<Li> Gradual erosion of the atmosphere by solar wind . On 5 November 2015, NASA announced that data from MAVEN shows that the erosion of Mars' atmosphere increases significantly during solar storms . This shift took place between about 4.2 to 3.7 billion years ago, as the shielding effect of the global magnetic field was lost when the planet's internal dynamo cooled . </Li> <Li> Catastrophic collision by a body large enough to blow away a significant percentage of the atmosphere; </Li> <Li> Mars' low gravity allowing the atmosphere to "blow off" into space by Jeans escape . </Li> <Ul> <Li> <P> Mars's thin atmosphere, visible on the horizon . </P> </Li> <Li> <P> Mars Pathfinder--Martian sky with water ice clouds . </P> </Li> <Li> <P> A storm front moves in </P> </Li> </Ul>

How do astronomers know that mars has an atmosphere mainly made of carbon dioxide