'NASA has selected six astrophysics Explorers Program proposals for concept studies. The proposed missions would study gamma-ray and X-ray emissions from clusters of galaxies and neutron star systems, as well as infrared emissions from galaxies in the early universe and atmospheres of exoplanets, which are planets outside of our solar system.
'The selected proposals, three Medium-Class Explorers missions and three Explorers Missions of Opportunity, call for focused scientific investigations and developments of instruments that fill the scientific gaps between the agency’s larger missions.
'The proposals were selected based on potential science value and feasibility of development plans. After concept studies and detailed evaluations, one of each mission type will be selected by 2019 to proceed with construction and launch. The earliest launch date would be in 2022. Medium-Class Explorer mission costs are capped at $250 million each, excluding the launch vehicle, and Mission of Opportunity costs are capped at $70 million each.
'Each astrophysics Medium-Class Explorer mission will receive $2 million to conduct a nine-month mission concept study. The selected proposals are:
Arcus: Exploring the Formation and Evolution of Clusters, Galaxies and Stars
- Arcus would study stars, galaxies and clusters of galaxies using high-resolution X-ray spectroscopy to characterize the interactions between these objects and the diffuse million-degrees gas that surrounds and permeates them.
- Principal investigator: Randall Smith at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.
- FINESSE would investigate the processes that govern planet formation and global climate, and probe the mechanisms that establish atmospheric chemical composition and shape atmospheric evolution. It would perform transit spectroscopy of at least 500 exoplanet atmospheres in the visible and near infrared range for planets ranging from super-Earths to sub-Neptunes to gas giants.
- Principal investigator: Mark Swain at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.
- SPHEREx would perform an all-sky near-infrared spectral survey to probe the origin of the universe, explore the origin and evolution of galaxies, and explore whether planets around other stars could harbor life.
- Principal investigator: James Bock at Caltech in Pasadena, California.
Compton Spectrometer and Imager Explorer (COSI-X), a Small Complete Superpressure Balloon Mission
- COSI-X is a balloon-borne, wide-field-of-view telescope designed to survey the gamma-ray sky at 0.2-5 MeV, performing high-resolution spectroscopy, wide-field imaging, and polarization measurements. COSI-X would map gamma-rays from antimatter around the Milky Way's center, as well as from newly-formed radioactive elements in the debris of stellar explosions.
- Principal investigator: Steven Boggs at the University of California, Berkeley.
- ISS-TAO is a wide-field X-ray transient detector aboard the International Space Station that would observe numerous events per year of X-ray transients related to compact objects. The mission’s primary goal is the detection of X-ray counterparts to gravitational waves produced by neutron stars merging with black holes and other neutron stars. Other targets would be supernova shocks, neutron star bursts, and high redshift gamma-ray bursts.
- Principal investigator: Jordan Camp at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Contribution to ARIEL Spectroscopy of Exoplanets (CASE)
- CASE would provide packaged detectors to ARIEL’s Fine Guidance Sensor assembly. ARIEL would measure the spectra of hundreds of warm and hot transiting gas giants, Neptunes, and super-Earths around a range of host star types. Observations of these exoplanets will allow us to understand the early stages of planetary and atmospheric formation during the nebular phase and the following few millions of years.
- Principal investigator: Mark Swain at JPL
'The program is managed by Goddard for NASA's Science Mission Directorate, which conducts a wide variety of research and scientific exploration programs for Earth studies, space weather, the solar system, and the universe.'