Near-Earth Object

Primary reference(s)

UN OOSA, no date. UN-SPIDER knowledge Portal, Near-Earth Objects. United Nations Office for Outer Space Affairs (UN OOSA). Accessed 1 April 2025.

Annotations

Key relevant UN convention / multilateral treaty

The Committee on the Peaceful Uses of Outer Space (COPUOS) was set up by the United Nations General Assembly in 1959 to govern the exploration and use of space for the benefit of all humanity: for peace, security and development (COPUOS, no date). The Committee was tasked with reviewing international cooperation in peaceful uses of outer space, studying space-related activities that could be undertaken by the United Nations, encouraging space research programmes, and studying legal problems arising from the exploration of outer space.

Drivers

Not Applicable

Impacts

Near-Earth Object- related impact hazards consist primarily of the risk of airbursts and meteorite impacts. 

The dominant hazards from airbursts consist of highly energetic shock fronts with overpressure, severe wind speeds and thermal radiation. Threat levels range from effects comparable to conventional explosives but can vary on many orders of magnitude, up to exceeding the highest levels of nuclear explosions (but without radioactivity). 

Small meteorite impacts, with parent bodies on the scale of no more than a few metres, will have only highly localized hazard potential, essentially comprised of material falling around terminal velocities. 

Decametre- sized parent objects can cause airbursts which may reach the ground and cause hazards through shock waves, overpressure and high wind speeds. In addition, larger masses can reach the ground at high speeds, causing localised explosions upon impact. 

Objects larger than about 50 metres in diameter (in addition to airburst effects) have the potential to cause sizeable craters, fully destroying the area occupied by the crater (varying with the size of an impactor) and posing further risk to the surrounding area upon impact, comparable to ground-level explosions of varying size. 

Objects of sizes more than 100 metres in diameter will pose a risk to areas of tens to hundreds of kilometres and should be avoided through internationally coordinated space-based deflection efforts. 

Multi-hazard context

The figure below summarises common interactions between near-Earth objects and other hazards. This information should be used with caution and not be solely relied upon in Disaster Risk Management, particularly as some interactions may not have been included. Note that hazardous events occurring together or locally in space or time may not necessarily cause, amplify, or be otherwise related to each other. Specific examples of multi-hazard context can be found in the ‘Hazard drivers’ and ‘Impacts’ sections above.

Multi-hazard diagram

Risk Management

The International Asteroid Warning Network (IAWN) was established in 2013 as a result of the UN-endorsed recommendations for an international response to a potential NEO impact threat, to create an international group of organisations involved in detecting, tracking, and characterising NEOs. IAWN is tasked with developing a strategy using well-defined communication plans and protocols to assist governments in the analysis of asteroid impact consequences and in the planning of mitigation responses. Currently, IAWN includes members from Europe, Asia, South and North America (IAWN, 2020). 

The European Space Agency’s (ESA) Space Safety Programme (S2P) partners with many countries, organisations and individuals. In particular, it has strong links with the United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS), which facilitates the Space Mission Planning Advisory Group (SMPAG) and IAWN. SMPAG and IAWN were both established in response to the need for an international response to the threat of NEO impacts. SMPAG coordinates the technological know-how of agencies, including ESA, recommending specific responses to asteroid threats, including basic research and development, impact mitigation measures and deflection missions. Depending on the capabilities and specific technologies available to each agency, options are made to ensure the best use is made of the resources of each organisation. ESA’s primary projects are the Space Safety Programme– especially the activities carried out by the Planetary Defence Office, such as Observation and Tracking of Near-Earth Objects (NEOs), Orbit determination and Impact monitoring and support of international mitigation activities, such as asteroid reconnaissance missions like Hera and the planned RAMSES mission to asteroid (99942). 

IAWN and SMPAG have agreed on the following criteria and thresholds for impact-response actions: 

1. IAWN shall warn of predicted impacts exceeding a probability of 1% for all objects characterised to be greater than 10 meters in size, or roughly equivalent to absolute magnitude of 28 if only brightness data can be collected. 

   Rationale: Impact probabilities greater than 1% are rare. Most objects greater than 10 meters in size will have effects (air blast and pieces) that could reach the Earth’s surface. IAWN is compelled to warn populations if bodies will have effects that reach the ground. Setting the threshold at 1% is a compromise between not being overly alarmist and not warning too late for necessary action to be initiated. It is a probability figure that individuals and governments can comprehend. An alert such as this demonstrates that the IAWN is functioning. Further, it ensures the flow of communication from IAWN to the public and the United Nations. 

2. Terrestrial preparedness planning is recommended to begin when warned of a possible impact is predicted to be within 20 years; the probability of impact is assessed to be greater than 10%; and the object is characterised to be greater than 20 meters in size, or roughly equivalent to absolute magnitude of 27 if only brightness data can be collected. 

   Rationale: Terrestrial preparedness and the increased potential for impact will also involve the determination of a ‘risk corridor’ from objects with 10% impact probabilities and impacts in less than 20 years. This provides populations and population centres on Earth with information to begin preparations for emergency preparedness if needed. The surprising effects of the Chelyabinsk event in 2013 from an object ~18 meters in size, in turn led to the establishment of a lower limit (20 meters) in these threshold criteria. 

3. SMPAG should start mission option(s) planning when warned of a possible impact predicted to be within 50 years; where the probability is assessed to be greater than 1%; and if the object is characterised to be greater than 50 meters in size, or roughly equivalent to absolute magnitude of 26 if only brightness data can be collected. 

   Rationale: Several decades warning, if available, enables sufficient lead time to mount characterisation missions. If a 1% probability on a 100-meter object is assessed, SMPAG will be informed immediately following verification of the precise orbit. Part of such a characterisation mission would likely deploy a transponder with the object.

Monitoring

Monitoring of the risk of Near-Earth Objects (NEOs) impacts can mostly be supplied via telescopic observations of various positions of an object. Observational data is exchanged via the Minor Planet Center (MPC). The acquired positional data can be used to determine current and predict future orbits and potential impact probabilities. This activity is being executed by several agencies, such as ESA (Aegis system), NASA (Sentry system) and SpaceDyS (NEODyS system). In case of identified impact threats, the International Asteroid Warning Network (IAWN) will coordinate and aggregate information and inform decision- makers and the general public.