Some asteroids have orbits that cross the
orbit of the Earth. That means that the Earth will be hit sometime. Recent
studies have shown that the Earth has been hit an alarmingly large number of
times in the past. One large impact is now thought to have contributed to the
quick demise of the dinosaurs about 65 million years ago.
Thermonuclear warhead Effect
The largest yield of a thermonuclear
warhead is around 50--100 megatons. The kinetic energy of the falling object is
converted to the explosion when it hits. The 10-kilometer object produces an
explosion of 6 × 107 megatons of TNT (equivalent to an earthquake of magnitude
12.4 on the Richter scale).
Hole in the atmosphere
On its way to the impact, the asteroid pushes aside the air in front of
it creating a hole in the atmosphere. The atmosphere above the impact site
is removed for several tens of seconds. Before the surrounding air can rush
back in to fill the gap, material from the impact: vaporized asteroid, crustal
material, and ocean water (if it lands in the ocean), escapes through the hole
and follows a ballistic flight back down. Within two minutes after impact,
about 105 cubic kilometers of ejecta (1013 tons) is lofted to about 100
kilometers.
Steam explosions
If the asteroid hits the ocean, the
surrounding water returning over the hot crater floor is vaporized, sending
more water vapor into the air as well as causing huge steam explosions.
Tsunami
The oceans cover about 75% of the Earth's
surface, so it is likely the asteroid will hit an ocean. The asteroid will push
the water aside and hit the ocean floor to create a large crater. The water
pushed aside will form a tsunami, a megatsunami.
The steam blasts from the water at the
crater site rushing back over the hot crater floor will also produce tsunamis
following the initial impact.
Global Firestorm
The material ejected from the impact
through the hole in the atmosphere will re-enter all over the globe and heat up
from the friction with the atmosphere. The chunks of material will be hot
enough to produce a lot of infrared light. The heat from the glowing material
will start fires around the globe.
Acid Rain
The heat from the shock wave of the
entering asteroid and reprocessing of the air close to the impact produces
nitric and nitrous acids over the next few months to one year.
Atmospheric NO2 is converted to nitric and
nitrous acids when it is mixed with water.These are really nasty acids. They
will wash out of the air when it rains---a worldwide deluge of acid rain with
damaging effects:
1.
destruction or damage of
foliage;
2.
great amounts of weathering of
continental rocks;
3.
the upper ocean organisms are
killed. These organisms are responsible for locking up carbon dioxide in their
shells (calcium carbonate) that would eventually become limestone. However, the
shells will dissolve in the acid water. That along with the "impact
winter" kills off about 90% of all marine nanoplankton species..
4. The ozone layer is destroyed by O3 reacting with NO. The amount of
ultraviolet light hitting the surface increases, killing small organisms and
plants (key parts of the food chain). The NO2 causes respiratory damage in
larger animals. Harmful elements like Beryllium, Mercury, Thallium, etc. are
let loose.
Temperature Effects (impact winter)
All of the dust in the air from the impact
and soot from the fires will block the Sun. The dramatic decrease of sunlight
reaching the surface produces a drastic short-term global reduction in
temperature, called impact winter.
Plant photosynthesis stops and the food chain collapses.
The cooling is followed by a much more
prolonged period of increased temperature due to a large increase in the
greenhouse effect. The greenhouse effect is increased because of the increase
of the carbon dioxide and water vapour in the air. The carbon dioxide level
rises because the plants are burned and most of the plankton are wiped out.
Also, water vapor in the air from the impact stays aloft for a while. The
temperatures are too warm for comfort for a while.
Beneficial Asteroid Impacts
The near-Earth asteroids are the most
worrisome ones for possible impacts but they could also be potentially very
beneficial to Earth if we could mine them for rare metals and use the asteroids
as convenient stepping stones to manned exploration of the solar system,
especially traveling to Mars.
The near-Earth asteroids are relatively abundant in heavy metals
like iron and nickel and the platinum-group metals (platinum, palladium,
rhodium, ruthenium, osmium, and iridium) used in modern technology.
In fact, all of the heavy metals in the
Earth's crust came from asteroid impacts after the Earth differentiated
The water from the asteroids could also be broken down
into oxygen and hydrogen to be used as rocket fuel.
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