NASA’s WFIRST telescope has a new approach to the hunt for exoplanets

NASA is working on a new instrument for spotting distant exoplanets — the Wide Field Infrared Survey Telescope, or WFIRST. This tool could be used to identify not only small, distant planets, but also other cosmic bodies like brown dwarfs and black holes.

Artist’s illustration of the WFIRST spacecraft.
Artist’s illustration of the WFIRST spacecraft. NASA’s Goddard Space Flight Center

Spotting exoplanets with microlensing

Most instruments for detecting exoplanets, such as NASA’s exoplanet hunter satellite TESS, work by using the transit method. This is where telescopes observe distant stars and look for periodic dimming in their brightness, which suggests the presence of a planet passing between the star and the telescope in an event called a transit.

WFIRST, however, will use both the transit method and a different method called microlensing. This is where, when a small planet passes in front of a star, it bends the light in a way that can be observed from a great distance. This technique works only on infrequent events where stars align just so, but the signals that these events produce are stronger than the signals from the transit method and can be used to detect smaller or more distant planets.

“Microlensing signals from small planets are rare and brief, but they’re stronger than the signals from other methods,” David Bennett, who leads the gravitational microlensing group at NASA’s Goddard Space Flight Center, said in a statement. “Since it’s a one-in-a-million event, the key to WFIRST finding low-mass planets is to search hundreds of millions of stars.”

WFIRST will make its microlensing observations in the direction of the center of the Milky Way galaxy. The higher density of stars will yield more exoplanet detections.
WFIRST will make its microlensing observations in the direction of the center of the Milky Way galaxy. The higher density of stars will yield more exoplanet detections. NASA's Goddard Space Flight Center/CI Lab

“Trying to interpret planet populations today is like trying to interpret a picture with half of it covered,” said Matthew Penny, an assistant professor of physics and astronomy at Louisiana State University in Baton Rouge who led a study to predict WFIRST’s microlensing survey capabilities. “To fully understand how planetary systems form we need to find planets of all masses at all distances. No one technique can do this, but WFIRST’s microlensing survey, combined with the results from Kepler and TESS, will reveal far more of the picture.”

“WFIRST’s microlensing survey will not only advance our understanding of planetary systems,” said Penny, “it will also enable a whole host of other studies of the variability of 200 million stars, the structure and formation of the inner Milky Way, and the population of black holes and other dark, compact objects that are hard or impossible to study in any other way.”

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