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Comets: The Rosetta Stone of the Solar System�

Bob Gehrz

Minnesota Institute for Astrophysics, University of Minnesota

RDG

3/22/2022

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Outline

Why comets are the Rosetta Stone of the Solar System
Contents of the Solar System – planets and debris fields
Comets’ role in formation and evolution of the solar system
What have we learned about the composition of comets
Comet and asteroid debris as a threat to the Earth – Giant

Impacts

Discussion and Q & A

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

3 of 44

Why comets are the Rosetta Stone of the Solar System

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

4 of 44

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3/22/2022

What is the Rosetta Stone?

The Rosetta Stone is part of a larger stone slab inscribed with a 196 BC royal decree in three languages — Egyptian hieroglyphics, Egyptian Demotic, and Greek

The Rosetta Stone was the key to cracking the ancient Egyptian hieroglyphic code

It is in the British Museum in London

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

5 of 44

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Why are Comets Called the Rosetta Stone of the Solar system?

The term 'Rosetta Stone' is now used figuratively for

a thing that provides clues to understanding

something that would otherwise be undecipherable

Astrophysicists believe the chemicals and minerals

that were present in the primitive solar system were

frozen into comet nuclei 4.7 billion years ago and that

understanding composition and structure of comets

is the key to understanding the origins of the solar

system and, perhaps, life on Earth

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Contents of the Solar System – planets and debris fields

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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The Terrestrial and Jovian Planets

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Properties of Impact Craters: Copernicus

Central uplift

Radial Rays

Shock waves

around the Rim

Secondary

Cratering

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

9 of 44

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Debris Fields: the Asteroid Belt; Meteorites

Rocky composition
Formed by accretion and impacts

243 Ida

Meteorite

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Debris Fields: the Kuiper Belt

Dwarf planets (Pluto is the prototype)
Short period comets (Halley, 76 years)
Bits of rock and ice

Flat distribution
Prograde rotation
In situ belt

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Debris Fields: The Oort Cloud

Spherical cloud of icy planetesimals surrounding the Sun at distances ranging from 2,000 to 200,000 AU (0.3 to 3.2 light years).
Scattered by gravitational interactions with the giant planets
Source of long period comets that come from all directions

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

12 of 44

Theory of the formation and evolution of the solar system

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Formation and Evolution of the Solar System

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Comet Nuclei: The building blocks of the Planets

Tempel 1 as seen by Deep Impact

P/Halley as seen by Giotto from 370 miles

Average density

of a comet nucleus

is 0.5 gm cm^-3

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

15 of 44

Comet NEOWISE

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3/22/2022

Ices and solids are

ablated from the

nucleus by solar

heating during

perihelion passage

to form the tails

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

16 of 44

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Comet Ion, Dust, and Anti Tails

Comet Encke trail (Gehrz

et al. 2006, AdvSpR, 38, 2031)

Comet NEOWISE 2020

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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What have we learned about the make-up of comets

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

18 of 44

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Infrared Spectroscopy of Comets at O’Brien Observatory

Data from Gehrz & Ney 1992, Icarus, 100, 162

Reflected solar radiation dominates the spectrum at short wavelengths

Thermal emission by dust grains that reradiate absorbed solar energy dominates the thermal infrared spectrum

The grains are composed of carbon and silicates and are the building blocks of planets

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

19 of 44

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Dust Grains in Comets

Both Comet dust and nova dust contain silicates and carbon

Comet dust grains are the size of the grains produced in

nova explosions

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Infrared Studies of Comets Provide Insight into Protoplanetary Disk Environments

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3/22/2022

50 microns

Solar System Comet

Disk System

The mineral composition of dust in proto-planetary disk systems is similar to that of the small grains released from comet nuclei
Some comet grains are crystalline due to high temperature processing in the inner disk

Some interplanetary

dust particles (IDP’s)

released from comets

are stardust

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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R. D. Gehrz

Comet Grains Formed in a Neon Nova Explosion

1985: R. D. Gehrz et al. (ApJ. 298, 147) discover a new type of nova explosion that produces copious amounts of neon (a neon nova)

Interplanetary dust particles collected by a high-flying NASA U2 as the Earth passed through the dust trails of trails comets showed a Neon isotope ratio consistent with their production in a neon nova explosion. (Data from Pepin, Palma, Gehrz, & Starrfield 2011, ApJ, 742, 86)

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

22 of 44

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Deep Impact Experiment on Comet Wild I

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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The chemistry of disks with radius and Age

High spatial and spectral

resolution can determine

where different species

reside in the disk

Small radii produce

double-peaked, wider lines.

Observing

many disks

at different

ages will trace

disk chemical

evolution

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

24 of 44

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3/22/2022

Where Cometary Water-Ice formed in the Solar Nebula

Water H₂O ortho/para (parallel/antiparallel) hydrogen spin isomer ratio gives the water-ice formation temperature; a similar analysis can done on ortho/para/meta spin isomers of CH₄

Woodward, Kelley, Bockelée-Morvan,

& Gehrz 2007, ApJ, 671, 1065

Bonev et al. 2007, ApJ, 661, L97

C/2003 K4

Spitzer

Theory

Uranus

Neptune

200 AU

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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The NASA Stardust Mission (1999 + 6)

Collected dust samples from

the coma of comet Wild 2 and

returned them to Earth for

analysis

Crystalline minerals showed

that grains formed at very

high-temperatures in the inner

Solar System were transferred

out to the Kuiper Belt

Grains contained the amino acid glycine, a fundamental

chemical building block of life

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

26 of 44

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ESA Rosetta: Organic Material in Comets

Rosetta was a space probe built by the European Space Agency (ESA) launched on 2 March 2004 to perform a detailed study of comet 67P/Churyumov–Gerasimenko (67P)

Rosetta mission found that organic matter made up 40% (by mass) of the nucleus of the comet

Organic compounds, combining carbon, hydrogen, nitrogen, and oxygen, are building blocks of life on Earth

These organic molecules were produced in interstellar space, well before the formation of the Solar System

Did comet nuclei seed life on Earth and on exoplanets in other stellar systems in the Galaxy?

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

27 of 44

Comet and asteroid debris as a threat to the Earth – Giant Impacts

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

28 of 44

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3/22/2022

Meteor Showers from Comet Debris

Perseids: Swift-Tuttle, August 12

Leonids: Tempel-Tuttle, November 17

Taurids: Encke, November 12

Eta Aquariids Halley, May 6

The Perseids

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

29 of 44

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Giant Impacts from Comet and Asteroid Debris

Diameter = 0.5 miles
Crater 5.0miles
Period = 2 years
Closest approach to Earth = 300,000 miles

Hermes, a rocky

Earth-crossing asteroid

Canyon Diablo (3900 ft

diamter crater)

Chicxulub (110 mile

Diameter crater)

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

30 of 44

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How we Know about Giant Impacts:

World-wide layers of Iridium and Soot

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Rate of Giant Near Earth Object (NEO) Impacts

Megatons of TNT

Diameter of Meteor or Comet Nucleus (Meters)

Time

Between

Impacts

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Congress has Mandated a Near Earth Object (NEO) Search

2005 George E. Brown, Jr. NEO Survey Act (Public Law No. 109-155) signed into law by President Bush on December 30, 2005

Detect, track, catalog, and characterize the physical characteristics of 90% of potential hazardous asteroids equal to or larger than 140 meters (460 feet) in diameter that come within 1.3 astronomical units (AU) or less from the Sun at closest approach

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Detecting Dangerous NEOs with the Vera Rubin Observatory

Cerro Pachón Ridge in north-central Chile.

8.4-meter (331-inch) Survey Telescope

3200-megapixel camera

Surveys the entire sky in three nights

Detects 460 foot diameter NEOs objects as far away as the asteroid belt

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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The NASA NEOWISE Mission

Near Earth Orbit (NEO) Wide-field Infrared Survey Explorer (WISE)

The NEOWISE mission uses a space telescope to hunt for asteroids and comets, including those that could pose a threat to Earth

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

35 of 44

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Dangerous NEOs that are being tracked

Apophis: Diameter = 0.1 miles,

1 mile wide crater

Bennu: Diameter = 0.3 miles

3 mile wide crater

1950 DA: Diameter = 0.8 miles

80 mile wide crater

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

36 of 44

RDG

3/22/2022

$1 Billion

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

37 of 44

RDG

3/22/2022

A web-based interactive tool produced in collaboration with the Aerospace Corporation at

Provides insight into the problem of deflecting an Earth threatening asteroid using a Kinetic Impactor (KI) mission.

App can answer such questions as:

What are the best times to deflect the asteroid?
How much velocity change is required to make the asteroid miss the Earth?
When could an impactor spacecraft be launched in order to intercept the asteroid?
What is the maximum size of asteroid that can be deflected with a single launch?
In which direction will the asteroid be deflected most easily?

https://cneos.jpl.nasa.gov/nda/

The NASA/JPL NEO Deflection App (NDA)

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

38 of 44

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Future Missions to Watch

NASA’s DART mission (Double Asteroid Redirect Test)

launched SpaceX Falcon 9 rocket. DART is NASA’s first

planetary defense test mission and will fire a kinetic

impactor into the asteroid Didymos B (Launched 11/24/21)

NASA NEO Surveyor Mission will launch in 2026

NASA recently down-selected the comet surface sample return

mission CAESAR (Comet Astrobiology Exploration Sample

Return) that would have returned solids only.

NASA now contemplating a cryogenic mission to return

ices as well as solids

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

39 of 44

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James Webb Space Telescope (JWST)

Bob Gehrz and Dave Chaney (Ball Aerospace) stand in front of JWST during a pre-flight technical review at Goddard Space Flight Center in 2018

JWST deployed

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

40 of 44

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The NASA Planetary Defense Coordination Office (PDCO)

https://www.nasa.gov/planetarydefense/faq

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

41 of 44

The End

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3/22/2022

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

42 of 44

Backup

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3/22/2022

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

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Origin of the Oort Cloud

https://video.search.yahoo.com/yhs/search;_ylt=AwrDQrby2QpiLswAhzEPxQt.;_ylu=Y29sbwNiZjEEcG9zAzEEdnRpZAMEc2VjA3BpdnM-?p=how+the+oort+cloud+was+formed&vm=r&type=dkff_9318_FFW_ZZ&hsimp=yhs-3&hspart=iba&grd=1&ei=UTF-8&fr=yhs-iba-3#id=1&vid=57f4116ca05d7ec7fd79a79626b6c3aa&action=view

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota

44 of 44

Origin of the Rosetta Stone

The Rosetta Stone decree was issued in Memphis, Egypt, in 196 BC during the Ptolemaic dynasty on behalf of King Ptolemy V Epiphanes. Late survivals of hieroglyphic use are found well into the Roman period, extending into the 4th century AD. With the final closing of pagan temples in the 5th century, knowledge of hieroglyphic writing was lost. Although attempts were made, the script remained undeciphered throughout the Middle Ages and the early modern period.

RDG

3/22/2022

Comets: the Rosetta Stone of the Solar System

Public Lecture, St. Paul, MN, Tuesday, March 22, 2022

Minnesota Institute for Astrophysics

University of

Minnesota