WFIRST, the Wide Field Infrared Survey Telescope, is a NASA flagship mission due to launch in the mid-2020s. It is designed to study dark energy and exoplanets, as well as providing a general wide-field infrared observing facility for astronomers and demonstrating the technologies necessary to directly image Earth-like planets. I work on the mission’s microlensing survey, which is expected to detect thousands of exoplanets, enabling the study of exoplanet demographics of planets as small as Mars beyond ~1 AU. I am the lead author on a paper describing detailed simulations of the WFIRST microlensing survey.
WFIRST will detect planets using the microlensing technique. Microlensing occurs when two stars become very precisely aligned with Earth due to their relative motions. When this happens, light from the more distant star is bent around the nearer star towards Earth, magnifying the light of the background star and causing it to appear brighter (hence the term “lensing” – the “micro” comes from the very precise alignment needed to see the effect). This brightening only lasts a short time as the stars move into and back out of alignment, and only occurs once for any given pair of stars. We visualize this brightening using a lightcurve, a plot of brightness against time, like the one shown below. If a planet orbiting the nearer star happens to lie close to the path of light being bent around the star, it can add its own lensing effect, and enable its detection by astronomers. Microlensing is most sensitive to planets residing a few AU from their host stars (an AU – astronomical unit – is the distance between Earth and the sun), and can detect planets as small as the larger moons in our solar system (e.g., Earth’s Moon, Jupiter’s Ganymede, and Saturn’s Titan).
By observing from space and using infrared detectors, WFIRST can search for microlensing through the dust that obscures the center of the Milky Way, where stars are most crowded and random alignments occur more frequently. It’s large, 2.4-meter telescope provides images 3 times sharper than possible from the best sites on the ground in the best conditions, and its large-format 288 megapixel camera allows it to capture ~30 million stars in each image. Additionally, from space WFIRST can observe stars continuously, allowing it to capture the short-lived signatures of planets in microlensing lightcurves, which can last for as little as 1 hour. The images below show where WFIRST will search for microlensing (near to the center of the Milky Way), and what its images will look like compared to ground-based telescopes (WFIRST on the left, ground-based telescopes on the right).
