A recent query about how astronomers work out the mass and radius of planets found through microlensing -- such as the so-called 'super-Earth' recently discovered 9000 light years from our Sun -- prompted Centauri Dreams to query one of the principals in that discovery. Andrew Gould, leader of the MicroFUN collaboration and professor of astronomy at Ohio State University, was kind enough to clarify how this fascinating science proceeds. Herewith his response: We obtain a planet-star mass ratio from a fit to the light curve. This parameter (q) is a standard output from fits to microlensing curves generated by binary lenses (two point masses, e.g., star and planet). Now, for low-magnification microlensing events, such as OGLE-2005-BLG-390Lb (which was announced by the PLANET team in January), it is generally possible to estimate the mass just by looking at the light curve. And in those cases it can be explained easily to the non-expert (although PLANET did not do this in their...

9000 light years away, a planet thirteen times as massive as the Earth orbits a star half the size of the Sun. At -330 degrees Fahrenheit, the newly discovered planet is one of the coldest worlds ever discovered. And its placement within its solar system is interesting indeed, for the icy object occupies an area where, in our system, the asteroid belt holds sway. "We've never seen a system like this before," said Andrew Gould (Ohio State University, and leader of the MicroFUN collaboration, "because we've never had the means to find them." MicroFUN (MicroLensing Follow-Up Network) is exoplanetary hunting via gravitational microlensing. A star crosses in front of a far more distant one as seen from Earth. The gravity of the intervening object bends light rays from the more distant star and magnifies the image, operating much like a lens. From our observational standpoint, the image of the star brightens as the 'lensing' star crosses in front of it, then fades as the lens moves further...

We have interesting exoplanetary news coming up in tomorrow's post, but until then let's talk about Pluto, and the latest Hubble findings about this intriguing system. The two recently found moons are now seen via Hubble imagery to have the same color as Charon, meaning that all three Plutonian satellites are roughly the same shade as Earth's moon. That's an interesting finding, because it suggests that all three moons were formed in the same event. It's also interesting given the reddish hue of Pluto itself, about which we'll learn more in the years leading to the New Horizons encounter in 2015. Image: The new HST/ACS observations made on March 2nd reveal that all three of Pluto's satellites are neutrally colored, unlike reddish Pluto itself. Pluto's reddish color is believed to be due to reddening agents created by the effects of sunlight acting on its nitrogen and methane surface ices. Charon's surface is known to consist primarily of water ice; the similar color of P1 and P2 may...

Centauri Dreams has written before about Grover Swartzlander (University of Arizona), who is developing new ways to screen out the light of a star to make it possible for astronomers to study the planets around it. At the heart of Swartzlander's effort is something called an optical vortex mask, which is said to be 'a thin, tiny, transparent glass chip that is etched with a series of steps in a pattern similar to a spiral staircase.' And here's how this chip does its job: incoming light slows down more in the thicker parts of the chip than in the thinner ones, with the result that some waves of light eventually becomes 180 degrees out of phase with others. Reaching the 'eye' of the vortex, the waves that are 180 degrees out of phase with one another cancel each other out, so that a dark central core remains. Swartzlander says the effect is like light following the threads of a bolt; the distance between adjacent threads is crucial to the outcome. So could this technology be used to...

An interesting specialty in exoplanetary science is the simulation of planetary orbits. It's intriguing, for example, to place a hypothetical terrestrial planet into a system with known giant planets to see what happens. After all, we know that many exoplanetary systems contain potentially stable orbits for such planets; in fact, one-fourth of known systems can support a planet in their habitable zone. And while we don't know yet whether such worlds exist, we can draw useful conclusions from modeling their orbits if they are there. Such are the premises of a new paper by Sean Raymond (University of Washington, Seattle) and Rory Barnes (Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder). The two simulate terrestrial planets in four systems: 55 Cancri, HD 38529, HD 37124, and HD 74156. And here is a key issue: most planets we've found so far are 'hot Jupiters,' in tight, close orbits around their primary. For a terrestrial planet to co-exist with such...

Centauri Dreams recently discussed the planets around HD 73526, as described in detail on astronomer Gregory Laughlin's Systemic site. HD 73526c seemed attractive as a venue for life-bearing moons -- a gas giant, it orbits well within its parent star's habitable zone. The post inspired questions from readers on whether the chances for life on any large moons of such a planet would be minimized by Jupiter-style radiation fields. And given the unusual orbital resonance between the two planets, questions also arose about how these gas giants might have formed. Laughlin (University of California, Santa Cruz) was kind enough to answer these queries. His responses follow, with my inserted comments in italics. The radiation environments around both HD 73526 b and c are probably more intense than in the vicinity of Jupiter. This increase would mainly be the result of the planets having larger masses than Jupiter, which gives them more vigorous interior convection and hence stronger magnetic...

HD 73526 is a G6 star (i.e., a solar-like main sequence dwarf) that has just made some interesting news. As Greg Laughlin writes in a new posting on his Systemic site, Paul Butler, Geoff Marcy, Chris Tinney and collaborators with the Anglo-Australian Planet Search Project have found that the planetary system around the star displays an unusual resonance whose motion over time can be viewed in this online mpeg file. But even more striking is the nature of the two gas giant planets found here. The inner (HD 73526b) orbits with a 188 day period, while the outer has a period of 379 days. Let Laughlin tell it: Planet c is a true room temperature gas giant. Liquid water likely blows in gusty sheets across its cloudy skies. (And it's worth noting that any large moons circling HD 73526 c lie pleasantly within the stellar habitable zone.) Got that? Centauri Dreams yields to no one when it comes to fascination over exoplanetary orbits, particularly unusual resonances between distant worlds,...

The budgetary demise of Terrestrial Planet Finder has cast a pall over some researchers, but it may have energized an entirely different solution. What if I told you that in the 2013-2015 time frame we may get conclusive images that tell us whether or not there are terrestrial worlds around Tau Ceti, Epsilon Eridani, and Centauri A and B? Images that allow us to examine the habitable zones of as many as 100 stars over a three-year period? With TPF gone, the idea sounds like a fantasy, but my recent conversation with astronomer Webster Cash revealed it to be anything but. Cash (University of Colorado at Boulder) has been involved in the development of a concept most recently called New Worlds Imager, one that began as an enormous 'pinhole camera' design, as I discussed in Centauri Dreams (the book) in 2004. Within the last 18 months, the design has morphed into a low-cost mission using an occulter (call it a 'starshade') to mask the light of the star being observed so as to reveal...

Margaret Turnbull (Carnegie Institution of Washington) has a job Centauri Dreams can't help but envy. The astronomer is a specialist in identifying stars that have habitable zones -- stars, in other words, where life is possible. Back in 2003, Turnbull and colleagues published a list of 17,129 such stars, based on factors such as age (how long does it take life to develop?), stellar mass (larger stars may not live long enough to produce productive habitable zones) and metallicity (a measure of the heavy metals needed for planetary formation). Narrowing a galaxy of between one and two hundred billion stars down to 17,129 candidates is no small feat, but Turnbull has now gone one better, choosing the top five candidate stars for those engaged in SETI, the search for extraterrestrial intelligence. That list involves choosing stars where technological civilizations are most likely to have developed, but Turnbull complements it with a second list of six stars likely to have Earth-like...

Greg Laughlin's systemic site, indispensable for those studying exoplanet detections, now offers a close look at Proxima Centauri, at 4.22 light years the closest known star to the Sun. Intriguing facts include these: While holding about 11 percent of the Sun's mass, Proxima has an average density several times that of lead (the Sun's average density is about 1.4 times that of water) Proxima's total luminosity is a thousand times less than the Sun's Because radiation alone cannot get Proxima's fusion energy from its interior to the surface, the star relies on convection -- the motion of stellar gases physically takes energy away from the core (by contrast, the Sun has a radiative core) All of which has powerful consequences, especially in terms of longevity -- Proxima Centauri will still be shining two trillion years from now. You'll want to read the entire post, which goes into the details of a paper Laughlin wrote (with Peter Bodenheimer and Fred Adams) that examines the fate of...

A fascinating post by Anthony Kendall cites the reasons why Terrestrial Planet Finder is such an important mission and goes on to call for NASA's being broken into separate entities, to make missions like this more likely to launch. From the Anthonares weblog: Gradually, constructing, launching, and operating missions in Earth orbits or in Lagrange points should be taken over by consortia similar to those that operate ground-based facilities today. As commercial satellite companies have demonstrated, they are more than capable of managing their own facilities. NASA's deep space expertise will necessitate the existence of an unmanned space probe agency for several decades at least, and perhaps indefinitely as we look to explore the stars. The TPF missions could be the first in step in this process. If the scientific community wants them badly enough, they have the lobbying ability (as demonstrated with Hubble and New Horizons) to get Congress to fund them. Since private consortia will...

The key lesson of exoplanetary science is surely humility. Over and over again, starting with the discovery of the first 'hot Jupiters,' we've been brought face to face with the fact that assumptions long enshrined in our thinking have to be reevaluated. Thus it's no surprise to learn of a new study identifying what appear to be enormous debris disks around two giant stars. In the past, stars of their size were considered unlikely candidates for planetary systems. The stars are R 66 and R 126, both located in the Large Magellanic Cloud; the former is 30 times more massive than our Sun, the latter 70 times. Both are thought to be descendants of the massive objects called type O stars, large enough that, if they were located in our own Solar System, they would swallow all the inner planets including Earth. Image: This illustration compares the size of a gargantuan star and its surrounding dusty disk (top) to that of our solar system. Monstrous disks like this one were discovered around...

Anyone involved in exoplanetary science shares a common dream: a view of a blue and green world returned from an advanced imaging system of the sort that may one day fly aboard Terrestrial Planet Finder or other missions. But as we wait for breakthroughs in space-based hardware, planetary detections keep occurring. And astronomer Greg Laughlin (University of California, Santa Cruz) has a thought on what we might find using today's technologies. Laughlin notes that that nine extrasolar planets are known to transit their parent stars (i.e., they pass in front of the star as seen from Earth). "It would be nice to find a transiting planet with a longer period," he adds. "Preferably, this would be a giant planet with towering thunderstorms and warm, drenching rains, and orbited by a habitable Earth-sized moon that we could detect with HST photometry." Nice indeed, for that moon would be our first candidate for a life-bearing world in the terrestrial mode, a real coup for transit studies....

Some further thoughts on OGLE-2005-BLG-390Lb, the planet whose discovery portends numerous microlensing breakthroughs to come. Note the distance between the Sun and the red dwarf in question, which is variously reported as between 20,000 and 28,000 light years. The red dwarf is in the constellation Sagittarius and lined up between us and the center of the galaxy, a location that is a natural consequence of the microlensing method used to find the new world. For microlensing relies upon a closer star passing in front of one farther away, thus causing the gravitational effects used to pinpoint OGLE-2005-BLG-390Lb. To maximize the chances of seeing such an event, you need to point toward the largest possible field of stars, which is exactly what the OGLE project does. OGLE stands for Optical Gravitational Lensing Experiment, a study whose telescopes scan the central Milky Way each night. The scans are fruitful, for more than 500 microlensing events are discovered every year. Bear in...

The most Earth-like planet yet found has been discovered by a team of astronomers in a collaborative effort that involved 73 scientists in 12 countries. When astronomers use the term 'Earth-like' in this context, they're referring to planets whose mass is closer to Earth's than previous discoveries. They're also talking about surface conditions, for OGLE-2005-BLG-390Lb seems to have a rocky surface, and is only five times as massive as Earth. And what a fascinating find from the standpoint of technique. This is no relatively nearby gas giant found through observing the radial velocity changes it caused in its star's path through space. Instead, the new world, some 20,000 light years away, was found through microlensing, where the gravity of an intervening star magnifies the light of a more distant star. Close study of the brightening phenomenon can reveal defects that are the telltale sign of a companion object. In this case, as the star and its planet passed in front of the...

Busy times. Centauri Dreams has three new Acta Astronautica papers waiting for review, but Stardust is about to return with cometary dust (and, we hope, interstellar materials), and, of course, New Horizons is just four days from liftoff. Add to that the usual flurry of news from the just concluded American Astronomical Society meeting and it's clear I'm going to be behind the curve for a week or so just trying to catch up. Bear with me, though, because fascinating stuff keeps rolling in, such as the singular exoplanet detection below. What's interesting is not just the new planet but the detection method. Normally, Doppler radial velocity measurements rely on spectographs mounted on large telescopes. A new instrument called the Exoplanet Tracker (ET) uses an interferometer instead, a device capable of more precise measurements because it can capture more light. Image: An artist's rendition shows a planet orbiting a very young, active star pocked with dark star spots and speckled...

Centauri Dreams readers will want to know about Systemic, a research collaboration led by astronomer Gregory Laughlin (University of California, Santa Cruz). Scheduled for launch in 2006, the Systemic Collaboration is a simulation that will study a catalog of 100,000 stars, some of which are surrounded by planetary systems created by the team. The idea is to observe these stars by running their radial velocity information through the Systemic Console, a java applet that has just been released in beta form for early use and debugging. Radial velocity measurements have been a key tool in the hunt for extrasolar planets, using slight perturbations in a star's motion as evidence for distant planetary systems. A radial velocity measurement, according to Laughlin, is ..."the component of the velocity of the star along the line of sight from the Earth to the star." We can get measurements of motion along this line of sight down to 1 meter per second, telling us how stars are moving in...