How NASA's SPHEREx Maps the Entire Sky in 102 Colors

A Telescope That Sees the Universe in 102 Shades of Infrared

Most space telescopes zoom in on specific targets—a distant galaxy, a nearby star, a single nebula. SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer) does the opposite. Launched on March 12, 2025, aboard a SpaceX Falcon 9 rocket, this NASA observatory is designed to photograph the entire sky in 102 infrared colors over a two-year primary mission, creating the most detailed spectral map of the cosmos ever assembled.

The result is not just a pretty picture. Each of those 102 wavelengths carries unique chemical and physical information, letting scientists pursue three ambitious science goals at once: probing the aftermath of the Big Bang, hunting for life's building blocks in interstellar space, and cataloguing hundreds of millions of galaxies in three dimensions.

How SPHEREx Works—Spectroscopy Meets Assembly Line

At the heart of the spacecraft sits a modest 20-centimeter aluminum telescope—roughly the diameter of a dinner plate—paired with six mercury-cadmium-telluride detector arrays. The telescope is radiatively cooled to about 80 K (−193 °C), with detectors chilled even further to 55 K, so they can pick up faint infrared signals without interference from the spacecraft's own heat.

SPHEREx uses a technique called spectrophotometry. Instead of taking one broadband snapshot, it images the same strip of sky 102 separate times, each through a different narrow-band filter. Think of it as photographing every patch of the universe through 102 differently tinted lenses. The filters span wavelengths from 0.75 to 5.0 micrometers, covering near-infrared light invisible to the human eye.

As the spacecraft orbits from pole to pole, it captures roughly 3,600 images per day along a circular strip. Earth's motion around the Sun gradually shifts the field of view, so after six months SPHEREx has scanned the full sky once. Over its two-year mission it will complete four full-sky surveys, with each pass improving the sensitivity and precision of the data.

Goal 1: Fingerprints of the Big Bang

One of the deepest questions in cosmology is what happened in the first fraction of a second after the Big Bang. The leading theory—cosmic inflation—proposes that the universe expanded by a factor of a trillion trillion in less than a billionth of a trillionth of a trillionth of a second. That explosive growth should have left subtle statistical patterns in the way galaxies are distributed across space.

SPHEREx will measure the positions and distances of more than 450 million galaxies, building a 3D map large enough to test competing models of inflation. Some galaxies in the survey are so distant their light has traveled 10 billion years to reach the telescope, offering a window into the universe's deep past.

Goal 2: Mapping Interstellar Ice

Life on Earth depends on water, carbon dioxide, and organic molecules—and all of them can be found frozen onto tiny dust grains drifting through interstellar space. SPHEREx's infrared vision is specially tuned to detect the chemical signatures of water ice, carbon dioxide ice, carbon monoxide ice, and methanol.

Early results have already delivered. In its first year, SPHEREx mapped interstellar ice across regions of the Milky Way more than 600 light-years wide, including the turbulent star-forming complex Cygnus X. These "interstellar glaciers" sit inside giant molecular clouds where new stars and planetary systems are born—meaning the icy material SPHEREx tracks could eventually become part of future planets, oceans, and perhaps life.

Goal 3: The Hidden Glow of Galaxies

Beyond individual galaxies, SPHEREx measures the cosmic infrared background—the collective glow produced by all galaxies, including those too faint or too distant to observe individually. By analyzing fluctuations in this background light, scientists can learn about galaxy populations that have never been directly detected, filling in gaps in our understanding of cosmic history.

Why SPHEREx Matters

Where the James Webb Space Telescope excels at deep, narrow observations of individual targets, SPHEREx trades depth for breadth. Its all-sky approach means every astronomer—from cosmologists to planetary scientists—can mine its publicly released data for new discoveries. The mission has already revealed unexpected structures in interstellar ice distribution and is expected to generate insights for decades after its final survey is complete.

For a spacecraft with a mirror no bigger than a dinner plate, SPHEREx is answering some of the biggest questions in science: How did the universe begin? Where does water come from? And how many galaxies are really out there?