Scientists Say: Exomoon | Science News for Students

Scientists Say: Exomoon

This is a moon that orbits a planet outside of our solar system
Jan 14, 2019 — 6:30 am EST
artist's vision of an exomoon

Planets orbiting far away stars may have moons. Scientists are hunting these potential exomoons.

NASA/ESA/L. Hustak

Exomoon (noun, “EX-oh-moon”)

This is a moon that orbits a planet found outside our solar system. Planets that orbit stars other than our sun, such as Alpha Centauri, are known as exoplanets. If those exoplanets have moons that orbit them? Those are exomoons.

Scientists have not yet confirmed that exomoons exist. But they’ve got some evidence from powerful space telescopes such as Hubble and Kepler. These telescopes have spotted dips in light in front of stars. That dimming is what happens when an exoplanet passes in front of the star. But sometimes, that dip is followed by a second dimming. That could be the exoplanet’s exomoon, trailing along behind.

In a sentence

When exoplanets are too hot or cold to support life, scientists might look to their exomoons for aliens instead.

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Power Words

(more about Power Words)

alien     A non-native organism. (in astronomy) Life on or from a distant world.

exomoon     A moon that orbits an exoplanet.

exoplanet     Short for extrasolar planet, it’s a planet that orbits a star outside our solar system.

moon     The natural satellite of any planet.

orbit     The curved path of a celestial object or spacecraft around a star, planet or moon. One complete circuit around a celestial body.

planet     A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood. To accomplish the third feat, the object must be big enough to have pulled neighboring objects into the planet itself or to have slung them around the planet and off into outer space. Astronomers of the International Astronomical Union (IAU) created this three-part scientific definition of a planet in August 2006 to determine Pluto’s status. Based on that definition, IAU ruled that Pluto did not qualify. The solar system now includes eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

solar system     The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

star     The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become dense enough to sustain nuclear-fusion reactions, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

telescope     Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.