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Last update: 2019-12-08 14:45:00 UTC


NEOCC Newsletter: December 2019

05 December 2019

The ESA SSA-NEO Coordination Centre has released the December newsletter summarising the most relevant data and events on asteroids and comets approaching the orbit of the Earth. Please, feel free to forward it to potentially interested people.

You can download the newsletter by clicking on the button below; to subscribe to the service, please fill in the form on page




The power of precoveries

15 October 2019

Asteroid 2017 US imaged by the Catalina Sky Survey on 13 October 2017, three days before their own discovery of the object. The detections are extremely faint, too faint to be detected automatically by the pipeline, but visible to the trained human eye.

Credit: Catalina Sky Survey / University of Arizona / NASA

If you check our current risk list, you will notice that a significant number of objects in the top positions are extremely “old”, discovered in the first decade of the century.

Some of them actually only have observations taken around the time of discovery, and have not been seen ever since. The orbits of these objects are now very uncertain, and it is therefore difficult to obtain new observations and revise the impact threat assessment, unless they are re-observed by chance.

There is however a way to get some additional data. It is called "precovery search", and it consists of a systematic search of existing image archives in order to locate additional detections of the object, not recognised at the time the images were obtained.

In the past, we successfully found precovery observations of a significant number of objects in our risk list. Some of them were actually sufficient to fully exclude the threat posed by the object.

In order to continue this systematic effort, we started a very promising collaboration with the Catalina Sky Survey, a project of NASA’s Planetary Defense Program, to search for precovery detections in their extremely large and complete image archive, collected over two decades of survey work. Last week we reported the first results of this search to the Minor Planet Center: precovery detections of three objects in the top-20 positions of our risk list (2008 JL3, 2008 UB7 and 2017 US).

An example of one such detection is presented in this image: the object, 2017 US, is extremely faint, but it is visible to the human eye on the CCD images, and its position is measurable with accurate astrometric tools. The corresponding measurements resulted in a revised assessment of the impact threat, which was slightly lowered. The threat for the two other objects was also revised as a result of the precovery detections: one remained basically unchanged, the other was slightly increased. Overall, our knowledge of the orbits for all three objects was improved, in some cases quite significantly.

This search shows the power of historical image archives for threat assessment, and in particular the value of the extensive archives generated by Catalina and by the other asteroid surveys.



A would-be interstellar new object currently visiting the Solar System

13 September 2019

Image of C/2018 Q4 (Borisov) obtained on the morning of 9 September with the 70 cm telescope at Chuguev, Ukraine.

Credit: ISON Chuguev (V.N.Karazin KhNU)

Over the past week, the Near-Earth Object (NEO) community in general, and ESA’s NEO Coordination Centre (NEOCC) in particular, have been involved in an interesting example of the process of discovering a new and exceptional object.

On 30 August 2019, Gennady Borisov, an amateur astronomer in Crimea, reported the discovery of a new object, likely cometary, to the Minor Planet Center (MPC). The object was given the temporary designation "gb00234" by the discoverer. As happens with all new peculiar objects, the corresponding observations were posted by the MPC on the NEO Confirmation Page. This is the place where new unconfirmed discoveries are presented to the community, in order to obtain the follow-up needed to characterise their orbits.

Within a few days, additional observations were collected. On 8 September 2019, the Scout alert system currently operating at NASA's JPL reported that the available data seemed to suggest this was not an NEO, nor a normal comet, but something far more unusual: its orbit seemed to be too eccentric to be gravitationally bound to our Sun. This could be the second case of an interstellar object discovered transiting our Solar System.

When this happened, we at the NEOCC, together with collaborators all over the world, started acquiring and analysing additional images of the object. Among them were some images obtained via our collaboration with the International Scientific Optical Network (ISON), using the 70 cm telescope in Chuguev, Ukraine. The images revealed that the object was indeed cometary, showing a nice tail almost an arcminute long. The corresponding astrometry further reinforced the determination that the comet's trajectory was indeed hyperbolic.

The object is unfortunately very close to the Sun, and therefore difficult to observe, because it is always located low on the horizon at twilight. Consequently, additional checks and verifications were needed to prove that the hyperbolic orbit was not an artefact of some problem with the observational data. After three more days of observations, collected all over the world, the MPC finally announced the object as C/2019 Q4 (Borisov), noting that the orbit is hyperbolic.

As of today, we know that C/2019 Q4 has an orbit with eccentricity of about 3.5, and entered our Solar System with a velocity of about 30 km/s. It will reach the closest distance to the Sun in early December 2019, at two astronomical units, and it will then reach about the same distance from the Earth later the same month. It is a bright object, currently at magnitude 18, so it will remain observable from the Earth for years, giving astronomers a great chance to study it in great detail.

For more information you can read ESA’s dedicated news at