The Ocean Worlds Exploration Program (OWEP) is a NASA program [1] to explore ocean worlds in the outer Solar System that could possess subsurface oceans to assess their habitability and to seek biosignatures of simple extraterrestrial life.
Prime targets include moons that harbor hidden oceans beneath a shell of ice: Europa, Enceladus, and Titan. A host of other bodies in the outer Solar System are inferred by a single type of observation or by theoretical modeling to have subsurface oceans.
The US House Appropriations Committee approved the bill on May 20, 2015, and directed NASA to create the Ocean Worlds Exploration Program. [2] The "Roadmaps to Ocean Worlds" (ROW) was started in 2016, [3] [4] and was presented in January 2019. [5] The formal program is being implemented within the agency by supporting the Europa Clipper orbiter mission to Europa, [3] [6] and the Dragonfly mission to Titan. The program is also supporting concept studies for a proposed Europa Lander, [7] and concepts to explore the moon Triton. [8] [5] Amanda Hendrix and Terry A. Hurford are the co-leads of the NASA Roadmaps to Oceans World Group. [5] [9]
The chief author of NASA's budget proposal is John Culberson, who was at the time the head of the science subcommittee in the House of Representatives. In Spring 2015 he presented a budget request, creating the possibility of an all-new NASA mission program. [11] [12] The House Appropriations Committee approved its version of the FY2016 House Appropriations Commerce-Justice-Science (CJS) bill on May 20, 2015. [6] Therefore, the Committee directed NASA to create the Ocean Worlds Exploration Program whose primary goal is to discover extant life on another world using a mix of Discovery, New Frontiers and Flagship class missions consistent with the recommendations of current and future Planetary Science Decadal Surveys. [3]
In the FY2017 Budget Request, the committee recommended $348 million for "Outer Planets" and "Ocean Worlds," of which not less than $260 million is for the Europa Clipper orbiter and lander, with launch of the orbiter in 2025 [13] and the potential Europa Lander shortly after. [14]
A 2017 technical analysis stated that the technical challenges are enormous, and that "Without a genuinely strategic program plan, the great promise of an OWEP [Ocean Worlds Exploration Program] is highly likely to remain unfulfilled." [15] The report noted that development of OWEP-enabling technologies must currently compete for priority with other Solar System objectives, which is not useful for strategic planning. The report recommends common, multi-mission technical infrastructure and secure funding to develop it. [15]
The Roadmaps to Ocean Worlds (ROW) report was submitted and it was published in January 2019. [5]
On Earth, itself an ocean world, liquid water is essential to life as we know it. A question is whether the dark, alien oceans of the outer Solar System could be habitable for simple life forms, and if so, what their biochemistry might be. [16]
The goals of the Ocean Worlds Exploration Program are to "identify ocean worlds, characterize their oceans, evaluate their habitability, search for life, and ultimately understand any life we find." [5]
Exploring these moons could help to answer the question of how life arose on Earth and whether it exists anywhere else in the Solar System. [17] It may also be possible to find pre-biotic chemistry occurring, which could provide clues to how life started on Earth. [18] Any life detected at the remote ocean worlds in the outer Solar System would likely have formed and evolved along an independent path from life on Earth, giving us a deeper understanding of the potential for life in the universe. [4]
Oceanographers, biologists and astrobiologists are part of the team developing the strategy roadmap. [3] The planning also considers implementing planetary protection measures to avoid contaminating extraterrestrial habitable environments with resilient stowaway bacteria on their landers. [3] [4]
Ocean worlds identified in the Solar System so far with reasonable certainty are the major moons Europa, Enceladus, Titan, Ganymede, and Callisto. [5] Of these, Europa and Enceladus have the highest priority because their icy shells are thinner than the others (Enceladus’ is less than 10 km; Europa's is about 40 km) and there is some evidence their oceans are in contact with the rocky mantle, which could provide both energy and chemicals for life to form. [5] Enceladus' ice crust has fractures at the south pole that allow ice and gas from the ocean to escape to space, where it has been sampled by mass spectrometers aboard the Cassini Saturn orbiter with tantalizing results. [19] Titan's ocean is the deepest, at 50 to 100 km, and no evidence for active plumes or ice volcanism have been observed.
Bodies such as Triton, Pluto, Ceres, Miranda, Ariel, and Dione are considered candidate ocean worlds, based on hints from limited spacecraft observations. [5]
The Ocean Worlds Exploration Program (OWEP) is supporting the Europa Clipper orbiter mission to Europa, which is the first planned target of this program to be launched in 2024. [3] [6] The second is the Dragonfly mission to Titan. [5]
The program is also supporting concept studies for a proposed Europa Lander, [7] and a concept to explore the moon Triton with Trident, a mission selected as a finalist in NASA's Discovery Program in 2020. [8] [5]
Astrobiology mission concepts to water worlds in the outer Solar System:
Astrobiology is a scientific field within the life and environmental sciences that studies the origins, early evolution, distribution, and future of life in the universe by investigating its deterministic conditions and contingent events. As a discipline, astrobiology is founded on the premise that life may exist beyond Earth.
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.
An ocean world, ocean planet or water world is a type of planet that contains a substantial amount of water in the form of oceans, as part of its hydrosphere, either beneath the surface, as subsurface oceans, or on the surface, potentially submerging all dry land. The term ocean world is also used sometimes for astronomical bodies with an ocean composed of a different fluid or thalassogen, such as lava, ammonia or hydrocarbons. The study of extraterrestrial oceans is referred to as planetary oceanography.
The exploration of Saturn has been solely performed by crewless probes. Three missions were flybys, which formed an extended foundation of knowledge about the system. The Cassini–Huygens spacecraft, launched in 1997, was in orbit from 2004 to 2017.
The habitability of natural satellites is the potential of moons to provide habitats for life, though it is not an indicator that they harbor it. Natural satellites are expected to outnumber planets by a large margin and the study of their habitability is therefore important to astrobiology and the search for extraterrestrial life. There are, nevertheless, significant environmental variables specific to moons.
Titan Saturn System Mission (TSSM) was a joint NASA–ESA proposal for an exploration of Saturn and its moons Titan and Enceladus, where many complex phenomena were revealed by Cassini. TSSM was proposed to launch in 2020, get gravity assists from Earth and Venus, and arrive at the Saturn system in 2029. The 4-year prime mission would include a two-year Saturn tour, a 2-month Titan aero-sampling phase, and a 20-month Titan orbit phase.
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.
The Uranus Orbiter and Probe is an orbiter mission concept to study Uranus and its moons. The orbiter would also deploy an atmospheric probe to characterize Uranus's atmosphere. The concept is being developed as a potential large strategic science mission for NASA. The science phase would last 4.5 years and include multiple flybys of each of the major moons.
Planetary oceanography, also called astro-oceanography or exo-oceanography, is the study of oceans on planets and moons other than Earth. Unlike other planetary sciences like astrobiology, astrochemistry, and planetary geology, it only began after the discovery of underground oceans in Saturn's moon Titan and Jupiter's moon Europa. This field remains speculative until further missions reach the oceans beneath the rock or ice layer of the moons. There are many theories about oceans or even ocean worlds of celestial bodies in the Solar System, from oceans made of liquid carbon with floating diamonds in Neptune to a gigantic ocean of liquid hydrogen that may exist underneath Jupiter's surface.
Enceladus Life Finder (ELF) is a proposed astrobiology mission concept for a NASA spacecraft intended to assess the habitability of the internal aquatic ocean of Enceladus, which is Saturn's sixth-largest moon of at least 146 total moons, and seemingly similar in chemical makeup to comets. The spaceprobe would orbit Saturn and fly through Enceladus's geyser-like plumes multiple times. It would be powered by energy supplied from solar panels on the spacecraft.
Journey to Enceladus and Titan (JET) is an astrobiology mission concept to assess the habitability potential of Enceladus and Titan, moons of Saturn.
Life Investigation For Enceladus (LIFE) was a proposed astrobiology mission concept that would capture icy particles from Saturn's moon Enceladus and return them to Earth, where they could be studied in detail for signs of life such as biomolecules.
THEO is a feasibility study for a New Frontiers class orbiter mission to Enceladus that would directly sample its south pole water plumes in order to study its internal habitability and to search for biosignatures. Specifically, it would take advantage of the direct sampling opportunities of a subsurface ocean.
The Europa Lander is an astrobiology mission concept by NASA to send a lander to Europa, an icy moon of Jupiter. If funded and developed as a large strategic science mission, it would be launched in 2027 to complement the studies by the Europa Clipper orbiter mission and perform analyses on site.
Oceanus is a NASA/JPL orbiter mission concept proposed in 2017 for the New Frontiers mission #4, but it was not selected for development. If selected at some future opportunity, Oceanus would travel to Saturn's moon Titan to assess its habitability. Studying Titan would help understand the early Earth and exoplanets which orbit other stars. The mission is named after Oceanus, the Greek god of oceans.
Explorer of Enceladus and Titan (E2T) is a space mission concept that would investigate the evolution and habitability of the Saturnian satellites Enceladus and Titan and is proposed by the European Space Agency in collaboration with NASA.
Enceladus Life Signatures and Habitability (ELSAH) is an astrobiology concept mission proposed in 2017 to NASA's New Frontiers program to send a spacecraft to Enceladus to search for biosignatures and assess its habitability. The Principal Investigator is Christopher P. McKay, an astrobiologist at NASA Ames Research Center, and the managing NASA center is Goddard Space Flight Center. No details of the mission have been made public, but observers speculate that it would be a plume-sampling orbiter mission.
Trident is a space mission concept to the outer planets proposed in 2019 to NASA's Discovery Program. The concept includes flybys of Jupiter and Neptune with a focus on Neptune's largest moon Triton.
Neptune Odyssey is an orbiter mission concept to study Neptune and its moons, particularly Triton. The orbiter would enter into a retrograde orbit of Neptune to facilitate simultaneous study of Triton and would launch an atmospheric probe to characterize Neptune's atmosphere. The concept is being developed as a potential large strategic science mission for NASA by a team led by the Applied Physics Laboratory at Johns Hopkins University. The current proposal targets a launch in 2033 using the Space Launch System with arrival at Neptune in 2049, although trajectories using gravity assists at Jupiter have also been considered with launch dates in 2031.
The Enceladus Orbilander is a proposed NASA Flagship mission to Saturn's moon Enceladus. The Enceladus Orbilander would spend a year and a half orbiting Enceladus and sampling its water plumes, which stretch into space, before landing on the surface for a two-year mission to study materials for evidence of life. The mission, with an estimated cost of $4.9 billion, could launch in the late 2030s on a Space Launch System or Falcon Heavy with a landing in the early 2050s. It was proposed in the 2023–2032 Planetary Science Decadal Survey as the third highest priority Flagship mission, after the Uranus Orbiter and Probe and the Mars Sample Return program.
In fact, the report accompanying the bill directs NASA to create an "Ocean Worlds Exploration Program" of which the Europa mission is part.