Asteroids
Also known as Minor Planets, Small Solar System Bodies, Near Earth Objects,
Trojans, Centaurs et al. These are the rocky components left over after
the formation of the Solar System and are dispersed throughout all regions of
the solar system (their location and orbit will determine the names we give
them).
Not to be confused with Comets, Asteroids are effectively just rock.
The smaller objects are gravitationally bound rubble piles. This means
that they comprise rock material from the size of fine powder up to boulders,
all bound together solely by gravity (the only other binding force is friction
between the individual components). There may or may not be ices (frozen
gas or water) inside these objects and they may also contain voids.
These objects range in size from the very large to the very small.
Until recently, Ceres was thought to be the largest but it has now been
reclassified as a dwarf planet, so Vesta would now be the largest. The
smallest, well how small is small? We can see/detect passing NEO's as
small as a couple of meters and these are still classified as a type of
Asteroid.
So why do we observe them - if you've seen one then you've seen them all -
right? Well we observe them to uncover their physical and orbital
parameters. Everything in the Solar System has a gravitational effect on
everything else in the solar system. If we want to generate accurate
orbits and models of any solar system body then we need to know what the rest
are doing. This is vitally important for uncovering the orbits of NEO's
and being able to accurately predict their positions for up to a century in the
future to work out if we (earth) are safe from collision. But we need to
know more about asteroids than just their orbits. How big are they, what
are the made of, how fast are they travelling, what is their mass.
Unfortunately from observation we know that these objects are very different
from each other. 2 asteroids of equal size and made of the same material
can have drastically different masses and be travelling at drastically different
speeds. More recently we have uncovered the fact that 25% of these small
bodies are actually multiple systems, that is the parent body has one or more
moons.
So in the world of planetary science we have 3 avenues available to us.
Astrometry - to uncover the objects orbit, Photometry - to uncover the objects
brightness changes and Spectroscopy to uncover the objects surface material
(then combined with Photometry to allow for derivation of the objects size)
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