Clues about the origin of the universe and of life are scattered across the sky. SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) is a next-generation space observatory designed to measure the infrared spectrum of 450 million galaxies and millions of stars in the Milky Way. With these spectra, SPHEREx will answer pressing questions about the history and origin of the universe, and reveal the abundance of water and other molecules associated with life in the Milky Way in unprecedented detail. Researchers from the Center for Astrophysics | Harvard & Smithsonian are involved in the design of the program to look for the interstellar molecules necessary for life as we know it. SPHEREx is targeted to launch in 2023.
The Telescope and the Science
Astronomy operates in two basic ways: broad surveys designed to study as much of the sky as possible, and deep focused observations. SPHEREx is in the first category: it will map the entire sky in infrared light four times during its 27-month mission. Its scientific mission has three parts:
Map the positions of 450 million galaxies in three dimensions, to look for signs of cosmic inflation. According to the theory of inflation, the universe expanded extremely rapidly during the first fraction of a second after the Big Bang. This expansion may have produced ripples in the density of the matter that formed the first galaxies, which SPHEREx could observe.
When the first stars, galaxies, and black holes formed, they “reionized” the gas in the universe: stripping electrons from atoms. SPHEREx will study this epoch of cosmic history to understand the earliest galaxies, and how they evolved over billions of years.
Mapping the whole sky means getting a detailed spectral map of the Milky Way. CfA scientists are leading SPHEREx program to study the chemical contents of newly forming star systems. Specifically, SPHEREx will be able to locate molecules important for the origins of life as we know it: water, carbon dioxide, methanol, and carbon monoxide.
As a space telescope, SPHEREx will have a mostly unimpeded view of the sky, not limited to one hemisphere or by weather and other problems created by the atmosphere. That makes the observatory complementary to the other next-generation telescopes, including NASA’s James Webb Space Telescope (JWST) and the ground-based Giant Magellan Telescope (GMT). These observatories will be valuable for following up on interesting sources identified by SPHEREx.
The mission is designed to have no moving parts. The scientific instrument on SPHEREx is a spectrophotometer, which measures both the spectrum of light emitted by a source and the quantity of light at each wavelength. The telescope will cover successive small patches of the sky, obtaining about 14 billion separate spectral measurements on each of its four surveys.
The SPHEREx collaboration is led by researchers at Caltech and NASA’s Jet Propulsion Laboratory. In addition to CfA, other project collaborators include University of California Irvine, Ohio State University, Arizona State University, Rochester Institute of Technology, Stanford University, Argonne National Laboratory, and Johns Hopkins University.