Astronomers give the asteroid moon a new name before NASA hits it with a spacecraft

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We wouldn’t be lucky if a killer asteroid were targeting Earth today, but NASA and ESA are gearing up for the first test of technology that could one day save the planet. The Double Asteroid Redirection Test (DART) mission will launch in a few years, and now its target has a name of its own. The little moon that was once known as Didymos B is now Dimorphos.

Astronomers discovered We didymos in 1996 without knowing that it would end up being the perfect target to test NASA’s asteroid redirection technology. Didymos passed close to Earth in 2003, revealing the existence of a small natural satellite in orbit. Didymos is less than a kilometer in diameter, but its satellite is only about 160 meters in diameter. After discovering the moon, astronomers renamed the Didymos object, which in Greek means twin. The moon ended up trapped with the awkward nickname “Didymos B”.

DART is a kinetic impactor mission: it will collide with Didymos B at high speed. This is an ideal way to test the effect of an impact because we can observe changes in its orbit around Didymos. That makes the asteroid moon an important object, and I wouldn’t go on calling it Didymos B. The International Astronomical Union (IAU) finally came up with a suggestion from Kleomenis Tsiganis, a planetary scientist at Aristotle University of Thessalonica and a member of the DART team. The name “Dimorphos” means “two shapes” in Greek, reflecting NASA’s impact to significantly change the object’s orbit.

In 2022, the DART spacecraft will be heading to the Didymos-Dimorphos system. The spacecraft will have a mass of approximately 500 kilograms (1,100 pounds in Earth’s gravity) and almost no scientific payload. The sun sensor, star tracker, and 20cm aperture camera will help the spacecraft locate and collide with Dimorphos at 3.7 miles per second (6 kilometers per second). The Italian Space Agency will send a cubesat together with DART, but it will separate before impact. This will allow scientists to monitor the immediate consequences, but we won’t have the full picture until ESA sends its Hera mission to Didymos in 2024. Hera will be able to accurately measure the change in Dimorphos’ orbit around Didymos.

DART’s impact analysis could tell us whether brute force is likely to deflect a dangerous space rock and, if so, how much warning we would need to deflect it off course. We could also learn that this is not an effective way to protect Earth, and other proposals like slowly pushing the asteroid with a rocket or tying it to a smaller rock are better ideas.

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