Why solar wind does not cool down as fast as expected? Simulating the solar wind. ESA's Solar Orbiter mission. Credit: ESA/ATG medialab Solar wind is a constant stream of plasma and particles emanating from the sun. This stream of energized and charged particles emanating from the sun travels at speeds as high as 900 km/s and a temperature of 1 million degrees (Celsius). These ejections significantly impact the conditions of our solar system and constantly hit the Earth. It has long puzzled scientists: why the bursts of hot gas from the sun do not cool down as fast as expected?