UranusThe 7th Planet

Presentation for SES4U

Location

Uranus’ position in the solar system can be seen in the diagram above (diameters and distances are not to scale).

The diameter of Uranus can be compared with other 7 planets and some dwarf planets in the picture below

Basic Information

7th planet from the sun Mean Distance 2,870,990,000 km (19.18 AU) Rotational Period 17.3 hours (0.72 days) Orbital Period 84.01 years Eccentricity 0.0461 (almost circular) Diameter 51,118 km

(4 times greater than Earth)3rd largest planet

Density 1.24 g/cm3 (22% of Earth) Mass 15 times greater than Earth

(63 times greater volume) Inclination of Axis 97.92° (Uranus appears to tilted

completely on its side)

Views of Uranus

Uranus has very fine, dark coloured rings

A Day on Uranus

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.

Origin of the Name

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).

History

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’s Doubts 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.

History continued

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.

Theories on the Formation of Uranus

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.

Formation of Uranus

The outer giant planets, Uranus and Neptune, pose a challenge to theories of planet formation. They exist in a region of the Solar System where long dynamical timescales and a low primordial density of material would have conspired to make the formation of such large bodies (~15 and 17 times as massive as the Earth, respectively) very difficult. In this work, a well-

established model of planet formation, together with numerical simulations, are used to show that such bodies are unlikely to have formed far beyond the region of Jupiter and Saturn. A model which addresses this problem is proposed: instead of forming in the trans-Saturnian region, Uranus and Neptune 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. Numerical simulations show this model to be very robust, readily reproducing the configuration of the outer Solar System for a wide range of initial conditions. Simultaneously, the model may also help to account for the present state of the asteroid belt and the Kuiper belt (the trans-Neptunian disk of comets).

The outer giant planets, Uranus and Neptune, pose a challenge to theories of planet formation. They exist in a region of the Solar System where long dynamical timescales and a low primordial density of material would have conspired to make the formation of such large bodies (~15 and 17 times as massive as the Earth, respectively) very difficult. In this work, a well-

established model of planet formation, together with numerical simulations, are used to show that such bodies are unlikely to have formed far beyond the region of Jupiter and Saturn. A model which addresses this problem is proposed: instead of forming in the trans-Saturnian region, Uranus and Neptune 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. Numerical simulations show this model to be very robust, readily reproducing the configuration of the outer Solar System for a wide range of initial conditions. Simultaneously, the model may also help to account for the present state of the asteroid belt and the Kuiper belt (the trans-Neptunian disk of comets).

The outer giant planets, Uranus and Neptune, pose a challenge to theories of planet formation. They exist in a region of the Solar System where long dynamical timescales and a low primordial density of material would have conspired to make the formation of such large bodies (~15 and 17 times as massive as the Earth, respectively) very difficult. In this work, a well-

established model of planet formation, together with numerical simulations, are used to show that such bodies are unlikely to have formed far beyond the region of Jupiter and Saturn. A model which addresses this problem is proposed: instead of forming in the trans-Saturnian region, Uranus and Neptune 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. Numerical simulations show this model to be very robust, readily reproducing the configuration of the outer Solar System for a wide range of initial conditions. Simultaneously, the model may also help to account for the present state of the asteroid belt and the Kuiper belt (the trans-Neptunian disk of comets).

Planets accreting from the early Solar Nebula. Note larger planetessimals are drawn together by gravity and collide.

Structure and Composition

http://www.freewebs.com/mdreyes3/outer_planets.jpg

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 jet-streams present on Uranus rather like those on the Earth.

A comparison of Atmospheres

Uranus’ Atmosphere 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 temperatures are about 2 to 3 K lower.

<>

Very faint cloud bands visible on the surface layers of Uranus.

Moons 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 characters.

Inner Moons of Uranus

Composition of the moons

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 low-impact 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.

Titania is the largest moon and is similar to Oberon.

Uranus’ five largest moons

The Minor MoonsAll 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 defined.

Moon DataName Diameter (km) Mass (kg) Orbital radius (km) Orbital period (days)

Ariel 1158 1.35E+21 191,020 2.520379Umbriel 1170 1.17E+21 266,300 4.144177Titânia 1578 3.52E+21 435,910 8.705872Oberon 1523 3.01E+21 583,520 13.463239Miranda 472 6.6E+19 129,390 1.413479Cordélia 40 4.5E+16 ? 49,770 0.335034Ofélia 42 5.4E+16 ? 53,790 0.376400Bianca 51 9.3E+16 ? 59,170 0.434579Cressida 80 3.43E+17 ? 61,780 0.463570Desdémona 64 1.78E+17 ? 62,680 0.473650Julieta 93 5.57E+17 ? 64,350 0.493065Pórcia 135 1.68E+18 ? 66,090 0.513196Rosalind 72 2.54E+17 ? 69,940 0.558460Belinda 80 3.57E+17 ? 75,260 0.623527Puck 162 2.89E+18 ? 86,010 0.761833Caliban 98 7.3E+17 ? 7,231,000 -579.7 ** Sycorax 190 5.4E+18 ? 12,179,000 -1288.3 ** Próspero 30 2.1E+16 ? 16,256,000 -1977.3 ** Setebos 30 2.1E+16 ? 17,418,000 -2234.8 ** Stefano 20 6E+15 ? 8,004,000 -677.4 ** Trinculo 10 Unknown 8,504,000 -759.0 ** S/1986 U 10 * 20 Unknown 76,420 0.638S/2001 U 2 * 12 Unknown 20,901,000 -2823.4 ** S/2001 U 3 * 12 Unknown 4,276,000 -266.6 ** S/2003 U 1 * 10 Unknown 97,734 0.923S/2003 U 2 * 10 Unknown 74,800 0.618S/2003 U 3* 11 Unknown 14,345,00 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.

Rings 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 arisen from the breakup of a small moon or moons due to cometary impact.

Views of the Rings

The Instability of Uranus’ Moons and RingsJack 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.

Missions to Uranus

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.

Voyager 2The 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

Hubble Space Telescope

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 “edge-on” 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.

Interesting Facts 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)

It’s Raining Diamonds!!! 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 float in a clear hydrocarbon liquid melted by the laser."

Planetary Mysteries

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?

Uranus is unusually cold

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).

What caused Uranus’ 98° rotational tilt?

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 spin of the proto-Uranus must have already been tilted 98 degrees as the planet was forming.

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.

Sources

http://www.solarviews.com/eng/uranus.htm http://nineplanets.org/uranus.html http://www.aerospaceguide.net/planeturanus.html http://www.windows2universe.org/uranus/discover.htm

l http://www.spacetoday.org/images/SolSys/Uranus/Uran

usHubbleDiscoveries400x543.jpg http://stardate.org/astro-guide/ssguide/uranus http://solarsystem.nasa.gov/planets/profile.cfm?Object

=Uranus http://www.universetoday.com/19279/10-interesting-fa

cts-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/Chap

13/FG13_10.jpg http://www.daviddarling.info/encyclopedia/U/Uranus_ri

ngs.html

True/False Questions

1) T FUranus is the 8th planet from the sun

2) T FUranus is a blue-green colour because of ammonia in its outer atmosphere.

3) T FUranus was discovered in the 18th century (the 1700’s)

4) T FThe moons of Uranus are named after Shakespeare’s characters

5) T FVoyager 1 was the first probe to visit Uranus.

Multiple Choice Questions1) Which one of these moons is not one of Uranus’ 5 largest

moons:a) Titania b) Oberon c) Rosalind d) Miranda e) Ariel

2) Which theory is most commonly accepted:a) Uranus formed in its present positionb) Uranus formed closer to Jupiter and Saturn and were pushed

outwardc) Uranus is an extraterrestrial object that was captured by the

Sun’s gravity

3) What is the approximate tilt of Uranus’ rotational axis?a) 0° b) 23.5° c) 36.5° d) 98° e) 177°

4) Uranus is most similar to :d) Saturn b) Earth c) Neptune d) Mars

5) The colour of Uranus’ atmosphere is due to:a) Methane b) Hydrogen c) Carbon Dioxide d) Ammonia

Matching Question

Short Answer Question

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.