306 The Poetry of Physics and The Physics of Poetry
Earth. The metallic meteors are 90% iron and 10% nickel with a trace of
cobalt. These objects are continuously bombarding the Earth with as
many as 90 million arriving each day. As they plunge to Earth they
collide with air molecules, which causes them to heat up, and glow. They
appear as shooting stars. The heating in the Earth’s atmosphere melts
the material of the meteor.
Most meteors melt in the atmosphere before they ever reach the
Earth. Those that fall to Earth are referred to as meteorites. Hundreds
of these objects have been found. The largest stony meteorite found
weights 900 kilograms and the largest metallic meteorite weights 31,000
kilograms. Larger meteors than those have fallen to Earth as is evidenced
by the many meteor craters, which dot the surface of the Earth. One such
crater, the Barrington Crater in Arizona, is 1.28 kilometers across and
174 meters deep. Over 30,000 kilograms of meteoric iron have been
gathered at the site. The largest surviving chunk weights 640 kilograms.
It is estimated that the meteor that originally caused this crater had a
diameter of 60 meters and weighted 900 million kilograms. This meteor
is believed to have been a chunk of an asteroid.
Frequently meteor showers occur in which thousands and thousands
of meteors descend all at once. This occurs whenever the Earth passes
through the debris of a comet or less frequently the tail of a comet. The
remains of a comet frequently spread themselves out evenly through the
entire orbit of the expired comet. One such swarm of meteors has an
orbit, which intersects the Earth’s orbit. The Earth passes through this
swarm of meteors every year. For two or three weeks around August 12
showers of meteors rain down upon the Earth. Meteors range in size
from asteroid chunks down to micro meteors, which are essentially large
size dust particles. Dust and meteors probably have a common origin.
They are the remains of the original nebular cloud. The interplanetary
gas, on the other hand, owes its origins to the solar winds emanating
from the Sun.
Exoplanets or Extrasolar Planets
We have just reviewed the structure of our own Solar System. We now
know that there are many other solar systems out there in space. As of
the beginning of 2010 astronomers have observed 405 exoplanets and in
a handful of cases two planets have been observed orbiting a single star.
It is estimated that there are innumerable numbers of Solar Systems in