Microlensing Planet Finder is a proposed mission that would use the gravitational lensing effect to achieve extraordinary detection capabilities. As presented in The Microlensing Planet Finder: Completing the Census of Extrasolar Planets in the Milky Way (PDF warning), MPF could find planets down to 0.1 Earth mass, in locations as close as 0.7 AU to their parent stars. And unlike any other planet-finding technology, MPF would be able to find free-floating planetary bodies unassociated with any star. Gravitational microlensing is perhaps the most exotic planet-finding technique. A star or planet can act as a kind of lens, magnifying a more distant bright star behind it. It is the gravitational field of the foreground star that, as Einstein predicted, focuses the light of the distant star, just as a glass lens focuses light in a telescope. By analyzing the light produced by such an event, astronomers can find telltale anomalies that indicate the presence of planets around the...

A new project called PlanetQuest will soon offer a way to get involved personally with the hunt for extrasolar planets. The idea is to use the power of distributed computing, as the hugely influential SETI@home project has already done, letting people run data analysis software as a screensaver that operates whenever their computer is idle. PlanetQuest will be designed to hunt for planets by studying high-density star regions looking for occlusions -- in other words, for evidence that an extrasolar planet has moved between us and its star. Laurance Doyle, an astrophysicist at the SETI Institute, notes that while occlusions may be rare (after all, the stellar system must be lined up with ours so that planetary orbits cross our line of vision), the hunt will also yield dividends in terms of our knowledge of variable stars, as well as broader issues like stellar stability and evolution. But even as we accumulate new data, we still have the problem of managing what we have. Consider the...

Terrestrial Planet Finder will one day help us detect Earth-like worlds around other stars, no matter which technologies are deployed (Centauri Dreams remains an advocate of Webster Cash's New Worlds Imager). But once we start finding such worlds, what sort of data signatures should we look for to help us identify habitable surface environments? That question has been addressed in a new way by Penn State Erie assistant professor of physics and astronomy Darren M. Williams. Working with the University of Hawaii's Eric Gaidos, Williams outlined a theory that planets with abundant water should show strong scattering of starlight from ocean surfaces and discussed ways of examining such data. From a summary of the presentation: "Here we simulate the specular reflection of starlight off the surface of Earth-like planets to calculate visible light curves for different viewing geometries, obliquities, and land-sea fractions. The amplitude and polarization of the reflected signal is found to...

An extrasolar planet the size of Neptune is news, and when that planet is in an orbit roughly analagous to Neptune's in our own solar system, researchers take special note. After all, almost all the planets we've discovered around other stars are huge gas giants orbiting extremely close to their parent stars. And this extrasolar planet is more anomalous still. It was back in May that a team from the University of Rochester led by Drs. Dan Watson and William Forrest, using NASA's Spitzer Space Telescope, discovered a gap in the dust around the star CoKu Tau 4, one of five young stars they surveyed in the constellation Taurus. The central part of the dust disk around the star was missing, a 'hole' that can only be explained by the presence of a planet, and a young one, at that. In fact, this planet is assumed to be between 100,000 to half a million years old, a toddler by any astronomer's definition. CoKu Tau 4 is itself about one million years old; by contrast, Earth is approximately...

An interesting article in the 30 October New Scientist discusses a new theory on how the solar system began. A team from the Arizona State University led by astronomer Jeff Hester argued last May in Science that isotopic evidence and accumulated astronomical observations argue for a violent, energetic region near high-mass stars as the birthplace of our system. Image: The Eagle Nebula, as photographed by the Hubble Space Telescope. This famous photo, often known as "The Pillars of Creation," shows giant nebular clouds being evaporated by the ferocious energy of massive stars, exposing emerging solar systems, much like our own. Credit: NASA/HST/Jeff Hester and Paul Scowen Forming near a massive, unstable star would have had interesting implications for the appearance of habitable planets. From an ASU press release: The process leaves a Sun-like star and its surrounding disk sitting in the interior of a low density cavity with a massive star close at hand. Massive stars die young,...

Astronomers from Japan's Ibaraki University, the Japan Aerospace Exploration Agency, the University of Tokyo, and the National Astronomical Observatory of Japan have analyzed the dust disk surrounding the star Beta Pictoris, with intriguing results. Using an instrument called the Cooled Mid-Infrared Camera and Spectrometer (COMICS) and the Subaru telescope, the team found that ring-like distributions of planetesimals (something like the asteroid belt in our own Solar System) occur at three locations, measured as 6, 16 and 30 AU from the star. An unseen planet some 12 AU from the star may be what is keeping these belts intact. The disk around Beta Pictoris, a young star whose disk is more or less edge-on to our solar system, has been studied for some twenty years. Working in the infrared, Yoshiko K. Okamoto of Ibaraki University in Japan and his colleagues have provided new details of its structure. Image: Depiction of a possible planet (upper left) flanked by bands of dust within the...

A new sky survey may reveal further evidence of massive 'super Jupiters' orbiting distant stars. The National Science Foundation's Very Large Array (VLA) is being used to conduct the survey at 74 MHz, a frequency far lower than those used for conventional radio astronomy. Normally, Earth's ionosphere makes low-frequency radio imaging difficult, but the survey has employed a set of techniques that promise to reveal new categories of deep-sky objects. "We expect to find very distant radio galaxies -- galaxies spewing jets of material at nearly light speed and powered by supermassive black holes," said Joseph Lazio of the Naval Research Laboratory in Washington, DC. "By determining just how distant these radio galaxies are, we will learn how early the black holes formed in the history of the Universe," he added. As for those 'super Jupiters,' they may show up through bursts of radio emission at the frequencies this survey is studying. Other possible catches include previously...

If planets form the way we used to think -- in a relatively smooth condensation out of material surrounding young stars -- then the dust discs from which they form should gradually fade from view. Planetary formation, in other words, should scour a solar system, leaving it relatively free of dust; other than their planets, older stars would show little signs of the material from which their systems were made. But NASA's Spitzer Space Telescope, working in the infrared, is telling a different tale. Studying the dusty discs around 266 nearby stars -- all similar in size but varying in age -- George Rieke of the University of Arizona, Tucson and colleagues have found 71 discs, presumably containing planets. And there goes the old theory, because within the first two hundred million years of a star's life, there is no necessary correlation between the density of the disc and the star's age. Image: The graph above shows the Spitzer findings. Along the vertical axis is the brightness (or...

Planetary systems dominated by huge 'hot Jupiters' -- the kind of systems we've found so far -- are unlikely to contain Earth-like worlds. Massive gas giants close to their star would probably disrupt stable planetary orbits further out, in the habitable zone. But systems with large planets in the 5 AU range, where our Solar System's Jupiter resides, may well have small, rocky inner worlds. And Greg Laughlin, an assistant professor of astronomy and astrophysics at UC Santa Cruz, thinks we'll soon be discovering plenty of systems like these. Laughlin is interested in what he calls 'metallicity,' which he believes is the determining factor in whether or not a system will have gas giants. In fact, the vast majority of planets detected around other stars, at least so far, have circled stars that are metal-rich. The planetary cores have accreted from hydrogen and helium, to be sure, but also from heavier elements that allow the cores to form fairly quickly, within a period of a few...

Is Proxima Centauri really the closest star? Possibly not, a fact that was driven home just last year with the discovery of the red dwarf SO25300.5+165258 (a catchier name would have helped). At 7.8 light years, this tiny neighbor is the third closest to the Sun, but M-class stars are cool and dim, making them hard to detect. Even harder to find are the cool, failed stars known as brown dwarfs. A new NASA mission called the Wide-field Infrared Survey Explorer will scan the sky in infrared looking for such objects, its detectors half a million times more sensitive than previous survey missions. "Approximately two-thirds of nearby stars are too cool to be detected with visible light," said Principal Investigator Dr. Edward Wright of the University of California, Los Angeles, who proposed the new mission to NASA. "The Wide-field Infrared Survey Explorer will see most of them." Another bonus: WISE should be able to spot planet-formation in the making by depicting the dust discs around...

And it's not a brown dwarf, either. That's the verdict of astronomers using the Keck II and Gemini North telescopes (supported by observations at Kitt Peak National Observatory), who have been studying a binary system with a difference. One of the stars involved has lost huge amounts of mass, enough that it no longer qualifies as a star. We do not, in fact, know what to call it. "Like the classic line about the aggrieved partner in a romantic relationship, the smaller donor star gave, and gave, and gave some more until it had nothing left to give," says Steve B. Howell, an astronomer with Wisconsin-Indiana-Yale-NOAO (WIYN) telescope and the National Optical Astronomy Observatory, Tucson, AZ. "Now the donor star has reached a dead end - it is far too massive to be considered a super-planet, its composition does not match known brown dwarfs, and it is far too low in mass to be a star. There's no true category for an object in such limbo." Image: EF Eridanus 500 Million Years Ago. Onset...

To the left is Epsilon Eridani. At 10.5 light years, it's a relatively nearby star, and we know it has planets. Can we find a way to view those planets, a way that will show us not just pinpoints of light but surface details? Missions like Terrestrial Planet Finder promise great things in this regard, but the technology that will fly on them is still being determined. To my mind, the most promising technique for viewing Earth-like planets around other stars is Webster Cash's New Worlds Imager. Discussed previously in these pages, New Worlds Imager can be described as an enormous pin-hole camera in space. An opaque starshade the size of a football field would contain a single aperture, a hole some 30 feet in diameter. Tens of thousands of miles away, a detector spacecraft would study the resultant light, with the planetary system of the target star spread out widely for study. Cash, a professor in the University of Colorado at Boulder's astrophysical and planetary sciences department,...

The Hubble Space Telescope cost far more to build and launch than the twin telescopes of Hawaii's W.M. Keck Observatory, but Keck gathers twenty times the light and offers four to five times better resolution. Assuming, of course, that we can find a way to cancel out the effects of atmospheric blurring on its images. That's where the science of adaptive optics comes in. By using a bright reference beacon nearby, an observatory like Keck can analyze atmospheric effects even as its observations are being made. That this technique can be used in the hunt for extrasolar planets is clear. The infrared image to the right (credit: Michael Liu, IFA-Hawaii/W. M. Keck Observatory) shows a dust disk surrounding the star AU Microscopii. The image is 100 AU wide, roughly the size of our Solar System; Keck's images are the sharpest ever obtained of a circumstellar disk, with an angular resolution of 1/25 of an arcsecond, about 1/500,000 the diameter of the full moon. But adaptive optics has a...

At 12 light years away, Tau Ceti is the nearest Sun-like star, and has long been of high biological interest among possible interstellar probe targets. But a British team using the James Clerk Maxwell Telescope in Hawaii (and aided by the world's most sensitive sub-millimeter camera, called SCUBA) has found a disk of cold dust around the star that bodes ill for stability among any planets that may be orbiting there. Says Jane Greaves, lead scientist on the study: "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." Image: Bombardment of a hypothetical planet around Tau Ceti: bad news for life? Credit: David Hardy. Frank...

A network of robotic telescopes called RoboNet-1.0 will soon join the hunt for Earth-like planets around other stars. RoboNet will look for the effects of gravitational micro-lensing, where distant light is bent around an unseen foreground object. A star whose light is undergoing such lensing would, if it had a planet, show a blip in its detected light which RoboNet should be able to follow-up. "The network," says a press release from the Particle Physics and Astronomy Research Council, which funded the project, "stands the best chance of any existing facility of actually finding another Earth due to the large size of the telescopes, their excellent sites and sensitive instrumentation." The globally distributed RoboNet offers astronomers the chance to search anywhere in the sky without regard to local light conditions by passing observations from one telescope to the next. The Liverpool Telescope (Canary Islands), Faulkes North (Maui) and Faulkes South (New South Wales) telescopes...

An interesting piece in Nature's online edition describes the race to see who has actually imaged a planet around another star. As discussed in Centauri Dreams earlier, a team in Chile at the European Southern Observatory has used infrared to reveal what may be a planet circling the star 2M1207, a brown dwarf, but there is still no conclusive evidence that the planetary candidate actually orbits the star. But another team, from Pennsylvania State University and using Hubble images, also believes it has found such an object, though they won't yet name the star or discuss its location for fear of being scooped. If the PSU object is indeed a planet, it is between five and ten times the mass of Jupiter and roughly 100 light years from Earth, in an orbit similar to that of Neptune around our Sun. Infrared is useful in both sets of observations because the contrast between a star and its planet is a thousand times less at these wavelengths; in visual light, the glow of a planet is...

Getting an image of a planet around another star has been an elusive goal for astronomers, and most candidates have proven to be background stars, or sometimes faint stellar members of what turned out to be binary systems. Now a new candidate has emerged. An international team of astronmers, using observations from the the ESO Paranal Observatory in northern Chile, has picked up what may be a gas giant planet orbiting the brown dwarf 2M1207 at approximately twice the distance between the Sun and Neptune. The object is located in the far southern sky in the direction of the constellation Hydra, and is approximately 230 light years away. The photograph at left is based on three near-infrared exposures (in the H, K and L' wavebands) with the NACO adaptive-optics facility at the 8.2-m VLT Yepun telescope at the ESO Paranal Observatory. More observations are needed, but what's interesting about this 'Giant Planet Candidate Companion,' as it is being called, is that its spectrum shows...

Planet-hunter Geoff Marcy is quoted in this story in The Oklahoman on the prevalence of planetary systems around other stars. His estimate: 20 billion systems in the Milky Way alone, and that's the lower end of the range. In fact, fully half of the galaxy's 200 billion stars may be capable of supporting planets. From the article: Marcy said astronomers may spot a rocky Earth-like planet as soon as five years from now, but will have to hypothesize about its life-sustaining possibilities until a robotic probe can be sent to the extrasolar planetary system. Exactly so, at least for close-up studies, but missions like Terrestrial Planet Finder may be able to analyze planetary atmospheres closely enough to find the methane and ozone signature of life. We'll need those missions (along with the earlier Kepler and Space Interferometry Mission projects) to help us choose our first targets for interstellar probes. Given the magnitude of the enterprise, we'll want our destination star to be...