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Office for Outer Space Affairs
UN-SPIDER Knowledge Portal
According to the Action Team on Near-Earth Objects established by the Committee on the Peaceful Uses of Outer Space , a near-Earth object (NEO) is an asteroid or comet whose trajectory brings it within 1.3 astronomical units of the Sun and hence within 0.3 astronomical units, or approximately 45 million kilometres, of the Earth’s orbit. This includes objects that will come close to the Earth at some point in their future orbital evolution. NEOs generally result from objects that have experienced gravitational perturbations from nearby planets, moving them into orbits that allow them to come near to the Earth.
A near-Earth asteroid is said to be a potentially hazardous asteroid when its orbit comes within 0.05 astronomical units of the Earth’s orbit and it has a measured absolute magnitude H<22 mag (an estimated diameter greater than 140 meters).
The International Asteroid Warning Network (IAWN) proposed the following definition: An asteroid, meteoroid, or a comet as it passes near Earth, enters the Earth’s atmosphere, and/or strikes the Earth, or provokes changes in inter-planetary conditions that effect the Earth’s magnetosphere, ionosphere, and thermosphere. Criteria and thresholds related to this definition are as follows:
IAWN and SMPAG Proposed criteria and thresholds for impact-response actions:
IAWN and the Space Mission Planning Advisory Group (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 per cent for all objects characterized 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 per cent 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 threshold at 1 per cent 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 communications from IAWN to the public and the United Nations.
(2) Terrestrial preparedness planning is recommended to begin when warned of a possible impact:
• Predicted to be within 20 years,
• Probability of impact is assessed to be greater than 10 per cent
• Object is characterized 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 determination of a “risk corridor” from objects with 10 per cent impact probabilities and impacts in less than 20 years. This provides populations and population centres on the Earth 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,
• Probability is assessed to be greater than 1 per cent, and
• Object is characterized 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 characterization missions. If a 1 per cent probability on a 100-meter object is assessed, SMPAG will be informed immediately following verification of the precise orbit. Part of such a characterization mission would likely deploy a transponder with the object.
As of 1 January 2020, 21,696 Near Earth Objects were registered by the Center for NEO Studies (CNEOS) of the Jet Propulsion Laboratory of the California Institute of Technology of the United States. According to the National Aeronautics and Space Administration of the United States (NASA), there are 931,886 known asteroids and 3,607 known comets.
CNEOS maintains statistics of NEOs discovered. These statistics are grouped in terms of cumulative totals, size, by type of survey used to discover them and those discovered through NASA’s WISE mission. They can be accessed on the following website: https://cneos.jpl.nasa.gov/stats/.
The European Space Agency keeps a chronology of NEOs discovered since 1801 and includes predictions of close approaches of NEOs to Earth up to the year 2200. It can be accessed on the following website: http://neo.ssa.esa.int/neo-chronology.
Today, 3 April 2023, the 8th IAA Planetary Defense Conference started in Vienna, Austria, taking place until 7 April as a hybrid conference with two venues.
The Vienna International Centre hosts the conference from 3-6 April, while the Austrian Academy of Sciences will host it on 7 April. The conference will cover a range of topics related to planetary defense, including ongoing and upcoming mission highlights, hypothetical asteroid threat exercise, key international and policy development, near-Earth object discovery and characterization, deflection and disruption modeling and testing, space mission and campaign design, impact effects and consequences, disaster management and impact response, public education and communications, and political, legal, social, and economic aspects.
Registered participants can join in-person or online and will have access to conference materials, including a decision tree, pocket reference, and decision-maker's guide. The conference...read more
La Oficina Regional de Apoyo (RSO) de ONU-SPIDER en Rumanía tiene su sede en la Agencia Espacial Rumana (ROSA). El acuerdo de cooperación entre ROSA y UNOOSA se firmó con ocasión de la 52ª COPUOS, el 4 de Junio de 2009.
Establecida en 1991, por la Decisión Gubernamental nº 923/ 20 Nov 1995, ROSA es una institución pública independiente.
La misión de la Agencia incluye:
On 24 November 2021, the American Space Agency NASA launched the Double Asteroid Redirection Test (Dart) into the path of asteroid Dimorphos, a small, harmless asteroid millions of miles from Earth. On 26 September 2022, the Dart spacecraft intentionally crashed into Dimorphos. It was planned that this would shift the orbit of the asteroid.
On Tuesday 11 October 2022, NASA announced first results of the test, presenting that the mission has been a success. According to statements by NASA, this has been the “first time ever, humanity has changed the orbit of a planetary body.”
NASA now hopes to be able to deflect and alter the course of any asteroid or comet that comes to pose a real threat to Earth. Such Near-Earth Objects (NEO) pose potential High-Impact Low-Probability (HILP) events. This successful test offers options for planetary defense actions, in case that an NEO would threat the Earth.
Image Credit:...read more
Asteroid Day as observed annually on 30 June is the United Nations sanctioned day of public awareness of the risks of asteroid impacts.
In December 2016 the United Nations General Assembly adopted resolution A/RES/71/90, declaring 30 June International Asteroid Day in order to "observe each year at the international level the anniversary of the Tunguska impact over Siberia, Russian Federation, on 30 June 1908, and to raise public awareness about the asteroid impact hazard."
International Asteroid Day aims to raise public awareness about the asteroid impact hazard and to inform the public about the crisis communication actions to be taken at the global level in case of a credible near-Earth object threat.
The General Assembly’s decision was made based on a proposal by the Association of Space Explorers, which was endorsed by Committee on the Peaceful Uses of Outer Space (COPUOS).
UN-SPIDER's association with the International Asteroid Warning Network (IAWN) and contribution to the IAA Planetary Defense Conference 2021 has resulted in a landmark publication in the International Journal of Disaster Risk Science. Read the abstract or follow the provided links to find more information.
Click here to find the full publication article.
"Near-Earth object (NEO) impact is one of the examples of high impact and low probability (HILP) event, same as the Covid-19 pandemic the world faces since the beginning of 2020. The 7th Planetary Defense Conference held by the International Academy of Astronautics (IAA) in April 2021 included an...read more
The International Academy of Astronautics (IAA) successfully concluded its 7th Planetary Defense Conference on 30 April 2021. The conference, which was carried out virtually from 26 to 30 April 2021, was hosted by the United Nations Office for Outer Space Affairs (UNOOSA) in collaboration with the European Space Agency (ESA) and attracted hundreds of experts from the space community. The conference addressed the threat to Earth posed by asteroids and comets and actions that might be taken to deflect a threatening object. The conference included welcoming remarks by high ranking authorities of IAA and a keynote speech by the Director of UNOOSA, Simonetta Di Pippo. Dr. Di Pippo welcomed participants to the conference and noted that IAA has been conducting these...read more
The UN-SPIDER Regional Support Office (RSO) in Romania is hosted by the Romanian Space Agency (ROSA). The cooperation agreement between ROSA and UNOOSA was signed on occasion of the 52nd COPUOS, 4 June 2009.
Established in 1991, by the Government Decision no. 923/ 20 Nov 1995, ROSA is an independent public institution.
The mission of the Agency:
ROSA is authorized to establish research and development centres oriented on specific objectives of the Romanian Space Programme.read more