Free Astronomy Magazine November-December 2022

NOVEMBER-DECEMBER 2022 nation of the orbital pe- riod is possible. Before the impact, Dimorphos took 11 hours and 55 minutes to complete one orbit around Didy- mos. Scientists had pre- dicted that after the impact this period could have varied by about 73 sec- onds, but the exact value was precisely the purpose of the ex- periment. To find it out, DART im- pacted Dimorphos at approximately 13,421 miles/hour (21,600 km/hour), while any signal sent to the space- craft took 28 seconds to reach the target. Since Dimorphos measures only 160 meters in diameter, it was impossible to maneuver the space- craft from Earth to direct it at Dimor- phos. For these reasons, the technical design included an automatic naviga- tion tool. A few days after the im- pact, s c i en - tists found that Dimorphos’ orbital period variation was much higher than expected: it was surpris- ingly shortened by 23 minutes. In the following pages, the most rel- evant phases of this historic achieve- ment are illustrated. by Ignacio Ferrín Institute of Physics University of Antioquia Medellin, Colombia T he Double Asteroid Redirec- tion Test spacecraft (DART), im- pacted Dimorphos, a satellite of the asteroid Didymos, on Monday 26 th September at 23 h 14 m UT. It is the first time planet Earth is attempting to divert an asteroid from its path, to learn how to do it in case we have to face such a threat in the future. Didymos was discovered in 1996 with the University of Arizona 0.9-meter Spacewatch Telescope, located at Kitt Peak National Observatory, some miles to the west of Tucson, Arizona. Didymos was selected to perform this test because the system is an eclipsing binary. Thus, by meas- uring eclipses, a very precise determi-