The SPHEREx Satellite Mission

SPHEREx, a NASA explorer satellite launched on 11 March 2025, is carrying out the first all-sky near-infrared spectral survey. The satellite observes in 102 spectral bands from 0.75 to 5.0 um with a resolving power ranging from 35 to 130 in 6.2 arcsecond pixels. The observatory obtains a 5-sigma depth of 19.5 - 19.9 AB mag for 0.75 to 3.8 um and 17.8 - 18.8 AB mag for 3.8 to 5.0 um after mapping the full sky four times over two years. Scientifically, SPHEREx will produce a large galaxy redshift survey over the full sky, intended to constrain the amplitude of inflationary non-Gaussianity. The observations will produce two deep spectral maps near the ecliptic poles that will use intensity mapping to probe the evolution of galaxies over cosmic history. By mapping the depth of infrared absorption features over the Galactic plane, SPHEREx will comprehensively survey the abundance and composition of water and other biogenic ice species in the interstellar medium. The initial data are rapidly released in the form of spectral images to the public. The project will release specialized data products over the life of the mission as the surveys proceed. The science team will also produce specialized spectral catalogs on planet-bearing and low-mass stars, solar system objects, and galaxy clusters 3 years after launch. We describe the design of the instrument and spacecraft, which flow from the core science requirements. Finally, we present an initial evaluation of the in-flight performance and key characteristics.

💡 Research Summary

The paper presents a comprehensive overview of the SPHEREx (Spectro‑Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer) mission, a NASA Explorer‑class satellite launched on 11 March 2025. SPHEREx conducts the first all‑sky near‑infrared (NIR) spectral survey, covering 0.75–5 µm in 102 contiguous spectral channels with a resolving power of λ/Δλ ≈ 35–130 and a pixel scale of 6.2 arcseconds. The instrument combines large‑format HgCdTe detector arrays, a three‑stage off‑axis telescope, and a Linear Variable Filter (LVF) that provides wavelength‑dependent transmission across the focal plane, enabling simultaneous acquisition of the full spectral range in a single scan.

The spacecraft’s thermal architecture employs a three‑stage radiative cooler that brings the detectors to ≈7 K, while a two‑stage cooler maintains the optics at ≈30 K, achieving the low dark current and noise required for a 5σ depth of 19.5–19.9 AB mag (0.75–3.8 µm) and 17.8–18.8 AB mag (3.8–5 µm). Over a two‑year baseline the satellite maps the entire sky four times, delivering a total of several hundred million galaxy spectra and millions of stellar and solar‑system object spectra. Redshift precision of σ_z ≈ 0.003 is targeted, sufficient for large‑scale‑structure (LSS) analyses.

Three primary science objectives drive the mission design. First, SPHEREx aims to constrain primordial non‑Gaussianity (parameter f_NL) by measuring both the galaxy power spectrum and bispectrum across the full sky. The scale‑dependent bias induced by f_NL enhances clustering on the largest scales; the bispectrum’s squeezed‑triangle configurations provide an independent probe. With hundreds of millions of galaxies, SPHEREx is expected to improve upon the Planck CMB constraint (f_NL = −0.9 ± 5.1) by a factor of one to two, potentially reaching |f_NL| ≈ 1, thereby discriminating between multi‑field and single‑field inflationary models.

Second, the mission investigates the history of galaxy formation through measurements of the extragalactic background light (EBL) fluctuations. By exploiting the many narrow spectral bands, cross‑spectra between adjacent channels trace redshift‑dependent emission, while auto‑spectra capture linear (2‑halo), non‑linear (1‑halo), and Poisson components of the clustering signal. Two deep fields (~100 deg² each) near the ecliptic poles receive substantially higher integration time, enabling detection of faint high‑redshift (z ≥ 6) signatures such as Ly α, Lyman‑break, and rest‑frame optical lines (