Bengaluru: The US’ National Aeronautics and Space Administration (NASA) Wednesday launched its Double Asteroid Redirection Test (DART) mission towards the asteroid Dimorphos, in order to intentionally crash into it. The DART mission seeks to test whether crashing a probe into an asteroid could alter its path and take it to a different trajectory.
If NASA’s mission is successful, it would pave the way for better planetary defence, and equip space agencies to deflect the path of near-Earth objects (NEO), many of which surround the planet and could potentially pose a threat one day.
The spacecraft was launched aboard a SpaceX Falcon 9 rocket from the Vandenberg Space Force Base in California at 10:21 pm local time Tuesday (11:51 am IST Wednesday). The 560-kg impactor will crash into Dimorphos, over 480 million km away, at a speed of 6.6 km per second.
Dimorphos is not headed towards Earth currently. It’s a small, 160-metre-wide asteroid, which is in orbit around a larger, 780 m-wide asteroid called Didymos. Dimorphos takes nearly 12 hours to orbit Didymos. The impact is expected to increase the orbital time of Dimorphos by at least 73 seconds, and likely by up to 10 or 20 minutes.
An Italian cubesat, called LICIACube (Light Italian CubeSat for Imaging of Asteroids) is piggybacking on the spacecraft and will image the impact and ejecta, having separated two days before impact. DART also carries a camera called DRACO (Didymos Reconnaissance and Asteroid Camera for Optical navigation), which will capture images until 20 seconds before impact.
The impact is expected to occur in late September or early October of next year, with a target date of 26 September 2022.
Trajectory and mission plan
The DART spacecraft will now make a full orbit around the Sun first before heading towards Dimorphos. It is expected to close in towards the end of September 2022, but could also do so by early October. Four hours before impact, the spacecraft will autonomously steer itself towards Dimorphos.
The moonlet has not been observed at close quarters before, and DRACO is expected to provide the first high resolution pictures of its shape, structure, and surface.
The NASA spacecraft — technically a kinetic impactor — will start to move towards the asteroid when it is just 1.4 pixels wide, and is capable of manoeuvring more before impact. It will provide final images with resolutions of 3cm/pixel.
The LICIACube will fly by the asteroid about 3 minutes after impact, providing detailed images of the impact, impact site, ejecta, and surface, at a resolution of 2m per pixel.
After impact, the binary asteroid system will continue to be monitored from Earth. In 2026, the European Space Agency (ESA)’s Hera mission will fly by Didymos for follow-up observations.
While NASA engineers know the velocity of the spacecraft, its mass, and that of the asteroid, the expected impact is dependent on the nature of Dimorphos. Owing to lack of close-up data, it is currently unclear whether the asteroid is substantially solid or is simply a loose pile of rubble held together by weak gravity.
The change in orbit is expected to be just a fraction of a percentage of its original orbit, but the orbital period will increase by a minimum of 73 seconds. Engineers expect it to be extended by 10-20 minutes, which will create an ample difference for it to be observable from Earth.
The confirmation of change in orbital period will be done through a transit method observation. As the smaller asteroid will pass in front of the larger Didymos when orbiting, it will be observed from Earth as a slight dimming of Didymos due to a passing obstruction. The frequency of these passes can be observed to confirm the success of the mission.
Success will demonstrate capability to potentially deflect any NEO, which are mostly asteroids, that come close to Earth and could potentially get sucked in by the planet’s gravity or collide head-on.
What are NEOs?
An object is described as a near-Earth object if its closest approach to the Sun is less than 19,44,77,230 km or 1.3 astronomical units (AU). One AU is the average distance between the Sun and Earth. Mars orbits at 1.5 AU.
If an NEO crosses earth’s orbit and it is over 140 metres in diameter, it is considered a potentially hazardous object. Objects that are mere metres wide could cause serious local damage, while larger ones could cause massive destruction including triggering deadly tsunamis.
The extinction of the dinosaurs, known as the Cretaceous-Paleogene extinction event, was caused by a 10-km wide impactor that crashed into what is today the Chicxulub crater in Mexico. In 2013, a 20 m wide asteroid exploded over Russia in what is called the Chelyabinsk meteor, releasing large amounts of energy and injuring over 1,500 people indirectly.
In 1908, in the Tunguska event, a meteor that was likely about 60 m wide flattened over 80 million trees over an area of 2,150 sq. km in Siberia, as it exploded in the air. It was the largest impact event in modern history on Earth.
Asteroid impacts have also been observed on other planets, such as the comet Shoemaker-Levy 9 crashing into Jupiter in 1994 after being pulled apart by its gravity two years earlier and breaking up into pieces.
Such observations and incidents, as well as the increasing number of objects being added to the Risk Table of NASA’s Sentry programme, which predicts impacts on Earth over the next century, has caused planetary scientists to take proactive measures for planetary defence against NEOs.
There are over 27,000 NEOs tracked by NASA so far. NEOs are typically asteroids but can sometimes be comets as well. Other than larger asteroids that pose a threat, smaller asteroids and meteors crash into earth on a daily basis with no real harm done to life.
(Edited by Amit Upadhyaya)
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