Astronomy (Jupiter, Saturn) & (Outer Worlds: Uranus, Neptune, and Pluto)

Jupiter’s Appearance in SKY

Second brightest planet most of the time.

Yellow-white in color.

Oppositions (Earth passing by it) every 13 months.

Jupiter’s Telescopic Appearance

Striped planet with parallel belts and zones. Belts are orange-brown, zones are yellow-white.

Storms seen as swirls and white ovals.​​

The Great Red Spot is visible every 10 hours.

The 4 large moons (Galiliean moons).

Jupiter as a World

Composition largely Hydrogen and Helium. 

Cloud Layers: Zones are Ammonia. Belts are Ammonium Hydrosulfide.

Internal Structure: Gaseous Molecular Hydrogen, Liquid Metallic Hydrogen, core of rock in plasma form.

Jupiter’s Internal Heat

Jupiter radiates more energy than it receives from the sun.

Energy is in the form of Radio and Infrared.

Cause: Leftover heat of formation, it is still cooling very slowly.

Jupiter’s Weather

Winds blow in excess of 300 mph, but not a record speed.

The Great Red Spot resembles an Earth hurricane in many respects, but is large enough to contain 3 Earths.

Many other storms near the equator come and go monthly, seen as white ovals.

Jupiter’s Magnetosphere

Jupiter has an incredible Magnetosphere second only to the Sun.

Magnetic tail extends past the planet Saturn.

The field is created in a liquid Hydrogen layer of interior. 

A torus or doughnut of material ejected from Jupiter’s volcanic moon lo is in the field.

A strong electrical connection runs between Jupiter and lo.

Solar wind particles and plasma from lo get caught in the magnetic field and spiral emitting energy in radio waves.

This is called Cyclotron radiation and makes Jupiter the second most powerful radio source in the sky. (18-40 MHZ).

Cyclotron Radiation

Solar wind particles and plasma from lo get caught in the magnetic field and spiral emitting energy in radio waves.

Makes Jupiter the second most powerful radio source in the sky. (18-40 MHZ).

Atmospheric Lights

Jupiter and all the gas giants have Auroras due to solar wind/atmosphere interaction.

Jupiter has lightning flashes in the atmosphere caused by thunderstorms.

Rings

Jupiter and all of the gas giants have ring systems.

Jupiter’s Moons

Jupiter has more than 90 known moons.

Most are tiny captured asteroids.

The Galilean moons are the largest. They vary in size from similar to Earth’s moon to one the size of planet Mercury.

Ganymede, Europa, and Callisto included.

Moons are stretched by the tidal pulls of Jupiter. This leads to lo being wildly volcanic.

Ganymede (Moon on Jupiter)

Largest moon in the SS, but third biggest moon away from Jupiter. Here tides are weaker.

Europa (Moon on Jupiter)

Has a cracked icy surface of water, ice and may have a salt water sea under the ice. Perhaps a great place to look for life.

Callisto (Moon on Jupiter)

The most distant of the big moons away from Jupiter. The surface is ancient and dead, covered with icy impact craters.

Jupiter’s Gravity Influences

Jupiter helped create the asteroid belt a long time ago.

There is an ongoing asteroid belt influence in the form of the Kirkwood gaps.

The belt has thick and thin areas like rings.

Jupiter is also the prime maker of short-period comets with P < 200 years.

Saturn’s Appearance in SKY

Saturn appears as a bright “star” about equal in brightness to a bright star.

Appearance is yellow.

Saturn has oppositions about every 13 months.

Saturn’s Telescopic Views

Saturn is known for its dramatic rings.

Overall the planet is striped with belts and zones like Jupiter. They are not as obvious due to ammonia haze.

Most telescopes show the A, B, C rings and up to 7 moons.

Rings experience season and go edgewise every 14.5 years.

Saturn as a World

Least dense planet in SS.

Composition of interior and clouds the same as Jupiter. Hydrogen, Helium, Methane, and water.

Polar tilt of 27 degrees causes seasons and ring tilt.

Great White Spot: Seasonal storm appears every 29 years.

Like all gas giants, Saturn has a magnetic field, auroras, and many moons (more than 60). 

Saturn’s Rings

The rings are thousands of miles wide and yet only 100 meters thick.

Composition is water ice and silicate dust.

Particles vary in size from grains to large boulders.

Thick areas are called ringlets, thin areas are gaps or divisions.

Structure induced by tidal pulls of Saturn and passing moons.

The inner rings orbit faster than outer rings, thus obeying Kepler’s law.

Most likely formation theory is the rings were formed by tidal break-up of one or more Saturnian moons.

If a moon passes within the Roche limit of a planet (2.5 planet radii) tidal forces will shred the moon to pieces.

Alternate ideas: Material from moon asteroid impacts or collisions between moons.

Thick Areas in Rings

Ringlets.

Thin Areas in Rings

Gaps or divisons.

How did the Rings form?

Formed by tidal break-up of one OR more Saturnian moons or material from moon asteroid impacts or collisions between moons.

Saturn’s Moons

Titan is the largest moon at Saturn.

• Surface shows lakes and rivers of methane. Titan may have active geysers and cryo-volcanoes. Very cold.

The moon Enceladus is a near twin of Jupiter’s moon Europa.

• The surface is very bright water ice covering a silicate rich moon.

• It is believed to have a salt water sea under the ice and has geysers erupting from the surface. (thermo energy caused by tides)

• This is a great place to find new life.

Titan (Moon on Saturn)

Titan is the largest moon at Saturn.

Surface shows lakes and rivers of methane. Titan may have active geysers and cryo-volcanoes. Very cold.

Enceladus (Moon on Saturn)

The moon Enceladus is a near twin of Jupiter’s moon Europa.

The surface is very bright water ice covering a silicate rich moon.

It is believed to have a salt water sea under the ice and has geysers erupting from the surface. (thermo energy caused by tides)

This is a great place to find new life.

Other Saturn Moon’s

Most of the other moons are small and unremarkable.

• Mimas has a huge crater.

• Dione and Rhea show signs of some surface activity in the form of wispy streaks.

• Tethys has a major canyon associated with a large impact basin.

Outer Worlds

Uranus, Neptune, and Pluto.

Uranus Basic Facts

Discovered 1781 by accident by William Herschel.

The appearance in the sky is right at the naked eye limit of 6th magnitude.

Before its discovery, other observers had plotted it as a “star” on published star atlases at least 20 times.

Uranus as a World

Cloud tops rich in Methane. Leads to blue-green color.

Both Uranus and Neptune are very much twins.

Polar tilt is 98 degrees. Planet orbits the sun on its side with seasons 21 years long.

Uranus has a magnetic field that is highly tilted and offset with respect to the rotational axis. Neptune is the same.

Uranus has at least 11 ringlets. The rings are dark and hard to see.

All ringed planets have rings inside the…

Roche Tidal Limit, suggesting rings form through tidal-break up of a moon.

The Moons of Uranus

The moons of Uranus are all small ice covered moons. More than 25 known.

The major moons have names taken from Shakespeare’s play “A Midsummer's Night Dream.”

Miranda is probably the most interesting. A nightmare of ice features.

Neptune Basic Facts

Neptune was discovered in 1847 as a result of a search based on gravitational pulls of a search based on gravitational pulls of a planet beyond Uranus displacing its position from expected positions.

Two mathematicians Laverrier and Adams independent of one another came up with the correct position.

Galileo had seen it and dismissed it 234 years earlier.

Neptune as a World

Composition the same as Uranus.

Significant weather has been observed by telescopes and spacecraft. Neptune has the highest winds in SS, about 1500 mph. 

Neptune Moons

Neptune has more than a dozen small icy moons.

The most interesting is Triton.

• Triton is active with surface geysers ejecting Nitrogen into space, but it is also a captured moon.

• Most likely a former dwarf planet.

Pluto Basic Facts

Pluto was discovered in 1930 after a planned search by Clyde Tombaugh of the Lowell observatory in Arizona.

To see Pluto requires at least a 6 inch telescope as the planet is 13th magnitude.

Pluto as a World

Composition is ice and rock.

Surface is made of a surprising amount of water ice and Pluto seems to be active with water ice volcanoes erupting.

Surface is a mix of smooth and mountain areas.

Pluto has a thin atmosphere giving it blue skies.

Volcanic vents exist on Pluto.

Pluto Moons

Pluto has 5 known moons: Charon, Nix, Hydra, Styx, and Kerberos.

Pluto is believed to be one of many dwarf planets in the outer SS.

• The biggest of all is Eris, found in 2003.

• In 1992, astronomer Alan Stern proposed the existence of thousands of Pluto-like bodies in the outer SS.

• From 1993 forward many have been found including Eris (2003) which is bigger than Pluto.

• Stern was the lead scientist for the New Horizons mission.

Describe four differences between the Jovian planets and the Terrestrial planets

The Jovian planets have many moons, low density, no real surface, and large masses.

The Terrestrial planets have low masses, solid surfaces, small diameters, and few if any moons.

If Jupiter had a satellite the size of our own Moon orbiting outside the orbit of Callisto, what would you predict for the satellite’s density and surface features?

I predict it would have a low density. Surface features would include impact craters and little signs of geological activities. 

Why are no craters seen on io and few seen on Europa? 

Impact craters are fastly erased and they are both geologically active. 

Why are the belts and zones in the atmosphere of Saturn less distinct than those in the atmosphere of Jupiter

They are deeper inside of Saturn’s atmosphere.

How can Titan keep an atmosphere when Titan is smaller than airless Ganymede?

Titan is farther away from the Sun.

What should the interior composition of Titan be if its density is 1.9 g/cm3? How do you know?

1.9 g/cm^3 would be largely made of ice. We know because Titan is primarily composed of ice and rock material. 

Both Uranus and Neptune have a blue-green tint when observed through a telescope. What does this color tell you about their atmospheric composition?

Methane in their atmospheres is what gives Uranus and Neptune a blue-green tint. The methane absorbs red light. 

How are the atmospheres of Earth and Triton similar? 

They both contain layers such as an exosphere, thermosphere, and troposphere.

Describe evidence of geological activity on Triton. 

On triton, geological activity includes geysers of liquid nitrogen found on the surface.  

When Neptune was discovered, how was its position predicted? 

Its position predicted positions of Uranus caused by gravitational interaction with Neptune. 

How can small worlds like triton and Pluto have atmospheres whereas a larger world such as Ganymede has none?

Small worlds like Triton and Pluto have atmospheres while the larger Ganymede has none because Ganymede is closer to the Sun while Triton and Pluto are farther away and have frozen gasses.

What evidence can you give that Pluto and Charon are mixtures of rock and ice?

They have the same density and they both have some ices shown by a spectra of the two. 

Why was Pluto reclassified as a dwarf planet?

Pluto isn’t large enough by definition.