Extra-solar Planet Imaged

ESO press release by Sygiinu · 2004-09-10 04:49 · Score: 4, Informative

Here's a link to the ESO press release.

Re:Awesome! by sartin · 2004-09-10 04:54 · Score: 5, Informative

They did identify it as 2M1207 at 230 light years. A quick google suggests this set of coordinates from some Prospero observations in February, coordinates reproduced here (the original file has observation configuration as well):

# Prospero Observation Template File
# Created: 2004 Feb 12 [9:36:32] by saveobs.pl Version 2.2
# For: John Gizis
#
PROJECT=UDEL-04A-0005
IMGTYPE=OBJECT
OBJECT=2M1207
RA=12 07 33.4
DEC=-39 32 54
EQUINOX=2000.0
MODE=DUAL

Re:Awesome! by sartin · 2004-09-10 05:47 · Score: 3, Informative

RA 12, DEC -39 puts it in Hyrda, which according to 5 seconds of looking in "Distant Suns" trial version on my work Windows box, is seriously blocked by the Sun these days. It's about 45 degrees south of Leo, whenever it becomes visible.

Unconfirmed by Theory+of+Everything · 2004-09-10 07:13 · Score: 4, Informative

This announcement was premature, at best. It is not responsible science.

The planet is not yet confirmed as such. It could very easily be a background star. This has happenned before, and the scientists got an awful lot of egg on their faces. Another unconfirmed "planet" image can be seen here, this one around a white dwarf.

The responsible thing to do is wait a few years to determine if the objects have common proper-motions--if they move through the sky together, they are probably physically linked, and one can determine that the companion object really is a planet. Without this confirmation, the simplest explanation is not that it is a planet.

Many teams of astronomers have images of planet candidates like this one. The responsible astronomers are the ones you aren't hearing from yet--the ones waiting to verify they have planets.

The press-release title should be "A dim spot imaged near a brown dwarf." Any further conclusions have no basis.

Re:Unconfirmed by Theory+of+Everything · 2004-09-10 08:19 · Score: 2, Informative

Indeed. If it's bright enough to be observed optically, shouldn't your first reaction be, "Wait--this must be a binary system with a dim companion"?

Normally the difference in brightness, or "contrast" between a star and a planet is very large--the stars is brighter by about 100 million times in visible wavelengths, and 1 million in the infrared (for something like Jupiter). However, the star in this case is not as bright as most stars--it is a brown dwarf. Brown dwarves are much, much fainter than regular stars. Astronomers know how bright brown dwarves tend to be. In this case, the astronomers measured the brightness of the companion spot relative to the brightness of the brown dwarf in the picture. The difference in brightness is such that if the companion object is equally far away from earth as is the brown dwarf, it would have the brightness one would expect a planet to be.

(well, I don't know exactly how big it is, but since it's on Hubble, it can't be too big) telescope on Hubble: the resolution of such a picture can't be too good.

Actually, the telescope used on that link was Hubble itself, not some additional instrument stuck to Hubble. Hubble is 2.4 meters in diameter. The largests single (non-interferometer) optical telescopes in the world are the Keck Telescopes, the SALT telescope, and the HET, each at 10 meters diameter. So Hubble is pretty big. Being in space, Hubble's resolution is limited only by its size. At the wavelengths Hubble works at (visible), this is about 50 milli-arcseconds (mas).

Today's announced "planet image" comes from one of Europe's 4 VLT telescopes, using adaptive optics. These are 8 meters in diameter. The resolution of these ground-based telescopes is limited by the atmosphere (seeing) and their diameters. Normally, the sky is completely dominant. In the infrared, a technique called Adaptive Optics (AO) can correct for the atmosphere in special circumstances. Right now, AO technology only works in the infrared, not at visible wavelengths. AO on a 8-10 meter ground-based telescope, in the infrared, gives a resolution of about 50 mas, same as Hubble in visible wavelengths.

It is often over-looked that AO has flaws. It only works on bright stars, so Hubble can see things much fainter, with high resolution simultaneously. Also, Hubble can look at things all over the sky--AO only works when a bright star is in the image. Of the most concern, AO is not a perfect correction for the atmosphere--some flaws remain in the image. These are extremely difficult to calibrate, making it difficult to use the data for high-precision work. But that's another topic entirely.
Re:Unconfirmed by Shigeru · 2004-09-10 09:38 · Score: 2, Informative

Actually, this is an interesting case in that if it is a false alarm, the most likely explanation is that it's a foreground brown dwarf. The ESO team seems to have a noisy spectrum and JHK photometry of the companion. The colors really do suggest an L-dwarf (as opposed to a background K star, say), and the methane feature in the spectrum does seem real, assuming those data were reduced correctly (Difficult under the best conditions, not made easier by a brighter object 0.7 arcseconds away).

But you're absolutely right, until the proper motion study is confirmed, they've got nothing besides staking their claim to the object on the chance they get lucky. The TW Hydra association (to which the "parent" brown dwarf belongs) moves on the sky at about 66 milli-arcseconds a year, so it should be possible in a few years to see if the companion is following or not.

For me, the kicker is trusting the models. All determinations of mass (including of the parent brown dwarf) are done by guessing age, measuring luminosity and/or color, and seeing what the models of brown dwarfs/extrasolar planets say the mass should be. These are cooling tracks calibrated to Jupiter at 5 billion years, predicting how bright something is at 8 million years. Even the people making the models are hesitant to trust their own numbers at the youngest ages (Heck, we don't even know how long it takes to form a large Jupiter out of the disk).

Right now, I'd set the odds at about 80% that it won't be confirmed as a proper motion pair. In which case, my guess would be a foreground brown dwarf of a much larger mass (older and dimmer, but closer to still put it at 18th magnitude in H). If I'm wrong, the open question of these thoroughly untested models remains the cloud of uncertainty hanging over all of this.

Re:Awesome! by Shigeru · 2004-09-10 10:05 · Score: 5, Informative

The preprint of the paper lists the parent brown dwarf as 2MASS J12073346-3932539 , which is indeed at the above coordinates. The candidate planet (much in the same way Ralph Nader is the candidate president, but there's my bias showing) will be 0.46 arcseconds south and 0.63 arcseconds east.

In case I didn't discourage any amateur astronomers thus far, here's some more: That's a separation of 0.77 arcseconds, when the seeing at most sites is of order 1 arcsecond. The companion is 100 times brighter than the parent brown dwarf in the K band. The parent brown dwarf has a K of about 12, and for an M8 spectral type, that's a V-magnitude of about 19 or 20. For those of you scoring at home, the parent brown dwarf is one million times fainter than anything you can see with the human eye.

The companion is an even redder object, so the colors will be much, much worse at V (there's a reason we try to detect these in the infrared). With a state-of-the-art AO system (look what we did with the same system earlier this year imaging the surface of Titan) on an 8 meter telescope with excellent infrared detectors, the companion lies one magnitude above the detection limit on their sensitivity/separation curves.

Sorry to depress people looking forward to pointing your telescope at this system tonight, but if it makes you feel better, it's probably not a planet.

I just checked that RA, by the way. It's behind the sun right now. You'll have to wait until January to observe it. Or to point your telescope there and not observe it, as the case may be.

Re:Awesome! by Shigeru · 2004-09-13 09:16 · Score: 2, Informative

As you get to the very lowest masses of the low-mass stars (about .08 solar masses, or 80 Jupiters), I think you do start getting water lines. The issue is that most stellar photospheres (like our sun's, say) are so hot you can't have molecules of any kind, whereas in cooler stars or brown dwarfs you can. Most people are at least vaguely familiar with the idea of atmoic spectra, where you get some number of sharp (more or less) lines throughout the visible, which, in theory, could be mistaken for one another (it certainly happens for some of the low-strength metal lines). Molecules, on the other hand, have large "bands" of absorption, where light over a large wavelength range is heavily absorbed. It's fun quantum mechanics, but basically the central line is some transition to do with the molecule vibrating (the distance between the oxygen and hydrogen atoms in the water molecule oscillating, say), which is then broadened by a number of transitions to do with the whole molecule rotating.

The end result is you get very distinctive molecular features. See the bottom image on this page on another way of looking for planets, where the black line is the spectrum of the first brown dwarf discovered, Gliesse 229B. Everything in that spectrum redward (longer wavelength) of 1.6 microns is heavily suppresed by methane (another common molecule, CH4)...and I think after about 1.8 you start getting into water bands, too, but don't quote me on that. Anyway, that's all a convoluted way of saying if it looks like water, it probably is water. But there's a large range of planets and brown dwarfs expected to have such water bands in the spectrum (indeed, the parent brown dwarf shows similiar spectral features to the companion)

As to the photo, the data have certainly gone through a lot of processing in the reduction process, but that shouldn't be though of as having photoshopped the result. I've used this same instrument, and there are some features I'm curious about (lack of diffraction spikes from spider arms, mainly), but it seems pretty legitimate. It's just important to realize what this image is showing.

For one thing, that isn't reflected light making the "planet" shine, but rather the planet is powering itself. When you form something like a planet or brown dwarf, and it isn't massive enough to start fusion, gravity will make the object contract. The potential energy of that contraction needs to go somewhere, so half of it heats the gas, the other half comes out as radiation (mostly infrared). As the object ages, the contraction slows, and it gets much fainter. As an aside, even after 5 billion years, Jupiter emits more radiation than it receives from the sun. That's part of the trouble with detecting planets in general, in cases like this we know how much energy is coming out of the object, roughly how old it is, and then we have to rely on theoretical models (which aren't well-tested at all) to tell us how massive the object should be.

The second point is to remember that the "size" of the two objects in that image aren't the physical sizes at all. In fact, the telescope is barely able to resolve the separation between the two, let alone physical structure of the surfaces of these bodies (a scale 10,000 times smaller or so). "Size" of the disk on the detector is simply a matter of our imperfect telescope optics (and basic physics of diffraction) taking the points of lights from parent and companion and smearing them out: brighter objects seem to reach further out on the detector. The diffuse structure near the edge of the bright parent is again introduced by the optics, and isn't a real feature.

The image itself is your typical false-color image. All the data are in the infrared, so for us to see it, a quick remapping has to be done. Rather than have red (0.65 microns), green (0.55 microns), and blue (0.45 microns) filters that are then reproduced by red, green, and blue pixels,

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