Category: Extrasolar Planets

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

An Earth-like planet could come together from a cloud of dust in as short as 3 million years according to a new report from researchers in Florida and Michigan. By studying the pre-planetary disks that form around other stars, the astronomers noticed that the disks form around young stars when they’re 1 million years old, but few stay longer than 3 million years, and none are present at 6 million years. This means that rocky planets, like the Earth, had to have formed during that time. Astronomers previously believed it took 10 million years for planets to form.

Astronomers from the Harvard-Smithsonian Center for Astrophysics announced today that they have discovered a Jupiter-class planet orbiting a star 5,000 light years away – the most distant ever found. The planet, called Ogle-TR-56b is important because it’s only the second planet ever discovered that passes directly in front of its star, dimming it slightly. More than 100 extrasolar planets have now been discovered. (BBC Article)

Image credit: NASA

Planet hunters have discovered a new extrasolar system that looks remarkable like our own Solar System. Until now, planets orbiting around other stars have had elongated and eccentric orbits, but a planet orbiting around 55 Cancri has almost the same distance as our own Jupiter (although, it does have 3.5-5 times the mass). The team of astronomers also announced an additional 13 new planets on the same day, bringing the total number of known planets outside our Solar System to over 90.

After 15 years of observation and a lot of patience, the world’s premier planet-hunting team has finally found a planetary system that reminds them of our own home solar system.

Dr. Geoffrey Marcy, astronomy professor at the University of California, Berkeley, and astronomer Dr. Paul Butler of the Carnegie Institution of Washington, Washington, D.C., today announced the discovery of a Jupiter-like planet orbiting a Sun-like star at nearly the same distance as the Jovian system orbits our Sun.

“All other extrasolar planets discovered up to now orbit closer to the parent star, and most of them have had elongated, eccentric orbits. This new planet orbits as far from its star as our own Jupiter orbits the Sun,” said Marcy. NASA and the National Science Foundation fund the planet-hunting team.

The star, 55 Cancri in the constellation Cancer, was already known to have one planet, announced by Butler and Marcy in 1996. That planet is a gas giant slightly smaller than the mass of Jupiter and whips around the star in 14.6 days at a distance only one-tenth that from Earth to the Sun.

Using as a yardstick the 93-million mile Earth-Sun distance, called an astronomical unit or AU, the newfound planet orbits at 5.5 AU, comparable to Jupiter’s distance from our Sun of 5.2 AU (about 824 million kilometers or 512 million miles). Its slightly elongated orbit takes it around the star in about 13 years, comparable to Jupiter’s orbital period of 11.86 years. It is 3.5 to 5 times the mass of Jupiter.

“We haven’t yet found an exact solar system analog, which would have a circular orbit and a mass closer to that of Jupiter. But this shows we are getting close, we are at the point of finding planets at distances greater than 4 AU from the host star,” said Butler. “I think we will be finding more of them among the 1,200 stars we are now monitoring.”

The team shared its data with Dr. Greg Laughlin, assistant professor of astronomy and astrophysics at the University of California, Santa Cruz. His dynamical calculations show that an Earth-sized planet could survive in a stable orbit between the two gas giants. For the foreseeable future, existence of any such planet around 55 Cancri will remain speculative.

“The existence of analogs to our solar system adds urgency to missions capable of detecting Earth-sized planets – first the Space Interferometry Mission and then the Terrestrial Planet Finder,” said Dr. Charles Beichman, NASA’s Origins Program chief scientist at the agency’s Jet Propulsion Laboratory, Pasadena, Calif.

“This planetary system will be the best candidate for direct pictures when the Terrestrial Planet Finder is launched later this decade,” said UC Berkeley astronomer Dr. Debra A. Fischer.

Marcy, Butler, Fischer and their team also announced a total of 13 new planets today, including the smallest ever detected: a planet circling the star HD49674 in the constellation Auriga at a distance of .05 AU, one-twentieth the distance from Earth to the Sun. Its mass is about 15 percent that of Jupiter and 40 times that of Earth. This brings the number of known planets outside our solar system to more than 90.

Discovery of a second planet orbiting 55 Cancri culminates 15 years of observations with the 3-meter (118-inch) telescope at Lick Observatory, owned and operated by the University of California. The team also includes Dr. Steve Vogt, University of California, Santa Cruz; Dr. Greg Henry, Tennessee State University, Nashville; and Dr. Dimitri Pourbaix, the Institut d’Astronomie et d’Astrophysique, Universit? Libre de Bruxelles.

The star 55 Cancri is 41 light years from Earth and is about 5-billion years old. Further data are needed to determine whether yet another planet is orbiting it, because the two known planets do not explain all the observed Doppler wobbling. One possible explanation is a Saturn-mass planet orbiting about .24 AU from the star.

Original Source: NASA/JPL News Release

One of the most exciting fields of research in astronomy is the search for extrasolar planets, and eventually the search for other Earth-like planets. So far more than 100 planets have been discovered, but none are remotely similar to our home. At a recent meeting of the Royal Astronomical Society, astronomers proposed criteria for searching for Earth-like planets, and even a few candidates. Unfortunately, the technology needed is still 15 years away.

Image credit: NASA

Locating the faint evidence of planets circling distant stars used to require high performance optics, like those on the Hubble Space Telescope, but two scientists are putting together a system for NASA that should do the trick with off-the-shelf components for less than $100,000. The system will watch a 5-degree square of sky continuously (about 100x the area of the full moon in the sky), searching for stars which “wink” regularly when a planet obscures it. (source: NASA/JPL)

It could fit on your desk, and it’s made mostly from parts bought at a camera shop, but two scientists believe their new instrument will help them find a slew of large planets orbiting stars in our Milky Way galaxy.

“An amateur astronomer could do this, except maybe for the debugging of the software, which requires several people working 10 hours a day,” said Dr. David Charbonneau of the California Institute of Technology in Pasadena. “But it’s easy to understand what’s going on and cheap to build the equipment. That’s why everyone thinks it’s an ideal project, if it works.”

The assembly of the new instrument is a cooperative effort between Charbonneau and Dr. John Trauger of NASA’S Jet Propulsion Laboratory in Pasadena, which is managed by Caltech. “David’s approach promises to locate new planets orbiting distant stars. The instrument is simple and straightforward, taking advantage of spare parts and computer code we already have on hand at JPL, and we hope to have it up and running in a few months,” Trauger said.

Charbonneau and his colleagues will soon use their gizmo to begin a three-year survey for extra-solar planets at Palomar Observatory in San Diego County. The instrument is based on a standard telephoto lens for a 35-millimeter camera. It will sweep the skies, looking for “hot Jupiters,” or large, gaseous planets, as their fast orbits take them in front of other stars, into the line of sight between a star and Earth. Astronomers will watch for the “wink” from the star as an orbiting planet partially blocks its light.

Charbonneau, a recent import to the Caltech astronomy staff from the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., is a leading authority on the search for such “transiting planets.”

The new instrument uses a standard 300-millimeter Leica camera lens, with a charge-coupled device, or CCD. The CCD, which costs $22,000, will be mounted in a specially constructed camera housing to fit at the back of the lens. The entire device will be fitted onto an inexpensive equatorial mount, available at many stores carrying amateur astronomical equipment.

“Basically, the philosophy of this project is that, if we can buy the stuff we need off the shelf, we’ll buy it,” Charbonneau said. The project costs $100,000, a fraction of the cost of most large Earth and space-based telescopes.

The Palomar staff will provide a small dome for the instrument, and the system will be automated so it can be operated remotely. The new telescope will be linked with an existing weather system, which will monitor atmospheric conditions and determine whether the dome should be opened.

Charbonneau will be able to photograph a single square of sky about five degrees by five degrees. About 100 full moons or an entire constellation could fit in that field of view. With special software Charbonneau helped develop at Harvard-Smithsonian and the National Center for Atmospheric Research, he will compare many pictures of the same patch of sky to see if any of the thousands of stars in each field has “winked.”

If the software reveals a star has dimmed slightly, it could mean a planet passed in front of the star between exposures. Repeated measurements will allow Charbonneau to measure the orbital period and size of each planet. Further work with the 10-meter (33-foot) telescopes at Keck Observatory at Mauna Kea, Hawaii, will provide spectrographic data, and thus, will infer more detailed information about the planet.

Weather permitting, Charbonneau will gather up to 300 images a night. With 20 good nights per month, about 6,000 images would be gathered each month for computer analysis. The ideal time will be in the fall and winter, when the Milky Way is in view, and an extremely high number of stars can be squeezed into each photograph.

“It’s estimated that about one in three stars in our field of view will be like the Sun, and one percent of Sun-like stars have a hot Jupiter, or a gas giant that is so close to the star that its orbit is about four or five days,” Charbonneau said. “One-tenth of this 1-percent will be inclined in the right direction so that it will pass in front of the star, so maybe one in 3,000 stars will have a planet we can detect. Or if you want to be conservative, about one in 6,000.”

Original Source: NASA/JPL News Release