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Io, Earth’s Moon and Europa have the highest densities (3000-3500 kg/m2). Ganymede, Titan and Callisto, the largest moons, have low densities (1600-1900 kg/m2). Triton and Pluto have low densities and medium sized diameters. Titania, Oberon, Iapetus, Rhea, Tethys, Ariel, Miranda, Umbriel and Charon have both low densities and small diameters. Moons such as Miranda and Umbriel are among those that have had the closest orbit with the Sun and yet maintained their integrity of shape; albeit they are heavily scarred. All  the other moons of the solar system which are less than 900 km in diameter are irregular in shape and should be classed as captured asteroids. They are fragments of a previous planet which has disintegrated. Among them, perhaps Hyperion has suffered the greatest damage by the effects of cavitation.


Planetary Collisions


There is a likelihood that some of these previous planets collided with existing planets after their ejection from their orbit with the Sun.


Our Moon was possibly one such previous planet which collided with Earth and was caught on the re-bound. If the impact, rather ran a fly-by, had occurred - then we should expect


1) A large impact crater            

2) An anomaly in the rotation (day-length) of Earth due to the transfer of momentum.

3) A massive extinction event due to catastrophic changes in the environment.

4) Large scale magma flooding


Are there any massive impact craters on Earth?


I scoured Google Earth for a site where the Moon or other previous planets could have impacted with Earth.


There are two areas in the Asian continent which could have been caused by large impact structures.


One is a mega basin which covers most of the area of Kazakhstan, a possible crater of 690 km diameter.


The other is the Tibetan Plateau area, just north of India, with a crater rim of 1300 km diameter. This structure has been considerably modified by the sub-duction of the Tethyan ocean bed which originally existed north of India and the lifting and tilting of the Himalayas.



















Above image - The Kazakhstan impact area



















Above image - The Tibetan Plateau impact area


































































There is a significant difference (42.6 million km) in Mars’ aphelion and perihelion, the maximum and minimum distances from the Sun during it’s orbit around it. This causes seasonal variations in temperature of around 14 degrees C. If Earth was in Mars’ orbital position some 330 million years ago then we can envisage the temperatures at the equator (where most life was concentrated) may have varied from 25 down to 10 degrees C. depending upon time of the year.


Mars takes 687 of our ‘days’ to orbit the Sun and so a Martian year is nearly twice as long (x 1.88) as Earth’s. These are parameters we need to bear in mind when looking for signs of seasonal periodicity in Carboniferous fossils (eg growth rings in bivalves).   

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