The SPHEREx Satellite Mission

TL;DR

SPHEREx addresses how the early universe and cosmic structures have evolved by delivering the first all-sky near-infrared spectral survey. It utilizes a passive-cooling, LVF-based spectrometer on a 3-mirror off-axis telescope to obtain 102 channels from 0.75–5 μm with $R \sim 35-130$, producing four full-sky maps over two years. The work integrates three core science pillars—inflationary non-Gaussianity via power spectrum and bispectrum measurements, the history of galaxy formation through EBL intensity mapping, and interstellar ices via absorption spectra toward millions of targets—plus three legacy spectral catalogs and public data releases through IRSA. The mission design emphasizes systematic-error control, high-sensitivity photometry, and robust data processing pipelines, enabling broad community access and synergies with contemporaneous facilities such as JWST, Gaia, Euclid, and Euclid-like surveys, with practical implications for cosmology, galaxy evolution, and astrochemistry.

Abstract

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.

Figures (21)

• Figure 1: Diagram of the SPHEREx observatory, showing (from top to bottom) the three conical photon shields with a cutaway view, the telescope, radiator panel for the mid-wave infrared (MWIR) detectors, the MWIR and short-wave infrared (SWIR) focal plane arrays (FPAs), and the 3-stage V-groove radiator assembly with penetrating bipods for supporting the telescope assembly. The BAE spacecraft at the bottom provides pointing, power, and telemetry and houses the instrument readout electronics.
• Figure 2: SPHEREx aims to establish strong constraints on non-Gaussianity $f_{NL}$ and running of the spectral index $\alpha_s$ in order to discriminate between broad classes of inflation models. The plot identifies families of models, where the blue-shaded region illustrates the distribution of plausible multi-field models deputter17 with $|f_{NL}| \sim 1$, while single-field models with $|f_{NL}| < 10^{-2}$ fall along the y-axis. Slow-roll models are shown in the hatched region with $|\alpha_s| < 10^{-3}$. The current range of allowed parameters from Planck CMB data is shown by the blue ellipse. SPHEREx's accuracy is shown for the power spectrum (PoS, yellow), the bispectrum (BiS, orange) and the combination (red). While the centers of the SPHEREx ellipses are unknown, we place them at a location that would rule out single-field inflation for illustration.
• Figure 3: Color of EBL fluctuations on large scales, $\ell \simeq 10^3$. Measurements from CIBER and Spitzer from feder25 (magenta points), all using the same mask of $\left\{\rm{J}=16.9,\rm{H}=16.9,\rm{IRAC}1=17.8 \right\}$, clearly exceed expectations from known galaxy populations fainter than the masking threshold (light green). Simple IHL models that adopt a linear relationship between the IHL fraction and dark matter halo mass (magenta band) can provide fluctuations at a level comparable to these available measurements, as suggested by previous work cooray12zemcov14. The sensitivity levels along the bottom (black lines) indicate SPHEREx's statistical sensitivity in the North Deep Field in a single $\ell$ bin $500 \leq \ell < 2000$ using idealized Knox errors, both in individual spectral channels (upper curves in black) and after binning into ten broad spectral bands (lower flat lines in black). Note that this $\ell$ bin, chosen to match the angular scale of linear galaxy clustering, is slightly wider than the measurements of feder25 at $\ell \sim$ 1300. Clearly, SPHEREx has sensitivity to galaxy populations across a broad range of redshift sub-intervals, including the EoR, as indicated by the annotated colored curves (model predictions from Mirocha et al., in prep.). Many spectral features may be visible in the EoR component, starting with Ly-$\alpha$ and the Lyman break at the blue edge of the wavelength range, and extending through strong rest-frame optical lines $[\rm{O}\textsc{II}]$, $[\rm{O}\textsc{III}]+\rm{H}\beta$, and finally $\rm{H}\alpha$ near the red edge of the SPHEREx band.
• Figure 4: SPHEREx measures the abundances and properties of ice species by taking absorption spectra toward background stars and protostars. This comprehensive survey toward $\sim$10 million targets spans the evolutionary stages of star and planet formation from dense molecular clouds to young solar systems with planetary disks.
• Figure 5: All-sky and deep field point source sensitivity derived from flight data (see § \ref{['ssec:sensitivity']} and Figure \ref{['fig:sensitivity']}) as a function of wavelength. The thick red curve corresponds to the all-sky sensitivity, while the thin red curve corresponds to the deep field sensitivity, both after 2 years of observations. The black dots represent the sensitivity in the 102 independent wavelength channels. For reference, we add the depth of unWISE Lang14Meisner17Meisner19Meisner22, 2MASS Skrutskie06 and the DESI Legacy Imaging Surveys catalog Dey19. Note that co-adding the SPHEREx spectral channels within the broad W1 and W2 bands gives an all-sky sensitivity that is very close to that of unWISE.