SPHEREx – Discovering Our Cosmic Origins
- 24th Feb 2025
- Author: Katie Holland
After more than a decade in the making, NASA’s SPHEREx mission is getting ready to launch at the beginning of March 2025. The mission will survey our night skies to determine the origins of our Universe. How do the team hope to achieve such a lofty task?
Mission Origins and Spacecraft Design
The SPHEREx mission was first proposed back in December 2014, submitted by a team based at the California Institute of Technology. Initially being rejected as a Small Explorers (SMEX) mission, SPHEREx was accepted as a Medium-Class Explorers (MIDEX) mission in February 2019. Six years later, the mission is in its final stages of preparation, with just days to go until its scheduled launch.
The name SPHEREx stands for the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer – quite the mouthful. What this name means is that the telescope will use light to look at the history of our Universe and search for the presence of water ice out in space.
Not only will the spacecraft carry out a unique mission, it also has quite a unique design. It's quite small for a space telescope, coming in at about 3.2 metres, a little smaller than a MINI Cooper. The megaphone-like shape of the spacecraft acts as a cooling system. This is called its 'V-groove radiator.' Each of the three stacked shields redirects any incoming infrared light so that it bounces out of the shields and back out into space, effectively protecting the spacecraft from any radiation from the Sun or Earth.
Main Scientific Objectives
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![The ‘Hubble Ultra Deep Field,’ a view of nearly 10,000 galaxies imaged by the Hubble Space Telescope.]()
NASA, ESA, and S. Beckwith (STScI) and the HUDF Team Determine the origins of our Universe
One of the leading theories regarding the beginnings of our Universe is that of the Big Bang. This theory states that the Universe began as an infinitely small point that rapidly expanded to what surrounds us today. If this theory were to be true, scientists could study the distribution of galaxies and other celestial objects to assess the effects of this 'bang'. SPHEREx will do just that – by producing a 3D map of hundreds of millions of galaxies, the mission team will be able to study the cosmic inflation thought to have occurred after the birth of our Universe.
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![Star formation in the Circinus molecular cloud complex, imaged by WISE.]()
NASA/JPL-Caltech/UCLA Examine the potential of life on other worlds
One of the most essential ingredients to life, as we know it, is water – every living thing that exists on planet Earth needs access to water at some point in its life cycle to survive. So, when scientists are looking for signs of extra-terrestrial life out in space, often the places they look first will be the places thought to contain water. While SPHEREx will not study such places in great detail like other missions (for example Europa Clipper), it will highlight how these places may form. It is believed that as much as 99% of interstellar water exists in the form of ice. Such ice is abundant in nebulae and molecular clouds, on tiny frozen dust particles. SPHEREx will identify these regions densely populated with ice, studying how it may help to form new habitable worlds.
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![The Andromeda Galaxy, imaged by GALEX.]()
NASA/JPL-Caltech Explore the evolution of galaxies
SPHEREx will measure the collective light output of hundreds of millions of galaxies, including those that are not easily measured by other space telescopes, because they may be too distant or too faint. By using spectroscopy, SPHEREx will not only produce a more accurate measure of light in our Universe, but also how the amount of light may have changed over time. Although the movement of light seems instantaneous here on Earth (turning on a light is as simple as flicking a switch, no waiting required!), on the scale of space, that travel time becomes much more noticeable. By studying distant objects in space, scientists are essentially looking back in time, seeing those objects as they appeared maybe billions of years ago.
The Big Picture
Approximately every six months, SPHEREx will image the entire sky around the Earth, using countless short exposures to piece the sky together. SPHEREx won't be the first observatory to map the sky in this way, with space telescopes like Euclid operating in a similar fashion. However, it will be the first survey telescope of its kind to produce all-sky spectral maps – this means that the telescope will use a process called spectroscopy to identify different chemicals (most importantly water!) out in space. The light from the celestial objects observed is split down into individual colours, acting as a "fingerprint" for the object's composition. By scanning the sky in 102 colour bands, SPHEREx will make significant improvements over previous sky maps, allowing for more precise identification of cosmic objects.
That being said, SPHEREx will not be observing the sky in the spectacular detail allowed by other space telescopes, like James Webb. This isn't to the mission's detriment – SPHEREx isn't intended to seek out those finer details, but rather to take a look at the bigger picture. Once SPHEREx's sky maps are complete, scientists will be able to use them to search for areas of interest to be studied in greater detail by other space telescopes.
Full references / credits:
(Banner) Artist’s impression of SPHEREx in orbit around Earth. The spacecraft has a cross-sectional view to highlight the cooling system. Credit: NASA/JPL-Caltech
(1) SPHEREx spacecraft at Astrotech Corporation Facility at Vandenberg Space Force Base. Credit: NASA/JPL-Caltech
(2a) The ‘Hubble Ultra Deep Field,’ a view of nearly 10,000 galaxies imaged by the Hubble Space Telescope. Credit: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team
(2b) Star formation in the Circinus molecular cloud complex, imaged by WISE. Credit: NASA/JPL-Caltech/UCLA
(2c) The Andromeda Galaxy, imaged by GALEX. Credit: NASA/JPL-Caltech
(3) The SPHEREx integration and test team (BAE/JPL) in front of the spacecraft. Credit: NASA/JPL-Caltech
