Earth Impact Rate

Impact Earth

Earth Impact Rate

Gravitational Focusing

• The Earth is hit about 10 times more frequently than the Moon by objects of the same size.
• Graph of crater diameter vs distance from the sun.

Earth Impact Rate (Small Stuff)

Historical Context: Kennedy's Moon Mission

• President John F. Kennedy's Special Message to the Congress on Urgent National Needs, May 25, 1961.
• Goal: landing a man on the moon and returning him safely to Earth before the end of the decade.

Hazards in Space

• Solar particles, solar heat, solar glare.
• Cosmic rays, micrometeorites.
• Meteorite shrapnel.
• Ultraviolet rays, X-rays, gamma rays.
• Lunar.

Kinetic Energy

• Formula for kinetic energy: $KE = (1/2) * m * v^2$

Energy Release

• Small masses moving at high speeds can release a large amount of energy.

Hypervelocity Impact

• Example: 1/2 oz (14 g) plastic at 15,000 mph (6.7 km/s).

Explorer Satellite Missions

• Explorer 16: Launched Dec 16, 1962.
• Explorer 23: Launched Nov 6, 1964.
• Satellites hit about once every 4 days.

Pegasus Satellite

• Meteoroid Technology Satellite.
• Objective: To orbit the Earth as a target for high-speed meteoroids.

Pegasus Missions

• Pegasus 1:
  • Launched: 16 February 1965
  • Decayed: 17 September 1978
• Pegasus 2:
  • Launched: 25 May 1965
  • Decayed: 3 November 1979
• Pegasus 3:
  • Launched: 30 July 1965
  • Decayed: 4 August 1969

Number of Hits in 400-μm Thickness

• Data from 1965, showing number of hits versus days of the year.
• Including Arietids, B Taurids, and Perseids.

Recent NASA Meteoroid Penetration Results from Satellites

• Graph of penetrations per square meter per second vs. thickness of aluminum (cm).
• Data from Explorer 16, Explorer 23, Pegasus 1, and Pegasus 2.
• Comparison with Whipple (1963) best estimate.

Design Study Dilemma

• Example: Design studies for a spacecraft found that adequate meteoroid protection could require an additional 12,500 pounds, severely impacting performance. Using a lower estimate resulted in no additional weight.

Gemini 12 Mission

• Gemini 12: Nov 11 1966
• Astronauts: Lovell and Aldrin

Gemini Missions Micrometeoroid Study

• Study of Thin-Film Penetration by Micrometeoroids on Gemini 9 and 12.

Gemini 9 and 12

• Gemini 9 capsule: A thin copper surface (3.23 × $10^{-4}$ m²) exposed for 17 hours and 47 minutes in June 1966.
• Gemini 12 capsule: Thin gold and aluminum surfaces (7.06 × $10^{-4}$ m² each) exposed for 6 hours and 24 minutes in November 1966.
• No evidence of impact with extraterrestrial particles found on any surfaces.
• Early data predicted 10 particles ≥5 μm would have impacted Gemini 9's surface, and 16 particles on each Gemini 12 surface, which was not supported by the mission results.

Long Duration Exposure Facility [LDEF]

• Launched via Challenger (Apr 1984), retrieved by Columbia (Jan 1990).
• Mission duration: 2076 days.
• Orbits completed: 32,422.
• Crew: Hart, van Hoften, Nelson, Crippen, Scobee.

LDEF Orbital Flight Orientation

• Gravity gradient stabilized attitude.
• Earth-facing end and space-facing end.
• AO Ram direction and orbital velocity.

Small Particle Mass Accretion

• The small particle mass accretion rate is approximately 20 metric tons per year.
• This is comparable with the average contribution from extraterrestrial bodies in the 1-cm to 10-km size range.

Micron Size Comparison

• Human hair: 100 microns
• Pencil tip: 200 microns
• Eye of needle: 300 microns

Material Sizes

• Beach Sand= 1400 microns
• Fine Sand= 250 microns

Interplanetary Dust Particle

• Size: ~1 μm

Annual Mass Accretion Rate

• 20 metric tons per year (~20,000 kg/yr).
• Equivalent to ~1 kg/min or ~1,500 particles/sec.

Earth Impact Rate (Reaching Surface)

Global Flux of Particles

• The global flux of particles in the 12-700 μm diameter range reaching the Earth's surface is ~5.5 metric tons per year.

Meteorite Definition

• Meteorite: a solid piece of debris from an object that originates in outer space and survives its passage through the atmosphere to reach the surface.

Terminal Velocity

• Definition: The highest velocity attainable by an object as it falls through a fluid (air).
• Explanation of forces on a falling sphere: drag force and gravitational force (mg).
• Illustration of forces during acceleration and at terminal velocity.

Terminal Velocity of a 10 cm Diameter Rock

• ~100 - 200 mph

Insurance Coverage

• General Conditions Chapter B- Damage to Vehicles.
• Coverage includes damages suffered by the vehicle as a consequence of a meteorite.

Historic Human Meteorite Interactions

• 1420 BC: Israel - Fatal meteorite impact.
• 588 AD: China - 10 deaths; siege towers destroyed.
• 1321-68: China - People & animals killed; homes ruined.
• 02/03/1490: Shansi, China - 10,000 deaths.
• 09/14/1511: Cremona, Italy - Monk, birds, & sheep killed.
• 07/24/1790: France - Farmer killed; home destroyed; cattle killed.
• 11/28/1954: Sylacauga, Alabama, USA - 4 kg meteorite struck home, lady injured.
  *August 22, 1888: Meteorites fell for about ten minutes, killing one man and seriously injuring another in Dilaver, Turkey.

Sylacauga, Alabama Incident (1954)

• A 4 kg meteorite crashed through the roof of a house and slightly injured Mrs. Hewlett Hodges.

Meteorite Crashes Through Ceiling and Lands on Woman's Bed

• Incident on Oct 3, 2021.

Number Hitting Earth per Year

• Graph showing number of impacts per year vs. mass [kg].

Comparison Sizes

• Sizes ranging from mouse to 10km asteroid

Meteorite Find Locations

Antarctic Meteorite Concentration

• Winds ablate ice, concentrating meteorites.
• Meteorites fall randomly over the continent.

Meteorite Collection Sites

• Antarctica: 19,884 (75.9%)
• NW Africa: 407 (1.6%)
• Algeria: 452 (1.7%)
• Oman: 511 (2.0%)
• Australia: 578 (2.2%)
• Libya: 1302 (5.0%)
• USA: 1346 (5.1%)
• All Others: 1375 (5.2%)

Comparison Sizes

• Sizes ranging from mouse to 10km asteroid

Examples of Fireballs and Meteor Events

• August 18, 1783: Windsor Castle
• August 10, 1972: Fireball event
• June 3, 2004: Possible meteorite crash near Olympia, Washington.
• Chelyabinsk meteor: 15 February 2013.
  *Thursday, May 7th 2020: Fireball seen over Puget Sound.

Gulf of California Fireball

• Observed on 2013-12-29.

Earth Impact Rate (Really Large)

Distribution of Impact Craters

Distribution of Impact Craters by Continent

• Total craters considered: 190
• Asia & Russia: 31 craters, 16% of Earth's land area
• Africa: 21 craters, 20% of Earth's land area, 11% of craters
• North America: 60 craters, 16% of Earth's land area, 32% of craters
• South America: 11 craters, 12% of Earth's land area, 6% of craters
• Antarctica: 0 craters, 9% of Earth's land area, 0% of craters
• Europe: 41 craters, 7% of Earth's land area, 22% of craters
• Australia: 27 craters, 6% of Earth's land area, 14% of craters

Comparison Sizes

• Sizes ranging from mouse to 10km asteroid

Comparison Sizes

• Sizes ranging from mouse to 10km asteroid
  Mostly Harmless Local to Global Devastation

Completeness of Discovered Impact Craters

• Analysis of how many impact craters on Earth are yet to be discovered.
• Shows predicted vs. discovered craters by diameter range.

Lunar Surface

• Crater Diameter vs Number per million sq km

Near-Earth Asteroids Discovered

• Total Discovered vs. Estimated Diameter
• Data as of (2025-Apr-14)

Asteroid Population

• Graph illustrating asteroid size vs. number in the population.
• Includes predicted population and percentage found.

Recent & Upcoming Earth-Asteroid Encounters:

• Table listing asteroid encounters, miss distance, velocity, and diameter for specified dates in 2025.

Fireballs Reported by US Government Sensors

• Graph showing Impact Energy from 1988-Apr-15 to 2025-Mar-27

Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO)

• The equipment relies on infrasound, the low-frequency shock waves created by explosions, to verify the ban on nuclear explosions for both military and civilian purposes. Similar shock waves are created by meteorite explosions

Integrated Operational NuDet (Nuclear Detonation) Detection System (IONDS)

• (1963 - Present)

Number Hitting Earth (1988 - 2023)

• Graph showing Impact Energy

Comparison Sizes

• Sizes ranging from mouse to 10km asteroid

Earth Impacts vs Time Between Impacts

• Average Time Between Earth Impacts [years] vs Object Size