NASA plans to land its next lunar rover beside a crater, named Nobile, near the Moon’s south pole, the agency has announced. But some scientists question whether the mission, set to launch in 2023, will efficiently find the lunar ice that it’s looking for.
The mission, known as the Volatiles Investigating Polar Exploration Rover (VIPER), aims to study ice on the lunar surface that could serve as a resource, for instance as a rocket-fuel ingredient for future astronauts. The Moon’s south pole has so far not been visited by any spacecraft, but holds great scientific promise: it receives little sunlight, so it has reserves of ice containing information about the origin and evolution of the Solar System, preserved for billions of years. VIPER will hunt for the ice in the lunar soil using various methods, including drilling up to 1 metre deep.
Lunar exploration is ramping up globally, with China, South Korea, India and Russia among the nations working on Moon missions. Amid these efforts, NASA aims to regain the glory of its 1969 crewed Moon landing by sending astronauts to the lunar surface somewhere near the south pole. The goal is to do so by the end of 2024, but that deadline will probably slip given budgetary and other constraints.
Ahead of the astronaut landing, NASA will send a fleet of robotic spacecraft to the Moon. Among them is VIPER, which will be the first-ever mission to provide on-the-ground measurements of lunar polar ice. VIPER will cost NASA around US$433 million to build and operate. Another $226 million will go to a private company, Astrobotic Technology in Pittsburgh, Pennsylvania, to deliver it to the Moon’s surface. If all goes well, after the rover touches down at its landing site near Nobile Crater, it will travel 25 kilometres or more over 100-plus days while mapping ice and drilling into it in a number of places.
But some researchers worry that the landing site, announced on 20 September, isn’t guaranteed to have an abundance of ice. So far, scientists have only been able to estimate polar-ice concentrations on the basis of data from orbiting spacecraft. According to that information, Nobile Crater does have ice in and around it, including inside several permanently shadowed regions that never see the Sun’s rays1,2. “We do have a lot of data that there is water ice there — we’re not going in blind,” says Amy Fagan, a planetary scientist at Western Carolina University in Cullowhee, North Carolina.
But some point out that lunar polar ice appears to be distributed in patches — with frost on the surface in some places and ice frozen more deeply in others, inaccessible even to VIPER’s drill. “It’s not like water ice is everywhere,” says Bethany Ehlmann, a planetary scientist at the California Institute of Technology in Pasadena. “The details matter in terms of where we go.”
The search for ice
Since 2017, when then-president Donald Trump tasked NASA to return astronauts to the Moon, many lunar scientists have been working to identify areas around the south pole, where robotic spacecraft or astronauts might have the best chance of finding ice or other geologically interesting terrain to explore3.
NASA chose Nobile Crater for VIPER partly because it offers a variety of locations where ice can be studied in the lunar soil. Other factors in the decision included that VIPER could easily travel across the terrain, that enough sunlight is available for the solar-powered rover to recharge its batteries regularly, and that the crater has a good line of sight to Earth, so engineers can communicate directly with the spacecraft.
The agency acknowledges that VIPER does not yet have a detailed map of where the ice is around Nobile, named after an Italian explorer who developed airships for Arctic exploration. “This is exactly why we’re going,” says Anthony Colaprete, VIPER’s project scientist at NASA’s Ames Research Center in Moffett Field, California. “Any new information is going to be enlightening beyond what we have right now.”
But some scientists say VIPER would be better off if NASA launched a different planned spacecraft, a small, $55-million satellite called Lunar Trailblazer, first. Lunar Trailblazer’s mission is to map water on the Moon. Researchers say the VIPER team could use these maps to plot which parts of Nobile the rover could efficiently travel to as it prospects for ice during its fast-paced, 100-day mission.
NASA, however, plans to keep Lunar Trailblazer in storage until 2025, when it is scheduled to ride to space alongside an unrelated spacecraft. Ehlmann, who is the principal investigator for Lunar Trailblazer, says it will be ready for launch in February 2023, well before VIPER, and could make advance maps for VIPER if NASA finds an earlier launch opportunity.
US lunar scientists discussed the issue last month at a meeting of the Lunar Exploration Analysis Group, which provides input to NASA on lunar activities. They supported launching Lunar Trailblazer as soon as possible but recognized that VIPER will still be successful without it, says Fagan, who is the group’s chair.
NASA defends its choice to launch VIPER first. “We absolutely have sufficient knowledge to fly the VIPER mission” before Trailblazer, says Lori Glaze, director of NASA’s planetary science division in Washington DC.
Despite concerns, VIPER will provide scientists’ best look yet at where ice might be around the lunar south pole. The rover can detect very low levels of ice in the soil, under one-tenth of a per cent by weight. Because of that sensitivity, says Kevin Cannon, a planetary scientist at the Colorado School of Mines in Golden, “I think there’s a pretty good chance of finding detectable ice.”
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