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Six billion miles and counting....

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  • Jeroen Kumeling
    Six billion miles and counting.... Last month NASA received a weak signal from Pioneer 10, twice as far from the Sun as Pluto and speeding toward the
    Message 1 of 1 , Mar 2, 2000
      Six billion miles and counting....
      Last month NASA received a weak signal from Pioneer 10, twice as far from
      the Sun as Pluto and speeding toward the constellation Taurus.

      March 2, 2000 -- With its red eye glittering in the southwestern sky just
      after sunset, Taurus the Bull is one of the most arresting winter
      constellations. Most stargazers know it well, but what many don't know is
      that the familiar constellation is also a very far out tourist destination.
      In about 30,000 years Taurus will receive a remarkable visitor from Earth --
      a well-traveled spacecraft named Pioneer 10.

      Pioneer 10 was launched on March 2, 1972 from Cape Kennedy aboard an Atlas
      Centaur rocket for a two-year mission to Jupiter. Twenty-eight years later,
      the probe is about twice as far from the Sun as Pluto. It's bound for
      interstellar space at 13 km/s (28,000 miles per hour) heading in the general
      direction of the first magnitude star Aldebaran.

      After many years in space, including dangerous passages through the asteroid
      belt and Jupiter's magnetosphere, Pioneer 10 might finally be nearing the
      end of its active scientific life. The craft is powered by electricity
      derived from the warmth of decaying plutonium 238. Although the half-life of
      the isotope is 92 years, the thermocouples that convert heat energy to
      electricity are degrading faster. Mission controllers think that there will
      not be enough electricity to power Pioneer's transmitter for much longer.

      Right: Where is Pioneer 10 heading? You can see for yourself. Just step
      outdoors around 8 p.m. local time and look to the southwest. This diagram
      shows the constellations Orion and Taurus and the bright planets Jupiter and
      Saturn. Pioneer 10 is coasting toward the red star Aldebaran, which lies 71
      light years away and shines 155 times more brightly than our own sun.

      The spacecraft's 8-watt signal, equal to the power of a night light, now
      reaches NASA's Deep Space Network antennas with the strength of .3
      billionths of a trillionth of a watt! Scientists are tracking the feeble
      transmissions as part of an advanced concept study of chaos theory and to
      learn more about conditions in the solar system beyond Pluto.

      In February, ground controllers sent commands to Pioneer instructing the
      craft to maneuver to improve the reception of its signal on Earth. Pioneer
      is so low on power that its transmitter had to be turned off to allow it to
      execute the turn. After 90 minutes of blind flight the transmitter was
      reactivated. After more than 10 hours -- the time it takes for light to
      travel 11 billion km (6.8 billion miles) from Pioneer 10 to Earth -- anxious
      ground controllers received a signal that the maneuver had been a success.

      Spacecraft Emeritus
      The distinction of being the first human artifact to venture beyond Pluto's
      orbit is just one in a long list of firsts for Pioneer 10. It was the first
      spacecraft to travel through the asteroid belt, the first to visit Jupiter,
      and the first to use a planet's gravity to change course and reach
      solar-system-escape velocity.

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      Many scientists rank the first crossing of the asteroid belt between Mars
      and Jupiter as Pioneer 10's most important achievement. Before the crossing,
      no one knew how many rocks, as well as grains of sand, speeding through
      space at thousands of miles per hour would impact and possibly disable the
      spacecraft. Pioneer 10 made the crossing nearly unscathed, thus opening the
      way for other spacecraft to explore beyond Mars.

      On December 8, 1992, when Pioneer was 8.4 billion km (5.2 billion miles)
      away, the probe experienced an unexpected course change. Astronomers think
      that the craft was diverted slightly by the gravitational pull of a Kuiper
      Belt Object (KBO). KBOs are frigid asteroid-sized bodies, similar in
      composition to Pluto, that circle the sun at vast distances beyond the
      outermost planets. If confirmed, the 1992 event would mark just the second
      time in history that a Solar System object has been discovered by its
      gravitational effect alone. The first was the planet Neptune which was
      discovered in 1846. Its position was predicted because of its gravitational
      tug on the planet Uranus.

      Above: Several NASA spacecraft are searching for the boundary between
      interstellar space and the heliosphere (a giant bubble blown by the solar
      wind). As a larger version of this diagram shows, only Pioneer 10 is moving
      in the opposite direction to the Sun's motion through the galaxy.

      Pioneer 10 is now exploring the outer limits of the heliosphere, a bubble
      carved out of the gaseous interstellar medium by the solar wind. It was once
      thought that this cavity didn't extend much farther from the Sun than
      Jupiter. Thanks to the Pioneer and Voyager space probes it's clear that the
      heliosphere is much bigger -- at least twice as large as the orbit of Pluto.
      The exact boundaries of the heliosphere are still unknown. Scientists want
      to monitor Pioneer 10 for as long as possible in hopes of recording the
      historic crossing into interstellar space.

      After Pioneer's power runs out, the 570 lb spacecraft will have a new job
      as ambassador to the stars. The probe will have its first stellar encounter
      in about 30,000 years when it passes within three light years of the red
      dwarf star Ross 248 in the constellation Taurus. In the next million years,
      Pioneer 10 will pass ten stars at distances ranging from three to nine light
      years, and will probably still be traveling through the Milky Way galaxy
      when the Sun becomes a red giant and destroys our planet five billion years

      Pioneer bears a message for any life forms that it might encounter on its
      trek across the galaxy. A gold-anodized aluminum plaque (pictured above) was
      designed by Dr. Frank Drake and the late Dr. Carl Sagan and bolted to the
      spacecraft before it blasted off in 1972. The plaque's engraving depicts a
      man and a woman, a map of Earth's solar system, and other symbols which may
      help intelligent beings interpret the message and understand something about
      the spacecraft's creators.
      As an emissary to the galaxy, Pioneer 10's greatest and most bizarre
      adventures may still lie ahead.

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