Chapters 14 and 15 - More Solar System Stuff With Doctor Bones aka Don R. Mueller, Ph.D.

1. Astonishing Astronomy 101
With Doctor Bones (Don R. Mueller, Ph.D.)
Educator
Entertainer
J
U
G
G
L
E
R
Scientist
Science
Explorer

2. Chapters 14 & 15
More Solar System Stuff

3. • In 1930, Pluto was discovered
and classified as a planet.
• Is Pluto a planet? The debate:
A planet must be massive enough:
(1) for its gravity to pull it into a roughly
spherical shape, and
(2) for it to have cleared out the
neighborhood of its orbit of
comparable mass objects.
• This means that the objects
lying in both the asteroid and
Kuiper belts are not planets.
• Alas, in 2006, Pluto was
reclassified as a dwarf planet.
Pluto?
1930
versus
Pluto?
1930
Pluto’s Reclassification:
Will the “Real” Pluto please stand up.

4. Pluto and its largest moon, Charon would fit within the U.S.
Charon orbits Pluto at a steep angle to the ecliptic.
Pluto and its Moons
Pluto
Pluto’s moon:
Charon

5. Pluto and its Moons
Two new moons were discovered
in 2005, Nix and in 2006, Hydra.
Pluto is a mix of water ice, rock,
methane and frozen nitrogen.
When Pluto is within Neptune’s
orbit it has an atmosphere.
As Pluto moves further out into
the solar system, the atmosphere
snows out onto the surface.

6. Pluto’s orbit about the Sun is
tipped by ~ 17°. This is called
Pluto’s orbital inclination.
Pluto
Sun 17°

7. Trans-Neptunian Worlds
• More than 130 have been
discovered, one of them
is larger than Pluto: Eris
• Plutinos are bodies that
orbit the Sun at more or
less the same distance as
Pluto.
• Small icy bodies orbiting
the Sun past Neptune’s
orbit are called Trans-
Neptunian Objects or
TNOs.
Please insert figure 46.9
Eris

8. Large Trans-Neptunian Worlds
Name Diameter (km) Mass (kg) Semi-major
axis (AU)
Orbital
Eccentricity
Eris 2600 1.7 × 1022
67.8 0.44
Pluto 2310 1.3 × 1022
39.4 0.25
2005 FY9 ~1600 ? 45.8 0.16
Sedna ~1500 ? 526 0.85
Charon 1210 1.5 × 1021
39.4 ?
Quaoar ~1000 ? 43.6 0.038
Orcus ~950 7.5 × 1020
39.4 0.22

9. The Structure of Comets: Ice and Dust
• Comets have two
primary parts, the
head and the tail:
• The head consists
of the nucleus, a
lump of frozen gas
mixed with loose
rock and dust.
• Only about 10 km
across. Dark in
color, probably
from dust and
other materials. The tail can be hundreds of millions of km
long, streaming directly away from the Sun.

10. The comet’s “coma” is the cloud of evaporated ices and
gases streaming from the surface of the nucleus.

11. Visiting Comets
Comet Halley, visited
by Giotto
Comet Wild 2, visited
by Stardust

12. Comet Tempel 1, visited
by Deep Impact
5 min
90 sec
20 sec
4 sec
Just after impact

13. The Origin of Comets
• Comets may originate in either the Oort
Cloud or the Kuiper Belt:
• Oort cloud: comet-like planetesimals that are
more than 100,000 AU (100 K AU) from the
Sun.
• Oort cloud objects may have formed near the
giant planets; then tossed outwards by
gravity.
• Passing stars or other gravitational influences
nudge the comets into the inner Solar System.

14. Kuiper Belt
Oort Cloud
Comet Orbit
Orbit of Neptune
50 AU
100 K AU

15. The Kuiper Belt
Outside the orbit of
Neptune lies the
Kuiper Belt:
Located around 40
AU from the Sun:
Trans-Neptunian
Objects (TNOs)
such as Pluto are
found here.
Many bodies smaller
and larger than
Pluto are in this
region, including
Eris and others.
Asteroid Belt
Kuiper Belt

16. Asteroid Belt
Kuiper Belt
~ 3 AU
~ 80 AU

17. • The Solar System is
surrounded by a
cloud of comet-like
bodies:
• Located around 50,000
AU from the Sun.
• The gravitational forces
from passing stars
occasionally send
comets into the Solar
System.
Please insert figure 32.3
The Opik – Oort Cloud:
Ernst Julius Öpik (1893 –1985) was an Estonian astronomer.
Jan Hendrik Oort (1900 – 1992) was a Dutch astronomer.

18. How a comet becomes visible
As a comet is warmed by
the sun, ice on the
surface sublimates and
streams away from the
comet’s nucleus:
Sublimation is a solid-to-
gas phase change
Sublimated gases form
the comet’s coma.
Solar photons strike the
comet’s dust particles,
pushing them away via
a process known as
radiation pressure.
Solar photons strike the
comet’s dust particles
Solar photons : Sunlight
Sun
Dust

19. The Two Tails of a Comet: Dust tail & Ion tail
Dust tail
Ion tail

20. Another View of the Comet process

21. Meteor Showers
• As a comet orbits the
sun, it leaves a trail of
dust.
• The Earth can pass
through the dust trail.
• Dust particles enter
Earth’s atmosphere and
burn up. We see them
as a meteor shower.
• If interplanetary matter
survives its descent to
Earth and you can pick
it up, you are holding?
a) meteoroid
b) meteor
c) meteorite
Meteor Showers
Perseus
Toward
Perseus

22. The Heating of Meteors
• When a meteoroid travels
through the atmosphere, it
ionizes the air around it.
Vaporized material and gas
begin to glow. It’s a meteor.

23. Meteorites
• Most meteors burn up in the
atmosphere.
• Some meteors survive the
journey to the surface.
These are called meteorites.
Three kinds of meteorites:
(1) Iron (2) Stony
(3) Stony-iron
Stony meteorites (Chondrites)
• Carbonaceous chondrite
• Ordinary chondrite
• Achondrite
Please insert figure 48.3A

24. A Chondritic Meteorite
Please insert figure 48.3B

25. The Energy of Impacts
• Eventually, a large meteoroid (>10
meter) will strike the Earth.
• Energy released by the impact is:
• With mass m of the meteoroid
and V its impact velocity.
• For a 100 kg meteoroid traveling
at 30 km/s, the energy released is
equal to 10 tons of dynamite.
• This was a small meteoroid.
2
K mV
2
1
E 

26. Giant Meteor Craters
• Giant meteor craters can
be found on Earth.
• Barringer Crater:
– Meteor was 50 meters
in diameter.
– Crater is a mile across.
• Manicouagan Crater:
– Meteor was 5 km in
diameter.
– Crater is 73 km across.

27. Mass Extinction Events
• About 65 million
years ago, a 10 km-
wide meteoroid
impacted the Yucatan
Peninsula.
• This impact caused
massive climate
changes, leading to
the extinction of the
dinosaurs and other
forms of life.
• Iridium found in a
layer of soil all over
the world is the
“smoking gun.”
Yucatan

28. The Asteroid Belt: Most asteroids can be found between
the orbits of Mars and Jupiter.
Using Bode’s Rule : The asteroid Ceres was
found between the orbits of Jupiter and Mars.
Jupiter
Mars
Jupiter’s Orbit
Mars’ Orbit
Trojan Asteroids:
Share an orbit
with a planet.

29. Bode’s Rule for Planets: Also used for asteroids
Bode’s Rule Number Planet True Distance
(0 + 4)/10 = 0.4 Mercury 0.39
(3 + 4)/10 = 0.7 Venus 0.72
(6 + 4)/10 = 1.0 Earth 1.00
(12 + 4)/10 = 1.6 Mars 1. 52
(24 + 4)/10 = 2.8 Ceres (dwarf) 2.78
(48 + 4)/10 = 5.2 Jupiter 5.20
(96 + 4)/10 = 10.0 Saturn 9.58
(192 + 4)/10 = 19.6 Uranus 19.2
(384 + 4)/10 = 38.8 Neptune 30.1
(768 + 4)/10 = 77.2 Pluto (dwarf) 39.5
(1536 + 4)/10 = 154.0 Eris (dwarf) 67.7
• Using Bode’s Rule (a simple mathematical formula) the asteroid
Ceres was discovered between the orbits of Jupiter and Mars.

30. The Shapes and Sizes of Asteroids
• Asteroids come in all shapes
and sizes: Big and small.
• Ceres is massive: Large
enough to pull itself into a
sphere and therefore be
classified as a Dwarf planet.
• Most asteroids are small
(tens of kilometers across).
• Still large enough to cause
tremendous damage if
impacting the Earth.
• Spacecraft have only
recently visited asteroids.
Eros
Ceres
Vesta

31. Asteroid Eros: Potato-shaped

32. Asteroid Composition
• Asteroids can be grouped into three basic types:
– Carbonaceous bodies:
• Carbon rich, coal-like substance
• Located in the outer part of the asteroid belt
– Silicate bodies:
• Composed primarily of silicates (low-density rock)
– Metallic iron-nickel bodies:
• Composed mostly of dense metals
• Located in the inner part of the asteroid belt
Iridium is the metallic element commonly associated with the
doomsday asteroid believed to have wiped out the dinosaurs.

33. Origin of Asteroids
Asteroids: fragments of planetesimals.
The planetesimal being a mixture of
rock and metals, differentiating and
thus creating dense metallic cores
and lighter, silicate-rich outer shells.
• Collisions with other asteroids
shattering the planetesimals:
• Fragments of the inner core form
the iron-nickel asteroids and
fragments of the outer shell, form
silicate asteroids.
Differentiated Asteroid

34. Asteroid Orbits
• It is likely that the asteroids were unable to form a planet due to
the gravitational tidal influence of Jupiter.
• Jupiter “stirs up” the asteroids, keeping them apart.
• Empty regions in the asteroid belt are called Kirkwood Gaps.
• These gaps are present at orbital resonances of Jupiter.
• Asteroids with an orbital resonance get periodic tugs from
Jupiter, pulling them out of position.
• Apollo asteroids orbit in the inner Solar system, occasionally
crossing Earth’s orbit.

35. Jupiter revolutions about the Sun
Asteroid revolutions about the Sun
Ceres
Jupiter
Trojan Asteroids
Distance from Sun (semi-major axis) AU

36. Finding Young Planets
• Although watching a planetary system evolve takes too long, it is
possible to find other systems in various stages of development.
• In the Orion Nebula, we find many protoplanetary disks of dark,
dusty material orbiting young stars.
• The one shown below is a baby of around 10 million years old.
Mark McCaughrean, C. Robert O’Dell and NASA

37. A popular theory of how solar systems are born concerns giant clouds of
molecular dust coalescing to create stars: After which, a gas dust cloud forms a
halo (disc) around the new star.
Dust and other particles in the disc collide and stick together and with time
form larger and larger masses. Bodies that get sufficiently massive will start to
“pull in” surrounding particles and other small objects via gravitational
attraction. Some of these bodies will form protoplanets: planetary embryo
originating from within this protoplanetary disc (halo).
The Advent of Protoplanets
Location
of Star
Disk

38. Please insert figure 34.3
A planet and its star revolve around a common center of mass. We do not detect
the planet directly, rather the resulting “wobble” in the central star. As the star
approaches us in its motion around the center of mass, its spectrum will be blue-
shifted. As it recedes, the spectrum will be red-shifted.
Detecting Exoplanets

39. Jupiter-Sized Worlds
Please insert figure 34.4
Most planets we detect are very large: the order of several Jupiter-masses.
Planets we detect must be large in order to create a large enough wobble.

40. A Sample of the Exoplanets
Please insert figure 34.5