Solar wind speeds on Mercury reach between 250 to 370 miles per second. The extreme wind speed that Mercury is subjected to is caused by a thin gas that contains electrically charged particles, called a plasma, which is released from the sun's surface.
The solar wind on Mercury carries particles that slam into Mercury's exterior and carry enough energy to propel some atoms into ballistic paths that reach and replenish the planet's atmosphere. Massive magnetic tornadoes can develop on the surface of the planet when magnetic fields within the solar wind merge with Mercury's magnetic field. On Oct. 8, 2006, the unmanned MESSENGER spacecraft observed magnetic tornadoes on Mercury that were 500 miles in diameter, which is equal to one-third of the planet's radius.