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How many moons are there in space?

Our question of the month
September 1, 2016
At the poles of the moon Ceres, scientists have found craters that are permanently in shadow (indicated by blue markings). Such craters are called "cold traps" if they remain below about minus 240 degrees Fahrenheit (minus 151 degrees Celsius). These shadowed craters may have been collecting ice for billions of years because they are so cold. Image by NASA

At the poles of the moon Ceres, scientists have found craters that are permanently in shadow (indicated by blue markings). Such craters are called "cold traps" if they remain below about minus 240 degrees Fahrenheit (minus 151 degrees Celsius). These shadowed craters may have been collecting ice for billions of years because they are so cold. Image by NASA

The bottom line: No one knows for sure.

How many moons are there in space?

Space is a really big place. There are billions of galaxies, and each one has billions of stars. Recent discoveries suggest that planetary systems are the rule and not the exception around stars. So the number of moons in space is uncountable.

I suspect you meant to ask how many moons there are in our solar system. When I was young, a long time ago, books about the solar system gave precise numbers for the moons of each planet. Then came the Pioneer and Voyager spacecrafts and vastly better telescopes. The answer is, “No one knows.” It seems every time we get a closer look at the distant planets, like Saturn, Uranus, or Neptune, we discover they have more moons than we previously thought. Even Pluto is now known to have at least two moons.

The dwarf planet Ceres, the largest body in the Asteroid Belt, currently has an artificial moon. NASA’s Dawn spacecraft has been orbiting this fascinating body since December 2014. The Lab even has instrumentation on Dawn in the form of its gamma-ray and neutron detectors.

Gordon McDonough, Museum science evangelist