Taking the Temperature of the Moon to See What’s Inside

The Moon is our nearest neighbor, but surprisingly little is known about its interior, even the temperature within its body. Now, by simulating lunar conditions in a laboratory here on Earth, a geoscientist from the University of Rhode Island (URI) has accomplished that feat.

The surface temperature of the Moon, measured by the astronauts of Apollo, peaks near -20 Celsius (-4 Fahrenheit), a temperature similar to that of a January day in New England. The region between the core and mantle of the Moon was found to have a temperature between 1,300 and 1,470 degrees Celsius (2,370–2,675 Fahrenheit), which is warmer than researchers predicted.

“In order to understand the interior structure of the Moon today, we needed to nail down the thermal state better. Now we have the two anchor points — the core-mantle boundary and the surface temperature measured by Apollo — and that will help us create a temperature profile through the Moon. We need that temperature profile to determine the internal state, structure and composition of the Moon,” said Ananya Mallik of URI.

Harrison Schmitt, a geologist, is the only scientist (so far) to have walked on the surface of the Moon. Here, Schmitt is shown on the lunar surface during the Apollo 17 mission in December 1972. Image credit: NASA

A Moon Almost Like Home

Like the Earth, the Moon has an iron core. Seismic experiments on the lunar surface revealed that between five and 30 percent of the material caught at the boundary of the mantle and core is found as a liquid.

The Moon is composed of an iron-rich core 480 kilometers (300 miles) in diameter, surrounded by a liquid iron shell 90 km (56 miles) in depth. A material of partially-molten olivine and pyroxene, 150 km (93 miles) deep, lies beneath the mantle. The crust which we see runs just 70 km (43 miles) deep on the side of the Moon facing the Earth, and 150 km (93 miles) on the far side of our planetary companion.

Ananya Mallik of URI, shown beneath the Moon which she helps the world better understand. Image credit: Nora Lewis

A Moon Away from the Moon

Mallik simulated conditions within the lunar mantle in her laboratory, utilizing material similar to that found on the Moon. This sample was subjected to pressures more than 45,000 times greater than air pressure on Earth, similar to conditions at the mantle/core boundary of the Moon, then heated until five to 30 percent of the sample became molten.

“Earth is complicated. Any similarity in the composition between Earth and the Moon can give us insight into how these two planetary bodies were formed, what were the energetics of the collision, and how elements were partitioned between them,” Mallik said.

Once thought to be dry and barren, we now know that the Moon is home to frozen water ice, concentrated at its northern and southern poles. Water not only forms on the lunar surface, but the material can also migrate once it forms, or is deposited on the surface by comets as they impact the Moon.

More Reasons to Love the Moon

Unlike the Earth, the Moon shows no signs of plate tectonics. On our own world, the shifting of continents, made possible (in part) by molten layers in the inner layers of our planet, plays vital roles in the evolution of the Earth. Volcanoes once erupted on the Moon, but they fell silent millions of years in the past. Our planetary companion has also greatly affected the development of our own world and the life which resides upon it.

The Orion spacecraft, launched aboard a Space Launch System (SLS) rocket, is designed to bring NASA astronauts back to the Moon, as well as to Mars. Image credit: NASA

“Our moon makes Earth a more livable planet by moderating our home planet’s wobble on its axis, leading to a relatively stable climate, and creating a tidal rhythm that has guided humans for thousands of years. The moon was likely formed after a Mars-sized body collided with Earth and the debris formed into the most prominent feature in our night sky,” NASA describes on a web page introducing lunar science.

Apollo 11 first put humans on the Moon 50 years ago, and today, NASA, along with other nations and private companies, aims to place space travelers on the face of the Moon once more, preparing for a mission to Mars.