1 Introduction
The high seas and outer space share more than a conceptual affinity as global commons beyond national sovereignty. Each is governed by a distinct corpus of international law, with individual foundational texts such as the United Nations Convention on the Law of the Sea (UNCLOS)(1) United Nations Convention on the Law of the Sea, adopted December 10, 1982, opened for signature at Montego Bay, Jamaica, entered into force November 16, 1994, 1833 U.N.T.S. 3. and the 1967 Outer Space Treaty (OST)(2) Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies, adopted January 27, 1967, opened for signature at London, Moscow, and Washington, D.C., entered into force October 10, 1967, 610 U.N.T.S. 205. respectively, and both affirm the shared nature of the zones, rooted in a prohibition on national appropriation of the zone itself. Yet, these two legal domains have evolved in isolation from one another to date, despite the routine descent of space objects through the atmosphere and into the ocean in areas beyond national jurisdiction (ABNJ).
The past decade has seen exponential growth in commercial spaceflights and satellite mega-constellations.(3) Mia M. Bennett, "Orbital Debris Requires Prevention and Mitigation across the Satellite Life Cycle," Communications Engineering 4, no. 1 (2025): 95, https://doi.org/10.1038/s44172-025-00430-5. This, in turn, has led to a sharp increase of both space objects, including debris, in and around Earth’s orbit, with the European Space Agency estimating that approximately 15,800 tons(4) Includes space objects. of space objects are currently circling the globe.(5) European Space Agency, ESA Space Environment Report 2025(Noordwijk: ESA, 2025), 12. Mitigation options for end-of-life space objects are limited, and rely heavily on the controlled and uncontrolled reentry into areas beyond national jurisdiction (ABNJ), principally the high seas, driving a surge in high seas reentries over the past five years.(6) Ibid. Between 2020 and 2023, there was an increase of 500% of re-entry of unmanned space objects. Currently, the average number of intact satellites or rocket bodies re-entering Earth’s atmosphere is over 3 per day. Industry practice has long operated under assumptions that the remoteness and distance from human civilization of well-used splashdown sites such as Point Nemo in the South Pacific renders environmental harm negligible.(7) Antonio García, "The Spacecraft Cemetery at the Loneliest Point on Earth," LBV Magazine, October 24, 2025, https://www.labrujulaverde.com/en/2025/10/the-spacecraft-cemetery-at-the-loneliest-point-on-earth/. Indeed, the European Space Agency’s “Zero Debris Charter” outlines the Agency’s ambitious goal to halt the generation of space debris by 2030 by utilizing splashdowns as the responsible solution to achieving this.(8) European Space Agency, "Zero Debris Charter" (March 2024), https://www.esa.int/Space_Safety/Zero_Debris_Charter. Legal scrutiny on environmental impacts ended at national borders, centred on potential liability and harm to human life.
While the rate of the space debris re-entries and splashdowns is rapidly increasing, it is not a new concern. Already in 2001, in the debates surrounding the deorbiting of the Russian space station MIR, the Rio Group of Latin American States raised formal concerns before the United Nations Committee on the Peaceful Uses of Outer Space, arguing that the splashdown practice risked turning the South Pacific Ocean from a “common province into a dumping site for dangerous materials.”(9) Vito De Lucia, “Splashing Down the International Space Station in the Pacific Ocean: Safe Disposal or Trashing the Ocean Commons?,” EJIL: Talk!, February 23, 2022, https://www.ejiltalk.org/splashing-down-the-international-space-station-in-the-pacific-ocean-safe-disposal-or-trashing-the-ocean-commons/. Although the concerns produced no binding legal response or resolution, the question they raised has not gone away.
The entry into force of the Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (the BBNJ) in January 2026 marks a transformative moment in the evolving international environmental law landscape.(10)Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction(BBNJ), opened for signature June 19, 2023, entered into force January 17, 2026, UN Doc. A/CONF.232/2023/4, UNTS 56940. In particular, the BBNJ operationalizes and clarifies responsibility to protect the global commons through mandatory Environmental Impact Assessment (EIA) procedures and area-based management tools. Its entry into force raises many questions on the environmental impact of the space sector, including if splashdown operations will forthwith be subject to binding procedural obligations that operators have historically operated without.
Employing the non-appropriation principle as a foundational normative bridge, this thesis analyses that question within the broader architecture of international law, examining how the governance of outer space and the high seas are increasingly linked by the physical reality of space object reentry.