an outline of planets and dwarf planets in the solar system

1. PLANETS OF THE
SOLAR SYSTEM
Dr. Basil Bemgba
Achie MBBS Ibadan

2. In 2006, The International Astronomical Union (IAU) defined
a Planet as follows:
A “planet” is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces
so that it assumes a hydrostatic equilibrium (a nearly round shape), and
(c) has ‘cleared the neighbourhood’ around its orbit.
A non-satellite body fulfilling only two of the IAU criteria is
classified as a dwarf planet.
The IUA recognizes eight known planets.
This presentation is an outline of the 8 planets and 5 dwarf
planets.

3. THE PLANETS
PLANET Surface temp. Orbit distance Orbit period Diameter
TERRESTRIAL/ROCKY PLANETS (INNER PLANETS) – composed primarily of silicate
rocks or metals.
1. MERCURY -173 to 427°C 0.39 AU 87.97 Earth
days
Polar 4,879 km
Equatorial 4,879 km
2. VENUS 462° C 0.73 AU 224.70 Earth
days
Polar 12,104 km
Equatorial 38,025
km
3. EARTH -88 to 58° C 149,598,262
km (1 AU)
365.26 Earth
days
Polar 12,714 km
Equatorial 40,030
km
4. MARS -87 to -5 °C 1.38 AU 1.88 Earth
years
Polar 6,755 km
Equatorial 21,297
km

4. PLANET Surface temp. Orbit distance Orbit period Diameter
THE GAS GIANTS (OUTER PLANETS) – giant planet composed mainly of Hydrogen and Helium.
5. JUPITER -108°C 5.20 AU 11.86 Earth years Polar 133,709 km
Equatorial 142,984 km
6. SATURN -139 °C 9.58 AU 29.45 Earth years Polar 108,728 km
Equatorial 120,536 km
ICE GIANTS (OUTER PLANETS) – giant planet composed mainly of elements heavier than hydrogen and helium
with freezing points above about 100kelvins such as ammonia, or methane.
7. URANUS -197 °C 19.22 AU 84.02 Earth years Polar 49,946 km
Equatorial 51,118 km
8. NEPTUNE -201 °C 30.10 AU 164.79 Earth years Polar 48,682 km
Equatorial 49,528 km

5. MERCURY
Mercury is the closest planet to the sun,
at a distance of 57 million km.
It is the smallest planet and second
densest after Earth.
Mercury has the most drastic average
surface temperature variations in the
Solar System, from 430 degrees Celsius
in the day to as low as minus 180
degrees Celsius at night.
Covered in craters from various impacts,
it is very similar to Earth’s moon in size
and appearance.
NASA’s Messenger spacecraft was the
first to orbit Mercury in March 2011. It
crashed into the planet in 2015 after
taking thousands of pictures.

6. VENUS
Venus was first recorded by
Babylonian astronomers in 14th
Century BC.
The brightest planet in the solar
system, it has a surface temperature
of 462° C.
Venus has a thick atmosphere made
up of carbon dioxide, sulfur dioxide
and nitrogen. These trap heat making
the planet the hottest in the solar
system.
Venus and Uranus rotate clockwise,
East to West (opposite the other
planets),
Because it is very similar to Earth in

7. EARTH
The third planet from the sun, Earth orbits
the sun at an average distance of 149 million
kilometers or one Astronomical Unit (1 AU)
It is the only planet not named after Greek or
Roman mythology,
The planet revolves around the sun in
365.25 days, ( one Earth year).
Only 29% of Earth is covered by land. Of the
71% covered by water, 97% is salt water
while 3% is fresh.
It is the only place known to harbor life as we
know it.

8. MARS
The fourth planet from the sun, the Red planet,
was named after the Roman god of war.
The planet was first observed with a telescope
by Galileo Galilei in 1610
Its rusty colour is due to iron-rich minerals in its
regolith, which oxidize giving the planet its red
colour.
Mars is home to the highest mountain
(Olympus Mons) and the deepest, longest valley
(Valles Marineris) in the Solar System.
Its average temperature is minus 60 degrees
Celsius.

9. JUPITER
Jupiter is the solar system’s largest
planet.
The gas giant contains more than
twice the mass of all the other
solar system planets combined.
The Great Red Spot is its biggest
storm and it’s more than twice the
width of planet Earth and has been
raging for at least 350 years.
The Great Red spot is observed to
be shrinking as recent observation
show its now just big enough to
contain one earth.

10. SATURN
Saturn is the sixth planet from the
sun and has the largest planetary
rings.
With a polar diameter of 108,728
km, it is the second largest planet
after Jupiter
The gas giant has a surface
temperature of -139 °C
It has the lowest density of all the
planets and can float on water.
The planet is largely made up of
methane which gives it a
brownish-yellow appearance.

11. URANUS
Uranus was discovered on March 13,
1781, by the English
astronomer William Herschel with the
aid of a telescope.
It has been sighted since 128 BC but
was always dismissed as a star.
Johann Bode first proposed the name
Uranus in 1782.
It is the coldest planet in the solar
system with a surface temperatures
dipping to minus 225 degrees Celsius.
Uranus rotates on its side, thus, it is
called the ‘side ways planet’, tilted on
its side by about 98%.
Its atmosphere is made up of
hydrogen, helium and methane.

12. NEPTUNE
Neptune is the eighth planet from the
sun.
Officially discovered in 1846 by Le
Verrier and Johann Galle, It is the first
planet to be discovered by
mathematical calculations and
predictions.
At an average distance of 30 AU
away from the Sun, it is the furthest of
the eight planets.
Neptune has a surface temperature
of -201 °C
It is an ice giant, that is, its rocky icy
core is proportionally larger than the

13. THE DWARF PLANETS
DWARF PLANET Surface temp. Orbit distance Orbit period Diameter
1. PLUTO -229°C 39.26 AU 247.92065 Earth years 2,368 km (+- 20km)
2. ERIS Between −243.2
and −217.2 °C
68 AU 558 Earth years 2,326 km
3. HAUMEA - 241°C 43.13 AU 283.28 Earth Years Equatorial -1,960 km – 1,518
km
Polar - 996 km
4. MAKEMAKE -239°C 45.79 AU 309.88 Earth Years Equatorial 1,434 km
Polar 1,422 km
5. CERES -105°C 2.77 AU 4.60 years 950 km

14. PLUTO
Discovered in 1930, by Clyde
Tombaugh,
Pluto was the ninth planet up until
2006 when it was demoted to
dwarf planet status after the IAU
defined the term “planet”.
It is made up mostly of ice and
rock and is smaller than Earth’s
moon (about one-sixth its mass,
and one-third of its volume)
It has a surface temperature of -
229°C
Average distance from the sun is
39.5 AU

15. ERIS
Eris is about the same size as Pluto
but has 28% more mass.
Located beyond the orbit of Neptune,
it is the most distant dwarf planet at an
average distance of 68AU.
Discovered in 2005 by Mike Brown
and his team, it was considered the
tenth planet until its demotion to dwarf
planet status along with Pluto.
Eris orbits the sun in 558 Earth years
and has a moon named Dysnomia.
It is extremely cold with a surface
temperature of between −243.2 and
−217.2 °C.

16. HAUMEA
Haumea is the fastest rotating dwarf
planet
The discovery of Haumea in 2004 is
disputed between Mike Brown and
his team and José Luis Ortiz Moreno
and his team.
The very fast rotation of Haumea
has distorted its shape into a trixial
ellipsoid.
It has two moons named Hi’iaka and
Namaka.
It has a surface temperature of -
241°C

17. MAKEMAKE
Located in the Kuiper belt, Makemake
is the second furthest dwarf planet
from the sun at 45.8 AU.
It was discovered on March 31, 2005
by astronomers at the Palomar
Observatory led by Mike Brown.
It has a surface temperature of -
239°C.
It has a satellite nicknamed MK 2

18. CERES
The only dwarf planet not located
in the Kuiper belt, Ceres is located
in the asteroid belt between Mars
and Jupiter.
It was discovered on 1st January
1801 by Italian astronomer
Giuseppe Piazzi who also named
it.
It was first classified as a planet at
discovery, then demoted to an
asteroid and finally declared a
dwarf planet in 2006.
Though 14 times smaller than
Pluto, Ceres is round because it is
large enough for gravity to mold it
into a sphere