NASA picks mission to explore a pit that may lead to a Moon cave

A mission to investigate a mysterious hole on the Moon that may open into a large underground cave has been selected for development under a NASA programme.

The project, called GIMLI, short for Geophysical Instruments for Marius Lunar pit Investigation, is led by the Planetary Science Institute in the United States. It will study the Marius Hills Pit, a deep opening in one of the Moon's most volcanically varied regions.

A hole in the Moon

The Marius Hills Pit was spotted by spacecraft orbiting the Moon. Scientists think it may be a skylight, a place where the roof of an underground lava tube has collapsed. Lava tubes form when the surface of a flow of molten rock cools and hardens while lava continues to flow beneath it. When the eruption ends, the lava drains away and leaves a hollow tunnel.

On Earth, lava tubes are found in volcanic regions such as Hawaii, Iceland and the Canary Islands. Because the Moon's gravity is much weaker, scientists think lunar lava tubes could be far larger.

What the mission will do

GIMLI would carry a set of instruments to the Moon's surface to look beneath it. They include ground-penetrating radar, an active-source seismic system, which sends vibrations into the ground and listens for echoes, a gravimeter, which measures tiny changes in gravity caused by empty spaces underground, and cameras to photograph the surface and the walls of the pit.

Combining seismic measurements with radar and gravity readings, the team said, "makes it all the more exciting".

Who is involved

The project is led by Than Putzig, associate director and senior scientist at the Planetary Science Institute, with Gareth Morgan as deputy principal investigator. Partners include Honeybee Robotics, the Norwegian Space Agency, Boise State University, Johns Hopkins University, the Lunar and Planetary Institute and the University of Oslo.

It has been selected through NASA's PRISM programme, which chooses science instruments to be delivered to the Moon by commercial landers under the Commercial Lunar Payload Services scheme.

Why caves matter

Underground caves could offer future astronauts natural shelter. The Moon has no atmosphere or magnetic field to protect against radiation from the Sun and from space, and surface temperatures swing from more than 100C in the day to below minus 170C at night. Inside a cave, conditions would be far more stable.

Caves could also preserve material that has been protected from radiation and tiny meteorite impacts for billions of years, helping scientists understand the Moon's volcanic history.

The return to the Moon

NASA's Artemis programme aims to return astronauts to the Moon. The Artemis II crew flew around the Moon earlier this year, and later missions are planned to land near the lunar south pole.

Not yet launched

The mission has not yet launched, and the date will depend on the availability of commercial landers. Scientists say it could provide the first direct evidence of what lies beneath a lunar pit.

See the Moon for yourself

The Marius Hills lie in the Oceanus Procellarum, the Ocean of Storms, on the western side of the Moon as seen from Earth. The pit itself is far too small to see with a telescope from Earth, but the dark lava plains around it are visible with binoculars.