Another discovery thanks to transits. The atmosphere of the exoplanet HD 209458b has been found to contain water vapor. And while that's not unexpected, the effectiveness of the transit method in making the find underlines how significant are the occasions when a planet passes in front of its star as seen from Earth. Studying the infrared spectrum, as Travis Barman did at Lowell Observatory, shows the apparent signature of water vapor absorption when compared to the visible spectrum. But don't expect an ocean world here. The planet involved orbits its star every three and a half days; HD 209458b is, in fact, a 'hot Jupiter,' its upper atmosphere heated to temperatures as high as 10,000 degrees K. The planet is doubtless losing thousands of tons of material every second as it vents gases into the incendiary environment so near its primary. Nonetheless, finding water vapor does provide confirmation of theories that suggest almost all extrasolar planets have water vapor in their...

Years ago I wrote a story called 'Rembrandt's Eye,' using as background a planet whose foliage was predominantly red. The story, which ran in a short-lived semi-pro magazine called Just Pulp, came back to mind when the news from Caltech arrived. Researchers at the Virtual Planetary Laboratory there now believe that Earth-type worlds may have foliage that is largely yellow, orange or, as in the case of my planet, red. The green of Earth's plant life is anything but a universal standard. This interesting conclusion emerges from computer models designed to provide pointers for the future search for plant life on exoplanets. After all, astronomers will need to know what they might see in the spectra we'll one day be able to harvest from space-borne observatories. Ponder everything that's involved, from the color of the main sequence primary star to the aquatic habitats of aqueous plants. The search involves the way photosynthesis might occur under varying conditions, with the filtering...

Since we've recently been discussing astrometry, the discipline that measures star distances and movements, now would be a good time to look at two significant projects that go beyond optical methods to use radio astrometry in planet hunting. The Radio Interferometric Planet Search (RIPL) will draw on the Very Long Baseline Array, ten dish antennae spanning more than 5000 miles, and the 100-meter Green Bank telescope in West Virginia. The target: 29 active low-mass stars to be examined in a three-year planet hunt. The targets are significant because they're a kind of star that's currently out of reach for radial velocity techniques. All are M dwarfs that are active, meaning they display 'starspots' (analogous to sunspots), flares or other activity in their chromospheres. The more active a faint star like this, the more likely that radial velocity measurements will be distorted with a 'jitter' that disturbs the precision of the measurement. RIPL ought to be able to sort out the...

A Neptune-class planet has been discovered around the nearby red dwarf GJ 674, and it's an intriguing one. Using the HARPS spectrograph on the European Southern Observatory's 3.6 meter telescope at La Silla (Chile), the discovery team determined that the new planet was 0.039 AU from its parent star, yielding a temperature of some 450 degrees K. With a minimum mass estimate of about 11 times the mass of Earth, it completes an orbit every 4.69 days. Whether GJ 674 b is largely gaseous or rocky is unknown, although further observations of its orbital eccentricity may yield clues. We're not down to Earth-mass planets yet, but this is an interesting find. This is the second-closest known planetary system (after Epsilon Eridani). GJ 674 is less than 15 light years away and it's one of the brightest M dwarfs in our field of view. That makes the transit situation interesting, as Greg Laughlin noted in this systemic post: At first glance, such an effort might appear to be hampered by the fact...

The number of stars with possible planets keeps going up. The astronomy books I read as a kid operated under the assumption that we needed to look at Sun-like stars to find planets, and that meant single rather than double or triple systems. The tantalizingly close Alpha Centauri stars were all but ruled out because of their assumed disruptive effects on planetary orbits. No, find a nice G-class star all by itself and there you might have a solar system something like our own and, who knows, a second Earth. Today we're fitting binary stars into the planetary picture with ease. Astronomers see little reason to rule them out. Consider what David Trilling (University of Arizona) has to say about the matter in an upcoming paper: "There appears to be no bias against having planetary system formation in binary systems. There could be countless planets out there with two or more suns." Just imagine the possible sunsets. Image: Our solitary sunsets here on Earth might not be all that common...

Sometimes I imagine an ancient place where a dim sun hangs unmoving at zenith, and a race of philosophers and poets works out life's verities under an unchanging sky. Could a place like this, on a terrestrial world orbiting an M-class red dwarf, really exist? A new paper by Jack Lissauer (NASA Ames) casts doubt on the idea. Lissauer argues that planets inside an M dwarf's habitable zone are probably lacking in water and other volatiles, and are thus unable to produce life as we know it. The question is important because M dwarfs make up as much as 75 percent of the stars in our part of the galaxy. If we include them as candidates for life, we add a hundred billion or more potential habitats in the Milky Way alone. We've known for some time that although the proximity of such a terrestrial M dwarf planet to its star would cause it to be tidally locked -- one side in constant light, the other in darkness -- habitable regions might still occur on the dayside given a dense enough...

If you want to put the hunt for planets around other stars in perspective, consider this. For almost all of our species' time on this planet, we have looked at the planets in our own Solar System as unresolved points of light that seemed to move upon a celestial sphere. The brief time that we have been able to see more is measured since the invention of the telescope, a tiny window compared to the millennia that went before. We are now working hard to see extrasolar planets as unresolved, moving points of light. In doing so, we're looking at ways to image these planets that would yield the greatest scientific return. Recall former NASA administrator Dan Goldin's wish to actually see the surfaces of distant exoplanets -- he talked to putting such images on the walls of our schools. One day, starshade technologies coupled with space-borne telescopes may make that possible. For now, though, there is the real potential of something closer: identifying exoplanets with oceans. The beauty...

Passed along by Greg Laughlin (UC-Santa Cruz), this call for papers: The ExoPlanet Task Force (ExoPTF), an Astronomy and Astrophysics Advisory Committee (AAAC) subcommittee formed at the request of NSF and NASA, announces a call for white papers to inform their assessment of techniques and approaches for extra-solar planet detection and characterization, using both space- and ground-based facilities. The ExoPTF has been asked to recommend a 15-year strategy to detect and characterize exoplanets and planetary systems, and their formation and evolution, including specifically the identification of nearby candidate Earth-like planets and study of their habitability. White papers may describe studies, measurements with existing facilities, new instruments, new facilities or missions, considerations from theoretical modeling, or other recommendations or information that can support the Task Force in its work as laid out in the charge. Submission instructions and other information can be...

Our first 'sniffs of air from an alien world,' as David Charbonneau calls them, have brought with them a bit of a surprise. Charbonneau (Harvard-Smithsonian Center for Astrophysics) is one of a team of astronomers who have measured the spectrum from the atmosphere of a transiting exoplanet. What the team expected to find was evidence of common molecules like water, methane and carbon dioxide. Yet the scientists found none of these. The spectrum they acquired was flat. HD 189733b is the world in question, orbiting a star about sixty light years from Earth in the constellation Vulpecula. The transiting planet is a 'hot Jupiter,' slightly larger and more massive than Jupiter itself, orbiting once every two days about three million miles from its star. This remarkable work consisted of studying the so-called 'secondary eclipse' that occurs when the planet disappears behind the star, thus extracting the planetary data from the much brighter stellar signature. Here's the method, as...

At just over 150 light years from Earth in the constellation Taurus, the Hyades is the nearest open star cluster to Earth. We've been scouting the terrain in clusters recently, looking at globular clusters like 47 Tucanae and open clusters like M37, both of which are under intense scrutiny. But the first exoplanet to be identified definitively in either kind of cluster seems to be Epsilon Tauri b in the Hyades [but see below re a 2.5 Jupiter mass planet in the system comprising pulsar PSR B1620?26 and its white dwarf companion -- that one is in the globular cluster M4]. It's an interesting world, a gas giant that's a little less than 2 AU out with an orbital period of 1.63 years. This is the first planet discovered around a red giant, its star the most massive of all planet hosts known. [My mistake: several planets evidently orbit red giants -- see comments below, and check here for another example]. That leads to intriguing speculation: Should we expect planets around other red...

Our Solar System in the distant future may look something like the Helix nebula today. That's because in about five billion years, the Sun will have become a white dwarf, its inner planets swallowed up by its earlier expansion, its outer planets, asteroids and comets surviving in distant orbits and colliding with each other to form a ring of dusty debris. The Sun will undergo, in other words, a kind of rejuvenation, experiencing what scientists call 'late bombardment' in a system that has become dynamically young again. Such a disk has now been found in the Helix nebula, some 700 light years away in Aquarius. It took the infrared tools of the Spitzer Space Telescope to sort out the glow of the dusty disk that circles the remnant white dwarf between 35 and 150 AU out. The assumption is that the disk is the result of smashups in the outer system, presumably involving objects like those in our Kuiper Belt or comets from an Oort-like cloud. Image: Spitzer's infrared view of the Helix...

It's good to see that Greg Laughlin's systemic project is getting some public attention. This article in the Santa Cruz Sentinel goes through the basics, explaining how amateurs can use the systemic console to identify possible planets around other stars. "We want to demonstrate that it's not just public outreach, it's a way of carrying out research," Laughlin adds, and that fusion is what the Net is bringing to exoplanetary studies.

Actually seeing something is so much more rewarding than just inferring its presence. But in the case of exoplanets, looking at the actual light bouncing off a distant planet does more than just satisfying our curiosity. Starshade concepts and other methods of terrestrial planet detection point to an ultimate payoff: We want to analyze the light of a distant world to learn what elements are found in its atmosphere. These become clues to conditions there, and even markers of possible life. Centauri Dreams readers know I'm a great admirer of the starshade concept, not only as developed by Webster Cash in his New Worlds Imager designs but also as widely studied for other possible missions (for more on starshades, see the UMBRAS site). Starshades are all about direct observation -- images, spectroscopy, photometry -- rather than methods like radial velocity studies that find planets through the motions of their parent stars. And I like starshade technologies because they seem to offer...

Want to build a starshade to spot Earth-like worlds around other stars? Start with a Hubble-like telescope a few million miles from Earth. Add a 30-meter wide disk with petal-like extensions, separated by 10,000 miles from the telescope. Watch what happens next. Using lasers, the two parts would line up, with the star shade just blocking out the light from a nearby star from the center of the telescope's view. Calculated mathematically to throw away the light from the star but keep the light from any planets it held (this is the "occulting" part of the occulted), the device would be able to detect planets smaller than Earth orbiting stars within 35 light years of Earth, Cash and his colleagues calculate. The key is the petal shape of the shade, which scatters starlight from the telescope's view. From an overview of planet-finder technologies by Dan Vergano in USA Today. Webster Cash, whose name is frequently found in the Centauri Dreams archives, is a major part of the...

Barrie Jones (The Open University, UK) will have an interesting job in ESA's planned Darwin mission. Darwin's goal is to find Earth-like worlds around other stars. Jones will prioritize planetary systems so the mission's telescopes -- three instruments mounted on separate spacecraft -- can concentrate on those most likely to have Earth-like planets in their habitable zones. He's already done computer modeling on many currently known planets, finding that half of them occur in systems where a stable orbit for a terrestrial world exists in the habitable zone. But much depends on how you deal with planetary migration, says Jones, discussing his computer modeling in a recent interview. A gas giant moving through the inner system to become a 'hot Jupiter' may or may not preclude the presence of an Earth-like planet -- recent work gives us hope that it will not, but the issue is still undecided. Says Jones: If Earths can form after the giants migrate toward the star and become "Hot...

If I were a betting man, I would put some money on this proposition: The first detection of a potentially habitable planet will be made before the end of this decade, and the planet will be found around an M-class red dwarf. The method will doubtless be photometry, picking up the slight drop in light caused by such a planet transiting its star. A planet the size of our Earth will block about one percent of the stellar flux, as a recent paper points out, and a one percent photometric dip is quite detectible. Image: An animation of a stellar transit around HD 209458. Credit: Transits of Extrasolar Planets Network. Although TEP concluded its work in 2001, you can still read about it online. So the key is to find the right M-dwarf, with its planetary system lined up so that the hypothetical terrestrial world passes between its star and us. That's no small challenge, but Paul Shankland (U.S. Naval Observatory), who is lead author on the paper mentioned above, is working with colleagues...

A globular cluster is a glorious thing. Consider Omega Centauri, a vast city of stars about 15,000 light years from Earth. Clusters like this one are composed of millions of Population II stars, meaning they're among the oldest observed stars and may date back as far as twelve billion years. A result of their early formation is that they remain deficient in metals (in astronomical terms, the elements above hydrogen and helium), making them ideal laboratories for a particular branch of exoplanet studies. Image: This image of Omega Centauri, the brightest and largest globular cluster in the sky, was obtained with the Danish 1.5 m telescope at the ESO La Silla observatory. It shows the central part only; the cluster is actually much larger than the field reproduced here. Credit: European Southern Observatory. A growing assumption about the massive 'hot Jupiters' we've found in our early planet hunting is that their existence depends upon a relatively high metallicity in their host star....