study coauthors Eric B. Ford of Princeton University and Debra A. Fischer of the University of California, Berkeley, determined that SIM is sensitive enough for the task.

Previously, Gould and Ohio State professor Darren DePoy and graduate student Joshua Pepper determined that another future NASA mission could be used to find habitable planets around very small stars, which are much more plentiful in the galaxy than stars like our sun.

That mission, the Kepler Mission, will detect planetary transits — events where planets pass in front of a star and block the star?s light from reaching earth. Transits of planets orbiting close to a star are easier to detect, and because these small stars are very dim, the habitable zone would also be very close to the star.

?The point is that the various methods for planet detection complement each other, and can be used to find habitable planets around a wide variety of stars,? Gould said.

NASA funded this research.

Original Source: OSU News Release

Image credit: Hubble

The Hubble Space Telescope was recently used to identify the oldest extrasolar planet ever discovered. The 2.5 Jupiter mass planet was originally discovered around a pulsar in the globular cluster M4 way back in 1988; astronomers detected a regular dimming of the pulsar’s radio wave emissions. By using Hubble, astronomers were better able to explain how the planet ended up around a pulsar. This discovery could reshape the current models of planetary development, which predicted that stars needed to go through at least one complete cycle to create the heavier elements that planets require.

Long before our Sun and Earth ever existed, a Jupiter-sized planet formed around a sun-like star. Now, 13 billion years later, NASA’s Hubble Space Telescope has precisely measured the mass of this farthest and oldest known planet. The ancient planet has had a remarkable history because it has wound up in an unlikely, rough neighborhood. It orbits a peculiar pair of burned-out stars in the crowded core of a globular star cluster.

The new Hubble findings close a decade of speculation and debate as to the true nature of this ancient world, which takes a century to complete each orbit. The planet is 2.5 times the mass of Jupiter. Its very existence provides tantalizing evidence that the first planets were formed rapidly, within a billion years of the Big Bang, leading astronomers to conclude that planets may be very abundant in the universe.

The planet now lies in the core of the ancient globular star cluster M4, located 5,600 light-years away in the summer constellation Scorpius. Globular clusters are deficient in heavier elements because they formed so early in the universe that heavier elements had not been cooked up in abundance in the nuclear furnaces of stars. Some astronomers have therefore argued that globular clusters cannot contain planets. This conclusion was bolstered in 1999 when Hubble failed to find close-orbiting “hot Jupiter”-type planets around the stars of the globular cluster 47 Tucanae. Now, it seems that astronomers were just looking in the wrong place, and that gas-giant worlds orbiting at greater distances from their stars could be common in globular clusters.

“Our Hubble measurement offers tantalizing evidence that planet formation processes are quite robust and efficient at making use of a small amount of heavier elements. This implies that planet formation happened very early in the universe,” says Steinn Sigurdsson of Pennsylvania State University.

“This is tremendously encouraging that planets are probably abundant in globular star clusters,” says Harvey Richer of the University of British Columbia. He bases this conclusion on the fact that a planet was uncovered in such an unlikely place, orbiting two captured stars ? a helium white dwarf and a rapidly spinning neutron star ? near the crowded core of a globular cluster, where fragile planetary systems tend to be ripped apart due to gravitational interactions with neighboring stars.

The story of this planet’s discovery began in 1988, when the pulsar, called PSR B1620-26, was discovered in M4. It is a neutron star spinning just under 100 times per second and emitting regular radio pulses like a lighthouse beam. The white dwarf was quickly found through its effect on the clock-like pulsar, as the two stars orbited each other twice per year. Sometime later, astronomers noticed further irregularities in the pulsar that implied that a third object was orbiting the others. This new object was suspected to be a planet, but it could also be a brown dwarf or a low-mass star. Debate over its true identity continued through the 1990s.

Sigurdsson, Richer, and their co-investigators settled the debate by at last measuring the planet’s actual mass through some ingenious celestial detective work. They had exquisite Hubble data from the mid-1990s, taken to study white dwarfs in M4. Sifting through these observations, they were able to detect the white dwarf orbiting the pulsar and measure its color and temperature. Using evolutionary models computed by Brad Hansen of the University of California, Los Angeles, the astronomers estimated the white dwarf’s mass. This in turn was compared to the amount of wobble in the pulsar’s signal, allowing the astronomers to calculate the tilt of the white dwarf’s orbit as seen from Earth. When combined with the radio studies of the wobbling pulsar, this critical piece of evidence told them the tilt of the planet’s orbit, too, and so the precise mass could at last be known. With a mass of only 2.5 Jupiters, the object is too small to be a star or brown dwarf, and must instead be a planet.

The planet has had a rough road over the last 13 billion years. When it was born, it probably orbited its youthful yellow sun at approximately the same distance Jupiter is from our Sun. The planet survived blistering ultraviolet radiation, supernova radiation, and shockwaves, which must have ravaged the young globular cluster in a furious firestorm of star birth in its early days. Around the time multi-celled life appeared on Earth, the planet and star were plunging into the core of M4. In this densely crowded region, the planet and its sun passed close to an ancient pulsar, formed in a supernova when the cluster was young, that had its own stellar companion. In a slow-motion gravitational dance, the sun and planet were captured by the pulsar, whose original companion was ejected into space and lost. The pulsar, sun, and planet were themselves flung by gravitational recoil into the less-dense outer regions of the cluster. Eventually, as the star aged it ballooned to a red giant and spilled matter onto the pulsar. The momentum carried with this matter caused the neutron star to “spin-up” and re-awaken as a millisecond pulsar. Meanwhile, the planet continued on its leisurely orbit at a distance of about 2 billion miles from the pair (approximately the same distance Uranus is from our Sun).

It is likely that the planet is a gas giant, without a solid surface like the Earth. Because it was formed so early in the life of the universe, it probably doesn’t have abundant quantities of elements such as carbon and oxygen. For these reasons, it is very improbable the planet would host life. Even if life arose on, for example, a solid moon orbiting the planet, it is unlikely to have survived the intense X-ray blast that would have accompanied the spin-up of the pulsar. Regrettably, it is unlikely that any civilization witnessed and recorded the dramatic history of this planet, which began at nearly the beginning of time itself.

Original Source: Hubble News Release

Image credit: ESA

The European Space Agency is planning a series of space-based observatories designed to search space for evidence of Earth-like worlds. But an easier target to spot should be waterworlds; six times the mass of the Earth and covered with an ocean 100km deep. The CNES/ESA mission Corot will launch in 2005, and should just barely be able to spot dimming stars as these “waterworlds” pass in front. Even more powerful Eddington will launch in 2008 and should be able to see planets half the size of Earth. Finally, Darwin will launch in 2014 and search for signs of life on Earthlike planets.

Science fiction writers and movie-makers have imagined a world completely covered by an ocean, but what if one really existed? Would such a world support life, and what would this life be like?

ESA could make science fiction become science fact when it finds such a world, if the predictions of a group of European astronomers are correct. The ESA mission Eddington, which is now in development, could be the key.

At the recent ESA co-sponsored ‘Towards Other Earths’ conference, nearly 250 of the world’s leading experts in planet detection discussed the strategy for finding Earth-like worlds. Alain L?ger and colleagues of the Institut d’Astrophysique Spatiale, France, described a new class of planets that could be awaiting discovery: ‘waterworlds’.

According to L?ger and his colleagues, these waterworlds would contain about six times the mass of Earth, in a sphere twice as wide as our planet. They would possess atmospheres and orbit their parent star at roughly the same distance that the Earth is from the Sun. Most excitingly, an ocean of water entirely covers each world and extends over 25 times deeper than the average depth of the oceans on Earth.

A hundred kilometres deep
According to calculations, the internal structure of a waterworld would consist of a metallic core with a radius of about 4000 kilometres. Then there would be a rocky mantle region extending to a height of 3500 kilometres above the core?s surface, covered by a second mantle made of ice up to 5000 kilometres thick. Finally, an ocean blankets the entire world to a depth of 100 kilometres, with an atmosphere on top of this.

With twice the radius of the Earth, they will be easily spotted by the Eddington spacecraft, which is designed to detect planets down to half the size of the Earth. “A waterworld passing in front of a star, somewhat cooler than the Sun, will cause a dimming in the stellar light by almost one part in a thousand. That’s almost ten times larger than the smallest variation Eddington is designed to detect. So, waterworlds ? if they exist ? will be a very easy catch for Eddington,” says Fabio Favata, ESA?s Eddington Project Scientist.

The CNES/ESA mission Corot, which is a smaller, precursor mission to Eddington due for launch around 2005, may also be just able to glimpse them, if they are close enough to their parent stars.

Origins of life
Scientists are now asking if such worlds could support life, and what would it be like, especially since water is a prime ingredient for life on Earth. While waterworlds seem to have everything to sustain life, there is a big question mark over whether they could actually allow it to start in the first place.

One of the leading theories for life’s origin in deep oceans is that it requires hot springs on the ocean floor, heated by volcanic activity like the ‘black smokers’ found here on Earth. On a waterworld however, 5000 kilometres of ice separate the ocean floor from any possible smokers. On the other hand, a water-surface origin may still be possible.

Perhaps the only way to know if anything lives on a waterworld will be to study them with ESA’s habitable-planet-finding mission, Darwin. When it launches in around 2014, this flotilla of spacecraft will look for tell-tale signs of life in the atmospheres of any planets, including waterworlds.

Original Source: ESA News Release

Image credit: PPARC

A team of international astronomers have discovered a planet which is remarkably similar to Jupiter. This new planet circles a star called HD70642 (in the constellation of Puppis) 90 light-years from Earth. It’s twice the mass of Jupiter and its orbit is nearly circular around HD70642 at a distance similar to Jupiter’s from our own Sun. Furthermore, there don’t seem to be any larger planets closer to the star. This planetary discovery is the most similar to our own solar system found so far.

Astronomers looking for planetary systems that resemble our own solar system have found the most similar formation so far. British astronomers, working with Australian and American colleagues, have discovered a planet like Jupiter in orbit round a nearby star that is very like our own Sun. Among the hundred found so far, this system is the one most similar to our Solar System. The planet’s orbit is like that of Jupiter in our own Solar System, especially as it is nearly circular and there are no bigger planets closer in to its star.

“This planet is going round in a nearly circular orbit three-fifths the size of our own Jupiter. This is the closest we have yet got to a real Solar System-like planet, and advances our search for systems that are even more like our own,” said UK team leader Hugh Jones of Liverpool John Moores University.

The planet was discovered using the 3.9-metre Anglo-Australian Telescope [AAT] in New South Wales, Australia. The discovery, which is part of a large search for solar systems that resemble our own, will be announced today (Thursday, July 3rd 2003) by Hugh Jones (Liverpool John Moores University) at a conference on “Extrasolar Planets: Today and Tomorrow” in Paris, France.

“It is the exquisite precision of our measurements that lets us search for these Jupiters – they are harder to find than the more exotic planets found so far. Perhaps most stars will be shown to have planets like our own Solar System”, said Dr Alan Penny, from the Rutherford Appleton Laboratory.

The new planet, which has a mass about twice that of Jupiter, circles its star (HD70642) about every six years. HD70642 can be found in the constellation Puppis and is about 90 light years away from Earth. The planet is 3.3 times further from its star as the Earth is from the Sun (about halfway between Mars and Jupiter if it were in our own system).

The long-term goal of this programme is the detection of true analogues to the Solar System: planetary systems with giant planets in long circular orbits and small rocky planets on shorter circular orbits. This discovery of a -Jupiter- like gas giant planet around a nearby star is a step toward this goal. The discovery of other such planets and planetary satellites within the next decade will help astronomers assess the Solar System’s place in the galaxy and whether planetary systems like our own are common or rare.

Prior to the discovery of extrasolar planets, planetary systems were generally predicted to be similar to the Solar System – giant planets orbiting beyond 4 Earth-Sun distances in circular orbits, and terrestrial mass planets in inner orbits. The danger of using theoretical ideas to extrapolate from just one example – our own Solar System – has been shown by the extrasolar planetary systems now known to exist which have very different properties. Planetary systems are much more diverse than ever imagined.

However these new planets have only been found around one-tenth of stars where they were looked for. It is possible that the harder-to-find very Solar System-like planets do exist around most stars.

The vast majority of the presently known extrasolar planets lie in elliptical orbits, which would preclude the existence of habitable terrestrial planets. Previously, the only gas giant found to orbit beyond 3 Earth-Sun distances in a near circular orbit was the outer planet of the 47 Ursa Majoris system – a system which also includes an inner gas giant at 2 Earth-Sun distances (unlike the Solar System). This discovery of a 3.3 Earth-Sun distance planet in a near circular orbit around a Sun-like star bears the closest likeness to our Solar System found to date and demonstrates our searches are precise enough to find Jupiter- like planets in Jupiter-like orbit.

To find evidence of planets, the astronomers use a high- precision technique developed by Paul Butler of the Carnegie Institute of Washington and Geoff Marcy of the University of California at Berkeley to measure how much a star “wobbles” in space as it is affected by a planet’s gravity. As an unseen planet orbits a distant star, the gravitational pull causes the star to move back and forth in space. That wobble can be detected by the ‘Doppler shifting’ it causes in the star’s light. This discovery demonstrates that the long term precision of the team’s technique is 3 metres per second (7mph) making the Anglo-Australian Planet Search at least as precise as any of the many planet search projects underway.

Original Source: PPARC News Release

Image credit: NASA

A team of European astronomers announced this week that they have discovered seven new planets, bringing the total of extrasolar planets discovered to 115. Six of the planets circle stars that weren’t previously known to contain planets. All are gas giants, ranging in size from slightly smaller than Jupiter up to eight times the mass of Jupiter. They were detected using the radial velocity method, where astronomers watch for back and forth movement of a star caused by interaction with its planet. There are currently 30 teams searching for planets around other stars.

European astronomers this week announced the discovery of seven new planets orbiting other stars, bringing to 115 the total number of known extrasolar planets. Six of the new planets circle stars not previously known to harbor planets, while the seventh orbits a star where another planet had been detected earlier.

All of the new planets are gas giants, ranging in size from slightly smaller than Jupiter to nearly eight-times the mass of Jupiter. They were detected using the radial velocity method, which infers the presence of an unseen companion because of the back-and-forth movement it induces in the host star. This movement is detectable as a periodic red shift and blue shift in the star’s spectral lines. (For more about this method, see the article Finding Planets.)

A team led by Michel Mayor, as part of the ongoing Geneva Extrasolar Planet Search program, was responsible for six of the new discoveries: HD 65216, HD111232, HD142415, HD216770, HD10647 and HD 169830. In 1995, Mayor was co-discoverer, along with Didier Queloz, of 51 Pegasi, the first known planet around another star.

Additionally, Japanese astronomers last week announced the discovery of a new planet around a giant star (also using radial velocity). This new planet, HD 104985 b, is more than six time the mass of Jupiter. It was the first to be discovered by a Japanese planet-search team, according the Extrasolar Planets Encyclopedia.

There are currently more than 30 planet-search programs under way worldwide using ground-based telescopes. While none of the planets detected thus far is believed to have the potential to support life, NASA is developing a suite of space-based missions that will be capable of detecting for smaller, habitable planets within the next decade. See the links at left under “Missions” for information on NASA’s planet-finding missions, which include the Space Interferometery Mission, Kepler and Terrestrial Planet Finder.

Original Source: NASA News Release