SPHEREx

SPHEREx (for Spectro-photometer for the History of the Universe, epoch of reionization, and Ices Explorer) is a NASA Medium-class Explorer Program (MIDEX) space mission for a telescope and spectrograph to survey the whole sky in the near infrared, launched in March 2025. It is a NASA MIDEX (Medium-class Explorers Program) project for a 20-cm telescope and spectrograph with a wide field of view and an angular resolution of 6.2 arcseconds, with spectrography covering a wavelength-range of 0.75 to 5.0 micrometers with spectral resolutions ranging from 41 to 130. It is to operate in a low, polar Earth orbit for two years, completing an all-sky survey each 6 months.

The spectrography is accomplished with filters effectively covering enough channels to produce the spectral resolution: they are linearly variable filters, which vary in the band they allow across one direction. The sky is to be continuously scanned so that at any instant, portions of the captured image are capturing different wavelengths. The spacecraft design minimizes moving parts. It is aimed at a number of scientific goals for which such a survey is useful, including more data regarding the history of large scale structures and galaxy formation as well as measurement of the water in molecular clouds that could contribute to habitable extra-solar planets. It is expected that it will uncover some gravitational lensing, and that cross correlation with data from other surveys will confirm Sunyaev-Zel'dovich effects and gravitational lensing effects, and correlation-efforts will produce new information about large scale structure.