That’s one large rock, one momentous shift in our relationship with space. On Wednesday, Nasa will launch a mission to deliberately slam a spacecraft into a pyramid-sized asteroid to try and alter its orbit – the first time humanity has tried to interfere in the gravitational dance of the solar system. The aim is to test drive a planetary defence system that could prevent us from going the same way as the dinosaurs, providing the first real data about what it would take to deflect an Armageddon-inducing asteroid away from Earth.
Our planet is constantly being bombarded with small pieces of debris, but these are usually burned – or broken up long before they hit the ground. Once in a while, however, something large enough to do significant damage hits the ground. About 66m years ago, one such collision is thought to have ended the reign of the dinosaurs, ejecting vast amounts of dust and debris into the upper atmosphere, which obscured the sun and caused food chains to collapse. Someday, something similar could call time on humanity’s reign – unless we can find a way to deflect it.
Nasa’s Double Asteroid Redirection Test (Dart) mission is the first attempt to test if such asteroid deflection is a realistic strategy: investigating whether a spacecraft can autonomously navigate to a target asteroid and intentionally collide with it, as well as measuring the amount of deflection.
“This is the first step to actually trial a way of preventing near-Earth object impact,” said Jay Tate, director of the National Near Earth Object Information Centre in Knighton, Powys. “If it works, it would be a big deal, because it would prove that we have the technical capability of protecting ourselves.”
The 610kg Dart spacecraft is scheduled to blast off from the Vandenberg Space Force Base in California onboard a SpaceX Falcon 9 rocket at about 6.21am (UK time) on Wednesday. Its target is the Didymos System – a harmless pair of asteroids consisting of a 163-metre “moonlet” asteroid called Dimorphos that orbits a larger 780-metre asteroid called Didymos (Greek for “twin”).
As they orbit the sun, these asteroids occasionally pass relatively close to Earth. The plan is to crash the spacecraft into Diamorphos when the asteroid system is at its closest – about 6.8m miles away – some time between 26 September and 1 October 2022.
About 10 days before impact, a miniaturised satellite called the Light Italian CubeSat for Imaging of Asteroids (LICIACube), will separate from the main spacecraft, enabling images of the impact to be relayed back to Earth. Combined with observations from ground-based telescopes, and an onboard camera that will capture the final moments before collision, these recordings should enable scientists to calculate the degree to which the impact has altered Dimorphos’s orbit.
The expectation is that it will change the speed of the smaller asteroid by a fraction of 1% and alter its orbital period around the larger asteroid by several minutes.
Then, in November 2024, the European Space Agency’s Hera spacecraft will visit the Didymos system and conduct a further close-up analysis of the consequences of this celestial snooker game, capturing details such as the precise mass, makeup and internal structure of Dimorphos, and the size and shape of the crater left by Dart. Such details are vital for transforming asteroid deflection into a scalable and repeatable technique, that could be deployed should an apocalyptic asteroid ever be detected heading towards Earth.
Even then, it is unlikely that any single deflection strategy would be enough. “Assuming it works, [this mission] will provide us with real time ground truths on the effects of a small impactor on a small asteroid,” said Tate. “The problem is that no two asteroids or comets objects are alike, and how you deflect one depends on a huge number of variables: what’s the thing made of, how it’s put together, how fast it’s spinning, and of course how much time you’ve got.
“There is no silver bullet in this game. What you need is a whole folder of different deflection methods for different types of target.”
So while this may be one small step towards planetary protection, many more are likely to be necessary to avoid Armageddon.