ESYS150 LECTURE 18 IMPACTS WITH SPACE OBJECTS. OUTLINE Impact scars and space objects Known impacts on Earth Environmental effects Events of the Twentieth Century Frequency of large events. IMPACT SCARS AND SPACE OBJECTS INTRODUCTION Comets and Asteroids.
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Impact scars and space objects
Known impacts on Earth
Events of the Twentieth Century
Frequency of large events
Computer enhanced image of a comet.
Earth moves through space occupied by comets and asteroids traveling on different paths.
Will these paths cross and could a comet or asteroid destroy the human race
Few scars earth. Wiped away by plate motion and erosion
Moon dead thus has a huge number of impact scars.
Most occurred early in formation before 3.9Ba.
Maria formed 3.8 - 3.2 Ba. Have many less impact craters.
Craters formed by same processes active today.
Meteoroids - pieces of asteroids and comets orbiting the sun
Meteors - shooting stars blazing through Earth’s Atmosphere
Meteorites - objects actually hitting the surface of the Earth. Either metallic (iron) or rocky (stony)
Though most objects reaching atmosphere are stony. Iron meteorites are more common because stony meteorites (a) tend to break up in the atmosphere, (b) easily eroded and (c ) are difficult to detect.
Solar system from the Sun to Jupiter in Astronomical units
Asteroid belt of rocky and metallic objects lies between inner rocky planets and outer gaseous planets where 10th planet should lie.
Most meteorites appear to come from the Asteroid belt.
Asteroids occasionally collide and jump into an eccentric orbit.
Clusters of Asteroids such as the Apollos and the Amors have orbits that intersect the orbits of Earth and Mars.
They are possible sources for large meteorites that slam into the Earth’s surface
Kuiper Belt - flattened disc of comets with orbits of < 200 years, orbits the Sun in a plane. Halley’s best known example
Oort Cloud - vast encircling envelope of comets around the Sun. Has a spherical distribution. Orbits > 200years.
Composition - ice and rocky debris (dirty snowball)
Tail - created by gases and trapped dust released after sublimation intersecting with the Solar Wind
Solar Wind - stream of sub-atomic particles streaming out of the Sun.
Tail - lines up with solar wind moving out from the sun.
Size - most comets less than 15 km in diameter
Comes every ~76 years. Elongate elliptical orbit is steeply inclined to the Earth’s orbit.
Seen 1910 and 1986.
1012 enter every day, almost all very small and burn up in atmosphere. Needs to weigh 350 tons to come through the atmosphere largely unaffected
Cosmic dust (0.001 mm) so small . Not altered. Rains down on Earth
Shooting stars (1mm) burn up in atmosphere. Glass drops to surface.
Meteorites (1gm) melt in the atmosphere but some get through. Mostly iron composition
Meteorites weighing more than 350 tons not slowed down.
164 known impact craters in the world
57 in US and Canada
Known to to be a meteorite crater for the following reasons:
1 Steep sides and closed, 2 Rim uplifted and tilted away from center
3 inverted piles of rock found outside the crater, 4 large blocks of limestone
found outside crater, 5 Crater has 265 m of shattered rock, 6 Numerous
pieces of nickel-iron found in the area and 7 High P/T rocks including fused
sandstone and shatter cones.
30 m diameter meteorite about 50,000 years ago.
Either side of the KT boundary have very different assemblages
Boundary well exposed. Has clay layer with Iridium 300 x normal.
Iridium common only in iron nickel meteorites.
Found Iridium everywhere at KT boundary in cores.
Around world at K/T boundary found large amounts of Iridium.
Rare on Earth. Common in meteorites. Suggested meteoritic collision with the Earth.
Evidence suggested came down in the Caribbean.
Circular gravity anomaly off the tip of the Yucatan Peninsula.
PMEX had drilled exploratory holes in the area which had encountered shattered rock and glasses
Geophysical surveys shoed circular structures at depth.
Seismic data showed an inner and outer ring of 80 and 195 km diameter.
Gravity and magnetic structures show some opening to the North west.
Suggests a 10 km asteroid slammed into the Earth at a 20 - 30 degree angle 64.98 Ma
Large meteorites form complex craters
2 Impact shock creates high P & T that vaporizes most of the crater rock and the meteoroid
Outer walls can have a diameter 100 times the depth.
Impact of K/T asteroid had major effects on surface temperature.
First, a fireball and hot gases that lasted many hours. Second, temperatures
dropped to winter conditions as dust and ash blocked out sunlight. Third,
after dust settled C02 remains aloft creating greenhouse warming of 10o C.
Also have major 300 m tsunami and a huge steam bubble.
Strange event in unpopulated Siberia. Massive fireball exploded 8 km above ground.
Produced very bright light in northern Europe.
Found all the trees in a 30 x 30 km area knocked down.
No impact crater or even broken ground. 30 to 50 m meteorite exploded above ground.
Expedition in 1958 found evidence of melted iron and silica rich rock.
If over Washington do tremendous damage.
22 March 1989 - Asteroid 1989FC a 500m body, missed the Earth by less than 6hrs or 700,000 km. Would have created 7 km crater
19 May 1996 - 150 m Asteroid missed Earth by 700,000 km. Four times larger than the crater that made Meteor Crater, Arizona.
?? 2028 - in late 90’s was predicted that an Asteroid labeled 1997XF11 might hit the Earth in 2028.
Near misses surprisingly high. About 50 house sized bodies pass between Earth and Moon every day. However, 50 m bodies burn up in Atmosphere. Only iron meteorites stay intact and they are uncommon.
Beyond 100 m diameter meteoroids have a devastating effect on life
BIGGEST NEAR EVENTS
Have Torino scale which assesses hazards on a 0 - 10 scale.
Enables calm communication about the threats.
Start by looking at moon. Maria 16% moons surface. Created 3.2 Ba. Find 5 craters > 50 km width and 24 craters > 25 - 50 km.
One major impact every 110 million years.
Comparing with the Earth. Earths surface 80 times that of Maria but land only 1/3 of earth’s surface. Would expect 720 impacts. Only have found 120. Most missing craters destroyed or buried.
Odds extremely small that a large asteroid will hit Earth during our life time. However, so many will be killed when does hit this will skew statistics.
Over 2000 NEO’s. 25-50% will eventually hit the earth.
Average time between impacts is 100,000 years.
Risk being killed by impact is 1 in 20,000. High because a huge number of people 1.5 Billion will be killed in an impact.
Have detected > 2000 NEO’s > 1 km in diameter. About 500 are NEA’s are potentially hazardous.
I in 300 chance of one hitting Earth in 2880.
1) Blow apart with Nuclear bomb
2) Attach rocket
3) Vaporize with sunlight
4) dig up rock mass.
Is for sure going to happen but not in our life times.