Friday, November 21, 2008

Another Young Planet Imaged?? In Beta Pic??

They seem to be coming fast and furious now -- which is expected, since the minute someone finds a winning formula, everyone tries to duplicate it.  A French team appears to have imaged a large gas giant (8x the mass of Jupiter) inside the dust debris disk surrounding the famous young star Beta Pictoris using the VLT (Very Large Telescope) in Chile.  The planet is apparently 8 AU (AU=Earth-Sun distance) from its parent star, which is supposedly the exact distance needed to explain the dynamics of the dust in the disk.

The reason I'm using these qualifiers is that unlike the previous detections, this one has not been confirmed by a second set of observations at a later time (in order to track the motion of the planet).  They are using arguments like "It's in the same orbital planet as the disk, and it's the right distance away, and... I really want it to be a planet...", but until they have conclusive proof that the object is actually bound to the star, this will have to be considered a "planet candidate".

But they are definitely right that it would fit in very nicely with previous results.  The Beta Pic disk is one of the most well-studied debris disks, and has long been known to have a very distinctive warp (see pic here) that is explained well by a planet on an inclined orbit at less than 20 AU (paper here).  However, we have no idea if the imaged object is on an inclined orbit, a circular orbit, an eccentric orbit, or any other kind of orbit - we have no information.  So we're going to have to wait and see if all the pieces fit together.

Wednesday, November 19, 2008

So, this is a post not about space specifically, but about popularizing science (which is another secret passion of mine - along with Fritos corn chips and the TV show Fringe - not in that order). I think it's fantastic that more people, both in academia and media, are talking about science in new ways that are tailored specifically for the new YouTube era.  From more weighty endeavors such as the Apple iTunesU (free online videos from university professors) and ScienceDebate2008 (harnessing the election obsession to shine the spotlight on how important science is to our country and our lives), to short science-oriented videos such as Slate's Grand Unified Weekly (a weekly update on cool science news, with flashy graphics), people are really getting energized about putting science front-and-center.  I personally think the obvious difference between the two presidential candidates on important science topics (even if they weren't pitched as science topics) made a big impact on the election, and I hope we can keep ratcheting up the exposure.  The more people realize how science makes life better, the more support science will receive.

Tuesday, November 18, 2008

A follow-up to the post from Friday about the new images of extra-solar planets:  a new paper coming out today searched for additional massive planets around Fomalhaut (the one with the planet at ~100 AU) and didn't find any between 15 AU and 40 AU (remember, an AU is an Earth-Sun distance).  The upper limit on mass is 2x that of Jupiter, so the search wasn't that sensitive (our whole Solar System would be undetectable), but it does at least tell us that the system isn't just an incredibly massive freak of nature.  So we're still left with the problem of how a massive planet (0.5 MJup or larger) would form at 100 AU in a normal planetary system.  More to come... 

Monday, November 17, 2008

OK, I've been newly energized by the first images of planets announced last week - plus I've finally started reading new research papers again - so I'm going to try to get back to writing a new post consistently.  Probably not every day, but whenever I see some new research that could use a nice little summary.

So here's today's new work - a paper on nano-diamonds in protoplanetary disks.  They observe the infrared signature of the dust particles at the exact wavelength coincident with the vibration of carbon-hydrogen bonds in diamond.  This isn't the first time emission from diamond has been observed, but so far there are only three objects that show it.  The diamond emission comes from the inner disk in stars that are bathed in X-ray radiation from low-mass companion stars - this heavy irradiation is required to turn the carbon molecules into diamond rather than graphite.  The current work nails this explanation by resolving different regions with diamond emission (inner disk) compared with non-diamond emission (outer disk).

You can use this idea to trace the disk chemistry - a very specific molecular structure can help tightly constrain the vertical disk structure and radiation environment - but it's not going to get you rich. The diamond particles are about 100 nm, which is the same size as your cellular chromosomes - kind of hard to put into an engagement ring.

Thursday, November 13, 2008

First Light from Planets!

It seems like they've finally done it:  an unambiguous image of an extrasolar planet (actually, several of them) around a main-sequence star (HR8799).  They've been getting close for several years - the image of 2M 1207b was an excellent start, but was often disparaged because 1) the imaged object (b) orbits a brown dwarf (a) rather than a "normal" star and 2) the mass of (b) may be large enough to place it in the brown dwarf range as well.  These new detections (as well as the detection of a planet around a well-known young star named Fomalhaut announced at the same time) have none of these uncertainties - the planet masses are well below the mass limit for a brown dwarf (~13x the mass of Jupiter), and the stars are both A-type main-sequence stars (1.5 - 2x the mass of our Sun).  Unless there turns out to be a major screw-up, the era of direct detection of exo-planets has begun!

Now let's turn to what's interesting about these two systems.  First, both stars are quite young (less than 100 Myr) - this means their planets are still hot from their formation, making them easier to detect.  It also means that much of the debris from planet formation still remains in the system, in the form of dust rings surrounding the planets.  These dust rings are much, much brighter than the planets themselves due to the much higher surface area available to radiate (look at the picture of Fomalhaut for a good idea of this), and this has lead many researchers to design ways to search for the presence of planets around young stars by looking for patterns in the dust created by their orbits.  These new detections corroborate these techniques - patterns can be seen in the dust that can be directly attributed to the planet, and help constrain the mass of the planet.

The second (and I think more interesting) fact is that all the planets are at very large distances from their parent stars - the three planets around HR8799 are between 25 and 70 AU (astron. units - Earth-Sun distance), while the planet around Fomalhaut has an orbital radius of 100 AU!!  For reference, the farthest giant planet in our own Solar System (Neptune) is thought to have formed at 15 AU from the Sun.  How do these massive planets form so far out?  Is it because the stars are larger?  This seems like it might explain the planet at 25 AU, but the others are really pushing it.  Do they form like stars - by collapsing out of the young protostellar cloud?  These planets form the opposite endpoint of the "Hot Jupiter" planets first discovered by radial velocity surveys - and they look like they will have the same mind-blowing effect on the planet formation community.