WFIRST’s findings with results from NASA’s Kepler and Transiting Exoplanet Survey Satellite (TESS) missions will complete the first planet census that is sensitive to a wide range of planet masses and orbits, bringing us a step closer to discovering habitable Earth-like worlds beyond our own.
WFIRST data can spot transits (planets when they pass in front of their host star in events called transits)too, but the mission will primarily watch for the opposite effect little surges of radiance produced by a light-bending phenomenon called microlensing.
WFIRST’s microlensing survey will help us find analogs to every planet in our solar system except Mercury, whose small orbit and low mass combine to put it beyond the mission’s reach. WFIRST will find planets that are the mass of Earth and even smaller perhaps even large moons, like Jupiter’s moon Ganymede.
WFIRST will find planets in other poorly studied categories, too. Microlensing is best suited to finding worlds from the habitable zone of their star and farther out. This includes ice giants, like Uranus and Neptune in our solar system, and even rogue planets worlds freely roaming the galaxy unbound to any stars.
WFIRST is an infrared telescope, it will see right through the clouds of dust that block other telescopes from studying planets in the crowded central region of our galaxy. Most ground-based microlensing observations to date have been in visible light, making the center of the galaxy largely uncharted exoplanet territory.
WFIRST will explore regions of the galaxy that haven’t yet been systematically scoured for exoplanets due to the different goals of previous missions.
Planets orbiting the foreground star may also modify the lensed light, acting as their own tiny lenses. The distortion they create allows astronomers to measure the planet’s mass and distance from its host star. This is how WFIRST will use microlensing to discover new worlds.