Friday, December 13, 2019

Three Classes Of Asteroids - And The Resources They Have To Justify Future Spacecraft Missions

Three asteroid classes to consider: (A)  Carbonaceous C-type, (B) Silicaceous or  S-type, and (C)  Metallic asteroids, or M-type.

In  a  previous post I pointed out the threat from asteroids and called them "the Celestial swords of Damocles", e.g.

Asteroids: The Celestial 'Swords of Damocles'

In which I wrote:

"For a ten kilometer asteroid (roughly 6 miles across) the explosive equivalent would translate into 13 million megatons. This would dwarf all man-made nuclear stocks and warheads, and is rightfully called ‘planet –killer’. An asteroid about this size is believed responsible for the extinction of the dinosaurs nearly 65 million years ago."

Although asteroids may well represent one possible  mode for human extinction, they may also be one means to ensure human survival by providing much needed resources - of the type we're exhausting on Earth. It is instructive, therefore, to consider each type of asteroid (see graphic for the classes) and what it offers.

Under (A) I give the Carbonaceous class or C-type asteroids, mainly because they are the most common, comprising 75 percent of all known asteroids.  A representative example is the Apollo asteroid Itokawa, shown in the image for (A).   Recall from the earlier post (link above) that Apollo asteroids have orbits that intersect the Earth's.  Hence, they are also the type that may one day collide with our planet.

Itokawa itself is a sub-kilometer scale body which planetary astronomers basically regard as a "rubbish pile".   That means it consists of numerous boulders of differing sizes rather than being a single large body.  The resources it offers include: water, ammonia, methane, nitrogen, oxygen and hydrogen.

Under (B) I list the S-type or silicaceous asteroids, which account for about 17 percent of the total, known asteroid assay.  The label indicates that they are stony asteroids composed of metallic iron, mixed with iron and magnesium silicates.   The representative example is Gaspra shown in image (B)  and in much higher detail in the image below:

Gaspra orbits very near to the inner edge of the Asteroid Belt.  It was also the first asteroid ever to be closely approached when it was visited by the Galileo spacecraft. That craft flew by o its way to Jupiter on October 29, 1991.  Gaspra is large in scale, with a mean diameter of 12.2 kilometers, or 7.6 ,miles, so it definitely qualifies as a planet killer. But on the positive side, what resources does it have to offer? These include: iron, nickel, magnesium and titanium.

Under (C) I put the metallic or M type asteroids.  These are represented by Psyche, depicted in image (C)  - i.e. artist's depiction.  These asteroids may well be the most valuable for Earth given they have the potential to replenish rare metals, especially cobalt. (Also nickel and iron).  No surprise because of the dense metallic composition (e.g. check the atomic weight of cobalt) Psyche is one of the ten most massive asteroids. It is also huge, over 200 kilometers (120 miles) in diameter.  It actually contains a little less than 1 percent of the mass of the whole Asteroid Belt. For that reason it's been surmised that it's an exposed core of a proto-planet.

In a future blog post I will examine some of the technology needed so that asteroid mining could conceivably be a trillion dollar industry.  That's assuming we aren't extinguished by the roiling climate crisis first.

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