NASA has just given the green light to a mission that will study multiple eras of cosmic history, from the earliest fractions of a second after the big bang to modern-day planetary formation. The space-based Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) will map the entire sky in the infrared—wavelengths that are mostly blocked by Earth’s atmosphere.
“It’s a great moment,” says SPHEREx Principal Investigator James Bock, an astronomer at the California Institute of Technology in Pasadena, who says he’s glad to be just one member of a large team. “If it was just me, I’d be really panicked.”
SPHEREx beat out one other finalist for NASA’s middle-class explorer program (MIDEX), a competitive mission line whose costs are capped at $250 million. Previous MIDEX missions include the Transiting Exoplanet Survey Satellite (TESS), which launched last year. SPHEREx has been awarded $242 million and is expected to launch in 2023.
One of SPHEREx’s main goals will be to determine the distance from Earth to 300 million galaxies and map out their 3D structure. By looking at over-densities and under-densities in their large-scale distribution, the mission might be able to tease out tiny effects from a hypothesized period in the early universe known as inflation, when the universe expanded exponentially in size in the moments after the big bang.
Primordial quantum mechanical fluctuations from the newborn universe, boosted by inflation, left ripples on the cosmic microwave background, the most distant light that telescopes can see. Similarly, inflation could have generated a signature on galactic distribution that would give researchers clues about its details. Some theories posit that the energy for inflation came from a field with an associated particle known as an inflaton.
“It’s possible that view is simplistic,” Bock says. “There are reasons to think there will be multiple fields involved.”
SPHEREx will also gather information about the total light emitted by galaxies, giving insights into an under-studied era known as reionization, when the first stars began lighting up the universe and heating up clouds of hydrogen. Finally, closer to home, the mission will map out the abundance of ices in molecular clouds within the Milky Way. As these clouds collapse, they form stars and planets, though the details of the process are still not well known.
“Ice on the dust grains may be important for accretion,” Bock says. “For instance, causing things to stick together better.”
In the MIDEX competition, SPHEREx won out over the Arcus satellite, which would have studied galaxies in x-rays to get a better understanding of the supermassive black holes at their centers. An exoplanet mission, the Fast INfrared Exoplanet Spectroscopy Survey Explorer (FINESSE), was originally another finalist. But NASA asked its designers to instead contribute technology and expertise to a similar observatory in development by the European Space Agency called the Atmospheric Remote-sensing Exoplanet Large-survey (ARIEL).