Astronomy

1. THE SOLAR SYSTEM:
AN INTRODUCTION TO
COMPARATIVE PLANETOLOGY
Solar System – sun and bodies orbiting it: the sun
and all the planets, satellites, asteroids, meteors, and
comets that are subject to its gravitational pull.
Planetology – study of planets: the branch of
astronomy that studies the origin and composition of
the planets and other solid bodies in the solar system
such as comets and meteors.
FACTS ABOUT THE SUN AND ITS PLANETS
Sun
 Our Sun is just one of billions of stars in the
disk-shaped galaxy called the Milky Way.
Bright star clusters are visible along with
darker areas of dust and gas. Our Sun is
located in one of the spiral arms of the Milky
Way.
 The approximate temperature of the Sun’s
surface is 5800 K, while the sunspot’s
temperature is approximately 8100°F.
Mercury
 Mercury orbits closer to the Sun than any
other planet, making it dry, hot, and virtually
airless. Although the planet’s cratered
surface resembles that of the Moon, it is
believed that the interior is actually similar to
Earth’s, consisting primarily of iron and other
heavy elements.
 The planet Mercury turns counter clockwise
(west to east).
Venus
 Venus is the brightest object in our sky, after
the sun and moon. Swirling clouds of sulfur
and sulfuric acid obscure Venus’s surface
and inhibited study of the planet from Earth
until technology permitted space vehicles,
outfitted with probes, to visit it. These probes
determined that Venus is the hottest of the
planets, with a surface temperature of about
460° C (about 860° F).
 Venus is the brightest object in the sky. It is
often called the morning and the evening
star.
Earth
 An oxygen-rich and protective atmosphere,
moderate temperatures, abundant water, and
a varied chemical composition enable Earth
to support life, the only planet known to
harbor life. The planet is composed of rock
and metal, which are present in molten form
beneath its surface.
 The Earth’s atmosphere includes
troposphere, stratosphere, mesosphere,
thermosphere and exosphere.
Mars
 Scientists have determined that the planet’s
atmosphere consists primarily of carbon
dioxide, with small amounts of nitrogen,
oxygen, water vapour, and other gases.
Because the atmosphere is extremely thin,
daily temperatures can vary as much as
100°C. In general, surface temperatures are
too cold and surface pressures too low for
water to exist in a liquid state on Mars. The
planet resembles a cold, high-altitude desert.
 Phobos and Deimos are named after the
sons of the Roman God, Mars. In which,
Phobos sets in the East while Deimos sets in
the West.
Jupiter
 Jupiter is the largest of the planets, with a
volume more than 1,300 times greater than
that of Earth. Jupiter’s colorful bands are
caused by strong atmospheric currents and
accentuated by a dense cloud cover. The
massive planet comes with its four largest
satellites: Io, Ganymede, Europa and
Callisto.
 Closer to Jupiter the strong field traps the
charged particles. The entire region of
particle-fields interactions is known as the
magnetosphere.
Saturn
 Saturn, distinguished by its rings, is the
second largest planet in the solar system.
 The discovery of the 9 moons of Saturn was
announced in June 2006 and an additional 4
moons were reported in 2007 and these are
in irregular shape and small.
Uranus
 Uranus’s blue-green colour comes from the
methane gas present in its cold, clear
atmosphere. The dark shadings at the right
edge of the sphere correspond to the day-
night boundary on the planet. Beyond this
boundary, Uranus’ northern hemisphere
remains in a four-decade-long period of
darkness because of the way the planet
rotates.
 Astronomers have identified 13 rings of
debris encircling Uranus’ equator. Five from
the innermost rings were called Alpha, Beta,
Gamma, Delta and Epsilon.
Neptune
 The large, dark oval surrounded by white
clouds near the planet’s equator is the Great
Dark Spot, a storm similar to Jupiter’s Great
Red Spot. The smaller dark oval with a bright

2. core below and to the right of the Great Dark
Spot is another storm known as Dark Spot 2.
 Neptune is also classified as an ice giant
planet, mainly made of the ice-forming
molecules water, ammonia and methane.
Pluto
 Pluto is farther from the Sun than the major
planets in the solar system, although it
occasionally moves in closer than Neptune
due to an irregular orbit.
 Charon, the moon, is about half of Pluto’s
size and would appear in Pluto’s sky to be
about six times the size of the Earth’s moon.
 Additional Facts about Pluto:
1. Discovered in 1930 by Clyde Tombaugh.
2. Long considered as the 9th planet in the
solar system.
3. Reclassified as dwarf planet (after the
discovery of the similar intriguing worlds
deeper in the distant Kuiper Belt;
because of the discovery of Eris).
4. Have five moons (Charon, Nix, Hydra,
Kerberos [P4], Styx [P5]).
5. Nix and Hydra, 2 – 3x farther away from
Pluto and Charon.
6. From 1979 to 1999, Pluto was actually
closer to the sun than Neptune, and in
1989, Pluto came to within 29.7 AU of the
sun, providing rare opportunities to study
this small, cold, distant world.
 Ceres, a dwarf planet like Pluto
which is residing in the asteroid belt.
Pluto always has been and always will be
part of the solar system. Pluto was just
downgraded from a "planet" to a "dwarf
planet", because the IAU set some new
requirements for an object to be classified as
a "planet", and Pluto does not meet all the
requirements. Pluto is still captured by the
Sun's gravitational pull, so, it is still part of our
solar system.
RELATIVE SIZE COMPARISON
The relative sizes of objects are drawn to scale; the
distances between them are not.
MAJOR PLANETARY POINTS
Mercury Scorched, heavily cratered
Venus Dense, Corrosive clouds cover
Earth Life Supporting
Mars Great dust storms
Jupiter Great Red Spot
Saturn Spectacular ring systems
Uranus Tilted on its side
Neptune Interesting Moons
Pluto Highly eccentric orbit
With the exception of Pluto, all the planets are
effectively in the equatorial plane of the Sun.
OVERALL LAYOUT OF THE SOLAR SYSTEM
A Mnemonic Device used to remember the
chronological sequences of the planets. (Ex. “My
Very Erotic Mate Joyfully Satisfied Unusual Needs
Passionately”)

3. Kepler discovers the properties of elliptical orbits.
TERMINOLOGIES
Kuiper Belt
 ring of orbiting celestial bodies: a ring of small
astronomical objects orbiting through the
outer solar system, beyond the farthest
planets, Neptune and Pluto.
 Objects found in the Kuiper Belt are known
as Kuiper Belt Objects or Transneptunian
Objects.
 It is believed that the Kuiper belt is a source
of comets.
Bow Shock
 shock wave in outer space: a shock wave,
about 21 billion miles from the Sun, caused
by solar winds colliding with the Earth's
magnetic field.
 Still further out, at about 227 AU (34 billion
km/21 billion mi) from the Sun, there is
probably a bow shock, another shock surface
where the flow of the interstellar medium is
suddenly slowed as it approaches the
heliosphere.
Termination Shock
 boundary of solar system: the continually
shifting boundary of the solar system and the
start of interstellar space, where the solar
wind abruptly slows down, 8 billion-9.5 billion
miles from the Sun.
Astronomical Unit (AU)
 distance in space: a unit of astronomical
distances, especially within the solar system,
equal to the mean distance between the
Earth and the Sun, about 150 million km/93
million mi.
Heliopause
 beginning of interstellar space: the point
marking the beginning of interstellar space
and the endpoint boundary of our solar
system, 10-15 billion miles from the Sun,
where the pressure from solar winds is in
balance with that of interstellar winds.
Interstellar Medium
 Space between two or more stars.
Oort Cloud
 collection of comets: a huge, roughly
spherical, orbiting collection of comets
thought to exist at the edge of the solar
system.
 Surround the Solar System almost to the
Alpha Centauri (the next star).
 Contains a sample of the primordial (existing
at the beginning of time or of the
development of something) material that
formed the planets.
TYPES OF SPACE MISSION
Flyby – The flights of the spacecraft close enough to
celestial bodies to gather scientific data.
 A flight passing close to a specified target or
position, specially a maneuver in which a
spacecraft or satellite passes sufficiently
close to a body to make detailed observation
without orbiting or landing.
Orbiter – A spacecraft designed to orbit a planet to
examine its environment without landing on it.
 Examine planets’ environment even more
precise.
 Search for evidence of water’s existence (on
surface or underground)
 Help identify scientifically interesting sites on
the surface for further investigation.

4. Landers – A space vehicle designed to land on a
celestial body to explore its surface.
 Scanning the terrain.
 Search for liquid water (for possible past or
present sign of life).
 Return sample rock or solid.
Rover – A crewed or uncrewed vehicle used in
exploring the terrain of a planet and its satellites.
 Ability to explore an area beyond the place
where landers touch down.
Aeroplane/ Airplane – A heavier-than-air powered
flying vehicle with fixed wings used to gather better
images of the planet’s surface.
 Could navigate on its own without human
pilot.
 Gather better images of the surface and
cover more territory than current orbiter or
rover.
Balloon – A large impermeable bag inflated with a
lighter-than-air gas, designed to rise or float in the
atmosphere to provide views of much broader areas
of the surface.
Subsurface Explorer – A spacecraft with carries
subsurface radar instrument that gives three-
dimensional understanding of where and how much
water may be distributed in the planet’s surface.
Hand-out for Sci. 4 – Astronomy
Topic: The Solar System: An Introduction To
Comparative Planetology
Prepared by:
BREN DALE M. MIRANDA
BEEd 4 – 20
AY 2015-2016