By the time the Earth gets to Venus’ orbital position (only 0.72 AU away from the
Sun) a state of inferno will exist and no life of any kind would be capable of surviving
on its surface. Only, deep down below ground - perhaps 15 -20 km - would the methanogens
(and other archaea) remain as the sole representatives of life. Temperatures would
be much higher than the 86 degrees C predicted from the graph - because of the effect
of green-house gases. Only these gases (carbon dioxide and sulphur dioxide)will remain
in the lower atmosphere. The energy of the solar wind, at this distance from the
Sun, will now be ‘cooking’ the planets and mantle material will start to diminish
through vaporisation and violent de-gassing. In this way the planet will gradually
diminish in size.
Mercury is at a distance of only 0.38 AU from the Sun and much of its mantle material
has already been lost. Much core material will also be lost as the planet ‘cooks’
at an even higher temperature. Diminishing in size, (now less than 40% of Earth’s
size) Mercury is a representative of a planet in the final stage of the planetary
It will either explode into many pieces and form asteroids and comet material - or
it will be violently ejected from its heliocentric orbit. Our Moon could be an example
of a previous planet which has been ejected in this way. Its diameter is some 30%
less than Mercury’s and this suggests that its ultimate orbital position was some
40 million km from the Sun.
The nature of the Moon is consistent with a close encounter scenario with the Sun.
Moon sampling has shown that its rocks, in comparison to Earth, have higher proportions
of elements such as zirconium and hafnium (with high melting points). Other elements
such as sodium and potassium (with low melting points) are more scarce on the Moon
than the Earth. Moon rocks are also devoid of hydrated materials.
The Moon’s surface is very similar to Mercury’s, being heavily pock-marked with craters
and having a scorched appearance.
The same ejection scenario may have happened with Pluto. Its diameter of 2274 km
means that it could have come to a final orbit of around 25 million kms from the
Sun before ejection.
The vast amount of asteroid material that is to be found in the Main Asteroid Belt
between Mars and Jupiter is likely to be the remains of a planet which disintegrated
when it reached proximity with the Sun. Close examination of some of these asteroids
by space probes reveals that they have crust-like formations and are not just amorphous
in the way one would expect, if they were just the material left over from the formation
of the Solar System.