We dream of finding a new home beyond Earth. Is Mars really a good choice?
Our Solar System is teaming with planets. Some are rocky and some are gaseous. Of the rocky planets, some have atmospheres and some don’t. Of the rocky planets with atmospheres, some have lots of water, and some don’t. So what is the difference?
First, distance from the Sun makes a big difference. Being close to the Sun, the solar wind blew away a lot of the gas in the planet forming disk in the early life of the Solar System, so the outer planets tended to form as gas giants but the closer planets tended to form as rock without all the gas. Mercury, closest to the Sun, doesn’t have much of an atmosphere for that reason.
Second, having a strong magnetic field – an ionosphere – plays a big part in a planet keeping whatever atmosphere a planet does have. Thus, Venus and Earth, which do have strong magnetic fields, have kept their atmospheres, not only formed from whatever was left over from the early planet forming disk (though likely meager), but also from outgassing from volcanic activity. The magnetic field protects a planet’s atmosphere from blowing away from the solar wind.
In addition, the magnetic field protects the planet from losing surface water. Surface water not only evaporates into the air and would be blown away with the atmosphere, if there were no atmosphere or less atmosphere, the water would boil away. So the Earth has its oceans and lakes and rivers and streams thanks to its strong magnetic field. Mars once had surface water and an atmosphere because it once had a relatively strong magnetic field, but because of its smaller size, it didn’t keep its magnetic field and lost both its atmosphere and its surface water.
Being much closer to the Sun, Venus probably once had surface water but it evaporated into the atmosphere due to the heat. It has a very dense atmosphere with high heat intensified both by its closeness to the Sun and runaway greenhouse effects from CO2. The atmosphere is protected by its magnetic field.
I say all this as humanity contemplates human habitation on Mars.
There was some time ago a series of books on the terraforming of Mars: Red Mars, Green Mars, and Blue Mars by Kim Stanley Robinson. They involved the natural turning of Mars from the sterile Mars we know today into a livable, breathable, livable Mars with an atmosphere and surface water like Earth within a few hundred years by slowly introducing plant life, turning carbon dioxide into oxygen, building and warming the atmosphere, and unfreezing the Martian polar ice caps and underground water.
Yet, how is any of that sustainable if Mars has no magnetic field to keep the Sun from blowing the atmosphere away and boiling off the water? Is humanity capable of living underground forever, becoming once again cave dwellers as they once were thousands of years ago?
There is a contest centered in the Netherlands (see Mars One) to send humans on a one-way trip to Mars to live there. I really wonder if that is a wise enterprise. At least until we know more of the science of sustainability.
Before we declare Mars our next best hope as a home away from home, we need to make sure we actually have a future there.