Last week, the Japanese Aerospace Exploration Agency‘s (JAXA) dropped an explosive warhead on the surface of asteroid 162173 Ryugu. You might think this was the opening line of an entirely-readable science fiction novel, but it’s totally true. The operation began on April 4th, when the Hayabusa2 spacecraft sent its Small Carry-on Impactor (SCI) down to Ryugu’s surface and then detonated it to create a crater.
This is the latest phase in the Hayabusa2‘s mission to study and return samples from a Near-Earth Object (NEO) in the hopes of learning more about the formation and evolution of the Solar System. This began shortly after the spacecraft rendezvoused with Ryugu in July of 2018 when the spacecraft deployed two rovers to the asteroid’s surface.
This was followed by the spacecraft sending the box-shaped Mobile Asteroid Surface sCOuT (MASCOT) lander to the surface, which analyzed samples of the asteroid’s regolith in two locations. And this past February, the spacecraft touched down on the surface for the first time, which resulted in it collecting the mission’s first samples.
Before the samples could be retrieved, however, the spacecraft had to break up the surface material by shooting it with “bullets” – 5 gram impactors made of tantalum metal that are fired from the spacecraft’s sampling horn at speeds of 300 m/s (670 mph). The same principle lies behind the SCI, a the system that consists of a 2.5 kg (5.5 lb) copper projectile.
This “bullet” is accelerated by a shaped charge containing 4.5 kg (~10 lbs) of plasticized HMX explosive (aka. octogen). This compound is the same used by military forces as the detonator in nuclear weapons, in plastic explosives, and as a solid rocket propellant. When combined with TNT, it creates octol, another military-grade explosive used in anti-tank missiles and laser-guided bombs.
After sending the SCI to the surface, the spacecraft rose to a safe altitude to avoid any damage from the explosion. The SCI was then detonated, sending a copper plate towards the surface at 1.9 km per second (1.2 miles per second). The size of the crater this generates will depend entirely on the composition of the surface material.
The Hayabusa2 captured the launch of the SCI with its wide-angle Optical Navigation Camera (ONC-W1), which they shared on the mission’s official twitter page. The explosion was also caught by a deployable camera – the DCAM3 – which the spacecraft deployed closer to the asteroid in order to monitor the impact experiment.
The camera was destroyed in the process, but the images it took will help Hayabusa2 locate the crater once it approaches the surface again. This will take place after all of the debris has settled; at which point, the mission team will determine whether or not it is safe to obtain a sample from the recently-created crater.
If this retrieval is deemed too dangerous, the spacecraft will be directed to one of the asteroid’s preexisting craters instead. However, the team hopes to grab samples from the crater they created, since the material uncovered by the explosion has not been exposed to space and subjected to radiation and space weathering for billions of years.
This is in keeping with a central goal of the mission, which is to examine material left over from the formation of the Solar System, ca. 4.5 billion years ago. As such, samples that come from the interior would be the most reliable source for discovering what kinds of materials were present during the early Solar System.
In examining these materials, scientists seek to learn more about key questions, not the least of which is how water and organic materials were distributed throughout our Solar System. This is believed to have taken place during the Late Heavy Bombardment, roughly 4.1 to 3.8 billion years ago, and was intrinsic to the emergence of life on Earth.
By examining samples of asteroids that are dated to this period, scientists could also theorize with greater confidence where else the materials necessary for life (as we know it) could have been distributed. And soon enough, Hayabusa2 will be providing us with some sample evidence that will help answer these questions.
And to think that was made possible thanks to the same technology used to blow up tanks! In the meantime, the spacecraft is providing real-time imagery of the asteroid with the ONC-W1 camera. Once it has concluded science operations around the asteroid, which are scheduled to end by December of 2019, it will return to Earth – scheduled for December of 2020.
What we stand to learn from the samples it bring home is sure to be exciting!
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