Voyager 1
1977
Launched 5 September 1977 for Jupiter and Saturn, Voyager 1 kept going. On 25 August 2012 it crossed the heliopause, where the Sun's wind yields to the galaxy, becoming the first human-made object in interstellar space. On 18 November 2026 it reaches exactly one light-day from Earth - a milestone no engineer alive expected to schedule.
Specs
Mass 825 kg; 3.7 m dish antenna; 1970s electronics; power from a plutonium generator that loses ~4 W a year, which is why instruments have been switched off one by one to keep the radio alive (cameras: 14 February 1990). Science today: magnetometer and plasma-wave detector only (NASA status table, 2026). One light-day = 299,792 km/s × 86,400 s ≈ 25,900,000,000 km (~16,100,000,000 miles) - NASA's milestone date, published on the mission page.
Why it matters
The farthest thing we listen to routinely: every signal arrives a day after it was sent, so Voyager 1 is a card about time as much as distance - radio, light-travel time and clocks are one measurement (see Related). It carries a gold-plated record of Earth's sounds, greetings and music - a mixtape as ambassador. And a Voyager 1 navigation photo held the first active volcano found beyond Earth: Io, spotted by Linda Morabito on 9 March 1979.