NASA has selected four small astrophysics mission concepts for further study as part of the experimental Pioneers program, which seeks SmallSat or balloon missions with $20 million cost caps that will give early-to-mid-career scientists an opportunity to lead their own mission.
[...] The four proposed missions are Aspera, Pandora, and Starburst (all SmallSat missions), and PEUO, a balloon mission into Earth's upper atmosphere.
Aspera would study galactic evolution via ultraviolet observations to examine not the galaxies themselves [twitter.com], but the hot gases in the space between them (the intergalactic medium) and how those gases flow inward and outward from various galaxies.
Pandora, the exoplanet mission, would study a total of 20 stars and their accompanying 39 exoplanets [twitter.com] in both the visible and infrared spectrums and would seek to better understand how starlight affects the measurement of exoplanet atmospheres, an outstanding issue in determining the potential habitability of worlds beyond our Sun's influence.
Starburst, on the other hand, would seek to study high-energy gamma rays created by the mergers of neutron stars [twitter.com], which has only ever been observed once before and from which heavier elements, like platinum and gold, are formed.
The one non-satellite mission is PUEO, a balloon flight that would lift off from Antarctica to detect signals from ultra high-energy neutrinos [twitter.com] — particles that contain valuable information about the processes governing the creation of black holes and neutron star mergers.