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I have been wondering for a while now about a scenario of where if you combined Venus & Mercury would it be habitable if located in the goldy locks zone? I have found in my little research that Venus doesn't have an internally generated magnetic field. But Mercury does indeed have an internally generated magnetic field. Though weaker than Earths of course.

I don't really know what other factors for making it to whether or not this new plant would be able to sustain life.

So my question is, would the new planet be habitable, or are there more factors needed to determine this?

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  • $\begingroup$ Interesting idea. I guess you want Mercury's core to become the core of the new planet. Mercury has a big iron core, and if the new planet is spinning fast enough that should give you a good magnetic field. Of course, moving planets around takes vast amounts of energy. $\endgroup$ – PM 2Ring Jan 29 '19 at 8:01
  • $\begingroup$ Also, it'll take a while for the new planet to cool down. According to Wikipedia, it took about 100 million years for Earth's crust to re-form after the Theia impact, although the Earth was still pretty hot pre-Theia, and it continued to suffer a lot of bombardments after Theia which would have added to the heat. $\endgroup$ – PM 2Ring Jan 29 '19 at 8:03
  • $\begingroup$ Why do you think an internally generated magnetic field is relevant to habitability? I'm guessing you're thinking of the commonly held belief that "magnetic fields protect atmospheres from erosion", but that's ambiguous at best, and maybe not true in general. $\endgroup$ – Peter Erwin Jan 29 '19 at 12:01
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    $\begingroup$ Further to my comment: Venus certainly doesn't need an internally generated magnetic field to keep its atmosphere from being eroded. $\endgroup$ – Peter Erwin Jan 29 '19 at 12:02
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    $\begingroup$ I'm voting to close this question as off-topic because the Help Centre says off-topic includes "Questions that are purely hypothetical, for example a question such as 'Could a black hole destroy the universe' or 'What if our solar system had two suns' (however, feel free to visit World Building)." $\endgroup$ – Chappo Hasn't Forgotten Monica Jan 31 '19 at 6:09
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The answer is "Probably, but not very quickly."

The energy of a collision comes from two sources, the kinetic energy of the collision and the gravitational energy. If Mercury were to impact Venus, even if it began by creeping up on it very, very slowly so as to have as little kinetic energy as possible, it would fall into Venus's gravitational well and release gravitational energy enough to melt both bodies. The resulting mess would take ca. 10-100 million years for a crust to resolidify.

The resulting body could evolve towards habitability. One theory of planetary development says that active plate tectonics are critical to habitability. We know that new rock absorbs large amounts of CO2 -- new volcanic rock in Indonesia has been estimated to absorb a quarter of the CO2 released each year. So the continuous exposure of new rock by plate tectonics may be a major force in preventing the runaway greenhouse effect that has made Venus uninhabitable.

We don't know for sure how plate tectonics starts or ends, but if the resulting planet had a particularly vigorous case of it, this might compensate for its closeness to the Sun.

On the down side, Venus is already short of hydrogen and thus water and a collision with Mercury would eject Venusian volatiles into space and Mercury would not add any new, so the resulting planet might be rather barren.

In any event, whatever happens, it's going to take a very long time for the resulting body to cool enough to be livable.

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