Jovian Satellites and Rings

nearly circular orbits in the equatorial plane of the planet All the Jovian planets have many known moons Jupiter 67 known moons (53 named, 14 provisional) Saturn 62 (53 named , 9 provisional) Uranus 27 (Named for characters from Shakespeare and Pope) Neptune 14 (13 named , 1 provisional) Note that both Ganymede and Titan are larger than Mercury! Most of the medium and large Jovian moons probably formed by accretion along with the planet: nearly circular orbits in the equatorial plane of the planet orbit in the same direction as the planet rotates Proteus

(You should know these from Jupiter outward) The Galilean moons of Jupiter – Galileo saw these through his telescope (You should know these from Jupiter outward)

Io – the most volcanically active body in the entire solar system

Five-image sequence of New Horizons images showing Io's volcano Tvashtar spewing material 330 km above its surface.

Io – the most volcanically active body in the entire solar system

Io – the most volcanically active body in the entire solar system - But WHY is its interior still so hot?

Io – the most volcanically active body in the entire solar system - Why is its orbit so elliptical?

Europa – An ice covered ocean?

Europa – An ice covered ocean? Physical properties suggest a global ocean, 100 km deep, exists under the ice. Salts have been observed on the ice that came from inside the moon. They indicate that the ocean is salty, most likely including organic molecules. While the evidence is indirect, the possibility that primitive life exists in that ocean are slight but very interesting.

Ganymede most likely has a DEEP global ocean beneath its icy surface (10x deeper than Earth’s oceans!) 2 years ago scientists reported on new evidence for this ocean based on studies of how the aurorae move across Ganymede’s surface

Thermodynamics of salt water suggests that there Artist's cut-away representation of the internal structure of Ganymede. Layers drawn to scale. Thermodynamics of salt water suggests that there may be multiple layers of ice and water, including a bottom layer in contact with the rocky mantle.

Saturn’s moon Enceladus is similar Some surface regions have lots of craters, some regions have none.

Notice that there are NO craters on this portion of the surface This is a FRESH surface!

Compare the visible “Tiger Stripes” to an infrared image of the same area

Cassini has flown through the spray and sampled it! There are at least 90 geysers around the south pole of Enceladus that are spraying material into space Cassini has flown through the spray and sampled it! It is water with about the same salinity as our oceans. It also contains organic molecules! (Just a cool picture!)

Scientists assembled years worth of photos of Enceladus, taken by Cassini, to study its wobble. The wobbling is consistent with a moon whose icy crust is completely mechanically disconnected from its core

Cassini made a very close pass by Enceladus’s south polar region (altitude = 30 miles) 2 years ago. It sampled the plumes again, and scientists are looking for the chemical signature of hydrothermal activity at the bottom of the ocean. This would be reminiscent of the “black smokers: at the bottom of Earth’s oceans – places where life exists without depending on photosynthesis.

Saturn has another fascinating and unique moon: Titan Like Venus, we cannot see the surface due to thick clouds Titan’s atmosphere is 90% nitrogen The rest is argon, methane, ethane, and other hydrogen compounds (Mimas)

This was the Huygens probe. The chemistry of this atmosphere is so interesting, we dropped a probe into it to gather more data. This was the Huygens probe.

It took pictures from the surface, too. Huygens took photos all the way down, and saw liquid methane river beds. It measured wind speeds, sampled the atmosphere, measured temperatures and pressures, and measured the acceleration upon to impact. It took pictures from the surface, too.

Methane lakes imaged by radar Meanwhile Cassini continued to observe Titan from Saturn orbit, using radar as well as near-IR, IR and other wavelengths Methane lakes imaged by radar

What does that suggest about its origin? Phoebe (110 km) Retrograde orbit What does that suggest about its origin?

They “swap positions” every time the inner one catches the other Janus “Coorbital moons” They “swap positions” every time the inner one catches the other Epimetheus

Iapetus (718 km) Trailing side is like dirty snow A 10 km high ridge along its equator spans nearly half its circumference. No one knows its origin, but it is likely tectonic Leading side is dark from dust collected over millennia

It is resonance with this moon that causes the Cassini division Mimas (199 km) It is resonance with this moon that causes the Cassini division

Hyperion (180x112 km) Sponge-like appearance due to solar heating of subsurface water-ice in craters Outgassing creates the pits Latest measurements suggest it is about 40% empty space!

Two of Neptune’s largest moons (Proteus is slightly larger than Nereid) Triton (1353 km) Nearly circular, but retrograde Nereid (170 km) Prograde, but VERY elliptical Proteus (210 km) orbits inside Triton. Very circular orbit, very low inclination

Saturn’s rings, backlit

Photo from the Cassini spacecraft

Ring details

Note the waves on either side: Pan (12 mi) Encke Gap Note the waves on either side: Kepler’s Laws allow us to understand them

Daphnis (4 mi) Keeler Gap

F ring Keeler Gap Where is Daphnis?

Remember, they do NOT orbit together! Shepherd moons Remember, they do NOT orbit together! Prometheus Pandora F ring Keeler Gap

Caused by orbital resonance with Mimas F ring Keeler Gap Encke Gap Cassini Division Caused by orbital resonance with Mimas NOT shepherd moons!

Cassini Division detail

Encke Gap detail

An oblique view shows many gaps and regions of differing densities

ALL of the Jovian planets have rings Ring material breaks down over time, blasted into tiny dust grains that eventually fall into the planet. So why are there still rings?

Impacts on the moonlets keep a supply of icy particles around so the rings don’t entirely disappear.

Astro-Cash Cab! Samantha Katy Daniel Augustine Jesse K.

1) Match these Jovian moons with their description: A) Titan _____ B) Enceladus _____ C) Io _____ 1) Organic molecules have been discovered spaying out of it 2) Most volcanic body in the solar system 3) Has a thick atmosphere that obscures the surface at visible wavelengths

Saturn’s rings are the debris left over from a Moon that never formed. 2) True or False? Saturn’s rings are the debris left over from a Moon that never formed.

3) Which is the only large moon that has a retrograde orbit? Io Titan Nereid Triton Ganymede Enceladus

4) Which Jovian planet’s moons are named after characters from William Shakespeare and Alexander Pope? Jupiter Saturn Uranus Neptune