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Announcements

!  Tonight’s observing session is cancelled!  we will try again next week

!  The 9th LearningCurve activity was due earlier today!  We will cover Chapter 9 today!  Assignment 9 and Quiz 9 will be due on Tue. Nov. 29!  Next week’s lecture will consist of:

!  a review for the exam (during the first half of the lecture)

!  a movie (during the second half)

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LearningSystem Course Evaluation

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!  As with other courses at Trent, you are asked to complete an evaluation of the course and instructor

!  The course evaluation will be available online (using LearningSystem, not LaunchPad)!  Starting date: Wed. Nov. 23!  Ending date: Wed. Dec. 7

!  Completely anonymous!  Please take the time to complete the evaluation

!  your feedback is very much appreciated!

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PHYS 1510H Final Exam

!  Tue. Dec. 20 from 7-9 p.m. in the Gym!  100 multiple choice questions!  Covers to the end of Chapter 9!  No aids allowed!  Bring your student card and an HB pencil!  The final lecture will include a review for the exam

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VAGABONDS OF THE SOLAR SYSTEM

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Topics We Will Cover Today

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!  Dwarf planets!  Asteroids!  Comets!  Meteoroids, meteors and meteorites

Introduction

!  In addition to the planets and their moons, many other objects orbit around the Sun

!  Most of these objects are very small, though some are large enough to be spherical in shape

!  These objects are generally classified as dwarf planets, asteroids, comets, or meteoroids

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The Discovery of Ceres

!  On January 1, 1801, a Sicilian monk named Giuseppe Piazzi discovered a faint object that moved with respect to the background stars

!  Further observations showed that it orbits the Sun, just like a planet!  initially, it was classified as a planet

!  However, it was found to be much smaller than any of the planets that were known at that time!  it is spherical, with a diameter of about 950 km!  this is about � the diameter of the Moon

!  This object was later named Ceres

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Sizes of the Earth, Moon, & Ceres

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The Discovery of Pluto

!  Pluto was discovered by Clyde Tombaugh in 1930, and was initially classified as a planet

!  Pluto is much fainter than the 8 modern-day planets!  at least a medium-sized

telescope is needed to spot it

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The Discovery of Eris

!  In 2005, astronomers announced the discovery of an object which is more massive than Pluto (though slightly smaller)

!  Named Eris, this object is currently nearly 100 AU from the Sun

!  It is orbited by a small moon named Dysnomia

!  This discovery led to a debate!  is Eris a planet?!  if not, is Pluto a planet?

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A New Definition of Planet

1)  In orbit around the Sun2)  Massive enough to be spherical in shape3)  Has cleared its orbital neighbourhood

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Objects which satisfy only the first two criteria are now called Dwarf Planets.

Planets and Dwarf Planets!  Eight solar system objects are now classified as planets

!  Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

!  Five solar system objects are now classified as dwarf planets!  Eris, Pluto, Ceres, Haumea, and Makemake

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The Study of Dwarf Planets

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!  Three dwarf planets – Eris, Makemake and Haumea – have never been visited by spacecraft

!  Two dwarf planets – Pluto and Ceres – have been visited by spacecraft recently!  the New Horizons spacecraft flew by Pluto in July 2015!  the DAWN spacecraft is currently in orbit around Ceres!

Pluto

!  Pluto is smaller than the 8 planets in our solar system!  it is also smaller than 7 solar system moons

!  Pluto is (usually) further from the Sun than the 8 planets, at an average distance of 40 AU (6 billion km)!  its elliptical orbit occasionally brings it closer to the Sun

than Neptune (most recently, from 1979-1999)!  it takes about 250 Earth years to orbit the Sun

!  It is very difficult to resolve detail on Pluto from Earth!  Pluto is 2/3 the size of our Moon but 1,200 times farther

away!  As a result, much of what we know about Pluto comes

from the New Horizons spacecraft

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New Horizons Imaging of Pluto

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Sputnik Planum

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The Edge of Sputnik Planum

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The Surface of Pluto

!  Pluto is probably made of roughly equal amounts of rock and ice

!  Most of Pluto’s surface is covered in nitrogen ice

!  There is tentative evidence for ice volcanoes on the surface of Pluto

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Pluto’s Atmosphere

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The Atmosphere of Pluto

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Sputnik Planum

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A recent simulation suggests that the Sputnik Planum heart-shaped region on Pluto may have been formed by a large impact from space.

Does Pluto Have a Subsurface Ocean?

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!  The structure and composition of Sputnik Planum suggests that an impact may have caused the upwelling of liquid water from an ocean on Pluto

!  This ocean could be at least 100 km deep!  The ocean would be warmed by Pluto’s interior

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Pluto’s Moons!  Pluto has one relatively large moon, named Charon

!  it wasn’t discovered until 1978!  Four additional small moons have been discovered

since 2005, using the Hubble Space Telescope!  their names are Nix, Hydra, Kerberos and Styx

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Charon (from New Horizons)

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Pluto’s Smaller Moons �(from New Horizons)

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Pluto’s Rotation

!  Pluto completes one rotation on its axis every 6.4 days!  This is equal to the length of time it takes for Charon

and Pluto to orbit one another!  Pluto and Charon are so close together that they both

have synchronous rotation!  if you were on Pluto, Charon would always be in the same

place in your sky (and vice versa)

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Asteroids!  Ceres is the largest of a class of rocky objects now

known as asteroids!  more than 600,000 asteroids have been detected so far!  there are likely millions of asteroids larger than 1 km

!  Most asteroids have irregular shapes

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Estimating Asteroid Sizes

!  In most cases, it is not possible to directly measure the size of an asteroid!  their apparent sizes are so small that most cannot be

resolved at all, even with large modern-day telescopes!  Instead, their sizes are usually estimated by measuring

the amount of light reflected!  this approach has some inherent uncertainty, since

asteroids vary somewhat in reflectivity!  The known asteroids vary in size from about 1000 km

diameter (Ceres) down to about 10 m

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The Dawn Mission to Ceres and Vesta!  NASA’s Dawn spacecraft

visited Vesta in 2011 and 2012!  it orbited Vesta for one year,

acquiring images and other data

!  It is now in orbit around Ceres

Asteroid masses

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Dwarf Planet Ceres: The Largest Asteroid

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!  Ceres orbits the Sun once every 4.6 years, at a distance of about 2.8 AU!  between Mars and Jupiter

!  Ceres contains about 30% of the mass of all the asteroids combined

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DAWN Image of Ceres

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The Topography of Ceres

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Occator Crater on Ceres

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Ahuna Mons

34 Ahuna Mons is a 4-km high cryovolcano on Ceres. This volcano has been active within the past 200 Myr.

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The Structure and Composition of Ceres

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Density measurements indicate that Ceres is 1/3 water-ice.

A Model for the Interior of Ceres

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A recent study found that pockets of briny liquid water likely exist below the surface of Ceres and occasionally escape to the surface.

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Dawn Image of Vesta

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Other Asteroids Visited by Spacecraft

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NEAR-Shoemaker visits Asteroid Eros

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Descent to Eros

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NEAR-Shoemaker Lands on Eros

!  NEAR-Shoemaker crash-landed on Eros in Feb. 2000!  this is the only time a

spacecraft has ever landed on an asteroid

!  It survived the landing and continued to send data back to the Earth

Final Image Before Landing.Taken From a height of 130 m.Resolution: about 10 cm.

6 metres!

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Ida & Dactyl: Asteroid & Moon

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Asteroid Itokawa

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The Asteroid Belt!  Most asteroids are found between Mars and Jupiter!  This region is called the Asteroid Belt!  Typical distances from the Sun are 2-4 AU

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The Origin of the Asteroids

!  Asteroids are made up mostly of rock and metal!  This material was left over from the early days of the

solar system, when the planets formed!  It would not have been possible for a planet to form in

the asteroid belt region, due to the disruptive gravitational influence of Jupiter

!  The combined mass of all the asteroids is likely less than 1/1000 of the mass of the Earth!  this is comparable to Pluto’s mass

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Comets

!  For centuries, people have occasionally seen fuzzy objects with tails in the night sky

!  These objects, called comets, were once thought to be bad omens

!  Scientific studies found that comets are icy objects traveling through the inner solar system

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Halley’s Comet

!  In the 1690s, Edmund Halley noticed that the orbits of several famous comets were very similar!  these comets were seen in the

years 1456, 1531, 1607, and 1682!  He deduced that they were

reappearances of the same comet!  orbital period of 75-76 years

!  He correctly predicted its return in 1758

!  Halley’s Comet last visited in 1986!  its next visit will be in 2061

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Short and Long Period Comets

!  Following Halley’s work, many comets were found to re-appear periodically

!  This is because they are in orbit around the Sun

!  Short-period comets typically return in less than 100 years

!  Long-period comets may take millions of years to return

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The Kuiper Belt!  The Kuiper Belt is a disk-shaped region lying beyond the

orbit of Neptune!  it is thought to contain at least 1015 small icy bodies!  most Kuiper Belt objects lie 30 to 200 AU from the Sun

!  Gravitational interaction with the outer planets can send these objects inward (short-period comets) or outward

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Detecting Kuiper Belt Objects!  Kuiper Belt Objects (KBOs) are extremely faint!

!  this is because they are far away, and also because there is very little sunlight for them to reflect

!  The “first” KBO was detected in 1992!  in hindsight, however, Pluto was in fact the first KBO

!  More than 1000 KBOs have been discovered since then

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Kuiper Belt Objects

!  Observations of Kuiper Belt Objects show that they are similar (in size and makeup) to comets

!  All but one of the known dwarf planets are KBOs!  Ceres is the only exception

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The Oort Cloud

!  Studies of long-period comets by Jan Oort lead him to conclude that these objects must have originated far beyond the Kuiper Belt

!  He proposed the existence of an immense cloud of comets surrounding the Sun and planets!  this is now known as the Oort cloud

!  It is estimated to extend at least 50,000 AU from the Sun, and is predicted to contain about 400 billion comets!!  even so, these comets would be millions of km apart

!  The total mass of comets in the Oort cloud is thought to be roughly 40 times that of the Earth

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Artist’s Depiction of the Oort Cloud

Radius: at least 50,000 AU 53

Artist’s Illustration of Sedna: The First Confirmed Member of the Oort Cloud

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Sedna

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!  Sedna is currently 90 AU from the Sun!  this is beyond the Kuiper belt

!  It takes 10,500 years to orbit the sun!  The orbit of Sedna is extremely elliptical

!  it will reach perihelion (76 AU) in 2075!  its aphelion distance is about 900 AU!

!  Sedna is about 1000 km in diameter

Other Members of the Oort Cloud!  The second confirmed Oort cloud member, called 2012

VP113, is about 400 km in diameter!  It is estimated that there may be about 1000 Sedna-

sized objects in the Oort cloud

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Planet 9?

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Planet Nine?!  The hypothesized Planet Nine is predicted to be larger

than Earth, but smaller than Uranus and Neptune!  Astronomers are working hard to see if Planet Nine

actually exists

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The Structure of a Comet

!  Comets in the outer solar system (Kuiper belt or Oort cloud) are very cold, solid icy objects

!  When a comet ventures near the Sun, its appearance can change dramatically

!  Radiation from the Sun vapourizes ice on its surface, forming an atmosphere!  this is called a comet’s coma!  the coma is much larger and brighter than the original

frozen body, which is called the nucleus

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The Structure of a Comet

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The Tails of a Comet

!  Solar radiation leaves a tail of dust behind the comet!  this tail curves away from

the direction opposite to the Sun

!  Solar wind produces a glowing tail of gas!  this tail points directly away

from the Sun

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Comet West in 1975

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Comet Hale-Bopp in 1997

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The Nucleus of Halley’s Comet

16 km

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Comet Wild 2

!  NASA’s Stardust spacecraft travelled through the coma of Comet Wild 2 in 2004

!  It took this image of the nucleus from a distance of 500 km

!  Stardust collected dust from this comet and returned it to Earth in 2006

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Impact on Tempel 1

!  The Deep Impact spacecraft collided with Comet Tempel 1 in July 2005

!  By studying the ejected material, scientists have learned that this comet nucleus is “porous and fluffy”

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Comet 103P/Hartley 2

!  The EPOXI/Deep Impact spacecraft passed within 700 km of the nucleus of this comet in Nov. 2010

!  This was the smallest comet nucleus seen up close (it is only 2 km long)

!  Numerous jets were detected, along with an ongoing snowstorm!

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Comet 67P/Churyumov-Gerasimenko

The Rosetta mission is the first to orbit a comet, and the first to land a probe on the surface of a comet.

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High Resolution Imaging of Comet 67P

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Jets on Comet 67P

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Sungrazing Comets

!  Some comets pass very close to the Sun!  these comets are called sungrazers!  they typically pass within a few hundred thousand km of

the Sun’s surface!  The first sungrazers were identified in the 1800’s

!  most have very similar orbits!  most are thought to be fragments of a single large comet

that broke up when passing close to the Sun!  Sun-monitoring telescopes discover lots of sungrazers

!  the SOHO telescope has found more than 2500 so far!  Many sungrazers do not survive their encounter with

the Sun

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A Sungrazing Comet

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Comet ISON

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!  In 2013, an Oort cloud comet called ISON had a very close encounter with the Sun!  it was torn apart and did not survive the encounter

!  ISON was the first know sungrazing Oort cloud comet

Meteoroids and Meteors

!  Solid objects that are smaller than comets or asteroids are referred to as meteoroids!  solid debris which is even smaller is called dust!  the vast majority of meteoroids are cometary in nature

but some have asteroidal origin as well!  When a meteoroid strikes our atmosphere at high

speed, friction causes it to burn up in a streak of light known as a meteor!  meteors are sometimes referred to as shooting stars

!  Occasionally, the Earth passes through a cloud of meteoroids and dust, causing a meteor shower or (more rarely) a meteor storm

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The Perseid Meteor Shower

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Looking Down at a Perseid Meteor

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Distribution of Meteors on the Sky

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Annual Meteor Showers

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The Leonid Meteor Storm of 2001

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Meteorites

!  Some meteoroids are large enough that they can survive the trip through Earth’s atmosphere

!  The part that is left after traveling through the air hits the Earth's surface and is called a meteorite

!  There are 3 main types of meteorites:!  95% are stony meteorites

!  this includes the carbonaceous chondrites, which are rich in carbon compounds and water

!  4% are iron meteorites!  1% are stony-iron meteorites

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Different Types of Meteorites

Stony

Carbonaceous chondriteIron

Stony-iron

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The Origin of Different Meteorite Types!  Differentiated asteroids can produce three types of meteorites

!  Iron meteorites from the core!  Stony-iron meteorites from the mantle!  Stony meteorites from outside the mantle

!  Undifferentiated asteroids produce chondrites!  these meteorites do not appear to have melted in the past

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Asteroids in the Inner Solar System

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Impact Craters on the Earth

!  Large meteorites can create large impact craters on the surface of the Earth

!  Barringer Meteor Crater, in Arizona, was the first feature on the Earth to be clearly identified as an impact crater!  this crater is 1.2 km in diameter !  it was formed about 49,000 years ago by the impact of a

50 m diameter meteoroid!  To date, nearly 200 impact craters have been identified

on the Earth’s surface!  some are on the ocean floor, or partially obscured by

vegetation, soil, sand, etc.

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Barringer Meteor Crater, Arizona

Diameter: 1.2 kmAge: about 49,000 years 85

Manicouagan Crater, Quebec

Diameter: 70 kmAge: 200 million years 86

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The Kamil Crater!  The Kamil crater was discovered in 2008 using Google Earth

!  it is located in a remote part of the Sahara desert!  The crater is 45 metres wide, and less than 5000 years old!  The original meteor is estimated to have been 1.3 metres wide!  5000 pieces of iron meteorite have been recovered from its

vicinity

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The Effects of Major Impacts

!  The vast majority of impactors are small (less than 50 m) and cause little or no damage

!  Larger asteroids or comets that are up to 1 km in diameter can cause serious localized damage

!  Those with diameters of roughly 1-10 km can have effects on a global scale!  those striking the oceans can cause huge tidal waves!  those striking land can trigger widespread forest fires

!  Those larger than about 10 km diameter have the potential to cause mass extinctions

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The Chelyabinsk Impact of 2013

!  This impact occurred over Russia on Feb. 15, 2013!  a fireball first became visible 92 km above the ground!  the meteor exploded 11 seconds later!  the resulting shockwave damaged thousands of homes

and injured more than 1000 people89

The Chelyabinsk Impact of 2013

!  A number of meteorites reached the ground!  the most massive was about 650 kg!  this fragment struck frozen Lake Chebarkul

!  The original asteroid is estimated to have been about 20 metres in diameter

!  This asteroid was previously unknown90

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The K-T Impact

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!  Roughly 66 million years ago, about 75% of the life forms on Earth became extinct within a short period of time!  this includes most of the

dinosaurs (birds evolved from some of the dinosaurs)

!  A 150-km diameter impact crater has been found near Chicxulub, in Mexico!  this crater is around 66 million

years old!  this crater could have been

formed by an asteroid with a diameter of about 10 km

Potentially Hazardous Asteroids (PHAs)

!  There are plenty of objects remaining in the solar system which have the potential to strike the Earth at some time in the future

!  Astronomers are attempting to find all objects which pose a serious threat to life

!  All asteroids larger than about 100 m which pass within 0.05 AU of the Earth are called Potentially Hazardous Asteroids (PHAs)

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PHA Orbits

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How Many PHAs Are There?

!  1738 PHAs have been detected as of Nov. 2016!  None of the known PHAs are predicted to strike the

Earth in the near future!  Roughly 20,000 PHAs are thought to exist, but most

have not yet been detected

From spaceweather.com

Name: Asteroid 2015 TB145Flyby: 1.3 LD on Oct. 31/15Size: 600 metresDiscovery date: Oct. 10/15! 94

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Before Next Class

!  Complete Assignment 9 and Quiz 9!  due on Tue. Nov. 29 at 2 p.m.

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