Never. The Hubble telescope has never left orbit around Earth.
Hubble has never "explored" Neptune. It is a telescope in orbit round Earth and from Earth it has "imaged" Neptune. It has done this several times eg 1996 and 1998 (there may be more times!).
The HST never has got to Neptune. It always orbited Earth at 569 km above the surface. You confuse HST with the Voyager spacecraft. Voyager 2 had the closest approach to Neptune on Aug. 25, 1989.
Never happened.
2005
Voyager 2 didn't actually orbit Neptune. It flew past it in 1989.
In what year was the moon called Proteus discovered? real answer is..... Answer: Discovered by Voyager 2 spacecraft in 1989, it is named after Proteus, the shape-changing sea god of Greek mythology. Proteus circles Neptune in a nearly equatorial orbit at the distance of about 4.75 equatorial radii of the planet.
The Hubble Space Telescope was put into the orbit in 1990 and is still there up until today. It already had to be repaired five times and is expected to stay in the orbit until at least 2013.
Voyager 2 flew past Neptune in August 1989. The HST took its first pix of Neptune in 2005.
Neptune takes about 165 Earth years to orbit around the sun once. This means Neptune's year is equal to approximately 165 Earth years.
All those planets which lie outside (relative to the sun) earth's orbit will take longer than earth (1 year) to orbit the sun. Mars Jupiter Saturn Uranus Neptune
Apollo 8 became the first manned spacecraft to orbit the moon on Christmas Eve in 1968.
Neptune has a longer year than Mercury. The closer to the sun a planet is, the faster the orbit and shorter the year. Neptune's orbital period (year) is a little under 165 Earth years. Mercury orbits the sun in just under 88 days.