Centauri Dreams marvels at the growth of the new lexicon whose definitions routintely fill these pages. Just the other day we encountered 'mascon' -- a concentration of mass denoting the presence of a long-obscured crater. Today we get 'planemos' -- planetary mass objects that float freely through space rather than orbiting a star. The latter come from new findings being discussed at the American Astronomical Society's Calgary meeting that started yesterday and runs through Thursday. We'll have a good deal to say about that meeting as the week progresses. But back to planemos, whose existence was suggested by earlier work on brown dwarfs, many of which are known to be surrounded by potentiallly planet-forming disks of material. "Now that we know of these planetary mass objects with their own little infant planetary systems, the definition of the word 'planet' has blurred even more," says Ray Jayawardhana (University of Toronto), who presented the findings in Calgary today. "In a way,...

One of the most exciting things about the exoplanet hunt is that it isn't confined to huge observatories, nor does it demand bankrolling by billionaires. Consider the news that a team of professional and amateur astronomers has collaborated on a new planetary find, using off-the-shelf equipment and modest telescopes. The Jupiter-sized world orbits a Sun-like star some 600 light years away in the constellation Corona Borealis. The work is significant not just for the planet it discovered but for its implications for future collaborative work. Four amateurs worked with Peter McCullough of the Space Telescope Science Institute (Baltimore) to nail down the discovery. McCullough used a 200-millimeter telephoto camera lens mounted on an inexpensive device called the XO telescope on the summit of the Haleakala volcano in Hawaii (total cost for the equipment: roughly $60,000), while the amateurs contributed their own telescopes. Here's the search method: McCullough's XO telescope makes...

Finding three planets around a single star is newsworthy in itself, but when the planets are Neptune-class things get more interesting. And when one of these worlds is found to be in the star's habitable zone, Centauri Dreams definitely drops everything for a closer look. Not only that, but the system around HD 69830, a Sun-like star some 41 light years away, is also the home of an asteroid belt, making the comparison with our Solar System that much closer. Here's what we know, as reported in a paper in the May 18 Nature: The orbital periods of the three planets are 8.67, 31.6 and 197 days, with that outer world located near the inner edge of the zone where liquid water could exist. In terms of mass, this planet is not Earth-like; in fact, the measurements show the new planets to be between 10 and 18 times the mass of Earth. So what we're probably detecting in the habitable zone is a planet with a rocky/icy core surrounded by a dense atmosphere. We know nothing, of course, about...

Yesterday's post on UMBRAS and occulter technology focuses attention on the characteristics of light, some of them counter-intuitive but well demonstrated. And since we've also been talking recently about the nearby star Epsilon Eridani, I've chosen an image of that star to illustrate some of the problems with planetary detections. What you see below is via Massimo Marengo (Harvard-Smithsonian Center for Astrophysics), who has done such outstanding recent work on untangling the riddle of Epsilon Eridani's debris disk. This is a false color image with red, yellow, green and blue representing different infrared wavelengths. I ran the same image last summer, when Marengo posted it on his own weblog (he had used it to illustrate his team's work in a presentation at the American Astronomical Society meeting in San Diego). Image: A false-color infrared image of Epsilon Eridani. Credit: Massimo Marengo (CfA). What I want to single out here are the artifacts in the image. The red/orange...

In Centauri Dreams' imagination, the name Epsilon Eridani is magic. Like many of us, my earliest speculations about life on other worlds always came back to the nearby, Sun-like stars like Tau Ceti, Epsilon Eridani and Centauri A and B. Frank Drake used the first two as his targets for Project Ozma in 1960, an effort that continues to inspire SETI work today. And Epsilon Eridani is joined by Vega, Fomalhaut and Beta Pictoris as the first stars found by the Infrared Astronomical Satellite (IRAS) to have a cool debris disk somewhat analogous to our own Kuiper Belt. The fact that this K2 star is likely to be orbited by the closest exoplanet to our Sun is also exciting. Its planet seems to be slightly larger than Jupiter, with estimates ranging from 0.8 to 1.6 Jupiter masses, and an eccentric orbit varying from 5.3 to 1.3 AU (here again we see how important it is to establish the effect of gas giants on terrestrial worlds in the habitable zone). At 10.5 light years from us, Epsilon...

I remember wondering, while still getting acclimated to the odd existence of 'hot Jupiters' in those amazing first years of exoplanet discovery, what the view from a terrestrial world in one of those systems might be like. After all, a Jupiter-sized mass in close solar orbit must make for some unusual visual effects. Do terrestrial worlds exist around these stars? For that matter, what are the constraints on terrestrial planet formation in systems where gas giants orbit farther out, well past the habitable zone? These questions are occasioned by the work of Sean Raymond (University of Colorado), whose paper on the subject will soon run in the Astrophysical Journal Letters. Raymond looks at how the presence of gas giants would affect the late stages of terrestrial world formation and presents the results of his simulations on same. Bear this in mind: gas giants, it is now thought, must form within the first few million years of the early protoplanetary disk. Whereas terrestrial worlds...

How planets form is not an issue that will be settled any time soon, but two models have emerged that continue to energize research. We saw yesterday in a review of Alan Boss' new paper that gravitational instability is one way to create a gas giant. But I spent most of yesterday's post talking about UV radiation and its effects on the atmospheres of planets around M stars, a key part of Boss' explanation of so-called 'super-Earths' in these environments. So let's back up and talk about gravitational instability itself. As early as 1997, the astrophysicist had proposed that planet-sized clumps could form relatively quickly due to instabilities in the disk of dust and gas surrounding a young star. Boss believed these clumps could be massive enough to form a gas envelope, but the model was hard to use in any predictive sense and demanded more intensive computer simulations than were then available. Later work by Thomas Quinn, however, bears Boss out. Quinn (University of Washington)...

What we know about the planets circling M-class dwarf stars is changing rapidly. Recent microlensing surveys have revealed the existence of two 'super-Earths' -- rocky worlds 5.5 and 13 times as massive as the Earth -- around distant red dwarfs. Microlensing has also produced two gas giants around such stars. And radial velocity surveys have found systems like Gl 876, an M-class star orbited by an outer pair of gas giants and an inner super-Earth. Other radial velocity catches are Gl 436 and Gl 581, each accompanied by a super-Earth in a short-period orbit. A curious fact emerging from these studies is that the frequency of gas giants around M dwarfs seems to be lower than around F, G and K-type stars. In a new paper, Alan Boss (Carnegie Institute of Washington) discusses the formation of these planetary types, arguing that disk instability rather than core accretion may be the cause of their formation. An additional, and in his view critical, factor: the loss of planetary gas...

That oh so interesting planetary system around 51 Peg continues to fascinate exoplanet hunters. After all, this was the first planetary discovery around a main sequence star, and the formidable dimensions of the radial velocity dataset accrued before and since the discovery may lead to other planets in the same system. For the latest on 51 Peg, check the online proceedings of last August's colloquium, in which eighty astronomers provide their thoughts on 'hot Jupiters' and discuss recent observational facts about this intriguing system. Centauri Dreams is always delighted to see conference proceedings made available online. The only catch here is that the format is PDF -- yes, it's a standard of sorts, but there has to be a better way...

Habitable zones, and our idea of what constitutes them, change over time. We know, for example, that the habitable zone around a given star should migrate outward as main sequence stars become brighter with age. Thus the notion of the 'continuously habitable zone' (CHZ) has emerged, the region where a planet remains in habitable conditions for a specified period of time. If you want to look for technological civilizations, that time frame might be 4 billion years, paralleling the experience of life on our own planet. If you're content to look for microbes, as little as a billion years might suffice, perhaps less. Among the numerous factors involved in creating the CHZ, ultraviolet radiation is significant. A new paper points out the need to assess UV and the limits it places upon emerging biospheres. Get too much of it and you inhibit photosynthesis, as well as damaging DNA and various proteins. Get too little and you dampen a primary energy source for the synthesis of biochemical...

Three new planets have just been announced, but contrary to expectations, the number of planetary detections has not been picking up in recent times. The peak rate was 34 planetary discoveries in 2002, with the years since showing about 25 planets per year. There are a number of reasons for the slowdown, among them the fact that readily detectible short-period planets for the most obvious candidate stars have already been detected, and it will take years for enough data to accumulate to snare the presumably numerous outer planets in these systems. Greg Laughlin's Systemic site provides the details. But we do have a nice set of three new worlds delivered to us courtesy of the radial velocity method, which remains the primary detection scheme as we tune up transit and microlensing searches. HD 224693 offers a 0.7 Jupiter mass world in a 27-day orbit and HD 33283 shows a Saturn-class world in an 18-day orbit. HD 86081 is the most intriguing; it seems to have a 1.5 Jupiter mass planet in...

Recent exoplanet detections like the 'super Earth' found orbiting a red dwarf 9000 light years away have put the spotlight on gravitational microlensing. The phenomenon occurs when light from a background star is deflected by the gravity of an intervening object; in other words, one star passing quite near or in front of a far more distant one (as seen from Earth) will cause a lensing effect that can be studied. We've seen that a distant quasar can be lensed by a foreground galaxy, producing eerie, multiple images of the same quasar. But things get trickier when it comes to microlensing within our own galaxy using individual stars. We can't resolve the images created by these events with current telescopes, but the lensing does produce a measurable amplification of the distant star's light. And any planets in orbit around the intervening star can perturb that lensing effect enough to signal their presence. The beauty of this is that microlensing is sensitive to planets down to...

A brief heads-up on the ongoing work on 51 Peg, which Greg Laughlin and team are studying to see if additional planets can be found in the voluminous data. 51 Peg, remember, was the first example of an extrasolar planet being found around a main-sequence star. The dataset goes back ten years and is far more extensive than those used in most other planet discoveries via radial velocity measurements. Using the Systemic Console, Laughlin sees evidence of a possible second planetary companion to 51 Peg, and it's a beauty: a Saturn-class world in an Earth-like orbit. "Does it really exist, this room-temperature Saturn?," Laughlin writes. "Is it really out there? Do furious anticyclonic storms spin through its cloud bands? Does it have rings? Does it loom as enormous white crescent in the deep blue twilight sky of a habitable moon?" 51 Peg c is a breaktaking, beautiful thought, but Laughlin is quick to caution that this cannot yet be described as an exoplanet discovery. Plenty of work...

It was not all that long ago that binary star systems were thought to preclude planets, and I can remember reading as a boy that stars like Tau Ceti and Epsilon Eridani were far more likely to have planetary systems than the close binaries Centauri A and B. Now, of course, all that has changed, and we know from theoretical work that stable planetary orbits are possible around both Centauri A and B, though naturally constrained to orbits in the inner systems of both (which includes, satisfyingly enough, their habitable zones). But what can we make out not just from theory but observation? A new study of the 131 planetary systems detected by radial-velocity measurements (as of July 1, 2005) has come up with interesting results. 23 percent of these exoplanetary systems have stellar companions. Many of these had been recognized before as binary systems, but the international team behind this work, led by Deepak Raghavan and Todd Henry (Georgia State) also found six stars in five systems...

Imagine the supernova leading to the formation of a pulsar. Also called a 'neutron star,' a pulsar is the remnant that survives the catastrophe. The explosion of a star at least 1.4 times the mass of the Sun leaves behind an object with a diameter of 10 miles, so dense that a teaspoon of its matter would weigh about two billion tons. It's hard to see such a pulsar as the forming ground for a new planetary system. But we know that such things happen, as at least one pulsar planetary system has already demonstrated. The pulsar PSR B1257+12 was found to have three planets orbiting it back in the early 1990s, two of them the size of the Earth. These were the first exoplanets ever discovered, and it seemed even then that they must have been created out of some kind of debris disk. After all, any planets originally orbiting a star that goes supernova will doubtless be incinerated, so pulsar planets are not survivors but entirely new worlds. Image: This artist's concept depicts the pulsar...

If the goal is to find terrestrial planets around nearby stars, the transit method is our best bet. Sure, microlensing can deliver powerful results, and is fully capable, we believe, of finding a small, rocky world around a distant star. But microlensing as currently used is limited to stars that are tens of thousands of light years from Earth. In other words, find a terrestrial planet with microlensing and you can't do much by way of follow-up study. But transit methods are different. If a star's system of planets is oriented so that the planets cross in front of the star as seen from Earth, it is possible not only to find the planets but to do spectroscopic analysis and learn something of their composition. All that makes Transitsearch.org an exciting thing to be a part of. As discussed earlier in these pages, it's a cooperative project that gets amateur astronomers and smaller observatories into the transit hunt, supplying dates and times when transits are thought to occur. Greg...

How many brown dwarfs await discovery near the Sun? Nobody knows, but the most recent is an interesting object indeed. Found some 12.7 light years from Earth as a companion to the red star SCR 1845-6357, it is the third closest brown dwarf yet discovered. "If you think of the galaxy as being the size of Tucson," says Laird Close (University of Arizona), "it's kind of like finding someone living in the upstairs of your house that you didn't know about before." And that's not all that makes the new dwarf interesting. Its surface temperature of 750 degrees Celsius makes it a remarkably cool object, one of the lowest-temperature dwarfs ever found. SCR 1845-6357 is some ten times less massive than our Sun; it is located in the southern hemisphere constellation Pavo (the Peacock). The small size of this star is interesting because until now, no brown dwarfs had been found around stars with less than half the mass of the Sun. And what we can deduce about its companion is that the brown...