April 29, 2022: Ingenuity flies over Perseverance's backshell and parachute

Artifacts in space, or space anthropo-archeology

The purpose of this project is to list all human-made objects that were sent in deep space, way beyond the Earth’s orbit. While most of them are now orbiting celestial bodies such as the Sun, the planets and the moons, some are permanently set on their surfaces. A few of them are on their way to leave the solar system.

Note that the Earth’s artificial satellites are not listed here, except those that were part of an interplanetary mission.

As of May 2022, over 4,500 objects have been identified, ranging from large probes to small pins and including spent injection stages, rovers, heat shields, parachutes, dust caps, weights, bolts, lanyards, hand tools, foam blocks, sample bags, etc.

The difficult task of making a comprehensive inventory

The exact number of artificial objects in outer space will never be known. It largely depends upon:

  • How objects are numbered, for instance a complex Apollo rover may be counted as one object or split into its detachable elements: antennas, camera, batteries, seats, console, hand tools carrier, fenders, etc. (see the Apollo 15’s rover in the picture above);
  • The number of debris resulting from impacts, collisions and spent stage breakups, provided those events will ever be known;
  • The number of objects that emerge from deployments and separation of spacecraft (explosive bolts, lens caps, dust covers, clamp bands, fairings, shrouds, etc.);
  • Untold or unknown events such as classified missions and experiments, private belongings secretly left on the moon by the Apollo astronauts, family items hidden into space hardware by mission staff and technicians, or Apollo hardware unofficially returned to Earth as souvenirs by the astronauts.
  • First objective: protecting our invaluable outer space heritage

    All these objects are witnesses of human activity in space and are as precious as archeological items buried several feet underneath us: like Egyptian mummies on Earth, it is important that we protect them for both their historical and scientific values which are beyond estimation (e.g. Perseverance and Ingenuity in the picture above).

    We must protect them not only against time and weathering but also from inadvertent destruction and misappropriation as space will become more accessible to private enterprise. Because small items such as cameras, geology tools and any detachable part are more prone to end as souvenirs for space tourists than large rovers or landers, their vulnerability must be emphasized.

    This catalogue, the most accurate to date, is a step in preserving them by establishing what’s actually out there and where it is precisely.

    Second objective: mitigating outer space derelict objects

    Before calling these relics ‘space junk’, it must be remembered that mass and space exploration are not compatible: a spacecraft can’t afford trailing unnecessary load, so items that are no more useful at one point into the mission become dead weight and must be shaved off quickly. For instance, the Apollo astronauts couldn’t clean up the ALSEP sites and bring back home all the deployment hardware (see picture above): if they had done so it would have been at the expense of the precious lunar rocks. As of today, there is no other viable option to guarantee mission success and there are no means to retrieve them.

    Thus, ‘derelict objects’ is a more appropriate word to qualify them and they can be classified into three groups:

  • Group 1: items that are inert and immobile, for instance aluminum parts or soft bags. As the space environment is harsher than their individual impact on it, they can be classified as ‘visual annoyance’ (see the Apollo 17’s ALSEP site in the picture above);
  • Group 2: chemically active items (e.g. spacecraft batteries or propellant tanks) that can induce pollution in probable organic or icy worlds such as Venus, Mars, Gas Giants Moons, comets and some asteroids;
  • Group 3: items that are travelling at orbital speed in the solar system. As they represent a threat to space navigation and to the surface of celestial bodies, they can be classified as hazardous objects.
  • While all cases should be remediated, both latter groups must be emphasized to mitigate consequences. This catalogue is a step in this direction.

    Additional information

    In order to ease reading, the data is split into several tables, each referring to a celestial body (sun, planet, moon, asteroid or comet), the location (orbit or surface) and the context of the object (systemic or archeological). Additionally, each table displays the artificial objects in chronological order of deployment. More explanation about the tables layout is available here.

    Pictures of the probes and items are visible on this page.

    The lists are as comprehensive as possible and we’re doing our best to complete and keep them up to date. Any help to improve them will be appreciated. Should you have any question or remark, please drop us a line.