More than 75 exoplanets in thirty different planetary systems is an impressive score, and that's what HARPS has compiled since its installation in 2003. The High Accuracy Radial Velocity Planet Searcher is the spectrograph for the European Southern Observatory's 3.6-meter telescope at La Silla (Chile). Built by a consortium led by Michel Mayor (Geneva Observatory), HARPS does its work by measuring the minute changes in a star's radial velocity that flag the presence of an unseen companion. Most of the roughly four hundred exoplanets discovered to date have been found through radial velocity methods. The figure of 400 includes the latest results from HARPS, which is back in the news with the announcement of 32 new exoplanets, found as part of a five year program using observing time given to the HARPS consortium in return for building the instrument. One of the new worlds is Gliese 667 Cb [see andy's note below], a six Earth-mass planet in a triple star system. The planets announced...

I'm a great believer in getting the most out of older systems. The computer I do most of my work on is now eight years old. I have access to newer equipment, but I built this box with an eye toward longevity and I'm still happy with it. With the pace of technological change, it's definitely gotten creaky despite additional memory, a new video card and various other upgrades. That means that Windows gets slower and slower on it, but then, I rarely use Windows, being an open source guy to the bone. Linux has always been my choice. Now the nice thing about Linux is that, no matter which version I run (and I've run quite a few by now), I can get snappy performance out of this old box. The astronomical analogy isn't too far to seek -- these days we're talking about building larger and larger Earth-based telescopes, and in fact have just inaugurated the Gran Telescopio Canarias on a 7,874-foot mountaintop in the Canary Islands, an instrument that has the largest segmented mirror -- 10.4...

Protoplanetary disks may not raise the same level of excitement that the discovery of new planets does, but to me, the idea of watching a planetary system form is awe-inspiring. I can't help but wonder whether, going back about five billion years or so, astronomers around some distant star weren't watching the early signs of planetary formation around our own star. Disks in their various stages give us a sense of the continuity of solar system development. Continuity, that is, in the sense that stars seem to form planets as a matter of course. But we're seeing yet more evidence this week that protoplanetary disks can vary markedly from star to star. Now comes news of the dust cloud around 51 Ophiuchi, which turns out to be not one but two distinct disks, an inner one with grains 10 micrometers and larger in diameter (based on infrared observations), and an outer one made up of primarily 0.1 micrometer grains. Image: This graphic compares the inner and outer disk of the 51 Ophiuchi...

?I love to run into genuine enthusiasm when someone is doing cutting-edge science, and Didier Queloz (Observatoire de Geneve) has not let me down. Here the astronomer is discussing CoRoT-7b, which new studies have determined is a rocky world: "This is science at its thrilling and amazing best. We did everything we could to learn what the object discovered by the CoRoT satellite looks like and we found a unique system." Amazing indeed. We knew from CoRoT's transit measurements that the radius of this planet was about twice that of Earth. Queloz and team went to work with the HARPS spectroscope (High Accuracy Radial velocity Planet Searcher) at ESO's La Silla site in Chile, gathering fully seventy hours of observations on the system. What emerged was the best mass measurement for an exoplanet yet. Combining that revealed mass -- five times that of the Earth -- with CoRoT's radius readings, we can deduce that CoRoT-7b is about as dense as Earth, and thus almost certainly a rocky world....

The exoplanet hunt has entered a significant new phase, one focused on transiting planets and the useful things we can learn about their physical properties and atmospheres through such events. Driven by CoRoT and Kepler, we're now in position to use those transits to spot smaller worlds than ever, down to terrestrial size, and naturally the focus is on Earth analogs located in the habitable zones of their stars. So think of it this way: We've gone from a broad-brush approach based largely on radial velocity methods to a more selective hunt, one that will take us to the realm of planets that can have liquid water on their surfaces and aren't so different from our own. Not that the continuing work on characterizing planetary systems is of any less importance, but we've found plenty of gas giants, and now we're trying to learn something about how common these smaller worlds may be. Putting an exclamation point on this focus is a conference called Pathways Towards Habitable Planets, to...

Any unexpected kink in the debris disk surrounding a young star is often attributed to a planet forming amongst the gas and dust. But that may not be the only explanation. In fact, new work by John Debes and team at NASA GSFC points to an alternative: The motion of the infant system through insterstellar gas. Thus we have yet another reminder that space is not truly empty, and that patches of gas can play their role in planet formation. Debes and colleagues have been looking at infant systems like that around the star HD 32297, some 340 light years from Earth in the constellation Orion. About 100 million years old, the star is surrounded by a dust disk that resembles what our Solar System probably looked like not long after the major planets formed. Noticing that the dust disk around the star was warped, the team was led to link the finding to the presence of nearby interstellar gas clouds. The idea of interstellar gas drag upon a stellar system moving through such a cloud seems a...

We often speak about planets migrating from the outer to the inner system of a star, something that helps us put 'hot Jupiters' in context. But what about migration within the galactic disk? It's an idea under continuing investigation. In the absence of direct observational evidence, we infer migration and assume that older stars often come from regions with significantly different metallicity than stars in their current environment. The presumed origin would be the inner disk, which Misha Haywood defines as that part of the galaxy inside the radius from galactic center to our Sun. Dave Moore sent me Haywood's latest paper a few months back and I've been slow in getting to it because I wanted to give its conclusions further thought. It's intriguing stuff. Haywood (Observatoire de Paris) takes note of the fact that we tend to find gas giants around stars that are rich in metals (here a pause to remind newcomers that by 'metals,' we mean elements higher than helium). And he wants to...

?by Larry Klaes Tau Zero journalist Larry Klaes here gives us a quick overview of the history and future of the Earth, so vital for understanding not only how life emerged here but how it may appear around other stars. It's good to keep this background in mind as Kepler and COROT go planet-hunting. Thus far we've had our share of surprises as we've explored other systems, and doubtless there will be many more as future instruments come online, both in space and on the ground. And as Larry reminds us, there is much we still have to learn about our own planet. Let's look at our celestial home’s place in time as well as space, namely the long and ancient history of its cosmic birth and development. This story includes a general history of the wide variety of living beings that dwell just about everywhere on this planet. Planet Formation and the Big Collision Earth’s geological history began about five billion years ago, roughly eight billion years after the Universe got its start in the...

A conference like the recent on in Aosta offers plenty of opportunity to listen in on fascinating conversations, one of which had to do with what would happen if we found a brown dwarf closer to the Earth than the Centauri stars. The general consensus was that such a find would be a powerful stimulus to the public imagination and would probably result in renewed interest in getting to and exploring such a place. A boon, in short, for all our interstellar efforts, an awakening to a new set of possibilities. But if there were a brown dwarf that close, wouldn't we have other signs of it? One figure I heard mentioned at Aosta was three light years. Here I have to do some checking, because I don't recall who dropped that figure or what paper he was referring to, but the upshot was that someone has argued that even a small brown dwarf closer to the Sun than three light years would leave an unmistakable signature in the orbits of our Solar System's planets. I'll see if I can track down the...

Why some planets are the size they are remains something of a mystery. I'm looking at the discovery paper for a planet called WASP-17b, which is said to be twice Jupiter's size but only half its mass. That raises questions about the mechanisms at work, for you can't explain the bloated nature of this world with the models of planetary evolution we're now working with without factoring in massive tidal effects. In one sense, WASP-17b is completely anomalous. In addition to its size, it orbits its star in retrograde fashion, opposite the direction of the star's spin. But in other important respects, the new planet joins the ranks of other bloated worlds like HD209458b (the first such world to be discovered), and a flock of other huge planets that includes TrES-4, WASP-12b, XO-3b and HAT-P-1b. TrES-4 shows a density about fifteen percent that of Jupiter, with a radius 1.78 times larger than Jupiter's. Image: Orbiting close to its parent star, WASP-17b may look something like this, a...

It doesn't take much observation to realize that the early Solar System was a violent place. Mercury seems stripped of its outer crust, doubtless the result of a massive impact, while Uranus was knocked to one side at some point in its history, aligning its spin axis with the plane of the ecliptic. Venus was hit so violently that it rotates clockwise as seen from above, opposite to the other planets. At least, a collision is one of several theories that may explain Venus' retrograde rotation, and it's more than plausible. 100 light years from Earth is a place that reminds us of the impact that produced Earth's own moon billions of years ago. HD 172555 is a young star in the southern constellation Pavo (the Peacock), its twelve-million year old system in its infancy. Spectral analysis from the Spitzer Space Telescope shows clear evidence of a collision much like that between the Earth and that early, Mars-sized object that once struck it. Image: This artist's concept shows a celestial...

Unlike the Cassini Saturn orbiter, which we looked at yesterday in the context of cryovolcanism on Titan, the Kepler spacecraft has but a single scientific instrument. It's a photometer based on a Schmidt telescope design with a 95 cm aperture and a field of view larger than 100 square degrees. Measuring brightness variations for over 100,000 stars, Kepler is the first mission that should be able to detect Earth-size planets in the habitable zones of their stars. That made yesterday's news conference an eagerly anticipated event, but we have to remember that it's going to be a while before we start talking about terrestrial planet detections. It takes multiple transits and much data analysis to make that possible, and a transiting world at roughly Earth-like distance from its star will demand several years of work. Kepler's baseline mission is three and a half years, more than enough to make such detections, and the good news is that the instrument works. Image: Magnified Kepler...

The hunt for exomoons -- satellites of planets around other stars -- gets more interesting all the time. This morning I received a note from David Kipping (University College London), who has been studying methods for finding such objects. Kipping and colleagues have a paper soon to be published by Monthly Notices of the Royal Astronomical Society that discusses how to detect habitable exomoons using Kepler-class instrumentation. And it turns out that finding such worlds is well within our present capabilities. A bit of background: Kipping's method is to analyze two useful sets of signals. Transit timing variations (TTV) are variations in the time it takes a planet to transit its star. Kipping and team acquire these data and then weave the TTV information together with what is called transit duration variation (TDV). The latter is detectable because as the planet and its moon orbit their common center of mass, velocity changes can be observed over time. Put TTV and TDV together and...

Imagine what space exploration would look like if the Sun were a member of a binary system. Suppose we had another star a few hundred AU away, one that had built its own planetary system. The second star, a thousand times brighter than any other star in our night sky, would be an object of obvious interest, its planets visible to our astronomers and reachable targets for early space technology. The question of life on a planet in that star's habitable zone would be relatively easy to resolve, and the imperative to study that world first-hand would surely drive space science. Now we learn that a binary system some 1300 light years from Earth may be evolving in a similar direction. Located in the Orion Nebula, a region rich in star-birth, the stars are about a third the mass of the Sun, considerably cooler and redder in color. One is known to be an M2 dwarf, while the other's spectral type hasn't been precisely identified because of obscuration by the disk. The stars are 400 AU apart,...

Gravitational microlensing has been actively employed in the search for MACHOs (Massive Astrophysical Compact Halo Objects) in the galactic halo, although with ambiguous results. The idea here is to find large, dark objects by detecting the microlensing effects they produce on stars behind them. While these dark matter studies have looked toward the Large Magellanic Cloud, we are using the same technique elsewhere in the planet hunt, finding that exoplanets can magnify the light of stars behind them in the galactic bulge, producing a clear detection. Remember, for this kind of work, you want a dense background field of stars because the alignment needed for microlensing is obviously rare. The Magellanics are ideal, as is the galactic bulge, and so, for that matter, is M31, the Andromeda galaxy. And if our early exoplanet work, relying on radial velocity and transit methods, has naturally produced large planets in the Jupiter class, microlensing can be quite effective at smaller...

Planets around binary stars continue to be a major interest here, given our fascination with nearby Alpha Centauri. Thus the recent radio interferometry images captured by the Submillimeter Array radio telescope system (Mauna Kea) come right to the top of the queue. We're looking at a young binary system called V4046 Sagittarii, providing a glimpse of planetary system formation occurring around two stars of roughly the Sun's mass. This system is approximately 240 light years from our own. Image: Submillimeter Array image of the rotating, gaseous disk surrounding the young twin-star system V4046 Sagittarii (located at the white dot in the image). Note the size of the V4046 Sagittarii disk relative to the orbit of Neptune, shown to scale at the lower right (the filled oval at lower left represents the size of the smallest structures that could be detected in the image). The disk is tipped from our perspective, such that it appears as elliptical rather than circular. The image is...

I love Greg Laughlin's remark to the Washington Post's Joel Achenbach in last week's article Astronomers Seek New Home Closer to Home. Having discussed Debra Fischer's ongoing search for Alpha Centauri planets and his own theories on planet formation around binary stars, Laughlin points out where we stand today: "We have what is to all appearances by far the best planet in the galaxy. And we have no workable backup plan." The Washington Post article doubtless draws on Lee Billings' earlier piece in SEED Magazine called The Long Shot, which discusses with an elegance rare in science writing the attempt to find planets around the Centauri stars by Fischer as well as Michel Mayor's Geneva team. Mayor has been using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at La Silla, the Cadillac of radial velocity instrumentation (and boy does that auto industry reference date me!). Competition can work wonders, and having two teams on the case can only bode well for quick...

We're now up to 347 detected exoplanets around 293 stars. The latest find turns out to be intriguing on several counts. VB 10 is a red dwarf about 20 light years away in the constellation Aquila. Its newly detected planet is a gas giant with a mass six times that of Jupiter, a 'cold Jupiter' not so different from our own. Interestingly, although the star is considerably more massive, both planet and star should have roughly the same diameter. Image: This artist's diagram compares our solar system (below) to the VB 10 star system. Astronomers successfully used the astrometry planet-hunting method for the first time to discover a gas planet, called VB 10b, around a very tiny star, VB 10. All of the bodies in this diagram are shown in circular insets at the same relative scales. Astrometry involves measuring the wobble of a star on the sky, caused by an unseen planet yanking it back and forth. Because the VB 10b planet is so big relative to its star, it really tugs the star around. The...

Anyone who thought the Deep Impact mission was over when the spacecraft drove an impactor into comet Tempel 1 some four years ago has been given a lesson in the strategy of extended missions. Now heading for a flyby of comet Hartley 2 (late in 2010), Deep Impact is also doing yeoman work in the study of extrasolar planets. That phase of the mission is called Extrasolar Planet Observations and Characterization (EPOCh), but the spacecraft housing both investigations is now referred to as EPOXI. If the acronyms can be confusing, the latest news from EPOXI is straightforward, and encouraging. A paper slated for summer publication in the Astrophysical Journal reports on the spacecraft's observations of our own planet, made in 2008 when it was between 17 and 33 million miles from Earth. The idea was to tune up our capabilities at observing distant planets, using spectral information to map the distribution of continents and oceans. EPOXI's High Resolution Imager thus set up a trial of...

Finding Earth-like planets around any star would be a stunning feat, and either Kepler or CoRoT may deliver such news before too long. But how much more exciting still if we find a planet like this around a star as close as Centauri B? After all, the Centauri stars are our closest stellar neighbors, close enough (a mere 40 trillion kilometers!) to conjure up the possibility of a robotic mission there and, if we play our propulsion cards right in the future, perhaps a manned trip as well. A Radial Velocity Long Shot But can we pick up the faint signature of a terrestrial world in this system, given that it would be akin to 'detecting a bacterium orbiting a meter from a sand grain -- from a distance of 10 kilometers'? The phrase is Lee Billings', from his fine essay in SEED called The Long Shot, on an ongoing project to do just that. Most radial velocity surveys are spread out over numerous stars, picking off close-in worlds whose traces should be obvious in short periods of time....