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00:00This is the moment a spacecraft crashed into an asteroid.
00:05Two years ago, NASA made history by intentionally slamming into an asteroid with its DART mission.
00:12The asteroid wasn't a threat to us here on Earth,
00:15but scientists wanted to see if they could change the path of an asteroid
00:18to test a technique that could one day protect us from a real threat.
00:23The experiment was a success. Humans can move an asteroid.
00:28But the bad news is that scientists aren't sure yet they understand why it worked.
00:33There is still a lot we don't know,
00:35like what exactly happened on the asteroid's surface after the impact,
00:39what the asteroid is made of and how well the deflection worked.
00:45But our HERA spacecraft will soon fly to that same asteroid to answer all of our questions.
00:51HERA will perform a close-up crash scene investigation,
00:55gathering data on the asteroid's mass, structure and makeup
00:59to turn this kinetic impact method of planetary defence into a well-understood and repeatable technique.
01:07Why do we need to protect our planet?
01:10In 1908, people reported a bright flash and a noise that sounded like a bomb.
01:15Ten minutes later, this was from the largest observed asteroid strike ever recorded,
01:20which occurred over the Tunguska region in Siberia.
01:24People up to 500 miles away reported seeing the flash.
01:28Some claimed it was even brighter than the sun.
01:31The explosion was massive, causing 80 million trees to flatten,
01:35windows up to 250 miles away to smash,
01:38and the effects of the shockwave could even be felt in London.
01:42This represented a lucky escape for Europe.
01:45It happened just a short distance from affecting heavily populated regions.
01:50As a result, ESA, NASA and other space agencies started closely monitoring space
01:55to track potentially dangerous asteroids.
01:58So far, we have found more than 35,000 asteroids whose orbits bring them dangerously close to Earth.
02:05But if one was on a collision course with us, what could we do?
02:09To answer this question, an international team came up with the first planetary defence mission.
02:15DART to hit the asteroid and HERA to gather data after the impact.
02:22Knowing there are so many asteroids that could be a danger to us, how did we pick one to explore?
02:28The asteroid that DART hit and that our HERA spacecraft will now visit is called Dimorphos.
02:34It's a small asteroid, about half the size of the Opheld Tower,
02:38but if it impacted Earth, it could devastate a small country or city.
02:44Dimorphos orbits a larger asteroid called Didymos, which HERA will also visit.
02:49Together, the two asteroids form the Didymos system.
02:53Here are some of the reasons why scientists decided to explore the Didymos system
02:57among all the asteroids out there.
03:00The two asteroids are not a real threat to Earth,
03:03so nudging one of them wouldn't accidentally set it on a crash course to Earth.
03:08The system passes relatively close to Earth, so they are not impossible to get to.
03:14The 150m diameter of Dimorphos is important.
03:18We know about 95% of all near-Earth objects larger than 1km in size,
03:24but the majority of smaller asteroids are yet to be discovered, despite their city-killing potential.
03:30Since Dimorphos orbits Didymos, we can easily see any changes in its orbit from Earth.
03:37So, what are we expecting to see on Dimorphos?
03:40We asked one of our experts, Patrick Michel,
03:43the principal investigator of the HERA mission, to find out more.
03:47So what do we expect to find on Dimorphos?
03:50That's a big question. Actually, we don't really know,
03:53because the DART mission by NASA made an impact on Dimorphos,
03:57and based on the current data that we have from this mission, there are different solutions.
04:02So, Dimorphos may host a crater whose size is unknown, or it could be completely reshaped.
04:09Prior to DART's impact, it took Dimorphos 11 hours and 55 minutes to orbit its larger parent asteroid.
04:17Since the collision, astronomers have found that the spacecraft's impact
04:21altered Dimorphos' orbit around Didymos by 33 minutes,
04:25shortening the orbit to 11 hours and 22 minutes.
04:29The mission was deemed a large success, but to learn more about these asteroids' physical properties
04:34and DART's impact outcome, we need to visit them.
04:38Initially, we thought that when DART crashed into Dimorphos, it would create a big impact crater,
04:44potentially the first one ever made by humans.
04:47But now, scientists think there might not be a crater on Dimorphos after all.
04:52More recent simulations suggest the impact might have completely changed the asteroid's shape.
04:57Scientists estimate that around 8% of the asteroid's mass was shifted around its body
05:03and 1% of the entire mass of Dimorphos was thrown into space,
05:08some of which may reach us here at Earth as small meteoroids.
05:12So the DART impact generated a lot of ejecta, a lot of material that is still, you know,
05:18escaping from the system at tens of thousands of kilometres from Dimorphos.
05:23And it may be that some small particles eventually reach Mars or the Earth,
05:28but in the form of shooting stars, like what you see in the sky during the night, so with no risk.
05:34We don't know what it looks like now, so there's going to be a lot of surprises.
05:38I'm so excited because in two years, we'll have the answer.
05:41Crater or no crater, we need to go back to Dimorphos to study the aftermath of the impact.
05:47This will help us turn the DART deflection experiment into a well-understood, repeatable technique
05:52that might one day be needed for real.
05:56So we know it will take us two years to reach the asteroids after launch, but how do we get there?
06:03On its way, HERA will make a swing by of Mars in March 2025,
06:08borrowing speed to help reach its destination.
06:11In the process, HERA will get us close to 6,000 kilometres from the surface of the Red Planet,
06:18closer than the orbits of the two Martian moons.
06:22HERA's trajectory will be tweaked so that it can train its science instruments
06:27onto Mars' smaller moon, Deimos, for less than 1,000 kilometres away,
06:32a practice run for when it reaches the asteroid system while also observing Mars itself.
06:40A second deep-space manoeuvre in February 2026 will line HERA up for arrival at the Didymos system.
06:48HERA will have an impulsive rendezvous with the system in October 2026,
06:53meaning it will be captured by their gravity and begin to orbit.
06:58Didymos' gravity is estimated to be around 40,000 times weaker than Earth's,
07:04while Deimos' is approximately 200,000 times weaker.
07:09This is so low that HERA must orbit around their common centre of gravity
07:13at very low velocity to remain captured.
07:16To maintain the optimal distance for studying the asteroids,
07:20HERA's orbit will need regular adjustments,
07:23otherwise the spacecraft could gradually drift away from them.
07:27The possibility of HERA touching down on one of the poles of Didymos
07:31at the end of its mission is being considered.
07:34Although it has not been specifically designed for landing,
07:37it could descend towards the surface.
07:40However, once on the surface, HERA will no longer be able to communicate with us on Earth,
07:45effectively bringing the mission to an end.
07:48What types of technology do we need to inspect an asteroid?
07:52Although HERA itself may not land on the asteroid,
07:55it is packed with new technologies which will allow us to study the asteroid in extraordinary detail.
08:02HERA carries a total of 12 instruments to explore the Didymos system.
08:07It has a state-of-the-art camera which will take detailed pictures of the asteroids,
08:12a laser altimeter which will create a map of the asteroid's surface,
08:17a camera which can look at the asteroids in different colours of light
08:21to find out exactly what they're made of,
08:23a radio science experiment which can use radio waves
08:27to figure out the mass and gravity of the asteroids.
08:31To explore dimorphous Didymos, HERA doesn't go by itself.
08:35Instead, the spacecraft carries two shoebox-sized CubeSats that resemble terrestrial drones,
08:42able to fly closer and take more risks and eventually even land, a world first.
08:48This is the first time that we send a spacecraft equipped with two CubeSats
08:53that will do deep space exploration of an asteroid.
08:56And the reason why we bring these CubeSats is because we want to go at very close proximity of the asteroid
09:02and we don't want to pose any risk to the main spacecraft.
09:06And these two CubeSats will contain their own instruments
09:09and for the first time, for instance, we'll be able to probe the internal property of an asteroid
09:15which has never been done so far, and that's on the Juventus CubeSat.
09:19On the second CubeSat, Milani, we'll measure the mineralogical composition of the asteroid
09:24and detect whether there is still dust around the body.
09:28The two CubeSats, called Juventus and Milani, will get up close and personal with the asteroid.
09:34Juventus will use radar, sending out radio waves that will bounce off the asteroids and come back.
09:40By measuring how long it takes for the waves to return,
09:43we will be able to tell how far away the asteroid is, at any given point, and even what shape it is.
09:50More importantly, it will allow us to explore what an asteroid is like on the inside for the first time.
09:57Is Dimorphos a rubble pile or a monolith covered with pebbles and gravels?
10:02Once it has inspected both asteroids, it will then descend to Dimorphos' surface
10:07to take detailed pictures of the surface features, including hopefully the exact spot of the dart impact.
10:14Once on the ground, it will use a gravimeter to increase our knowledge of the gravity field of the asteroid.
10:20The other CubeSat, Milani, will measure the mineralogical composition of the asteroid
10:25and will analyse any surrounding dust.
10:28Later on, it will also attempt a landing on Dimorphos.
10:32Its onboard instruments will gather valuable data on the landing
10:36and any subsequent bounces to give insights into the surface properties of the asteroid.
10:42If Milani lands safely, its FISTA instruments will analyse the dust on Dimorphos' surface.
10:50By the end of the six-month exploration by these three spacecraft,
10:53scientists will have a better understanding of the delicate art of asteroid deflection,
10:58and asteroid impacts will become the first avoidable natural disaster.
11:04At first glance, an asteroid is just a tiny dot of light in the sky.
11:08We require more observations to see if it is a real threat.
11:12Planetary defence is a global problem and therefore we need to be able to work together
11:17with other space agencies to protect our planet, and HERA is the perfect demonstration of that.