NASA picked four missions for additional studies as the next step in deciding what will be the next mid-size planetary exploration probe in its Discovery series. Two of the four would investigate Venus. The other two would go to moons in the outer solar system, Jupiter’s Io and Neptune’s Triton. NASA plans to select two for launch in the mid-late 2020s.

Teams from NASA field centers, the Jet Propulsion Laboratory, and academic institutions led by Principal Investigators (PIs) compete for a chance to be selected for the Discovery program. Proposals must not only be scientifically compelling, but technically achievable for no more than $500 million (in FY2019 dollars), not including launch or operations.

This is the ninth selection since the program was initiated in 1992. Eleven missions have been flown so far to Earth’s moon, asteroids, comets, Mars, and Mercury.

The PI-led teams of the four missions selected today will each get $3 million for 9-month Phase A concept studies. NASA will then choose two to proceed into development. One will launch between December 31, 2025 and December 31, 2026. The other will launch in the July 1, 2028 – December 31, 2029 time period.

Two of the missions would investigate Venus. The last U.S. mission specifically designed to study Venus was Magellan, launched in 1989, which orbited the planet and provided a detailed radar map of the surface. The last U.S. probe that descended through the toxic Venusian atmosphere was Pioneer Venus 2 in 1978. The two chosen for concept studies today are DAVINCI+ and VERITAS.

DAVINCI+ (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging Plus)

would descend through the atmosphere to precisely measure its composition down to the surface. The data will aid in understanding how Venus formed, evolved and determine whether it ever had an ocean. PI: James Garvin, NASA Goddard Space Flight Center, Greenbelt, MD. Goddard would provide project management.

VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) would map Venus’ surface from orbit using a synthetic aperture radar to create three-dimensional reconstructions of topography and confirm whether processes, such as plate tectonics and volcanism, are still active on Venus. It would also map infrared emissions from the surface to map Venus’ geology. PI: Suzanne Smrekar, JPL, Pasadena, CA. JPL would provide project management.

The other two would conduct studies of two outer planet moons. Jupiter’s moon Io was dubbed the “pizza moon” after the first close-up images were acquired by NASA’s Galileo spacecraft showing colorful deposits from volcanoes that erupt on the moon. It is one of the four Galilean moons discovered by Galileo in 1610 and is the fourth-largest moon in the solar system and the most volcanically active.

Io Volcano Observer (IVO) would explore Io through 10 close-in flybys to learn how tidal forces shape planetary bodies and determine if a magma ocean exists in its interior. It could revolutionize our understanding of the formation and evolution of rocky, terrestrial bodies, as well as icy ocean worlds in our solar system, and extrasolar planets across the universe. PI: Alfred McEwen, University of Arizona, Tucson. The Johns Hopkins University Applied Physics Laboratory would provide project management.

Neptune’s moon Triton is an icy world first seen in some detail by NASA’s Voyager 2 mission as it flew past in 1989. Data showed that active resurfacing takes place there and scientists say it has the second youngest surface in the solar system. They think it also may have an interior ocean and studying it could help in understanding how habitable worlds form.

TRIDENT would explore Triton in a single fly-by that would map the moon, characterize active processes, and determine whether the predicted subsurface ocean exists. PI: Louise Prockter, Lunar and Planetary Institute/Universities Space Research Association, Houston, TX. JPL would provide project management.

Hear about these missions directly from their PIs thanks to these tweets from Thomas Zurbuchen, the head of NASA’s Science Mission Directorate.

Jupiter’s moon Io is extremely active and may have a magma ocean. The Io Volcano Observer (IVO) would explore this world – which is the most volcanically active body in our solar system. Congratulations to Principal Investigator Alfred McEwen and his team! pic.twitter.com/BVxNvRBanc — Thomas Zurbuchen (@Dr_ThomasZ) February 13, 2020