NASA has selected the newest space mission to join its Explorer program. Its goal is summed up in its name: the Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx). The spacecraft will scan the skies in optical and near-infrared light to search for the ingredients of life in the Milky Way, and peer as far as 10 billion years back in time.

The SPHEREx mission is set to examine over 300 million galaxies at varying distances, while also studying our own in greater detail by looking at 100 million stars in the Milky Way. Every six months during its run, the space telescope will perform an all-sky survey, so that by the end of the mission it will have mapped the entire sky in 96 different color bands – far more than previous all-sky surveys have managed.

The mission will set out to achieve three main goals. First up, SPHEREx will study the physics of the expansion of the universe. Basically, as the inflation of the universe pushes clumps of matter like galaxies further apart, the wavelengths of light from them stretch out towards the red end of the spectrum. SPHEREx will measure that "red shift" in new detail, by looking at more galaxies across a wider range of the sky than other surveys.

The second goal is to investigate the history of light produced by these galaxies. It'll do this by using those all-sky maps to get a clearer understanding of the extragalactic background light that pervades everything, then searching for slight fluctuations that might indicate when some of the first stars and galaxies flared into existence.

"This amazing mission will be a treasure trove of unique data for astronomers," says Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate. "It will deliver an unprecedented galactic map containing 'fingerprints' from the first moments in the universe's history. And we'll have new clues to one of the greatest mysteries in science: What made the universe expand so quickly less than a nanosecond after the Big Bang?"

The third branch of the mission will examine a major mystery a little closer to home – how common are the ingredients for life in the Milky Way? Astronomers will use SPHEREx to study millions of stars in our cosmic neighborhood, searching for the telltale signatures of water and organic molecules like carbon monoxide, carbon dioxide, and methanol, which are essential for life as we know it. In particular, the telescope will look for these compounds in places where new stars and planets are forming.

Along with these goals, SPHEREx could also help pinpoint targets that can then be studied in more detail by upcoming instruments like the James Webb Space Telescope and the Wide Field Infrared Survey Telescope.

SPHEREx was selected from among nine proposals submitted after NASA's Astrophysics Explorers Program put out a request in September 2016. A panel of scientists and engineers conducted a thorough review of the feasibility and potential benefits to science of each proposal, and decided that SPHEREx was the most promising.

The mission is due to launch in 2023, and will cost US$242 million – not including the costs of launch itself.

Sources: NASA, SPHEREx