While the Radial Velocity and Transit methods account for the majority of exoplanet discoveries, other more exotic techniques can add a richer palette to the picture of the alien world.
Gravitational Microlensing: A Single-Use Solar Telescope
If direct imaging is a Nikon digital camera, then
Gravitational Microlensing is a godly super-camera… except disposable. Every so often, the gravitational field of a sun and/or planet can form what amounts to a giant lens, magnifying the light of a distant background star. This gives us windows to star systems otherwise too far off to view. Unfortunately, the “lensing” effect happens only once (ever) in brief windows of only weeks or days, and is a one-time-only deal, dealing with planets at distances too far to be later investigated by other methods
(Beaulieu, Discovery...Through Gravitational Microlensing) .
Astroseismology: Solar Sonics
Earthquakes, dangerous as they are, at least provide cheerful geologists the means to study the Earth’s interior via the frequency of its vibrations.
Astroseismology, meanwhile, monitors distant “star-quakes” for oscillations in brightness as the entire star vibrates, or “rings.”
As Natalie Batalha explained to NatGeo, "A tiny star would yield different [vibration] frequencies than a large one, just as when you strum a violin you're going to get a different sound than when you strum a cello.”
(Lovett, National Geographic, 10-Jan-11)
Studying these pulses can allow astronomers to characterize a star almost as intimately as our own Sun, including its size, mass, and age, and the stage and direction in its lifetime. While this technique is targeted at stars rather than planets, all these traits in turn hint at the characteristics of a planet; a star’s size will reveal its planets’ size, and the star’s life-stage can allow astronomers to judge the planets’ likelihood for alien life.
Pulsar Timing: A Syncopated Tick
Pulsars, the super-dense remains of former stars, are so named for their regular pulse of radio-waves into space. The pulse is so regular that any variation can hint at a wobble in its orbit, similar to the radial velocity method. By noting the changes in the pulsar’s position through pulse anomalies, we can gain a highly sensitive means of planet detection, capable of picking up exoplanets so small they normally go under the radar of the other techniques, down to a tenth the size of earth
(Townsend, The Search for Exoplanets).
The downside? Look at the sky. See lots of stars? Good. See any pulsars? If you didn't, this is probably because you're not at a Chilean observatory. Pulsars are, unfortunately, quite elusive, and for this reason, the Pulsar Timing method itself remains unreliable.
Painting the Picture
In the end, no single one of these techniques is a magic bullet in certainty or scope. To paint a real picture of a planet, one worthy of a prog-rock album cover, requires the combination of several methods. For example, when combining transit (which measures a planet’s size) with the radial velocity method (which determines the planet's mass) one can determine the density of the planet, and hence learn something about the planet's physical structure. Each technique has a unique strength to offer, of which we, Earth’s nerdy populace, are the ultimate beneficiaries.
In the next article, we’ll continue by checking out some of the top tools used by modern planet hunters, including the volcano-top spectrometers, French star-quake hunters, the SuperWASP, and of course, Johannes Kepler’s likely favorite, the Kepler Space Camera.
There are no comments. Get the conversation started!
