"When the astronauts go into space, what protects them from solar radiation (microwaves, etc.) which the ozone and atmosphere protect the Earth from?"
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Question
The primitive Earth collided with a Mars sized protoplanet and created the moon, Venus had a similar collision which drastically slowed its rotation and now it seems that Mars had a major collision which reshaped one of its poles. This would suggest that as a planetary systems form, two(or possibly more) planets can coaless in each orbital slot. Do you think it is possible that on rare occasions, the size and velocity of the dual planets might match, to leave a stable system of identical planets in the same orbit, but on opposite sides of the star?
The situation you describe, with nearly identical planets in the same orbit but on opposite sides of the the star, is dynamically unstable. So no, this configuration is not possible. In addition, of course, we could easily detect such a "counter-Earth" if it existed, since even if it remained hidden behind the Sun, this object would exert an easily measured gravitational force on asteroids and other objects in the inner solar system.
David Morrison
NAI Senior Scientist
August 18, 2008
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