EARTH – The discovery by NASA rover Curiosity of evidence that water once flowed on Mars – the most Earth-like planet in the solar system – should intensify interest in what the future could hold for mankind. The only thing stopping Earth having a lifeless environment like Mars is the magnetic field that shields us from deadly solar radiation and helps some animals migrate, and it may be a lot more fragile and febrile than one might think. Scientists say earth’s magnetic field is weakening and could all but disappear in as little as 500 years as a precursor to flipping upside down.