How fast do meteorites hit the ground?

When a meteoroid, a rocky or metallic body from outer space, enters Earth’s atmosphere, it’s called a meteor. If it’s large enough, it can survive the atmospheric entry and reach the Earth’s surface at tremendous speeds, becoming a meteorite. But just how fast do meteorites hit the ground?

Meteoroids, rocky or metallic bodies from outer space, enter the Earth’s atmosphere at very high speeds, ranging from 11 km/sec to 72 km/sec (25,000 mph to 160,000 mph or 40,000 km/h to 257,000 km/h).

For comparison, the International Space Station (ISS) orbits Earth at 7.66 km/s (about 17,000 mph / 28,000 km/h).

The fastest bullets travel at about 1,800 mph (2,900 km/h). So meteoroids (and, in general, celestial objects) are fast!

But, due to atmospheric drag, the meteoroid will rapidly decelerate as it penetrates increasingly denser portions of the atmosphere.

Because of this atmospheric drag, if the meteoroid is small enough, it will not produce a meteor but will decelerate slowly enough to remain intact and then float gently to the Earth’s surface.

Most meteorites, ranging from a few kilograms up to about 8 tons (7,000 kg), will lose all of their cosmic velocity and after a certain point called the retardation point, they begin to accelerate again, under the influence of the Earth’s gravity (9.8 meters per second squared).

The meteorite will then quickly reach its terminal velocity of 200 to 400 miles per hour (90 to 180 meters per second or 320 to 640 km/h).

Terminal velocity, the maximum velocity attainable by an object as it falls through a fluid or air, occurs when the acceleration due to gravity is exactly balanced by the deceleration due to atmospheric drag.

But, if the meteoroid is large enough, some fraction of it will survive the ablative entry through the Earth’s atmosphere and land on the surface with enormous speed.

So, how fast do meteorites hit the ground?

According to astronomers, when a meteorite hits the Earth’s ground, the maximum theoretical impact speeds are:

• The estimated fastest impact speed of a near-Earth asteroid is 21 km/s (46,976 mph or 75,600 km/h).
• For a short-period comet, the maximum impact speed is estimated at 41 km/s (91,714 mph or 147,600 km/h).
• For a long-period comet, the fastest impact velocity is about 53 km/s (118,558 mph or 190,800 km/h).

With these very high speeds, meteorites can create huge impact craters when they hit the ground.

Scientists also estimate that the Chicxulub Impactor that killed the dinosaurs 66 million years ago (it was an asteroid or comet at least 10 kilometers / 6 miles in diameter) hit the Earth at around 17.7 km/s (40,000 mph or 64,000 kilometers per hour).

Fastest meteorite impact on record

On March 19, 2013, an impact occurred on the Moon that was visible from Earth, when a 30 cm (11.8 inches) meteoroid slammed into the lunar surface at 25 km/s (56,000 mph or 90,000 km/h) creating a 20-meter (66 feet) crater. This is the fastest meteorite impact on record.

Since there is no air on the Moon, nothing slowed the meteoroid down.

What’s the Difference Between a Meteoroid, a Meteor, a Meteorite, an Asteroid, and a Comet?

• Asteroids are minor planets or rocky objects smaller than planets. There are millions of asteroids and most of them orbit in the asteroid belt between the orbits of Mars and Jupiter. Many asteroids are thought to be the shattered remnants of planetesimals, bodies within the young Sun’s solar nebula that never grew large enough to become planets. In other words, they are leftovers from the formation of our solar system. The size of asteroids varies greatly, the largest is almost 1,000 km (625 miles) across.
• Comets are also formed around the same time as asteroids and they are leftovers from the formation of our Solar System too. The biggest difference between an asteroid and a comet is what they are made of. Since they formed at farther distances from the Sun than the asteroids, comets are icy bodies, unlike rocky asteroids. When a comet passes close to the Sun, warms and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail which can be seen from the Earth without the aid of a telescope, if it’s bright enough.
• Meteoroids are also rocky or metallic bodies in outer space, but they are significantly smaller than asteroids. There is no well-defined size range for a meteoroid, their range in size is from small grains to one-kilometer-wide objects. Objects smaller than this are classified as micrometeoroids or space dust. Most meteoroids are fragments of comets or asteroids.
• If a meteoroid comes close enough to Earth and enters the atmosphere, it vaporizes and creates a visual phenomenon known as a meteor, appearing as a beautiful streak of light in the sky. These streaks, often erroneously called “shooting stars,” are not stars at all but rather bits of rock. Sometimes, meteoroids explode in the atmosphere. However, if a meteoroid is small enough, it may not produce a bright meteor but instead decelerate slowly enough to remain intact and gently reach the Earth’s surface.
• If the meteoroid is large enough, some fraction of it will survive the ablative entry through the atmosphere and hit the surface. This part of the meteoroid is then called a meteorite.
• If a meteor is extremely bright, then it’s called a bolide. One definition describes a bolide as a fireball reaching an apparent magnitude of -14 or brighter (more than twice as bright as the full moon). A superbolide is a bolide that reaches an apparent magnitude of -17 or brighter. A superbolide can be brighter than the Sun, which has an apparent magnitude (m) of -26.74. The apparent magnitude (m) of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth.

Sources

• Cover photo by Juskteez Vu on Unsplash
• “Asteroid, Meteor, Meteorite, and Comet: What’s the Difference?”, an article by “Everyday Einstein” Sabrina Stierwalt on the Scientific American website
• “What’s the Difference Between a Meteoroid, a Meteor, and a Meteorite?” on the Encyclopedia Britannica website, written by Jonathan Hogeback
• “What Is The Difference Between Asteroids And Comets?” by Nancy Atkinson on Universe Today
• Asteroid on Wikipedia
• Comet on Wikipedia
• “Meteoroids – A Proposed Classification By Size” on the Australian Space Academy website
• “Asteroid or Meteor: What’s the difference?” on NASA Space Place
• “Meteors and Meteorites” on the NASA website