1

Lecture 13

Dwarf Planets and Solar

System Debris

October 17, 2018

2

Pluto -- Basic

Information

• Discovered by Clyde

Tombaugh in 1930

• Period: Porb = 248 years

• Distance: a = 39.5 AU

• 3 moons (Charon, Nix, Hydra)

• Demoted to Dwarf Planet in 2006

3

General Characteristics

• Mass = 0.0025 times the Earth

– Determined by using General form of Kepler’s 3rd Law

• Radius = 0.2 Earth

– Determined from eclipses of Charon, then by New Horizons

• = 2300 kg/m3

made primarily of ice and rock

• Little was known due to its large distance

• Pluto is tilted on its side.

4

A portrait from the final approach. Pluto and Charon display

striking color and brightness contrast in this composite image

from July 11, showing high-resolution black-and-white

LORRI images colorized with Ralph data collected from the

last rotation of Pluto. Color data being returned by the

spacecraft now will update these images, bringing color

contrast into sharper focus.

Credits: NASA-JHUAPL-SWRI

Charon Pluto

1208 km diameter 2370 km diameter

(Earth’s Moon: 3474 km)

5

Spin and Orbit

• Highly elliptical orbit (e = 0.25)

– Pluto is sometimes closer to the Sun than Neptune

– Orbit is tipped 17° from ecliptic

– Aphelion = 49.3 AU

– Perihelion = 29.7 AU

• Both Pluto and Charon are tidally locked in synchronous rotation.

– Pspin= 6.4 days (Pluto and Charon)

– Porb = 6.4 days (Charon)

6

Surface Properties

• Predominantly water ice

• Frozen methane detected on surface

• May have thin methane atmosphere

Has a surprisingly thick, layered nitrogen

and methane atmosphere… though it is

likely seasonal

• Similar in some respects to Triton

Surface Features – Hubble Space Telescope

Pluto had never been visited by a spacecraft (until the New Horizons probe arrived in

2015) so there were no clear images of its surface. At left are Hubble Space Telescope

global maps of Pluto (smaller insets are actual images) that show bright and dark areas

visible as the dwarf planet rotates. At right is a composite image in true color that is

derived from eclipses by Charon.

7

Pluto’s surface8

Four images from New Horizons’ Long Range Reconnaissance Imager (LORRI) were combined with color data from the

Ralph instrument to create this sharper global view of Pluto. (The lower right edge of Pluto in this view currently lacks high-

resolution color coverage.) The images, taken when the spacecraft was 280,000 miles (450,000 kilometers) away from Pluto,

show features as small as 1.4 miles (2.2 kilometers). That’s twice the resolution of the single-image view captured on July 13

and revealed at the approximate time of New Horizons’ July 14 closest approach.

Pluto’s surface9

This high-resolution image captured by NASA’s New Horizons spacecraft combines blue, red and infrared images

taken by the Ralph/Multispectral Visual Imaging Camera (MVIC). The bright expanse is the western lobe of the

“heart,” informally called Sputnik Planum, which has been found to be rich in nitrogen, carbon monoxide and

methane ices. Credits: NASA/JHUAPL/SwRI

Pluto’s surface10

New close-up images of a region near Pluto’s equator reveal a giant surprise: a range of youthful mountains rising as high as

11,000 feet (3,500 meters) above the surface of the icy body. Although methane and nitrogen ice covers much of the surface

of Pluto, these materials are not strong enough to build the mountains. Instead, a stiffer material, most likely water-ice,

created the peaks. The close-up image was taken about 1.5 hours before New Horizons closest approach to Pluto, when the

craft was 47,800 miles (77,000 kilometers) from the surface of the planet. The image easily resolves structures smaller than a

mile across. Image Credit: NASA-JHUAPL-SwRI

Pluto’s surface11

In this extended color image of Pluto taken by NASA’s New Horizons spacecraft, rounded and bizarrely textured

mountains, informally named the Tartarus Dorsa, rise up along Pluto’s day-night terminator and show intricate but

puzzling patterns of blue-gray ridges and reddish material in between. This view, roughly 330 miles (530

kilometers) across, combines blue, red and infrared images taken by the Ralph/Multispectral Visual Imaging

Camera (MVIC) on July 14, 2015, and resolves details and colors on scales as small as 0.8 miles (1.3 km).

Pluto’s surface12

This image from the heart of Pluto’s heart feature shows the plains’ enigmatic cellular pattern (at left) as well as unusual

clusters of small pits and troughs (from lower left to upper right). This image was taken by the Long Range

Reconnaissance Imager (LORRI) on NASA's New Horizons spacecraft shortly before closest approach to Pluto on July

14, 2015; it resolves details as small as 270 yards (250 meters). The scene shown is about 130 miles (210 kilometers)

across. The sun illuminates the scene from the left, and north is to the upper left. Credits: NASA/JHUAPL/SwRI

Pluto’s atmosphere13

Pluto's haze layer shows its blue color in this picture taken by the New Horizons Ralph/Multispectral Visible Imaging

Camera (MVIC). The high-altitude haze is thought to be similar in nature to that seen at Saturn’s moon Titan. The source of

both hazes likely involves sunlight-initiated chemical reactions of nitrogen and methane, leading to relatively small, soot-like

particles (called tholins) that grow as they settle toward the surface. This image was generated by software that combines

information from blue, red and near-infrared images to replicate the color a human eye would perceive as closely as possible.

Charon’s surface14

Charon in Enhanced Color NASA's New Horizons captured this high-resolution enhanced color view of Charon

just before closest approach on July 14, 2015. The image combines blue, red and infrared images taken by the

spacecraft’s Ralph/Multispectral Visual Imaging Camera (MVIC); the colors are processed to best highlight the

variation of surface properties across Charon. Charon’s color palette is not as diverse as Pluto’s; most striking is

the reddish north (top) polar region, informally named Mordor Macula. Charon is 754 miles (1,214 kilometers)

across; this image resolves details as small as 1.8 miles (2.9 kilometers). Credits: NASA/JHUAPL/SwRI

If Pluto is sometimes closer to the Sun than

Neptune, why doesn’t it ever collide with

Neptune?

15

A. They do collide every few thousand years.

B. Neptune is primarily made of gases, so Pluto

would pass right through it.

C. Pluto’s orbit is steeply tilted with respect to

Neptune’s, so they never actually cross.

D. The synchronized timing of their orbit periods

ensures a collision never occurs.

16

Origins of Pluto• Composition much more

like a moon

• Other objects similar to

Pluto (such as Sedna,

below) are being found in

the Kuiper Belt

http://photojournal.jpl.nasa.gov/catalog/PIA05568

http://photojournal.jpl.nasa.gov/catalog/PIA05567

17

Comparison of distant planets

Object Year

discovered

Diameter

(km)

Perhelion

(AU)

Aphelion

(AU)

Pluto 1930 2380 29.7 49.3

Eris 2005 2326 37.9 97.7

Haumea 2004 1632 35.0 51.5

2007 OR10 2007 1535 33.1 101

Makemake 2005 1430 38.6 52.8

Quaoar 2002 1110 41.9 44.9

Kuiper Belt Objects18

Updated art

from Wikimedia28 April 2017

If you were standing on Pluto, and Charon was on

your meridian, how would it move in the sky over

time?

A. It would move slowly west.

B. It would move slowly east.

C. It would move slowly north

along the meridian.

D. It wouldn’t move at all.

19

Solar System Debris

• After formation of the Solar System, some

material was left over.

• Asteroids, comets, and meteoroids give

clues to composition of early solar system.

– Have undergone little processing (heating,

weathering).

20

21

Comets• Made of ices and some rocky material

• Travel in very elliptical orbits about the Sun.

Comet

McNaught,

January

2007. Click

on image for

more info.

• Long period comets

– May orbit once every

million years

– Origin in Oort Cloud --

spherical cloud up to

100,000 AU from Sun

22

• Short period comets

– Periods < 200 years

– Origin in Kuiper Belt --

disk shape 30-100 AU

from Sun.

Anatomy of a Comet

• Nucleus

– few km in diameter

– ices and rocky material (“dirty ice ball”)

– Only part of a comet that

exists away from the

Sun.

• Coma -- Gases

evaporated off of

surface of nucleus as

Sun heats it.

23

Tails -- Always point away from the Sun

– Dust tail -- small dust particles, slightly curved in

direction of orbit.

– Ion tail -- ionized molecules pushed straight back

by solar wind

24

25

ion (plasma) tail

points away from Sun

curved dust tail

Comet NEAT

26

Halley’s Comet

•Nucleus almost

completely dark

•Period: 76 years

•Next Visit: 2061

27

Halley’s Comet

28

Comet Shoemaker-Levy 9

•Comet struck Jupiter in

July 1994

•Original comet ~2-10

km in diameter

•Before impact it broke

into many small pieces

29

Comet Tempel 1 – Deep Impact

http://www.nasa.gov/mission_pages/deepimpact/multimedia/HRI-937.html

30

Comet Tempel 1

• Deep Impact revealed the composition of the

comet Tempel 1

• Some of the expected constituents: silicates

(sand), water ice

• …and some surprises:

– Clay, and carbonates (how did these form without

liquid water?)

– iron compounds

– aromatic hydrocarbons

31

Comet 67P/Churyumov–Gerasimenko• Short period comet (P = 6.45 y) discovered in 1969

• 4.3 km × 4.1 km about the size of Stevens Point

• Rosetta spacecraft orbiting the comet since September 10, 2014

• Philae landed on November 12, 2014, but

it bounced and landed oddly, lost contact

with Rosetta

32

This animation consists of 86 images

acquired by Rosetta  ' s NavCam as it

approached 67P in August 2014.

Mosaic of four images taken by Rosetta's

navigation camera (NAVCAM) on 19 Sept

2014 at 28.6 km (17.8 mi) from the center

of comet 67P/Churyumov–Gerasimenko.

Philae lander lost!33

Philae's final landing site, estimated by CONSERT.

Credits: ESA/Rosetta/Philae/CONSERT

OSIRIS image of the Philae lander, as it descended toward,

and then bounced off, the surface of Comet 67P during

touchdown on 12 November 2014 Credit: ESA/Rosetta/MPS for

OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

The first image from the surface of

Comet 67P, by the CIVA camera.

One of the lander's three feet can be

seen in the foreground. The image

is a two-image mosaic. Credit: ESA/Rosetta/Philae/CIVA

Philae lander found! (Sept 2016)

34

Surface of Comet 67P35

Rosetta’s lander Philae is safely on the surface of Comet 67P/Churyumov-Gerasimenko, as these first two CIVA images

confirm. One of the lander’s three feet can be seen in the foreground. The image is a two-image mosaic.

Comet 46P/WirtanenAstronomers are calling Comet 46P/Wirtanen the "comet of the year." On December 16,

2018 the kilometer-wide ball of dirty ice will come within 11.5 million km of Earth,

making it one of the 10 closest-approaching comets of the Space Age. Comet

46P/Wirtanen will probably become a naked eye object for several weeks during the

holidays. (Spaceweather.com)

36

Yasushi Aoshima of Ishikawa, Japan, took this picture 10/07/18 using a 12-inch telescope. It

shows the comet's green atmosphere which is, impressively, almost twice as wide as the planet

Jupiter. The green color comes from diatomic carbon (C2)--a gaseous substance common in

comet atmospheres that glows green in the near-vacuum of space.

Astronomers think that most short-period

comets come from

37

A. the Oort Cloud.

B. the Kuiper Belt.

C. condensation of gas in the Sun’s hot

outer atmosphere.

D. material ejected by volcanic eruptions on

the moons of the outer planets.

The ionized gas tail of a comet is always aligned with

A. the ecliptic plane.

B. the comet’s direction of

motion.

C. the line between the

comet and the Sun.

D. the gravitational field of

the nearest planet.

38

39

Asteroids

• Bodies of rock (some iron)

• Irregular shape

• Typically 0.1 - 600 km

• Total number of visible asteroids may be

100,000.

• Detected by movement with respect to stars.

• Average distance between asteroids

~1,000,000 km

Path of Asteroid

40

Orbits of Asteroids

• Most orbit Sun in Asteroid Belt between

Mars and Jupiter

• Debris that was not able to form a planet

due to pull from Jupiter.

• Apollo Asteroids

– high orbital eccentricities.

– Cross the orbit of the Earth

43

44

A diagram showing the Apollo asteroids,

compared to the orbits of the terrestrial

planets Mercury(H), Venus(V), Earth(E)

and Mars (M). As of 2015, the Apollo

asteroid group includes a total of 6,923

known objects of which 991 are numbered

(JPL SBDB)

Apollo asteroids

Gaspra -- Galileo Image

Size: 19 x

12 x 11 km

45

243 Ida and Dactyl -- Galileo Image

Size: 58 x 23 km

46

Size: 1.4 km

Eros -- NEAR Image

Size: 33 x 13 km

47

Hayabusa mission48

Hayabusa 2 was launched 3 Dec 2014 and will arrive at asteroid 162173 Ryugu in July 2018

• First ever successful landing on an asteroid

• Launched 2 May 2003

• Landed on asteroid Itokawa 19 November 2005

• Returned sample of asteroid dust 13 June 2010

• Analysis of results published 26 August 2011 issue of Science

Mission web site

Asteroid 25143 Itokawa

Hayabusa 2

49

(Image credit) The very first photograph taken from a surface-operational

spacecraft on an asteroid, taken by the Japan Aerospace Exploration

Agency (JAXA) MINERVA-II-1 Rover-1A, one of three landing components

of the Hayabusa2 asteroid orbital reconnaissance and sample return mission

to 162173 Ryugu. The photograph was taken during the spacecraft's first

"hop", following its successful landing minutes earlier.

Image credit: JAXA

• Orbiting asteroid 162173 Ryugu

(arrived 27 June 2018)

• Four rovers that can “hop”

• Planned to depart asteroid in

December 2019 and return

samples to Earth December 2020

The group of asteroids that cross the Earth’s orbit are

A. The Apollo asteroids

B. The Trojan asteroids

C. The trans-neptunian

asteroids

D. The Kirkwood asteroids

50

Meteoroids

• Meteoroids -- small debris in space, usually

< 100 m in diameter

• Meteor -- meteoroid falling through Earth’s

atmosphere.

– Friction with air causes it to heat and burn up.

– Seen as “shooting star”

– Most burn completely, only largest make it to

the Earth

• Meteorite -- meteoroid that makes it to the

surface of the Earth.

51

Meteor Showers

• Some cometary

orbits cross orbit of

the Earth.

• When they break up

they leave debris in

orbit.

• Earth passes through

debris, many

meteors are seen.

52

Meteor Shower53

ShowerDate of Maximum

intensity

Typical

hourly rateConstellation

Quadrantids January 3 40 Boötes

Lyrids April 22 15 Lyra

Eta Aquarids May 4 20 Aquarius

Delta Aquarids July 30 20 Aquarius

Perseids August 12 80 Perseus

Orionids October 21 20 Orion

Taurids November 4 15 Taurus

Leonids November 16 15 Leo Major

Geminids December 13 50 Gemini

Ursids December 22 15 Ursa Major

Meteor Showers

54

Meteorites

Iron Stony-Iron

Stony

55

Earth Impacts

• Earth is continually being bombarded.

Barringer Meteor Crater, Arizona

Diameter: 1.2 km

Age: ~50,000 years

56

Tunguska Event -- Siberia (1908)

• Asteroid

destroyed in

atmosphere.

• Leveled trees

for over 20 km

from

explosion.

57

Chelyabinsk MeteorFebruary 15, 2013

58

The impacting asteroid started to brighten up in the general direction of

the Pegasus constellation, close to the East horizon where the Sun was starting to

rise. The impactor belonged to the Apollo group of near-Earth asteroids.

The asteroid had an approximate size of 18 metres (59 ft) and a mass of about 9,100

tonnes (10,000 short tons) before it entered the denser parts of Earth's atmosphere

and started to ablate. At an altitude of about 23.3 km (14.5 miles) the body

exploded in anair burst. Meteorite fragments of the body landed on the ground.

Chicxulub Crater -- Yucatan

Peninsula, Mexico

Diameter ~170 km

Chicxulub

• Dinosaurs -- possibly destroyed by asteroid

impact ~65 million years ago

– Alvarez & Alvarez found iridium rich layer of

clay

59

Risks of ImpactDiameter

20m 200m 2km

60

© The New Yorker Collection 1998 Frank Cotham from cartoonbank.com. All Rights Reserved

61