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<\/p>\nOn Sept. 26, 2022, NASA\u2019s Double Asteroid Redirection Test (DART) spacecraft slammed into the side of the 170-meter-wide asteroid Dimorphos to test future asteroid deflection tactics in the event an asteroid was threatening Earth. Following impact, DART teams confirmed that the spacecraft\u2019s collision with the asteroid had successfully deflected the asteroid by a small amount \u2014 proving the design of the deflector and allowing scientists and engineers to better understand the ways we can protect Earth from asteroids.<\/p>\n
However, a new study from a group of scientists shows that DART\u2019s collision with Dimorphos not only changed the shape of its orbit around its host asteroid Didymos but also significantly changed the shape of the asteroid.<\/p>\n<\/p>\n
Before the collision, Dimorphos was known to be a roughly symmetrical \u201coblate spheroid\u201d shaped asteroid, similar to a squished ball that is wider than it is tall. Additionally, it took the asteroid around 11 hours and 55 minutes to complete one orbit around Didymos, which, as mentioned, has since been altered following DART\u2019s impact with Dimorphos.<\/p>\n
\u201cWhen DART made impact, things got very interesting. Dimorphos\u2019 orbit is no longer circular: Its orbital period is now 33 minutes and 15 seconds shorter. And the entire shape of the asteroid has changed, from a relatively symmetrical object to a \u2018triaxial ellipsoid\u2019 \u2013 something more like an oblong watermelon,\u201d said navigation engineer and lead author Shantanu Naidu of NASA\u2019s Jet Propulsion Laboratory (JPL) in California.<\/p>\n
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Illustration showing the shape of Dimorphos both before and after DART\u2019s impact. (Credit: NASA\/JPL-Caltech)<\/p>\n
To better understand how Dimorphos\u2019 shape and orbit changed following DART\u2019s impact, Naidu et al. employed computer models that utilized three data sources that collected data during DART\u2019s impact. The first source was the images DART\u2019s Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO) camera captured of Didymos in the hours, minutes, and seconds before impact. DRACO\u2019s images were transmitted from DART to the Deep Space Network (DSN), and the images allowed the scientists to perform close-up measurements and gauge the dimensions of both Didymos and Dimorphos before impact.<\/p>\n
The DSN\u2019s Goldstone Solar System Radar was the second data source, which is located in Barstow, California. During DART\u2019s impact sequence, the Goldstone Radar bounced radio waves off of Dimorphos and Didymos to measure the position and velocity of Dimorphos around Didymos precisely before and after DART\u2019s collision. These measurements are what allowed NASA teams to quickly discern whether or not DART\u2019s impact had indeed deflected Dimorphos in its orbit around Didymos. Teams would eventually find that the effect of DART\u2019s impact on the asteroid greatly exceeded the minimum expectations for the mission.<\/p>\n
The final and most significant data source utilized in Naidu et al.\u2019s study was ground telescopes located around Earth that measured the light curve \u2014 how sunlight reflects off the surface of the asteroids over time \u2014 from both asteroids. Comparing the asteroids\u2019 light curves before and after impact allowed the team to learn more about how DART altered Dimorphos\u2019 position around Didymos.<\/p>\n
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\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. Before 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 said co-author Steve Chesley of JPL.<\/p>\n<\/p>\n