Why NASA Crashed Spacecraft Into an Asteroid

NASA just intentionally flew a spacecraft right into an asteroid to alter its trajectory. To many, this may sound like the plot of a science fiction novel – only it’s not. In the 1998 film, Armageddon, directed by Micheal Bay, NASA hires oil driller Harry Stamper (played by Bruce Willis) and his team to destroy an asteroid the size of Manhattan, headed towards Earth.

NASA, through its Double Asteroid Redirection Test (DART) Mission, did something similar this time. The DART demonstration was part of the overall planetary defence strategy developed by NASA to counter threats from celestial bodies. It was the world's first planetary defence test mission.

"At its core, DART represents an unprecedented success for planetary defence, but it is also a mission of unity with a real benefit for all humanity. 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," said NASA administrator Bill Nelson.

DART Mission

The spacecraft was developed at Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland. After being in space for about 10 months, DART targeted the asteroid moonlet Dimorphos, which is about 160 metres in diameter and crashed into it at a speed of 14,000 km/hr. Dimorphos orbits around the larger asteroid Didymos – about 780-metre in diameter. While both asteroids did not pose any threats to Earth, NASA expects DART to help accumulate important data which in turn will help prepare for a similar event in the future.

Dimorphos asteroid to scale with Rome's Colosseum ( Source: The European Space Agency)

NASA said DART was not meant to destroy Dimorphos. In terms of size, DART weighed around 570 kg, whereas the weight of Dimporphos was around 5 billion kg. But they believe the impact should be sufficient to alter Didymos' course. While the anticipated orbital shift of 1%, might not sound like much, such a shift could prove to be significant in time. It could take a few days to even a month to fully understand the impact. Scientists will investigate the Didymos system, which is within 11 million km of Earth, using ground-based telescopes. 

"The DART mission will help the space agency determine the effectiveness of this mitigation approach and assess how best to apply it to future planetary defence scenarios, as well as how accurate the computer simulations are and how well they reflect the behaviour of a real asteroid," NASA said.

https://twitter.com/NASA/status/1574539270987173903

Planetary defence

Currently, there are tens of thousands of asteroids flying in the close vicinity to Earth, some of them as huge as 500 feet wide. A collision with Earth could be devastating. Dinosaurs' extinction 66 million years ago was caused by a major asteroid strike. So, it would be foolish to assume that such a catastrophic event won't happen again. "The dinosaurs didn't have a space programme to help them know what was coming, but we do," NASA's senior climate adviser Katherine Calvin said.

Threats of extinction from an asteroid can't be put off easily. In 2013, a meteor, around 20 metres in size, entered Earth's atmosphere and exploded over Chelyabinsk in Russia at the height of around 29.7 km, creating an airburst and shockwave that struck six cities across the country. The incident was a stark reminder that threats from asteroids are real.

In this regard, the US has entrusted the National Nuclear Security Administration (NNSA) with the responsibility to protect Earth from celestial bodies like asteroids and comets. NNSA works with the Planetary Defence Coordination Office, the Department of Homeland Security's Federal Emergency Management Agency (FEMA), NASA and other space agencies as well.

https://www.youtube.com/watch?v=DCH88oy_sB8&t=13s

Twenty years ago, former astronauts and physicists founded B612 Foundation, an organisation dedicated to protecting Earth from asteroid strikes. Over the years, they have been pushing for a mission like DART.

Mission Hera 

The European Space Agency (ESA) is planning to launch Mission Hera in October 2024. The Hera spacecraft will closely measure the internal properties of Dimorphos and the crater made by DART to measure the efficiency of the momentum transfer. 

"Hera will turn the grand-scale experiment into a well-understood and repeatable planetary defence technique. Demonstrating new technologies from autonomous navigation around an asteroid to low gravity proximity operations, Hera will be humankind's first probe to rendezvous with a binary asteroid system and Europe's flagship Planetary Defender," ESA said.