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Exploring Our Solar System
and Its Origin
Chapter 4: Exploring Our Evolving Solar System
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The planets are tiny compared to the distances between
them (a million times smaller than shown here), but they
exhibit clear patterns of composition and motion.
The patterns are far more important and interesting than
numbers, names, and other trivia
Sun
• Over 99.9% of solar system’s mass
• Made mostly of H/He gas (plasma)
• Converts 4 million tons of mass into energy each second
Mercury
• made of metal and rock; large iron core
• desolate, cratered; long, tall, steep cliffs
• very hot and very cold: 425°C (day), –170°C (night)
Venus
• nearly identical in size to Earth; surface hidden by thick clouds
• hellish conditions due to an extreme greenhouse effect:
• even hotter than Mercury: 470°C, both day and night
• atmospheric pressure equiv. to pressure 1 km deep in oceans
• no oxygen, no water, …
• perhaps more than any other planet, makes us ask: how did it end
up so different from Earth?
Earth and
Moon to
scale
Earth and
Moon to scale
Earth
• An oasis of life
• The only surface liquid water in the solar system; about 3/4
of surface covered by water
• A surprisingly large moon
Mars
• Looks almost Earth-like, but don’t go without a spacesuit!
• Giant volcanoes, a huge canyon, polar caps, more…
• Water flowed in the distant past; could there have been life?
Jupiter
• Much farther from
Sun than inner 4
planets (more than
twice Mars distance)
• Also very different in
composition: mostly
H/He; no solid surface.
• Gigantic for a planet:
300  Earth mass;
>1,000  Earth volume.
• Many moons, rings…
Great Red Spot
SATURN
Giant and gaseous
like Jupiter
• most spectacular
rings of the 4 jovian
planets
• many moons,
including cloudcovered Titan
• currently under
study by the Cassini
spacecraft
Uranus
• much smaller than Jupiter
or Saturn, but still much
larger than Earth
• made of H/He gas, and
hydrogen compounds
(H2O, NH3, CH4)
• extreme axis tilt — nearly
tipped on its “side” — makes
extreme seasons during its
84-year orbit.
• moons also tipped in their
orbits…
Neptune
• Very similar to
Uranus (but much
smaller axis tilt)
• Many moons,
including unusual
Triton: orbits
“backward”; and is
larger than Pluto.
Wispy white clouds
are thought to be
crystals of methane.
Pluto
• A “misfit” among the planets: far from Sun like large jovian
planets, but much smaller than any terrestrial planet.
• Comet-like composition (ices, rock) and orbit (eccentric,
inclined to ecliptic plane, long -- 248 years).
• Its moon Charon is half Pluto’s size in diameter
• Best current photo above;
New Horizons
mission launch
Jan 2006, arrival
at Pluto in
2015…
Asteroids
*100,000+ rocky objects within the
orbit of Jupiter
*Also called minor planets
*The largest, Ceres, has a diameter of
about 900 km or ~ (560 mi)
*Orbit the Sun in the same direction
as the planets
*Most orbit the Sun at distances of
2 to 3.5 AU, in the asteroid belt
TNOs - Trans-Neptunian
Objects
*1,000+ small bodies orbiting
beyond the orbit of Neptune
*The largest of these are
known as dwarf planets
*Include Pluto, Eris, Charon,
Makemake, etc.
*Orbit the Sun in the same
direction as the planets
*Most orbit within the Kuiper
belt at 30 AU to 50 AU
Comets
•Objects that result when Kuiper belt objects collide
•Fragments a few kilometers across, diverted into new and
elongated orbits
•The Sun’s radiation vaporizes ices, producing tails of gas and
dust particles
•Astronomers deduce composition by studying the spectra of
these tails created by reflected sunlight
•Oort cloud comets orbit out to 50,000 AU
Clues to the Formation
of Our Solar System
Our Goals for Learning
• What features of our solar system
provide clues to how it formed?
• What theory best explains the
features of our solar system?
Common Properties of
Planet Orbits in Our
Solar System
As viewed from above, all
of the planets orbit the Sun
in a counter-clockwise
direction.
The planets orbit in nearly
the same plane. All
planets except Pluto have
an orbital inclination of
less than 7°.
Terrestrial
Smaller Mass and size
Jovians
Larger mass and size
higher density
low density
made of rock and metal
mostly H, He, &
hydrocarbon compounds
Have solid surfaces
few moons
no rings
Closer to Sun and closer together
No solid surface
many moons
rings
Farther from sun and farther apart
Rocky asteroids
between Mars &
Jupiter
Icy comets in vicinity
of Neptune and
beyond
Asteroids and comets
far outnumber the
planets and their
moons
A successful
theory of solar
system formation
must allow for
exceptions to
general rules
Summary: Four Major Features of our Solar System
Classifying the Planets
The planets (except Pluto) fit into two groups:
The Terrestrials or
Inner Planets:
The Jovians or
Outer Planets:
Mercury
Jupiter
Venus
Saturn
Earth
Uranus
Mars
Neptune
10
Size, Mass, and Density
The Jovian planets have much bigger
diameters and even larger masses than the
terrestrial planets.
Though less massive than the Jovians,
Terrestrial planets are much more
dense.
Again, with the exception of ODD
BALL Pluto, the rotation rates of
Jovian planets on their axes are
much faster than the Terrestrial
planets.
Despite these fast rotation rates,
the diameters of the Jovian
planets are tremendously larger
than those of the Terrestrial
Planets.
What theory best explains the
features of our solar system?
According to the
nebular theory our
solar system formed
from a giant cloud of
interstellar gas
(nebula = cloud)
The lightest and simplest elements, hydrogen and helium, are
abundant in the universe. Heavier elements, such as iron and
silicon, are created by thermonuclear reactions in the interiors of
stars, and then ejected into space by those stars.
Ejection of Matter from Stars
LARGE STAR
NEAR THE END
OF ITS LIFE
FORMATION OF
PLANETARY
NEBULA
SUPERNOVA
EXPLOSIONS
Great clouds of gas and dust
ejected from old stars are
gathered into regions from
which new stars can be
made.
This region in the
constellation of Orion shows
new stars still surrounded
by the nebula from which
they were formed.
Summary of the
Nebular Model
for formation of
the solar system.
Other Star Systems Forming
We can look at young star systems
developing today. The planets
orbiting these stars are formed from
the surrounding disks of gas and
dust, called protoplanetary disks or
proplyds.
PLANET FORMATION
Within the disk that surrounds
the protosun, solid grains
collide and clump together into
planetesimals.
The terrestrial planets are built up
by collisions and the accretion of
planetesimals by gravitational
attraction.
The Jovian-like planets are
formed by gas accretion.
Common Properties of
Planet Orbits in Our
Solar System
As viewed from above, all
of the planets orbit the Sun
in a counter-clockwise
direction.
The planets orbit in nearly
the same plane. All
planets except Pluto have
an orbital inclination of
less than 7°.
Why are there two types of planets?
1. Outer planets get bigger because
abundant hydrogen compounds
condense to form ICES.
2. Outer planets accrete and keep H &
He gas because they’re bigger.
3. Inner planets too hot, gases evaporate
Fig 9.5
Inside the frost line: too hot for hydrogen compounds to
form ices.
Outside the frost line: cold enough for ices to form.
Inner parts of
disk are hotter
than outer
parts.
Rock can be
solid at much
higher
temperatures
than ice.
Four Unexplained Features of our
Solar System
√ Why do large bodies in our solar system have
orderly motions?
√ Why are there two types of planets?
--> 3) Where did the comets and asteroids
come from?
4) How can we explain the exceptions the the
‘rules’ above?
Comets and asteroids
are leftover
planetesimals.
• Asteroids are rocky
because they formed
inside the frostline.
• Comets are icy
because they formed
outside the frostline
Four Unexplained Features of our
Solar System
√ Why do large bodies in our solar system have
orderly motions?
√ Why are there two types of planets?
√ Where did the comets and asteroids come
from?
How do we explain the existence of
our Moon and other “exceptions to the
rules”?
--> 4)
Earth’s moon was
probably created
when a big
planetesimal
slammed into the
newly forming
Earth
Remember! Early in history of solar
system, such impacts far more common
Other large
impacts may be
responsible for
other exceptions
like rotation of
Venus and Uranus
Review of
nebular theory
Fig 6.27
Four Features of our Solar System Explained
√ Why do large bodies in our solar system have
orderly motions?
√ Why are there two types of planets?
√ Where did the comets and asteroids come
from?
√ How do we explain the existence of our Moon
and other “exceptions to the rules”?
When did the planets form?
We cannot find the age of a planet, but we
can find the ages of the rocks that make it
up
We can determine the age of a rock
through careful analysis of the
proportions of various atoms and
isotopes within it
The decay of radioactive elements into
other elements is a key tool in
finding the ages of rocks
Age dating of
meteorites that are
unchanged since
they condensed and
accreted tell us that
the solar system is
about 4.6 billion
years old.
Since 2008, the oldest rock on earth has been discovered by
McGill University in the Nuvvuagittuq greenstone belt on the
coast of Hudson Bay, in northern Quebec, and is dated from
3.8 to 4.28 billion years old, based on isotopes of neodymium
and samarium
Other Planetary Systems
Our Goals for Learning
• How do we detect planets around
other stars?
• What have other planetary
systems taught us about our own?
Most common
Extrasolar planets are
usually too dim or too
close to the stars they
orbit to observe
directly, however
Kepler craft can see
many transient events.
However, we can
detect the effect they
have on the spectra
from their star to
confirm their
existence. newest
Kepler mission
The gravitational fields of a star and its planet will cause
passing light to change direction. The focusing of light by
gravity is called microlensing.
We detect
planets around
other stars by
looking for a
periodic motion
of the stars they
orbit.
We measure the
motion through
the Doppler shift
of the star’s
spectrum –very
small shifts ~
0.000044 nm
The size of the
wobble tells us
the planet’s
mass
Earth mass .00314
The period of
the wobble tells
us the radius of
its orbit
(Kepler’s 3rd
law)
We can
also detect
planets if
they
eclipse
their star
Fraction of
starlight
blocked
tells us
planet’s
size
These are only a few of the many ways in which
our planet is special and perhaps unique
1. Orbits in habitable zone (liquid water exists)
2. Has a large, fairly close moon
3. Orbits right type star @ right time
4. Solar system is in right region of the galaxy
5. Planet is right size, not too big or too small
6. Has plate tectonics
7. Solar system has a Jupiter size planet, not too close
8. Stable, nearly circular orbits
9. Etc . . .
We do know there are currently 1056 extrasolar
planets found in 802 planetary systems as of
Jan.10,2014. Source : www.exoplanet.eu
539 planets in 405 systems by astrometry/radial velocity
430 planets in 327 systems by transiting planets
26 planets in 24 systems by microlensing
46 planets in 42 systems by imaging
15 planets in 12 systems by timing (pulsar planets)
Let’s see how many of these are even remotely
earthlike.
We will observe first of all that the Earth’s orbit and
mass are quite unusual
16 planets out of 1056 with
masses within 100% of the Earth
Stars with low metallicity (elements > He) are unlikely to have
rocky planets. In plot below The sun is the reference @ 0
Earth’s Mass
(.00314 MJ)
Earth’s orbit
16 planets out of 1056 with
masses within 100% of the Earth
The majority of extrasolar
planets orbit inside Earth’s
orbit, very close to their host
star.
All known extrasolar
planets with masses
from 0 to 0.01 Mjup
Earth
Earth
Mass
Earth
All known extrasolar planets
with orbits between 0.8 AU
and 1.2 Au and masses
between Earth (.00314 MJ )
and at least 100 Earth masses
(.314 MJ ).
Mass
Radius
a
(MEarth)
(REarth)
(AU)
Planet △
PSR 1257 12 b
0.022248
—
0.19
—
KOI-1843 b
0.31783
0.582867
Kepler-70 c
0.667443
0.8743
KOI-2700 b
0.86
1.06
Kepler-42 d
0.95349
0.571658
alf Cen B b
1.144188
Kepler-307 c
1.207754
2.802245
1.69
1.2
Kepler-177 b
1.700391
2.903126
—
Kepler-88 b
1.756456
4.219845
—
Kepler-11 b
1.9
1.8
0.091
Kepler-42 c
1.90698
0.728584
0.006
Kepler-78 b
Gl 581 e
1.938763
0.0076
—
0.0154
—
0.04
—
0.01
—
3
2.05
0.15
Kepler-20 e
3.082951
0.8743
0.0507
HD 215152 c
3.082951
—
0.0852
3.1783
—
0.66
HD 40307 e
3.49613
—
0.1886
HD 85512 b
3.49613
—
0.26
HD 39194 b
3.718611
—
0.0519
3.81396
—
0.46
MOA-2007-BLG192-L b
KOI-82 d
KOI-115 d
2
1.91
0.077
Kepler-65 d
2
1.513212
0.084
Kepler-11 f
2
2.49
0.25
HD 20794 c
2.415508
0.2036
Kepler-307 b
2.510857
HD 20794 b
2.701555
—
0.1207
GJ 667C f
2.701555
—
0.156
GJ 667C e
2.701555
—
0.213
HD 215152 b
2.765121
—
0.0652
3.205768
KOI-111 c
PSR 1257 12 d
0.028
—
50 lightest planets known
—
Kepler-42 b
2.86047
0.784629
0.0116
Kepler-11 c
2.9
2.87
0.106
KOI-117 b
3
1.58
0.045
KOI-82 c
3
1.34
0.086
4
0.69
—
0.067
HD 40307 b
4.004658
0.0468
Kepler-62 c
4.004658
0.538031
0.0929
Kepler-79 e
4.100007
3.497202
0.386
4.13179
—
0.36
HD 156668 b
4.163573
—
0.05
GJ 667C c
4.258922
—
0.1251
Kepler-70 b
4.44962
GJ 676A d
4.44962
PSR 1257 12 c
0.762211
—
0.006
0.0413
Kepler-36 b
4.46
1.48
0.1153
Kepler-10 b
4.6
1.46
0.01687
—
GJ 667C g
4.608535
Kepler-68 c
4.76745
HD 20794 d
4.76745
Kepler-114 d
4.799233
2.533229
0.09
5
4.819861
0.066
KOI-115 C
0.549
0.907927
—
0.09059
0.3499
50 planets with lowest masses from 0.86 to 5 ME
How many of these have a mass between 0.1ME
and 10ME ? Exactly 29 planets
Of these 29 planets how many have an orbit radius between
0.8 to 1.2 AU ? 0
3 lightest planets in ME
PSR 1257 12 b, 0.0225 Orbits at 0.19 AU
KOI-1843 b 0.3178 orbits at ?? AU
Kepler-70 c 0.6674 orbits at .0076 AU
4 planets closest to ME
KOI-2700 b, 0.86ME at ???
Kepler-42 d, 0.953 at 0.015 AU
alf Cen B b, 1.144 at 0.04 AU
Kepler-307 c, 2.80 at ??
www.exoplanet.eu
Typical Extrasolar system compared with our solar system
Solar system
masses in
terms of
Jupiter mass
I would
weigh
more than
900
pounds
6 x ME
Mercury a = .00017
Venus
b = .00256
Earth
c = .00315
Mars
d = .00034
Jupiter e = 1.0
Our solar system
a
b c
d
e
Based on the 1056 known extrasolar planets
as of Jan. 2014, what can we conclude?
First, most are more massive than Jupiter and
closer to their star than Earth is to Sun. Our
solar system is unusual.
Revisions to the nebular theory are necessary!
Planets can apparently migrate inward from
their birthplaces.
Highly eccentric orbits are the norm
Secondly, the sun is not an average star, it ranks in
the top 10% of all stars in size. The average star is
a small, very cool M class star.
The sun also has a high metal content. Stars with
low metal content will not have rocky planets.
The sun is also unusually stable for a main sequence
star, whose luminosity (brightness) has increased only
a few % over the last 2 billion years, providing a
very long term stable environment for life to flourish
and develop
Survey of stars
in the solar
neighborhood
heavier
Very few have
masses greater
than the sun
Mass weighted
avg. of the
319 stars is
0.45 M/Mo
most common
stars are 0.1
to 0.2 M/M0`
Our Sun
lighter
Is Earth Unusual?
• No Earth-like planets
found yet.
• Data aren’t good
enough to tell if they
are common or rare
• Kepler mission has
provided more data
on Earth size planets.
• Earth probably IS
unusual
conclusion
Based on the multiple lines of evidence from a
variety of scientific areas ( and I have only
presented a very small sample of a large body of
evidence) what is one to conclude ?
Based on almost any reasonable criteria that
one could devise, the existence of intelligent
life on Earth
and perhaps in the Universe as well
is an ENIGMA....
without GOD