April 2023 Newsletter

In the month of December, (29075) 1950 DA, an old NEA, entered the risk list in a peculiar way: the addition is not based on new observations but it is the combined result of an already existing good observational coverage for this object, together with a newly implemented dynamical model now available at NEODYS.

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.

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”.

In recent years, it has become increasingly common for ground-based surveys to discover small objects that seem to be in distant Earth-centred orbits. Most of them turn out to be man-made spacecraft or upper stages of spent rockets residing in Earth’s region.

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).

During the month of September a news circulated on European media claiming that between 22 and 28 September the Earth would have been hit by meteorites and other cataclysmic events.

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.

On 22 June 2019, around 21:26 UT (17:26 local time), a roughly 5-metre object entered the atmosphere over the Caribbean Sea, and exploded at an altitude of about 25 km over the sea surface, releasing an energy roughly equivalent to 3 kt of TNT. The explosion was first detected by the Geostationary Lightning Mapper (GLM) instrument on board the GOES-16 geostationary satellite.

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.

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.

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.

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.

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.

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.

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.

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.

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;

Some media attention was given to the distant fly-by of asteroid (1566) Icarus. Although the event in itself posed no collision threat whatsoever,Icarus is indeed an interesting object for the history of NEOs.

November was a month of close approaches of many small objects. A particularly interesting case was 2015 VY105, which came to less than 30 000 km from the Earth’s surface on 15 November.

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.

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 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.

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 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 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.

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.

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.

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.

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.

May 2020 Newsletter

March 2021 Newsletter