FYI.

This story is over 5 years old.

Tech

NASA's Gravity Atlas of the Moon Is a Guide to Finding the Biggest Lunar Bounce

Also: insights into the Moon's internal structure, composition, and thermal evolution.

Though we’ve sent men to walk on its surface and have spent more time studying it than any other body in the Solar System, the Moon continues to surprise us. Last week, NASA released an incredible image showing the Moon in unprecedented detail—specifically, the fine structure of the varied gravity environment of the Moon’s southern latitudes.

The data behind this image comes courtesy of NASA’s Gravity Recovery and Interior Laboratory mission, otherwise known as the GRAIL mission. This specialized mission was designed to combine high-resolution gravitational data with topographical data to give scientists keener insights into the Moon’s internal structure, composition, and ultimately a better understanding of its thermal evolution; that is, how the Moon cooled and how it developed over its lifetime. As a more practical application, a better understanding of the Moon’s gravitational environment will lead to better navigational aides for future lunar missions.

Advertisement

It turns out that the Moon’s gravity environment is a lot less regular than we might think. If the Moon were perfectly round and smooth inside and out, its gravity map would be represented by an even, uniform colour. There would be no features to create any variety. But it’s not. The Moon’s surface is bumpy and its internal structure is lumpy, both irregularities that combine to create variations in gravity.

This new free-air gravity map, which uses terrain data from NASA’s Lunar Reconnaissance mission, shows the Moon’s deviations from the mean gravity if it were a uniform sphere. It’s basically a topographical map for gravity; it shows gravitational deviations from the mean instead of altitude deviations from sea level.

The deviations in this case are measured in milliGals, a unit of acceleration named after Galileo. (As a reference, one Gal is defined as one centimeter per second squared.) The purple in the image is at the low end of the gravity spectrum as it were, a deficit of mass and therefore gravity of around -400 mGals. The red areas are at the high end of gravitational pull scale, an excess of mass yielding about +400 mGals. Yellow is the mean.

The Moon isn’t the only body without a uniform gravity environment. All rocky bodies in the solar system are non-uniform. The Earth is similarly superficially bumpy and internally lumpy, giving our home a similarly varied gravity. On Earth, the force of gravity is slightly weaker at the equator thanks to the centrifugal forces produced by the planet's rotation, and at higher altitudes that are further from the centre of the planet.

Like variations in lunar gravity affecting navigation, the slight variations on Earth aren’t something we’re aware of. They’re more important for scientists studying climate science and weather patterns. Though if you really wanted to experience a slight change in gravity for yourself you could take a scale to the top of Mount Everest and test it out.