While space is largely devoid of matter, it does contain some gas and dust that floats between stars, material known as the interstellar medium. NASA has selected the Galactic/Extragalactic ULDB Spectroscopic Terahertz Observatory (GUSTO) mission to conduct the first complete study of this matter, to better understand how it behaves.
Interstellar objects such as stars, black holes, and galaxies get a lot of attention from scientists, but the interstellar medium isn’t a trivial thing to study: it makes up about 15 percent of the total mass in the Milky Way; 99 percent of that is free-floating gas, mostly hydrogen and helium. While space is still pretty empty (we’re talking a density of an atom per cubic centimeter), the vast distances mean that those small amounts add up.
The $40 million GUSTO mission, led by University of Arizona professor of astronomy Christopher Walker, will launch an Ultralong-Duration Balloon over Antarctica in 2021, which will carry a telescope that can detect carbon, oxygen, and nitrogen spectral emissions. This equipment will allow the research team to study and map out parts of the Milky Way and the Large Magellanic Cloud.
The mission will “provide the first complete study of all phases of the stellar life cycle,” ays Paul Hertz, the astrophysics division director in the Science Mission Directorate in Washington, “from the formation of molecular clouds, through star birth and evolution, to the formation of gas clouds and the re-initiation of the cycle.” This will help scientists better understand the conditions that can ultimately lead to the formation of stars. "If we want to understand where we came from, we have to understand the interstellar medium," Walker explains, "because 4.6 billion years ago, we were interstellar medium."
The mission is expected to launch in December 2021 from McMurdo Station in Antarctica. There, it will fly for up to 170 days, depending on the weather. The balloon will fly at an altitude of 110,000 and 120,000 feet, which will allow researchers to avoid water vapor in the atmosphere that could obscure their readings. In December 2016, the team launched the Stratospheric Terahertz Observatory, a predecessor to GUSTO, which flew for three weeks over Antarctica.