Self-Motivation
David Goggins
Former Navy Seal
Career Development
Bryan Cranston
Actor
Critical Thinking
Liv Boeree
International Poker Champion
Emotional Intelligence
Amaryllis Fox
Former CIA Clandestine Operative
Management
Chris Hadfield
Retired Canadian Astronaut & Author
Learn
from the world's big
thinkers
Start Learning

The moon is shrinking — also, moonquakes are a thing

A new NASA report shakes up lunar geology.

  • The moon is indeed shrinking. It has been since it formed.
  • The shrinking is producing thousands of fault lines.
  • Archived seismometer data from Apollo missions show moonquakes.

If you're looking up at a bright full moon and notice it's getting smaller, you're so slightly right that you're closer to being wrong. The moon is shrinking, but only very slowly, and it always has been since its formation, from which it's still cooling down. You've never seen it when it wasn't shrinking.

NASA has just announced, though, that this gradual reduction in size is producing moonquakes. The seemingly lifeless satellite is actually pretty dynamic from a geological point of view, a surprise to the scientific community. Blame shrinkage. Also the pull of earth's gravity.

The research was published May 13 in Nature Geoscience.

In the beginning, revised

Image source: SueC/Shutterstock

We don't really know how the moon formed, but there are suspicions, and the leading theory is that a Mars-sized object slammed into the Earth about 4.5 billion years ago. The object itself, as well as debris from Earth, was ejected into Earth orbit as a molten satellite that's been slowly cooling ever since.

It took about 100 million years for it to crystallize into rocks, with the least dense of them floating upward in the slurry to form the moon's crust and surface. As of this writing, NASA's About the moon webpage says that, "Since the ancient time of volcanism, the arid, lifeless Moon has remained nearly unchanged." They'll likely update that soon — we know now that's it's not true.

Spotted from orbit

Signs of movement: Arrows show boulder fields, patches of relatively high bright soil or regolith.

Image source: NASA/GSFC/Arizona State University/Smithsonian

Orbiting the moon as you read this is NASA's Lunar Reconnaissance Orbiter (LRO), which was launched in June 2009 and has been taking pictures of the Moon's surface since it arrived in lunar orbit a year and four days later.

Captured by its high-resolution 0.5–2m per pixel cameras were a "vast network" of scarps that indicated a variety of interactions between thrust faults. In addition, the faults' crisp appearance, as well as other characteristics, suggest that they're pretty young in geological terms, less than 50 million years old. Though their existence was already known — Apollo 17's Astronauts Eugene Cernan and Harrison Schmitt had to zig-zag their rover up and over the cliff face of one — the sheer number of faults, in the thousands, and their complexity was only made clear by LRO.

NASA compares the faults to the wrinkles formed on a grape's skin as it shrinks into a raisin. The main difference is that where a raisin's skin is soft and pliable, the Moon's crust is brittle and thus fractures and cracks as the Moon continues to cool and shrink at a rate of about 150 feet every few hundred million years.

Digging through Apollo data

Buzz Aldrin deploys a seismometer during the Apollo 11 mission.

Image source: NASA

To gain a fuller understanding of their origin, a team of scientists led by Thomas Watters, senior scientist in the Center for Earth and Planetary Studies at the Smithsonian's National Air and Space Museum took a closer look at data from four seismometers left on the moon by the Apollo 12, 14, 15 and 16 missions at their landing sites. While the Apollo 11 device was active only for about three weeks, the others recorded 28 shallow moonquakes from 1969 to 1977, and there's no reason to think the quakes have stopped since then.

Watters' team developed an algorithm for identifying the quake epicenters from the seismometers' data, and found that at least eight of them were within 30 kilometers of a visible scarps, lending support to the idea that movement of those scarps created the moonquakes. "We think it's very likely that these eight quakes were produced by faults slipping as stress built up when the lunar crust was compressed by global contraction and tidal forces," Watters summarizes, "indicating that the Apollo seismometers recorded the shrinking moon and the moon is still tectonically active." These were not all subtle temblors, either. "Some of these quakes can be fairly strong, around five on the Richter scale."

The algorithm also revealed that six of the eight quakes occurred when the Earth's tidal pull on the Moon was at its maximum, when the moon was at its farthest point, or apogee, from Earth. It's likely that at these times the Moon's crust is under exceptional stress, and so it's more likely for fault slips to occur.

An interesting sidetone is that China's Chang'e-4 dark-side lunar mission may have just found bits of mantle rock on the moon's surface, perhaps a sign of continued geological movement of the Moon's crust and mantle.

Lee Lincoln Scarp at the Apollo 17 Landing Site

Old data, new insight

As LRO Project Scientist John Keller of NASA's Goddard Space Flight Center in Maryland points out, "It's really remarkable to see how data from nearly 50 years ago and from the LRO mission has been combined to advance our understanding of the moon, while suggesting where future missions intent on studying the Moon's interior processes should go."

LIVE EVENT | Radical innovation: Unlocking the future of human invention

Innovation in manufacturing has crawled since the 1950s. That's about to speed up.

Big Think LIVE

Add event to calendar

AppleGoogleOffice 365OutlookOutlook.comYahoo


Keep reading Show less

Bubonic plague case reported in China

Health officials in China reported that a man was infected with bubonic plague, the infectious disease that caused the Black Death.

Vials Of Bacteria That May Cause Plague Missing From TX University

(Photo by Centers for Disease Control and Prevention/Getty Images)
Coronavirus
  • The case was reported in the city of Bayannur, which has issued a level-three plague prevention warning.
  • Modern antibiotics can effectively treat bubonic plague, which spreads mainly by fleas.
  • Chinese health officials are also monitoring a newly discovered type of swine flu that has the potential to develop into a pandemic virus.
Keep reading Show less

Self-driving cars to race for $1.5 million at Indianapolis Motor Speedway ​

So far, 30 student teams have entered the Indy Autonomous Challenge, scheduled for October 2021.

Illustration of cockpit of a self-driving car

Indy Autonomous Challenge
Technology & Innovation
  • The Indy Autonomous Challenge will task student teams with developing self-driving software for race cars.
  • The competition requires cars to complete 20 laps within 25 minutes, meaning cars would need to average about 110 mph.
  • The organizers say they hope to advance the field of driverless cars and "inspire the next generation of STEM talent."
Keep reading Show less

The dangers of the chemical imbalance theory of depression

A new Harvard study finds that the language you use affects patient outcome.

Image: solarseven / Shutterstock
Mind & Brain
  • A study at Harvard's McLean Hospital claims that using the language of chemical imbalances worsens patient outcomes.
  • Though psychiatry has largely abandoned DSM categories, professor Joseph E Davis writes that the field continues to strive for a "brain-based diagnostic system."
  • Chemical explanations of mental health appear to benefit pharmaceutical companies far more than patients.
Keep reading Show less
Videos

Navy SEALs: How to build a warrior mindset

SEAL training is the ultimate test of both mental and physical strength.

Scroll down to load more…
Quantcast