Facts About Comets

When I was in college, I took a Natural Catastrophes class. Although I cannot remember all the details from the class, I do recall the professor telling his students at the end of the first class that "there are support groups for people who study geology." By the end of the quarter, I understood. Everything we had learned in class made me fear the world was going to end at any minute for any number of reasons. However, I did learn a lot of interesting things, including information about comets. So, here are some interesting, and somewhat scary, facts about comets:

Comets, also known as "dirty snowballs," are similar to asteroids but are made of ice and rock. Comets also travel at higher velocities than asteroids.

Comets make up the Oort cloud, which forms a vast spherical region around the sun.

Comets have orbits outside our solar system but become visible when they pass close to the sun or Earth.

Comets travel at speeds up to 60-70 km per second; therefore impact with Earth would be a catastrophe. If there were an impact, bolides would break up in the atmosphere into 5-10 fragments that still travel about 50 percent of the original velocity. These smaller masses would cause a widespread reaction between nitrogen and oxygen in the atmosphere to generate nitrates that would combine with water and form nitric acid (acid rain).

The overall densities of comets are similar to water at 1.0 grams per cubic centimeter.

Some 10-12 percent of impacts on the Earth and moon are from comets, and all impacts produce craters.

If the comet Hale-Bopp had collided with Earth, the energy expended would be tens to hundreds of times larger than the asteroid that killed the dinosaurs 65 million years ago.

On impact, the kinetic energy of the incoming object is converted to heat and vaporization of the comet and target materials near it. This melts more rock, excavates a crater and blasts out rock and droplets of molten glass (it turns into a huge fireball that heats and melts rock and burns everything combustible).

If a comet impacted an ocean, a tsunami would be formed by water flowing into and back out of the crater (the wave can be as high as 200m). A large impact, such as an asteroid 10-15 km in diameter, roughly 6-9 miles, would kill virtually everything on Earth. It would cause acid rain and mass extinctions of any species far enough away to survive the impact would occur. Acid rain would kill vegetation and sea life. Dust, soot from fires, and nitrogen dioxide would blot out the sun so animals not incinerated would freeze and starve to death. Plants would die of the drop in temperature and lack of sunlight. Land temperatures would drop to freezing levels within a week to two months. Widespread fires would ignite from lightning strikes after the vegetation died.

If there were a comet inside the moon's orbit, by the time we saw it, it would be three hours from impact. It would look like a bright star at first and become noticeably brighter every few minutes. An hour from impact, it would appear as an irregular mass, rapidly growing in size. Three seconds from impact, it would enter Earth's atmosphere traveling about 30 km per second.

Reference:

Professor Kellogg, University of California, Santa Barbara