Is NASA launching too many asteroid missions?

Not all scientists are happy about recent Discovery mission picks

lucy and psyche missions
NASA's latest missions, name Lucy and Psyche, will visit two new types of asteroids. Some scientists think a mission to Venus should have been chosen instead.SwRI and SSL/Peter Rubin

NASA has been on a bit of an asteroid kick lately. First, in 2015, the Dawn mission arrived at Ceres, the biggest rock in the asteroid belt. Then came plans for OSIRIS-REx, a mission to scoop up some asteroid dirt and carry it back to Earth.

Now the space agency has announced two more relatively low-budget missions to asteroids. Lucy will fly to the Trojan asteroids that swarm around Jupiter, while Psyche will be the first spacecraft to visit a metal asteroid. The program will also extend funding for NEOCam, a space telescope that would search for near Earth asteroids.

Asteroids represent some of the solar system's best time capsules—frozen and untouched, they may contain clues about the beginnings of our cosmic neighborhood.

But while everyone agrees that these missions are worthy of selection, some scientists are raising concerns about the lack of diversity in NASA's recent funding choices.

It's worth noting that the Discovery Program is also in the midst of funding the Mars InSight mission, which will launch in 2018 to study seismology on the red planet, and the Lunar Reconnaissance Orbiter, which is currently mapping the moon in 3D. And NASA as a whole has many exciting ongoing missions. So it's not all asteroids all the time, but the next few decades will be slim pickings for scientists who want to study atmospheres on other worlds*. Even the study of Earth's own atmosphere may be in jeopardy.

There's only so much NASA can do on its limited budget, and every decision to fund one mission means others won't get off the ground. Of the 28 projects that applied for funding through NASA's Discovery Program, five made it to the semi-finals—three asteroid-related missions, and two Venus missions.

In response to a tweet from Sarah Hörst, a planetary scientist at Johns Hopkins and a member of the DAVINCI proposal to study Venus' atmosphere, many scientists are voicing disappointment and concern over NASA's selections.

"I thought for sure they'd pick a Venus mission," Mark Marley, who studies the atmospheres of exoplanets, told Popular Science. Marley works for NASA but wasn't involved in the selection process, and emphasizes that his own opinions don't represent those of NASA as a whole. "I found it pretty surprising."

Marley says a mission to Venus would help him study worlds around other stars. "If we're trying to understand atmospheres on exoplanets, we really need to understand as much as we can about our own Venus. It's very hard to get exoplanet data, and it's always lower quality than what you can get in the solar system."

Today's funding choices, he says, "will have an impact downrange."

In a teleconference, Jim Green, NASA's planetary science director explained that the Venus proposals didn't score as high in NASA's evaluations. These evaluations were based on each project's science objectives, risk, and cost.

In 2017, NASA will be selecting one New Frontiers mission to fund, and a Venus atmospheric probe and lander is one of the space agency's priorities. New Frontiers missions generally get a bigger budget than Discovery missions, so it's not as though all hope is not lost for Venus enthusiasts. But NASA also wants to prioritize missions that would explore Saturn's atmosphere and land in the lunar south pole, among other things.

*Clarification: A previous version of this sentence implied that there are no current missions studying atmospheres, whereas the issue is that future missions may be lacking in atmospheric science. We have changed the sentence to clarify.