Past studies: EuNEOs

More detailed information on the EuNEOs mission is available on the Executive Summary

Mission overview

EUNEOS is space survey from an inner Solar System orbit discovering the most dangerous NEOs, the so-called Potentially Hazardous Objects (PHOs). Often they are also the ones that are most difficult to detect from ground-based observatories: those whose aparent distance to the Sun on the sky is small (i.e. those having small solar elengations).

After a launch with Soyuz-Fregat, the spacecraft will be trasfered to a 0.5 x 0.7 AU eliptical orbit using its own chemical propulsion system and Venus gravity assist manouvre. From this orbit the system will carry out a survey of the +/- 20 deg ecliptic latitude and +/-130 deg solar elongation band every three days.

The spacecraft payload will consist of 30 cm aperture telescope, derived from the Corotel instrument design proposed for CNES´s COROT mission. A very large FOV (3.0° x 3.0°) and small pixel angular size (to improve the SNR and cope with the contribution of the zodiacal light) require the use of a large CCD mosaic. Polarimetry measurements, providing clues on the albedo of the observed object, will also be an option.

Mission rationale

The EUNEOS project is the natural outcome of a study on the distribution of Near Earth Objects, commissioned by ESA to the group of planetary science of Observatoire de la Cote d'Azur in Nice (France), and performed jointly with scientists at the Southwest Research Institute in Boulder (Colorado) and Lunar & Planetary Laboratory in Tucson (Arizona). The results of this study are available to the public at

The study pointed out that that finding NEOs should be an easier task if the observation point is moved closer to the Sun than the Earth is. In theory the closer to the Sun, the better though in practical terms there are other effects, such as the zodiacal light that can hinder the observations carried out from very small heliocentric distances.

Performing a survey of the entire NEO population down to a certain size might also be an unnecesary effort. Most NEOs, infact, despite having perihelion distance q<1 AU and aphelion distance Q>1 AU do not cross the Earth’s orbit in the 3-dimensional space, and therefore they do not carry any collision hazard for our planet. For this reason, the astronomers have introduced the notion of Minimal Orbit IntersectionDistance (MOID) which is defined as the minimal distance that the asteroid and the Earth can have assuming random position along the respective orbits. NEOs with MOID < 0.05 AU are called Potentially Hazardous Objects (PHOs), because these bodies do pass close to the Earth’s orbit, and theirorbital changes forced by the gravitational interactions with the planets over a century could bring themto collide with the Earth.

The initial study therefore recommended to give very serious consideration to the idea of developing a dedicated space-based NEO survey system and to put most of the emphasis in the cataloguing of the PHO population. This system would consist mainly of a spacecraft carrying a medium-sized telescope and placed in an orbit interior to that of the Earth´s. The EUNEOS concept responds to this recommendation by studying of the best possibilities to find NEOs from space and determining the optimal trade-off between survey strategy, telescope size, satellite orbit, observation wavelength, and ultimately, between performance and cost.

During the study it has been estimated that EUNEOS could achive a 80 % complete survey of the PHO population down to sizes of ~300 meters in 5 years. "Object recovery" by ground based facilities should be possible in 70 % of the cases (and this is important to obtain all orbits) with the support of a ground based telescope capable of pointing at small solar elongations. Therefore, it might well be that the future of NEO searches is in space.

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