Planet 180 degrees from earth in same orbit?

origin said:
Only twice as much sunlight? That seems like a lot to me.
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And Mercury receives 3.5 times as much sunlight as Venus, yet its surface temp varies from 426°C on the day lit side to -173°C on the night side, while Venus surface temp is 462°C over its entire surface. The point is that while moving Venus out to Earth distance would cool it some, it wouldn't be enough to cool it to habitable temps. Also consider that Venus geometric albedo is 0.65 compared to the Earth's 0.30, so it reflects more than twice as much sunlight back into space a Earth does. (Mercury has an albedo of 0.11, so it reflects only ~1/6 as much of the sunlight falling on it back into space as Venus does)
It was once considered possible that Venus could have a habitable surface since the amount of light it reflects back out to space could compensate for the increased intensity of the sunlight striking it.
 
I responded without giving the issue much thought.

Symmetric configurations tend to fail to remain symmetric unless totally isolated. It only takes a minor disturbance to destroy such symmetries.

A planet 180 degrees from Earth at the same distance from the sun has orbital symmetry, even if it has a different mass.

A solar system with only two planets, each without a moon might retain such a symmetry, although I would not bet on it. With other objects in the solar system, gravitational interactions would destroy such a symmetry.
 
Janus58 said:
It was once considered possible that Venus could have a habitable surface since the amount of light it reflects back out to space could compensate for the increased intensity of the sunlight striking it
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With the shrinking of the polar ice caps (diminishing albedo) will the earth reflect less sunlight back out to space and therefore retain more heat at the surface level?
 
Question: Have we ever flown past the sun, or are our probes always directed away from the sun?
 
Write4U said:
Question: Have we ever flown past the sun, or are our probes always directed away from the sun?
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IIRC several probes have used the Sun for a gravity assist. Pointing a camera at the Sun inside the orbit of Mercury would be doubleplus ungood.
 
Write4U said:
Question: Have we ever flown past the sun, or are our probes always directed away from the sun?
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Helios 1 & 2 were launched in the mid-seventies and both passed within ~75% of the distance of Mercury in order to study the Sun.
Later this year, the Parker Solar probe will be launched, and its trajectory will take it through the corona.
 
Write4U said:
With the shrinking of the polar ice caps (diminishing albedo) will the earth reflect less sunlight back out to space and therefore retain more heat at the surface level?
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Yes. Not only that, but the rising water level caused by the shrinking Antarctic ice cap decreases the average albedo of the Earth. Land has an albedo that ranges from 0.1 to 0.4 while typical ocean albedo is 0.06.
 
Write4U said:
Question: Have we ever flown past the sun, or are our probes always directed away from the sun?
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Lots of our probes go into independent orbits around the sun, where they rendezvous with other planets for fly-by (i.e. gravity assist). They most certainly spend time on the other side of the sun.
 
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