Re: If you could move another planet into Earth's orbit could people live there

While temperatures would certainly become more Earthlike on the new planets, atmospheric compositions would not necessarily be right for us; none of the others, for instance, has any significant amount of free oxygen present, since this, it is now believed, has been created on Earth by the photosynthetic activity of microscopic plants during the first 2-2.5 billion years here( the Archean Age) Thus Mars, for instance, would warm up, outgas much water vapour, and even liquid water, but would still have an anoxic atmosphere. With biotechnology and advanced ecological techniques, however, we could doubtless grow a life supporting ecosystem from the bottom up, and, in time, render the planet habitable. Also the soil contains oxygen as iron oxides, which developed microbes could work on for us Indeed, one such scheme has been proposed for Mars in its present location!

With Venus, the problem of losing the 90 atmospheres of carbon dioxide would still have to be faced, since, even in our orbit, and after some cooling, the surface temperature would still be well above the boiling point of water.

Of course, the archaeobacteria class of suboceanic life, now found around smoking underseas volcanos, might be called into service to help consume this excessive gas- but at the present, this is pure speculation (but not unreasonable) Mercury would still have no atmosphere, and would essentially resemble our Moon; small bodies cannot retain an atmosphere, and so would not be a longterm habitat for Man, anyway, except insofar as we would live in enclosed artificial environments; in these circumstances, many planets and satellites could be ultimately made habitable if placed in our orbit, since temperature control would be much easier. But it would take time, and creativity on our part to adapt both the new worlds, and ourselves to new modes of life.

All the gas giants are far too massive, and have no discernible solid surface- a bit of a problem for a human settlement. Brought to Earth's location some of the massive atmospheres would, over time, be boiled off, leaving a small solid core of unknown composition, possibly covered by oceans; their larger moons might be much more interesting, if they shared the ride. Europa and Callisto, after all, are known to be water rich, while Europa's atmosphere has a whiff of oxygen; perhaps in its new location things would improve, but not permanently , given Europa's low gravity. This enterprise would be an enormously creative adventure, and allow our species to become something of real significance in a vast cosmos. However, we face a really tough challenge- how to do these things with the planets where they are presently located!

There is , however, another way - why not build our own planets from scratch? Imagine a space city, the size, of say, New York, assembled from asteroid materials, fuelled by solar energy, and parked in a suitable orbit. An ecosystem could be built up and nourished by space based industry, and settlers- probably initially tourists on long vacation, could move in! Such an idea is described in great depth in Gerard O Neill's "The High Frontier", 1974, and fired a whole generation of space enthusiasts; many of the names you now encounter in this field were inspired by this work To sum up; human destiny could well be to grow from one planet , to several, then none!