How is the Moon Changing?
From Earth’s perspective, the Moon is constantly changing. It rises and sets at different times each day, it appears to take different shapes throughout the month, and it’s slowly moving away from Earth. Still, as a world, the Moon is much steadier than our own planet. With no flowing water or gusting winds to wear away its landscape, geologic features like craters, cliffs, and lava flow last much longer on the Moon than they do on Earth – but five decades and counting of lunar exploration have shown that the Moon is more dynamic than previously thought. Here are just a few of the ways the Moon transforms over time.Craters
Unlike Earth, the Moon does not have a protective atmosphere and so the Moon is constantly bombarded by rocks and dust from space. Each object leaves a record of its arrival. Larger and fast-moving objects create craters, or holes in the ground. Scientists study impact craters’ sizes, shapes, and positions to find out what kinds of objects are hitting the Moon, how frequently they arrive, and how these patterns have changed over time. NASA’s Lunar Reconnaissance Orbiter has even observed new craters forming on the Moon.
Some pieces of space debris are too small to make craters, but they still disturb the lunar surface. Impacts of all sizes mix up the Moon’s outermost layers and expose fresh material that was once hidden underground. This process is called impact gardening.A Shrinking Moon
A Shrinking Moon
Cliffs in the lunar crust, observed by the Apollo astronauts and by NASA’s Lunar Reconnaissance Orbiter, indicate that the Moon shrank globally in the geologically recent past and is likely still shrinking today. The Moon formed in a chaotic environment of intense bombardment by asteroids and meteors. These collisions, along with the decay of radioactive elements, made the Moon hot. Since its inception, the Moon has been cooling. As it cools, it shrinks and its brittle surface breaks, forming thrust faults where a section of the crust breaks away from and juts out over another. Scientists estimate that, in the last several hundred million years, the diameter of the Moon has gotten about 150 feet (50 meters) smaller.Moonquakes
Seismometers left on the surface of the Moon by Apollo astronauts have revealed that the Moon experiences moonquakes. Deep moonquakes, occurring hundreds of miles beneath the lunar surface, are tidal events – they result from the pull of Earth’s gravity tugging and stretching the Moon’s internal structures. Another type of moonquake is caused by the Moon shrinking as it cools ― a process that has been happening since the Moon first formed nearly 4.5 billion years ago. These moonquakes originate at the moderately shallow depths of 20-30 km, can register up to a startling 5.5 on the Richter scale, and can last for over 10 minutes! Moonquakes originating on or near the surface can be caused by meteoroid impacts with the Moon. Another type of extremely shallow moonquake can come from thermal expansion and contraction of rock on or near the surface as it goes from the frigid lunar night to the very hot lunar daytime.
“Weather” on the Moon is nothing like the weather we know at home. Earth’s weather comes from its windy, water-rich atmosphere; lunar weather comes straight from space. Solar wind, galactic cosmic rays, and bursts of high-energy particles shower radiation across the lunar surface.
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Water on the Moon
You won’t find deep oceans or rainfall on the Moon, but the Moon does contain water buried within rocks and dust. Scientists are still working to understand where this water comes from, where exactly it is located, how plentiful it is, and how it behaves based on temperature changes between lunar day and lunar night.
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Writers: Caela Barry & Molly Wasser, NASA's Goddard Space Flight Center
Science Advisor: Andrea Jones, NASA's Goddard Space Flight Center