After 36 years, NASA's twin Voyager spacecraft are still going strong and still sending home information. Voyager I, the younger twin, is fast approaching the heliosheath, the very edge of our solar system. (The bubble of the heliosheath is grey in this artist's conception.) Beyond the heliosheath are the unexplored reaches of the interstellar medium. Outer space!

Image courtesy NASA/JPL-Caltech

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    On September 5, 1977, NASA launched the Voyager I spacecraft. Nearly 40 years later, the phenomenally successful Voyager I and its sister spacecraft, Voyager II (which actually launched earlier), continue to return data and receive commands.
    The primary mission of the Voyager program was to explore the planets Jupiter and Saturn, as well as their moon and ring systems. Voyager II went on to explore our solar system’s other gas giants, Uranus and Neptune. As of 2014, it is still the only spacecraft to have flown by those planets.
    Voyager I has traveled more than 19.1 billion kilometers (11.9 billion miles) from Earth—the farthest of any spacecraft. Voyager I has actually left our solar system and is now traveling through the interstellar medium at about 520 million kilometers (325 million miles) per year. The spacecraft is expected to transmit data until about 2025.
  • Term Part of Speech Definition Encyclopedic Entry
    asteroid Noun

    irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter.

    comet Noun

    celestial object made up of ice, gas, and dust that orbits the sun and leaves a tail of debris.

    command Noun

    an order or direction.

    data Plural Noun

    (singular: datum) information collected during a scientific study.

    gas giant Noun

    one of the four enormous outermost planets in the solar system (Jupiter, Saturn, Neptune, Uranus), composed mostly of gases instead of rock. Also called a Jovian planet.

    interstellar medium Noun

    material in the space between star systems, mostly hydrogen plasma and cosmic dust.

    launch Verb

    to start or instigate.

    mission Noun

    important goal or purpose.

    moon Noun

    natural satellite of a planet.

    Encyclopedic Entry: moon
    NASA Noun

    (National Aeronautics and Space Administration) the U.S. space agency, whose mission statement is "To reach for new heights and reveal the unknown so that what we do and learn will benefit all humankind."

    outer space Noun

    space beyond Earth's atmosphere.

    phenomenal Adjective

    very impressive.

    planet Noun

    large, spherical celestial body that regularly rotates around a star.

    Encyclopedic Entry: planet
    primary Adjective

    first or most important.

    receive Verb

    to get or accept.

    ring system Noun

    thin circles of dust, gas, and rocks that orbit a planet.

    solar system Noun

    the sun and the planets, asteroids, comets, and other bodies that orbit around it.

    spacecraft Noun

    vehicle designed for travel outside Earth's atmosphere.

    transmit Verb

    to pass along information or communicate.

    travel Noun

    movement from one place to another.