Spotting alien Earths on the cheap


Spotting Earth-like planets orbiting other stars is all the rage these days. But unless you have access to a space-based telescope it’s kinda tricky.

The problem is that the reflected light from a Jupiter-sized planet is roughly 10^4 fainter than the parent star. That’s hard to spot at any time but when this is coupled with the distortion that the Earth’s  atmosphere introduces, these planets become almost impossible to see.

One way around this is to use adaptive optics to smooth out distortions in the wavefront from the star system as it hits the telescope’s mirror. But these systems are expensive and the demands of higher resolution make them increasingly complex too.

Another option is to take exposures that are much shorter than the time over which the atmospheric distortion occurs. Then post processing of the image compared to the image of a reference star allows the distortion to be removed.

The trouble with this technique is that the wavefront distortion varies over the entire area of the telescope’s mirror. So this kind of processing ends up averaging the distortion rather than removing it.

Takayuki Kotani from the  Observatoire de Paris in France et amis are pioneering a technique called pupil remapping that could get around this.  Their idea is to place a bundle of optical fibres at the focal point of the telescope. These channel the light from each point in the mirror separately, which avoids the problem of averaging out the distortion and allows much better image processing.

They’ve tested the idea on an optical bench showing that it can achieve near theoretical performance. Installed in a decent telescope, it should allow a dynamic range of around 10^6. That will allow the detection of much fainter planets than is now possible and at a fraction of the cost of high resolution adaptive optics  or space-based telescopes.

Expect to see this technique producing good results in ground-based telescopes within months.

Ref: Pupil Remapping for High Contrast Astronomy: Results From an Optical Testbed

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