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.
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
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
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).