Deep space exploration as NASA’s SPHEREx maps the galaxies

In a world that often measures itself in days, years, decades and centuries, a second seems insignificant. But a lot can happen in an instant. It takes a lightning bolt just 30 microseconds to strike a tree or a house, for example. When you touch something hot or cold, it takes the nerve impulse mere milliseconds to reach your brain. And when you use your computer or smartphone, it takes the hardware only a few billionths of a second to interpret the click of your mouse or the tap of your finger.To truly comprehend what’s possible in the span of a second, however, consider the big bang — the miraculous moment some 13.8 billion years ago when a very tiny, very dense and very hot speck of energy and matter began to suddenly expand, creating the universe as we know it today. A phenomenon known as “inflation,” that initial moment of abrupt and exponential expansion lasted only a fraction of a second, according to astrophysicist John Wisniewski, who says the universe expanded a trillion-trillionfold in less than the blink of an eye.Although scientists are confident that inflation occurred, they don’t yet understand how it actually happened. A new and novel NASA mission that’s currently underway hopes to change that. Launched in March from California’s Vandenberg Space Force Base, the Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) mission will spend the next two years plotting the entire celestial sky to create a 3D map of more than 450 million galaxies using technology that’s never been deployed before. Doing so could help scientists understand for the first time what happened immediately after the big bang, says Wisniewski, who serves as program scientist for the SPHEREx mission.“SPHEREx is all about origins,” Wisniewski explains. “It’s mapping out the three-dimensional distribution of hundreds of millions of galaxies in our universe, which is going to allow us to answer a fundamental question: What caused inflation? In other words, how did the universe start? That is a pretty big origin question.”

Investigating Inflation

To understand the physics behind inflation, SPHEREx is using a technique known as spectroscopy. Basically, it’s capturing infrared light — light emitted by warm objects, including stars and galaxies, in wavelengths that are invisible to the human eye — and separating it into 102 distinct colors, the same way prisms split sunlight into rainbows. Observing those colors can help scientists analyze objects’ composition and, in the case of galaxies, calculate their distance from Earth.“We’re a space telescope that’s mapping the entire sky in spectroscopy, which has never been done before,” says Jamie Bock, SPHEREx’s principal investigator and a professor of physics at the California Institute of Technology. “When you cover the whole sky and capture all these colors, it’s an incredible dataset. There’s a ton of things you can do with that.”To seek answers about inflation, scientists will scrutinize the celestial layout of galaxies next to each other in groups, which looks haphazard but is actually conspicuously organized. “Galaxies cluster, and clustering was set up in the early universe,” Bock explains. “If we study the distribution of galaxies in three dimensions, how they cluster can tell us something about the process of inflation.”But inflation isn’t the only phenomenon SPHEREx is investigating. In addition to understanding how the universe formed, it will attempt to understand how galaxies grow over time, which it can accomplish by measuring fluctuations in extragalactic background light — a faint glow of light from outside our galaxy, the source of which is accumulated radiation from all the stars that have ever existed in the observable universe.“With SPHEREx, we can see what the total glow produced by galaxies is,” Bock says. “That glow encodes all emissions over cosmic history. So, by studying it, we can work out in an independent way what the history of light production was.”A third and final goal of SPHEREx is to take an inventory of frozen water and carbon dioxide in our galaxy, which could shed light on the origins of life. “We know that water is important for life on Earth, and it may be important for life elsewhere,” explains Bock, who says scientists believe the water on Earth traveled there after initially developing inside clouds that form in the space between stars. “There’s basically these interstellar reservoirs of water in space, but that water is actually in the form of ice.”By determining where in the galaxy that ice exists and under what circumstances, SPHEREx could help explain how water forms and the processes that deliver it to planets such as Earth.

A Cool Design — Literally

To answer the big questions, it wants to answer, SPHEREx relies on a novel design, the centerpiece of which is three concentric metallic cones that help protect the telescope from the heat of Earth and the sun.“SPHEREx is in low Earth orbit, which is approximately 400 miles above Earth. To do the sensitive infrared observations that it’s designed to do, you need to get the telescope really cold — down to temperatures of about minus 350 degrees Fahrenheit,” Wisniewski says. “To get to that temperature, you’d normally have to go out much farther, to approximately 1 million miles above Earth. Or you’d have to use active coolants.”Although active coolants such as cryogen are effective, they’re finite, they add complexity and weight to the spacecraft, and they require electricity.“SPHEREx is doing all of its cooling using a passive radiator,” continues Wisniewski, who says the aforementioned cones give SPHEREx a distinctive martini-glass shape. “The martini glass — what we call photon shields — is basically reflecting earthshine and sunshine away from the telescope.”Also unique are SPHEREx’s linear-variable filters, which the telescope uses to efficiently separate infrared light into myriad discrete colors without the use of bulky parts or moving components. Basically, as it scans the sky, the telescope observes stars and galaxies multiple times through different parts of the same filter, capturing a different wavelength of infrared light every time.“With these spectral filters, the wavelength we capture varies along the length of the filter, and therefore over the length of the detector that the filter is sandwiched over,” explains Beth Fabinsky, SPHEREx project manager. “If we point at something, we get one color. If we nudge our pointing a tiny bit, we get a slightly different color. That’s how we collect multiple spectra for a single object in the sky.”Adds Wisniewski, “Imagine that the camera in your iPhone can only observe red, orange and yellow in the top part of the camera and can only observe green, blue and violet in the bottom part of the camera. That’s what a linear-variable filter does. It allows you to observe one color in one part of the camera and another color in another part. So, if you want to take a selfie in full color, you basically have to take two pictures — one that puts yourself in the bottom part of the camera and one that puts yourself in the top part of the camera. SPHEREx is doing exactly this, which is a really novel way to get all-sky coverage extremely fast.”

‘A Natural Human Question’

Over its 25 months of planned survey operations, SPHEREx will complete more than 11,000 orbits, circling Earth about 14.5 times per day and capturing hundreds of thousands of images that will be digitally woven together to create four different maps of the entire observable sky. NASA has promised to make those maps — which will contain encyclopedic information about hundreds of millions of celestial objects, including stars, galaxies and asteroids — freely available to scientists around the world.“It’s going to be a literal treasure trove for decades for the current and next generation of astronomers,” Wisniewski says.It’s not just astronomers who should be excited by SPHEREx, however. It’s everyone, insists Bock. “SPHEREx is all about understanding the origin of the universe, the origin of our galaxy and the origin of materials that foster life on Earth,” he says. “I can’t think of a single person on Earth who doesn’t want to know where we come from and how it all started. It’s a natural human question.”