Radar A system that is used to locate distant objects and find their position, speed, and direction. Devices that use radar send out radio waves in all directions and receive the waves back after they bounce off an object.

Glacier A large mass of ice flowing very slowly through a valley or spreading outward from a central point.

Glaciologist A person who studies glaciers.

Crevasse A fracture in a glacier.

Subglacial lake A lake under a glacier, typically an ice cap or ice sheet.

GPS (global positioning system) A system that shows the exact position of objects on Earth by displaying their latitude and longitude on a computer screen. The instruments in the GPS get their information by exchanging signals with satellites in orbit around the Earth.

Satellite An object that moves around a larger object in outer space or an object that is made by people and sent into outer space to move around the Earth or another planet or the sun.

Evaporate When a liquid changes into a vapor because the liquid is below its boiling point.

Bacteria Living things that are made up of single cells, each without a cell nucleus. Bacteria are found in all of the Earth’s environments and usually live off other organisms.

Cell The most basic part of a living thing, made up of a jelly-like substance called cytoplasm that is enclosed by a thin membrane.

Jupiter The planet that is fifth in distance from the sun.

Europa The sixth moon of the planet Jupiter.