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In the Beginning……

The Origin of the Solar System

The Early Earth

Impacts of Extraterrestrial Objects

The Origin of the Solar System

The Sun and the planets that orbit around it began as a Nebula (an immense cloud of gas and dust in space; also called a “molecular cloud”).

Nebular Hypothesis

Star Birth Clouds:Hubble Telescope imageof Eagle Nebula.

Image is approximately1 light year across.

Within the Nebula the pressure of the gases act outwards to cause it to expand while gravitational forces (forces that pull bodies towards each other) act to cause the Nebula to collapse onto itself.

As the diameter of the Nebula is reduced, the rate of spin increases.

Gravity prevails and the Nebula collapses and begins to spin.

Due to the interaction of the pressure and gravitational forces,as the Nebula spins it becomes flatter and forms a broad disk over time as the Nebula continues to collapse.

Within the cloud swirling eddies develop drawing matter towards their centres to form the Protoplanets.

As the density of the centre of the disk increases it heats up to form the Protosun.

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The protoplanets become solid planets and continue their orbit, governed by the initial spin of the swirling nebula.

As the Protosun becomes even hotter the gases are driven out of the inner planets of the Solar System.

Orion Nebula (1500 light years from Earth)‏

The Nebular Hypothesis is attractive because it explains many features of the Solar System:

•The orbits of the planets lie in a plane with the sun at its centre (the plane of the early disk-shaped Nebula).

(ecliptic plane)‏

•The planets all orbit around the Sun in the same direction (inherited from the spin of the nebula which caused the orbital motion of the protoplanets).

•The planets mostly rotate in the same direction; their axes of rotation are nearly perpendicular to the orbital plane.

•The direction of rotation is inherited from the direction of spin of the eddies in the spinning nebula.

The Planets of the Solar System

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The outcome for our Solar System:

The Inner Planets: Earth-like planets: metallic cores, dominated by silicon and oxygen compounds

Mercury 4,880 (38%) 0.367

Venus 12,103 (95%) 0.723

Earth 12,756 1.0

Mars 6,787 (53%) 1.52

Name Diameter (km)‏% of Earth in brackets

Distance from Sun(AU)1

1Astronomical Units: 1 unit is the distance from Earth to the Sun, 149,597,900 km.

The Outer Planets: “Gas Giants” with thick atmospheres that thicken and become hotter towards their rocky or icy cores.

Name Diameter (km)‏% of Earth in brackets

Distance from Sun(AU) ‏

Jupiter 143,800 (1,127%) 5.2

Saturn 120,660 (946%) 9.5

Neptune 49,500 (388%) 30.1

Uranus 51,120 (401%) 19.2

Why do the outer planets diminish in diameter as they are farther from the sun?

Inner planets lost their early atmospheres so they are smaller than the outer planets.

The thickness of the disk thins away from the sun so the the diameter of possible planets becomes smaller away from the sun.

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Orbits of the planets of the Solar SystemExamples of orbit eccentricity

Variation in Earth’s orbital eccentricity over time.

Eccentricity: a measure of how much a planet’s orbit varies from a circular path.

Most recently this was the case from January 1979 through February 1999.

It rotates in the opposite direction to most planets.

Pluto’s orbit crosses Neptune’s orbit so that at times it is closer to the sun than Neptune.

Many believe that Pluto is not a true planet but is a large body that was “captured” by the Sun’s gravitational attraction.

The problem with Pluto!

It is NOT a gas giant.Pluto has a strongly eccentric orbit (it is elliptical rather than circular and not in the same plane as the other planets) and it is tilted at 17° to the plane of the orbits of the other planets.

Planets: orbit a star (the sun), have enough mass to produce gravity strong enough to make them spherical, not a star or moon of another planet (minimum diameter approximately 800 km).

“Classical planets” include the original 9 although Pluto seemed to be an exception.

This appears to make 800km the maximum size for asteroids!

The August 2006 proposal

Plutons: “planets” with orbits of more than 200 years (i.e., beyond Neptune’s orbit); they also have more eccentric orbits than the first 8 of the “classical planets”.

Pluto’s orbit about the sun takes 249 years and the orbit is very eccentric making it the innermost pluton and not really a “classical planet ”.

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Charon which was considered to be a moon of Pluto would beconsidered to be a double planet (pluton?) paired with “ Pluto ”.

The proposal would allow UB313 into the group of planets, along withpossibly 50 or more other objects.

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Dwarf planets: informally defined as relatively small planets.

Ceres is the only one right now but more will likely be forthcoming.

No maximum size is defined but Pluto, Charon and UB313 seem to be considered a dwarf planets (plutons)!

New definitions:“Planet” is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearlyround) shape, and (c) has “cleared the neighbourhood1” around its orbit. (Pluto’s orbit crosses the orbits of many “plutinos” in the Kuiper Belt).

Source: http://www.universetoday.com/2006/08/24/plutos-out-of-the-planet-club/

1Used its gravity to “absorb” or control other bodies in the vicinity of its orbit (i.e., its neighborhood).

A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearlyround) shape , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

All other objects except satellites orbiting the Sun (Planets?) shall be referred to collectively as “Small Solar-System Bodies”.

Source: http://www.universetoday.com/2006/08/24/plutos-out-of-the-planet-club/

The outcome…

Charon continues to be a moon of Pluto.

KBO = Kuiper Belt Objects

Planetary update:

The object formerly known as 2003 UB 313 was officially named “Eris”, the Greek god of discord.

Its moon will be named Dysomia (the daughter of Eris).

The (now) dwarf planet Pluto has a new official name:

134340 Pluto

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Orbits of the planets of the Solar SystemWhy does the asteroid belt exist?

The Titus-Bode Law is a mathematical expression for the position of the orbits of the planets with distance from the sun.

The Titus-Bode Law predicts that the planets will be located as shown by the blue squares.

How well does the law work ?

How well does the law work ? How well does the law work ?

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How well does the law work ? How well does the law work ?

How well does the law work ? How well does the law work ?

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Where is the missing planet ?

In 1800 a call went out for astronomers to search for a planet in the region of space where a planet should reside.

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On January 1, 1802, a relatively large object was foundand named Ceres…then believed to be the missing planet.

Ceres was considered a planet until so many asteroids were found that the uniqueness of Ceres was lost and Ceres was reclassified as an asteroid.

How would a planet be destroyed?A major collision following planetary construction?An explosion due to the high internal temperature and pressure following planet formation?A nuclear explosion due to high concentrations of Uranium235 shortly after planetary construction?Is Mars actually a moon that orbited the missing planet?

Thousands of asteroids are now known to exist in the region called the asteroid belt.

Some suggest that the asteroids were derived from some planet that once followed the orbit now occupied by asteroids.

Material that didn’t come together to form a planet?

Solar System Oddities

Venus and Uranus do not rotate in the same direction as the other planets.

Venus’s rotational axis is at right angles to the plane of the planets (the ecliptic plane) but it rotates in the opposite direction compared to the other planets.

Uranus rotates about an axis that is almost parallel to the plane of the planets.

Modern thinking is that both planets were rotated by major collisions early in their history.

The early history of the EarthAccumulation to form the planet: a three-stage process that was completed by about 4.56 Billion years ago.

Stage 1:

•Dust grains in the Nebula begin to “stick” together forming larger particles that grow into large, discrete objects with their own gravitational field.

Stage 1 accretion of small particles to form larger objects.

•The gravitational attraction of the large objects pulls smaller objects into them and they grow into “planetary embryos” (up to a few hundred kilometres in diameter).

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Stage 2:

•Planetary embryos came together during a phase of relatively rapid accretion (collisions forming larger objects).

•Created tens of objects larger than the moon.

•This stage took approximately 1 millions years to complete.

Stage 3:

•Large objects from Stage 2 are attracted to each other due to their gravity; colliding and forming larger objects (the actual formation of the planets).

•Solar wind (particles emitted from the Sun) drove off the gases that made up the early atmosphere of the Inner Planets.

•The Earth evolved its own atmosphere later in its history.

•During Stage 3 the Moon came into existence.

•Stage 3 was complete after 50 to 100 million years.

The birth of the Earth

How did the Moon form?

The Lunar orbit suggests that it was captured from debris ejected from the Earth during a stage 3 impact.

Lunar orbit if it was captured planetary embryo.

Lunar orbit if it was generated by debris from Earth.

•The circular orbit suggests that the Moon was derived from the Earth.

•Towards the end of Stage 3 the Earth had a Magma Ocean; melting due the energy released from frequent large collisions.

•One or possibly two, oblique collisions ejected a ring of molten debris into orbit about the Earth.

•Once in orbit the molten debris accreted (came together) in a manner similar to the accretion of the planets.

•Initially the moon was a molten mass but it cooled to form a solid crust when impact frequency and magnitude diminished.

•It is estimated that the Moon was pretty much complete after a decade following the causal collisions with Earth.

•Just following completion of Lunar construction it was in an orbit about the Earth that was about 15 time closer than the current orbit.

•A billion years later the orbit was 4 times closer than today; it has been moving away from the Earth ever since it formed.

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View of the Moon over Brighton today. View of the Moon over Brighton 4.5 Billion years ago.

Origin of the moon….

The Movie

Comets, Asteroids and Meteoroids

Peekskill Meteorite The Peekskill Meteorite

http://leroy.cc.uregina.ca/~astro/mb_5.html

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Ever since the formation of the Earth it has been bombarded by debris from space.

Debris in space comes in a variety of forms:Comet: a mixture of ices , both water and frozen gases (carbon dioxide, methane, ammonia) and dust.

•Material that was not incorporated into planets when the solar system was formed (most comets are 4.6 billion years old, or so).

•Often called a “dirty snowball”.

•Most comets have elliptical orbits about the sun that often take them well beyond Pluto.

Nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solids.

Anatomy of a Comet

Coma: dense cloud of water, carbon dioxide and other neutral gases derived from the nucleus.

Dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye.

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•A comet is visible only when its orbit takes it near the Sun.

Comet Hale-Bopp in 1997.Photo by John Laborde

•Ultraviolet light from the Sun causes the comet to fluoresce and some gases to escape.

•After several hundreds of passes by the Sun a comet loses its gas and ice and only a rocky object remains.

Where do comets come from?

Answer: the Kuiper Belt and the Oort Cloud.

Both are regions of space around our Solar system that, combined, contain up to trillions of small, icy bodies that become comets when their orbits are disturbed.

Kuiper Belt: a disc-shaped region past the orbit of Neptune, 30 to 100 AU from the Sun.

Oort Cloud: a huge spherical “cloud” of many billions of icy bodies, surrounding the outer limits of the Solar System and extending approximately 3 light years (about 30 trillion kilometers) from the Sun.

Gravitational interaction with the outer planets can disturb the orbit of icy bodies, sending them on their elliptical comet orbits.

On July 4, 2005, JPL’s spacecraft Deep Impact’s mission was complete when its impactor collided with Comet Temple 1.

The purpose of the mission was to observe the formation of a crater and to analyze the debris that was ejected to determine the comet’s composition.

The following movies and images are from the Deep Impact home page at:

http://deepimpact.jpl.nasa.gov/home/index.html

The impact crater was made by a 370 kg mass that was launched from Deep Impact.

Here is the Quicktime movie of the impactor’s approach to Temple 1’s nucleus.

5 minutes before impact before impact.

Here’s a QuickTime animation of the mission.

1 minute before impact.

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20 seconds before impact.

Impact

By analyzing the dust ejected from Temple with a spectrometer, molecules of material making up the comet are identified.

This spectra shows water, hydrocarbons, carbon dioxide and carbon monoxide.

The birth of the Earth

Asteroids: small (metres to less than 800 kilometres?), dense objects that orbit the Sun.

Made up of inner solar system material that was not formed into planets and masses of planetary material produced by major collisions.

Not massive enough to develop a spherical shape.

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Asteroid Ida is large enough to have its own satellite in orbit around it.

Asteroid ErosOrbit: 172,800,000 km from the sun

Size: 33 x 13 x 13 km

Eros

Eros’s giant gouge….a past collision?

Eros rotates with a clumsy wobble

NEAR-Shoemaker spacecraft landed on Eros on Monday, February 12, 2001.

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Near-Shoemaker landingon Eros

1150 metres above the surface⇐ 54 metres ⇒

700 metres above the surface⇐ 33 metres ⇒

250 metres above the surface⇐ 12 metres ⇒

120 metres above the surface⇐ 6 metres ⇒ Itokawa: 690 x 300 metres.

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Asteroids are classified according to how much light that they reflect.

Albedo: the proportion of incoming light that is reflected from a surface. Albedo = 1, perfect reflector; Albedo=0.01, reflects very little incoming light.

•C-type, > 75% of known asteroids: extremely dark (albedo 0.03); approximately the same chemical composition as the Sun minus gases.

•S-type, 17%: relatively bright (albedo .10-.22); metallic nickel-iron mixed with iron- and magnesium-silicates.

•M-type, most of the rest: bright (albedo .10-.18); pure nickel-iron.

Classes of Asteroids:

Most asteroids are in orbit within the Asteroid Belt

http://cfa-www.harvard.edu/iau/Animations/Animations.html http://cfa-www.harvard.edu/iau/Animations/Animations.html

Meteoroid: a piece of stone or metal that travels in space (smaller than an asteroid, from dust size to a metre or so)‏

Meteorite: a meteor that lands on the Earth’s surface.

Bolide: a large, particularly bright meteor that often explodes (syn. fireball).

Meteor: a meteoroid that falls towards the Earth, heating up due to friction and glowing as it crosses the sky.

It is estimated that between 20,000 and 100,000 tons of material from space collides with Earth each year….much of this burns up in the atmosphere.

Small space objects

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http://www.geocities.com/ultrastupidneal/Knowledge-Astronomy-Meteorite.html

World’s largest meteorites

Hoba West Meteorite, 60 metric tons, Namibia

http://www.geo.ucalgary.ca/cdnmeteorites/

The Canadian Meteorites Site(University of Calgary)‏

The Risk of Space Objects to HumansToday there is considerable concern about space objects colliding with Earth, despite the paucity of recorded strikes directly on humans:

•Ancient records from China indicate that people have been killed by falling meteorites; no such deaths are known from modern times.

•Elizabeth Hodges, of Sylacauga, Alabama, was given a terrible bruise on the side by a falling meteorite in 1954.

•A young boy was struck on the head by a meteorite that had been slowed down by the leaves of a banana plant in Uganda in 1992.

•A meteorite killed a dog when it fell in Egypt in 1911.

Three events over the 20th Century heightened interest in evaluating the risk of impacts of space objects on Earth.

The K/T boundary impact, the Tunguska Event and the Comet SL-9 impact on Jupiter.

1. Recognition that a major impact led to the extinction of the dinosaurs and much other life prompted detailed studies of the effects of such an impact and smaller impacts.

2. The Tunguska Event was an atmospheric explosion of an asteroid in 1908. Such events happen in our own time!

So why the concern today? On June 30, 1908, at 7:30am a 15 megaton blast was felt over a large area of Siberia (the Hiroshima nuclear explosion was about 0.02 megatons; 750 X Hiroshima).The blast was an airburst (explosion) of a 60 m diameter asteroid.

The explosion was heard in London England.

Over 60,000 trees were flattened over an are of 800 mi2

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3. In 1992, Comet Shoemaker-Levy 9 (SL-9) passed near to Jupiter when it broke up into at least 21 separate fragments, up to 2 km in diameter, dispersed over several million kilometres along its orbit.

•Between 16 July 1994 and 22 July 1994 the fragments impacted the upper atmosphere of Jupiter.

The first collision of two solar system bodies ever witnessed.

•The first fragment struck Jupiter with energy equal to about 225,000 megatons of TNT creating plume which rose about 1000 km above the planet.

•A later fragment struck with an estimated energy equal to 6,000,000 megatons of TNT (about 600 times the estimated arsenal of the world). The fireball rose about 3000 km above the surface of the planet.

These three events illustrated that:

Such impacts were possible and not just the stuff of SciFi. We could see it happen (with the aid of space telescopes).

Major impacts can have a devastating effect on all life on Earth.

Even minor impacts on Earth (Tunguska) that have taken place in recent record could kill millions and cause billions of dollars in damage.

Governments and insurance companies developed concern regarding the risks and costs of such events.

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In light of these three 20th Century events researchers have focused on several questions:

What has been the frequency of impacts with Earth?

How many objects are close enough to Earth to pose a risk?

What happens when an object of a given size arrives at Earth?

What does the geologic record tell us about major impacts (the past is the key to the present)?

How do we assign a level of “risk” to space objects?

What is the frequency of impacts with Earth?

These are average values; large events can happen at any time!

Based on estimates of modern objects and the geological record of impacts worldwide.

http://www.unb.ca/passc/ImpactDatabase/essayimages/nucwin.gif

Zhamanshin Impact (Siberia): 13.5 km crater, 1 km diameter object.

For the Tunguska-class impacts:

Average interval between impacts for populated areas of Earth: 3,000 years (given the population distribution on Earth; about 10% of Earth surface area is populated).

Average interval between impacts for world urban areas (0.3% of Earth surface): 100,000 yearsAverage interval between impacts for U.S. urban areas (0.03 of Earth surface): 1,000,000 years

Source: http://impact.arc.nasa.gov/reports/spaceguard/index.html

Average interval between impacts for total Earth: 300 years

Average time between impacts can be resolved for smaller regions of Earth to evaluate human risk:

Near Earth Objects (NEOs) ‏

Asteroids those whose orbits are within 1.3 AU of the Sun.

Comets with orbits within 1.3 AU of the sun and with orbital periods (time to complete one orbit) of less than 200 years.

Potentially hazardous asteroids (PHA): asteroids that are larger than 110 metres in diameter with orbits that bring them within 0.05 AU of Earth.

How many objects are close enough to Earth to pose a risk?

Defined as:

The NEO Program (within NASA) aims to find 90% of all NEOs within 10 years. The program began in 1998.

•A part of NASA’s Spaceguard Effort to avoid catastrophic impacts

•Data largely from photographs from wide-field telescopes.

•The NEO Program’s budget is 10.5 million dollars/year

•Overlays of sequential photos allow identification of moving objects.

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Lincoln Near-Earth Asteroid Research Telescope

http://neo.jpl.nasa.gov/stats/

Estimated size distribution of NEOs

>30 m >50,000,000

>100 m >320,000

>500 m >9,200

>1,000 m >2,100

>2,000 m >400

Size Estimated numberof near-Earth objects

Source: Thomas Grollman; http://www.gcr.com/sharedfile/pdf/Topics11Grollmann-en.pdf

As of October 23, 2008, a total of 5,647 Near Earth Asteroids have been identified. 757 are larger than 1 km in diameter. 991 are considered to be Potentially Hazardous Asteroids.

http://neo.jpl.nasa.gov/orbits/

NASA provides details on PHA orbits at :

Orbits, dates and other data are available for particularly close approaches at:

http://neo.jpl.nasa.gov/neo/close.html

PHA orbit example

Awesome Asteroids: Introduction To Asteroids,Small Bodies In Out Solar System

From the Near Earth Objects Program

What happens when a meteoroid or asteroid reaches the Earth?

Asteroids approach the Earth at speeds of 15 to 25 km/sec (54,000-90,000 km/hr).

Comets can approach the Earth at speeds up to 70 km/sec (252,000 km/hr).

Depending on the mass (volume X density) the atmosphere may slow the object down to about 200 km/hr.

The energy released upon impact is the Kinetic Energy of the object.

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Kinetic Energy = E = ½ mV2

Where m is the mass of the object and V is its velocity.

As the mass (size) of the object increases so does the Kinetic Energy

Double the mass leads to a doubling of the Kinetic Energy

The Kinetic Energy increases with the square of the velocity.

When velocity increases by a factor of two (i.e., it doubles) the Kinetic Energy increases by a factor of 4 (four times the value).

Most of the debris in space is small but it's travelling extremely fast. Below altitudes of 2,000 km, the average relative impact speed is 36,000km/h.

http://www.bbc.co.uk/science/space/solarsystem/earth/spacejunk.shtml

A 1mm metal chip could do as much damage as a .22-caliber long rifle bullet.Bits this size don't generally pose a large threat to spacecraft, but can erode more sensitive surfaces and disrupt missions.

•The current estimate is that there are over a million bits of debris orbiting the Earth. About 70,000 objects about the size of a postage stamp have been detected between 850 - 1,000 km above the Earth. They are probably frozen bits of nuclear reactor coolant that are leaking from old satellites

A metal sphere the size of a tennis ball is as lethal as 25 sticks of dynamite.This debris will penetrate and seriously damage a spacecraft.

Kinetic Energy = E = ½ mV2

A pea-sized ball moving this fast is as dangerous as a 400-lb safe travelling at 100 km/h. Debris this large may penetrate a spacecraft; this could be fatal.

Heat wave: travels kms per second; due to the release of energy from the asteroid as it explodes in the air or impacts on the Earth’s surface.

Incineration of the area close to the event; start fires on the ground around the site.

Specific effects at impact can include:

The available Kinetic Energy determines the effect of the impact because that Energy is released upon impact of meteorites, asteroids and comets.

Pressure wave: shock wave in the air followed by winds >200km/hr; results from the compression of the air due to an explosion or impact.

Shock wave knocks down buildings/trees; winds cause hurricane-like devastation; winds may blow out fires.

The pressure wave of the exploding Tunguska object knocked down over 60,000 trees.

Wolf Creek Australia.The crater is 875 m across and the rim rises ~25 meters above the surrounding plains and the crater floor is ~50 meters below the rim. 300,000 yrs old.

Impact crater formation: impact displaces crustal material, ejecting it into the atmosphere leaving a large crater on the surface (1 km diameter asteroid produces a 20 to 30 km diameter crater).

Total devastation at the crater site.

Earthquake: much of the energy released as shock waves through the Earth; magnitude 12 earthquakes are possible.

Surface shock waves can devastate the landscape (including buildings) hundreds of killometres from the impact site.

Rain of small rocks and dust: material ejected from a crater (both asteroid and Earth material) or produced as an object explodes in the air can travel for thousands of kilometres. Large debris falls relatively close to the impact whereas dust is carried in the atmosphere for years.Secondary damage to anything remaining in the region around the impact or explosion; global cooling due to the reduction in sunlight caused by the atmospheric dust.

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Tsunamis: when an asteroid impacts on a large water body (e.g., the ocean) a wave is generated that travels very quickly over the water surface, steepening and flowing onshore along coasts. Wave speeds have been recorded at almost 800 kilometres per hour (generated by earthquakes, not asteroids).

At the shoreline waves can reach over 100 metres in height and wash out buildings for kilometres from the shore.

Grollman described the types of damages as evaluated by the insurance industry:

Type I Asteroid: ranging from 0-30 m in diameter; 10,000 – 50,000/year.

Type II Asteroid: 50 m diameter; every 250 yrs.

Type III Asteroid. 1 km diameter; every 100,000 yrs.

Type IV Asteroid. 10 km diameter; every 50 million yrs.

Type I: <30 metre diameter:

•Normally explodes before impact into dust and small fragments.

•On March 27, 2003, such an explosion took place and the fragments (the size of tennis balls) crashed into several houses.

•Fragments cause damage but no risk of heat, shock, earthquakes, etc.

Type II: 50 metre diameter:

•Explodes in the air.

•Over land the heat wave starts fires within several kilometres below the explosion.•Heat and pressure wave causes extensive damage within 25 or 30 kilometres of explosion.

•Diminishing damage from pressure wave and winds to almost 100 kilometres.

•Damage can exceed that of a major Earthquake.

•10-15 metre tsunamis can cause extensive damage to large coastal cities (e.g., Vancouver, San Francisco, Tokyo if the Pacific receives the impact).

Type III: 1 km diameter:

•Objects of this size impact the surface; a 1 km object would create a 20 to 30 km diameter crater.•Very heavy damage for 500 km around the impact site due to heat and pressure wave.

•Forest fires rage across the entire continent due to extensive heat wave and falling hot debris.

•Major earthquake would add to extensive damage.

•Local climatic change would have an effect on fauna and flora for decades to come.

•An impact at sea would send masses of water upwards to 10 km. Tsunamis would make landfall as waves hundreds of metres high. Los Angeles, Tokyo, Hong Kong, Miama…..destroyed except for concrete-reinforced ruins.

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Type IV: 10 km diameter (K/T impact):

•Impact crater: 300 km in diameter.

•Entire continent destroyed.

•Falling masses of molten rock would start forest fires world-wide.•Magnitude 12 earthquake would just add to the devastation.

•Global climate change due to dust in the atmosphere.

•Auxiliary damage as nuclear power plants are destroyed.

•Global food supply jeopardized.

How do we assign a level of “risk” to space objects?

Level of risk depends on the frequency of the event causing risk and its scale (extent of damage and # people affected).

Car accidents: high frequency, very small scale (affects a few people per accident): High frequency results in fairly high risk.

Airplane crashes: low frequency, moderate scale (may affect hundreds): Low risk due to the low frequency.

Asteroid impacts: very low frequency, potentially very large scale (may affect billions): Low risk due to the low frequency.

The risk of being killed by an 1.5 km diameter asteroid impact has been determined to be approximately equal to the risk of being killed in an airplane crash or by an electric shock!

Torino Scale: a measure of the Risk posed by a given asteroid or comet.

Based on the probability of collision (closeness of passing by Earth) and the Kinetic Energy upon impact (size and speed).

http://neo.jpl.nasa.gov/risk/

The following link shows the estimated risk posed over the next 100 years by a large number of asteroids:

Asteroid 1950 DA

> 1 km diameter with a 1 in 300 chance of collision in March, 2880.

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“With so many of even the larger NEOs remaining undiscovered, themost likely warning today would be zero -- the first indication of a collision would be the flash of light and the shaking of the ground as it hit.

How much warning will we have?

Here’s the answer from David Morrison of NASA:

In contrast, if the current surveys actually discover a NEO on acollision course, we would expect many decades of warning. Any NEO that is going to hit the Earth will swing near our planet many times before it hits, and it should be discovered by comprehensive sky searches like Spaceguard. In almost all cases, we will either have a long lead time or none at all.”

Impact craters on Earth

Crater anatomy.

How they form.

Major craters on Earthand elsewhere.

A crater is generally 20 to 30 times the diameter of the object that creates it.

The formation of impact craters

Three stages to crater formation:

1. Contact/compression Stage.

2. Excavation Stage.

3. Modification Stage.

1. Contact/compression Stage.

•A very brief stage (fraction of a second) when pressure and temperature due to the impact are intense.

•Rock in immediate contact is vaporized, surrounding rock melts due to the high temperatures.

•Rock adjacent to the impact is displaced upwards and other material is ejected.

•Spalled material is derived from the impacting object.

2. Excavation Stage

•This is the stage when material is ejected upwards, away from the impact site.

•Rock beneath the impact is compressed into a short-lived “transient” crater.

•The Chixulub crater would have taken less than 2 minutes to complete this stage.

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3. Modification Stage.

•The crater walls slump into the crater.

•For craters >4km diameter a peak rises up in the centre as rock that was compressed and pushed downwards lifts upward.

•Central up lift reaches 10% of the crater diameter.

•The uplift event takes a few minutes.

Anatomy of a crater

Here’s an animation of crater formation from

http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Animation.gif

Earth’s moon: craters in craters. A crater chain on the moon.

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A crater chain on Jupiter’s moon Ganymede.Martian complex crater

Impact Crater Images

http://www.unb.ca/passc/ImpactDatabase/index.html

The Geological Survey of Canada (GSC) maintains a list of all major impact sites world-wide at:

Haviland crater, Kansas

< 1000 years old

15 metres diameter

Macha Crater, Russia, 300 m, 7000 years old. Meteor Crater Arizona

Rim diameter: 1.2 km diameter Age:49,000 years

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Rim diameter: 3.4 km Age: 1.4 ± 0.1 million years

Impact crater in Namibia. The rim of the crater rises 160 metres above the surrounding country-side.

New Quebec Crater

Rim diameter: 3.4km Age: 1.4 million years

Brent Ontario

Rim diameter: 3.8 km Age: 400 million years

Sudbury Impact Structure

Rim diameter: 250 km diameterAge: 1900 million years

Holleford, Ontario

Rim diameter: 2.35 km Age: 550million years

Is the Hudson Bay “bight” an impact crater?

The GSC says no for now but one geologist is gathering evidence for a 2 billion year old event on a scale that is almost unimaginable.

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Erosion and plate tectonics have reduced the number of preserved craters on Earth

Wednesday, September 29, 200409:35:28 h EDT

The 4.8 km long Asteroid 4179 Toutatis was within 1.55 million km of Earth

Toutatis has not approached as close to Earth since the 12th Century AD.

It will not come as close again for another 500 years.

What space object has posed the greatest risk?

2002 NT7?A 2 km diameter asteroid with an impact velocity of 28 km/s

Initially thought to be incoming January 19, 2019

http://neo.jpl.nasa.gov/cgi-bin/db_shm?sstr=2002+nt7&group=all&search=Search

2002 NT7 was the first space object to be assigned a high risk of impact when it was first discovered.

With further observations it was removed from the list of threatening objects.

June 14, 2002Asteroid 2002 MN passed within the moon’s orbit

of the Earth (within 120,000 km of Earth).About 1/3 the distance from the Earth to the moon.

The size of a football field (50 – 120 m in diameter)‏traveling 37,000 km/hr

Point: close approaches have always happened but we have just begun to be able to see them coming.

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Which Potentially Hazardous Asteroid will come closest?

Apophis

Orbital information

Approximately 0.5 km in diameter.

Closest approach 0.0002534 AU

9.7% of the distance from the Earth to the Moon!

April 13, 2029

Asteroid and Comet Defense?

Identify all Near Earth Objects and determine the probability of a collisions with Earth

Two approaches to dealing with high probability collisions with sufficient lead time:

1. Land astronauts on the object, drill into it and plant nuclear bombs.

The explosions should break the object up into smaller, harmless pieces.

2. Detonate nuclear weapons at selected locations in nearby space.

The blasts will “nudge” the object in the opposite direction, sending it off course for collision with Earth.