The 7th Planet
Presentation for SES4U
The diameter of Uranus can be
compared with other 7 planets and
some dwarf planets in the picture
below
Uranus’ position in the solar system
can be seen in the diagram above
(diameters and distances are not to
scale).

7th planet from the sun





Mean Distance
Rotational Period
Orbital Period
Eccentricity
Diameter


Density
Mass

Inclination of Axis
2,870,990,000 km (19.18 AU)
17.3 hours (0.72 days)
84.01 years
0.0461 (almost circular)
51,118 km
(4 times greater than Earth)
3rd largest planet
1.24 g/cm3 (22% of Earth)
15 times greater than Earth
(63 times greater volume)
97.92° (Uranus appears to tilted
completely on its side)
Uranus has very fine, dark
coloured rings

A day on Uranus is only about 17 hours. But the tilt of Uranus works out so
that one pole is usually pointed towards the Sun. This means that a day at
the north pole of Uranus lasts half of a Uranian year. So, if you could stand
on the north pole of Uranus, you would see the Sun rise in the sky, circle
overhead slowly for 42 years, and finally dip down below the horizon. Then
you would have 42 years of darkness.

Pronounced Yoor-a-nus

Uranus is the ancient
Greek god of the Heavens,
the earliest supreme god.
Uranus was the son and
mate of Gaia, the father of
Saturn and of the Cyclopes
and Titans (predecessors
of the Olympian gods).

Uranus, the first planet
discovered in modern times
(i.e. the first planet that was
not known to the ancients)
and was the first planet to be
discovered using a telescope.
Uranus was discovered by
William Herschel while
systematically searching the
sky with his telescope on
March 13, 1781.
Using a telescope of his own design, Herschel
looked out from the garden of his house in the town
of Bath, England. Herschel initially reported that this
irregularly moving object was a comet.
Herschel recorded in his journal that the object was "In the quartile
near ζ Tauri was either [a] Nebulous star or perhaps a comet". On
March 17, he noted, "I looked for the Comet or Nebulous Star and
found that it is a Comet, for it has changed its place". When he
presented his discovery to the Royal Society, he continued to believe
that he had found a comet despite giving a description more likely to
fit a planet.
 Herschel notified the Astronomer Royal, Nevil Maskelyne, of his
discovery and received this reply from him: "I don't know what to call
it. It is as likely to be a regular planet moving in an orbit nearly
circular to the sun as a Comet moving in a very eccentric ellipsis. I
have not yet seen any coma or tail to it”.
 by November 1781, the German astronomer Bode had calculated its
orbit. It was clearly a planet, with an orbit that placed it twice as far
from the Sun as Saturn. Herschel estimated the disk of the planet as
54,700 kilometers across, more than four times the diameter of the
Earth. This was a surprisingly good estimate, compared to the
correct modern value of 51,200 kilometers, and a tribute to
Herschel's outstanding observational skills.


Uranus had actually been seen many times before
but ignored as simply another star. The earliest
recorded sighting was in 1690 when John
Flamsteed catalogued it as 34 Tauri.

Herschel named it "the Georgium Sidus" (the
Georgian Planet) in honor of King George III of
England; others called it "Herschel".

The name "Uranus" was first proposed by Bode in
conformity with the other planetary names from
classical mythology but that name didn't come into
common use until 1850.
The large gas planets seemed to have formed by
accumulating gas from the “proto-star nebula” after
accreting solid cores of about 5-15 Earth masses. But the
outer giant planets, Uranus and Neptune, seem unlikely to
have formed this way. They exist in a region of the Solar
System where there is not enough material to form
planets of their masses (15 and 17 Earth masses
respectively).
 Models suggest that they underwent most of their growth
among proto-Jupiter and -Saturn, and were scattered
outward to their present orbits when Jupiter acquired its
massive gas envelope. Computer simulations support this
model which also works to explain the present state of the
asteroid belt and the Kuiper belt.

The outer giant planets,
Uranus
and Neptune, pose a challenge to theories of planet
formation. They exis
Planets accreting from the early Solar Nebula. Note larger
planetessimals are drawn together by gravity and collide.
Voyager data favours a model for the
internal structure of the planet with a
fairly small, rocky core surrounded by
a deep, super-dense atmosphere of
gases and ices of water, ammonia
and methane. Above this there is an
atmosphere of hydrogen and helium
with clouds of methane, ammonia and
water-ice. The methane gives the
planet it’s blue colour. The
temperature at the 'surface' is 214°C. Uranus has a magnetic field.
Uranus’ rotation rate is determined
from the few cloud structures seen,
indicating that there are strong jetstreams present on Uranus rather like
those on the Earth.
http://www.freewebs.com/mdreyes3/outer_planets.jpg
<
>



Very faint cloud bands visible

on the surface layers of Uranus.

Like Jupiter and Saturn, an envelope of hydrogen and
helium lies below the thin upper layers of Uranus'
atmosphere. On Uranus, though, the layer of hydrogen
and helium is not as thick as on the larger planets,
extending perhaps only one-fifth of the distance down
from its cloud tops.
Uranus receives little heat from the Sun, and it does not
produce much on its own, so there is no energy source
to produce the dramatic cloud bands and weather
systems seen on other worlds.
The sunlit hemisphere also was found to radiate large
amounts of ultraviolet light, a phenomenon that Voyager
scientists have dubbed "dayglow."
The average temperature on Uranus is about 60 Kelvin
(-210° C).
Surprisingly, the illuminated and dark poles, and most of
the planet, show nearly the same temperature below the
tropopause. Voyager instruments did detect a somewhat
colder band between 15 and 40 degrees latitude, where
Uranus has 27 known moons. Only
the 5 largest moons were known
before the Voyager missions. The
outer moons (and rings) were
detected by the Hubble Space
Telescope.
 The 5 largest moons – Miranda,
Ariel, Umbriel, Oberon and Titania
are found beyond the rings. 9 very
small moons are found well beyond
the large moons and 13 moons are
found within the rings.
 The two largest moons – Oberon
and Titania were discovered by
Herschel.
 Unlike most planets whose moons
are named from Greek and Roman
mythology, the moons of Uranus are
named for Shakespearian

Inner Moons of Uranus
Uranus’ five largest moons



The Minor Moons

All of Uranus's inner moons (those observed by
Voyager 2) appear to be roughly half water ice
and half rock. The composition of the moons
outside the orbit of Oberon remains unknown,

but they are likely captured asteroids. Cordelia
and Ophelia are shepherd moons that keep
Uranus' thin, outermost "epsilon" ring well
The 5 Large Moons
Miranda, the innermost and smallest of the
five major satellites, has a surface unlike any
other moon that's been seen. It has giant fault
canyons as much as 12 times as deep as the
Grand Canyon, terraced layers and surfaces
that appear very old, and others that look
much younger.
Ariel has the brightest and possibly the
youngest surface among all the moons of
Uranus. It has few large craters and many
small ones, indicating that fairly recent lowimpact collisions wiped out the large craters
that would have been left by much earlier,
bigger strikes. Intersecting valleys pitted with
craters scars its surface.
Umbriel is ancient, and the darkest of the five
large moons. It has many old, large craters
and sports a mysterious bright ring on one
side.
Oberon, the outermost of the five major
moons, is old, heavily cratered, and shows
little signs of internal activity. Unidentified
dark material appears on the floors of many
of its craters.
Name
Ariel
Umbriel
Titânia
Oberon
Miranda
Cordélia
Ofélia
Bianca
Cressida
Desdémona
Julieta
Pórcia
Rosalind
Belinda
Puck
Caliban
Sycorax
Próspero
Setebos
Stefano
Trinculo
S/1986 U 10 *
S/2001 U 2 *
S/2001 U 3 *
S/2003 U 1 *
S/2003 U 2 *
S/2003 U 3*
Diameter (km)
Mass (kg)
Orbital radius (km)
Orbital period (days)
1158
1170
1578
1523
472
40
42
51
80
64
93
135
72
80
162
98
190
30
30
20
10
20
12
12
10
10
11
1.35E+21
1.17E+21
3.52E+21
3.01E+21
6.6E+19
4.5E+16 ?
5.4E+16 ?
9.3E+16 ?
3.43E+17 ?
1.78E+17 ?
5.57E+17 ?
1.68E+18 ?
2.54E+17 ?
3.57E+17 ?
2.89E+18 ?
7.3E+17 ?
5.4E+18 ?
2.1E+16 ?
2.1E+16 ?
6E+15 ?
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
191,020
266,300
435,910
583,520
129,390
49,770
53,790
59,170
61,780
62,680
64,350
66,090
69,940
75,260
86,010
7,231,000
12,179,000
16,256,000
17,418,000
8,004,000
8,504,000
76,420
20,901,000
4,276,000
97,734
74,800
14,345,00
2.520379
4.144177
8.705872
13.463239
1.413479
0.335034
0.376400
0.434579
0.463570
0.473650
0.493065
0.513196
0.558460
0.623527
0.761833
-579.7 **
-1288.3 **
-1977.3 **
-2234.8 **
-677.4 **
-759.0 **
0.638
-2823.4 **
-266.6 **
0.923
0.618
1694.8
Rosalind
Named for the daughter of the
banished Duke in
Shakespeare’s play As You
Like It.
Discovered in 1986 by Voyager
2. It has an approximate
diameter of 54 km., orbits the
planet from 69630 km and has
an orbital period of 0.559 days.




All 13 rings are thin and very
tenuous.
The particles in the rings range from
about the size of a softball to the
size of a car, but the rings are
relatively free of small particles,
which suggests a rapid rate of
depletion. Collisions between large
particles should create many small
particles, but if so, such small
particles are being removed quickly.
Voyager 2 detected an extended
upper atmosphere of hydrogen that
is slowly depleting the rings, causing
their particles to fall down to the
planet.
The rings are believed to have
The Instability of Uranus’ Moons and Rings
Jack Lissauer synthesized the available observations of the moons and rings and
discovered that Uranus' system of moons and rings has witnessed several changes since
1994. They have suggested that Uranus' system in unstable. Lissauer has computed that
Uranus' moons will collide within a few million years, which is extraordinarily short
compared to the 4.5 billion year age of the Uranian system. At this rate, Uranus' system
has formed its moons have collided and reformed around 10 times.

The 1980’s were a rare opportunity for NASA scientists as the outer
planets were all aligned. After flying by Jupiter and Saturn, the NASA
Voyager 2 probe performed a flyby of Uranus, with closest approach on
24 January 1986. Planning for the encounter had been meticulous, since
there was only one chance to get it right and Voyager 2 was showing its
age. To complicate matters, the spacecraft's flyby would occur when the
one of the planet's poles was aligned with the Sun, meaning that the
probe would fly through the plane of the orbits of the planet's moons, not
along it, minimizing the time available for observations.
The only spacecraft to ever visit Uranus is the
Voyager 2 probe. The Voyager 2 probe was
launched on August 20, 1977 and reached
Uranus on January 24, 1986. The Voyager 2
discovered additional moons of Uranus and
while the rings of Uranus were discovered on
Earth, the probe did capture some nice images
of these very faint rings.
NASA scientists had to deal with several
problems with the Voyager 2 craft:
1) steady degradation of the electrical output
of its atomic radioisotope thermoelectric
generators (engine)
2) controlling the cameras and limited data
storage.
3) the data rate of communications fell as the
distance of the probe from Earth increased
and the received signal grew weaker
View of Uranus from Voyager 2
The Hubble Space
Telescope has allowed
scientists to observe
atmospheric changes
and surprisingly,
changes to the shape
of its rings.
Astronomers were able
to see the rare “edgeon” view as Earth
became aligned with
Uranus’ rings in August
2007. No future
spacecraft missions are
planned for Uranus.
Note of Interest: Uranus can be seen from Earth with binoculars.


If experiments at the University of
California, Berkeley, are any indication,
future explorers of our solar system may
well find diamonds hailing down through
the atmospheres of Neptune and Uranus.
These planets contain a high proportion of
methane, which UC Berkeley researchers
have now shown can turn into diamond at
the high temperatures and pressures found
inside these planets. "Once these
diamonds form, they fall like raindrops or
hailstones toward the center of the planet,“
Neptune and Uranus are estimated to
contain about 10 to 15 percent methane
under an outer atmosphere of hydrogen
and helium. (See graphic for presumed
internal structure of Neptune)

Recently some theorists in Italy also
concluded that diamonds were likely.
Benedetti and Jeanloz decided to try the
obvious experiment -- squeeze liquid methane
and see if they could make diamond dust.
The liquid methane, cooled with liquid
nitrogen, was placed in a diamond anvil cell
and squeezed to between 10 and 50 billion
pascals (gigapascals), or about 100,000 500,000 times atmospheric pressure. The
researchers then heated the compressed
methane with an infrared laser to about 2,000
to 3,000 Kelvin (3600-5400 degrees
Fahrenheit). "It's really cool to watch," said
Benedetti. "When you turn on the laser the
methane turns black because of all the
diamonds created. The black diamond specks




Why doesn't Uranus radiate more heat than it
receives from the Sun as the other gas planets
do? Is its interior cold?
Why is its axis so unusually tilted? Was it due to a
massive collision?
Why do Uranus and Neptune have so much less
hydrogen and helium than Jupiter and Saturn? Is
it simply because they are smaller? or because
they're farther from the Sun?
What will happen to Uranus's weather as it
progresses through its seasons?

Unlike the other large planets in the Solar
System, Uranus actually gives off less heat
than it absorbs from the Sun. The other large
planets have tremendously hot cores, and
radiate infrared radiation. But something
made the core of Uranus cool down to the
point that it doesn’t radiate much heat. The
temperature of the cloud tops on Uranus can
dip down to 49 K (?224 °C).
Many astronomers think that a large proto-planet
smashed into Uranus billions of years ago. This
collision set the planet tumbling. Eventually it
settled into its current axial tilt.
However, some astronomers think Uranus moons
tell a different story. The outer 8 are distant, small
and move in elliptical retrograde orbits that are
highly inclined. This suggest that they are
captured asteroids (or KBOs, or Centaurs) and are
not related to this problem.
The inner 18 moons are close to the planet, are of varying sizes, but are all in
almost perfectly circular orbits that are right on Uranus's equator. Every single
one of them has a very low inclination to Uranus's equator and a less eccentric
orbit than our moon has. They undoubtedly were formed at the same time as
Uranus.
A collision with a comet (or any other object) certainly could not have shifted
Uranus's tilt by 98 degrees or so and at the same time shifted the inclinations of
18 satelites, not to mention a ring system, by exactly the same amount. In fact, it
is very difficult to conceive of any mechanism that could manage that trick. So the














http://www.solarviews.com/eng/uranus.htm
http://nineplanets.org/uranus.html
http://www.aerospaceguide.net/planeturanus.html
http://www.windows2universe.org/uranus/discover.html
http://www.spacetoday.org/images/SolSys/Uranus/UranusHubbleDiscov
eries400x543.jpg
http://stardate.org/astro-guide/ssguide/uranus
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Uranus
http://www.universetoday.com/19279/10-interesting-facts-about-uranus/
www.spacetoday.org/SolSys/Uranus/UranusMoons.html
http://www.spacedaily.com/news/carbon-99d.html
http://www.freewebs.com/mdreyes3/outer_planets.jpg
http://www.planetsalive.com/
http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap13/FG13_10.jpg
http://www.daviddarling.info/encyclopedia/U/Uranus_rings.html
1)
2)
T
T
F
F
3)
T
F
4)
T
F
5)
T
F
Uranus is the 8th planet from the sun
Uranus is a blue-green colour because
of ammonia in its outer atmosphere.
Uranus was discovered in the 18th
century (the 1700’s)
The moons of Uranus are named after
Shakespeare’s characters
Voyager 1 was the first probe to visit
Uranus.
1)
a)
2)
a)
b)
c)
Which one of these moons is not one of Uranus’ 5 largest moons:
Titania
b) Oberon
c) Rosalind
d) Miranda
e) Ariel
Which theory is most commonly accepted:
Uranus formed in its present position
Uranus formed closer to Jupiter and Saturn and were pushed outward
Uranus is an extraterrestrial object that was captured by the Sun’s
gravity
3)
a)
What is the approximate tilt of Uranus’ rotational axis?
0°
b) 23.5° c) 36.5°
d) 98°
e) 177°
4)
Uranus is most similar to :
Saturn
b) Earth
c) Neptune
a)
d) Mars
The colour of Uranus’ atmosphere is due to:
a) Methane
b) Hydrogen
c) Carbon Dioxide
5)
d) Ammonia




1) Uranus was not known to Ancient people –
how was uranus discovered and who is
credited with the discovery.
2) Draw a cross-section of Uranus – describe
each “layer”
3) Describe the formation of Uranus
4) Discuss the theories as to why Uranus has
a large axial tilt.