space probe

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A spacecraft carrying instruments intended for use in exploration of the physical properties of outer space or celestial bodies other than Earth.

from the GNU version of the Collaborative International Dictionary of English.

• noun an unmanned rocket carrying instruments to explore objects or conditions in outer space; -- used mostly for vehicles travelling beyond the earth's gravitational field, rather than in orbital or suborbital flight.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An unmanned space vehicle designed to voyage beyond Earth orbit

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a rocket-propelled guided missile that can escape the earth's atmosphere; makes observations of the solar system that cannot be made by terrestrial observation