Sciency Words: Siliceous Asteroids

Today’s post is part of a special series that first appeared on Planet Pailly. Every Thursday, we take a look at a new and interesting scientific term to help us all expand our scientific vocabularies together. Today’s sciency words are:


It’s a tale of two asteroids, one in the inner asteroid belt, the other in the outer region.


Both asteroids started off much the same but wound up quite different. The inner belt asteroid, being closer to the Sun, got blasted by the solar wind, losing many of its lighter materials: water, organic compounds, other volatiles…


The outer belt asteroid, being farther away from the Sun, still feels the solar wind’s effects, but less so.

And so one asteroid becomes a carbonaceous asteroid, retaining many of the lightweight materials that are so appealing to life and perhaps some day asteroid mining corporations. The other became a siliceous asteroid.


Siliceous asteroids, also known as S-type asteroids or sometimes stony asteroids, are basically great big rocks. They’re composed of a mixture of silicon with additional metals and/or minerals. Astronomers estimate 15-20% of asteroids in the Solar System are siliceous, and most reside (not surprisingly) in the inner asteroid belt.

If you’ve seen Star Wars: The Empire Strikes Back, you should have some idea what siliceous asteroids look like. They’re a lighter color than their carbonaceous cousins, making them a bit easier to spot against the dark backdrop of space. They also tend to be reddish brown or sometimes greenish brown, depending on which combinations of metals and minerals they contain.

However, since they’re depleted of water, carbon, and such, it’s unlikely siliceous asteroids could host large populations of mynocks, as seen in Star Wars. They’re also not the most exciting prospects for future asteroid mining operations. Not when there are far more valuable M-type asteroids out there, which will be the subject of next week’s edition of Sciency Words.


Asteroid Mining from Astronomy Source.

Asteroid Mining 101: Wealth for the New Space Economy by John Lewis.

Today’s post is part of asteroid belt month for the 2015 Mission to the Solar System. Click here for more about this series.

Article by James Pailly. Check out James’ blog for more great science articles.

  • John H Reiher Jr

    I wonder how many S-type asteroids are rubble piles and not solid bodies? From the looks of it, 433 Eros, which was visited twice by NEAR Shoemaker, looks fairly solid.