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Tuesday, March 01, 2016


Steve Cole's thoughts on the rocky planets of our inner solar system.

1. Mercury is an interesting planet, in that it's mostly an iron core with far less magma of the other rocky planets. Whenever Mercury acquired another proto-planet by way of collision, the iron cores merged but most of the silicates (thrown into orbit) did not fall back down as crust. Instead, they were sucked into the sun.

2. Venus should have been our twin, being about the same size, but it's just too close to the sun and all of that extra heat turned it into an acidic oven. Probes can't survive long and humans cannot ever land there because the landing craft will absorb heat with no way to get rid of it. (A refrigerator works by transferring heat out of the insulated box to the air behind the appliance.) Also, Venus rotates very slowly because the last proto-planet it absorbed hit it on the advancing edge, stopping the rotation.

3. Earth is probably not unique in the cosmos, but it is certainly unusual. All rocky planets form by gathering up more and more dust, rocks, gas, comets, and whatever. The final phase of this is when proto-planets the size of the moon start running into each other and merging. About 4.7 billion years ago, the final merger occurred, combining Earth-1.0 with a planet called Thera into what is now Earth-2.0. The angle was just right, and Earth-2.0 got both iron cores (which is why we have a magnetic field), Earth-2.0 got half of the silicate crust material, and the other half turned into the Moon. It has been determined by scientists that Earth-1.0 had life (at least microbial) because we can find the carbon layers life leaves behind.

4. Living on Mars is likely to be problematic, even on a terra-formed Mars with oceans and grass. That planet has no magnetic field which means it is bombarded with cosmic radiation that makes living there just impossible (unless you mean underground colonies, which is possible for a few scientists but not for a population of a billion or two). The science fiction fantasy of steering comets into Mars to provide it with water and an atmosphere won't work either. Without that magnetic field, the solar wind steadily strips away any kind of atmosphere. For whatever reason (probably the gravity of Jupiter) Mars just collected less stuff than Earth, and being smaller it cooled more quickly and the molten iron core solidified. No spinning molten iron core means no magnetic field.

5. No one will ever know how many, but we are missing some proto-planets that were thrown out of the solar system by gravity interactions before 4.7 billion years ago. We have detected at least one of them (it passed in front of a star and we saw it by accident) that is several times as far away as Pluto.