September 2015 Newsletter

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.

Over the past few days there has been a significant media interest in 2015 TB145, a large asteroid that flew past Earth on the night of Halloween. Apart for the popularity of the event generated by the date,the fly-by itself is interesting from a scientific perspective, because it was discovered only three weeks before its closest approach.

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.

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.

A new release of our NEO Web Portal is on-line at http://neo.ssa.esa.int/. It represents a major update of the SSA-NEO system since it includes a number of new functionalities and an improved graphics. The possibility of visualizing the actual trajectory of an NEO including gravitational perturbations and an enlarged plot at close encounter has been implemented.

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.