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Two of the four finalists for NASA’s newest Discovery mission propose to visit Venus.

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NASA mission finalists would explore Venus or outer-planet moons

Venus may be Earth’s closest cousin, but for many planetary scientists, it can seem a distant dream. It’s been nearly 30 years since a NASA spacecraft has visited the planet. But that could change, as missions to Venus are two of the four finalists for the agency’s next two $500 million planetary missions, NASA announced today.

The Venus finalists have been here before: Versions of both proposals were in the same position in 2017, but NASA ultimately selected two missions to asteroids instead. This time, the Venus missions will face stiff competition from proposals to visit Io, Jupiter’s large volcanic moon, and Triton, Neptune’s icy moon, neither of which has been closely explored. Each proposal receives $3 million to flesh out their concept over the next year. After that, NASA plans to select two for flight. None would likely launch until the middle of this decade at the earliest.

The first Venus proposal, DAVINCI+ (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging Plus) from NASA’s Goddard Space Flight Center, would send an armored pressure sphere plunging through the planet’s atmosphere, its instruments measuring noble gases to sort out the planet’s origins, and sniffing for sulfur and carbon near the surface for evidence of recent volcanic activity. Unlike Goddard’s past Venus proposal, this mission would also include an orbiter to map the planet’s geology, including its mysterious highlands. (The previous DAVINCI proposal was led by Lori Glaze, now the chief of planetary science at NASA headquarters.)

The second Venus proposal, VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) from NASA’s Jet Propulsion Lab (JPL), would use synthetic aperture radar to peer through the planet’s thick clouds and recreate its topography, revealing whether volcanoes or variants of plate tectonics are active on its surface. Previous missions have revealed evocative evidence of hotspots but lacked the resolution to answer questions of why Venus’s fate differed so starkly from Earth’s.

The third proposal, the Io Volcano Observer (IVO), from the University of Arizona and the Johns Hopkins University Applied Physics Laboratory, would travel to the volcanic furnace that is Io, one of Jupiter’s large moons. Heated by Jupiter’s gravitational pull, Io’s interior and surface remain a mystery. Through a series of flybys, IVO would answer questions such as whether a magma ocean sits in Io’s interior and the volume of its eruptions.

Finally, the Trident mission, from the Lunar and Planetary Institute and JPL, would explore Triton, the icy moon of Neptune, at the Solar System’s outskirts. Although Voyager 2 flew past the planet, Neptune and its moons have never seen a dedicated mission. Voyager 2 did reveal that Triton is active, with a young active surface that could host eruptive plumes and be hiding an interior ocean. Trident would fly past Triton once, much like New Horizons flew past Pluto, mapping the moon as it passed.

Unlike its larger mission lines, NASA’s Discovery program is open to targets throughout the Solar System. The agency’s two most recent selections—Lucy, set to fly past a series of asteroids that follow Jupiter’s orbit, and Psyche, which will explore an oddball metallic asteroid—are set to launch in 2021 and 2022, respectively.