Death From the Skies

Death From the Skies

Learning Objectives! Use the Titius-Bode Rule to list the planet s distances. What connects the Titius-Bode Rule to the asteroids?! How big is Ceres? How big are typical asteroids? What are asteroids made of? How many asteroids are there?! What and where is the Asteroid Belt? How might the Belt have formed? How far apart are asteroids in the Belt? Are the Trojans and the Apollos in the Asteroid Belt?! What are meteors, meteoroids and meteorites? Why is dating meteorites useful?! Why does the Earth have few craters? Is the Earth not impacted by meteoroids? What is the Iridium Layer?! Will large asteroids hit the Earth in the future?

Titius-Bode Rule! Bizarre relation popularized in the 1760s! Set distance from Sun to Mercury to be a Merc = 4 units : Then:! a Venus is 4 + (3 x 2 0 ) = 7 such units! a Earth is 4 + (3 x 2 1 ) = 10 such units (i.e. the mysterious unit is actually a tenth of an AU)! a Mars is 4 + (3 x 2 2 ) = 16 such units!???? is 4 + (3 x 2 3 ) = 28 such units! a Jupiter is 4 + (3 x 2 4 ) = 52 such units! a Saturn is 4 + (3 x 2 5 ) = 100 such units

Titius-Bode Rule! It s actually even more bizarre than this.! a Venus is 4 + (3 x 2 0 ) = 7 such units! a Earth is 4 + (3 x 2 1 ) = 10 such units! a Mars is 4 + (3 x 2 2 ) = 16 such units!???? is 4 + (3 x 2 3 ) = 28 such units! a Jupiter is 4 + (3 x 2 4 ) = 52 such units! a Saturn is 4 + (3 x 2 5 ) = 100 such units! a Uranus is 4 + (3 x 2 6 ) = 196 such units! Uranus, discovered in 1781, fit the rule too!! The rule works so well that the search was on to find the planet (????) in the gap

Titius-Bode Rule! Set a Merc = 4 units : Then:! a Venus is 4 + (3 x 2 0 ) = 7 such units! a Earth is 4 + (3 x 2 1 ) = 10 such units! a Mars is 4 + (3 x 2 2 ) = 16 such units! a Ceres is 4 + (3 x 2 3 ) = 28 such units!!!! a Jupiter is 4 + (3 x 2 4 ) = 52 such units! a Saturn is 4 + (3 x 2 5 ) = 100 such units! a Uranus is 4 + (3 x 2 6 ) = 196 such units! Ceres seemed to fill the gap quite nicely! Ceres was considered a planet for over fifty years, largely because it fit the Titius-Bode Rule

Titius-Bode Rule Accuracy Planet T-B Rule (AU) Distance (AU) Mercury 0.4 0.39 Venus 0.7 0.72 Earth 1.0 1.00 Mars 1.6 1.52 Ceres 2.8 2.77 Jupiter 5.2 5.20 Saturn 10.0 9.54 Uranus 19.6 19.2 Neptune 38.8 30.06

Asteroids! Small sizes! Largest Ceres: 940 km across! Only 3 more than 300 km! About 240 bigger than 100 km! Millions under 1 km! Composition! Rocks (silicates) and iron/nickel 55 km Ida and Dactyl from Galileo

The Asteroid Belt! Most asteroids are found between 2 and 3.5 AU! Between Mars & Jupiter! Region is called the Asteroid Belt

The possibility of successfully navigating an asteroid field! NASA has sent many probes into the Asteroid Belt! Unlike its depiction in science fiction, the Asteroid Belt is not particularly crowded! Average separation between asteroids is 10 million km (a ship would have to be about 100,000x the size of the Denver metropolitan area before it had any navigation issues)

Apollos and Trojans! Apollo asteroids are those that cross the Earth s orbit! About 8200 are known! In 1972, a ~10m asteroid skipped off the Earth s atmosphere (~35 miles from the surface)! The largest known Apollo asteroid is 8500m in size! Other asteroids share Jupiter s orbit! These are called Trojan asteroids! Lead and trail Jupiter around the Sun

1I/2017 U1 Oumuamua! In late 2017 a 230 x 35 meter asteroid on a hyperbolic orbit crossed the inner Solar System! The object was moving at nearly 60,000 mph! So fast that the object must have originated outside of our Solar System Robert Weryk/Pan-STARRS/nagualdesign/Tomruen! Oumuamua is the first rock to ever be discovered from interstellar space

Meteor Jargon! When you see a shooting star, that is a meteor! A space rock (meteoroid) entering our atmosphere! A meteoroid is about 1 m or less in size (an asteroid is bigger than about 1 m)! Most burn up or break apart in our atmosphere, but some do strike the Earth! These are meteorites! Composition: rock, some metals

Meteorites and the Earth! Many bodies in the Solar System show massive amounts of cratering! Earth is relatively crater free! But we do know of many impact sites (~190, in total)

Earth s Craters! Near Winslow, Arizona! Occurred 50,000 years ago 200 m deep! http://antwrp.gsfc.nasa.gov/apod/ap971117.html A 50 meter meteoroid struck the ground at 40,000 km/hr 1.2 km across

Earth s Craters Clearwater Lakes in Quebec, Canada 26 km wide (290 million years old) http://www.unb.ca/fredericton/science/research/passc/

Earth s Craters Manicouagan Crater, also in Quebec, Canada 100 km wide http://www.unb.ca/fredericton/science/research/passc/

Extinctions! Paleontologists have identified 5-6 mass extinctions in Earth s history. The two largest possibly coincide with major meteoroid (i.e. asteroid) impacts % of marine genera gone extinct? Millions of years ago

What Killed the Dinosaurs?! 65 million years ago, 75% or more of all the species on the Earth disappeared! 2nd largest known mass extinction in geological history! Was an asteroid impact to blame?

! In 1979 a layer of Iridium-rich clay was found in numerous places around the world! Deposited about 65 million years ago The Iridium Layer! Iridium is an element that is much more common in asteroids or comets than in rocks that are near the Earth's surface

The Chicxulub Crater! A nearly 200 km diameter crater under the northwest corner of the Yucatan peninsula! It is estimated to be about 66 million years old http://antwrp.gsfc.nasa.gov/apod/ap000226.html

Massive Impacts = Extinctions?! Scientists have found evidence possibly linking one other extinction event (~ 250 million years ago) to an impact! Will it happen again?!yes. There are many asteroids with Earth- crossing orbits!but the chance of being hit by a large asteroid in the next few thousand years is probably small

Next Time Making a Solar System