![Image captured by the Italian Space Agency's LICIACube minutes after NASA's Double Asteroid Redirection Test (DART) mission intentionally collided with its target asteroid, Dimorphos, captured on September 26, 2022. Credit: ASI Shadowhunters Capture Stars Eclipsing Asteroid Didymos](https://oponame.com/wp-content/uploads/2022/10/Shadowhunters-Capture-Stars-Eclipsing-Asteroid-Didymos.jpg)
Image captured by the Italian Space Agency’s LICIACube minutes after NASA’s Double Asteroid Redirection Test (DART) mission intentionally collided with its target asteroid, Dimorphos, captured on September 26, 2022. Credit: ASI
After months of effort, astronomers have managed to capture the momentary shadow cast by the asteroid Didymos, tens of millions of miles away as it streaked past distant stars – an observational feat made possible only when the asteroid’s trajectory and the precise location of the stars are known. Even then, to have any chance of success, multiple observers had to be placed in carefully planned locations in the shadow’s path, to catch a glimpse of the star’s fleeting fading in just a fraction of a second.
Why even attempt such an ambitious challenge? Because “stellar occultations”, as they are called, are an extraordinary tool for obtaining information about the shapes and positions of objects in the solar system, with a precision otherwise impossible for distant observers. And, crucially, the ultra-precise three-dimensional star maps generated by ESA’s Gaia satellite have made this technique much more feasible in recent years.
To target near-Earth asteroid occultations in particular, an ESA-supported project called ACROSS, Asteroid Collaborative Research via Occultation Systematic Survey, was supported by ESA’s Discovery program via a call on the Agency open space innovation, seeking promising space research. support ideas.
Paolo Tanga of the Côte d’Azur Observatory, ACROSS project manager and solar system data processing manager at Gaia, comments that “Astrometry based on the observation of ‘stellar occultations’ has been initially exploited for main-belt asteroids between Mars and Jupiter, then for distant transneputian objects, but ACROSS is extending its systematic exploitation to near-Earth asteroids as well. That’s the challenge: because NEAs move fast and are small, producing thus shorter events and much narrower shadows cast on the ground.”
How do you catch NEA then, using cloaks? By improving the accuracy of their trajectories, by broadcasting accurate predictions of where and when events are visible, and by mobilizing networks composed of both citizen scientists (motivated amateur astronomers) and professionals, on a global scale.
ACROSS is particularly focused on Didymos – actually a binary asteroid system, with its 780m diameter main asteroid orbited by a smaller 160m diameter moon called Dimorphos – the target of the twin asteroid redirect test of NASA, DART. On the night of September 26, the DART spacecraft collided with the smaller of the two asteroids, shifting its orbit.
ESA will then fly the Hera spacecraft to the Didymos system to perform a close survey of the post-impact asteroid. Repeated occultations over several years will even make it possible to measure the deviation of the system’s trajectory around the Sun induced by the impact of DART, which cannot be done by DART or Hera alone.
![Occultation of the asteroid Didymos recorded on October 18 in Granada, Spain. Credit: Miguel Sanchez Shadowhunters Capture Stars Eclipsing Asteroid Didymos](https://oponame.com/wp-content/uploads/2022/10/1666304036_229_Shadowhunters-Capture-Stars-Eclipsing-Asteroid-Didymos.jpg)
Occultation of the asteroid Didymos recorded on October 18 in Granada, Spain. Credit: Miguel Sanchez
ACROSS co-investigator, Professor Kleomenis Tsiganis of Aristotle University of Thessaloniki, AUTh, adds that “to make such campaigns possible, we needed to perform independent orbit enhancement calculations from currently available data, reduce the uncertainty of the occultation path to a few kilometers, and deploy observers accordingly to pick up a momentary blink of the star which must be measured in milliseconds.”
Logistical efforts have been enormous and fruitless for several weeks, as in the case of the 45 observers deployed in Portugal, Spain and Algeria on August 25, but prevented from observing by unfavorable weather conditions.
Meanwhile, efforts on all fronts, including close collaboration with Steve Chesley of NASA’s Jet Propulsion Laboratory on the DART team, have further improved the predictions.
And then success came: the first confirmation came on October 15 of the deployment of six telescopes, five of which were supervised by a single observer, Roger Venable, in northern Oklahoma, United States, the other by Robert Dunford. One of them – at 9:02 a.m. CEST – clearly picked up the fading of the star over about 0.13 seconds, just a bit shorter than the maximum possible duration.
Then, on October 18, it was the turn of a team led by Jose-Luis Ortiz to observe an event very close to his home institute, the Instituto de Astrofisica de Andalucia-CSIC, near Granada in Spain. Miguel Sanchez, equipped with a 28 cm aperture portable telescope, clearly recorded the occultation with excellent agreement with the predictions.
Later the same day, in Japan, some seven telescopes were deployed; those of Hayato Watanabe and Miyoshi Ida through the Japan Occultation Information Network (JOIN) were the luckiest – this is the first event observed by two sites.
With the eclipse of stars behind Didymos captured for the first time by astronomers, future events will be easier to catch. Observing more should provide much more accurate tracking of Didymos’ orbit, possibly allowing the detection of a tiny change in Didymos’ heliocentric orbit due to the DART impact, and even hopefully learning more about the scars. left by the impact of the DART.
NASA’s Hubble spots twin tails in new image after DART impact
Provided by the European Space Agency
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