In this image released April 25, 2011, taken atop Cerro Paranal, the 2,600-meter-high mountain in Chile’s Atacama Desert, home to the VLT, the atmospheric conditions are so exceptional that fleeting events such as the “green flash” of the setting Sun are seen relatively frequently. ESO Electronics Engineer Gerhard Hudeepohl captured an even rarer sight: a green flash from the Moon, instead of the Sun. (Reuters/ESO/G.Huedepohl)
** Synopsis: There is one year to go until asteroid 2015 TB145 approaches Earth once again, just as it did in 2015 around the night of Halloween, an occasion which astronomers did not pass up to study its characteristics. This dark object measures between 625 and 700 metres, its rotation period is around three hours and, in certain lighting conditions, it resembles a human skull. **
An asteroid zipped past on 31 October 2015, relatively close to us, just 486,000 km away, 1.3 times the distance separating us from the Moon. The object is called 2015 TB145 and was discovered a few days earlier – on 10 October – from Hawaii using the Pan-STARRS telescope, however, the fact that it came closest to our planet on Halloween also helped it become known as the Halloween asteroid.
Different teams of astronomers pointed their instruments towards 2015 TB145, including NASA, which captured it using the Green Bank (West Virginia, USA) and Arecibo (Puerto Rico) radio telescopes. In some of the images registered by the latter, the rotating asteroid was seen at times to resemble a human skull due to the lighting conditions at particular moments during its rotation.
European scientists, including the researcher Pablo Santos-Sanz from the Institute of Astrophysics of Andalusia (IAA-CSIC), also organised observing campaigns of the Halloween asteroid to discover its characteristics. The results have been published in the journal Astronomy & Astrophysics.
“It is an Apollo-type near-Earth asteroid (NEA),” Santos-Sanz explains to SINC. “The proximity of this small object meant greater brightness, so we decided to study it using various observation techniques: on the one hand, we used optical telescopes from the Sierra Nevada Observatory in Granada, the Calar Alto Observatory in Almería and the La Hita Observatory in Toledo; and on the other, we analysed it in the mid-infrared using the Very Large Telescope (VLT) VISIR instrument at the European Southern Observatory (ESO) in Cerro Paranal, Chile.”
“From the observations from Spain, we discovered that this object’s most likely rotation period is 2.94 hours, in other words, this is the approximate length of its day, although we cannot rule out another possibility: 4.78 hours, another solution which is consistent with our optical data,” the expert points out.
Thanks to the observations in the mid-infrared made from the VLT, the authors were able to detect the thermal emission of the object. Using this information and a thermophysical model, various properties of 2015 TB145 could be discerned.
Santos-Sanz mentions a few of these: “The object measures between 625 m and 700 m, its shape is a slightly flattened ellipsoid, and its rotation axis was roughly perpendicular to the Earth at the time of its closest proximity. Furthermore, its thermal inertia (the amount of heat which it retains and the speed at which it absorbs or transfers heat) is consistent with that of similar sized asteroids.”
The reflectivity or albedo of the surface of this asteroid is around 5 or 6%, which means that it reflects approximately 5 to 6% of sunlight. “This means that it is very dark, only slightly more reflective than charcoal,” the Spanish astrophysicist explains.
Researchers are confident of obtaining more data on 2015 TB145 the next time it approaches our planet, which will happen in November 2018, although this time it will zip past much further away than the last, at a distance 105 times the average lunar distance. “Although this approach shall not be so favourable, we will be able to obtain new data which could help improve our knowledge of this mass and other similar masses that come close to our planet,” Santos-Sanz says.
“It is currently 3.7 astronomical units away from Earth, that is 3.7 times the average distance from the Earth to the Sun,” he points out. “It has a magnitude of 26.5, which means it is only visible from Earth using very large telescopes or space telescopes.”
Thomas G. Müller, researcher from the Max-Planck-Institut für Extraterrestrische Physik (Germany) and co-author of the study, adds: “The next slightly more exciting encounter will be around Halloween’s day in the year 2088, when the object approaches Earth to a distance of about 20 lunar distances. The encounter on Halloween’s day 2015 was the closest approach of an object of that size since 2006, and the next known similar event is the passage of 137108 (1999 AN10) on August 7, 2027. Later, 99942 Apophis will follow on April 13, 2029, with an Earth passage at approximately 0.1 lunar distances.”
This study has received funding from the ‘Small Bodies: Near and Far’ (SBNAF) European project. “We formed a team of expert astronomers from Poland, Hungary, Spain, and Germany,” Müller explains. The goal of the project is to characterise small objects at various distances from the Sun, including near-Earth asteroids like the Halloween asteroid. 2015 TB145 was one of our first targets where we combined different observations, modeling techniques, and concepts for the scientific interpretation. It is going to be interesting to compare our results with future findings and to apply our techniques to many more potentially hazardous objects.”
Scientists think that the Halloween asteroid could in fact be an extinct comet which lost its volatile compounds after orbiting the Sun numerous times. In general, asteroids and comets are distinguished by their composition (the former being more rocky and metallic, while the latter have a higher proportion of ice and rock) and type of orbit around the Sun, but at times it is not easy to tell them apart. The boundaries between them are becoming increasingly diffuse. In any case, both were formed and witnessed the first stages of our solar system, which was born around 4,600 million years ago.
TOP IMAGE….This image of asteroid 2015 TB145 was generated using radar data collected by the National Science Foundation’s Arecibo Observatory in Puerto Rico. / NAIC-Arecibo/NSF
CENTRE IMAGE….Artist´s impression of the Halloween asteroid 2015 TB145, which resembles a human skull in certain light conditions. / J. A. Peñas/SINC
LOWER IMAGE….Orbit diagram of 2015 TB145 and current position. / JPL-NASA
There is one year to go until asteroid 2015 TB145 approaches Earth once again, just as it did in 2015 around the night of Halloween, an occasion which astronomers did not pass up to study its characteristics. This dark object measures between 625 and 700 metres, its rotation period is around three hours and, in certain lighting conditions, it resembles a human skull.
An asteroid zipped past on 31 October 2015, relatively close to us, just 486,000 km away, 1.3 times the distance separating us from the Moon. The object is called 2015 TB145 and was discovered a few days earlier -on 10 October- from Hawaii using the Pan-STARRS telescope, however, the fact that it came closest to our planet on Halloween also helped it become known as the Halloween asteroid.
Through the Years → Mary, Crown Princess of Denmark (333/∞)
12 March 2013 | The Crown Prince of Denmark, Frederick and his wife Mary Donaldson visit the residence of late Chilean poet Pablo Neruda in Isla Negra, Chile. Frederick and his wife will in Chile until March 15 and during that time they will visit the Cerro Paranal observatory among other places. (Photo credit CLAUDIO SANTANA/AFP/Getty Images)
En diciembre del año 2012, y gracias al telescopio VLT , se descubrió el quásar con la salida más energética que se había visto hasta ahora.
El telescopio VLT pertenece al Observatorio Europeo del Sur y está ubicado en el cerro Paranal, una montaña situada en el desierto de Atacama, al norte de Chile.
Esta potentísima salida energética se encuentra a unos mil años luz de un agujero negro súpermasivo, justo en el centro del quásar , que se mueve a una velocidad de 8.000 kilómetros por segundo. El tipo de energía que expulsa a alta velocidad es como mínimo equivalente a dos millones de millones de veces la potencia de salida del Sol. Más concretamente, es aproximadamente 100 veces mayor que la potencia total de la galaxia de la Vía Láctea.
First light for the Four Laser Guide Star Facility on ESO’s Very Large Telescope
On 26 April 2016 ESO’s Paranal Observatory in Chile hosted an event to mark the first light for the four powerful lasers that form a crucial part of the adaptive optics systems on ESO’s Very Large Telescope. Attendees were treated to a spectacular display of cutting-edge laser technology against the majestic skies of Paranal. These are the most powerful laser guide stars ever used for astronomy and the event marks the first use of multiple laser guide stars at ESO.
ESO staff were present for the event, along with senior representatives of the companies that have manufactured the different components of the new system.
The Four Laser Guide Star Facility (4LGSF) shines four 22-watt laser beams into the sky to create artificial guide stars by making sodium atoms in the upper atmosphere glow so that they look just like real stars . The artificial stars allow the adaptive optics systems to compensate for the blurring caused by the Earth’s atmosphere and so that the telescope can create sharp images. Using more than one laser allows the turbulence in the atmosphere to be mapped in far greater detail to significantly improve the image quality over a larger field of view.
The Four Laser Guide Star Facility is an example of how ESO enables European industry to lead complex research and development projects. The fibre laser used by the 4LGSF is also one of the most successful transfers of ESO technology to industry.
TOPTICA, the German main contractor, was responsible for the laser system and provided the oscillator, the frequency doubler, and the system control software. Wilhelm Kaenders, president of TOPTICA, said: “TOPTICA has enjoyed the collaboration with ESO tremendously. It is not only the personal thrill of being engaged with astronomy, an old passion, again, and working with very clever ESO technologists; it is also the inspiration that we have received for our own commercial product development.” 
MPBC of Canada provided the fibre laser pumps and Raman amplifiers, which are based on an ESO licensed patent. Jane Bachynski, President of MPB Communications Inc. said: “MPBC is proud to have worked with ESO in the development of Raman fibre amplifiers to much higher powers, allowing MPBC to bring this technology to the stars. This event marks the culmination of many years of hard work on behalf of all involved.” 
TNO in the Netherlands manufactured the optical tube assemblies, which expand the laser beams and direct them into the sky. Paul de Krom, CEO of TNO, said: “TNO valued the cooperative working environment during the development of the optical tube assemblies and looks forward to the opportunity to work with ESO and the other partners in the 4LGSF project in the future.” 
The 4LGSF is part of the Adaptive Optics Facility on Unit Telescope 4 of the VLT, designed specifically to provide the adaptive optics systems GALACSI/MUSE and GRAAL/HAWK-I with four sodium laser guide stars. With this new facility, Paranal Observatory continues to have the most advanced and the largest number of adaptive optics systems in operation today.
The 4LGSF lasers were developed by ESO with industry and have already been procured, among others, by the Keck Observatory (which contributed to the industrial laser development cost along with the European Commission) and the Subaru Telescope. In the future these industrial lasers will also feature on the telescopes at the Gemini Observatory and will be the preferred choice for several other observatories and extremely large telescope projects.
The new techniques developed for the Four Laser Guide Star Facility pave the way for the adaptive optics system of the European Extremely Large Telescope (E-ELT), the world’s biggest eye on the sky.
 The 4LGSF is the second generation laser guide star facility, built by ESO for the Adaptive Optics Facility on the UT4 VLT telescope. The two critical long-lead items for the 4LGSF, the laser system and the optical tube assemblies for the laser launch telescope systems have been procured from industry. The fibre Raman laser technology, on which the 4LGSF laser system is based, has been developed at ESO, patented and licensed to industry.
 This project has allowed TOPTICA to extend its products into a new wavelength and output power regime. It now produces the SodiumStar 20/2, which is recognised as a quasi-standard for existing and planned telescopes around the world. All next generation extremely large telescope projects, for example, use the SodiumStar laser as their baseline. During the seven years of collaboration with ESO the company has grown from 80 people to more than 200 today.
 MPBC’s collaboration with ESO has also generated an additional benefit, in the form of an offshoot product line of single frequency amplification products at virtually any wavelength, supporting novel applications for the scientific and commercial research community.
 The developments by TNO also involved contributions from many suppliers from the Netherlands (Vernooy, Vacutech, Rovasta, Schott Benelux, Maxon Motor Benelux, IPS technology, Sensordata and WestEnd) and other international companies (RMI, Qioptiq, Laser Components, Carl Zeiss, GLP, Faes, Farnell, Eriks and Pfeiffer). The knowledge and technologies advanced by working with ESO feed into TNO’s Dutch and European partners, in fields including astronomy, communications, semiconductor manufacturing, medical devices, space science and Earth observation.
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Through the Years → Mary, Crown Princess of Denmark (332/∞)
11 March 2013 | Crown Princess Mary of Denmark, attends a military ceremony in front of La Moneda Presidential palace in Santiago. Frederick and his wife will visit Chile until March 15, during which they will visit late Chilean poet Pablo Neruda’s residence and the Cerro Paranal observatory, among other places. (Photo credit CLAUDIO SANTANA / AFP / Getty Images)