Earth Sciences 1086F/G Lecture 12: chapter 12
13 Jan 2020
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Earth Science Final Review:
Chapter 12: Asteroids
• - asteroids are primordial objects left over from the formation of the solar system
• - small chunks of rock drifting between the orbits of Mars and Jupiter
• - asteroids are the last remains of the planetesimals that built the planets 4.57 billion
years ago
• - many asteroids discovered in the gap between Mars and Jupiter have accurately
known
orbits
• - this concentration of objects is known as the main asteroid belt
• - asteroid belt appears mostly empty — asteroids are spread over such a large volume
that it would be highly improbable that you could see one from another
• - collisions can occur
- may fragment an asteroid into smaller pieces - may glue two asteroids together
• - many asteroids not in the main belt - some can be really dangerous
Asteroid Discovery:
• - in 1998 there was a new asteroid detective called the Lincoln Near Earth Asteroid
Research (LINEAR) telescope
- highly sensitive electro-optical detector with something called a CCD (a charge
coupled device) which is an array of light-sensitive elements that can record very faint
images
- as of 2011 it has found over 231,000 new objects
• - between 750,000 and 1.7 million asteroids in the main asteroid belt that are larger
than 1 km
in diameter
• - ~6139 Near Earth Asteroids have been identified
• - when an asteroid is discovered it is assigned a number
- e.g. 1 Ceres
Asteroid Distribution and the Jupiter Effect:
• - why did asteroids tend to cluster between mars and jupiter?
o - they probably didn’t
o - in the early solar system, the asteroids were distributed more or less uniformly
within the
inner solar system
o - when the planets began to form, much asteroid material was gathered up by
the growing
planets
o - the asteroids that did not meet this fatal end were flung outward and ended up
within the
influence of Jupiter
o - much of this redistribution could have happened as the ‘big four’ planets
migrated outward
• - if the inner solar system asteroids were bashed around, why is there such a well-
organized population between Mars and Jupiter?
o - Jupiter’s mass is so large that its gravity dramatically affects the motions of
small bodies
anywhere close to it
o - gravitational perturbations caused by Jupiter’s gravity prevented any of those
objects from
coalescing into a single planet-sized body
Gaps in the Asteroid Belt:
• - gaps in the belt where no asteroids seemed to exist
o - prominent gaps at 2.50, 2.83, and 3.28 AU
o - Kirkwood provided an explanation for these gaps
o - the distances between the gaps corresponded to simple fractions of the orbital
period of
Jupiter
o - within these gaps, the gravitational disruptions are particularly strong
• - two major forces are acting on the asteroids:
- gravity of the sun
- gravity of Jupiter
• - over a long period, each asteroid is influenced by these forces to change its position
and
swing either outward or inward from Jupiter, leaving a gap where it used to be
• - asteroids or meteoroids entering the Kirkwood gaps are booted out by Jupiter’s
gravitational
disruption forces at great velocities
- they are so great that they escape the limits of the Asteroid Belt
• - these gaps allow asteroids and meteoroids to escape Jupiter’s influence and move
into the
inner solar system
- they can possibly come to earth
Asteroid Classification:
• - asteroids closer to the sun are brighter and have higher metal content
• - asteroids further from the sun are darker and richer in carbon
• - look closely at the asteroid’s albedo
- an object with a lot of metal showing would be highly reflecting
Document Summary
Asteroids are primordial objects left over from the formation of the solar system. Small chunks of rock drifting between the orbits of mars and jupiter. Asteroids are the last remains of the planetesimals that built the planets 4. 57 billion years ago. Many asteroids discovered in the gap between mars and jupiter have accurately known orbits. This concentration of objects is known as the main asteroid belt. Asteroid belt appears mostly empty asteroids are spread over such a large volume that it would be highly improbable that you could see one from another. May fragment an asteroid into smaller pieces - may glue two asteroids together. Many asteroids not in the main belt - some can be really dangerous. In 1998 there was a new asteroid detective called the lincoln near earth asteroid. Highly sensitive electro-optical detector with something called a ccd (a charge coupled device) which is an array of light-sensitive elements that can record very faint images.
