Today (September 12, 2013) NASA announced that Voyager I has officially left the solar system. The probe is the first human-made object to enter interstellar space: it is farther away from Earth than anything else people have ever made. Launched on September 5, 1977, Voyager’s primary mission was to fly by Jupiter and Saturn and take pictures (and electromagnetic radiation readings) of the two worlds and their systems. The probe reached Jupiter in 1979 and Saturn in 1980. After a close fly-by of Titan, the moon with an atmosphere, the spacecraft was flung out of the plane of the solar system. Only this summer has it reached the heliopause, where the sun’s electromagnetic energy is matched by the ambient energy of the cosmos (although since only minimal instruments are running on Voyager, astrophysicists may be a long time arguing about when exactly the craft slipped out of the solar system).
Voyager is not moving as quickly as the solar probes mentioned in yesterday’s post, but neither is it moving slowly (its current velocity is 38,000 miles per hour). However such speed is minimal in the face of interstellar vastness (although Voyager is due to pass within 1.6 light years of the red dwarf star Gliese 445 in 40,000 years).