It’s Full Of – Planets!
They Told Me It Couldn’t Be Done. Ha!
I can almost quote exactly the professor who told me that we’d never “see” planets orbiting stars other than our sun in our lifetimes. By “see”, he meant “image”, and if you really pegged him down, he meant image them in visible light. He probably suspected that planets circling other stars might be detectable indirectly, eventually, but certainly not directly. He clearly didn’t foresee last week’s announcements.
Two teams comprising researchers from Canada, the US and the UK have taken what appear to be the first “bona fide” direct images of planets orbiting stars outside the Solar System, an achievement that has long been considered vital in the search for planets like our own.
All credits for this achievement go to Christian Marois and his team in the US and Canada, and Paul Kalas (US) using the Hubble Space Telescope.
So if you’re asking “What’s the big deal? Haven’t we found tons of planets before?” The answer is, yes we have, but indirectly. Confidently, but indirectly. Direct imaging of a planet orbiting a distant star is like trying to get a picture of a firefly circling a searchlight, from across the city. Oh, go ahead – try it. ’tain’t easy.
Oh heck, even the indirect measurements are hard. I’ve got some experience with light curves, and the extreme lengths that you have to go through to remove the “noise” from the data (while not throwing the baby out with the bath water) is daunting. What’s usually done to find planets is to make a careful search for a periodic drift in the absorption lines seen in the star’s spectrum. If a drift is there, it is caused either by pulsations in the star’s atmosphere or by a planet. You have to use other means to rule out pulsations (usually done by checking to be sure that the star’s total light remains constant. It won’t if the star is pulsating). Of course, the drift in the absorption lines is incredibly small, and It’s easy to see that any sort of periodic effect that affects your instruments will mimic what you’re looking for. You’d need many, many cycles just to weed out the random (and atmospheric) things that hide the signal, and still you’d never be 100% sure that some other periodic effect isn’t fooling you into thinking you’ve detected the planet.
So to get a clean image of a planet is an amazing confidence builder. Phil Plait give a sense of the feeling it generated.
This is incredible: For the first time, ever, astronomers have captured an optical image of a planet orbiting a star like our own.
And that’s not all: we also have a second picture showing TWO planets orbiting a second star!
(Calm down. Breathe, breathe.)
While Phil recovers from his hyperventilation, we’ll have Emily Lakdawalla give us a calm recitation of the facts.
One announcement came from Hubble, which has taken a photo of a three-Jupiter-mass planet orbiting the bright southern star Fomalhaut, which is 25 light years from Earth. The other announcement was the combined effort of astronomers at the Gemini North and Keck II telescopes on Mauna Kea: working together, they imaged three planets of ten, ten, and seven Jupiter masses in orbit around a young, massive star called HR 8799. This one is 130 light years from Earth.
That, my friends, is quite a feat! Keeping in mind that ground based telescopes did this the day after Hubble, it’s clear that the great advances we’ve seen in Astronomy these past few decades have come because of advances in instrumentation (especially detector sensitivity) and computational speed.