PHY 113 Lecture Notes - Lecture 14: Solar Wind, Kuiper Belt, Aerogel

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9 Jun 2018

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Chapter 14 Solar System Debris
14.1 Asteroids
Asteroids are quite small, and most have eccentric orbits in the asteroid belt between Mars
and Jupiter. The inset shows Ceres, the largest known asteroid.
Asteroids are rocky; over 500,000 have been identified so far. New information being
collected DAWN spacecraft:
Three largest
Ceres (technically a “dwarf planet” like Pluto, not an asteroid)
Pallas Vesta
940 km
580 km 540 km
14.1 Asteroids
DAWN Ceres update:
Origin of asteroids isn’t fully certain, but best explanation is that they are remnants of the
formation of the solar systemgravity from Mars and Jupiter kept anything from coalescing
in the region.
Other leading theory was that there was once an object near asteroid belt that broke into
pieces, but asteroids show a broad range in compositions probably not all from a single solid
Vesta shows evidence of volcanism; the reason is not understood. Perhaps it was part of some
larger object in the past, and broke off?
Asteroids are classified in types:
C-type (~75%): carbonaceous, dark S-type (~15%): silicate (rocky)
M-type (~10%): metallic; iron and nickel
Two small S-type asteroids, Gaspra and Ida, were visited by the Galileo probe. Gaspra (left)
is in false color; it is really gray. Note that Ida (right) has a small moon, Dactyl.
The NEAR spacecraft visited the C-type asteroid Mathilde, on its way to its main target, Eros.
Mathilde, like many other asteroids, has a very low density and is probably not solid more
like a puffy pile of rubble, loosely held together.
Some asteroids, called Trojan asteroids, points of Jupiter’s orbit
Some asteroids have orbits so eccentric that they cross Earth’s orbit. They are called Apollo
asteroids and raise the concern of a possible collision.
6500 such asteroids have been discovered so far, of which about 1000 have been designated
as potentially hazardous, due to their size.
NASA tracks “Near Earth Objects” to look for possible threats
Even “small-size” meteors can release a lot of energy, in sudden, violent ways.
On February 15, 2013, a meteor exploded in the atmosphere in Chelyabinsk, Russia.
Here is a video showing what this explosion looked like (from various viewpoints):
The effect of an impact of a “mid-size” meteor impact is like a nuclear bomb explosion... or
The most recent decently-large meteor impact on Earth was the Tunguska event of 1908 in
Luckily the impact site was very remote (we didn’t know it happened until afterward)
Discovery 14-1: What Killed the Dinosaurs?
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