We know that from the amounts of XENON GAS in the soil and the air there. There is only one way that can be - and that is through explosive burning of Radio Active material. So who set off the Nuclear devices on Mars ? Most likely the Anunnaki. Where ever they go, they bring Nuclear power and destruction. After you read this, say this one thing loud to yourself: "No Marsens - unless they have altered the Genetics and adapted to live in the radiation - which they obviously have.