SPHEREx a New Mission to Investigate the History of the Universe
A new observatory launched into space on March 11, 2025. NASA’s Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) will survey the entire sky in 102 different colors, making the most colorful all-sky map ever. I
The Telescope
SPHEREx is a small telescope with a significant mission. This 20 cm diameter telescope, with an 11 deg x 3.5 deg field of view, will observe light in the Near Infrared (NIR) wavelength range. Its design, proven effective in previous missions, will allow SPHEREx to make a unique contribution to the field of astronomy.
SPHEREx, with its six 2K x 2K detector arrays, will obtain all the colors, or spectra, without the need for moving parts. It will achieve this through multiple exposures, placing a given source at multiple positions in the field of view, where it is measured at multiple wavelengths by repointing the spacecraft.
Orbit and operation
Unlike the large NIR telescopes like JWST, SPHEREx will orbit close to Earth. The spacecraft will be in a Sun-synchronous low Earth orbit, where its position relative to the Sun remains the same throughout the year, shielding the detector from its light and heat. Within an orbit of approximately 98-minutes, the SPHEREx telescope will observe 360-degree strip of the celestial sky. As Earth’s orbit around the Sun progresses, that strip slowly advances, enabling SPHEREx to image almost the entire sky in six months.
Similarly to other NIR telescopes, SPHEREx will operate at very low temperatures, about minus 350 degrees Fahrenheit (about minus 210 degrees Celsius). At higher temperatures, the telescope structure will generate an NIR glow brighter than the faint emission it will try to observe. The telescope achieves these lower temperatures via passive cooling and three cone-shaped shields. These shields protect the telescope from the heat of the Earth and the Sun. Also, beneath the shields, a mirrored structure directs the heat generated by the instrument out into space.
SPHEREx will observe in the same wavelength range, or type of light, as the NIR instruments in the James Webb Space Telescope (JWST), but with much less detail. In SPHEREx, the information of one pixel will be the blurred information from about 100 pixels of JWST; however, it will cover a much larger area in the sky, mapping the entire celestial sky four times in two years.
With its spectroscopic capabilities, SPHEREx will be able to create 3D maps of galaxies and the dust in our Galaxy. Observing each object in all those colors is incredibly important. It can reveal various properties of these objects, including their composition and, in the case of galaxies, their distance from Earth.
Scientific Goals
No other all-sky survey has performed spectroscopy in so many wavelengths and of so many sources as SPHEREx. In its two years of operation, SPHEREx will observe 450 million galaxies, providing insight into the physics behind the universe’s origin, the origin and history of galaxies, and a complete picture of the major sources of light in the universe. It will also look at more than 100 million stars in our own Milky Way, into stellar nurseries, regions where stars are born from gas and dust, and disks around stars where new planets could be forming. With its spectroscopy capabilities, SPHEREx will provide an unprecedented survey of the location and abundance of these icy compounds — water and organic molecules— giving researchers better insight into the interstellar chemistry that set the stage for life as we know it.
References:
1- https://www.nasa.gov/missions/spherex
2- https://www.jpl.nasa.gov/missions/spherex/
3- https://www.nasa.gov/missions/spherex/cosmic-mapmaker-nasas-spherex-space-telescope-ready-to-launch/
4- https://spherex.caltech.edu/page/instrument