Of what does our solar system consist? There are the big and obvious things: the sun, the planets, and the moons which orbit those planets. The cloud of gas and dust from which all this condensed 4.6 billion years ago also spawned hundreds of thousands of smaller objects that still remain. Let’s focus on one type of such objects: carbonaceous asteroids.
As the name indicates, these small bodies contain relatively large amounts of carbon. Occasionally chunks broken off of these asteroids fall to Earth and are collected as carbonaceous chondrite meteorites. These are highly prized by scientists seeking to understand the earliest history of our solar system, because they are mostly unaltered from their formation billions of years ago. They are pristine—the original stuff from which the sun and the planets were made. They are, however, altered by their long exposure to the space environment, their searing path through our atmosphere, and if not collected immediately after their fall, by weathering on the Earth’s surface.
For complex reasons, most of these carbonaceous asteroids lie in the outer reaches of the solar system, making them difficult to reach with spacecraft. Spacecraft are also limited in the analytical instruments they can carry. How do you know what instruments to include when the whole point is that you aren’t sure what you will find?
There are, however, some carbonaceous asteroids that orbit the sun nearer the Earth, making them more easily accessible. One of these, Ryugu, has been the target of a Japanese mission named Hayabusa2. The orbit of Ryugu is shown below; I backed up to an August date to separate Earth and Ryugu enough to be able to read their labels.
Image from JPL Small-Body Database Browser: https://ssd.jpl.nasa.gov/sbdb.cgi
Some analysis can certainly be done on site once a spacecraft is close enough to deploy its suite of instruments. Of course, images are key in selecting areas for further study.
https://upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Ryugu_rotation.gif/220px-Ryugu_rotation.gif
Ryugu is roughly a kilometer (0.6 mile) in diameter, a spinning top whose equatorial bulge is a result of centrifugal forces and its 7.6 hour rotation period. It is a rubble pile rather than a solid body, with half its volume being empty space.
What planetary scientists would prize above all else are truly pristine samples, gathered in space from the asteroid, stored away, returned to Earth, and analyzed with all the sophisticated tools we can muster in Earth-based laboratories.
https://upload.wikimedia.org/wikipedia/commons/b/bf/Hayabusa2_SCI_impact_and_subsurface_sampling.gif
As shown above, the spacecraft deployed a separate “gun” and then moved itself a safe distance away. From an altitude of about 500 meters, a metal projectile was fired into the surface, excavating a crater about 10 meters in diameter. Most importantly, it exposed pristine material from below the surface which had not been subjected to space weathering—alteration of surface material by micrometeorite impact and radiation both cosmic and solar. Three months later, the main spacecraft touched down and collected material that will be returned to Earth very soon.
On December 6, the main spacecraft will deploy a sample return vehicle and then change its course to fly past Earth (TCM stands for Trajectory Correction Maneuver.) The return capsule will make a fiery re-entry and descend by parachute to the Woomera Desert in Australia.
Image from http://www.hayabusa2.jaxa.jp/en/
You can be assured that planetary scientists all across the world will be eager to get their hands on this precious cargo!
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