SOLAR  SYSTEM  GEOLOGY
 

.  Firstly I will introduce a number of rocks that I have brought along and which are most abundant in the solar system. All except haematite are igneous rocks.

   1. Meteorite. This is an iron nickel meteorite showing the crystalline structure characteristic of iron meteorites when sectioned. Meteorites are either the debris of a planet that broke up, or aggregations that never formed into a planet. Which of these origins is correct is still disputed.

2.   Quartz. Oxygen and silicon are the two most abundant elements making up the Earth, with metals like iron, aluminium, nickel, and sodium, potassium, and calcium following on. Silicon oxide is quartz or silica or sand, and on Earth is widespread. The silicon in silicon chips is the pure element.

3.   Iron oxide (haematite), and Aluminium oxide (corundum). These are typical metal oxides. Metal ores are usually metal oxides or sulphides, and widespread on Earth.

   Most rocks consist of combinations or chemical compounds of metal oxides and quartz, the whole lot having been melted at considerable depth, under which conditions a very wide range of metal silicates - rocks - form. If there is an excess of quartz some of this will be left over in the final rock, as is the case with the specimen here.

  4.   Granite, from Dartmoor. This consists of grains of quartz in and among the mineral feldspar, a series of metal silicates. When cooled fast quartz rich rocks can form obsidian, a natural glass.

  Casting your minds back many years, you may remember the chemistry teacher ramming home the statement, Acid + Base (metal oxide) gives Salt + Water. This applied to reactions in water but rock formation at thousands of degrees centigrade is the same. Silica corresponds to ‘acid’, metal oxides are bases and metal silicates are ‘salts’. Consequently silica rich rocks are known as ‘acid’ rocks. If, on the other hand, there is a shortage of silica, then there will be no quartz left over to form granules when the rock cools. Again, when a rock consists of many varied metal silicates these tend to have a higher proportion of metal - metal oxide - in them, and these are known as basic rocks. Examples of silica deficient or basic rocks are :-

5.   Basalt. A fine grained rock, typically occurring in volcanic eruptions, and this specimen is from Lake Myvatin, Iceland. 

 6.  Gabbro. It has a similar chemical make-up to basalt, but is coarse grained, due to the fact that it formed at great depths and cooled more slowly. This piece came from the Lizard area.

  [ The rest of the talk was illustrated with slides which may now be with Bristol Astronomical Society. In the original text there is a brief marginal mention of the slide and the numbers used, and this is replicated here in square brackets at the end of the relevant paragraph. There are also diagrams on paper for reproduction on a screen (or to be made into slides). They cover the Moon, Mercury, Jupiter, Ganymede, Europa, Callisto and Io.]

 

 After that brief look at rocks we will turn to the Solar System.

  EARTH.  As is well known, Earth has a crust comprised of light weight granitic rocks forming the elevated continental masses and a thinner basaltic crust coinciding with the oceans. The mantle consists of basic and ultrabasic rocks which gradually give way to iron and nickel at the core. [Whole Earth section; Lava 1 and 2; 6 air (?) shots, the last one GB]

  The Earth’s surface has a vast range of sediments, not seen on other planets except, perhaps, Mars, because Earth has both large land masses and oceans.

 

   MOON. The Moon’s surface has been given descriptive area names of “Seas” or “Maria”, and “Highlands” for the more rugged areas. [Section ; 3 rocks.]

   The Maria are basalt lava flows which solidified 3.4 to 3.8 T.M.(thousand million) years ago and this dates the formation of these basalt plains. The principle minerals were pyroxene and plagioclase feldspar.

   The Highlands rocks are about 4.0 to 4.2 T.M. years old, and are nearly all breccias - rocks made up of crushed and broken pieces of other rock. The rock type is gabbro, largely plagioclase feldspar with olivine pyroxene. At a specific site, the “Barrows Ceresis” the rock was 90 % pure plagioclase feldspar.

 

   VENUS.  Studies of the planet’s magnetic field and density ( worked out from its size and orbital behaviour ) suggest the interior is similar to Earth’s, a metal core and a rocky mantle. The atmosphere, however, is 100 times that of the Earth and composed of H2 SO4.             [Venus, whole view ; Surface ; Artist’s Impression.]

 

  MERCURY.  It has a relatively large metal core and a heavily cratered surface, but so hot it would melt lead. 10% of the surface was mapped by a spacecraft which entered Mercury’s orbit and made three passes.        [Mercury, whole view ; Section ; Artist’s Impression. ]

 

  SUN. No rock, simply gas / plasma. The power of the Sun is, of course, provided by nuclear fusion. Hydrogen atoms combine to form helium atoms, the next element up. Helium weighs slightly less than hydrogen, being caused by energy.  [Sun, whole view; Section ; Flare.]

 

  MARS. The rocks are almost certainly basalt in which haematite is present, creating the red colour visible from Earth. Photos from the Viking probes show evidence of water erosion in the distant past, the water having washed volcanic rock to the plains and depositing it as sediment.  [Mars, whole view; Surface 6; Moons of Mars,1of each.]  

 

  JUPITER. The planet is likely to consist of four bands of material. It has an outer atmosphere of hydrogen, 2 - 3000 kms deep, within which is a band of liquid hydrogen some 30,000 kms deep. Below this, a 35,000 km deep band of solid hydrogen probably encompasses a relatively small rocky core, perhaps 10,000 kms in diameter. Should a spacecraft attempt to land on Jupiter it would go into the atmosphere which, judging by cloud movement, has winds exceeding 1000 miles an hour. At the bottom, 3000 kms down, the atmospheric pressure would be many thousands of times that at the surface, and if the liquid hydrogen was reached waves miles high would be encountered. The spacecraft would by this time be holed and, sinking through the liquid hydrogen at 10 ft a second, it would take two months to reach the solid hydrogen surface.    [Jupiter, whole view; Whole disc section; Artist’s Impression.]

   Jupiter’s Satellites. CALLISTO. A rock core some 3000 kms across, enclosed by ice and slush 1000 kms thick. GANYMEDE. Similar to Callisto. EUROPA. Small - a rocky core 2000 kms diameter, covered by a frozen ‘ocean’ 10 - 50 kms deep. IO. A molten core (kept molten by tidal forces), around 2000 kms diameter, with a thin crust, covered with volcanoes and sulphur deposits. ALMALTHEOS ?? [ Can’t understand the writing. No other details,] [Drawn Illustrations: Callisto 2; Ganymede 3; Europa 3; Io 2. These have been used to provide the descriptions above.] 

   SATURN. Similar to Jupiter. [ Whole view; Whole disc: Artist’s Impression.]

   TITAN. A rocky core, enclosed by bands of ammonia, methane, water and ice. [Artist’s Impression.]

   URANUS, NEPTUNE & PLUTO. Similar to Jupiter and Saturn, but no solid, metallic hydrogen, and a layer of ice between the liquid hydrogen and the rocky core. [Artist’s Impression.]

   COMETS. There are two schools of thought. One, that they are a small rocky core enclosed by a mass of ice, the whole being but a few miles across. The second is  that of a ‘flying gravel bank’ with a core of loosely attracted sand and pebble sized particles, along with ice and gas. On approach to the sun the volatiles are drawn off, giving a tail.

  ASTEROIDS. What can you say? They probably contain iron ,nickel and basalt / gabbro, and who can dispute it ? [Artist’s Impression.]

  METEORITES. Rocks or stones containing iron.