The first picture of a visible aurora on Mars, taken by Perseverance

astronaut: Someone trained to travel into space for research and exploration.

atmosphere: The envelope of gases surrounding Earth, another planet or a moon.

aurora: A light display in the sky caused when incoming energetic particles from the sun collide with gas molecules in a planet’s upper atmosphere. The best known of these is Earth’s aurora borealis, or northern lights. On some outer gas planets, like Jupiter and Saturn, the combination of a fast rate of rotation and strong magnetic field leads to high electrical currents in the upper atmosphere, above the planets’ poles. This, too, can cause auroral “light” shows in their upper atmosphere.

crust: (in geology) Earth’s outermost surface, usually made from dense, solid rock (in planetary science) the outermost surface of rocky planets, dwarf planets and natural satellites.

ejection: A sudden or forceful removal or jettisoning of something from its position, container or housing.

equator: An imaginary line around Earth that divides Earth into the Northern and Southern Hemispheres.

magnetic field: An area of influence created by certain materials, called magnets, or by the movement of electric charges.

Mars: The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.

particle: A minute amount of something.

solar: Having to do with the sun or the radiation it emits. It comes from sol, Latin for sun.

solar system: The eight major planets and their moons in orbit around our sun, together with smaller bodies in the form of dwarf planets, asteroids, meteoroids and comets.

subtle: Adjective for something that may be important, but can be hard to see or describe. For instance, the first cellular changes that signal the start of a cancer may be only subtly different — as in small and hard to distinguish from nearby healthy tissues.

sun: The star at the center of Earth’s solar system. It is about 27,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.

wavelength: The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.