Published 2 years ago
- Is the largest and most massive planet in our solar system.
- Radius is derived from angular size and distance.
- 11 times the radius of the earth, the we know the volume and it can hold 1400 Earths.
- Mass measured from the orbits of its many moons
- M 4π2 d3/ p2
- Average density 1.33 gm/cm3, just slightly more than water. This tells us that it is mostly hydrogen.
- Rotation takes only 9.9 hours even though it is so large very high speed causes Jupiter to have a bulging equator.
Jupiter’s Interior Structure
- We cannot measure Jupiter’s seismic waves.
- We derive the interior structure using computer calculations (we try to compute what Jupiter is like and then try to compare it with our observations).
- Use the average density of 1.33 gm/cm3 to estimate the composition.
- Use the balance between weight and pressure.
- A thick atmosphere of hydrogen gas and molecules containing a lot of hydrogen.
- Below the atmosphere is a deep ocean of hydrogen compressed to a liquid.
- Below that is another deep ocean of hydrogen compressed to a liquid metal capable of conducting electricity.
- At the centre is a core of rock and metal with a mass of about 18 MEarth.
- The core temperature 30,000 K is about 5 times hotter than the Sun’s surface temperature.
- Heat comes from Jupiter’s formation;
- From slowly shrinking energy of gravity (gets transferred into energy in the core)
- Jupiter’s atmosphere is very different from Earth’s:
- Made of hydrogen and hydrogen molecules not O2 and N2.
- Much thicker.
- Much faster rotation- jet streams of cloud belts, not swirls.
- Receives more energy from the interior than from sunlight.
- No solid land below the atmosphere, just liquid.
- Unique feature Great Red Spot
- A hurricane that doesn’t go away
- Has existed for centuries because it was never cut off from its course of energy.
Jupiter’s Magnetic Field
- In Ch 6 we learned that Earth has a magnetic field created by the dynamo of its molten metallic core.
- We have observed Jupiter for centuries from earth, but we never saw its rings.
- In 1979 the spacecraft Voyager 1 found the rings by taking pictures from behind Jupiter looking for lightening.
- The rings are probably from dust blasted from tiny moons by impact.
- Galileo discovered the 4 large moons of Jupiter in 1609 the Galilean moons Io, Europa, Ganymede, Callisto.
- We have discovered a total of 69 moons.
- They form a miniature “solar system” with Jupiter acting like the Sun recall in we learned that Galileo
- Io is the Galilean moon closest to Jupiter
- We observe that its surface is bright and has no impact craters Io must be resurfaced continually.
- Constant volcanic eruptions fill in any craters created by impacts.
- Therefore, Io’s interior must still be very hot, but it is about the size of our Moon?
Why is Io still so hot?
- Io orbits close to Jupiter, the most massive planet in the solar system.
- Therefore, Io experiences powerful tides.
- Io is a member of a large family of moons that interact with each other.
- These interactions prevent it from having a synchronized spin so it cannot escape from tidal heating as our moon has (so since it cannot avoid the tidal heating like our moon can, it is a more complicated environment, more powerful tides are combing to do this)
- We have measured that Io’s lava is rich in sulfur, which is common in earth’s lava too
- Sulfur is commonly yellow, but it changes colour depending on its temperature explaining the appearance of Io.
- Europa is the smallest Galilean moon, and the second closest to Jupiter
- Its surface is white with long cracks and no large craters.
- White surface water ice like our arctic.
- No craters constant resurfacing by liquid water from below the surface.
- Heating by tides from Jupiter’s gravity. (the stretching from the tides from the moon’s gravity provides enough heat to melt ice. Energy from tides).
- The existence of liquid water on a moon so far from the sun was a surprise.
- Shows that heating from tides can be as significant as sunlight.
- The liquid water makes Europa a place where life could exist.
- The largest moon in the solar system, even larger than Mercury.
- Its average density is only 1.94 g/cm3 mixture of metal, rock, and water/ice.
- Its surface has white craters ice just below the dark surface.
- It surface has cratered and new regions
- It has a magnetic field molten core?
- Average density 1.85 g/cm3 also a mixture of metal, rock, and water/ice.
- Its surface is heavily cratered showing no signs of shifting.
- Callisto’s gravitational pull on our space crafts indicates it does not have a differentiated core and mantle structure.
- Jupiter’s 65 moons are:
- Much smaller than the Galileans moons.
- Much more random orbits.
- Are not spherical.
- This suggests they have probably been captured by Jupiter’s strong gravity rather than having been born with Jupiter, like the Galilean moons.
- Saturn is the second largest planet
- Mass 95 MEarth
- Radius 9.5 Reath, vol. could hold 860 Earths
- Average density is only 0.7 g/cm3, which is less than water mostly hydrogen.
- Galileo observed that Saturn was not round, but his telescope was not good enough to see it’s rings
- The width of the rings is about 100,000 km, but they are only about 100 m thick - stars can be seen through them.
- The great width and tiny thickness tells us that the rings are not a solid structure.
- Instead they are swarms of trillions of separate particles orbiting Saturn , each particle follows Kepler’s 3rd Law.
- The particles in the rings range in size from a few meters down to mm.
- Studying the ring’s reflected sunlight they are mostly ice with a mixture of rock.
- A number of gaps exist in the rings which are caused by the gravity of some of Saturn’s moons.
What Causes Ring’s
- When we thought that Saturn was the only planet…
- Then we discovered that Jupiter has rings.
- Possible important factors:
- Each Jovian planet has many moons made of rock and ice. Collisions between moons can break off rock and ice creating the rings
- The strong gravity of the Jovian planets will pull the debris apart if it comes too close to the planet Roche limit.
- Like Jupiter, Saturn has many moons:
- 1 large moon Titan.
- 62 small moons.
- Titan is slightly larger than Mercury , and it has the densest atmosphere of any moon
- Even denser than Earth’s atmosphere
- Titan is so cold at 9.6 AU from the sun that is gravity can hold an atmosphere
Titan’s Atmosphere and Surface
- Our spacecraft have found:
- Titan’s atmosphere is mostly nitrogen like Earth’s.
- Its clouds are hydrogen molecules not water.
- Its surface has rivers and lakes, not water but liquid hydrogen molecules like methane CH4 and ethane C2H6
- The probe Huygens landed on Titan surface showing water-ice “rocks” as small as 10 cm.
Small Moons of Saturn
- The small moons of Saturn also have very intriguing properties.
- Some have odd surface features
- Enceladus has eruptions of liquid water from its surface caused by tidal heating from Saturn possible location for life from tidal energy, not sunlight.
- The planets Mercury Saturn are visible without a telescope, and they have always been known.
- Uranus was discovered using a telescope in 1781 by the musician/astronomer William Herschel.
Physical Properties of Uranus
- Diameter angular size x distance 4 x Earth
- Mass from its moons’ orbits 14.5 x Earth.
- Average density 1.27gm/cm3 almost the same as Jupiter ( I think that’s what it said)
- But Uranus’ mass is lower than Jupiter, so it is less compressed less H gas and more water and hydrogen molecules.
Atmosphere of Uranus
- Uranus appears very blue, quite different than Jupiter or Saturn.
- (The colour of Uranus and Neptune are very blue unlike the other planets).
- The blue colour is cause by Uranus’ very cold temperature 76 K -197 degrees Celsius.
- As a result, certain types of gas freeze out of the atmosphere and become ice particles ( in both Neptune and Uranus).
- Methane (CH4) gas remains, which is a very efficient absorber of red light
- Turns out methane is a very good absorber of red light, so what’s left is reflected which is mostly blue.
The Tilt of Uranus’ Rotation Axis
- One very strange property of Uranus is the tilt of its rotation axis to its orbit: 97.86 degrees.
- Most of the moons of Uranus orbit aligned over its equator, so they too are tilted.
- The rings of Uranus are also aligned over the equator and share the same tilt.
- The extreme tilt of the rotation axis causes very extreme sunlight and seasons.
- Was discovered in 1846 when it was noticed that Uranus was deviating from its unexpected orbit.
- The deviation was used to predict the location of an unknown planet.
- Observing that location of the solar system found Neptune.
- Today a similar each is being done searching for planet X.
Neptune's Physical Properties
- The mass, radius, average density and appearance of Neptune are very similar to Uranus (only based on calculations)
- Saturn the most, Uranus not so much, Neptune not so much