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The Voyager program is an American scientific program that employs two interstellar probes, Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable alignment of the two gas giants Jupiter and Saturn and the ice giants, Uranus and Neptune, to fly near them while collecting data for transmission back to Earth. After launch, the decision was made to send Voyager 2 near Uranus and Neptune to collect data for transmission back to Earth.

On 25 August 2012, data from Voyager 1 indicated that it had entered interstellar space. On 5 November 2019, data from Voyager 2 indicated that it also had entered interstellar space. On 4 November 2019, scientists reported that, on 5 November 2018, the Voyager 2 probe had officially reached the interstellar medium (ISM), a region of outer space beyond the influence of the solar wind, as did Voyager 1 in 2012. In August 2018, NASA confirmed, based on results by the New Horizons spacecraft, the existence of a " hydrogen wall " at the outer edges of the Solar System that was first detected in 1992 by the two Voyager spacecraft.

As of 2024, the Voyagers are still in operation beyond the outer boundary of the heliosphere in interstellar space. Voyager 1 is moving with a velocity of 61,198 kilometers per hour (38,027 mph), or 17 km/s, relative to the Sun, and is 24,475,900,000 kilometers (1.52086 × 10 mi) from the Sun reaching a distance of 162 AU (24.2 billion km; 15.1 billion mi) from Earth as of May 25, 2024. As of 2024, Voyager 2 is moving with a velocity of 55,347 kilometers per hour (34,391 mph), or 15 km/s, relative to the Sun, and is 20,439,100,000 kilometers (1.27003 × 10 mi) from the Sun reaching a distance of 136.627 AU (20.4 billion km; 12.7 billion mi) from Earth as of May 25, 2024.