Traditional methods of exoplanet detection all rely on indirect means of inferring the existence of orbiting bodies. These methods include:
- Astrometry – watching a star move slightly due to the gravitational influence of a nearby planet
- Observing Doppler shifts of the stars spectrum due to the star's movement
- Observing the amount of light from a star change as an extrasolar planet transits the star, preventing a portion of the light from reaching the observer.
- Pulsar timing
- Gravitational microlensing
- Observing radiation from Circumstellar disks in the infrared.
All of these methods provide convincing evidence for the existence of extrasolar planets, however none of them provide actual images of the planets.
The goal of the New Worlds Mission is to block the light coming from nearby stars with an occulter. This would allow the direct observation of orbiting planets. The occulter would be a large sheet disc flown thousands of kilometers along the line of sight. The disc would likely be several tens of meters in diameter and would fit inside existing expendable launch vehicles and be deployed after launch.
One difficulty with this concept is that light incoming from the target star would diffract around the disc and constructively interfere along the central axis. Thus the starlight would still be easily visible, making planet detection impossible. This concept was first famously theorized by Siméon Poisson in order to disprove the wave theory of light, as he believed the existence of a bright spot at the center of the shadow to be nonsensical. However Dominique Arago experimentally verified the existence of the spot of Arago. Fortunately this effect can be negated by specifically shaping the occulter. By adding specially shaped petals to the outer edge of the disc, the spot of Arago will disappear, allowing the suppression of the star's light.
This technique would make planetary detection possible for stars within approximately 10 parsecs (about 32 light years) of Earth. It is estimated that there could be as many as several thousands of exoplanets within that distance.
Read more about this topic: New Worlds Mission
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