Earth Sterilizing Impact

Mass Extinction Impact

Civilization Threatening Impact

EROS Asteroid 433EROS Asteroid 433

KLEOPATRA Asteroid 216KLEOPATRA Asteroid 216

Terrestrial Impact FrequencyTerrestrial Impact Frequency

year

century

million yr.

billion yr.

ten thousand yr.

100 millionmillion10,00010010.01

Hiroshima

Tunguska

K/T

TNT equivalent yield (MT)

Global catastrophe

Tsunami danger

What Happens When an Impact Takes Place?What Happens When an Impact Takes Place?

Bolides (up to 5 MT)• Great fireworks display, no damage

Tunguska-class (15 MT) impact• Damage similar to large nuclear bomb (city-killer)• Average interval for whole Earth: 100 yr.• Minor risk relative to other natural disasters

(earthquakes, etc.)

Larger local or regional catastrophes (e.g. 10,000 MT)• Destroys area equivalent to small country • Average interval for whole Earth: 100,000 yr.• Moderate risk relative to other natural disasters

Global catastrophe (> 1 million MT)• Global environmental damage, threatening civilization• Average interval for whole Earth: 1 million years• Major risk relative to other natural disasters

Types of Craters

Physics of Cratering

There are general forms of impact craters: simple and complex

Simple craters:• Bowl shaped pits, usually less than 5km in diameter• Raised circular rim and a nearly parabolic interior• Depth to diameter ratios are between 1/5 and 1/3• Floored by a pool of broken rock ( breccia ) mixed with shocked debris and impact melt.• There is usually evidence of melting that has drained back into into the crater over time.

Complex Craters:

• These types of craters have a more complicated morphology than simple craters

• At a transition diameter of 2 to 4 km, gravity causes the walls of the complex crater to slump downward and inward.

• This movement creates a complex structure with a central peak or peak ring and a shallow depth to diameter ratio of between 1/10 and 1/20.

• The central peak or peak ring is formed by the initial rebound from the compressional shock of the impact.

• Slumping of the rim further modifies and enlarges the crater

Physics of Cratering

Location: 35 deg N, 111 deg W Diameter: 1.186 km

Age: 49,000 yearsFirst recognized impact crater on Earth

Barringer Meteor Impact Crater

Wolf Creek Crater, Western Australia:The location of this crater is 19°10'S, 127°46'E. The rim diameter is 800 m Distance from the rim crest to the present crater floor is 60 m.The age is approximately 10,000-20,000 years.

This is classified as a simple crater and Meteorite fragments have been recovered from the crater floor, attesting to its origin.

The impact occurred 214 million years ago.

The asteroid probably had a diameter of about 5 km and it may have produced a mass extinction.

Manicouagan Crater Northern Quebec, CanadaLocation: (Lat 51 23N, Long 68 42W).

Diameter is about 100 km, with an inner ring which is lake with a diameter of 70 km

Landsat satellite photo

Site of Impact Craters on Earth

• After its formation, the earth went through a period of intense bombardment by extraterrestrial bodies, at least 100 times higher than the present impact flux.

• This bombardment period lasted from 4.6 to about 3.9 billion years ago.

• Most of the terrestrial impact craters that ever formed, however, have been obliterated by other terrestrial geological phenomena.

• Approximately 150 impact craters have been identified on Earth.

• Almost all of these craters have been identified since 1950 and more are being discovered each year as the result of improvements in imaging technology from orbiting satellites.

• Although the number of known impact craters on Earth is relatively small, the preserved sample is an extremely important resource for understanding impact phenomena and they provide the only ground-truth data currently available.

Fast Facts Related to Impact Craters on Earth

•The impact event known as the (K-T) event, is believed to have caused mass extinction on Earth because of the amount of material that was ejected into the atmosphere as the result of the impact.

•From estimates of the terrestrial cratering rate, the frequency of K-T-sized events on Earth is of the order of one every 50-100 million years.

•Smaller, but still significant impact events, occur on shorter time scales and will affect the terrestrial climate and biosphere to varying degrees.

•Impacts are a random process not only in space but in time.

•At the present, no systems or procedures are in place specifically for mitigating the effects of an impact.

Fast Fact Related to Impact Craters on Earth – cont.

LINEAR NEO Search Systems

Spaceguard Survey ProgressSpaceguard Survey Progress

Spaceguard Survey originally proposed by NASA panel in 1992 • Additional support from US Congress in 1995• Adopted as NASA goal in 1998 (in collaboration with USAF)

Survey Objective: Discover and track 90% of the Near Earth Asteroids (NEAs) with diameter greater than 1 km within ten years (by 2008)• Estimated number of NEAs larger than 1 km: approximately 900• Number discovered through end of 2000: approximately 430• Estimated completion date (to 90%): 2012

Most NEAs discovered by MIT-Lincoln Lab LINEAR search system• Two USAF 1-m telescopes with NASA operating funds• Discovery rate approximately 5 / month

International program for follow-up and orbit determination

Threatening NEAs (if any) should be identified decadesbefore impact

FOR MORE INFORMATIONFOR MORE INFORMATION

NASA Impact Hazard Website

http:// impact.arc.nasa.gov

NASA NEO Program Website

http:// neo.jpl.nasa.gov