Digital Universe Guide - Hayden Planetarium

136 3. THE MILKY WAY ATLAS
Voyager 2 visited Saturn in summer 1981 and was the first spacecraft to visit Uranus, in January
1986, and Neptune, in the summer of 1989. Neptune then boosted Voyager 2 out of the Solar System’s
plane.
The interstellar mission involves the investigation of the outer reaches of the Sun’s influence. As the
Sun moves through space, it is plowing into the gas that surrounds it. This sets up a shock whereby the
particles streaming from the Sun ram into the particles of the interstellar gas. The Voyager spacecraft
will one day encounter that shock and return data on the nature of this interstellar gas unaffected by the
Sun. The spacecraft should begin entering this region in the next five years and cross it entirely 10 to
20 years after reaching the shock. Beyond this, Voyager will continue to sail into the Milky Way. In about
296,000 years, Voyager 2 will pass within 5 light-years of the bright star Sirius in Canis Major.
Scientists continue to communicate with the Voyager craft. Both are traveling at about 3.5 AU/year.
On February 17, 1998, Voyager 1 surpassed Pioneer 10 to be the farthest man-made object.
The Trajectories Each of the four trajectories begins from Earth’s orbit, and their point of departure
marks the location of Earth when the probes were launched. The trajectories extend to the year 2050.
Labels appear either at planetary encounters or every 10 years once the spacecraft leave the planetary
plane. Alongside each year, we include the light-travel time in light-minutes (lm) or light-hours (lh).
If you turn on the 1-light-month grid (1lmo), you will see that the probes will be about 1 light-day from
Earth in 2050. One light-day is about 26 billion kilometers, or 16 billion miles, the distance light travels in
one day.