With Hubble's Space Telescope Imaging Spectrograph now out of commission, the study of exoplanetary atmospheres becomes a bit more problematic. But Seth Redfield (University of Texas at Austin) has now used a ground-based instrument to detect the atmosphere of a planet orbiting the star HD189733, some 63 light years away in the constellation Vulpecula. Discovered in 2004, this transiting world is about twenty percent more massive than Jupiter, orbiting its parent ten times closer than Mercury orbits our Sun. Working from the ground is tricky but the odds go up when you observe more than a single transit. Redfield worked with eleven transits observed over the course of a year, using the Hobby-Eberly Telescope (HET) at McDonald Observatory in Austin. Studying the chemical composition of a distant atmosphere involves taking a spectrum during a transit and another when no transit is occurring. Working with the difference and comparing results over multiple transits helps you put together...

Since we've just been looking at young stars -- protostars, at that -- the news from Ann Arbor seems timely. Astronomers at the University of Michigan are announcing systems around UX Tau A and Lk Ca 15, young stars each, located about 450 light years away in the Taurus star formation region. What they're actually observing at infrared wavelengths are gaps in the protoplanetary disks around these stars, the assumed result of planets sweeping the area clear of debris. Unlike the infant star-in-the-making we looked at yesterday, UX Tau A and Lk Ca 15 are old enough -- about a million years each -- for planetary formation. Both are still pre-main sequence, deriving their energy from gravitational contraction instead of hydrogen-to-helium burning. To reach any conclusion about what's happening around them, the Michigan team has to rule out photoevaporation, which is what happens when the dust and gas of a protoplanetary cloud heats up, evaporates and begins to dissipate. Catherine...

A flattened envelope of gas and dust surrounding the young protostar L1157 gives us some idea of what our Solar System may have looked like as it began to form. The object is only a few thousand years old, the central star hidden, with its envelope detectable in silhouette as a black bar. The view from the Spitzer Space Telescope (below) shows how infrared can look within the dust to see structure. While the telescope cannot penetrate the envelope (itself hard to see in this image), enormous jets whose hottest points appear in white are clearly defined. These jets are interesting. They're being emitted from the protostar's two magnetic poles, and are approximately one and one half light years from end to end. The envelope of material is too thick for Spitzer to penetrate and appears in black, its thickest part visible as a black line crossing the jets. The envelope is roughly centered on the polar jets and perpendicular to them, showing up more clearly in the grayscale image below,...

One thing we'd like to know about exoplanets is where they are likely to be found. We've located more than 250 of them, but most are confined within about 650 light years. That's very much in the local neighborhood by galactic standards -- our methods have led us to nearby, bright stars. We do have a small number of planets detected through microlensing, some as far away as 6000 parsecs (about 19,500 light years), but our radial velocity detections, which form the great bulk of the current catalog, tend to be confined to relatively close higher mass stars. Other similarities? The exoplanet host stars we know about are generally metal rich. And because they're nearby, they're located in the galactic disk. This leaves us with some key questions, among them whether planets are equally abundant elsewhere in the galaxy. Other issues: Do planets occur with the same frequency around lower mass stars? Does the presence of heavy elements favor particular parts of the galaxy for planet...

Having just written about dust formation around HD 23514, a Sun-like star in the Pleiades, I was drawn to this quote by Nadya Gorlova (University of Florida, Gainesville), whose recent work suggests that if moons like our own were common, we'd be seeing more dust than we do around other stars. "When a moon forms from a violent collision, dust should be blasted everywhere," says Gorlova. "If there were lots of moons forming, we would have seen dust around lots of stars -- but we didn't." By contrast, the UCLA study on the Pleiades sees major collisions as common in young solar systems, though to be sure it didn't focus its conclusions on the 30 million year age range, as the Florida study did. Gorlova's team used data from the Spitzer Space Telescope and operated under current assumptions about lunar formation, in which an impactor the size of Mars is thought to have struck the Earth, creating a vast debris field that fell into Earth orbit and eventually became the Moon. The theory...

Where will we be in the exoplanet hunt by the year 2020? A few of my own guesses would take this form: We should, within even the next year or two, have detected a terrestrial world in a truly unambiguous position within the habitable zone of a star. That star will doubtless be a red dwarf, like Gliese 581, but we can hope for a result that doesn't lend itself to so many conflicting interpretations. The detection method will surely be planetary transit, but even by 2020 we may not know if life exists there. It's also easy to surmise that by 2020 we'll have a terrestrial-class world located within a stellar system not completely dissimilar to our own; i.e., one involving a star much like the Sun, orbited by a rocky world in the habitable zone. We can hope that by 2020 the tools will have been put in place to do spectroscopic observations of the planetary atmospheres involved in small rocky worlds, though so much depends on budgets and the needed tuning up of exquisitely sensitive...

I've always enjoyed Lynette Cook's work. As you can see in the image below, this space artist captures the drama of celestial events by drawing on recent findings. Like Chesley Bonestell, Cook can take you to an exotic place and leave you staring, but her focus is tighter, homing in on exoplanets as filtered through ongoing work at observatories worldwide. The wonders she'll have to work with as we find more and more such worlds can only be imagined. The dazzling collision below is her take on what may be happening as rocky planets form around HD 23514. The star's designation doesn't jump out but its location does, the oft-studied Pleiades star cluster. Joseph Rhee (UCLA) and collaborators have been working infrared wavelengths using the Gemini North Telescope (Mauna Kea) and space-based infrared instruments, measuring the hot dust around this 100-million year old star. HD 23514 is Sun-like enough to add to the intrigue of this exercise, and it's orbited by hundreds of thousands of...