When engineers at a control center in Turin, Italy, sent a faint radio signal into space, they set off a world-first experiment. The message reached NASA\u2019s Double Asteroid Redirection Test spacecraft, better known as DART, more than 5 million miles away. In response, the spacecraft released its traveling partner, a shoebox-sized satellite named LICIACube.<\/p>\n
Fifteen days later, DART deliberately collided head-on with Dimorphos, a small moon orbiting a larger asteroid<\/a> called Didymos. While the spacecraft was destroyed, LICIACube flew past at high speed, capturing the only close-up images of the historic impact. The photos gave scientists the data they needed to calculate how much material was blasted away from the asteroid and how the collision changed its motion.<\/p>\n The Science of the Impact<\/p>\n When DART struck, the tiny spacecraft transferred its energy into Dimorphos. But the real surprise came from what happened next. Scientists analyzing LICIACube\u2019s images reported in The Planetary Science Journal<\/a> that 35.3 million pounds of rock and dust were ejected. That\u2019s the weight of about 100 fully loaded jumbo jets, hurled into space in seconds.<\/p>\n The tail of material that formed behind Dimorphos was prominent almost 12 days after the DART impact, giving the asteroid a comet-like appearance, as seen in this image captured by NASA\u2019s Hubble Space Telescope in October 2022. (CREDIT: NASA) <\/p>\n Though this debris made up less than half a percent of Dimorphos\u2019 total mass, it was still 30,000 times greater than the spacecraft\u2019s weight. The flying rubble acted like a booster rocket, giving Dimorphos an extra push that far exceeded the direct effect of the crash.<\/p>\n \u201cThe plume of material released from the asteroid was like a short burst from a rocket engine<\/a>,\u201d explained Ramin Lolachi of NASA\u2019s Goddard Space Flight Center. The resulting momentum shifted Dimorphos\u2019 orbit around Didymos by 33 minutes, a change that was easily measured from telescopes on Earth.<\/p>\n How LICIACube Captured the Scene<\/p>\n LICIACube had just one minute to complete its vital task. As it sped by at 15,000 miles per hour, it snapped photos once every three seconds. The closest image was taken from only 53 miles above Dimorphos. The spacecraft\u2019s camera, called LUKE, recorded the event in multiple colors of light. Scientists studied 18 images taken from different angles, watching the debris plume evolve. Early shots showed the cloud shining brightly under direct sunlight. Later images revealed a dimmer glow as sunlight scattered through the dust.<\/p>\n Related Stories<\/p>\n This fading light told researchers that the cloud contained mostly larger particles \u2014 many about a millimeter across. Because the innermost region was so thick that no light could pass through, the team relied on models to estimate the unseen mass. Timothy Stubbs, a planetary scientist at NASA Goddard, explained, \u201cWe estimated that this hidden material accounted for almost 45% of the plume\u2019s total mass.\u201d<\/p>\n Weighing the Plume<\/p>\n To make sense of the images, researchers compared them with laboratory scattering experiments and computer models. The goal was to understand how particles of different sizes reflect light. By integrating plume brightness across the camera\u2019s field of view, they calculated the amount of material ejected.<\/p>\n Initial estimates suggested at least 19 million pounds were blasted away. But when scientists accounted for the hidden inner plume, the total rose by 77%. The final calculation of 35.3 million pounds is now considered the most accurate measurement. The particle size distribution followed a simple mathematical pattern, known as a power law, where smaller particles are much more common than larger ones. This type of distribution is typical of debris clouds<\/a> from violent impacts.<\/p>\n LICIACube image acquired after impact of the DART spacecraft, showing a complex system of ejecta rays with filamentary structures. (CREDIT: Ramin Lolachi, et al.) What Dimorphos Is Made Of<\/p>\n The experiment also shed light on Dimorphos itself. The asteroid is what scientists call a \u201crubble pile\u201d \u2014 a loose clump of boulders and dust bound together weakly by gravity<\/a>. Calculations suggest its strength is less than 50 pascals, softer than compacted snow. That explains why such a small spacecraft could release so much material.<\/p>\n