What Makes One Earth-Like Planet More Habitable Than Another? When it comes to finding the right kind of planet to target in the search for life elsewhere in the universe, the size of the planet matters.All planets are believed to form by a process of competitive cannibalism, in a disk of material around a nascent star. Small pieces of dust collide and grow, devouring their neighbours. As they get larger, their ability to consume all around them increases and their growth accelerates.If a planet swells to more than around ten times the mass of the Earth before the nuclear furnace within its host ignites, it will be able to accrete vast amounts of gas. It will grow to become a gas giant, like Jupiter and Saturn in our own solar system. Such planets would definitely not be good places to look for life. At the other end of the spectrum, an object that is too small and of too low a mass (such as Mercury, or Earth’s moon) won’t have enough gravity to hold an atmosphere.Typically, the more massive the planet, the more massive the atmosphere it can acquire and maintain.This is important because the mass of a planet’s atmosphere will directly influence its climate. The location of the “habitable zone” around a star will therefore be a function of the mass of the planet in question. A more massive planet, with a more massive atmosphere, will likely have a stronger greenhouse effect. Such a planet would most likely be habitable at distances that would result in smaller planets icing over.Similarly, a smaller planet, with a thinner atmosphere, will likely be habitable at distances at which the oceans of a more massive world would boil.Magnetic field While a planet needs to be sufficiently massive to acquire and host a thick enough atmosphere to support life, there is more to the story.Particularly in their youth, stars are violent hosts. They fling material to space and continually bombard their planets with radiation. To some degree, that is vital for life. Without the energy the Earth receives from the sun, there would be no light and our planet would be a frozen ice-ball. But with the blessing of light comes a curse – the wind blowing from a star can tear away the atmosphere of a planet, stripping it to nothingness.Fortunately for life on Earth, our planet is protected from the worst vagaries of the solar wind by its strong magnetic field.As the solar wind strikes Earth’s magnetic field, it is deflected around, shielding the planet within. Only the strongest solar storms, and the most energetic particles, can penetrate that shielding.Cascades of charged particles that penetrate the Earth’s magnetic shield pour down to the poles, causing the magnificent Aurora Boraelis and Australis.But what if the Earth had no magnetic field? The situation would be grave. Our nearest planetary neighbour, Mars, lacks a strong magnetic field and most likely has been unshielded since the early youth of the solar system. That lack of shielding has caused the planet to pay a terrible price – Mars’s once thick atmosphere has been whittled away to almost nothing. The presence of a magnetic field is particularly important during a planet’s youth – when its host star is still young and excitable, and energetically shedding material to space. As stars age they usually mellow but remain capable of slowly stripping planets of their gaseous shrouds.It is clear, therefore, that for a planet to be considered a promising target in the search for life, it must possess a strong magnetic shield to protect its atmosphere. But how doese earth have mention above qualities? iflscience/space/what-makes-one-earth-planet-more-habitable-another
Posted on: Sat, 17 Jan 2015 10:16:24 +0000
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