Planets have been found around stars that are very far away. Based on the star dimming. That makes sense.
But I wonder how they figure out the planet size ? That would seem to be very hard. Also the same problem would be true on the distance from the star to the planet. If the planet is 1400 light years away, the distance from star to planet is some very,very small percent of that .
The first planets to be discovered outside the Solar System were detected because of the star’s ‘wobble’. In other words, the star gets pulled around, a very small amount, as the planet orbits around it. By observing the period of the wobble, scientists know the period of the planet’s orbit; from that, they can figure out the planet’s distance from the star. Based on the magnitude of the wobble, they can figure out the planet’s mass.
and the wobble is measured by what technique?
A wobbleometer.
(OK, seriously: Kepler space telescope - Wikipedia)
By the “Radial velocity method”, in which small doppler shifts in the star’s light spectrum indicate that it’s moving alternately towards or away from us in proportion to the magnitude of a planet’s tug on it. The planet’s pull on the star depends on its distance from the star, and its mass.
They can actually deduce the radius of the planet by measuring how much the parent star’s brightness decreases during the transit.
Wouldn’t that get immensely complicated at best and totally confounded at worst, if the star has multiple planets whizzing around it, which may all be on various sides of the star at any time?
As for the distance from the star: They don’t consider it a proper detection via the occultation method until they’ve observed it happen two or three times (which, yes, does take years). This means that they can determine the period, and given that and the star’s mass (which can be inferred from its spectral type), it’s easy to calculate the average orbital period.
As a double-check, you can also infer the star’s size from its spectral type, and given that, the orbital distance and speed, and the inclination (which you can get from the shape of the dip in brightness), you can calculate how long the occultation should last. Compare that with the duration you actually measure.
Not really. A simple Fourier transform will separate out all of the information into neat little piles, one corresponding to each planet. Some of them will have a larger spike than others, and those will be the ones detected first, but with patience and good data, you can find the others.
The very first extra-solar planets were actually discovered around a type of star no one expected to have planets: a neutron star. It was also a pulsar and the planets caused irregularities in the timing of its pulses.
However, such pulsar planets are very rare and the next planets were discovered by the wobble method (which method is not what Kepler uses).
Well, the pulsar planets were still detected by the wobble; it’s just that the wobble was detected in a different way than with most stars.
I never understood this… I can see clearly how this would work on a solar system with 1 planet, but I think most have more than 1.
How could you determine anything about say, earth, by observing the wobble of our sun? There are a ton of more planets pulling and tugging at our star.
I swear my browser only rendered the first post when I replied to this. Weird.
So a Fourier transform. Amazing, that function is.
For what it’s worth, our instruments would not be able to detect Earth (or rather, a planet of the same size and distance) around any other star (except possibly a pulsar) via the wobble method. For that matter, we’d have an extremely hard time even finding Jupiter that way. Most of the planets found via wobble are “hot Jupiters”, gas giants closer to their star than Mercury is to ours.
We can detect Earthlike planets via occultation, but only if we’re lucky (the plane of the orbit has to be nearly exactly edge-on to us). We make that luck by the simple method of checking a great many stars.