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 planetary alignment to explore the two gas giants Jupiter and Saturn and potentially also the ice giants, Uranus and Neptune - to fly near them while collecting data for transmission back to Earth. After Voyager 1 successfully completed its flyby of Saturn and its moon Titan, it was decided to send Voyager 2 on flybys of Uranus and Neptune.[1]
After the planetary flybys were complete, decisions were made to keep the probes in operation to explore interstellar space and the outer regions of the solar system. On 25 August 2012, data from Voyager 1 indicated that it had entered interstellar space.[2] On 5 November 2019, data from Voyager 2 indicated that it also had entered interstellar space.[3] 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.[4][5][6] 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.[7][8][9]
As of 2024,[update] 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 (1.52086×1010 mi) from the Sun[10] reaching a distance of 162 AU (24.2 billion km; 15.1 billion mi) from Earth as of May 25, 2024.[11] As of 2024[update], 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 (1.27003×1010 mi) from the Sun[12] reaching a distance of 136.627 AU (20.4 billion km; 12.7 billion mi) from Earth as of May 25, 2024.[11]
The two Voyagers are the only human-made objects to date that have passed into interstellar space—a record they will hold until at least the 2040's—and Voyager 1 is the farthest human-made object from Earth.[13]
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