This month, while reading this newsletter, you will find an object designated with a “non-standard” name: XDg2F93. Labels like this, not following the standard form of year + letters + numbers,are called “temporary designations”.

We took the opportunity of the ExoMars 2016 launch to organize a ground-based observational campaign. The goal was to test, in a reverse mode, the observational scenario needed to monitor the approach of a small Earth impactor. The spacecraft and other hardware related to the launch was successfully imaged;

On 9 May the planet Mercury will transit the Sun as seen from Earth. Although not an asteroid event, this gives us a chance to talk about how transits have been used in the past to probe the population of small asteroids extremely close to the Sun (the so-called Vulcanoids).

The NEO Coordination Centre is collaborating with the European Commission project NEOShield-2 on the dissemination of NEO physical properties. Our EARN-based physical properties database will be enhanced to host additional data.

The newly discovered asteroid (469219) 2016 HO3 has been attracting the interest of the NEO community becauseof its peculiar orbital path. Having the same period of revolution of the Earth but a higher eccentricity and being properly phased, this object appears to circle our planet in a retrograde “quasi-satellite” orbit with period one year.

2016 NA39 is a newly-discovered asteroid that for a few days in mid-July deserved attention. Because of its large size, around one kilometre, it became the highest rated object with possible impacts in the current century, scoring as high as Palermo Scale of —2.6.

The NEO Coordination Centre web portal is an evolving environment: new services are added whenever ready to be made publicly available. This is the case for two software packages addressing key issues in NEO science: an updated NEO population model and an NEO propagator.

The month of September was unusually rich of close approaches. Nine objects,all with a diameter of about 10 metres, flew by our planet closer than about the distance of the Moon.

The number of known near-Earth asteroids has just surpassed the threshold of 15000. That is a 50% increase with respect to 2013, when the 10000th object was found, highlighting the ever increasing success of ground-based NEO detection surveys.

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”.

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.

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 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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

On 27 June 2018, after a cruise phase of 3.5 years, the Japanese Hayabusa 2 spacecraft rendezvoused with its target, near-Earth asteroid (162173) Ryugu. The first images sent back by the mission's cameras show a nearly spherical object, much more symmetric

The Fly-Eye Telescope is an innovative project of ESA‘s SSA-NEO Segment that will focus on survey and follow-up of NEOs. Another important milestone on the way to build the telescope was achieved: from 30 July to 1 August ESA attended the acceptance test of the equatorial mount at its production site in Verona, Italy.

Ten years ago, on 6 October 2008,Richard Kowalski, an observer of the Catalina Sky Survey, spotted the first-ever asteroid found on an imminent collision course with the Earth. Over the following hours, hundreds of astrometric observations, plus light curves and spectroscopic data, were collected by observers all over the world.

On 19 October a very small asteroid, designated as 2018 UA, was discovered by the Catalina Sky Survey, and quickly flagged as a potential very close approacher. Immediate follow-up observations by both Catalina and the Spacewatch project led to a much more accurate orbit solution.

The month of December this year marks the fifth anniversary of the launch of ESA’s Gaia spacecraft. The mission, now operating continuously near the Earth-Sun L2 Lagrangian point, has already revolutionized many fields of astronomy, thanks to the broad and exquisite quality of the data it is producing.

For the first time since 2012 the year that just ended did not break all records of annual NEO discoveries. This was mostly due to unusually poor weather in Hawaii, where many current NEO discovery surveys are located.

This year on 8 February marks the 50th anniversary of the fall of the Allende meteorite, the largest carbonaceous chondrite ever found. The atmospheric entry and impact happened at night local time, and were therefore well observed over the entire Northern Mexico. About 2 tonnes of fragments were later collected on ground in a strewn field of about 50 km size.

On 1 February 2019 a bright daytime fireball was seen by multiple eyewitnesses around the area of Gulf of Mexico. It exploded over the western tip of Cuba, producing a significant shockwave felt by local residents, and the fall of a large number of stony meteorites, mostly near the village of Viflales.

The first edition of the Planetary Defense Conference (PDC) managed by the International Academy of Astronautics happened exactly 10 years ago,in the week of 27-30 April 2009 (before the IAA became involved, there were two other PDCs, both in the USA). The conference was held in Granada, Spain, and was the first of a biennial IAA series that is continuing this month, with the 6th conference being held in College Park, USA.

The number of known NEAs reached the round total of 20 000 at the end oflast month. This group of asteroids is steadily growing at a pace of roughly 160 new discoveries each month, thanks to the work done by the main asteroid surveys.

May will likely be the last month before summer with an average rate of NEO discoveries. Starting in June, most surveys in the South-West of the United States will likely temporarily decrease their productivity due to the summer monsoon season.