In focus: Moonquakes
- Moon is a one-plate world unlike a number of plates (major and minor) on earth.
- Further since moon also has no atmosphere, it was believed to be a dead world geologically.
Origin of Moonquakes
- The moon’s upper mantle is much more rigid and less fluid than the interior of the Earth as shown in the figure.
- As a result there is no evidence for plate tectonics on the lunar surface.
- However the seismometers placed by Apollo Mission detected about 3000 moonquakes every year.
- Since there are no plate motions the question was ‘What causes moonquakes?’
- The natural explanation was that the Earth’s tidal forces deform the solid body of the Moon triggering moonquakes.
- As a result it was seen that moonquakes were recorded predominantly at perigee when moon is nearest the Earth.
Results of new study
- The new study found that six of the quakes happened when the moon was at its apogee, farthest point from the Earth in its orbit.
- Earth’s tidal influence is not the only reason for moonquakes.
- The moon is gradually shrinking and has shrinked by about 50 meters in over millions of years.
- The shrinking of moon has caused its surface to wrinkle (imagine a grape that wrinkle on shrinking)
- Since the moons crust is brittle it breaks thus forming ‘thrust faults’ at breaking points as shown in the figure.
- According to data these faults are still active and likely producing moonquakes. Thus it can be concluded that moon is continuing shrink.
- It is for the 1st time we have evidence to show that moon is not geologically dead as it was believed.
- It has active tectonic activity though very feeble compared to earth’s plate tectonics.
- The surface features revealing the fault lines and resultant landforms like cliffs and boulder show the target of future missions.
- However since the mass of the moon is not changing it is unlikely that it will have any effect on the tides on earth.
Section : Science & Tech