Near-Earth Objects - NEO Segment

ESA Space Situational Awareness: detecting space hazards
Space Situational Awareness - Near Earth Objects

Near-Earth objects (NEOs) are asteroids or comets with sizes ranging from meters to tens of kilometres that orbit the Sun and whose orbits come close to that of Earth's. Of the more than 600 000 known asteroids in our Solar System, almost 10 000 are NEOs. 

An example of a near-Earth object is 25143 Itokawa, an object about 300 m in diameter that was visited by the Japanese spacecraft Hayabusa in 2005.

About NEOs

NEOs could potentially hit our planet and, depending on their size, produce considerable damage. While the chance of a large object hitting the Earth is very small, it would produce a great deal of destruction; thus NEOs merit active detection and tracking efforts.

The goal of SSA's Near-Earth Object Segment (SSA-NEO) is to:

  • Become aware of the current and future position of NEOs relative to our planet
  • Estimate the likelihood of Earth impacts
  • Assess the consequences of any possible impact
  • Develop NEO deflection methods

The NEO Segment observes NEOs, predicts their orbits, produces impact warnings when necessary and is involved in potential mitigation measures.

ROLEProvide warnings on potential asteroid impact hazards, including discovery, identification, orbit prediction and civil alert capabilities
COORDINATION CENTRESSA NEO Coordination Centre at ESA/ESRIN, Italy, inauguration in May 2013
  • Now: Mix of professional/amateur telescopes supported by tracking databases, plus other European assets
  • Future: Fully integrated system supporting alerts for civil authorities
+ Monitoring and warning of potential Earth impactors with tracking of newly discovered objects and global alerting capability +

NEO Segment

ESA's own Optical Ground Station, Tenerife, provides data to the SSA-NEO Coordination Centre

The SSA-NEO system is based on syndicating and federating observation and tracking data provided by a large number of European and international sources.

The key components include:

  • Observatories and astronomers with telescopes of various sizes, both professional and amateur
  • A central SSA NEO Coordination Centre (to evolve into the 'Small Bodies Data Centre'), which uses astrometric measurements collected by the Minor Planet Center (USA)
  • An analysis capability to predict possible impact locations and assess dangers
  • Analyses related to risk mitigation, including the possible deflection of an asteroid
  • A system for issuing warnings and alerts to civil authorities in Europe

Data on NEOs are collected from telescopes and radar systems worldwide. Each of these submit observations to the Minor Planet Center (MPC), operated by the International Astronomical Union (IAU) at Cambridge, Massachusetts, USA, which acts as a central clearing house for asteroid and comet observations.

The measurements collected there are retrieved by the SSA NEO Coordination Centre; orbits and miss distances are computed. In case of high-risk impact predictions, the data will be cross-checked with NASA's SENTRY system, operated by the Jet Propulsion Laboratory (JPL), California, before issuing alerts.

The NEO team

Within Europe, we have developed world-class capabilities and expertise in observing, discovering and assessing NEOs.

The NEO team is based at ESA's SSA NEO Coordination Centre at ESA/ESRIN and at ESA/ESTEC under the leadership of Dr Detlef Koschny, an experienced planetary scientist. He has worked on numerous ESA missions, including Smart-1, Venus Express and the Agency's comet chaser, Rosetta, as well as the asteroid sample return mission studies for Marco Polo-R. He is supported by Gerhard Drolshagen, an expert in the space environment and its effects who has studied meteoroids and space debris and performed impact risk assessments for numerous ESA missions.

The SSA-NEO team also includes ESA scientists with expertise in space debris studies, NEO mission analysis, planetary and asteroid science, astronomy and astrometry. These are supported by experts in scientific institutes and European industry, which are helping to create a functional and effective NEO warning system.

"Within Europe, we have developed world-class capabilities and expertise in observing, discovering and assessing NEOs. Our goal now is to coordinate and support local experts and make their observations available in a consistent system that offers benefits to all citizens – including those outside Europe," says Dr Koschny.

Precursor services overview

The necessary elements for providing NEO survey services to Europeans are already in place. However, they are operated by diverse scientific institutions having limited resources. During 2009-2012, the SSA-NEO Activity implemented precursor services, provided via the SSA NEO Coordination Centre at ESA/ESRIN, Italy. These can be accessed via a technical website at

Impact crater near Carancas, Peru, 2007

These precursor services integrate existing NEO information and ensure they are available 24 hrs/day. Activities include:

  • Establish the required infrastructure at ESA/ESRIN – mainly computer hardware and an expert coordination team
  • In collaboration with European scientific and research institutes: develop a new central database for Europe's NEO information (while maintaining current services)
  • Assess capabilities of existing European resources, including infrastructure (observatories, catalogues, networks) and expertise
  • Integrate and federate these resources into SSA-NEO with guaranteed service and performance agreements
  • Study and assess, in cooperation with relevant international scientific and political bodies (IAU, UN, etc.), the best way to coordinate warnings if a potential Earth impactor is detected

Facilities and infrastructure

Orbit and location of asteroid 2011 AG5 as of 15 June 2012
Orbit and location of asteroid 2011 AG5 as of 15 June 2012

The current precursor services are provided via the SSA NEO Coordination Centre (NEOCC) located at ESA/ESRIN (formal inauguration May 2013).

It supports the integration and initial operation of ESA's NEO information distribution. In the current phase of the SSA programme (Period II, 2012-2016), the focus lies in the operation and further expansion of the NEOCC to evolve into the fully capable Small Bodies Data Centre (SBDC). Today and in the future, the NEOCC will support experts in the field through upgraded systems and sensors, and by performing scientific studies needed to improve NEO warning services.  

The current NEO SSA Coordination Centre is supporting the integration and initial operation of the NEO precursor services. The NEOCC's activities focus on the provision of information to European customers.

Copyright 2000 - 2017 © European Space Agency. All rights reserved.