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Exploration

In situ exploration by spacecraft includes Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Ulysses, Galileo, Cassini–Huygens, and New Horizons. Planned missions include Juno Jupiter Orbiter and possibly the Outer Planet Flagship Missions; there are various proposals too, such as Uranus orbiter and probe. Ongoing missions for the outer planets as of 2011 include Cassini probe, orbiting Saturn, New Horizons, headed for Pluto, and Juno, headed for Jupiter. Cassini and New Horizons also visited Jupiter with a flyby.

One of the breakthroughs that made exploration of the outer planets much easier, was the concept of the planetary gravity assist.^[1] Discovered in the 1960s, a spacecraft approaches a planet like Jupiter in such a way as to be accelerated to a higher speed. This allows a much smaller rocket to be used for a given launch.^[1]

Another promising technology, tested on Deep Space 1, is the ion engine. Ion engines can make much more efficient use of propellant than existing chemical rockets.^[1]

Spacecraft Exploration Summary
Spacecraft	Launch Year	Jupiter	Saturn	Uranus	Neptune	End Year
Pioneer 10	1972	flyby				2003
Pioneer 11	1973	flyby	flyby			1995
Voyager 1	1977	flyby	flyby			—
Voyager 2	1977	flyby	flyby	flyby	flyby	—
Galileo	1989	orbiter				2003
Galileo Probe	1989	entry				1995
Ulysses	1990	flyby				2009
Cassini	1997	flyby	orbiter			2017
New Horizons	2006	flyby				—
Juno	2011	orbiter				—

Mission concepts

List of mission concepts:

Argo^[2] - Jupiter, Saturn, Neptune, Kuiper belt flyby
AVIATR (Titan Airplane)^[3]
Chiron Orbiter Mission Concept Study^[4]
Enceladus Flyby & Sample Return Concept Studies^[4]
Enceladus Orbiter Concept Study^[4]
Europa Flyby^[5]
Europa Flyby Study^[6]
Europa Lander^[5]
Europa Lander Study^[6]
Europa Orbiter^[5]
Exploration of Jovian Atmosphere Using Nuclear Ramjet Flyer^[7]
Ganymede Orbiter Concept Study^[4]
Io Observer Concept Study^[4]
Journey to Enceladus and Titan (JET)^[8]
Jupiter Europa Orbiter Study^[4]
Life Investigation For Enceladus (LIFE) - flyby sample return for Enceladus and Saturn's E-ring.^[9]
Neptune-Triton-Kuiper Belt Objects Mission Concept Study^[4]
Saturn Atmospheric Entry Probe Study^[4]
Saturn Ring Observer Concept Study^[4]
Titan Lake Probe Concept Study^[4]
Titan Saturn System Mission^[4]
Titan Rover^[10]
Trojan Tour Concept Study^[4]
Uranus and Neptune Orbiter and Probe Concept Studies^[4]
Uranus orbiter and probe
Uranus Pathfinder^[11]

References

External links

[traj-1] Basics of Spaceflight - Chapter 4. Interplanetary Trajectories

[2] Argo - A Voyage Through the Outer Solar System

[3] AVIATR

[dec-4] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Planetary Science Decadal Survey Mission & Technology Studies

[march12-5] March 2012 OPAG Meeting

[OPAG-6] OPAG

[7] G. Maise - Exploration of Jovian Atmosphere Using Nuclear Ramjet Flyer

[8] JET - Cost Capped Titan-Enceladus Proposal

[9] Tsou, et al. - LIFE link courtesy of Future Planetary Exploration

[10] ARPS Enabled Titan Rover Concept with Inflatable Wheels Archived 2010-02-06 at the Wayback Machine

[11] Uranus Pathfinder

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-{{distinguish|Outer World|Outer Worlds|Outworld (disambiguation)}}
-[[Image:Gas giants in the solar system.jpg|thumb|250px|From top to bottom: [[Neptune]], [[Uranus]], [[Saturn]], and [[Jupiter]] to approximate scale and color.]]
-The '''outer planets''' are those planets in the [[Solar System]] beyond the [[asteroid belt]], and hence refers to the [[gas giant]]s and [[ice giant]]s, which are in order of their distance from the Sun:
-* [[Jupiter]] is the largest planet in the Solar System. It has four very large satellites (moons).
-* [[Saturn]] is the second-largest planet, with a large and bright ring system.
-* [[Uranus]] is the third-largest planet and the least massive of the four outer planets.<ref name=sp/> It is tilted almost onto the plane of its orbit.
-* [[Neptune]] is the fourth-largest planet, as smallest of the four outer planets, but third-most massive. It has one big [[retrograde orbit|retrograde]] moon and many small ones.
-The outer planets all have ring systems, although all but Saturn's are faint when viewed from Earth.<ref name="sp">{{cite web |title=How big is Neptune? - space.com |url= http://www.space.com/18924-how-big-is-neptune.html |agency= Space.com |date=2015 |access-date= 2016-04-04}} The 2nd-largest planet is Saturn, 3rd-largest is Uranus, 4th-largest is Neptune, while 2nd-most massive planet is Saturn, 3rd-most massive is Neptune, but 4th-most massive is Uranus.</ref>
-Another aspect common to the gas giants is their many natural satellites (moons), two of which are larger than the planet Mercury (Jupiter's [[Ganymede (moon)|Ganymede]] and Saturn's [[Titan (moon)|Titan]]). That pair and [[Io (moon)|Io]], [[Callisto (moon)|Callisto]], [[Europa (moon)|Europa]], and [[Triton (moon)|Triton]], are larger than Pluto and [[Eris (dwarf planet)|Eris]].
-This region of space is also occupied by [[Centaur (minor planet)|centaurs]], various fields of [[Trojan (astronomy)|trojans]], and many [[comet]]s.
-[[Pluto]] was considered to be an outer planet from its discovery in 1930 until its [[IAU definition of planet|reclassification]] as a [[dwarf planet]] in 2006 (see also: [[Kuiper belt]]).
 == Exploration ==