Asteroid spectral types facts for kids

Asteroids are like space rocks that orbit the Sun. Scientists group them into different types based on things like their color and how much light they reflect (called albedo). This helps us understand what they are made of. For small asteroids, their surface and inside are probably similar. But bigger ones, like Ceres and 4 Vesta, have different layers inside, just like Earth.

You can find a list of these types at asteroid spectral classes.

How Asteroids Are Grouped Today

The way we classify asteroids started in 1975 with three main groups:

• C-type for dark, carbon-rich asteroids.
• S-type for stony (rocky) asteroids.
• U-type for those that didn't fit into C or S.

Since then, scientists have made these groups more detailed. There are now several ways to classify asteroids, and sometimes an asteroid might fit into different groups depending on the system used. The two most common ways are explained below:

Tholen Classification

The Tholen classification was used widely for over ten years, starting in 1984. This system looked at how asteroids reflected light across different colors and also their albedo (how shiny they are). It was first based on nearly 1,000 asteroids.

This system has 14 types. Most asteroids fall into one of three big groups, with a few smaller types:

• C-group (dark, carbon-rich objects):
  • B-type (like 2 Pallas)
  • F-type (like 704 Interamnia)
  • G-type (like 1 Ceres)
  • C-type (like 10 Hygiea) - This is the most common type, making up about 75% of all asteroids.
• S-type (stony objects):
  • Like 15 Eunomia and 3 Juno. This group makes up about 17% of all asteroids.
• X-group (mostly metallic objects):
  • M-type (like 16 Psyche) - This is the third most common group.
  • E-type (like 44 Nysa) - These are similar to M-types but reflect a lot of light.
  • P-type (like 259 Aletheia) - These are similar to M-types but reflect very little light.

There are also smaller, less common types:

• A-type (like 446 Aeternitas)
• D-type (like 624 Hektor)
• T-type (like 96 Aegle)
• Q-type (like 1862 Apollo)
• R-type (like 349 Dembowska)
• V-type (like 4 Vesta)

Sometimes, an asteroid might be given a combined type, like "CG," if it has features from more than one type.

SMASS Classification

This is a newer way to classify asteroids, created in 2002 by Schelte J. Bus and Richard P. Binzel. It uses more detailed information about how asteroids reflect light. This system looked at 1,447 asteroids. It didn't consider how shiny they were (albedo).

Even though it uses different data, it tried to match the Tholen system as much as possible. Asteroids are sorted into 24 types. Most still fall into the C, S, and X groups, with some unusual ones in smaller types:

• C-group (carbon-rich objects):
  • B-type (similar to Tholen's B and F types).
  • C-type (the most common carbon-rich type).
  • Cg, Ch, Cgh (somewhat like Tholen's G type).
  • Cb (in-between C and B types).
• S-group (stony objects):
  • A-type
  • Q-type
  • R-type
  • K-type (a new type, like 181 Eucharis)
  • L-type (a new type, like 83 Beatrix)
  • S-type (the most common stony type).
  • Sa, Sq, Sr, Sk, Sl (in-between S and other types in this group).
• X-group (mostly metallic objects):
  • X-type (the most common X type, includes Tholen's M, E, or P types).
  • Xe, Xc, Xk (in-between X and other types).

Other types include:

• T-type
• D-type
• Ld-type (a new type with stronger features than L-type).
• O-type (a small group, like 3628 Boznemcová)
• V-type

Many small asteroids were found to be Q, R, and V types in this system. In the Tholen system, these types only had one example each. In the SMASS system, each asteroid was given only one type.

Some Near-Earth Objects (asteroids that come close to Earth) have very different light patterns. This might be because they are much smaller than main belt asteroids. Their surfaces might be younger or made of a less varied mix of minerals.

Why Classifying Asteroids Matters

Scientists are still working to make these classification systems even better. For now, these ways of grouping asteroids based on their light patterns are still the main methods. It's hard to get very detailed information for lots of asteroids, which makes it tricky to agree on a perfect system.

The three main groups of asteroids are thought to be related to the three basic types of meteorites (rocks that fall to Earth from space):

• C-type asteroids are like Carbonaceous chondrite meteorites.
• S-type asteroids are like Stony meteorites.
• M-type asteroids are like Iron meteorites.

Images for kids

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  This image shows different wavelengths of light, which scientists use to study asteroids.

See also

In Spanish: Tipo espectral (asteroides) para niños