The ICON spacecraft orbited in a part of our planet’s outermost layer of the atmosphere, called the ionosphere, where it studied what events impact the ionosphere, including Earth’s weather from below and space weather from above. The ionosphere is the lowest boundary of space, located between 55 miles to 360 miles above Earth’s surface. It is made up of a sea of particles that have been ionized: a mix of positively charged ions and negatively charged electrons called plasma.