Though space is about a thousand times emptier than even the best laboratory vacuums on Earth, it’s not completely devoid of matter.

The sun’s constant outflow of solar wind fills space with a thin and tenuous wash of particles, fields, and plasma. This solar wind, along with other solar events like giant explosions called coronal mass ejections, influences the very nature of space and can interact with the magnetic systems of Earth and other worlds. Such effects also change the radiation environment through which our spacecraft – and, one day, our astronauts headed to Mars – travel. 

A magnetosphere is the region around a planet dominated by the planet's magnetic field.

Other planets in our solar system have magnetospheres, but Earth has the strongest one of all the rocky planets: Earth's magnetosphere is a vast, comet-shaped bubble, which has played a crucial role in our planet's habitability. Life on Earth initially developed and continues to be sustained under the protection of this magnetic environment.

NASA’s heliophysics researches the ionosphere-thermosphere-mesosphere region where our neutral atmosphere transitions into the ionized plasma of space.

In this thin shell that surrounds our home planet, the atmosphere is in constant motion, shaped by the influence of both solar activity and changes in the lower atmosphere and in near-Earth space. But this region is more than just a passive boundary — energy is not only deposited but also transformed in and transported through this region, and it’s an active source of energy and plasma into the magnetosphere.

The sun sends out a constant flow of charged particles called the solar wind, which ultimately travels past all the planets to some three times the distance to Pluto before being impeded by the interstellar medium.

This forms a giant bubble around the sun and its planets, known as the heliosphere. NASA studies the heliosphere to better understand the fundamental physics of the space surrounding us - which, in turn, provides information regarding space throughout the rest of the universe, as well as regarding what makes planets habitable.

NASA studies solar eclipses on the ground, in our atmosphere, and in space, influencing solar and Earth science.

Sometimes when the moon orbits Earth, it moves between the sun and Earth. This doesn't happen every month, because the moon doesn't orbit in the exact same plane that the sun and Earth do – but it does happen occasionally. When it happens, the moon blocks the light of the sun from reaching Earth. This causes an eclipse of the sun, or solar eclipse. During a solar eclipse, the moon casts a shadow onto Earth.