Observations and the Solar System : Lecture 8

Saturn

The next planet we meet coming from the sun is Saturn. Saturn has many similarities to Jupiter. It is also a gas giant (but "only" 95 times as heavy as the earth). It does have very spectacular Rings These can be seen with a small telescope and are an extremely attractive feature. There are composed of rocks orbiting Saturn together in the rings. On close inspection they have divisions and much structure. Features include, 10 hrs 13mins rotation period cloudtop temperatures of -180 C Less dense atmoshpere than Jupiter One major satelite -Titan

Titan was the target for the Huygens probe on the Cassini Mission . It is the only moon in the solar system with a atmosphere. It is thought that it in many ways ressembles a prototype earth but one caught in "deep-freeze"

We discussed the Cassini Mission as an example of Solar System Exploration and in particular the role of the Huygens probe which is ESA (European Space Agency) contribution and which will land on Titan.
Titan was a major target of the Voyager missions but the, surprising, dense atmoshpere prohibited pictures of the moon's surface. Vayoager data suggest Titan's has

• A surface pressure of 1.6 At - more than earths!
• Atmospheric composition of 90 percent Nitrogen , 10 Percent Methane
• Surface Temperature of -178 C

• image of storm on Saturn
• image taken by voyager (with 2 small moons visable
• image showing moons Tethys and Dione (inc shadow).
• HST image of Saturn showing thinness of rings
• HST image of Saturn (false colour)
• Composite HST images of Saturn
• Voyager image of Saturn looking back as it moved onwards
• image of rings (false colour)
• image of rings (false colour). Differing colors indicate differing chemical,composition
• image of moon Titan - note the thick hazy atmosphere
• image of moon Dione - with impact craters
• image of moon Mimas - with an 100km wide impact crater which must almost have destroyed it
• image of moon Enclades: moon with subsurface water (see here and here )

• image of the spacecraft and flight path ,

Uranus and Neptune

Both have ring structures and many small moons Some images of Uranus and Neptune are,

• image of Neptune
• image closer image of Neptune
• image of Neptun's blue spot
• HST images of Neptune

Dwarf Planets

The Solar system contains, at present, five objects designated to be dwarf planets . It is expected that more will be found with time

Pluto and Charon

Pluto has only just been visited this year by the Horizons probe and is curently sending data back to Earth. It is unusual in several aspects. Firstly it is NOT a gas planets but is small and probably composed of rock/ice. Its orbit is also peculular. It has rather an eceentric orbit sometimes it is closer to the sun than Neptune. Its distance from the sun varies from between 30 and 50 A.U. Its orbit's plane is also significantly different from the other planets. Pluto has a moon Charon which is almost as big as Pluto itself ( its diameter is about half)

It is thought that Pluto is just one (perhaps the largest) of many small rocky worlds existing in the outer reaches of the solar system in the ``Kuiper belt''. It is thought that Triton could be one of these objects "captured" by Neptune. The images of Pluto and charon include a few HST images -

• an image of the pair and the best image of the surface of pluto- turned into a map

and some images from the Gemini telescope

• image of the pair over a few nights

Ceres

Ceres lies in the asteroid belt

Eris (formally designated Xena)

Orbit of Eris It is expected that mny more objects will be discoved in coming decade. Details of the five accepted dwarf planets is to be found on the planet data sheet The following figure compares these objects (excluding ceres) together with potential still to be acknowledge dwarf planets

---