Asteroids, Comets & Dwarf Planets

Home , 15 Eunomia, 2 Pallas, 4 Vesta, 511 Davida, 52 Europa, 65 Cybele

Northeastern Illinois University

Greg Anderson Department of Physics & Astronomy Northeastern Illinois University

Fall 2019

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 1 / 104 Northeastern Illinois Overview University

Asteroids Meteors & Meteorites Comets TNOs Impacts Review

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 2 / 104 Asteroids & Comets

b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Kuiperb Belt b b b b b b Asteroidb b Belt b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Oort Cloudb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Northeastern Illinois Zodiacal Light University Zodiacal light: faint glow near the ecliptic from sunlight scattered oﬀ the zodiacal cloud, a pancake shaped cloud of interplanetary dust.

Origin: Continually replenished by comet disintegration & asteroid collisions. Recent estimates: 85% from Jupiter family comets. Size 10 − 300 µm c 2012-2019G. Anderson Universe: Past, Present & Future – slide 4 / 104 Zodiacal light scattered from the Zodiacal Cloud

c G.Anderson LowerCanyonsoftheRioGrande Zodiacal light scattered from the Zodiacal Cloud

c G.Anderson LowerCanyonsoftheRioGrande Northeastern Illinois University

Asteroids & Comets Zodiacal Light Zodiacal Light

Asteroids Asteroid Facts Discovering Missions Largest Ceres & Vesta Q: Ceres? Asteroids Asteroids Main Belt Main Belt Eros from NEAR Q: Shape Albedo Spectral Types asteroid orbits Histogram vs a Scatter i vs a Asteroid Families asteroid orbits Trojans Q: Trojans Origin Theories Kirkwood Gaps Migrations c 2012-2019G. Anderson Universe: Past, Present & Future – slide 6 / 104 Q: Gaps Northeastern Illinois Asteroid Facts University

Relatively small, rocky objects orbiting the Sun. • Leftover rocky planetesimals • Majority between Mars and Jupiter

• Total mass ≪ MMoon • Largest Ceres, d ≈ 950 km • 1.1 − 1.9 million with d> 1 km. • > 400, 000 cataloged

Vesta

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 7 / 104 Northeastern Illinois Discovering Asteroids University

Time exposures with false color paral- lax: from Paranal and from La Silla.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 8 / 104 Northeastern Illinois Asteroid Missions to Asteroids University

• DAWN (NASA) 2007–, Ceres (2015), Vesta (2011) • Rosetta (ESA) 2004–, Comet Churyumov-Gerasimenko, Asteroids 21 & 2867 • Hayabusa (JAXA) 2003-2010, sampled asteroid Itokawa and returned samples to earth • Genesis (NASA) 2001– • Stardust - NASA • Deep Space 1 - NASA • Cassini - NASA/ESA • NASA Near Earth Asteroid Rendezvous (NEAR-Shoemaker) • Galileo - NASA

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 9 / 104 Northeastern Illinois Largest Asteroids (by Diameter) University Name Discovered a (AU) d (km) Class 1 Ceres 1801 2.77 975 C 4 Vesta 1807 2.36 525 V 2 Pallas 1802 2.77 512 B 10 Hygeia 1849 3.14 431 C 704 Interamnia 1910 3.06 326 C 52 Europa 1858 3.10 315 C 511 Davida 1903 3.18 289 C 87 Sylvia 1866 3.49 286 X 65 Cybele 1861 3.44 273 C 15 Eunomia 1851 2.64 268 S

1 The 4 largest asteroids contain over 2 the mass of the asteroid belt.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 10 / 104 Northeastern Illinois Asteroids Ceres & Vesta University

Ceres, The Moon, & Earth Vesta, Ceres & The Moon

• Ceres is large enough to be classiﬁed as a dwarf planet. • Ceres and Vesta were large enough to undergo diﬀerentiation.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 11 / 104 Northeastern Illinois How big is Ceres? University

The largest asteroid, Ceres, was also the ﬁrst asteroid to be discovered (1801). What is the approximate diameter of Ceres?

A) 1 km

B) 10 km

C) 100 km

D) 1,000 km

E) 10,000 km

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 12 / 104 Northeastern Illinois How big is Ceres? University

The largest asteroid, Ceres, was also the ﬁrst asteroid to be discovered (1801). What is the approximate diameter of Ceres?

A) 1 km

B) 10 km

C) 100 km

D) 1,000 km

E) 10,000 km

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 12 / 104

Apollo Asteroid Itokawa, a 535 × 294 × 209 m rubble pile, ρ =1.9 g/cm3 Asteroid Eros Northeastern Illinois Q: Asteroid Shape University

Why aren’t small asteroids spherical in shape? A) The strength of gravity on small asteroids is less than the strength of the rock. B) Small asteroids have odd shapes because they were all chipped oﬀ larger objects. C) Large asteroids were once molten and therefore became spherical, but small asteroids were never molten. D) Large asteroids became spherical because many small collisions chipped oﬀ pieces until only a sphere was left; this did not occur with small asteroids. c 2012-2019G. Anderson Universe: Past, Present & Future – slide 17 / 104 Northeastern Illinois Q: Asteroid Shape University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 18 / 104 Northeastern Illinois Asteroid Spectral Types University Asteroids can be classified based on spectral type: C-type (Carbon-rich), most undifferentiated? (Ceres?) 75% of known asteroids and even higher % of outer belt. Dark: albedo 0.03 − 0.09. Surface composition similar to carbonaceous chondrite meteorites. S-type (siliceous, stony) 17% of known asteroids. Albedo of 0.10 − 0.22. Composition: iron and magnesium silicates. Dominate inner asteroid belt. M-type (metallic), differentiated. 10% of known asteroids. Metallic fragments of iron-nickle cores. Albedo 0.10 − 0.18. Middle region of main belt. . .

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 19 / 104 Northeastern Illinois Asteroid Orbital Classiﬁcation University

• Asteroid Belt, 75% (2.2 AU 8000 Amor a> 1 AU, 32% Apollo* a> 1AU, 62% Aten* a< 1 AU, 6%

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 20 / 104

Northeastern Illinois Asteroid Orbital Classiﬁcation University

• Asteroid Belt, 75% (2.2 AU 8000 Amor a> 1 AU, 32% Apollo* a> 1AU, 62% Aten* a< 1 AU, 6%

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 24 / 104 Northeastern Illinois Trojans University

Lagrangian points L4: Greeks

60%

L3 L1 L2 60%

L5: Trojans

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 25 / 104 Northeastern Illinois Q: Trojan Asteroids University

Where are the Trojan asteroids located? A) along Jupiter’s orbit, 60◦ ahead of and behind Jupiter

B) in the center of the asteroid belt C) on orbits that cross Earth’s orbit D) on orbits that cross Mars’s orbit

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 26 / 104 Northeastern Illinois Q: Trojan Asteroids University

Where are the Trojan asteroids located? A) along Jupiter’s orbit, 60◦ ahead of and behind Jupiter B) in the center of the asteroid belt C) on orbits that cross Earth’s orbit D) on orbits that cross Mars’s orbit

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 26 / 104 Northeastern Illinois Origin Theories University

Concentration of asteroids between Mars and Jupiter suggested two possible explanations: • Fragments of a much larger planet - Heinrich Olbers Cons: significant chemical differences among asteroids. Not enough mass Mtotal ≈ 0.04MMoon. • Jupiter kept planitesimals from accreting into a planet. – Gravitational effect of Jupiter, through influence of orbital resonances lead to scattering and shattering of planitesimals instead of accretion into a planet. Periodic nudges from Jupiter removed asteroids from resonant orbits. It is estimated that Jupiter has ejected over 90% of the planitesimals originally in the asteroid belt.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 27 / 104 Northeastern Illinois Origin Theories University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 27 / 104

Northeastern Illinois Q: Kirkwood Gaps University

Kirkwood gaps in the asteroid belt occur at distances where

A) the density of asteroids is high enough for a large collision to pulverize a number of asteroids.

B) the period of an orbiting asteroid would be a simple fraction (like 1/3 or 1/4) of Jupiter’s orbital period.

C) the period of an orbiting asteroid would be the same as Jupiter’s orbital period.

D) the period of an orbiting asteroid would be the same as Mars’s orbital period.

E) the orbit would take the asteroid beyond the ”frost line” in the solar system.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 30 / 104 Northeastern Illinois Q: Kirkwood Gaps University

Kirkwood gaps in the asteroid belt occur at distances where

A) the density of asteroids is high enough for a large collision to pulverize a number of asteroids.

B) the period of an orbiting asteroid would be a simple fraction (like 1/3 or 1/4) of Jupiter’s orbital period.

C) the period of an orbiting asteroid would be the same as Jupiter’s orbital period.

D) the period of an orbiting asteroid would be the same as Mars’s orbital period.

E) the orbit would take the asteroid beyond the ”frost line” in the solar system.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 30 / 104 Northeastern Illinois Q: Asteroids beyond Jupiter University

Why are there very few asteroids beyond Jupiter’s orbit? A) There was no rocky material beyond Jupiter’s orbit. B) The heaviest rocks sank toward the center of the solar system. C) Ice could form in the outer solar system. D) A passing star probably stripped away all of those asteroids, even if they were there at one time.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 31 / 104 Northeastern Illinois Q: Asteroids beyond Jupiter University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 31 / 104 Northeastern Illinois University

Asteroids & Comets Zodiacal Light Zodiacal Light

Asteroids Meteors & Meteorites Meteors and Meteorites Willamette Meteorite Primitive vs. Meteors & Meteorites Processed Chondrite Classiﬁcation Meteorites from the Moon and Mars Meteorite Cross-sections Meteoric Iron Meteor Showers Showers Leonid Shower: Ayers Rock Selected Meteor Showers Meteoroid Summary Q: “Shooting Star” Q: c Meteorite2012-2019G. Anderson Universe: Past, Present & Future – slide 32 / 104 Origin Northeastern Illinois Meteors and Meteorites University

Meteoroid: Small rocky debris from asteroid fragments or comet disintegration. Meteor: The ﬂash of light produced when a meteoroid enters Earth’s atmosphere. Meteorites: Meteoroids that survive passage through the Earth’s atmosphere and impact on the ground. Most meteorites from the asteroid belt, some lunar and martian meteorites

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 33 / 104 Northeastern Illinois Willamette Meteorite University

• Largest in North America • 32,000 lbs • 10’ x 6’ • 91% Iron, 8% Nickle

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 34 / 104 Northeastern Illinois Primitive vs. Processed University

Primitive: Remnants of the solar nebula, containing intermixed rock, metal ﬂakes, and sometimes carbon compounds. Age: 4.6 billion years old Processed: Pieces of larger asteroids that underwent volcanism or diﬀerentiation - can be metallic like a planet’s core or rocky like its mantle or crust. Age: A few hundred million years younger than primitive meteorites

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 35 / 104 Thin sections by: O. Richard Norton Northeastern Illinois Classification University Warning: There is not a consensus on meteorite classification Groups based on physical properties: Chondrites Pieces of undifferentiated, unmelted bodies. Made of three components: Calcium-Aluminum rich Inclusions (CAI), the chondrules, and the matrix which holds them together. Most meteorites on Earth. 86% of meteorites. Origin: small to medium sized asteroids. Achondrites A stony meteorite that does not contain chondrules. Originated on a differentiated body. 8% of meteorites. Origin: Moon, Mars, Vesta,... Iron Meteorites Composed of Iron and Nickle. From the metal core of a differentiated body. Stony-Iron Meteorites Differentiated, equal parts iron and silicates

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 37 / 104 Northeastern Illinois Meteorites from the Moon and Mars University

• A few meteorites arrive on Earth from the Moon and Mars. • How do we know? Elemental composition and isotope ratios diﬀers from asteroid fragments and terrestrial rock.

Meteorites Total Finds > 30, 000 Martian: 120 known. Lunar: 164 known

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 38 / 104 meteorites.wustle.edu Northeastern Illinois Meteorite Cross-sections University

c SaharaMet/R. Pelisson

More meteorite photographs at: • http://www.saharamet.org • http://www.meteorlab.com/

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 39 / 104 Northeastern Illinois Meteoric Iron University

• Meteoric iron was the only source of iron metal before the invention of iron smelting. • Bronz age iron is all meteoric

Tutankhamun’s dagger 1300 BC

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 40 / 104 Northeastern Illinois Meteor Showers University

Sand to pebble sized particles ejected by comets form trail of invisible debris, responsible for most meteors and meteor showers. Comet debris

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 41 / 104 Northeastern Illinois Showers University

Asteroids & Comets Zodiacal Light Zodiacal Light

Asteroids Meteors & Meteorites Meteors and Meteorites Willamette Meteorite Primitive vs. Processed Chondrite Classiﬁcation Meteorites from the Moon and Mars Meteorite Cross-sections Meteoric Iron Meteor Showers Showers Leonid Shower: Ayers Rock Selected Meteor Showers Meteoroid Summary Q: “Shooting Star” Q: c Meteorite2012-2019G. Anderson Universe: Past, Present & Future – slide 42 / 104 Origin Northeastern Illinois Leonid Shower: Ayers Rock University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 43 / 104 Northeastern Illinois Selected Meteor Showers University

Meteor Shower Peak Date Origin Quandrantids January 2 2003 EH1 Lyrids April 21 Thatcher Eta Aquarids May 5 Halley Perseids August 12-13 Swift-Tuttle Draconids October 7 Giacobini-Zinne Orionids October 22 Halley Leonids November 17 Temple-Tuttle Geminids December 14 Phaethon

For up to date meteor information see: • International Meteor Organization (IMO) • IAS Meteor Data Center (MDC)

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 44 / 104 Northeastern Illinois Meteoroid Summary University

• Most meteorites are pieces of asteroids. • Most meteor showers have their origins with comets. • Primitive meteorites are remnants from solar nebula. • Processed meteorites are fragments of larger bodies that underwent diﬀerentiation. • 106–107 kg of meteorites fall on Earth each year.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 45 / 104 Northeastern Illinois Q: “Shooting Star” University

A typical “shooting star” in a meteor shower is caused by a entering Earth’s atmosphere. A) boulder-size particle from an asteroid B) boulder-size particle from a comet C) pea-size particle from an asteroid D) pea-size particle from a comet E) microscopic particle of interstellar dust

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 46 / 104 Northeastern Illinois Q: “Shooting Star” University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 46 / 104 Northeastern Illinois Q: Meteorite Origin University

Meteorites can come from A) the cores of asteroids. B) the crusts and mantles of asteroids C) the Moon. D) Mars E) all of the above

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 47 / 104 Northeastern Illinois Q: Meteorite Origin University

Meteorites can come from A) the cores of asteroids. B) the crusts and mantles of asteroids C) the Moon. D) Mars E) all of the above

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 47 / 104 Northeastern Illinois University

Asteroids & Comets Zodiacal Light Zodiacal Light

Asteroids Meteors & Meteorites

Comets Comet Comet Summary Comets Anatomy of a Comet Nucleus Halley’s Comet Fig. 9.09 Comet Holmes Comet Hyakutake Comet Hyakutake Halley’s Comet Comet Hale-Bopp Kuiper Belt & Oort Cloud Comet Orbits Capturing Comets Missions to Comets – Deep c 2012-2019G. Impact Anderson Universe: Past, Present & Future slide 48 / 104 Comet: A relatively small and ice-rich object that orbits a star

Comet Hale-Bopp Northeastern Illinois Comet Summary University

• Icy left over planetesimals: Formed beyond the frost line, comets are icy counterparts to asteroids. • The nucleus of a comet is like a “dirty snowball.” • Most comets remain perpetually frozen in the outer solar system. • Most comets do not have tails, Only comets that enter the inner solar system grow tails. • Comets in plane of solar system come from the Kuiper Belt. • Comets on random orbits come from Oort Cloud.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 50 / 104 Northeastern Illinois Anatomy of a Comet University

Hydrogen Halo (107 km) Dust Tail Coma (106 km)

Plasma Tail to Sun Nucleus (10 km)

Nucleus: The dirty snowball.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 51 / 104 Northeastern Illinois Anatomy of a Comet University

Hydrogen Halo (107 km) Dust Tail Coma (106 km)

Plasma Tail to Sun Nucleus (10 km)

Coma: sublimated cloud of gas and dust as ice-ball nears the sun

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 51 / 104 Northeastern Illinois Anatomy of a Comet University

Hydrogen Halo (107 km) Dust Tail Coma (106 km)

Plasma Tail to Sun Nucleus (10 km)

Plasma or Ion Tail: gas escaping from coma, ionized by UV radiation and pushed by solar wind (stream of charged particles)

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 51 / 104 Northeastern Illinois Anatomy of a Comet University

Hydrogen Halo (107 km) Dust Tail Coma (106 km)

Plasma Tail to Sun Nucleus (10 km)

Dust tail: liberated dust sized particles pushed by radiation pressure (photons).

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 51 / 104 Nucleus: Halley’s Comet

Comet Holmes Northeastern Illinois Comet Hyakutake University

The Great Comet of 1996, T = 70, 000 years.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 55 / 104 Northeastern Illinois Comet Hyakutake University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 56 / 104 Halley’s Comet Northeastern Illinois Comet Hale-Bopp University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 58 / 104 NOT to scale!

b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Kuiper Belt b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b r = 30 − 100 AU b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Oort Cloud b b b b b b b b b b b b b b b b b b b b b b b b r , b b ∼ 50 000 AU ∼ 1ly b Northeastern Illinois Comet Orbits University

Only a tiny number of comets enter the inner solar system; most stay far from the Sun. Kuiper Belt: Comets on orderly orbits at 30-100 AU in disk of solar system. Kuiper Belt comets formed in the Kuiper Belt. • Flat plane aligned with the plane of planetary orbits • Orbiting in the same direction as the planets

Oort Cloud: Comets on random orbits extending to about 50,000 AU. Oort Cloud comets were once closer to the Sun, but they were kicked farther out by gravitational interactions with Jovian planets. c 2012-2019G. Anderson Universe: Past, Present & Future – slide 60 / 104 • Spherical distribution b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b

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b b b b b b b b b b b b b b b b orbit before Jupiterb encounter b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b

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b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Northeastern Illinois Missions to Comets University

The United Stats (NASA), Soviet Union, Japan and the European Union (ESA) have all conducted satellite missins to Several comets. Recent satellite missions include: • NASA Stardust: Collected dust from comet Wild 2, and returned samples to Earth. • NASA Deep Impact: impactor successfully collideed with comet 9P/Tempel in 2005. Click for movie • Rosetta (ESA): Studied and landed a probe on comet 67P/Churyumov-Gerasimenko in 2014.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 62 / 104 Deep Impact and Comet Tempel Rosetta selﬁe with comet 67P/Churyumov-Gerasimenko. Northeastern Illinois Comet Summary University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 65 / 104 Northeastern Illinois University

Asteroids & Comets Zodiacal Light Zodiacal Light

Asteroids Meteors & Meteorites Comets Trans-Neptunian TNOs Trans-Neptunian Objects (TNOs) Trans-Neptunian Objects Objects Trans-Neptunian Objects Q: Kuiper Belt Formation Ultima Thule Dwarf Planet: Pluto Pluto & Charon Pluto: Comet or Planet? Planets Dwarf Planets TNO Summary Other Resources

Impacts – Review c 2012-2019G. Anderson Universe: Past, Present & Future slide 66 / 104 Northeastern Illinois Trans-Neptunian Objects (TNOs) University

Trans-Neptunian objects, any object with a>a[. Classes: • Kuiper Belt objects (KBOs) – Classical KBOs: Torus of objects with nearly circular orbits, small inclination, 30-50 AU. – Resonant KBOs: e.g. plutinos are in 3:2 resonance with Neptune. – Scattered KBOs: Source of short-period comets. Former KBOs scattering by gas giants to eccentric and inclined orbits, 30-100 AU.

• Oort Cloud Objects (OCOs) Spherical cloud of icy planitesials at 100,000 AU - 2 ly. Source of long-period comets. There are 1547 known TNO’s

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 67 / 104

Northeastern Illinois Q: Kuiper Belt Formation University

According to the nebular theory, how did the Kuiper belt form?

A) It is material left over from the interstellar cloud that never contracted with the rest of the gases to form the solar nebula.

B) It is made of planetesimals that formed beyond Neptune’s orbit and never accreted to form a planet.

C) It consists of objects that fragmented from the protosun during a catastrophic collision early in the formation of the solar system.

D) It is made of planetesimals between the orbits of Mars and Jupiter that never formed into a planet.

E) It is made of planetesimals formed in the outer solar system that were ﬂung into distant orbits by encounters with the Jovian planets. c 2012-2019G. Anderson Universe: Past, Present & Future – slide 70 / 104 Northeastern Illinois Q: Kuiper Belt Formation University

According to the nebular theory, how did the Kuiper belt form?

A) It is material left over from the interstellar cloud that never contracted with the rest of the gases to form the solar nebula.

B) It is made of planetesimals that formed beyond Neptune’s orbit and never accreted to form a planet.

C) It consists of objects that fragmented from the protosun during a catastrophic collision early in the formation of the solar system.

D) It is made of planetesimals between the orbits of Mars and Jupiter that never formed into a planet.

E) It is made of planetesimals formed in the outer solar system that were ﬂung into distant orbits by encounters with the Jovian planets. c 2012-2019G. Anderson Universe: Past, Present & Future – slide 70 / 104 Ultima Thule (486958) 2014 MU69 Pluto Pluto and Charon Northeastern Illinois Pluto: Comet or Planet? University

Pluto has much more in common with comets than with the eight major planets: • Much smaller than the eight major planets • Not a gas giant like the outer planets • Has an icy composition like a comet • Has a very elliptical, inclined orbit

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 74 / 104 Northeastern Illinois Planets University

A planet is a moderately large object that orbits a star and shines primarily by reﬂecting light from its star. Following the 2006 IAU resolution, an object can only be considered a planet if: 1. It orbits a star 2. it is large enough for its own gravity to make it round. 3. It has cleared most other objects from its orbital path. An object which only meets the ﬁrst two criteria is a dwarf planet. e.g. Pluto.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 75 / 104 Northeastern Illinois Dwarf Planets University

The IAU currently recognizes ﬁve dwarf planets. name d(AU) M inc region res Pluto 29-49 1.3 × 1022 17◦ rKBO 3:2 Eris 38-98 1.67 × 1022 44◦ SDO - Haumea 35-51 4 × 1022 44◦ rKBO 7:12 Makemake 39-53 - 29◦ cKBO - Ceres 2.6-3 9 × 1020 11◦ Ast -

Another 100 known objects in the solar system may satisfy the deﬁnition of dwarf planets, and our solar sytem may contain 10,000 dwarf planets.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 76 / 104 Northeastern Illinois TNO Summary University

What are Pluto and other large objects of the Kuiper Belt like? • The Kuiper Belt contains objects as large as Pluto. • Pluto and other “dwarf planets” are more like large comets than like major planets. • Large objects in the Kuiper Belt have tilted, elliptical orbits and icy compositions like those of comets.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 77 / 104 Northeastern Illinois Other Resources University

For recent information on minor planets please consult: • The IAU Minor Planet Center (MPC) – Inner Solar System – Outer Solar System – Minor Planet Census

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 78 / 104 Northeastern Illinois University

Asteroids & Comets Zodiacal Light Zodiacal Light

Asteroids Meteors & Meteorites

Comets TNOs Impacts Impacts SL9 SL9 Jupiter Impact Ganymede Craters Callisto Crater Chain Bolide Events Impact Craters Tunguska Event Tunguska 2013 Russian Meteorite Winslow Arizona Vredefort Dome Asteroid approaches Earth Mass c 2012-2019G. Extinctions Anderson Universe: Past, Present & Future – slide 79 / 104 Chicxulub Northeastern Illinois Tidal forces and SL9 University

The tidal forces from Jupiter broke the nucleus of SL9 into a chain of smaller nuclei.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 80 / 104 SL9 Impact with Jupiter Northeastern Illinois Ganymede Crater Chain University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 82 / 104 Northeastern Illinois Callisto Crater Chain University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 83 / 104

Northeastern Illinois Impact Craters University Over 150 impact craters have been identiﬁed on Earth:

Impact Crater: Carancas, Peru • Video of Ten Impact Craters c 2012-2019G. Anderson Universe: Past, Present & Future – slide 85 / 104 Northeastern Illinois 1908 Tunguska Event University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 86 / 104 Northeastern Illinois Tunguska University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 87 / 104 Northeastern Illinois 2013 Russian Meteorite University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 88 / 104 Northeastern Illinois Winslow Arizona University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 89 / 104 Northeastern Illinois Vredefort Dome University

South Africa (2.023 Ga) d> 300 km. c 2012-2019G. Anderson Universe: Past, Present & Future – slide 90 / 104

Northeastern Illinois Mass Extinctions University

• Fossil record shows occasional large dips in the diversity of species: mass extinctions. • The most recent, was 66 million years ago, ending the reign of the dinosaurs. • Iridium is very rare in Earth surface rocks but is often found in meteorites. • Luis and Walter Alvarez found a worldwide layer containing iridium, laid down 66 million years ago, probably by a meteorite impact. • All dinosaur fossils all lie below this layer.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 92 / 104

Northeastern Illinois Evidence for the (K-Pg) Event University

The Cretaceous-Paleogene (K-Pg) extinction event: • Mass extinction of 3/4 of plant and animal species on Earth 66 million years ago. • Thin layer of 66 million year old sediment spread over Earth containing high levels of iridium (Ir). • K-Pg boundary clay full of tiny spherules of rock formed from rock melted by impact. • 180 km wide Chicxulub crater is the source of K-Pg boundary clay. • K-Pg boundary contains shocked quartz. • Evidence of ancient giant tsunami beds along the Gulf coat and Carribean.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 94 / 104 Northeastern Illinois Iridium Anomaly at K-Pg Boundary University

No Dinosaur fossils Layer rich in iridium and soot

Dinosaur fossils

Trinidad, CO c 2012-2019G. Anderson Universe: Past, Present & Future – slide 95 / 104

Northeastern Illinois Consequences University

Consequences of an Impact • A meteorite 10 km in size would send large amounts of debris into the atmosphere. • Debris would reduce the amount of sunlight reaching Earth’s surface. by 10-20%, for at least 10 years. • The resulting climate change may have caused mass extinction.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 98 / 104 Northeastern Illinois Frequency of Impacts University

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 99 / 104 Northeastern Illinois Impacts with Earth University

• Asteroids and comets have hit Earth in the past. • Major impacts are very rare, but another major impact is only a matter of time: not if but when. • Extinction level events ∼ tens of millions of years • Major damage ∼ tens to hundreds of years The asteroid or comet with our name on it: • We haven’t seen it yet. • Deﬂection is more probable with years of advance warning. • Breaking a big asteroid into a bunch of little asteroids is unlikely to help. • We get less advance warning of a killer comet.

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 100 / 104 Northeastern Illinois Hazards University

Near-Earth Objects (NEOs): Comets and asteroids with orbits that bring them close to the Earth. Potentially Hazardous Objects (PHOs): Near Earth Objects (NEOs) large enough to create signiﬁcant damage in the case of an impact.

Detection and monitoring of Near Earth Objects • NASA Center for Near Earth Object Studies – Earth Impact Monitoring

• IAU/MPCs list of PHAs

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 101 / 104 Northeastern Illinois Further Study University

• Mapping of the Asteroid Belt, DeMeo & Carry • Ten things you don’t know about Comets • Rosetta & Comet 67P/Churymov-Gerasimenko • Crash Course Astronomy #21: Comets • Crash Course Astronomy #22: The Oort Cloud • Crash Course Astronomy #23: Meteors • Charon on Google Maps

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 102 / 104 Northeastern Illinois University

Asteroids & Comets Zodiacal Light Zodiacal Light

Asteroids Meteors & Meteorites

Comets TNOs Review Impacts

Review Review

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 103 / 104 Northeastern Illinois Review University

• How does the composition of comets compare to asteroids? • How is that related to the two types of planets? • Describe the Oort cloud and the Kuiper belt. • What are Kirkwood gaps? What causes them? • Why aren’t small asteroids spherical in shape? • Where can you ﬁnd 75% of asteroids? • What is the name of the largest asteroid? How big is it? • Where does the tail of a comet point? • What event is likely responsible for the extinction of the dinosaurs?

c 2012-2019G. Anderson Universe: Past, Present & Future – slide 104 / 104