Heat flow of the Moon

My research focuses on the heat that is released from a planetary body such as Earth, Moon, and Mars. Most planets and moons are much hotter inside than their surfaces. So heat flows from their center outward. Figuring out how much heat comes out of the surface of a moon/planet and how it varies geographically, planetary scientists infer its temperature distribution, chemical composition, and geologic history.

The Apollo astronauts measured the flow of heat at two locations on the Moon in 1971 and 1972 (Fig. 2). Heat flow at the Apollo 15 landing site was a little greater than at the Apollo 17 landing site (21 mW/m2 vs. 16 mW/m2).

Later, observations from lunar orbiting spacecrafts (NASA’s Lunar Prospector mission, 1998 – 1999, and Kaguya by the Japanese space agency, 2007- 2009) mapped out abundance of heat-producing elements (U, Th, and K) on the Moon’s surface soil (regolith) (Fig. 4). The map showed that the Apollo 15 site is more abundant in these elements. Some researchers believe that is why heat flow is higher there. But, the heat flow is also influenced by how the Moon has cooled since its formation and the crust and the mantle separated, etc. So, we need to learn more about the internal structure and composition of the Moon before we can sense of the heat flow data.

Figure 4. Heat flow measurements were made at the Apollo 15 and 17 sites. The color coding of this map shows the abundance of Thorium on surface regolith, estimated from spacecraft Kaguya of the Japanese space agency.

Further Readings on the Heat Flow of the Moon

Nagihara, S., Kiefer, W.S., Taylor, P.T., Williams, D.R., Nakamura, Y., 2018. Examination of the Long-Term Subsurface Warming Observed at the Apollo 15 and 17 Sites Utilizing the Newly Restored Heat Flow Experiment Data From 1975 to 1977. Journal of Geophysical Research: Planets 123, 1125-1139.

Return to the Moon

NASA, in partnership with US companies, is now preparing to send a number of scientific instruments to the Moon. The instruments will be mounted on robotically operated ‘landers’. NASA is planning to send two landers to the Moon every year starting in 2021. The landers will be built and operated by US companies. The payload instruments are now being built at NASA’s research centers, US universities, and companies.

I lead a team of scientists and engineers who are building one of these instruments destined for the Moon. This instrument is designed to measure the heat that flows out of the surface of the Moon. It is scheduled to fly to the Moon in late 2022, along with several other geophysical instruments. After the lander touches down, the probe penetrates 2- to 3-m into the Moon’s regolith and senses the heat that flows out of the deeper interior (Fig. 5). This instrument is currently being built and tested at Honeybee Robotics, Ltd. In Pasadena, CA (honeybeerobotics.com).

Figure 5. The heat flow instrument, named ‘LSTER’, it will be mounted on the lander’s leg. Its probe will penetrate up to 3 m into the lunar regolith. A conceptional drawing courtesy of Honeybee Robotics.