Download the earth and other planets

THE EARTH
AND OTHER PLANETS
• The Solar System
– The Planets
– Kuiper Belt
– Oort Cloud
– Origin of the Solar System
• Extrasolar Planets
• Earth-Moon System
The planets known to the ancients included
Mercury through Saturn, including the moon
and the sun, making 7 celestial bodies other
than the earth.
We divide the planets of our solar system
into two major groups:
– The Terrestrial Planets
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Mercury
Venus
Earth
Mars
– The Gas Giants
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Jupiter
Saturn
Uranus
Neptune
To Escape Earth
• Wernher von Braun’s dream
• Space Race
– Soviets first into space and set many initial
records: sputnik, Gagarin, Tereshkova, Korolev
– USA behind but caught up after Mercury (e.g.
Shepard & Glenn) and Gemini. Apollo 1 disaster
followed mostly by success until moon landing
(e.g. Armstrong and Aldrin)
– Probes to the planets
Mercury☿
• Diameter =4.9X103km
• ~0.39 AU from the sun, but
very eccentric
• Orbit ~0.24 earth years
• 1 day = 176 earth days
• 1 mercurial day for each 2
orbits (as seen from Mercury)
• No moons
• Very dense (second only to
earth)
• Large liquid core
• Probes: Mariner 10 (1974-75)
and Global MESSENGER
(2008-present)
Mercury from a mosaic of photographs
taken by the Mercury Global
MESSENGER
Venus
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Diameter =12.1X103km
~0.72 AU from the sun
Orbit ~0.62 earth years
1 day = 243 earth days, but the
rotation is retrograde relative to
the other planets
No moons
Not as dense as the earth or
Mercury
Seems to have a liquid core and
active vulcanism
Probes from the USA, USSR, EU
from 1961 to present
Radar image by the probe Magellan
1990-1994
Mars
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Diameter =6.7X103km
~1.5 AU from the sun
Orbit =1.88 earth years
1 day = 0.98 earth days
2 moons (likely captured
asteroids)
• Density lowest of the
terrestrial planets (3.9g/ml)
• Evidence of past geological
activity
• Many active probes: flyby,
orbitals and landers
Mars image mosaic from images taken by
Mars Global Surveyor (1999-2004).
Shows northern water ice cap and Valles
Marinaris. Olympus Mons shrouded in
clouds.
Asteroids and Bode’s Law
• A numerical sequence
defined by Titus and
Bode successfully
defined the relative
positions of the planets
Mercury through Saturn
• a=4+n
where n = 0,3,6,12,24,48
• Gap in the sequence
between Mars and
Jupiter
• Search initiated for
missing planet. Franz
von Zach and Guiseppe
Piazzi found Ceres at the
right distance
Johann Elert Bode
(1747-1826), Germany
Johann Daniel Titus
(1729-1796), Germany
Ceres, the largest
asteroid (950km) and
only dwarf planet in
the inner solar
system. Image by HST
Jupiter
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Diameter =142.8X103km
~5.2AU from the sun
Orbit =11.9 earth years
1 day =0.41 earth days
~61 moons; Ganymede is larger
than Mercury; thin ring
• Density =1.3g/ml
• Gas giant planet mainly of
Composite image of Jupiter by the
Cassini probe. The black dot is the
hydrogen and helium.
shadow of Europa.
Atmosphere banded with giant
red spot. Core with layers of
metallic hydrogen
• Many probes to study the
Galilean moons (L-R): Io, Europa, Ganymede,
planet and its moons
and Callisto
Saturn
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Diameter = 120X103km
~9.8 AU from the sun
Orbit =29.5 earth years
1 day =0.43 earth days
~30 moons and large system
of rings; Titan is larger than
Mercury and has an
atmosphere
• Density =0.7g/ml
• Gas giant with a core
surrounded by metallic
hydrogen with outer layers of
liquid hydrogen and helium
• Many probes to study the
planet, its rings and moons
Saturn photographed by Cassini in 2004
Composite
image of
Saturn and
its largest
moons
taken by
Voyager 1 in
1980
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Uranus
Diameter =51.8X103km
~19.2 AU from the sun
Orbit =84 earth years
1 day =0.72 earth days
More than 30 moons and a ring
system
• Density =1.3g/ml
• Gas giant with an axial tilt of 97
degrees. A solid core surrounded by a
mantle of ices (water, ammonia,
methane), an atmosphere (hydrogen,
helium & methane), and an outer
atmosphere
• Studied up close by Voyager 2 (1986)
Uranus taken with HTS;
north is on the right
Discovery of Uranus
• Minor deviations by Saturn
suggested the influence of another
planet
• It had been observed earlier but not
recognized as a planet
• William Herschel (March 1781)
initially thought it was a comet
• The orbit was determined to be
circular by Russian astronomer
Anders Johan Lexell and Bode said it
must be a planet
• Herschel, recognized as its
discoverer held naming rights and
wanted to call it Georgian Star –not
popular
• Named Uranus (the only planet with
a Greek, rather than Roman name).
Ouranos was the Greek god of the
sky and father of Cronos (Saturn),
who was father of Zeus (Jupiter)
Frederick William Herschel
(1738-1822); Britain; astronomer
and composer
Neptune
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Diameter =49.5X103km
~30.1 AU from the sun
Orbit =164.9 earth years
1 day =0.67 earth days
More than 11 moons
Density =1.8g/ml
Gas giant similar to Uranus.
Solid core; mantle (water,
methane & ammonia ices);
atmosphere (hydrogen,
helium, & methane)
• Visited by a few probes
including Voyager 2 in 1988
Image of Neptune by Voyager 2. Note
banded appearance of the atmosphere
and 2 dark spots
Discovery of Neptune
• Observed by Galileo but not
recognized as a planet
• Independently, John Couch
Adams and Urbain Le
Verrier noted that Uranus
moved as though it were
perturbed by a large outer
planet
• Did not conform to Bode’s
Law
• Adams and Le Verrier given
joint credit for the discovery
John Couch
Adams (18191892), Britain
Urbain Jean Le
Verrier (18111877), France
Discovery of Planet X
• Percival Lowell convinced of the
existence of a ninth planet,
founded the Lowell Observatory in
Flagstaff, AZ in 1894
• Searched until 1916 when he died
• Legal battle with Lowell’s widow
delayed search until 1929
• Clyde Tombaugh began the search
and found Planet X in 1930
• Called Pluto PL
Percival Lawrence
Lowell (1855-1916),
USA
Clyde William
Tombaugh (19061997), USA
Pluto
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Diameter =2,306km
29.7-48.9 AU from sun
Orbit =247.7 earth years
1 day =366.7 earth days
Up to 5 moons, Charon is the
largest
• Density =2.1g/ml
• New Horizons probe
HST image
New Horizons image
International Astronomical Union’s
Definition of a Planet
• Must be in orbit around the
sun
• Sufficient mass to assume a
spherical shape
• Must have cleared out its
orbital neighborhood
Current classifications of natural objects in
the solar system
12 candidate planets under
the old designation
The Fall of Pluto
• Designation changed to a
dwarf planet in 2006
because:
• Its orbit is strongly
elliptical
• Its orbit strongly
inclines relative to the
ecliptic
• It does not seem to
have cleared out its
orbital path (mass only
.07% of other objects
in its orbital path
Kuiper Belt
• A belt from 30-50AU
from the sun
• Collectively called
Trans-Neptunian
Objects (TNO), many
of which are dwarf
planets (aka plutinos)
• Mainly in the ecliptic
Oort Cloud
Origin of the Solar System
• A nebular hypothesis
proposed by
Descartes
• Developed by Kant
and Laplace to
explain the ecliptic
and orbital intervals
Immanual Kant (17241804), Prussia
Pierre-Simon,
Marquis de Laplace
(1749-1827), France
EXTRASOLAR PLANETS
• Campbell, B., G. A. H.
Walker, and S. Yang.
1988. A search for
substellar companions to
solar-type stars. The
Astrophysical
Journal. 331: 902.
• Kepler mission launched
March 6, 2009
• As of February 22, 2017,
3,453 confirmed planets
have been found
Gamma Cephei Ab, the first exoplanet
discovered. 45 light-years distant
Size Distribution of Exoplanets
Origin of the Earth-Moon System
• Centrifugal Origin by
George Darwin
• Formed in place as a
double planet
• The Capture Theory –
resurrected as a capture
from Venus (2013)
• Giant Impact Hypothesis
Giant Impact Hypothesis
• Moon rocks brought back
by Apollo demonstrate
the same isotopic
signature as the earth
• Moon much less dense
than the earth
• Defined in 1974 by
William Ward & Al
Cameron (on collision
from Harvard) together
with William Hartman &
Donald Davis (on Great
Bombardment from
Arizona)
Tides and Phases
First considered by
Galileo but studied
and explained by
George Darwin
George Howard Darwin
(1845-1912), Britain
Earth
• Diameter =12,756km
• Density =5.5g/ml
• Third planet from the
sun
• Most of the surface
covered by water
• Relatively little CO2 in
the atmosphere
• Inclined 23o
• Tectonically active
The earth photographed by Apollo 17