A new model by researchers at Chengdu University of Technology proposes that tidal heating from Earth's gravity may have kept the Moon's interior warm enough to help produce volcanic rocks billions of years after its formation, offering a possible explanation for samples from China's Chang'e-5 mission.
The Moon formed about 4.5 billion years ago from debris after a giant impact and was expected to cool rapidly, becoming geologically dormant. However, basaltic rocks returned by Chang'e-5 and dated to around two billion years old appeared to be volcanic in origin, despite expectations that the Moon would have cooled. Radioactive decay could not provide enough heat, while asteroid strikes could cause localized heat spikes; the heavy bombardment period had ended long before the basalts formed.
In a paper published in the journal Planet, Miao Chen and colleagues suggest that tidal heating was the missing ingredient. Around two billion years ago, the Moon's orbit around Earth was closer and more elliptical than it is today. This caused Earth's gravity to rhythmically squeeze and stretch the Moon's interior, generating heat. The team's simulations, which incorporated a realistic, layered interior with a low-viscosity zone between core and mantle, showed that tidal strain concentrated energy in two symmetric regions at the core-mantle boundary. They termed these Tidal Heating Anomaly Zones (THAZs). Around 3.2 billion years ago, the tidal heating in these zones delivered an estimated 150 gigawatts of power, more than four times the energy generated by radioactive decay.
This heat source could have sustained a magnetic field longer than expected and driven mantle plumes that later produced the basalts seen in Chang'e-5 samples. The tidal engine eventually calmed down. The model remains theoretical, and future lunar missions may provide more definitive data about the Moon's geological history.
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- SupportedThe headline says a tidal-heating model suggests Earth’s gravity kept the early Moon warm.Universe Today: “A new paper from Miao Chen of the Chengdu University of Technology and his colleagues, and recently published in the journal Planet, offers an explanation - tidal heating.”
- SupportedThe summary says researchers propose that gravitational squeezing may help explain volcanic rocks around two billion years old returned by Chang’e-5.Universe Today: “some lunar material returned from the Chang’e-5 mission was notably formed only around two billion years ago, yet appeared to be volcanic in origin.”
- Partly supportedThe story attributes the new model to researchers at Chengdu University of Technology.Universe Today: “A new paper from Miao Chen of the Chengdu University of Technology and his colleagues”
- SupportedChang’e-5 returned basalts dated to around two billion years old that appeared volcanic in origin.Universe Today: “But when Chang’e-5 returned some lunar basalts from Oceanus Procellarum back to Earth, laboratory dating showed them to be only around two billion years old.”
- SupportedRadioactive decay could not provide enough heat to form basalt two billion years ago.Universe Today: “But there wasn’t enough un-decayed material left on the Moon to offer the amount of heat needed to form basalt two billion years ago.”
- SupportedAround two billion years ago, the Moon’s orbit was closer to Earth and more elliptical than it is today.Universe Today: “However, two billion years ago, the Moon was much closer to the Earth than it is today, orbiting our planet in sixteen days rather than the twenty seven it takes now. Its orbit was also much more eccentric”
- SupportedEarth’s gravity rhythmically squeezed and stretched the Moon’s interior, generating heat.Universe Today: “All of which means that Earth itself exerted huge rhythmic tidal forces on the Moon' s interior during the course of its orbit.”
- SupportedThe simulations showed tidal strain concentrating energy in two symmetric regions at the core-mantle boundary.Universe Today: “they noticed that a ton of energy was directed specifically at two symmetric regions along the lunar core-mantle boundary.”
- SupportedAround 3.2 billion years ago, tidal strain in the zones delivered an estimated 150 gigawatts, more than four times the energy generated by radioactive decay.Universe Today: “They calculated that, around 3.2 billion years ago, despite taking up only 2.5% of the mantle’s total volume, the tidal strain on these regions delivered 150 gigawatts of power - more than four times the amount of energy generated by radioactive decay.”
- SupportedThe heat helped sustain a magnetic field longer than models originally predicted.Universe Today: “It helped keep the lunar core warm, which helped sustain a magnetic field for much longer the models originally predicted”
- SupportedThe heat drove mantle plumes that later produced the basalts seen in Chang’e-5 samples.Universe Today: “It also drove huge mantle plumes that swelled toward the crust. Billions of years later, long after the tidal engine has calmed down, those stranded pockets of mantle melted to produce the basalts seen in the Chang’e-5 samples.”
- SupportedThe model remains theoretical, and future lunar missions may provide more definitive data.Universe Today: “but as of now it’s still only a theory. Maybe some of the numerous lunar missions planned over the next decade will be able to provide more definitive data”
