End of Chapter 15
-Origin - larger bodies (up to planetesimal size),
some of which differentiated,
-fragmented over time by collisions.
- placement dictated by physical properties of Jupiter.
Titius-Bode Law – don’t worry about the math, just learn the significance
Titius devised a curious mathematical tool that showed the spacing of the planets
as a mathematical progression. He began a sequence of numbers beginning with zero,
then 3, then doubled each number thereafter: 0, 3, 6, 12, 24, 48, 96. He then added 4 to
each number and then divided the resultant numbers by 10. The sequence became 0.4
), 0.7 (
), 1.0 (
), 1.6 (
), 2.8 (just little
), 5.2 (
). These numbers represent almost exactly the mean distances of the planets in
AUs from Sun to the last planet then known, Saturn. Bode, another German astronomer,
applied Titius’ progression to argue for the existence of another big planet in the Mars –
Jupiter gap (Fig.15-2). The progression became known as the Titius-Bode Rule. By the
way, nobody really took the progression seriously until the planet Uranus was discovered
in 1781 at 19.18 AU; the Titius-Bode Rule had predicted it at 19.6 AU!
Asteroid Discovery – know about LINEAR, identification procedure
In March 1998 a new asteroid detective hit the skies: the
Lincoln Near Earth
(LINEAR) telescope. This is a very sophisticated and 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. LINEAR
is currently discovering between 50-75 asteroids per year, but has had discovery rates as
high as 182/year. More significantly, it has defined some 2700 asteroids to be in orbits
very close to Earth, thus potentially harmful to Earth.
When an asteroid is discovered, the discoverer is allowed to choose a name for it,