Editing Space exploration (section)

===Mercury===
{{main|Exploration of Mercury}}
[[File:MESSENGER EN0108828359M.png|thumb|A ''MESSENGER'' image from 18,000&nbsp;km showing a region about 500&nbsp;km across (2008)]]
[[Mercury (planet)|Mercury]] remains the least explored of the [[Terrestrial planets]]. As of May 2013, the [[Mariner 10]] and ''[[MESSENGER]]'' missions have been the only missions that have made close observations of Mercury. ''MESSENGER'' entered orbit around Mercury in March 2011, to further investigate the observations made by Mariner 10 in 1975 (Munsell, 2006b). A third mission to Mercury, scheduled to arrive in 2025, [[BepiColombo]] is to include two [[space probe|probes]]. BepiColombo is a joint mission between Japan and the [[European Space Agency]]. ''MESSENGER'' and BepiColombo are intended to gather complementary data to help scientists understand many of the mysteries discovered by Mariner 10's [[Gravitational slingshot|flybys]].

Flights to other planets within the Solar System are accomplished at a cost in energy, which is described by the net change in velocity of the spacecraft, or [[delta-v]]. Due to the relatively high delta-v to reach Mercury and its proximity to the Sun, it is difficult to explore and orbits around it are rather unstable.