What are ways to find extra solar planetary systems?

Question

I know about the doppler wobble, what are the other options?

Answer 1

2.1 Optical lensing
Practically reliant on sheer luck, optical lensing is an unlikely way to find an exoplanet. It has been used to suggest the existence of a planet in a quasar (“quasi-stellar radio source” very distant objects in our universe, more luminous than several typical galaxies combined). When a quasar happens to lense itself into two lobes between itself and our line of sight, one lobe can become perturbed by the presence of a planet. This gives us a particularly uncertain suggestion towards a planet in another galaxy.



2.2 Astrometry
Astrometry measures changes in the proper motion of a planet by comparing its position to the positions of more distant stars. Slight variations in the star’s position can suggest the presence of a planet, as the planet’s gravity tugs the star around their common center of mass, as is suggested by Kepler’s Third Law and the subsequent relation of masses (equation 1). This was the method used to find planets around Bernard’s Star. If a predictable motion can be found, the degree of the “wobble” will suggest the mass and orbit of the planet. This method, although simple in explanation, is not the most practical. A planet would need to be very massive and in a large orbit so that it can tug the star substantially and the center of mass that the star will orbit is far enough away, respectively.

(1)
m1a1 = m2a2
m = mass of the body; a = semimajor axis

2.3 Direct imaging/ “optical detection”
Perhaps less practical than astrometry is the direct imaging method which seeks to obtain an actual image of a planet near another star. In theory this is possible for very large planets because a planet will reflect its star’s light to us (gas giants tend to have higher albedos or reflectivity). Still, the reflected light would be miniscule when compared to the light of the star. There are two ways to overcome this. First, one can cancel out the light of the star with nulling, where the crests of the light waves are matched with the troughs of the star’s light (and hence, visa versa). If this process is not carefully done, however, it can affect the detection. Another way to attempt to overcome the star’s overwhelming starlight is to use a physical coronagraph which will block out most of the star’s light.

2.4 Radial velocity/ Doppler spectroscopy
The radial velocity method has been the primary method of planet detection thus far, particularly in the 1990s. It uses the Doppler Effect to find planets similarly to, but more precisely than, astrometry. This method also relies on the tug of a planet on a star causing the star to wobble around the common center of mass. With precise spectrographs, one can compare the spectrums of a star over a period of time to find a red-shift, blue-shift pattern. When a light emitting object, like a star, moves towards us its light waves are essentially compressed or shortened, making them more blue (or, rather shorter wavelengths: blue waves are at the shorter wavelength end of the visible spectrum). Conversely, when a star moves away from us its light waves are stretched out, making them more red (or longer wavelengths). We don’t actually see the star change colors but the absorption lines detected by spectroscopy will shift towards shorter or longer wavelengths as the star moves towards or away from us. (Figure 1) A planet will cause a periodic blue-shift and red-shift.
Difficulties arise as this depends on a substantial movement of the star (although it is more precise than astrometry as has been stated). Radial velocity will only find larger planets or those fairly close to the star. Also radial velocity cannot give a very definite figure for the orbit of the planet because there is no way to tell how inclined the orbit is to Earth’s line of sight. As its name blatantly suggests, it can only give us the radial motion of the star: the motion that is in line with our line of sight. Therefore it is a minimum velocity that is given. (Figure 2)

2.5 Transit method/ photometry/ occultation
Transit method is dependant on the good fortune of having the planet pass between the star and the Earth’s line of sight. This produces an occultation . Sensitive instruments can detect the change in the brightness of a star. If there is a periodic dip in the star’s brightness it is likely a planet.(Figure 3) The orbital period can be found with the data obtained from more than one occultation, as well as the approximate size of the planet using the times of first, second, third and fourth contact (equation 2). More details about the orbit and the planet’s mass can be obtained by comparing this data with the data from a radial velocity measurement (we now know approximately how inclined the orbit is and can find the orbital velocity).



(2)
(Rp/a) = (π(t2-t1))/P
(Rs/a) = (π(t4-t2))/P
Rs=radius of star; Rp=radius of planet; a=orbital radius; P=orbital period
t1 through t4 = contacts 1, 2, 3, 4


-my paper :)

Answer 2

The wobble and the doppler wobble are the oldest methods but they only work for very large planets. If you're looking for Earth-sized planets, you need something along the following lines. A very very large space telescope or two large space telescopes a long way apart and a digital way to cancel out the light from the star so the glare doesn't hide the planet or a way to measure the way the star's light is partly eclipsed when a planet passes in front of it. And if we could look at the spectrum of the planet's atmosphere and detect free oxygen it would be interesting, because the only process we know about that produces it is photosynthesis. Similarly for any other reactive gas like the halogens. Possibly an ET life form could breathe fluorine. In the absence of life all these gases would be combined with other elements in minerals. Try googling Daedalus Project. One day we'll send automatic probes to other stellar systems; maybe in a couple of decades.

Answer 3

Well first of all usually depending it's distance to a star , a planet will have light on it. Like the way our sun shines on Jupiter & saturn and even our moon !

As an Astronomer I get questions like this at our observatory and I know a planet hunter so he wrote this to answer your question ... his name is Andrew Gould and here is a page about him ...

http://researchnews.osu.edu/archive/suprerth.htm

~~~~~~~~~~~~~~
Hi ! I'm Andrew Gould

What us planet hunters do is take lots and lots of pictures every night of the sky and if we see one seems to be in a different spot than another picture we look tosee if it's been recorded from other observatory's all over Earth .
Then if it hasn't been a planet not found yet we ask then to photograph it's movements. Then if it hasn't been discovered it becomes a new planet !

Geoff Marcy .. One of the top planet hunters in the world sees if it's traveling by a star , he checks to see if that star has any known planets orbiting it . If there is no record of it ..it becomes a new planet and gets named by whoever discovered it !

That's how new planets get spotted!

Answer 4

Not to take away from a couple really good thorough answers here, but there is an article in the current (October 2006) issue of Sky and Telescope magazine describing some internet based computer models intended for play and learning about all there concepts.

Answer 5

There is also occultation, where the magnitude of the primary star is monitored for a planet which moves in front of it and reduces the light which reaches us. This only works when the planet is very large or close to its star, and requires a lot of observations.

Answer 6

The forthcoming Kepler mission has been designed with ultra-sensitive optics that should be able to detect the tiniest fluctuations of light coming from a star when a planet crosses its face. See these website for more detailed info about the Kepler mission ==>http://kepler.nasa.gov/media/KEPLER.SWF
http://planetquest.jpl.nasa.gov/Kepler/kepler_index.cfm

Answer 7

Another good website for this information is http://exoplanets.org
That's the website for the California & Carnegie Planet Search. In addition to listing all the currently known exoplanets, they also describe all the ways in which exoplanets can be detected.

Answer 8

idk... telescope? just kidding. i think NASA or sumwhere should make a space cruiser so tht then we can explore the universe. maybe even make hyperspeed so it wont take centuries to get pluto!