What is the most distant planet from the earth that a spacecraft visited has visited so far? What was the mission and when did it happen?
2 Answers
In 1989, Voyager 2 did a fly-by of the planet Neptune. The orignal plan for the Grand Tour would have included Pluto, but the Voyager series was reduced from four craft to just two.
The New Horizons craft, launched in 2006, made it's closes approach to Pluto on July 14, 2015, at 11:49 UTC (2,500 km/7,800 mi). Technically, Neptune is still be the most distant visited "planet" since Pluto has been reclassified as a dwarf planet.
More generally, regarding the furthest explored astronomical "feature", in 2013, it was determined that Voyager 1 crossed the heliopause and entered interstellar space. The nature of the heliopause is more subtle, though, and probably not directly observable without instrumentation.
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$\begingroup$ Pluto is regaining 'planet' status, after New Horizons' success, but the distance margin it can claim over Vger2 was less than 2 AU. $\endgroup$– amICommented Nov 14, 2018 at 3:26
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1$\begingroup$ I do not see Pluto regaining planet status. Rather the trend is in the opposite direction: the complex features, geologic activity, and even prospects for life that once seemed to require a "planet" are now known to be available on multiple classes of bodies. $\endgroup$ Commented Mar 13, 2019 at 22:26
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2$\begingroup$ If dwarf planets and other bodies are included, consider new horizons extended mission. $\endgroup$– lijatCommented Mar 14, 2019 at 7:45
Among objects called "planets" and defining a visit as actually making contact with the body, I nominate Jupiter as second farthest, and Saturn as No. 1. Galileo included a space probe that descended from orbit, entered what we now call Jupiter proper, and performed and reported analysis. It did not last long, but it counts as a visit in my book. Similarly for Saturn, where Cassini made its atmospheric entry even if (as was the case for Galileo diving into Jupiter) it was the craft's swan song.
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$\begingroup$ But then Saturn should be nominated as well as second most distant planet, because of the atmospheric entry of Cassini. $\endgroup$– UweCommented Mar 13, 2019 at 23:03
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$\begingroup$ Cassini also included Huygens, which performed a proper landing on Saturn's moon Titan. $\endgroup$– HobbesCommented Mar 14, 2019 at 7:45
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$\begingroup$ Which was in another comment. Did not want to be redundant. $\endgroup$ Commented Mar 14, 2019 at 10:31