Meteor

How long

Sonic booms

Of the several 10s of tons of cosmic material entering Earth’s atmosphere each day, only about one ton reaches the surface.
An object’s chance of survival depends on its initial mass, speed and angle of entry, and friability (tendency to break up). Micrometeoroids radiate heat so effectively that they are dramatically slowed without being vaporized and fall as a continuous, gentle, invisible rain. Meteoroids with masses between 10-6 g and 1 kg tend to burn up completely as meteors. Friable meteoroids break up and are destroyed at altitudes of 80 to 90 km. Those which are tougher survive longer and produce fireballs as their surface undergo
melting and ablation at temperatures of several thousand degrees. If meteoroids avoid destruction high up, they enter the lower, denser part of the atmosphere where they are rapidly decelerated.

 

Most meteors become visible at around 60 miles (96.5 kilometers) up. Some large meteors splatter, causing a brighter flash called a fireball, which can often be seen during the day and heard up to 30 miles (48 km) away. On average, meteors can speed through the atmosphere at about 30,000 mph (48,280 kph) and reach temperatures of about 3,000 degrees Fahrenheit (1,648 degrees Celsius).

The term meteor does not refer to the asteroid, meteoroid or large micrometeoroid itself, but to the light phenomenon (flash and/or streak of light) created during its high speed entry into a planet’s atmosphere when the ionized particles that are vaporized from that object’s outer layer interact with the planet’s atmosphere. Though most of these interstellar objects are only a few mm across, when their paths intersect a planet’s orbit, they do so at such extreme speed that the object compresses the atmosphere in front of them. On Earth, this compression raises the surface temperature of the object to >2,000 K causing the object’s outer layer to continuously vaporize in a process called ablation. The vaporized atoms collide with air molecules to create an ionized “trail”, that produces the bright steak of light that is only ~1 m across but it can be many km (typically 20-30 km) long depending on the speed of the meteoroid. It may also display different colors, the result of the de-excitation of different atmospheric molecules. Most meteors appear at altitudes of 100 – 120 km (lower thermosphere) and will enter dark flight at an altitude of approximately 50 km (lower limit of the mesosphere) when the increasingly dense atmosphere has slowed the object below the speed where ablation can occur.

If we assume that the Earth moves around the Sun at about 30 km/sec (108,000 km/h or 67,000 mph) and the escape velocity from the solar system (velocity of an object arriving from infinity) at the orbit of the Earth is 42 km/s (151,000 km/h or 94,000 mph), then we can determine the theoretical slowest and fastest velocity for a meteor entering Earth’s atmosphere.

  1. The fastest velocity will occur when the Earth and the meteor are moving towards each other on a direct collision course. So, the fastest theoretical entry velocity is 42 km/s + 30 km/s, an astounding 72 km/s (259,0000 km/h or 161,000 mph)!
  2. The slowest velocity will occur when the meteor is moving in from behind the Earth. So, the slowest theoretical entry velocity is 42 km/s – 30 km/s, a still impressive 12 km/s (43,000 km/h or 27,000 mph)!

A very large meteor is known as a fireball and is usually caused by a larger body. A meteoroid or asteroid the size of a boulder or car will produce a very large and bright fireball even in the daylight. (NOTE: The International Astronomical Union defines a fireball as “a meteor brighter than any of the planets” (magnitude -4 or greater)).

Large meteor events may produce meteorites, but the combination of ablation and fracturing causes more than 80% of the original mass (prior to atmospheric entry) to be lost. During atmospheric passage, the object also moves far faster than the speed of sound (0.343 km/s at 20 oC) thus compressing the sound waves of its entry and creating sonic booms of such magnitude that they can sometimes be destructive as was experienced in the Feb. 2013 in Russia during the fall of the Chelyabinsk meteorite. It is not unusual for these sonic booms to rattle windows when they pass over populated areas. Witnesses during the 1912 Holbrook meteorite shower are said to have heard a protracted rumble which lasted roughly 2 minutes.

Video of Chely HERE