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: https://neo.ssa.esa.int/subscribe-to-services.

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NEOCC has just finished the implementation of a service for the VESPA portal. VESPA (Virtual European Solar and Planetary Access) is a Europlanet activity which connects planetary science data providers to allow easy access, interoperability and cross-correlation of databases.

The VESPA portal is just one of the ways to access our data. From the NEOCC, the data shared comprises orbital information for every asteroid contained in our database. The VESPA portal allows easy querying of targets and shows which services have data related to that object. It also helps going through every data provider and finding information about its source and structure from a unified interface.

Apart from that, it allows you to query data by using VO tools such as TOPCAT, as VESPA relies on the TAP protocol. At its core, every data provider is exposing a TAP server with a well-defined structure, which allows to retrieve data from different providers in the same query.

We expect this to facilitate additional access to our data and provide users with useful insights by comparing it with other asteroid information providers, as well as enriching other datasets.

VESPA logo. Credits: Virtual European Solar and Planetary Access.

NEOCC has just finished the implementation of a service for the VESPA portal. VESPA (Virtual European Solar and Planetary Access) is a Europlanet activity which connects planetary science data providers to allow easy access, interoperability and cross-correlation of databases.

The VESPA portal is just one of the ways to access our data. From the NEOCC, the data shared comprises orbital information for every asteroid contained in our database. The VESPA portal allows easy querying of targets and shows which services have data related to that object. It also helps going through every data provider and finding information about its source and structure from a unified interface.

Apart from that, it allows you to query data by using VO tools such as TOPCAT, as VESPA relies on the TAP protocol. At its core, every data provider is exposing a TAP server with a well-defined structure, which allows to retrieve data from different providers in the same query.

We expect this to facilitate additional access to our data and provide users with useful insights by comparing it with other asteroid information providers, as well as enriching other datasets.

VESPA logo. Credits: Virtual European Solar and Planetary Access.

Last night at 23:14 UTC NASA's DART spacecraft successfully hit Dimorphos, the moonlet orbiting around near-Earth asteroid Didymos. About 38 seconds later, the time it took for the light to reach Earth, people all over the world saw the abrupt end of the live streaming from the spacecraft, signaling that the impact had happened successfully.

At the same time, astronomers in a small slice of our planet surface, extending from Southern and Eastern Africa to the Indian Ocean and the Arabian Peninsula, could actually watch it live with their telescopes. Among those were a half dozen stations joined together for a dedicated observing campaign organized by our ESA Planetary Defence Office, and coordinated by the team of observers of the NEO Coordination Centre. As usual, when such a timely astronomical event happens, not all stations were successful in their observations: clouds, technical problems and other issues always affect real-life observations. 

However, a few of our collaborating stations could immediately report a successful direct confirmation of the impact. Among them was the team of the Les Makes Observatory, on the French island of La Reunion, in the Indian Ocean. The sequence of images they provided in real time was impressive: the asteroid immediately started brightening upon impact, and within a few seconds it was already noticeably brighter. Within less than a minute a cloud of ejected material became visible, and we could follow it while it drifted Eastward and slowly dissipated.

The emotion of following the event live was the conclusion of weeks of discussions, meetings, accurate planning and observational design by our team, together with the local observers and scientists at all the collaborating stations. A fantastic campaign that produced data that our astronomers, together with the whole DART collaboration, will now begin analysing in order to extract valuable scientific information on the effects of the impact. The results will prepare us for the visit of ESA's Hera spacecraft to the Didymos system to examine the aftermath of the DART's impact a few years from now.

Observations of Didymos during the DART impact. A clear brightnening just after the impact can be observed, followed by a cloud of material ejected from Dimorphos. Credits: Les Makes observatory, J. Berthier, F. Vachier / T. Santana-Ros / ESA NEOCC, D. Föhring, E. Petrescu, M. Micheli

The European Commission and ESA’s Planetary Defence Office together are organising the “EU-ESA Workshop on Size Determination of Potentially Hazardous Near-Earth Objects” on 11-13 November 2024 at the European Space Operations Centre (ESOC) in Darmstadt, Germany.

The meeting's purpose is to gather the asteroid community to discuss how we can improve the size determination of asteroids, mainly focusing on near-Earth objects. During this workshop, we will discuss how the H magnitude is currently determined from observations, how the different physical characterisation techniques are used to determine the albedo, and the different techniques directly used to determine the object size. By convening the community, we aim to formulate suggestions, guidelines, and actions for the community to altogether work toward obtaining better size determination for potentially hazardous NEOs. Hoping that, if and when, an asteroid is discovered on a collision course with Earth, we will be able to obtain reliable and robust size determination.

A link to the event web portal can be found here.

The workshop sessions are the following:

• Photometric observations and H magnitude determination
• Thermal infra-red observations and modelling, shape modelling
• Polarimetric observations and albedo determination of NEOs
• General observation on NEOs

Workshop presentations have been organised by invitation of relevant speakers. Speakers and interested participants are invited to register to the event up to 31 October 2024. Ample slots have been allocated in the programme to allow discussions between the experts. A limited number of presentation slots are still available. If a workshop attendee considers having a relevant contribution in the subject and would like to present it at the workshop, please send a message to the organisers with a proposed title and abstract (maximum of 300 words) before 15 October 2024. The workshop will be hybrid, with local and remote attendance possible. A limited capacity of up to 40 people will be available for local attendance to the event. These will be available to the speakers wanting to attend in person and on a first come, first served for the rest of attendees.

As part of our observational activities, we do not only observe natural objects, but occasionally also artificial satellites. Sometimes we use them as proxies for a potential threating asteroid (as we did in 2020 with BepiColombo). Other times we use them as training subjects or for calibration purposes. In this occasion, it was for a collaboration with ESA's Space Debris Office to support the orbit determination of a target of their interest.  

This artificial satellite is "Salsa", one of the four identical satellites of ESA's Cluster mission (the other three are similarly nicknamed Rumba, Samba and Tango). These satellites were designed to study the Earth's magnetosphere and its interaction with the solar wind. In order to achieve their mission goals, they are placed in an uncommon orbit (HEO – high-eccentricity orbit), which allows for a neat disposal at the end of its lifecycle . Moreover, this orbit positions the satellite, for a significant time of its orbit, well beyond the LEO and MEO regimes, resulting in sky conditions closer to those commonly seen for NEOs (farther and slower than most of Earth satellites). This regime enables a synergy between PDO and SDO, with the use of the PDO assets and techniques for NEOs applied to satellites.   

Observing an object like Salsa is therefore an excellent opportunity for us to train in the observation of very fast objects. Only a few regular NEOs become as fast as Salsa could get, and they are typically of special relevance when they become 'impactors', because they help learning about the nature of the asteroids and their interaction with the atmosphere, both fundamental for the mitigation activities in case of a threat. Until now, only nine asteroids have been observed before impact, and they were all tiny, intrinsically faint and therefore challenging because of the need of fast response times and short visibility times.  

However, with Salsa we had a large visibility window and excellent predictability of its motion, allowing us to plan our observing strategy in advance. Thus every 2 days and a quarter, the object provided us with a very low perigee, with an observational geometry resembling an impact. We thus took the opportunity to observe Salsa for a few months, with different telescopes from which we routinely observe NEOs (ESA's Optical Ground Station – OGS, CAHA's Schmidt), in order to test and validate the different formats and interfaces between the two teams, PDO and SDO, who usually work in different units and with different definitions.  

All of this preliminary work was part of the preparation for the final campaign, to be performed during the very last orbits of Salsa, when there was a risk of losing telemetry (and therefore trajectory information) at any time, because the already battered batteries were suffering more and more from the longer eclipses as Salsa was getting closer to Earth. Moreover, simulations showed that the last perigee passage of Salsa could be low enough to damage the spacecraft, leaving it with no communication and active tracking channels during its last orbit before the final plunge. From the moment telemetry would cease, any orbital determination would rely mainly on optical observations, bringing us to the same situation we have when we track a natural and thus unresponsive asteroid. And that was when the asteroid experience of the PDO team could really help: the observation recovery and following orbital determination after the last perigee was essential to determine the exact actual reentry point, where an airplane was going to monitor the reentry process.  

There was some positional uncertainty after the last perigee passage because of the difficulty of modelling the atmospheric interaction. We had to observe Salsa as soon as possible after perigee, because the uncertainty would keep growing. We decided to use our telescope network to observe it as soon as it became visible from somewhere around the world. We recovered it from Australia, less than an hour after perigee, but when the spacecraft was already 12 500 km above the planet surface. The target was very close to the Flight Dynamics and SDO predictions. We observed it from the Canary Islands, mainland Spain and from South Africa, to add parallax and improve the orbit determination. 

The following night Salsa was close to apogee and adding more observations would not help much to improve the orbital knowledge. However, there was still a chance to improve the orbit if we could observe it just before impact, when the object was briefly visible during twilight from Namibia. The object could be observable down to a range of less than 12 000 km, while moving in the sky at an angular speed of almost 90"/s. The conditions were challenging, but we could detect the object and, with proper calibration, the accuracy of the impact point location was improved. Flight dynamics got a last contact from Kourou tracking station and therefore we have a ground truth to validate our calculations. Finally the reentry took place as expected and it was observed from the air by the airborne observation mission ‘ROSIE-Salsa‘. 

This adventure just starts here, with all the experience to be used in the upcoming reentry of the three remaining Cluster spacecraft. With aging hardware, the potential need for optical observations is significant, and we are ready to execute them and to apply our expertise again to support the reentry of decommissioned spacecraft.  

Composite image showing Salsa satellite crossing a small portion of the field of view of Optical Ground Station, OGS, 1m telescope located at Izaña, Canary Islands, Spain. Credits: ESA / PDO.

Animated gif showing Salsa satellite crossing a small portion of the field of view of Optical Ground Station, OGS, 1m telescope located at Izaña, Canary Islands, Spain. Credits: ESA / PDO.

The Near Earth Objects Coordinator Centre's (NEOCC) image archive has reached a significant milestone – 1 million images! This vast collection of data will greatly enhance our understanding of near-Earth objects and aid in their precovery and tracking.

A key factor behind this growth is the expansion of the NEOCC’s observational network, which has enabled NEOCC to collaborate with international teams, including those at Schiaparelli Observatory, Tautenburg, 6ROADS telescope network, and other leading research facilities. Their images have already proven invaluable in discovering, precovering or following up known asteroids.

The integration of the NEOCC image archive with the Solar System Object Image Search (SSOIS) system promises to unlock new discoveries in asteroid research. With this enhanced dataset available, scientists can better understand asteroid behaviour, identify potential threats more effectively, and develop strategies for mitigating these risks.

This achievement highlights the importance of planetary defence and asteroid research. The 1 million images now available through NEOCC's Image Archive (that grows as you read this) represent a significant resource for scientists working on this critical area of study.

Caption: Distribution of NEOCC Image Archive collected data per observatory. Credits: ESA / PDO.

The ESA S2P-NEO Coordination Centre has released a Close Approach Fact Sheet (CAFS) for asteroid 2024 MK, passing by Earth on 29 June. Please, feel free to forward it to potentially interested people.

You can download the CAFS by clicking on the button below. For subscribing to our releases, please fill in the form on page https://neo.ssa.esa.int/subscribe-to-services.

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On Thursday, 6 June 2024, at 09:21 UTC a small asteroid, of 2 to 4 meters, was discovered by the Catalina Sky Survey on top of the Catalina Mountains in the desert of Arizona. A few minutes after the reports of their discovery to the Minor Planet Center, our imminent impact monitoring system (Meerkat) issued an alert. That alert was actually not for an impact, but for a very close approach. Indeed, a few hours later at 14:01 the new object (known under the name of C43AUL1 at the time) flew over the Catalina Sky Survey telescope itself at distance of 1750 km. Such a close fly-by is actually the second closest observed (non-impacting) fly-by from a known asteroid, the closest being 2020 VT4 that flew at a distance of only 373 km from the surface.

A few minutes before the closest approach, our team of observers at the NEOCC observed 2024 LH1 from the Haleakala Observatory located in Hawaii to improve its orbit, but also to obtain valuable physical properties information. The object was moving so fast on the sky that the only way to observe the object was to start a 20 seconds exposure tracking the stars and let the asteroid pass-by in the field of view.

On the image of the trail of the asteroid, one can notice that the asteroid look like blinking. This is not an artefact, and this blinking is due to the rotation of the object. Using a newly developed tool by our team, we were able to extract the lightcurve of 2024 LH1 and determine that it rotates around itself once every 3.68 seconds. This is the third fastest rotation rate for an asteroid ever observed. The fastest being 2024 BX1 whose rotation is 2.5888 seconds and has been obtained using the same technique.

Caption: Observation of 2024 LH1 by one of the Las Cumbres Observatory 0.4m Clamshell telescope located at the Haleakala Observatory on the island of Maui in Hawaii.

ESA’s NEO Coordination Centre has just expanded its suite of tools within the NEO Toolkit with the Synodic Orbit Visualisation Tool (SOVT). The SOVT is an advanced NEO trajectory visualiser which uses a rotating reference frame that follows the motion of Earth about the Sun. The tool allows to represent the relative trajectory of an NEO in a 3D synodic reference system. It can also show the NEO observability region in 3D for a certain telescope on Earth (defined by the telescope limiting visual magnitude), in a shape that we call the “detection polar”. This allows creating an instant overview about if and when an object might be observable. The tool makes use of the H-G magnitude system in order to compute this 3D detection polar.

Read the full article here.

Caption: Synodic trajectory of Apophis with respect to the Earth between March 2021 and March 2034. The observability of the asteroid in a telescope with a limiting visual magnitude of 18 mag is provided through the detection polar surfaces represented in yellow. Credits: ESA / PDO.

Over the last year, ESA has commissioned and started operating the second so-called "Test-Bed Telescope" (TBT), a 56 cm wide-field optical telescope located on the premises of ESO's La Silla Observatory, on the Chilean Andes. This is the second unit, after the first one already installed in ESA’s tracking station in Cebreros, Spain. The TBTs have been designed to support NEO and space debris observations, and especially networked and collaborative experiments. They are intentionally composed of “commercial off-the-shelf” components, to demonstrate the capabilities of current instrumentation options and, in particular, to allow easy testing of novel observational approaches.

As a first test for these instruments as an NEO observing tool, we began operating the telescope almost nightly as a follow-up facility after it was assigned an MPC code W57 in late 2022. Observations from La Silla benefit from the extremely high percentage of clear nights and the Southern declination coverage offered by the telescope's location. The observatory quickly rose in the ranks of NEO follow-up facilities worldwide, significantly contributing to NEO confirmation efforts in the Southern hemisphere.

In recent months, however, we decided to devote a fraction of the telescope's time to NEO discovery survey. We developed a synthetic tracking pipeline, based on the Tycho Tracker software package and exposed and analysed a few fields per night. Our observing strategy alternates between low elongation fields and regular follow-up near the opposition region. Every candidate detection is carefully validated by our professional observers, to ensure that only reliable detections are submitted to the MPC and published.

Months of dedicated work finally paid off on Thursday, 14 March, when we were rewarded with our first discovery using this newly developed telescope and pipeline system. A set of images exposed in the Southern constellation of Hydra contained an unknown magnitude ~20.5 asteroid, which our observers immediately recognised as having a high likelihood of being real. The candidate was temporarily labelled PDO0002 and reported to the MPC, where it promptly appeared on the NEO Confirmation Page.

We immediately obtained follow-up observations with our network of telescopes and collaborators, including the Las Cumbres Observatory network, the Calar Alto Schmidt and the TRAPPIST North and South telescopes in Morocco and Chile. Thanks to the resulting astrometry we now know that the object is an NEO, similar in size to the Tunguska impactor, with a relatively small MOID of 0.006 au. Other stations also reported follow-up, and the Pan-STARRS team located a “prediscovery” unreported detection from two weeks earlier, which further improved the orbit determination.

The object has now been designated 2024 EL4. Aegis, our impact monitoring system, has processed all the available observations and shows that the object doesn’t pose any impact risk with Earth over the next century.

We hope that this discovery is just the first of many more to come, not just with these test-bed telescopes but also with ESA's dedicated discovery machine, the Flyeye telescope, which is ready to be installed and commissioned in Southern Italy.

Hot off the presses: just 4 days after discovering 2024 EL4, the same system found another NEO, which has now been confirmed and designated 2024 FS1.

Caption: The discovery image of 2024 EL4 was generated by stacking 31 images taken with a chilled CCD camera. Credits: ESA / PDO.

For the third time in recent history of asteroid detection a NEO was detected a few hours before it entered the Earth atmosphere (the two previous cases were 2008 TC3 and 2014 AA).

Asteroid 2018 LA was discovered by the Catalina Sky Survey in the early morning (European time) of this Saturday, 2 June.&imagePreview=1

​​​​​​In a matter of hours additional observations were made and it became very probable that it would collide with the Earth. The approximate impact corridor was over a thin stripe crossing Botswana and Namibia. The same evening a number of local observations started to arrive at the International Meteor Organisation reporting a very bright fireball detected in the mentioned area. It was confirmed that the observed fireball actually corresponded to 2018 LA. Details about the observed fireball can be found here: https://www.imo.net/asteroid-2018-la-hit-the-atmosphere-over-botswana-on-june-2/

The object had a size of 2 to 5 m and approached the Earth with a relative velocity of approximately 17 km/s from the night side. Due to its small size and high entry velocity the object could only be detected on its final plunge to Earth. It is expected to have completely disintegrated in the atmosphere.

Discovery images of 2018 LA obtained on 2 June 2018 with the 1.5 m telescope at Mt. Lemmon, Arizona (USA). Credit: Catalina Sky Survey / University of Arizona / NASA

For the seventh time, a meteoroid has been discovered before impacting the Earth. This one-metre asteroid has been discovered by Krisztián Sárneczky with the 60-cm Schmidt telescope of the Piszkéstető Observatory in Hungary. It is his second discovery of an impactor, after the impact of 2022 EB5 less than a year ago, in March 2022.

At 20:18:07 UTC on 12 February 2023 the new asteroid, now officially designated 2023 CX1, was imaged from Piszkéstető Observatory in Hungary and reported with a second position to the MPC at 20:49 UTC. About 40 minutes later some follow-up observations reported by the Višnjan Observatory in Croatia confirmed the object, and at this point the various impact assessment systems found a 100% impact probability in the area of the English Channel between 02 and 04 UTC. The estimated asteroid size was around 1 meter of diameter and posed no risk of damage for the people in the area.

During the next seven hours astronomers all around the globe observed the object and pinpointed the impact corridor over the English Channel, with a trajectory coming from West to East. The object was observed up to around 10 minutes before impact, only 5 minutes before getting into Earth’s shadow and becoming unobservable. The last image was taken at 02:46:56 UTC, by our collaborators of the Rantiga Observatory in Italy.

The fireball event happened at the predicted time (02:59 UTC) and location, with observations mostly from Southern UK and France, but also from Belgium, the Netherlands and even Germany. It is likely that some fragments of the meteoroid may have survived the atmospheric pass and fell somewhere onshore close to the coast north of Rouen, in Normandy, France.

The team at ESA’s Planetary Defence Office contributed to the event both with the timely notifications from its Meerkat system, and with the use of a network of optical telescopes established for these occasions. The observing facilities were specifically chosen to provide data useful to increase the accuracy in the determination of the impact circumstances. Astrometry from South Africa, quickly after the initial trigger, and later from the US, extended the observational baseline to continents outside Europe, providing larger parallax. Also, in the few minutes before impact, they triggered accurately-timed observations useful to reduce uncertainty of the impact time to less than 1 second.

First impact assessment by ESA’s tool Meerkat as reported at 21:33 UTC with only 7 measurements, already indicating an impact probability of ~100%. Credit: ESA / PDO

First impact corridor reported by ESA’s tool Meerkat as reported at 21:33 UTC, with the actual impact time 02:59 UTC in the middle of the uncertainty window. Credit: ESA / PDO

Asteroid 2023 CX1 entering Earth's atmosphere captured in the skies over the southern Netherlands. Credit: Gijs de Reijke

At 19:24 UTC on 11 March 2022, Krisztián Sárneczky discovered a new bright and fast moving object with the 60 cm Schmidt telescope of the Piszkéstető Observatory in Hungary. After collecting 4 observations in quick sequence, at 19:38 UTC he reported them to the Minor Planet Center, with the internal observer-assigned designation of Sar2593.

They were quickly published and used by the various impact assessment systems to estimate the possibility of an impact, which seemed unlikely at that time, with a probability of less than 1%.

In the meantime, he began collecting more observations, and at 20:16 UTC he submitted a second batch of 10 additional measurements, now extending the observed arc to about 40 minutes.

As soon as they were published and picked up by the automatic systems, a completely different scenario became clear. At 20:25 UTC ESA’s own internal monitoring system, called “Meerkat”, triggered an alert to our team, reporting a 100% chance of impact for the object. The expected impact time was between 21:21 and 21:25 UTC, less than an hour later. The impact location was already predictable with an accuracy of about a thousand kilometres, and was located a few hundred kilometres North of Iceland.

In response to this alert, and similar ones quickly distributed by other alert systems, many professional and amateur observers all over Europe and in Asia quickly began observing the imminent impactor. Detecting it was extremely challenging, since the object was already very close (less than 50 000 km from the Earth) and moving very fast in the sky.

Another observatory from Slovakia soon reported its successful observations, together with many more detections from the original discoverer. When added to the trajectory computation, they pinpointed the location of the impact with a precision of just a few seconds and kilometres: the asteroid was going to enter the upper layers of our atmosphere roughly 140 km South of the Jan Mayen island, at 21:22:42 UTC, less than 2 hours after being discovered. From its observed brightness, the object appeared to be very small, roughly a metre in diameter.

In the few minutes just before impact more observatories obtained detections, including a last set at 21:10 UTC, by our collaborators of the Kleť Observatory. Shortly after the expected time of impact the Minor Planet Center designated the asteroid as 2022 EB5, the fifth known impactor observed in space before hitting our planet, and the first discovered from Europe.

Some cameras on the Norwegian island of Jan Mayen (900 km from the coast of Norway) recorded at least the flash of light from the incoming object. No visual evidence has arrived from Iceland, located roughly 700 km away from the impact point, probably because of to low-altitude clouds.

Nevertheless, there is independent evidence that the impact did in fact occur thanks to the international network of infrasound detectors. Signals from the impact were detected from Iceland and Greenland, suggesting an energy release equivalent to 2 to 3 kt of TNT. This is more than what would have been expected from a metre-sized impactor, and pointed to a likely larger diameter of 3 to 4 metres. The discrepancy is likely the result of the measurement uncertainties in both the optical observations and the infrasound detections.

Predicted impact point and time computed by ESA’s imminent impactor alert system “Meerkat” at 20:25 UTC, with the initial 14 observations. The impact location was later refined with more observations, and proved correct. Credit: ESA / PDO

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Asteroid 2022 EB5 detected by the Kleť Observatory at 21:10 UTC, less than 13 minutes before it impacted the Earth. Credit: Kleť Observatory

Asteroid 2023 TB2 recently provided us with an interesting example of how important it is to have access to optimal telescope resources when presented with the threat of some specific asteroid.

This asteroid was discovered by the Catalina Sky Survey's Mt. Lemmon station on 3 October 2023, as a fairly typical magnitude 21 NEO candidate. It is a moderately large asteroid, estimated to be between 50 and 100 metres in diameter, and its orbit brings it close to the Earth every few years.

Within a few days, an initial orbit determination by ESA's impact monitoring system showed that future collisions with this asteroid were possible, every few years starting in 2083. In total, this asteroid would have about a 1 in 6000 chance of hitting our planet over the subsequent four decades.

The object was then bright and easy to observe, and observations kept coming in, leading to almost daily orbit updates. By 9 October, the overall impact probability had risen to 1 in 1400, and for the first time the asteroid reached level 1 on the so-called "Torino Scale", bringing it to the attention of the community of NEO observers.

With new observations over the next 3 weeks, the estimated impact probability changed a bit, but by the end of October it was still roughly 1 chance in 2100. There was a problem though: the object was now moving away from the Earth, and at the same time it was getting closer to the position of the Sun in the sky. This meant that it was getting much fainter (almost magnitude 24), but also much more challenging to observe from the ground (with an elongation of 60°), because objects close to the Sun are only above the horizon at nighttime for a short time window each night.

In order to get additional data, we needed a telescope capable of detecting a magnitude 24 asteroid in just a few minutes of observing time. In addition, the object's northern declination required a telescope in the Northern hemisphere, thus precluding the use of ESO's VLT as we typically do for these faint targets.

Fortunately, there's a telescope that is just perfect for this observation: Spain's 10.4-m Gran Telescopio Canarias (GTC), the largest single-aperture optical telescope on the planet. Thanks to our collaboration with Javier Licandro and Julia de León, researchers at the Instituto de Astrofísica de Canarias, who have granted time at the GTC, we had access to this great facility.

On the evening of 3 November 2023, GTC observed 2023 TB2 for about half an hour. In the resulting dataset, the asteroid was extremely well detected, allowing us to extract very accurate astrometric measurements of its position. When included in the orbit computation process, these measurements single-handedly improved our knowledge of the object's orbit by almost a factor of four, and allowed us to revise our estimates of the future impact probability, which dropped from 1 in 2100 to just 1 in 40 000.

Furthermore, thanks to the GTC observation, we now know the future trajectory of this asteroid well enough to easily re-observe it the next time it becomes visible, in 2025. We expect that additional observations taken at that time will likely fully clarify whether the small remaining impact threat remains or not, still half a century before a possible impact date and with plenty of time to organise a DART-like mission, in the unlikely chance the threat becomes significant.

Caption: Trajectory of 2023 TB2 projected over the Ecliptic plane and in a rotating reference frame that follows the Earth in its motion around the Sun. The asteroid is located in the position where it was observed by the GTC, which also corresponds to a position in the Northern side of the Ecliptic. N.B.: the Earth, Sun and asteroid sizes are not to scale, while the orbits are. Credits: ESA / PDO.

The Orbit Determination and Impact Monitoring system of the ESA NEO Coordination Centre, also known as Aegis, underwent a big update about one year ago. Since then, the Risk Assessment team at the NEOCC has been working to develop new automated services to make available to users.

One of the most important upgrades introduced in the system is an automated algorithm to identify NEOs whose dynamics are affected by the Yarkovsky effect. This effect is a non-gravitational force typically noticeable on small asteroids. This tiny force is caused by sunlight, which is absorbed by the asteroid surface and then re-emitted away as heat, causing a small but continuous thrust that subtly perturbs the orbit of small celestial bodies. This effect, which is inversely proportional to the object size (see figure), causes the semi-major axis of an NEA to drift, leading to significant positional uncertainties over time.

Understanding the Yarkovsky effect is important for several reasons: for accurate orbital predictions and reliable impact hazard assessment of NEAs, to get insights about the physical composition of asteroids, and to better understand the formation of asteroid families.

With the new algorithm we introduced, data about the Yarkovsky effect on NEAs will be updated after every monthly release of the Minor Planet Center, ensuring a continuous availability of the most recent data to users through our portal. A complete description of the procedure can be found in the corresponding paper published in Astronomy & Astrophysics. Up to now, our portal shows more than 340 positive detections of the Yarkovsky effect. This number is expected to grow in the next years with the beginning of the operational phase of new high-technology observational surveys, such as the Vera Rubin Observatory and the ESA Flyeye Telescope.

Caption: Diameter vs. Yarkovsky semi-major axis drift for all the detections with signal-to-noise ratio larger than 3. Black and green dots are NEAs for which the detection is accepted. Black dots are those objects for which the diameter is known, while green dots are those for which the diameter is only estimated by the physical model. Red dots are detections that are considered spurious by the algorithm, thus discarded. The blue dashed line is a linear fit of the data, which is completely compatible with the predicted 1/D trend with the diameter. Credits: ESA / PDO.

Krisztián Sárneczky has repeated himself for the third time, finding another small imminent impactor just before its impact with Earth in Europe.

The story began on Saturday, 20 January, at 21:48 UTC, the time of the first discovery image obtained from the Piszkéstető Observatory. Less than 30 minutes later, collecting more images and detecting the asteroid, the first set of astrometric positions was received by the Minor Planet Center and posted on the NEO Confirmation Page with the temporary designation Sar2736.

With just 3 positions, it was nearly impossible to know that the object was on a collision course with our planet. However, just 20 minutes later, the discoverers reported 4 more positions, and that's when the impact monitoring systems, including our own Meerkat, produced its first impact alert. It already gave an impact probability of 100% for the object, with an impact location placed somewhere between Germany and Sweden.

The discoverers continued reporting astrometry, and was soon joined by other European observers. Within minutes, the impact event circumstances became clear: this small metre-sized asteroid was going to impact Earth less than two hours later, roughly 50 km west of Berlin, Germany.

Over the next couple of hours more than a dozen observatories in mainland Europe, and our team from Tenerife, were able to obtain follow-up observations, until the latest possible instant: at 00:25 UTC the asteroid entered the shadow of the Earth and disappeared from view, while still under the watch of the Schiaparelli Observatory in Italy (see image).

Less than 8 minutes later, it became visible again as a bright fireball, observed by dozens of people all across central Europe. Some of them had been alerted through social media posts triggered by our imminent impactor systems, closing the loop from NEO discovery to fireball event. And all over a period of less than two hours, from first alert to impact, a success story for both the NEO and the fireball communities.

The asteroid was designated as 2024 BX1 by the Minor Planet Center, just after its impact. Congratulations to Krisztián, the Piszkéstető Observatory and all involved for this impressive third success in less than 2 years, a truly remarkable achievement.

Caption: The last detection of 2024 BX1 (then known as Sar2736) obtained by Luca Buzzi from the Schiaparelli Observatory in Italy (MPC code 204). The exposure was started at 00:24:55 UTC. The asteroid is moving from the bottom to the top of the image (heading North), and it is visible as a fading trail, due to its entrance into Earth’s shadow over the following 10 seconds. Credits: L. Buzzi, G. V. Schiaparelli Observatory.

It is well known that the asteroid (99942) Apophis will have a very close approach with the Earth on 13 April 2029. The object will pass at a distance less than that at which the geostationary satellites orbit the Earth and will be visible to the naked eye from some parts of the world. Such a close approach by an object the size of Apophis typically occurs only once every 10 000 years.

To take advantage of this opportunity, ESA, NASA and other space agencies are planning dedicated space missions, or have extended other missions (as in the case of OSIRIS-REx, which is now called OSIRIS-APEX), to reach Apophis around this epoch.

While the case of Apophis in 2029 is certainly very noteworthy, it is also interesting to realise that in the period between mid of 2027 and the end of 2029 there will be several large NEAs that will have close approaches with the Earth (see figure below). In fact, during this 2-year period, the following five large known NEAs (in addition to Apophis) will pass within four lunar distances (LD) of Earth:

• (153814) 2001 WN5, with a diameter of 930 m and passing at 0.65 LD on 26 June 2028,
• (137108) 1999 AN10, with an estimated diameter of 800 m and passing at 1.01 LD on 7 August 2027,
• (35396) 1997 XF11, with a diameter of 700 m and passing at 2.42 LD on 26 October 2028,
• (292220) 2006 SU49, with an estimated diameter of 400 m and passing at 3.19 LD on 28 January 2029, and
• 2023 GQ2, with an estimated diameter of 400 m and passing at 3.95 LD on 16 November 2028.

If a rendezvous mission to one of these bodies were planned, the delta-V requirements for such a mission would be between 5 km/s and 15 km/s. For asteroid missions after Apophis, the situation is not exactly the same as in the 2-year interval mentioned, but there are still feasible candidates. These can be seen in the figure below, where the following medium to large objects will have approaches to Earth of less than 5 LD by 2040:

• 2002 NY40, with a diameter of 280 m and passing at 2.8 LD on 11 February 2038,
• 2021 TG4, with an estimated diameter of 400 m and passing at 2.9 LD on 4 May 2034,
• (536531) 2015 DV215, with an estimated diameter of 290 m and passing at 2.9 LD on 6 October 2035,
• (613403) 2006 GB, with an estimated diameter of 300 m and passing at 4.1 LD on 22 March 2037,
• 2021 PC7, with an estimated diameter of 500 m and passing at 4.2 LD on 16 September 2033,
• (216985) 2000 QK130, with an estimated diameter of 200 m and passing at 4.4 LD on 15 March 2036,
• (369057) 2008 DK5, with an estimated diameter of 200 m and passing at 4.5 LD on 28 February 2039,
• (549948) 2011 WL2, with an estimated diameter of 250 m and passing at 4.7 LD on 21 April 2038,
• 2019 OQ2, with an estimated diameter of 300 m and passing at 4.8 LD on 04 April 2039.

Therefore, alternative mission options could be flown to the above objects, which could also be filtered in terms of the delta-V required to reach them, and also in terms of their taxonomy and other properties.

Caption: Close approaches of known large NEAs by 2040 and the approximate delta-V required for a rendezvous mission. Plot based on an idea by Dotson et al. 2022. Credits: ESA / PDO

ESA’s NEO Coordination Centre turned 10 years old this 22 of May. The Centre was inaugurated back in 2013 inside ESA’s ESRIN establishment close to Rome (Italy). It was a lucky coincidence that the Centre was opened just a few months after the most relevant asteroid impact event of the last hundred years, i.e. the Chelyabinsk event over Russia, which has fostered a surge on Planetary Defence activities ever since. The then ESA’s Space Situational Awareness Programme (since 2020 renamed as the Space Safety Programme) had been active since 2009 and had paved the way to the creation of the NEOCC.

At the time the NEOCC was inaugurated, slightly less than 10 000 NEOs had already been discovered. In just 10 years, that number has multiplied by more than three: during that period there have been twice as many discoveries as in the previous 100 years!

Since the start of operations of ESA’s NEOCC, the capabilities of the centre have steadily improved and expanded, starting from an initial federation of already existing services, and evolving into a fully independent operational system. A summary of some relevant achievements reached in these 10 years follows:

• May 2013: inauguration of the NEOCC at ESRIN, including the federation of several European NEO services (e.g. NEODyS data, EARN data, NEO chronology, NEO priority list, etc)
• April 2015: ESA and the NEOCC host the 4th Planetary Defense Conference at ESRIN
• Mid-2015: inauguration of the Test-Bed Telescope #1 in Cebreros (Spain)
• Nov 2018: incorporation into the NEOCC of full orbit determination capabilities
• Nov 2020: incorporation into the NEOCC of full impact monitoring capabilities
• March 2021: release of a new version of the NEOCC web portal
• April 2021: inauguration of the Test-Bed Telescope #2 in La Silla (Chile)
• Oct 2021: inauguration of the new NEOCC building at ESRIN
• Sep 2022: release of the NEO Toolkit in the NEOCC web portal

A recording of the inauguration session and the 2013 talks is available in this link.

To celebrate the event, the NEOCC staff visited the Specola Vaticana in Castel Gandolfo (in the Roman outskirts) and its meteorite collection. We are very grateful for the kind visit to the premises provided by Br. Robert Macke.

NEOCC staff at the Specola Vaticana. Credit: ESA / PDO / Vatican Observatory

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ESA's Optical Ground Station (OGS) is 2400 m above sea level on the volcanic island of Tenerife.