Before the deluge

[del_c]

With the ESA satellite COROT nearing its first 300 days in orbit, I hear that a truckload of new extrasolar planets are due to be announced to the world soon. These detections will be based on planetary transits, which means this may be the last time my graph of exoplanets detected by doppler spectroscopy (based on data from exoplanet.eu) represent

Comments

[bungo]

Nice picture!

It would be nice to see Uranus and Neptune on here for comparison. (I think the Earth would be just off the bottom of your vertical axis.) Jupiter is the red dot just above the 'i' in 'Jupiter', right?

Am I right that planetary transits give us period, so orbital radius if the star mass is known (but not periastron and apastron), but they won't give us planetary mass, unless we make some guesses about size and density.

[del_c]

I used to have Uranus, but it was a bit too far to the right for me to want to keep in this version. I had to take out some of the bells and whistles for low resolution. Neptune was always too far out for me to bother with, just as Earth is still too far down.

You don't get mass with transiting planets, but you do get radius, which you don't get with dopplering planets. And some planets are both doppler detectable and at the right angle for transiting; astonishingly, there are amateur astronomy groups involved in searching for transits of planets previously detected by doppler methods.

(you don't know that a planet detected will be lined up right for a transit, but you do know precisely when that planet would transit, if it was, and amateurs can detect the difference in stellar brightness if they have equipment capable of photometry accurate to 1%)

For planets that are both massive enough to show up on doppler, and at a low enough inclination to transit, we can obtain both their mass and their radius, and hence their density.

[bungo]

Ah, yes. Planetary radius is what I would have meant by size.

You'd have to be pretty lucky for the planet's orbital plane to pass close enough to our line of sight for a transit to be visible. I should think about this with a piece of paper.

Thanks for the transitsearch link. One day I hope to have a big telescope, clear skies, and lots of spare time.

[del_c]

These planets are after all a shockingly small number of stellar radii from their parent stars. The blog at oklo.org claims that the probability of alignment can be as high as 10% or more-11% in the case of HD 17156b, and they got lucky there and did indeed catch it.

Subsequently, their measurements showed such a dip in photometry in the Lyman-α spectral line, that they describe the planet as having a comet-like wind of hydrogen coming off it. I wonder if that would be visible? It surely can't be fierce enough to actually diminish the planet's mass by much: giant planets are too good at hanging on to even hydrogen, even at those >1000K temperatures, and of course they have so very much hydrogen to spare.