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Direct hit: DART mission hits Dimorphos in a planetary defence test 

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In some science fiction films, a group of scientists are faced with an asteroid heading straight for Earth. The solution? A spacecraft that hits it directly. Deflect it, destroy it, the goal is to save the planet from destruction. Now we will legitimately be able to uncover how feasible it is to solve such a situation. 

NASA announced that the Double Asteroid Redirection Test (DART) mission successfully made impact with the moonlet asteroid – Dimorphos – on Monday 26, at 7:14 pm EDT (00:14 in London). After ten months in space – the spacecraft was released in November 2021 – mission control at the John Hopkins Applied Physics Laboratory (APL) received the news of the impact. It is NASA’s first attempt in hitting an asteroid, proving we are capable of deviating from potential space hazards using technology. The DART mission impact was livestreamed online on NASA social networks.

APL was in charge of building and managing the DART spacecraft and coordinating the investigation team. The DART Investigation team was composed of 240 investigators from all over the world, led by Andrew Cheng and Andrew Revkin – both researchers of John Hopkins APL. 

DART is part of NASA’s planetary defence project and represents a demonstration of a viable mitigation technique for protecting the Earth from asteroids and comets. The mission attempted to demonstrate kinetic impactor technology by impacting Dimorphos in order to modify its path and speed. DART is NASA’s first spacecraft mission developed to achieve a planetary defence objective and the first mission flown by the Planetary Defence Coordination Office (PDCO), created in 2016 to manage the agency’s ongoing planetary defence efforts.

Dimorphos is one body of a binary asteroid system called Didymos, translating to ‘twin’ in Greek. It is composed of two asteroids, the bigger one employing the same as the system, while the smaller one labelled Dimorphos – the target of DART. Dimorphos is a moonlet asteroid, which orbits the Didymos asteroid, and has a diameter of 160 meters. Neither asteroid poses a threat to Earth.

Before the impact, the distance between the two asteroids was 1.18 kilometres, according to the DART mission webpage. Didymos was, in the words of the DART team, the ideal target. It was chosen carefully, considering its orbit path did not intersect Earth at any point even after contact was made. Earth-based telescopes were also able to measure the variation in brightness to determine the distance of the orbit before and after the collision. Before the impact, it took 11 hours and 55 minutes for Dimorphos to complete the orbit around Didymos. NASA expects this to change for several minutes, with the intention to shorten the distance between the two asteroids.

The DART spacecraft was equipped with a high-resolution imager named DRACO, which helped to support navigation and targeting. It spotted Dimorphos for the first time one hour before hitting it. The DART camera returned an image per second until the impact, when half the screen went red due to loss of signal. The pictures sent back by the DART spacecraft were shown live on NASA’s social media, with a small window of the mission controllers in APL, until the stream cut as the probe was obliterated.

“At its core, DART represents an unprecedented success for planetary defense, but it is also a mission of unity with a real benefit for all humanity,” said NASA Administrator Bill Nelson, “As NASA studies the cosmos and our home planet, we’re also working to protect that home, and this international collaboration turned science fiction into science fact, demonstrating one way to protect Earth.”

The DART mission is not the only one planned around the Didymos system. The Hera mission is a program in the European Space Agency’s (ESA) space safety and security activities. The spacecraft is planned to be launched in 2024 and arrive in the Didymos system by 2026. Its objectives are to investigate the binary asteroid – including its internal properties – and to measure extensively the outcomes of NASA’s DART mission kinetic impactor test from ground-based observatories. The main goal being to understand more about the asteroid’s geophysics for future asteroid deflection missions.

The focus on planetary defence is growing, as can be seen in the increased number of initiatives that NASA has sponsored over recent years. One of which being the Vera Rubin Observatory, a new telescope in Chile financed by the United States that can systematically scan the night sky, with the possibility of identifying thousands of potentially hazardous asteroids. Another being the NEO Surveyor, a space-based telescope that NASA is working to build to aid in finding threats that are hard to spot from Earth.

The work for planetary defence is just beginning.

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