Science

Science Goals and Objectives

NASA’s SPHEREx observatory will create a 3D map of the entire sky in 102 colors (each an individual wavelength of light) to help scientists answer big-picture questions about the origins of our universe, galaxies, and key ingredients for life in our galaxy, such as water. While this all-sky map can be used for a wide variety of science investigations, the SPHEREx mission will focus on three key science goals:

• Create a 3D map of hundreds of millions of galaxies in order to study inflation, which is the rapid expansion of the universe by a trillion-trillion-fold in less than a second after the big bang.
• Measure the total collective glow of galaxies near and far, including the light from sources that may be hidden or haven’t yet been individually observed, such as faint or distant galaxies or populations of stars that have been pushed to peripheries of galaxies.
• Search the Milky Way galaxy for hidden reservoirs of water, carbon dioxide, and other essential ingredients for life, and measure their abundance and availability for newly forming planets.

Science Technique

SPHEREx will achieve these goals using a technique called spectroscopy, which splits light into different wavelengths, like a prism creates a rainbow from sunlight.

What human eyes perceive as colors are actually different wavelengths of light. The wavelengths that SPHEREx can detect — in the infrared range — are slightly longer than what human eyes can see. When astronomers image a cosmic object, they see all the wavelengths emitted by that object mixed together. Through spectroscopy, SPHEREx can separate the colors to reveal the composition of objects; that’s possible because chemical elements and molecules leave a unique signature in the colors they absorb and emit. Spectroscopy can also help scientists measure how far away objects are, making it ideal for studying distant galaxies and mapping their locations in 3D.

The observatory will sweep across the sky, taking about 600 exposures each day that can be combined to create an all-sky mosaic. Every section of the sky will be imaged 102 times, each time using a different color filter that blocks all wavelengths except one. Combining those images, scientists can see the total emission from that section of the sky or look at an individual wavelength.

Wavelength Range

The SPHEREx telescope will collect light in the infrared range, which includes some of the predominant wavelengths emitted by stars and galaxies, making it ideal for SPHEREx’s study of the collective galactic glow. Infrared is also useful for studying distant galaxies, whose visible light is stretched by the universe’s expansion, shifting it into the infrared range. A third advantage of operating in the infrared: The spectroscopic chemical signatures for water, carbon dioxide, and carbon monoxide are in that range.

Survey Telescopes vs. Targeted Telescopes

Generally speaking, most space telescopes are either survey telescopes or targeted telescopes. As a survey telescope, SPHEREx is designed to study large portions of the sky relatively quickly. Other survey telescopes include the first infrared space telescope, NASA’s IRAS mission (short for Infrared All-Sky Survey), which launched in 1983. Many others have followed, including NASA’s WISE (Wide-Field Infrared Survey Explorer) launched in 2009, the agency’s upcoming Nancy Grace Roman Space Telescope, which is scheduled to launch by 2027, and the ESA (European Space Agency) Euclid telescope, which launched in 2023.

Targeted telescopes typically have narrower fields of view but higher resolution compared to survey telescopes and are capable of observing fewer objects in much better detail. NASA’s Webb and Hubble space telescopes are prime examples.

Scientists use both types of telescopes to understand the universe. Survey missions, for example, can scan large sections of the sky and identify objects of interest for targeted telescopes to study in more detail. Targeted telescopes can provide intricate details about how individual objects like stars and black holes affect their surroundings, while survey telescopes can provide information about the average properties of these objects on a population level.

Science Goals in Detail

Many space telescopes look closely at cosmic objects to provide insights into the cosmos, but trying to answer some questions about the universe requires a wider view. Here’s what scientists expect to learn from SPHEREx’s spectroscopic all-sky map.

Origins of the Universe

The mission will map the position of hundreds of millions of galaxies in 3D to study the physics of inflation, the event that caused the universe to expand by a trillion-trillionfold in less than a second after the big bang. Because this event subtly influenced the distribution of matter in the universe, taking a precise look at the distribution of galaxies today enables scientists to investigate the turbulent beginnings of the universe nearly 14 billion years ago.

No other known event or process in the universe involves the amount of energy required to drive inflation; studying it presents a unique opportunity to understand more deeply how our universe works. By mapping the positions of so many galaxies and measuring the average distribution of matter across the universe, SPHEREx will help dramatically narrow down the number of theoretical models of inflation.

Origins of the Galactic Glow

By measuring the collective glow created by all galaxies near and far, SPHEREx will calculate the total amount of light emitted by galaxies over cosmic history. Scientists have tried to estimate this total light output by observing individual galaxies and extrapolating to the trillions of galaxies in the universe. But such counts may leave out some faint or hidden sources of light — galaxies that are too small or too distant for telescopes to easily detect, for instance, or stars at the periphery of galaxies, which may have been pushed there when two galaxies merged. SPHEREx will give scientists a more complete picture of all the objects and sources of light in the universe.

Because light takes time to travel through space, we see distant objects as they were in the past: Astronomers looking at objects billions of light-years away are seeing those objects as they were billions of years ago. Spectroscopy enables scientists to discern how far light has traveled to reach us and when in the universe’s history it was released. Using the technique, SPHEREx can also show astronomers how this total galactic light output has changed over time. For example, the telescope may reveal that the first generation of galaxies in the universe produced more light than previously thought, either because there were more of them or because they were bigger and brighter than current estimates suggest.

Having a better estimate of the total number of galaxies at different epochs in the universe’s history can improve computer models and simulations of how galaxies form and evolve.

Origins of Water in the Milky Way

How do planets form and where do water and other ingredients for life as we know it come from? SPHEREx will make more than 9 million observations of the Milky Way galaxy to search for hidden reservoirs of water, carbon dioxide, and other molecules in the space between stars. In this largely empty space, gas and dust can cluster together in molecular clouds, which are dense regions where stars and planets eventually form. These clouds likely contain the raw materials that could form rocky worlds with large oceans, like Earth.

Previous attempts to look for these materials in molecular clouds in the form of gas have found less of them than scientists expected. Further analysis and observations suggest that significant amounts of water and other molecules likely exist not as gas but in the form of ice attached to small dust grains, which can eventually become part of newly forming planets.

Spectroscopy can be used to identify water ice and other frozen elements because these molecules leave a specific chemical fingerprint in the wavelengths of light they absorb and emit — wavelengths that SPHEREx can detect.

Targeted observatories have detected these ices in our galaxy. As a survey telescope, SPHEREx will make millions of measurements, providing a comprehensive view of the abundance and distribution of these molecules throughout the galaxy. Targeted telescopes could then follow up on these observations and obtain more detailed views of individual molecular clouds or even newly forming star and planet systems.