Here’s why NASA sent a probe to crash into an asteroid

A SpaceX Falcon 9 rocket roared its engines and soared into the dark California skies early on Wednesday, November 24, carrying a small probe that could teach NASA how to save Earth from dangerous asteroids. The space agency is not aware of any asteroids heading towards Earth in the next 100 years.

However, the organization expects huge space rocks to approach our planet someday, and they have a plan to push them away. A new spacecraft – a mission called Double Asteroid Redirection Test (DART) – is testing this plan. Its only mission: to crash head-on into the center of a distant asteroid. The probe, a box smaller than a golf cart, took off aboard the Falcon 9 on November 24. Once released into space by the rocket, the DART probe will spend about two hours deploying its solar panels.

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A Falcon 9 rocket takes off with the DART probe at the Vandenberg space base, November 24, 2021 NASA TV

If all goes well, the probe will head towards a pair of asteroids. One, a satellite called Dimorphos, revolves around the other, Didymos. DART targets the satellite, which is about the size of a football stadium. It should reach its target, located 6.8 million kilometers from Earth, in September 2022.

“We’re going to hit hard, but we’re doing it with a very small vehicle,” Ed Reynolds, DART project manager at the Johns Hopkins Applied Physics Laboratory, told a press conference Monday. “When you’re trying to figure out what it takes to deflect an asteroid away from Earth – with enough time, you can do big things with small vehicles,” he added.

Falcon 9 rocket payload protective fairing closes around DART spacecraft NASA/Johns Hopkins APL/Ed Whitman

This boost should be enough to bring Dimorphos closer to Didymos, causing him to orbit the larger asteroid about 10 minutes shorter than before – every 11 hours and 45 minutes instead of every 11 hours and 55 minutes. minutes.

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If successful, DART will prove that technology can alter the trajectory of dangerous asteroids. It will also provide NASA with valuable data on how the collision affects the asteroid and how large a probe must be to move its target.

“I could imagine, for example, that we would have a series of impactors like this – a small number – that are actually in orbit and ready to go in case a threat arises,” said Thomas Zurbuchen, an associate administrator. from NASA, during a pre-launch press conference on November 22.

Everything will be based on the last moments of DART

NASA does not track all of the asteroids in the vicinity of our solar system. Astronomers have identified around 40% of nearby asteroids that are 140 meters or more wide – those that are large enough to level a city. Dimorphos, with its 160 meters, is a perfect model of such a city destroyer.

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Dimorphos is as big as the Colosseum in Rome ESA-Science Office

But other than its size and the speed at which it circles Didymos, scientists know little about their target. They cannot observe it directly with telescopes on Earth, but glean information from changes in Didymos’ light as the small moon passes between the larger asteroid and Earth.

NASA won’t even know what shape Dimorphos has until DART’s camera sees it about an hour before the collision. When the space rock is in sight, a probe system called SMART Nav will be programmed to quickly calculate the center of the looming asteroid. The probe’s navigation system will then trigger its thrusters to direct it towards the target.

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During its final approach, the DART probe is programmed to transmit a new photo to Earth every second. A small Italian spacecraft, LICIACube, is expected to detach from DART 10 days before the collision, fly alongside the NASA probe and record the crash.

The spacecraft is expected to hit the center of the asteroid at a speed of 24,140 kilometers per hour, transferring its kinetic energy to the asteroid and pushing it closer to Didymos. NASA estimates the impact will cause an explosion and the ejection of 9,970 to 99,970 kilograms of rock material, which could give the asteroid even greater thrust than DART itself.

The European Space Agency (ESA) plans to launch a follow-up mission, called Hera, to examine Didymos and Dimorphos in 2026. In addition to studying the consequences of the impact, Hera will map Dimorphos, accurately measure its mass, and examine the crater. that DART left there.

NASA is only effective if it has enough time to reach an asteroid

Asteroid killer satellite concept NASA/JPL-Caltech

In order to use a DART-style mission to hijack an earth rock, NASA needs five to ten years before an asteroid arrives, experts told Insider. This is because it takes years to design and build a spaceship, and then months or years to get to the asteroid. In addition, the probe will likely have to hit an asteroid a year or two before its orbit intersects with Earth. The slight boost from the impact of a spaceship only slightly deviates the boulder from its course at first. But over time, this change pulls it away from Earth.

In order to identify dangerous asteroids with sufficient lead time, the US space agency is building a telescope called the Near-Earth Object Surveyor to monitor large asteroids orbiting the Sun near Earth. NASA hopes the telescope will identify 90% of asteroids 140 meters or larger.

“If we don’t find these objects that could pose a threat of impact on Earth – a danger to Earth – there is nothing we can do about them,” said Lindley Johnson, head of planetary defense at NASA, during the briefing on November 22.

Version originale : Morgan McFall-Johnsen / Insider

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