AST 301, Catastrophe Lecture

James Lattimer

Department of Physics & Astronomy 449 ESS Bldg. Stony Brook University

March 12, 2019

Cosmic Catastrophes [email protected]

James Lattimer AST 301, Catastrophe Lecture Catastrophe Theory

3 I Consider a potential function V (x) = x + ax.

I When a < 0 there is both a stable minimum (dots) and an unstable maximum in the potential.

I As a is slowly increased, the equilibrium system moves smoothly to p smaller x: xeq = −a/3.

I When a = 0, the stable minimum disappears, and for a inﬁnitesimally positive, the system moves abruptly to a new equilibrium very far removed from the old.

James Lattimer AST 301, Catastrophe Lecture Catastrophes and Evolution

I Extinction was not widely accepted before 1800. I Extinction was established as a fact by Georges Cuvier in 1796, critical for catastrophism, he also opposed Lamarckian evolution theories. I Over 99% of all species that have ever existed are now extinct. I Extinctions occur at an uneven rate. I There have been 6 major and many minor (up to 20) extinctions observed in the fossil record. Nearly all divisions among geological eras, eons and periods are marked by extinctions and originations. Cambrian-Ordovician transition 488 Myr A series of extinctions that eliminated many brachiopods and tribolites. Ordovician-Silurian transition 444 Myr Second largest extinction. Late Devonian 360 Myr A series of extinctions near the Devonian-Carboniferous transition, lasted 20 Myr with several pulses. Permian-Triassic extintinction 251 Myr Earth’s largest extinction killed 96% of all marine species and 70% of land species (plants, insects, vertebrates). Ended dominance of mammal-like reptiles and led to dinosaur dominance. Triassic-Jurassic extinction 200 Myr Last of large amphibians extinguished. Cretacious-Tertiary extinction 65 Myr About 50% of all species, including dinosaurs, were extinguished. Holocene extinction, now About 70% of biologists view the present as a mass extinction, due to human intervention. Not universally accepted as many argue there are signiﬁcant diﬀerences from extinctions.

James Lattimer AST 301, Catastrophe Lecture Major Extinctions

Rohde & Muller, Nature, 2005

James Lattimer AST 301, Catastrophe Lecture Theories of Extinctions

I A theory should

I explain all the losses, not just a few groups like dinosaurs

I explain why some organisms survived and others didn’t

I be based on events that actually happened. I Flood basalt events, triggered by extensive volcanic activity, have been recorded 11 times and each is connected to an extinction event. I Sea level falls have been recorded 12 times and 7 are associated with extinctions. I Asteroid impacts producting craters over 100 km wide have been recorded once and associated with a mass extinction. These could produce intense volcanic activity as well as prolong heating or cooling due to deposition of soot and aerosols into atmosphere. I Asteroid impacts producing craters less than 100 km wide have been recorded over 50 times, but most not connected to any extinctions. I Other astronomical events, like supernovae and gamma ray bursts, could irradiate the Earth and destroy the ozone layer among other things. It’s been suggested a supernova was connected with the Ordovician-Silurian transition, but this is only weakly supported by evidence. I Other terrestrial events connected with global warming or cooling, like Snowball Earth or continental drift.

James Lattimer AST 301, Catastrophe Lecture The Cretaceous-Tertiary Boundary Layer

Raton Pass, NM

Gubbio, Italy

James Lattimer AST 301, Catastrophe Lecture The Cretacious-Tertiary Boundary Layer

James Lattimer AST 301, Catastrophe Lecture Cretacious-Tertiary Extinction Available evidence points strongly to an asteroid impact: Iridium enhancements In 1980, Alvarez, Alvarez, Asaro and Michels discovered that sedimentary layers at the K-T boundary contain concentrations of iridium and other rare-earth elements between 30 and 130 times normal. These elements are rare in the Earth’s crust, having been drained to Earth’s core when the Earth was molten as part of the Earth’s diﬀerentiation. But the same elements are corresondingly abundant in asteroids and comets. The amount of the excess iridium suggested an impactor of 10-15 km diameter. 2 3 2 1/3 4πR⊕d = 4πR /3 ⇒ R = (3R⊕d) d = 0.1 cm, R⊕ = 6373 km ⇒ R = 5 km Spherules Droplets of rock melted by high temperatures. Shocked quartz Formed under high pressure conditions, but never in conjunction with vulcanism. Soot Ash amounts consistent with burning most of Earth’s biota. Worldwide distribution Liklihood A 10-km body will impact the Earth about once per 100 million years, and the K-T extinction occurred 65 Myr ago. Craters Several craters with ages of 65 Myrs found: Chicxulub, Mexico; Boltysh crater in Ukraine; Silverpit crater in the North Sea Crater size An impactor produces a crater 20 times its own size, so a 10-km impactor makes a 200 km crater. Chicxulub crater is about 180 km in diameter. Lack of SN proucts No 244Pu (halﬂife 80 Myrs) found.

James Lattimer AST 301, Catastrophe Lecture Chicxulub Crater w.tdn.uuﬁ jkorteni/space/boundary www.student.oulu.ﬁ/

James Lattimer AST 301, Catastrophe Lecture Iridium Concentrations

Alvarez et al. 1980

James Lattimer AST 301, Catastrophe Lecture Spherule Distribution

James Lattimer AST 301, Catastrophe Lecture Alternative Extinction Theories

James Lattimer AST 301, Catastrophe Lecture Simple Crater Formation Craters are always circular. Gilbert suggested in 1890’s that lunar craters are impacts. He wondered why they are always round. Wouldn’t an oblique impact make an elliptical crater? Volumes of crater and debris rim equal.

Energy comes from kinetic energy of impactor and is much larger than the equivalent release of chemical energy (TNT).

Impact speed is the Earth’s escape speed plus the original space velocity.

1. Compression by impact, milliseconds 2. Excavation by shock (origin below surface), minutes 3. Modiﬁcation from fall back and sliding, hours

James Lattimer AST 301, Catastrophe Lecture Lesson 3: Crater Morphology - Overhead 2 Impact Eﬀects

I Equate kinetic energy of impactor with gravitational potential energy. Establishes an estimate of impact velocity that is equivalent to the Earth’s escape velocity. s 1 2 GmM⊕ 2GM⊕ −1 mvesc = ⇒ vesc = = 11 km s ' 25, 000 mph 2 R⊕ R⊕ In fact, an impactor is likely to crash with about 50% more velocity. I The kinetic energy per projectile mass m is 1 v 2 = 1.3 · 1012 erg g−1 ' 100 × TNT. 2 I A 1 km-diameter projectile has a mass 4π m = ρ(D/2)3 = 1.6 · 1015 g 3 which strikes with an energy equivalent to 1.6 · 105 MT of TNT. I A general rule of thumb is that, on the Earth, a meteoroid will create a crater that is about 20 times bigger than itself. I On the Moon, the crater will be about 12 times the size of the impactor. James Lattimer AST 301, Catastrophe Lecture Deep Imact Mission Findings

I Comet Tempel 1 has a fluffy structure made of fine dust that is weaker than a bank of powder snow. I The luminous flash seen on impact was much fainter than expected, indicating a surface layer composed 75% of empty space, i.e., it has a high porosity. This disproved theories that a comet’s surface is armored with a solid crust that impedes outgassing. I The comet’s material is held together almost completely by gravity. I Other impact craters are seen on the comet’s surface. Their erosion was observed to take place in discrete events (catastrophes) rather than slowly and continuously (sound familiar?). I The ejecta plume contained a large increase in carbonaceous material, implying the interior contains substantial organic material. Comets could bring an appreciable amount to the early Earth. I The comet’s interior is well-shielded from solar heating, so that it is still primordial. I Comparisons of Tempel 1 and Hartley 2 showed that short-period comets formed under warmer conditions than long-period comets, and therefore closer to the Sun than the Kuiper Belt.

James Lattimer AST 301, Catastrophe Lecture Impacts

0.005 0.02 0.15 0.8 2.0 10.0 D (km)

Chapman and Morrison, Nature, 1994

James Lattimer AST 301, Catastrophe Lecture Impact Rate Revised

NASA NEO Science Deﬁnition Team, 2003

James Lattimer AST 301, Catastrophe Lecture Detection Progress

(0,0) 2019

James Lattimer AST 301, Catastrophe Lecture Impact-Earthquake Similarities

James Lattimer AST 301, Catastrophe Lecture Impact Fatalities

Chapman and Morrison, Nature, 1994

James Lattimer AST 301, Catastrophe Lecture Impact Fatalities

Harris, Space Sciences Institute

James Lattimer AST 301, Catastrophe Lecture Impact Fatalities

Rumpf, Lewis and Atkinson 2017

James Lattimer AST 301, Catastrophe Lecture Impact Fatalities: Land vs. Water

Rumpf, Lewis and Atkinson 2017

James Lattimer AST 301, Catastrophe Lecture Fatalities Per Year

Chapman and Morrison, Nature, 1994

James Lattimer AST 301, Catastrophe Lecture Impact Fatality Estimates

Simulation of 100,000 years duration, keeping worst event per decade Asteroid/comet # # % Fatal Average Average Annual risk diameter (m) events fatal events yield (MT)∗ fatalities∗ of fatal event 13-99 9792 949 10 18 43 000 1 in 100 100-199 173 124 72 300 280 000 1 in 800 200-499 31 29 94 2000 700 000 1 in 3500 500-999 3 3 100 35 000 13 million 1 in 30 000 All 9999 1105 11 170 120 000 1 in 90 ∗per fatal event Simulation of 1 million years duration, keeping worst event per century Asteroid/comet # # % Fatal Average Average Annual risk diameter (m) events fatal events yield (MT)∗ fatalities∗ of fatal event 13-99 8563 2619 31 30 92 000 1 in 382 100-199 1065 736 69 300 310 000 1 in 1359 200-499 311 295 95 3900 1.8 milion 1 in 3390 500-999 45 44 98 29 000 14 million 1 in 22 727 1000-1999 14 14 100 220 000 180 million 1 in 71 429 2000+ 2 2 100 2 million 1.7 billion 1 in 500 000 All 10 000 3710 37 2 600 2 million 1 in 270 ∗per fatal event J. Lewis, U. of Arizona

James Lattimer AST 301, Catastrophe Lecture Web-Based Impact Eﬀect Calculator

www.lpl.arizona.edu/impacteffects Focuses on the consequences of an impact event for the regional environment; that is, from the impact location to a few thousand km away. I Impactor enters upper atmosphere with v = 11 − 72 km/s anywhere from vertical to grazing, with the most likely angle 45◦. I Large surviving objects deform but form an impact crater; small ones are slowed too much. Intermediate ones deform and then explode (airburst). I The impactor and target are compressed to high pressures and temperatures, forming a temporary crater and shock wave underneath it. I Target is fractured, shock-heated, shaken and excavated. I Temporary crater collapses. I Large volumes of debris ejected to form a rim and blanket, dust cover and secondary craters. I Impactor kinetic energy conerted to thermal energy, seismic energy and kinetic energy of ejecta. I Thermal energy melts and vaporizes impactor and some target material. I Hot plume (fireball) radiates thermal energy igniting fires. I Seismic energy causes violent shaking several crater diameters away. I Shock wave compresses air which pulverizes things in its path; it is followed by violent winds that flatten forests and scatter debris.

James Lattimer AST 301, Catastrophe Lecture Impact Parameters

−3 I Asteroids are stony with density ρI = 2 − 3 g cm or iron ρI = 8 g cm−3, incident with v = 12 − 20 km s−1. −3 I Comets are icy with ρI = 0.3 − 1.5 g cm , incident with v = 30 − 70 km s−3.

I From Near-Earth Object Science Deﬁnition Team (2003): N(> D) ' 1148(D/km)−2.354. 0.78 I Recurrence time is TR ' 109(E/MT ) . 4 −3 3 −1 2 I Impact energy E ' 2.5 · 10 (ρ/g cm )(D/km) (v/20 km s ) MT

I Comets represent 1% of small NEO population, but larger proportions of large NEOs.

I Iron asteroids represent 2-10% of total impactors.

In the following calculations, we assume an impactor density ρI = 3 g −3 −1 ◦ cm and initial velocity v0 = 15 km s at a constant angle θ = 45 to the ground. The line colors refer to initial impactor diameters D0 (see the second figure for the key). The solid (dashed) lines in the first figure show velocities without (with) effects of changes to D(z) (deformation).

James Lattimer AST 301, Catastrophe Lecture Impact: Deformation (Flattening) Atmospheric density −z/H ρ = ρ0e , H = 8 km, −3 −3 ρ0 = 10 g cm . Atmospheric drag: dv 3ρC = − D v 2. dt 4ρI D v is velocity, CD = 2. ρI is impactor density, D (D0) is (initial) diameter. z is altitude; dz/dt = −v sin θ. d ln v 3ρC = D . dz 4ρI D sin θ

v 3ρCD H If D = D0, ln = − . v0 4ρI D sin θ Pressure on the leading side of impactor is P = ρv 2. The critical pressure −3 √ to induce deformation is log10(PB /erg cm ) ' 3.107 + 1.973 ρI (yield −3 strength). Even at zero density it is PB ' 1280 erg cm .

The critical deformation altitude z∗ is where P = PB and is about 50 km. James Lattimer AST 301, Catastrophe Lecture Deformation and Airbursts

The impactor deforms and pancakes when z < z∗. It ﬂattens laterally (squishes) due to the diﬀerential pressue between the leading (pressure P = ρv 2) and trailing (pressure = 0) sides, so dP/dx ∼ P/D. 2 2 d D CD P CD ρv dD 2 = = , D = D0 and = 0 when z = z∗. dt ρI D ρI D dt Eliminate v with dz/dt = −v sin θ:

2 d D CD ρ 1 3 dD D 2 = − . dz ρI sin θ sin θ 4 dz

This is integrated from z∗ to the ground where D = DG . For small (D0 < 0.01 km) impactors, D(z)/D0 can exceed 7, at which point experiments show airbursts result. Larger impactors strike the ground. For z < z∗, D(z) is no longer constant; v(z) changes according to the dln v/dz equation. James Lattimer AST 301, Catastrophe Lecture Crater Size

Experiments (up to nuclear weapon scales) and simulations to extrapolate to larger energies suggest

D ρ 1/3 D 0.78 v 0.44 g 0.22 crater ' 4.02 I G G E sin1/3 θ. km ρT km km/s gT

vG is the impact velocity at the ground, v(z = 0). This is generally only slightly smaller than v0 since objects small enough to be appreciably slowed in the atmosphere result in airbursts instead of impacts. For impacts in water, replace 4.02 by 3.74. The crater depth, from an analysis of venusian craters, is

0.3 ddepth ' 0.4 (Dcrater /km) km.

James Lattimer AST 301, Catastrophe Lecture Fatality Odds For USA

Terrorism−→

C. R. Chapman

James Lattimer AST 301, Catastrophe Lecture Fatality Rates

C. R. Chapman

James Lattimer AST 301, Catastrophe Lecture Impact Probability

Boslough et al. 2012

James Lattimer AST 301, Catastrophe Lecture Fatality Estimates Prior to Spaceguard Survey

Harris, Space Sciences Institute

James Lattimer AST 301, Catastrophe Lecture Fatality Estimates After Spaceguard Survey

Harris, Space Sciences Institute

James Lattimer AST 301, Catastrophe Lecture Fatality Estimates

Harris, Space Sciences Institute

Climate change > 150, 000 Huybers (2009) and Sokolov (2009) estimate that a global climate catastrophe is 40,000 times more likely than an impact catastrophe by 2100. James Lattimer AST 301, Catastrophe Lecture Minority Report from WHO

James Lattimer AST 301, Catastrophe Lecture How To Date the Most Recent Lunar Craters

James Lattimer AST 301, Catastrophe Lecture Changes in Recent Cratering Frequency

I Lunar craters were analyzed for ages using the radiometer on the Lunar Reconnaissance Orbiter’s Diviner instrument.

I 111 lunar craters younger than 1 Gyrs were analyzed.

I The number of lunar craters younger than 290 Myrs is about 2.5 times as high as the average expected over the last 1 Gyrs.

I Cratering history of the moon should be the same as the Earth.

I This could explain the paucity of craters on the Earth from 290 Myrs old to 650 Myrs old.

I Could have been caused by a breakup of an asteroid about 300 Myrs ago.

James Lattimer AST 301, Catastrophe Lecture Should We Try to Find All Impactors?

We currently ﬁnd about 1000 NEOs of 20 m and larger per year.

It will take over 1000 years to ﬁnd the expected total number, 1 million.

The LSST, beginning in 2022, should ﬁnd an increasing number of NEOs.

To ﬁnd 100,000 NEOs per year will require more instruments.

Possibilities include 1) NEOCAM, an infrared space telescope at the L1 Lagrange point 1 million miles from Earth; 2) the Sentinel IR space telescope in orbit between the Earth and Venus. This will orbit faster than the Earth, making it easier to see objects with 1 year orbital periods, and will see parts of Earth’s orbit not visible from Earth (less overlap with LSST).

Is this worth it?

James Lattimer AST 301, Catastrophe Lecture Prediction Consequences Nature of Problem Mistaken or exaggerated media report of near-miss or near-term predicted impact causes panic and demands for official action. Probability of Happening Has already occurred, and likely to happen again. Most likely way of impact hazard becoming of urgent concern to public officials. Warning Time Page-one stories develop in hours with officials being totally surprised. Mitigation Public education in science and risk, in particular. Development of critical thinking concerning risk. Science education and journalism need improvement. Examples

I Near miss by 100-m asteroid 60,000 km away. Will people believe official statements? I Mistaken famous astronomer predicts impact in 10 years, but report not withdrawn for days. I Official IAU prediction of 1-in-a-few-hundred impact possibility later in century; not refined until later (Asteroid 1997 XF11). I Grotesque media hype of one of above cases. From C. R. Chapman, Southwest Research Institute

James Lattimer AST 301, Catastrophe Lecture Mitigation

I The energy needed to pulverize an impactor that has a kinetic energy of 1 MT is about 0.0001 MT. −8 I The energy needed to deﬂect an impactor is about 3 · 10 of that needed to pulverize it. Power of sunlight: R 2 d −2 P = 4.3 · 1016 erg/s 1 km 1 AU Acceleration: a = 2P/(Mc). Deﬂection distance: ∆ = at2/2

Pt2 d −2 1 km t 2 ∆ = = 1.4 km Mc 1 AU r 1 yr I For ∆ ' 8000 km, the size of the Earth, t ' 76 yrs. is needed if the impactor is at a mean distance of 1 AU from the Sun and is about 1 km in radius. I The space shuttle main engines could deflect a 1-km body with a lead time of about 30 years. I Delta 2 1st stage rocket could deflect 100-m body with lead time of 6 months. I Danger of a bomb attack is that it could lead to many impactors producing damage over a wider range with a cumulative effect at least as large if not larger than the original impactor. James Lattimer AST 301, Catastrophe Lecture But Breaking Up Is Hard To Do (Apologies to Neil Sedaka)

Studies of impacts of small asteroids into larger ones have suggested the target asteroid could be completely destroyed by a moderate impact. These models were based on properties of smallish rocks. However, it is now known that fractures in rocks propagate much more slowly in large solid objects. Granular flow and pore collapse introduce additional energy dissipation. A new study at Johns Hopkins models a 1.21-km basalt asteroid hitting a 25-km asteroid at 5 km/s. Initially, millions of cracks form and ripple through the asteroid. Parts of the asteroid flow like sand and a crater is produced. The asteroid is fragmented, but not completely disrupted, with a has a large damaged, granular, core that survives. The gravitational pull of the surviving core then slows and reverses the motions of the outer parts that initially flew off the asteroid which then reassemble. Thus, significantly more energy than previously realized is needed to pulverize asteroids. These studies are not just applicable to mitigation efforts, but are also useful to decide how to best mine asteroids. James Lattimer AST 301, Catastrophe Lecture Mining Asteroids

In order to be suitable targets, an asteroid worth mining must have a market value exceeding $1B. This means having a diameter greater than 1 km, containing more than 10 parts per million of platinum and other rare earth elements, and having a velocity relative to the Earth less than 4.5 km/s. Of the estimated 17,000 total near-Earth asteroids larger than 1 km, roughly 4% are metallic. Of those, only about 10 are also projected to have suitable orbits and velocities. A speciﬁc target list has not yet been compiled, and this will require a suitably sensitive remote spectrograph with enough resolution. Proposed targets would be sampled with probes that would photograph them and identify suitable landing places for sample return missions. One concern is that there are no regulations regarding this industry, although the UN oversees the Outer Space Treaty that has been signed by 106 countries. A new Wild West situation could easily develop. The prospect of mining is attracting scientiﬁc attention and venture capitalist funds, such as UK’s Asteroid Mining Corporation.

James Lattimer AST 301, Catastrophe Lecture Many Solar System Objects May Have Had Catastrophes

I Mercury - Several scenarios involving impacts to explain it’s extremely high iron abundance and retention of volatiles.

I Venus - Merger of two proto-planetary bodies could explain it’s lack of angular momentum and a moon.

I Moon - Collision of Earth with Mars-sized object could explain moon’s formation, it’s hemispheric dichotomy, it’s lack of volatiles and other chemical features.

I Mars - Martian hemispheric dichotomy could be explained by an asteroidal impact that melted half it’s surface.

I Saturn - Rings formed by a shredded moon or comet in the last 10 to 100 million years explains their very low mass.

I Mimas - Large impact that created Herschel crater all but shattered it and formed shock-related features on it’s far side.

I Uranus - Impact with twice-Earth-massed object could have knocked it on it’s side and tilted it’s magnetic axis, and created heat-trapping layer that keeps it’s atmosphere cold, while not changing it’s orbit and regular moon system.

James Lattimer AST 301, Catastrophe Lecture Mercury

Mercury is anomalous because it is estimated to be 65% iron, compared to the Earth’s 32% and similarly low iron fractions in Venus and Mars. How does one explain the loss of Mercury’s mantle while retaining substantial amounts of volatiles, signiﬁcantly more than the moon? A giant impact has often been proposed, but this fails to explain the retention of volatiles. Another theory is that Mercury suﬀered a series of ’hit-and-run’ glancing collisions with a larger planet (proto-Venus or proto-Earth), which would strip away the mantle without an intense shock that would obliterate volatiles. SImulations indicate there were once about 20 original bodies that eventually accreted into the observed planets. In this scenario, Mars and Mercury were lucky to have survived, while the others eventually accumulated into Venus and Earth. Mars missed most collisions, being further out, but Mercury did not. There should be asteroids and meteorites from these glancing impacts. The absence of a mantle-stripped meteorite population with shock features supports the hypothesis they accreted into Venus and Earth.

James Lattimer AST 301, Catastrophe Lecture Venus

Venus has the same mass, radius, and gross chemical composition as the Earth, but lacks water, is hot enough to melt lead, has an extremely thick atmosphere, and spins backwards. One explanation is that two proto-planetary bodies collided and merged to form Venus. This led to the loss of volatile materials like water and slowed the spin. 40Ar, produced by the decay of 40K, is lacking, indicating it has not yet vented into the atmosphere. Early water loss prevents plate tectonics, so water and Ar do not outgas. However, deuterium (D) is 150 times as abundant as on Earth. This can be explained by water’s photo-dissociation by sunlight and preferential escape of higher- velocity H relative to D. If 90% of the D has been lost, about 99.9% of the H (and therefore water) has been lost. Loss of water doesn’t imply an impact. A head-on impact would have destroyed angular momentum and made a moon’s formation from debris all but impossible.

James Lattimer AST 301, Catastrophe Lecture Moon

Thought to have formed from the collision of a hypothesized protoplanet, Theia (mother of Selene), with Earth 4.4 Gyrs ago at moderate velocity (4 km/s) and a steep impact angle to explain mixing deduced from lunar O isotope analysis. Theia’s iron core settled into the Earth’s core, and most of its mantle mixed with the Earth’s mantle. A substantial mass from both mantles was ejected into Earth’s orbit, which coalesced into the moon near the Earth’s Roche limit.

The orbits would be coplanar, and the Earth would gain angular momentum, rotating every 5 hours. Models suggest a second moon of diameter 1000 km formed at a Lagrange point, but tidal eﬀects would destabiize it’s orbit. It eventually pancake-collides with the far side of the moon. This explains the moon’s dichotomy: the near side has a thinner crust with maria as opposed to the far side.

James Lattimer AST 301, Catastrophe Lecture Mars

Mars may have once been hit by a giant asteroid that resulted in melting of half the planet’s surface. This could explain the Martian hemispheric dichotomy: the drop in surface elevation and crustal thickness near Mars’ equator. The northern hemisphere is 5.5 km lower with a crust 26 km thinner, on average, than the southern hemisphere. Simulations predict a 4000 km body impacted near the south pole 4.5 Gyrs ago. A magma ocean would cover the southern hemisphere. After solidifying would result in a thicker crust and higher elevation. Also explains why there are more volcanoes in southern Mars Orbiter Laser hemisphere. Altimeter, NASA James Lattimer AST 301, Catastrophe Lecture Saturn Cassini measured gravitational field of Saturn and it’s rings by turning off thrusters during portions of it’s final five orbits that took it between Saturn and it’s innermost rings. Measured Saturn’s rings to have a total mass of 1.5 · 1021 g, or 1/4700 times the moon’s mass. Also measured amounts of dust falling into rings. Combined, these measurements mean that the age of the rings is between 10 and 100 Myrs, much younger than Saturn itself.

James Lattimer AST 301, Catastrophe Lecture Mimas Mimas clears the material from the Cassini Division, the gap between Saturn’s two widest rings, because the gap is in a 2:1 orbital resonance. Impact that produced the Herschel crater almost shattered Mimas; an equivalently-sized crater on the Earth would be as wide as the U.S. Shock waves formed features at it’s anti-podal point.

James Lattimer AST 301, Catastrophe Lecture Uranus

I An impact with a twice Earth-massed object could have knocked Uranus on it’s side and tilted it’s magnetic axis 60◦ from it’s rotation axis about 4 Gyrs ago.

I However, Uranus has an almost circular orbit and a regular moon system.

I Impact would have been grazing, allowing retention of atmosphere.

I Debris formed a thin shell in interior, trapping heat and explaining why the atmosphere is colder than expected.

I Debris could also have formed some of Uranus’ 27 moons and altered the orbits of already-existing moons.

I Molten ice and rock lumps inside the planet could have tilted its magnetic ﬁeld.

James Lattimer AST 301, Catastrophe Lecture Worlds in Collision?

I The star BD+20 307 in the constellation Aries has been found to have about a million times as much dust as is orbiting our sun using Chandra X-ray data (Zuckerman, Henry and Muno).

I Weinberger found BD+20 307 to be a 3.42-day close binary.

I Fekel and Williamson determined the stars’ chemical composition using spectroscopy and dated the stellar system to be several Gyrs.

I Dust indicates the presence of planets: this would be the ﬁrst known case of planets in a close binary system.

I Dust should have been swept out by stellar radiation billions of years ago: therefore, it has recently appeared (last few hundred thousand years at most). There must have been a planetary collision.

James Lattimer AST 301, Catastrophe Lecture Worlds in Collision • Best selling book (1950) by Immanuel Velikovsky describes celestial wars among planets in historical times. Around 1500 BC a comet (Venus) was ejected from Jupiter and passed near the Earth, changed its orbit and axis, and caused innumerable catastrophes, explaining many mythologies and religious documents. 52 years later, another encounter stopped the Earth’s rotation and caused more catastrophes. Finally, by 700 BC, it dislodged Mars from its orbit which passed close to the Earth and causes a whole new set of catastrophes. Venus must still be hot as it’s young, and rich in hydrocarbons with an abnormal orbit. ••He stated Jupiter emits radio noises, Earth’s magneto- sphere reaches to the moon, Sun has an electrostatic potential of 1019 V, and Earth’s rotation affected by fields. • The theory is summarily rejected by scientists. Simply, it violates Newtonian mechanics. Sagan pointed out it was already known Venus has a large greenhouse effect due to its thick CO2 atmosphere. Also, the moon’s orbit is extremely stable; the Jewish calendar is based on the lunar month and hasn’t changed in 5800 years! Ice core studies rule out the possibility of large-scale catastrophes during the last 10,000 years. Finally, Cecilia Payne- Gaposhkin disputes Velikovsky’s versions of mythologies. James Lattimer AST 301, Catastrophe Lecture James Lattimer AST 301, Catastrophe Lecture Are Impacts Periodic?

I Many publications suggest a likely impact periodicity of about 26 ± 2 Myr. I A simple exercise is to take the 50 or so dated impacts on the Earth in the last 250 million years and run a periodicity study. I Assume a model of impact rate N˙ = y[1 + sin(ωt + θ)]. I ω = 2π/P where P is the period. θ is the phase. R T ˙ I Determine the amplitude y by requiring 0 Ndt = N, where N is the number of craters in the study and T = 250 Myr is the duration. h i−1 y = N T + ω−1(cos(θ) − cos(ωT + θ))

I Bin the cratering data: M bins of time width ∆, the ith bin has Hi craters. R ti I The model is that the number of impacts in bin i is Mi = Ndt˙ . ti−1 h −1 i Mi = y ∆ + ω (cos(ωti−1 + θ) − cos(ωti + θ))

2 P 2 I For fixed bin size ∆, minimize χ = i (Mi − Hi ) /(M − 2) with respect to ω and θ, where M = T /∆ is the number of bins. 2 I To be significant, the minimum value of χ should be smaller than 1, the difference between the maximum and minimum values of χ2 should be much larger than 1, and the determined period should not be very sensitive to ∆.

James Lattimer AST 301, Catastrophe Lecture Cratering Data

James Lattimer AST 301, Catastrophe Lecture Computational Results

James Lattimer AST 301, Catastrophe Lecture Planetary Migration

James Lattimer AST 301, Catastrophe Lecture James Lattimer AST 301, Catastrophe Lecture The Late Permian Extinction

Magnetism reveals world-wide glaciations have occurred.

James Lattimer AST 301, Catastrophe Lecture The Late Permian Extinction

Oxygen generated by aerobic photosynthesis eliminated methane and initiated global cooling.

James Lattimer AST 301, Catastrophe Lecture