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Home , 87 Sylvia, Asteroid spectral types, Comet Holmes, Zodiacal light

, & Dwarf

Orin Harris and Greg Anderson Department of Physics & Northeastern Illinois University

Spring 2021

c 2012-2021G.Anderson.,O.Harris :Past,Present&Future – slide 1 / 109 Overview

Asteroids Meteors & Comets TNOs Impacts Review

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 2 / 109 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 b b b b b b b b b b b b b b b b b Kuiper Beltb b b b b b b b Belt 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 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 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 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 Zodiacal

Zodiacal light: faint glow near the from scattered off the zodiacal cloud, a pancake shaped cloud of interplanetary .

Origin: Continually replenished by disintegration & asteroid collisions. Recent estimates: 85% from family comets. Size 10 − 300 µm c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 4 / 109 Asteroids & Comets Zodiacal Light

Asteroids Hayabusa Bennu Asteroid Facts Meteoric Iron Discovering Missions Asteroids Largest & Vesta Q: Ceres? Asteroids Main Belt Main Belt Eros from NEAR Q: Shape Spectral Types asteroid Histogram vs a Scatter i vs a Scatter i vs a asteroid orbits Trojans Q: Trojans c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 5 / 109 Origin Theories Rover 1A Hops on Asteroid Ryugu Osiris/Bennu (video link) Asteroid Facts

Relatively small, rocky objects - ing the . • Leftover rocky • Majority between and Jupiter

• Total ≪ MMoon • Largest Ceres, d ≈ 950 km • 1.1 − 1.9 million with d> 1 km. • > 500, 000 cataloged

Vesta

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 8 / 109 Meteoric Iron

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

Tutankhamun’s dagger 1300 BC

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 9 / 109 WidmansAattenˆ pattern requires millions of years of cooling Discovering Asteroids

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 11 / 109 Asteroid Missions to Asteroids

• (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 • Genesis (NASA) 2001– • Stardust - NASA • Deep Space 1 - NASA • Cassini - NASA/ESA • NASA Near Earth Asteroid Rendezvous (NEAR-Shoemaker) • Galileo - NASA

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 12 / 109 Largest Asteroids (by Diameter)

Name Discovered a (AU) d (km) Class 1 Ceres 1801 2.77 975 C 1807 2.36 525 V 1802 2.77 512 B 10 Hygeia 1849 3.14 431 C 1910 3.06 326 C 52 1858 3.10 315 C 1903 3.18 289 C 1866 3.49 286 X 1861 3.44 273 C 1851 2.64 268 S

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 13 / 109 Asteroids Ceres & Vesta

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

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 14 / 109 How big is Ceres?

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 15 / 109 How big is Ceres?

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 15 / 109

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

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 20 / 109 Q: Asteroid Shape

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 20 / 109 Albedo reflected light albedo = incident light Perfect Absorber 0 Bare soil 0.17 Desert Sand 0.4 Ocean Ice 0.5 − 0.7 Snow 0.8 − 0.9 Perfect reflecter 1

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 21 / 109

Asteroids can be classified based on spectral type: C-type (-rich), most undifferentiated? (Ceres?) 75% of known asteroids and even higher % of outer belt. Dark: albedo 0.03 − 0.09. Surface composition similar to 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 22 / 109 Asteroid Orbital Classification

• Asteroid Belt, 75% (2.2 AU 18000 Amor a> 1 AU, 32% Apollo* a> 1AU, 62% Aten* a< 1 AU, 6%

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 23 / 109

Asteroid Orbital Classification

• Asteroid Belt, 75% (2.2 AU 18000 Amor a> 1 AU, 32% Apollo* a> 1AU, 62% Aten* a< 1 AU, 6%

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 27 / 109 Trojans

Lagrangian points L4: Greeks

60%

L3 L1 L2 60%

L5: Trojans

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 28 / 109 Q: Asteroids

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 29 / 109 Q: Trojan Asteroids

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 29 / 109 Origin Theories

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 and shattering of planitesimals instead of 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 30 / 109

Q: Kirkwood Gaps

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 .

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 .

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 32 / 109 Q: Kirkwood Gaps

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 32 / 109 Q: Asteroids beyond Jupiter

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 33 / 109 First Known Interstellar Asteroid, Oumuamua, 2017 Asteroids & Comets Zodiacal Light

Asteroids Meteors & Meteorites Meteors and Meteorites Willamette Meteorite Primitive vs. Processed Meteors & Meteorites Chondrite Classification Meteorites from the Moon and Mars Meteorite Cross-sections Meteor Showers Showers Leonid Shower: Ayers Rock Selected Meteor Showers Summary Q: “Shooting Star” Q: Meteorite Origin

Comets c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 35 / 109 Meteors and Meteorites

Meteoroid: Small rocky debris from asteroid fragments or comet disintegration. Meteor: The flash of light produced when a meteoroid enters Earth’s atmosphere. Meteorites: 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 36 / 109 Willamette Meteorite

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 37 / 109 Primitive vs. Processed

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 38 / 109 Thin sections by: O. Richard Norton Classification

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 40 / 109 Meteorites from the Moon and Mars

• 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 41 / 109 meteorites.wustle.edu Meteorite Cross-sections

c SaharaMet/R. Pelisson

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 42 / 109 Meteor Showers

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 43 / 109 Showers

Asteroids & Comets Zodiacal Light

Asteroids Meteors & Meteorites Meteors and Meteorites Willamette Meteorite Primitive vs. Processed Chondrite Classification Meteorites from the Moon and Mars Meteorite Cross-sections Meteor Showers Showers Leonid Shower: Ayers Rock Selected Meteor Showers Meteoroid Summary Q: “Shooting Star” Q: Meteorite Origin

Comets c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 44 / 109 Leonid Shower: Ayers Rock

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 45 / 109 Selected Meteor Showers

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 46 / 109 Meteoroid Summary

• 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 47 / 109 Q: “Shooting Star”

A typical “shooting star” in a 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 48 / 109 Q: “Shooting Star”

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 48 / 109 Q: Meteorite Origin

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 49 / 109 Asteroids & Comets Zodiacal Light

Asteroids Meteors & Meteorites

Comets Comet Comet Summary Anatomy of a Comet Comets Nucleus Halley’s Comet Fig. 9.09 Comet Holmes Comet Hyakutake Halley’s Comet Comet Hale-Bopp & Comet Orbits Capturing Comets Missions to Comets Deep Impact – Rosetta c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future slide 50 / 109 Comet: A relatively small and ice-rich object that orbits a star

Comet Hale-Bopp Comet Summary

• 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 52 / 109 Anatomy of a Comet

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

Plasma Tail to Sun Nucleus (10 km)

v

Nucleus: The dirty snowball.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 53 / 109 Anatomy of a Comet

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

Plasma Tail to Sun Nucleus (10 km)

v

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 53 / 109 Anatomy of a Comet

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

Plasma Tail to Sun Nucleus (10 km)

v

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 53 / 109 Anatomy of a Comet

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

Plasma Tail to Sun Nucleus (10 km)

v

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 53 / 109 Nucleus: Halley’s Comet

Comet Holmes Comet Hyakutake

The of 1996, T = 70, 000 years.

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 57 / 109 Comet Hyakutake

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 58 / 109 Halley’s Comet Comet Hale-Bopp

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 60 / 109 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 b b b b b 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 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 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 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 b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b 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 b b b r , b b b b b ∼ 50 000 AU ∼ 1ly b Comet Orbits

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. • Spherical distribution • Orbiting in any direction

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 62 / 109 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 b b b b b b b b b b b b b b b b b b b b Missions to Comets

Several comets have been visited by satellites. These 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 64 / 109 Deep Impact and Comet Tempel Rosetta selfie with comet 67P/Churyumov-Gerasimenko. Video of orbit of 13-foot ‘churymoon’ Rosetta on comet 67P/Churyumov-Gerasimenko. Blizzard on Churyumov-Gerasimenko First observed interstellar comet, discovered in 2019 by amateur astronomer Gennadiy Borisov

The trajectory of 2I/Borisov () as it crosses the ecliptic plane between the orbits of Mars () and Jupiter (purple) during December 2019. Comet Summary

• 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 71 / 109 Asteroids & Comets Zodiacal Light

Asteroids Meteors & Meteorites

Comets

TNOs Trans-Neptunian Trans-Neptunian Objects (TNOs) Kuiper belt object Ultima Thule Objects Trans-Neptunian Objects Trans-Neptunian Objects Q: Kuiper Belt Formation : Pluto: Comet or Planet? Planets Dwarf Planets TNO Summary Other Resources

Impacts

Review c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 72 / 109 Trans-Neptunian Objects (TNOs)

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. are in 3:2 resonance with . – 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 73 / 109 Ultima Thule

Q: Kuiper Belt Formation

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

A) It is material left over from the 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 77 / 109 Q: Kuiper Belt Formation

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 77 / 109 Pluto Pluto: Comet or Planet?

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 79 / 109 Planets

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 80 / 109 Dwarf Planets

The IAU currently recognizes five dwarf planets. name d(AU) M inc region res Pluto 29-49 1.3 × 1022 17◦ rKBO 3:2 38-98 1.67 × 1022 44◦ SDO - 35-51 4 × 1022 44◦ rKBO 7:12 39-53 3 × 1021 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 81 / 109 TNO Summary

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 82 / 109 Other Resources

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 83 / 109 Asteroids & Comets Zodiacal Light

Asteroids Meteors & Meteorites

Comets

TNOs Impacts Impacts SL9 SL9 Jupiter Impact Craters Crater Chain Bolide Events Impact Craters Tunguska Event Tunguska 2013 Russian Meteorite Winslow Arizona Vredefort Dome Asteroid approaches Earth Mass Extinctions Chicxulub c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 84 / 109 Impact Tidal forces and SL9

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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 85 / 109 SL9 Impact with Jupiter Ganymede Crater Chain

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 87 / 109 Callisto Crater Chain

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 88 / 109

Impact Craters

Over 150 impact craters have been identified on Earth:

Impact Crater: Carancas, Peru • Video of Ten Impact Craters c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 90 / 109 1908 Tunguska Event

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 91 / 109 Tunguska

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 92 / 109 2013 Russian Meteorite

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 93 / 109 Winslow Arizona

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 94 / 109 Vredefort Dome

South Africa (2.023 Ga) d> 300 km. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 95 / 109

Mass Extinctions

• 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 97 / 109

Evidence for the (K-Pg) Event

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 99 / 109 Iridium Anomaly at K-Pg Boundary

Trinidad, CO

No Dinosaur fossils Layer rich in iridium and soot

Dinosaur fossils

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 100 / 109

Consequences

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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 103 / 109 Frequency of Impacts

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 104 / 109 Impacts with Earth

• 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 105 / 109 Hazards

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 Near Earth Object Program • NASA Impact Hazards • IAU/MPCs list of PHAs

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 106 / 109 Further Study

• 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

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 107 / 109 Asteroids & Comets Zodiacal Light

Asteroids Meteors & Meteorites

Comets

TNOs Impacts Review Review Review

c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 108 / 109 Review

• 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 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 109 / 109