The science case for returning to the Moon

Geopolitics may be driving the Trump administration's planned return to the Moon by 2024, but, if risk and reward are balanced, science could benefit from the lunar return as well.

The big picture: The Moon acts as a time capsule of our solar system and Earth specifically. Clues into how the Moon formed 4.5 billion years ago — after a large object slammed into the Earth, carving out our natural satellite — are preserved in its geology.

• "Understanding the Moon has such critical importance for understanding the Earth, for starters, because the Earth's earliest history is essentially lost" due to plate tectonics and weathering, planetary geologist Brett Denevi, of Johns Hopkins University's Applied Physics Laboratory, tells Axios.
• That preservation allows scientists to turn back the clock, revealing clues about our part of space when life was just forming about 3.9 billion years ago.

"This is going to be a treasure trove for planetary science," says Alan Stern, a planetary scientist at the Southwest Research Institute.

But, but, but: Human spaceflight is expensive and risky. In President Trump's budget released in March, the agency requested $10.7 billion to continue developing and building the components needed to send people back to the moon by 2028.

• For that price, NASA could send 4 Curiosity rovers to Mars with money to spare.
• NASA is weighing the added cost of an accelerated timeline.
• That money could also be used to explore worlds we've only gotten a tantalizing look at so far, like Neptune or Uranus, which have never been studied from close range by a dedicated except mission for Voyager 2's flybys.

"... [t]here are good science cases for sending people to the moon. I think that a lot of those science cases, when you factor in the cost, the timing and all that, a lot of that could be done with robotic missions," theoretical astrophysicist Katie Mack tells Axios.

On the other hand: Rovers and landers are incredibly useful for science, but the science they do is often cumbersome by comparison to what a human can accomplish on the ground.

• It might take weeks of planning to set a rover on a certain course to investigate a rock formation just a few feet away, whereas a person could simply walk over to an outcropping.
• A human mission to the moon would also allow astronauts to bring home hundreds of pounds of moon rocks, as opposed to robotic sample return, which has historically only resulted in grams of material.
• The Apollo cache of rocks is still viable for scientific inquiry, but a new trove of rocks from a different part of the moon that is preserved using modern scientific standards would be a boon for study.

The bottom line: The Apollo program was motivated by a determination to beat the Soviet Union to the lunar surface, but science still gained from it.

• There's no reason to think that won't be the case this time either, no matter the underlying political reasons for NASA's lunar return.

Go deeper:

• NASA pushes its Moon and Mars ambitions
• What we can learn from a return to the Moon