A new study by NASA and the Naval Research Institute has found that exhaust from the space shuttle can create high altitude clouds over Antarctica, just a few days after launch. Exhaust released at an altitude of 110 km (69 miles) can form Antarctic polar clouds in the mesosphere (the second highest layer of the atmosphere). Scientists originally discovered the connection when they noticed iron particles in clouds above Antarctica, and couldn't imagine a natural process that could put them into the high atmosphere.