The Kepler Mission - wow
So I’m listening to episode #212 of the SGU and apparently - this is mental, right - the Kepler Mission, a NASA telescope launched earlier this year, is so sensitive that it can detect the change in light coming from distant stars as planets that pass around the star cause the total light coming from the system to change.
I can’t do that in one sentence; allow me to expand. Imagine a star. It beams out light. If there are no planets around that star, in theory the amount of light reaching us stays mostly constant. We can thus infer that “there are no planets there”. Easy (and boring).
Now picture a planet orbiting that star. As it passes in front, it blocks some of the light; we thus infer the (interesting) conclusion, that is “there is a planet orbiting that star” (and, pretty please, there might be life on it).
In its simplest sense then, the Kepler type of mission looks for the reduction in light reaching the Earth as the now-detected planet passes in front of its star. The planet casts a shadow on the Earth, if you like (albeit a miniscule one).
We can detect that. That’s pretty cool. We can’t be talking more than thousands of photons a second, surely. (“Citation needed” and all that. I’ll do the research.)
But wait! Kepler can do more. Kepler can actually detect the phases of the planet as it orbits its star, so much so that when the planet passes behind its star (so that it would be invisible to us, if we could resolve that amount of detail (which we can’t)) the amount of light from the star actually appears to reduce.
Why would it reduce when the planet passes behind the star? Well, when the planet is alongside the star - picture it to the left or right - it reflects some of the light from that star. When it goes behind the star, no more reflection.
Kepler is sensitive enough to detect this extra little bit of light. Oh, and by the way, it monitors about 100,000 stars. At the same time.
Astronomy is an astonishing, humbling science.
Update: and of course this stuff doesn’t just appear overnight. The planet has to orbit its star at least twice for us to know that this is a regular, normal, planetary transition and not some anomaly. We need the light to dim (first time), then dim again (second time), then dim again (third time), and for the time between the first and the second to be the same as the time between the second and the third. Get it? And bear in mind that this extrasolar planet’s orbit may be way, way longer than our Earth’s. A year is only a year on Earth.
Mental.
