NASA’s SPHEREx Space Telescope will create the world’s most complete sky survey

The sky is about to get a lot clearer.

NASA’s latest infrared space telescope, SPHEREx—short for Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer—will assemble the world’s most complete sky survey to better explain how the universe evolved.

The $488 million mission will observe far-off galaxies and gather data on more than 550 million galaxies and stars, measure the collective glow of the universe, and search for water and organic molecules in the interstellar gas and dust clouds where stars and new planets form. 

The 1107-lb., 8.5 x 10.5-foot spacecraft is slated to launch March 2 at 10:09 pm (ET) aboard a SpaceX Falcon 9 rocket from Vandenberg Space Force Base in California. (Catch the launch on NASA+ and other platforms.) From low-Earth orbit, it will produce 102 maps in 102 infrared wavelengths every six months over two years, creating a 3D map of the entire night sky that glimpses back in time at various points in the universe’s history to fractions of a second after the Big Bang nearly 14 billion years ago. Onboard spectroscopy instruments will help determine the distances between objects and their chemical compositions, including water and other key ingredients for life.

SPHEREx Prepared for Thermal Vacuum Testing [Photo: NASA/JPL-Caltech/BAE Systems]

Mapping how matter dispersed over time will help scientists better understand the physics of inflation—the instantaneous expansion of the universe after the Big Bang and the reigning theory that best accounts for the universe’s uniform, weblike structure and flat geometry. Scientists hypothesize the universe exploded in a split-second, from smaller than an atom to many trillions of times in size, producing ripples in the temperature and density of the expanding matter to form the first galaxies.

“SPHEREx is trying to get at the origins of the universe—what happened in those very few first instances after the Big Bang,” says SPHEREx instrument scientist Phil Korngut. “If we can produce a map of what the universe looks like today and understand that structure, we can tie it back to those original moments just after the Big Bang.”

[Photo: BAE Systems/Benjamin Fry]

SPHEREx’s approach to observing the history and evolution of galaxies differs from space observatories that pinpoint objects. To account for galaxies existing beyond the detection threshold, it will study a signal called the extragalactic background light. Instead of identifying individual objects, SPHEREx will measure the total integrated light emission that comes from going back through cosmic time by overlaying maps of all of its scans. If the findings highlight areas of interest, scientists can turn to the Hubble and James Webb space telescopes to zoom in for more precise observations.

To prevent spacecraft heat from obscuring the faint light from cosmic sources, its telescope and instruments must operate in extreme cold, nearing—380 degrees Fahrenheit. To achieve this, SPHEREx relies on a passive cooling system, meaning no electricity or coolants, that uses three cone-shaped photon shields and a mirrored structure beneath them to block the heat of Earth and the Sun and direct it into space.

Searching for life

In scouting for water and ice, the observatory will focus on collections of gas and dust called molecular clouds. Every molecule absorbs light at different wavelengths, like a spectral fingerprint. Measuring how much the light changes across the wavelengths indicates the amount of each molecule present.

“It’s likely the water in Earth’s oceans originated in a molecular cloud,” says SPHEREx science data center lead Rachel Akeson. “While other space telescopes have found reservoirs of water in hundreds of locations, SPHEREx will give us more than nine million targets. Knowing the water content around the galaxy is a clue to how many locations could potentially host life.”

More philosophically, finding those ingredients for life “connects the questions of how `did the universe evolve?’ and `how did we get here?’ to `where can life exist?’ and `are we alone in that universe?’” says Shawn Domagal-Goldman, acting director of NASA’s Astrophysics Division.

Solar wind study

The SpaceX rocket will also carry another two-year mission, the Polarimeter to Unify the Corona and Heliosphere (PUNCH), to study the solar wind and how it affects Earth. Its four small satellites will focus on the sun’s outer atmosphere, the corona, and how it moves through the solar system and bombards Earth’s magnetic field, creating beautiful auroras but endangering satellites and spacecraft. The mission’s four suitcase-size satellites will use polarizing filters that piece together a 3D view of the corona capture data that helps determine the solar wind speed and direction.

“That helps us better understand and predict the space weather that affects us on Earth,” says PUNCH mission scientist Nicholeen Viall. “This`thing’ that we’ve thought of as being big, empty space between the sun and the Earth, now we’re gonna understand exactly what’s within it.”

PUNCH will combine its data with observations from other NASA solar missions, including Coronal Diagnostic Experiment (CODEX), which views the inner corona from the International Space Station; Electrojet Zeeman Imaging Explorer (EZIE), which launches in March to investigate the relationship between magnetic field fluctuations and auroras; and Interstellar Mapping and Acceleration Probe (IMAP), which launches later this year to study solar wind particle acceleration through the solar system and its interaction with the interstellar environment.

A long journey

SPHEREx spent years in development before its greenlight in 2019. NASA’s Jet Propulsion Laboratory managed the mission, enlisting BAE Systems to build the telescope and spacecraft bus, and finalizing it as the Los Angeles’s January wildfires threatened its campus. Scientists from 13 institutions in the U.S., South Korea, and Taiwan will analyze the resulting data, which CalTech’s Infrared Processing & Analysis Center will process and house, and the NASA/IPAC Infrared Science Archive will make publicly available.

[Image: JPL]

“I am so unbelievably excited to get my hands on those first images from SPHEREx,” says Korngut. “I’ve been working on this mission since 2012 as a young postdoc and the journey it’s taken from conceptual designs to here on the launcher is just so amazing.”

Adds Viall, “All the PowerPoints are now worth it.”

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