The Kuiper belt is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times as wide and 20–200 times as massive. Like the asteroid belt, it consists mainly of small bodies or remnants from when the Solar System formed. While many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles, such as methane, ammonia, and water. The Kuiper belt is home to most of the objects that astronomers generally accept as dwarf planets: Orcus, Pluto, Haumea, Quaoar, and Makemake. Some of the Solar System's moons, such as Neptune's Triton and Saturn's Phoebe, may have originated in the region.
New Horizons is an interplanetary space probe launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institute (SwRI), with a team led by Alan Stern, the spacecraft was launched in 2006 with the primary mission to perform a flyby study of the Pluto system in 2015, and a secondary mission to fly by and study one or more other Kuiper belt objects (KBOs) in the decade to follow, which became a mission to 486958 Arrokoth. It is the fifth space probe to achieve the escape velocity needed to leave the Solar System.
Pluto Kuiper Express was an interplanetary space probe that was proposed by Jet Propulsion Laboratory (JPL) scientists and engineers and under development by NASA. The spacecraft was intended to be launched to study Pluto and its moon Charon, along with one or more other Kuiper belt objects (KBOs). The proposal was the third of its kind, after the Pluto 350 and a proposal to send a Mariner Mark II spacecraft to Pluto.
The New Frontiers program is a series of space exploration missions being conducted by NASA with the purpose of furthering the understanding of the Solar System. The program selects medium-class missions which can provide high science returns.
Neptune has been directly explored by one space probe, Voyager 2, in 1989. As of 2024, there are no confirmed future missions to visit the Neptunian system, although a tentative Chinese mission has been planned for launch. NASA, ESA, and independent academic groups have proposed future scientific missions to visit Neptune. Some mission plans are still active, while others have been abandoned or put on hold.
The exploration of Pluto began with the arrival of the New Horizons probe in July 2015, though proposals for such a mission had been studied for many decades. There are no plans as yet for a follow-up mission, though follow-up concepts have been studied.
The Planetary Science Decadal Survey is a serial publication of the United States National Research Council produced for NASA and other United States Government Agencies such as the National Science Foundation. The documents identify key questions facing planetary science and outlines recommendations for space and ground-based exploration ten years into the future. Missions to gather data to answer these big questions are described and prioritized, where appropriate. Similar decadal surveys cover astronomy and astrophysics, earth science, and heliophysics.
Argo was a 2009 spacecraft mission concept by NASA to the outer planets and beyond. The concept included flybys of Jupiter, Saturn, Neptune, and a Kuiper belt object. A focus on Neptune and its largest moon Triton would have helped answer some of the questions generated by Voyager 2's flyby in 1989, and would have provided clues to ice giant formation and evolution.
486958 Arrokoth (provisional designation 2014 MU69; formerly nicknamed Ultima Thule) is a trans-Neptunian object located in the Kuiper belt. Arrokoth became the farthest and most primitive object in the Solar System visited by a spacecraft when the NASA space probe New Horizons conducted a flyby on 1 January 2019. Arrokoth is a contact binary 36 km (22 mi) long, composed of two planetesimals 21 and 15 km (13 and 9 mi) across, that are joined along their major axes. With an orbital period of about 298 years and a low orbital inclination and eccentricity, Arrokoth is classified as a cold classical Kuiper belt object.
2014 PN70 (internally designated g12000JZ, g1 and PT3) is a trans-Neptunian object from the cold classical Kuiper belt located in the outermost region of the Solar System. It measures approximately 40 kilometers (25 miles) in diameter. The object was first observed by the New Horizons Search Team using the Hubble Space Telescope on 6 August 2014, and was a proposed flyby target for the New Horizons probe until 2015, when the alternative target 486958 Arrokoth was selected.
2014 OS393, unofficially designated e31007AI, e3 and PT2, is a binary trans-Neptunian object in the classical Kuiper belt, the outermost region of the Solar System. It was first observed by the New Horizons KBO Search using the Hubble Space Telescope on 30 July 2014. Until 2015, when the object 486958 Arrokoth was selected, it was a potential flyby target for the New Horizons probe. Estimated to be approximately 42 kilometres (26 mi) in diameter, the object had a poorly determined orbit as it had been observed for only a few months. With MPEC 2024-E99 the Minor Planet Center published on 6 March 2024 additional observations by New Horizons KBO Search-Subaru which allowed to compute a fairly reliable orbit.
2014 MT69 (internally designated 0720090F in the context of the Hubble Space Telescope, and 7 in the context of the New Horizons mission) is a cold classical Kuiper belt object (KBO) and was formerly a potential flyby target for the New Horizons probe. The object measures approximately 20–90 kilometers (12–56 miles) in diameter.
A flyby is a spaceflight operation in which a spacecraft passes in proximity to another body, usually a target of its space exploration mission and/or a source of a gravity assist to impel it towards another target. Spacecraft which are specifically designed for this purpose are known as flyby spacecraft, although the term has also been used in regard to asteroid flybys of Earth for example. Important parameters are the time and distance of closest approach.
The Planetary Missions Program Office is a division of NASA headquartered at the Marshall Space Flight Center, formed by the agency's Science Mission Directorate (SMD). Succeeding the Discovery and New Frontiers Program Office, it was established in 2014 to manage the Discovery and New Frontiers programs of low and medium-cost missions by third-party institutions, and the Solar System Exploration program of NASA-led missions that focus on prioritized planetary science objectives. The Discovery and New Frontiers programs were established in 1992 and 2001 respectively, and have launched fourteen primary missions together, along with two missions launched under the administration of the Planetary Missions Program Office. The Solar System Exploration Program was established alongside the office, with three missions planned for launch under the new program.
Shensuo, formerly Interstellar Express, is a proposed Chinese National Space Administration program designed to explore the heliosphere and interstellar space. The program will feature two or three space probes that were initially planned to be launched in 2024 and follow differing trajectories to encounter Jupiter to assist them out of the Solar System. The first probe, IHP-1, will travel toward the nose of the heliosphere, while the second probe, IHP-2, will fly near to the tail, skimming by Neptune and Triton in January 2038. There may be another probe—tentatively IHP-3—which would launch in 2030 to explore to the northern half of the heliosphere. IHP-1 and IHP-2 would be the sixth and seventh spacecraft to leave the Solar System, as well as first non-NASA probes to achieve this status.
Timeline for the New Horizons interplanetary space probe lists the significant events of the launch, transition phases as well as subsequent significant operational mission events; by date and brief description.
