by Paul Gilster | Oct 14, 2006 | Outer Solar System |
This image is simply too beautiful not to run for the weekend, even though it’s getting play everywhere. The Sun is, of course, behind Saturn, backlighting the rings to reveal hitherto unseen detail.
Image credit: NASA/JPL/Space Science Institute
Gorgeous as it is, bear in mind that this is a composite in which the colors have been exaggerated. 165 Cassini images went into its production, taken with the spacecraft’s wide-angle camera over a three hour stretch on September 15. Ultraviolet, infrared and clear filter images went into the composite, which was then adjusted to get as close to natural color as possible. Much good science is coming out of these observations, but for now absorb the beauty of the scene, surely a view that will stand as one of Cassini’s defining moments.
by Paul Gilster | Oct 14, 2006 | Deep Sky Astronomy & Telescopes |
Next week we’ll take a look at some interesting new work on the formation of rocky worlds around red dwarfs (including what might show up in the habitable zone around such stars), and a French study on the characteristics of gas giant exoplanets. I also want to talk about a new SETI attempt looking for signal leakage from a nearby solar system rather than directed beacons.
For the weekend, though, ponder a project to get the public involved in deep sky astronomy by using the Internet to deliver live video of observing sessions. The company involved, Astrochannels.com, is still in beta testing, but the plan seems to be to stream views of galaxies, globular clusters, nebulae and other intriguing objects, along with a commentary, during scheduled live showings. Users will be able to vote on objects to be studied and participate in online forums.
The next showing is tonight starting at about 10:20 Eastern time (0220 UTC), with the viewing schedule available here (Comet SWAN is an interesting possibility). I have no idea how this concept will play out, but I’m hoping that by making more alternatives available for those without telescopes, the Internet can become an even more effective aid in spreading public interest in astronomy.
I’m remembering, too, the New Trends in Astrodynamics conference in Princeton a year ago, when even the most jaded in the audience gasped in delight at the astronomical vistas shown by a resident amateur with high-end equipment. Let’s hope Astrochannels.com can ignite that feeling in a new audience.
by Paul Gilster | Oct 13, 2006 | Exoplanetary Science |
Imagine being able to measure day and night temperatures on a planet circling another star. That’s just what the Spitzer Space Telescope has managed, homing in on the atmosphere of Upsilon Andromedae b, a ‘hot Jupiter’ orbiting its parent star every 4.6 days. The results are, as you might expect for a planet this close to its star, extreme. The temperature difference between the two sides of this world is a whopping 1400 degrees Celsius (2550 degrees Fahrenheit).
We’re looking at a planet that seems to be tidally locked to the star it circles, but unlike other tidally locked objects like our Moon, this one has a thick atmosphere that could be circulating faster than the interior. The scientists behind this work are essentially doing meteorology, as witness this remark by Joe Harrington (University of Central Florida):
“This planet has a giant hot spot in the hemisphere that faces the star. The temperature difference between the day and night sides tells about how energy flows in the planet’s atmosphere. Essentially, we’re studying weather on an exotic planet.”
Exotic is right — fire and ice — but the hard facts are presented in the paper for which Harrington is lead author, published online yesterday in Science. Upsilon Andromedae is known to have three planets; the one under study is at least 0.69 as massive as Jupiter, and the authors describe their work on its properties as “…the first demonstration that such planets possess distinct hot substellar (day) and cold antistellar (night) faces.”
Image: Spitzer was able to determine the difference in temperature between the two sides of this planet by measuring the planet’s infrared light, or heat, at five points during its 4.6-day-long trip around its star. The temperature rose and fell depending on which face, the sunlit or dark, was pointed toward Spitzer’s cameras. Those temperature oscillations are traced by the wavy orange curve. They indicate that Upsilon Andromedae b has an extreme range of temperatures across its surface, about 1,400 degrees Celsius (2,550 degrees Fahrenheit). This means that hot gas moving across the bright side of the planet cools off by the time it reaches the dark side. Credit: NASA/JPL-Caltech/Univ. of Central Florida.
Notice the bottom graph in the image above. It’s what you would have expected to see if this ‘hot Jupiter’ were circled by bands of different temperatures, like our own Jupiter. The Spitzer data show that, for Upsilon Andromedae b at least, the temperature differences between day and night side are profound. This is an atmosphere that is apparently able to absorb and reradiate sunlight fast enough that the gas enveloping the planet cools off quickly.
Studying how the Upsilon Andromedae system dims and brightens in synch with the gas giant’s orbit made these results possible. The changes in heat result from the planet’s varying faces as presented to Spitzer on the line of sight to Earth. It’s stunning work, found in Harrington et al., “The Phase-Dependent Infrared Brightness of the Extrasolar Planet Upsilon Andromeda b,” with abstract available here.
by Paul Gilster | Oct 12, 2006 | Exoplanetary Science
The new planet discovered around the red dwarf GJ 849 isn’t just another footnote in the unfolding story of exoplanet discoveries. This world, a gas giant about 80 percent as massive as Jupiter, promises to teach us more about planet formation around M-class stars, by far the most common stellar objects in the galaxy (with the possible exception of brown dwarfs). And the more we learn about the so-called core accretion model, the more we’ll understand what to expect as we point our telescopes in the direction of other red dwarfs.
Not bad for a planet circling one of the 152 stars within 200 parsecs of the Sun known to have planets. But bear this in mind: most of the stars around which we’ve found these planets have been like our Sun, in the range of 0.7 to 1.3 times its mass. We’ve studied over 200 M-class dwarf stars with planet detection in mind, but until now had discovered planets around only three. GJ 436 shows a Neptune-class world, as does GJ 581, while GJ 876 seems to be a triple system, and is the only one known to contain Jupiter-sized planets. GJ 849 thus makes the fourth M-class planetary system.
Red dwarfs are tiny objects, but that makes planets of a certain mass easier to detect, and the fact that we’ve found so few gas giants around them could be seen as evidence that the disks out of which planets form are less robust around red dwarfs than Sun-like stars. That would make a certain amount of sense, for the core accretion model says that when gas giants form, rocky cores build up through collisions in protoplanetary disks around young stars, reaching a critical mass after which gas from the disk accumulates in runaway fashion.
So if red dwarfs have smaller, less massive protoplanetary disks, the planets forming there may never reach the needed critical mass. That would suggest that red dwarfs are probably more likely to have Neptune-class ‘ice giants’ than planets like Jupiter. But here’s the problem: our data only produce information about planets orbiting around 2 AU and closer to the parent star. In other words, we need longer observation periods to see whether there are not in fact Jupiter-class worlds further out in the systems around such stars.
So the new planet is an exciting find. GJ 849 b is a gas giant some 2.35 AU out, an order of magnitude further than any other M-class planet, and only the second Jupiter-mass world found around a red dwarf. More data are now required to see whether there are more gas giants around these stars than current thinking suggests. If there are, we may have to revise our ideas about core accretion in red dwarf systems, whose protoplanetary disks may turn out to be more massive than previously imagined.
The paper on this work is R. Paul Butler et al., “A Long-period Jupiter-mass Planet Orbiting the Nearby M Dwarf GJ 849,” available here in preprint form. And note this item from the paper: “At 8.8 pc, the orbital separation of GJ 849 b corresponds to a projected separation 0″.27. Thus, the proximity of GJ 849 provides a unique opportunity for high-resolution imaging using adaptive optics and future space-borne astrometric missions such as the Space Interferometry Mission.”
by Paul Gilster | Oct 11, 2006 | Exoplanetary Science, Research Tools |
Just how representative are the 200+ planets we have now found around other stars? Consider that the most frequently used detection method involves radial velocity searches, looking for the tiny wobbles in a star’s motion that provide clues to the gravitational presence of a planet. It’s a solid technique that has found numerous ‘hot Jupiters,’ but the method introduces a bias for the kind of massive planets close to their star that create effects most visible from Earth.
And consider other factors: telescope time is sharply limited, and so are the swatches of sky most likely to be observed based on where the best telescopes are housed. We get more data on some exoplanetary systems, much less on others, and our view of what may be representative needs serious work.
Which is why the Systemic project was created, and why it is clearly gaining momentum. Regular Centauri Dreams readers know that Systemic is a simulation based on a dataset of 100,000 stars, one that can be accessed at the project’s Web site. What’s fascinating here is that whether you’re an astronomer or just an interested layman with a PC, you can play around with exoplanet properties like mass and vary the orbital parameters of hypothetical worlds to find a workable fit.
Make no mistake, these are simulated planet searches, but they perform a valuable function. Taking observational biases based on our methods into consideration, Systemic can get a better idea of how accurate our current search process is. “How good are we at detecting strange systems? Stars with three planets instead of two? Two instead of one? There are a lot of questions like this that can be addressed with a large-scale simulation,” said Greg Laughlin, who founded the project with a team of collaborators.
Consider this a renewed call for volunteers. You don’t need an expensive telescope to get involved, just an Internet connection and a desire to participate in a hunt that to my mind is one of the most exciting things going. Like SETI@home, which also uses the distributed power of legions of small computers around the world, Systemic relies on wide-scale involvement. The introductory phase it’s now in is a good time to learn to use the powerful software tools it offers.
