triaxial ellipsoid\u2019 \u2013 something more like an oblong watermelon.\u201d<\/p>\nNaidu\u2019s team used three data sources in their computer models to deduce what had happened to the asteroid after impact. The first source was aboard DART: The spacecraft captured images as it approached the asteroid and sent them back to Earth via NASA\u2019s Deep Space Network (DSN). These images provided close-up measurements of the gap between Didymos and Dimorphos while also gauging the dimensions of both asteroids just prior to impact.<\/p>\n
The second data source was the DSN\u2019s Goldstone Solar System Radar, located near Barstow, California, which bounced radio waves off both asteroids to precisely measure the position and velocity of Dimorphos relative to Didymos after impact. Radar observations quickly helped NASA conclude that DART\u2019s effect on the asteroid greatly exceeded the minimum expectations.<\/p>\n
The third and most significant source of data: ground telescopes around the world that measured both asteroids\u2019 \u201clight curve,\u201d or how the sunlight reflecting off the asteroids\u2019 surfaces changed over time. By comparing the light curves before and after impact, the researchers could learn how DART altered Dimorphos\u2019 motion.<\/p>\n
As Dimorphos orbits, it periodically passes in front of and then behind Didymos. In these so-called \u201cmutual events,\u201d one asteroid can cast a shadow on the other, or block our view from Earth. In either case, a temporary dimming \u2013 a dip in the light curve \u2013 will be recorded by telescopes.<\/p>\n
\u201cWe used the timing of this precise series of light-curve dips to deduce the shape of the orbit, and because our models were so sensitive, we could also figure out the shape of the asteroid,\u201d said Steve Chesley, a senior research scientist at JPL and study co-author. The team found Dimorphos\u2019 orbit is now slightly elongated, or eccentric. \u201cBefore impact,\u201d Chesley continued, \u201cthe times of the events occurred regularly, showing a circular orbit. After impact, there were very slight timing differences, showing something was askew. We never expected to get this kind of accuracy.\u201d<\/p>\n
The models are so precise, they even show that Dimorphos rocks back and forth as it orbits Didymos, Naidu said.<\/p>\n
The team\u2019s models also calculated how Dimorphos\u2019 orbital period evolved. Immediately after impact, DART reduced the average distance between the two asteroids, shortening Dimorphos\u2019 orbital period by 32 minutes and 42 seconds, to 11 hours, 22 minutes, and 37 seconds.<\/p>\n
Over the following weeks, the asteroid\u2019s orbital period continued to shorten as Dimorphos lost more rocky material to space, finally settling at 11 hours, 22 minutes, and 3 seconds per orbit \u2013 33 minutes and 15 seconds less time than before impact. This calculation is accurate to within 1 \u00bd seconds, Naidu said. Dimorphos now has a mean orbital distance from Didymos of about 3,780 feet (1,152 meters) \u2013 about 120 feet (37 meters) closer than before impact.<\/p>\n
\u201cThe results of this study agree with others that are being published,\u201d said Tom Statler, lead scientist for solar system small bodies at NASA Headquarters in Washington. \u201cSeeing separate groups analyze the data and independently come to the same conclusions is a hallmark of a solid scientific result. DART is not only showing us the pathway to an asteroid-deflection technology, it\u2019s revealing new fundamental understanding of what asteroids are and how they behave.\u201d<\/p>\n
These results and observations of the debris left after impact indicate that Dimorphos is a loosely packed \u201crubble pile\u201d object, similar to asteroid Bennu. ESA\u2019s (European Space Agency) Hera mission, planned to launch in October 2024, will travel to the asteroid pair to carry out a detailed survey and confirm how DART reshaped Dimorphos.<\/p>\n
DART was designed, built, and operated by the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, for NASA\u2019s Planetary Defense Coordination Office, which oversees the agency\u2019s ongoing efforts in planetary defense. DART was humanity\u2019s first mission to intentionally move a celestial object.<\/p>\n
JPL, a division of Caltech in Pasadena, California, manages the DSN for NASA\u2019s Space Communications and Navigation (SCaN) program within the Space Operations Mission Directorate at the agency\u2019s headquarters in Washington.<\/p>\n
Ian J. O\u2019Neill
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-2649
ian.j.oneill@jpl.nasa.gov<\/p>\n
Karen Fox \/ Charles Blue
NASA Headquarters
karen.c.fox@nasa.gov \/ charles.e.blue@nasa.gov<\/p>\n
2024-029<\/p>\n<\/div>\n
\n
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