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 telescope launched in March 2025, to survey the whole sky in the near infrared. Its 20-cm telescope has a wide field of view and an angular resolution of 6.2 arcseconds. It carries out spectrography over a wavelength-range of 0.75 to 5.0 micrometers, with spectral resolutions ranging from 41 to 130. It operates in a low, polar Earth orbit, completing an all-sky survey each 6 months. The spacecraft's primary mission is to cover the sky four times over two years.

It carries out spectrography using filters that effectively cover 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 continuously scanned so that at any instant, portions of the captured image are capturing different wavelengths. The spacecraft design minimizes moving parts.

The mission 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 to uncover some gravitational lensing. Cross correlation with data from other surveys is expected to confirm Sunyaev-Zel'dovich effects and gravitational lensing effects, and correlation-efforts are expected to produce new information about large scale structure.