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Upcoming space telescope can pick out distant exoplanets against glare of stars

An optical engineer at NASA’s Jet Propulsion Laboratory, in Pasadena, California, Camilo Mejia Prada, shines a light on the interior of a testbed for an instrument called a coronagraph that will fly aboard the WFIRST space telescope. NASA/JPL-Caltech/Matthew Luem

For the last few years, NASA has been quietly working away on a new space telescope even more advanced than the Hubble Space Telescope. The Wide Field Infrared Survey Telescope (WFIRST) was announced in 2016 and will have 100 times the field of view of the Hubble. Now, NASA has shared an update on the progress of the WFIRST and in particular how its coronagraph instrument will operate.

A coronagraph is a tool for blocking out the glare of bright sunlight so fainter stars and the planets that orbit around them can be observed. NASA cheerfully describes the instrument as a pair of “starglasses,” created from a “system of masks, prisms, detectors and even self-flexing mirrors” which can block out the light from stars so it doesn’t overwhelm the faint light given off by planets. “What we’re trying to do is cancel out a billion photons from the star for every one we capture from the planet,” Jason Rhodes, a WFIRST project scientist explained in a statement.

The complex WFIRST coronagraph has just completed its preliminary design review, which means the design has met requirements of schedule and budget so construction of the hardware can begin. The instrument includes two flexible mirrors that change shape in response to the movements of thousands of actuators, allowing compensation for tiny flaws in the optics. “Changes on the mirrors’ surfaces are so precise they can compensate for errors smaller than the width of a strand of DNA,” NASA explained in a blog post.

NASA has some practice with building coronagraphs, as one is also included in the James Webb Space Telescope, but the one on WFIRST will have stronger starlight suppression than the one in the James Webb. In terms of its ability to distinguish a planet from a star, “WFIRST should be two or three orders of magnitude more powerful than any other coronagraph ever flown,” according to Rhodes.

The aim is to launch WFIRST in the mid-2020s when it will be used to study topics like dark energy as well as being used to detect distant exoplanets.

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