In October 2017 the Pan-STARRS survey discovered the first known interstellar object transiting through our Solar System. Named ‘Oumuamua by the discoverers, it soon became the focus of numerous observations by the world's largest professional telescopes.

Current NEO statistics About 4% of the known NEO population is in the risk list. This value has remained roughly constant over the past years even if the discovery rate has increased.

On 25 April 2018 ESA’s Gaia Data Processing and Analysis Consortium published the second release of the mission data products (known as Data Release 2, or DR2 for short). For the first time, Gaia astrometry of more than 14 000 known asteroids was made public, showing that the spacecraft can achieve astrometric precisions at the milliarcsecond level.

Over the past few weeks some media outlets discussed the future impact possibilities of asteroid (101955) Bennu, the target of the ongoing NASA mission Osiris-REx. Bennu is indeed ranked near the top of our risk list, but the earliest year when an impact is possible is 2175, not 2135 as some reports stated.

In our newsletter of December last year, we devoted this section to the discovery of asteroid 1997 XF11. Twenty years ago, on 11 March 1998, astronomer B. Marsden released an IAU Circular stating that the asteroid would pass within 0.002 au of Earth on 26 October 2028.

On 10 February 1896 at 09:30 a large fireball appeared in the sky over the Spanish capital, Madrid. The bolide exploded at high-altitude and an air-burst was reported by many observers. Slightly more than one minute after the explosion the shock wave reached the city, causing quite some fear among the population.

For the first time in the history of NEA observations more than 2 000 new NEAs have been discovered in one calendar year, resulting in a monthly average of nearly 170 new asteroids. In addition, 2017 was the fifth year in a row with NEA discoveries above a thousand.

The Spacewatch project, located in Arizona, is probably the oldest of the asteroid survey still active today. They were the dominant discoverers of new asteroids in the ‘gos, and the pioneers of using CCDs to find new NEOs.

Current NEO statistics During the last month the global numbered asteroid catalogue (including main belt asteroid) surpassed the threshold of half million objects. The number of known NEOs surpassed 17 000, thanks to more than 300 discoveries in a single month.

Asteroid 2012 TC4is the target of an international observing campaign that will culminate this month during its close fly-by with Earth. The object will safely fly at about 44 000 km from the Earth surface, with no chance of collision with our planet.

Asteroid 2012 TC4, discovered five years ago by the Pan-STARRS survey,will come back close to Earth on 12 October 2077.It will fly-by at 44 000 km from the surface, providing a rare chance to carefully observe a small known object during its entire approach to our planet.

Near-Earth asteroid 3122 Florence will have a close pass by Earth on1 September when it will be at a closest distance of 0.0472 au (18.4 LD), which makes it a Potentially Hazardous Asteroid (PHA). This Amor object, named after nurse Florence Nightingale (1820-1910), has an estimated diameter of ~4.35 km and was discovered in March 1981 by S.J. Bus at Siding Spring Observatory.

The month of June 2002, 15 years ago, marked the kick-off of six parallel preliminary studies carried out by ESA’s General Studies Programme (GSP) in order to analyse possible asteroid missions. Three of those studies were devoted to in-orbit telescopes for NEO discovery and characterization, other two were devoted to asteroid rendezvous missions and finally one for asteroid rendezvous and impact.

Just a few days before the edition of the present newsletter a large bolide crossed the Italian northern sky. The event was observed by many people and in particular by a newly installed fireball network PRISMA (see next page). Such images have been used to determine the trajectory of the entering object.

In the acronym "NEO"the final letter O stands for "Object", because the group is generally understood to include both asteroids and comets that come close to Earth. It is however interesting to note that most aspects of the NEO discovery process we commonly associate with asteroids happened first for comets

The closest approach distance is not the only important parameter for assessing the asteroid hazard. The velocity plays a crucial role in shaping the outcome of a close encounter as well as in evaluating the consequences of an impact. The speed at which an asteroid flies by the Earth results from geometrical and dynamical considerations characterizing its pre-encounter orbit.

During the past year ESA funded the refurbishment and modernization of the 0.8 m Schmidt reflector located at the Calar Alto Observatory in Spain. The telescope, identified with the MPC code Z84,is now operational and can be remotely controlled.

Every month about 40 known or recently discovered asteroids come within 0.05 astronomical units, or about 19 lunar radii, from our planet. In some cases, such as in the month of December 2016,four or even five objects reach their closest approach distance on the same day.

During 2015-2016 ESA funded the development of two small robotic observatories, called the Test-Bed Telescopes (TBTs). The main goal is to develop and test a fully automated telescope control system to observe NEOs and space debris.

Whenever a new set of observations for an object is published, our Impact Monitoring routines perform a new search for possibly impacting orbits compatible with such set of observations. The system is capable of detecting all possibly impacting orbits down to an impact probability threshold, named “generic completeness level”.