Large Program of Asteroids using VLT/SPHERE instruments

The Director of the Astronomical Institute of the Romanian Academy (AIRA), Dr. Mirel Bîrlan is part of the international team that used the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile, and imaged the largest objects in the asteroid belt, located between Mars and Jupiter.

Never before had such a large group of 42 asteroids been imaged so sharply. The observations reveal a wide range of peculiar shapes, from spherical to dog-bone, and are helping astronomers trace the origins of the asteroids in our Solar System.

The detailed images of these 42 objects are a leap forward in exploring asteroids, made possible thanks to ground-based telescopes, and contribute to answering the ultimate question of life, the Universe, and everything [1].

“Only three large main belt asteroids, Ceres, Vesta and Lutetia, have been imaged with a high level of detail so far, as they were visited by the space missions Dawn and Rosetta of NASA and the European Space Agency, respectively,” explains Pierre Vernazza, from the Laboratoire d’Astrophysique de Marseille in France, who led the asteroid study published today in Astronomy & Astrophysics.

The previously small number of detailed observations of asteroids meant that, until now, key characteristics such as their 3D shape or density had remained largely unknown.

”Between 2017 and 2019, Pierre Vernazza successfully and efficiently led an international team of which I was part and which aimed to fill this gap by conducting a thorough survey of the major bodies in the asteroid belt”, said Dr. Mirel Bîrlan, the Director of the Astronomical Institute of The Romanian Academy (AIRA).

Most of the 42 objects in their sample are larger than 100 km in size; in particular, the team imaged nearly all of the belt asteroids larger than 200 kilometres, 20 out of 23. The two biggest objects the team probed were Ceres and Vesta, which are around 940 and 520 kilometres in diameter, whereas the two smallest asteroids are Urania and Ausonia, each only about 90 kilometres.

By reconstructing the objects’ shapes, the team realised that the observed asteroids are mainly divided into two families. Some are almost perfectly spherical, such as Hygiea and Ceres, while others have a more peculiar, “elongated” shape, their undisputed queen being the asteroid Kleopatra.

By combining the asteroids’ shapes with information on their masses, the team found that the densities change significantly across the sample. The four least dense asteroids studied, including Lamberta and Sylvia, have densities of about 1.3 grams per cubic centimetre, approximately the density of coal. The highest, Psyche and Kalliope, have densities of 3.9 and 4.4 grammes per cubic centimetre, respectively, which is higher than the density of diamond (3.5 grammes per cubic centimetre).

This large difference in density suggests the asteroids’ composition varies significantly, supporting the theory that the celestial objects were formed in different areas of the Solar System and migrated to their current location.

These findings were made possible thanks to the sensitivity of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument mounted on ESO’s VLT.

Astronomers will be able to image even more asteroids in fine detail with ESO’s upcoming Extremely Large Telescope (ELT), currently under construction in Chile and set to start operations later this decade.

”The study of asteroids is a field where Romanian researchers contribute constantly and significantly. As an associate astronomer of the Astronomical Institute of the Romanian Academy and astronomer of the Paris Observatory, I encouraged and facilitated collaborations between researchers from Romania and France. We have two Romanian doctoral students and researchers with the title of doctor who study small bodies - comets, asteroids, meteoroids - in the Solar System, "said Mirel Bîrlan.

Among the recent results of Romanian researchers are observations of the potentially dangerous asteroid (99942) Apophis, made at the Astronomical Observatory in Cluj-Napoca, Feleacu station, observations of the asteroid Pallas, observations of the asteroid (6478) Gault.

"The Institute's strategy will continue to support research efforts in these directions. Our projects include studies of asteroids approaching dangerously close to Earth, the relationships between asteroids, comets and meteors, the interaction of interplanetary matter with Earth, studies of the dynamics of natural and artificial objects near Earth, "said AIRA Director Mirel Bîrlan.

Notes
[1] In The Hitchhiker's Guide to the Galaxy by Douglas Adams, the number 42 is the answer to the "Ultimate Question of Life, the Universe, and Everything." Today, 12 October 2021, is the 42nd anniversary of the publication of the book.

More information: This research was presented in a paper to appear in Astronomy & Astrophysics https://www.aanda.org/articles/aa/full_html/2021/10/aa41781-21/aa41781-21.html.
Original Press release colud be find at the address: http://rosa.ro/index.php/en/news-menu/stiri/5704-meet-some-of-the-42-biggest-asteroids-in-our-solar-system

Poster of 42 largest asteroids observed during the Large Program VLT/SPHERE (credit ESO public release)
Autumn equinox 2021 graphics

Autumn equinox 2021

By definition, the moment of autumn equinox in the Northern Hemisphere corresponds to the precise time when the apparent geocentric longitude of the Sun is equal to 180 degrees. But, a more common understanding of this phenomenon in our society is that it happens on a certain day of September when daytime equals the duration of nighttime. In 2021, the autumn equinox will arrive on Wednesday, 22nd of September, at 19 hours 21 minutes and 06.77 seconds UTC, respectively at 22 hours 21 minutes and 06.77 seconds (UTC+3h) which is the Current Local Time in Romania, as we use the Eastern European Summer Time (EEST). At the moment of the autumn equinox, in 2021, the geocentric latitude of the Sun equals -0.56″, the right ascension has a value of 11 hours 59 minutes and 59.985 seconds, while his declination is -0.52″. As we can see by looking at the values of geocentric latitude and right ascension, they are close to 0 and respectively to 12 hours. This is the reason why we use to say about the Sun during this moment of the autumn equinox that it is in a direction opposite to that of the vernal point. Scientifically, this statement is considered partially true and it can be generally accepted as the apparent diameter of the Sun is about 30 arcminutes. The autumn equinox in the Northern Hemisphere of the Earth corresponds to the spring equinox in the Southern Hemisphere. The calendar used nowadays in Romania is the Gregorian calendar. This time instrument was created in 1582 in order to adjust the calendar drift with respect to the succession of the seasons. Therefore, according to the Gregorian calendar, the dates of the autumn equinox will always be during 21-24 September. Actually, in most years, the autumn equinox will arrive on the 22nd or 23rd of September while the dates when this will occur on the 21st or on the 24th of September are less frequent. For example, in the year 2092, the autumn equinox will occur on the 21st of September for the first time since the creation of the Gregorian calendar. Similarly, in 1803 the autumn equinox took place on the 24th of September, for the first time since the creation of the Gregorian calendar. Image in full resolution is available here.

Solar image, AIRA - 01.09.2021

A chromospheric solar image with the active region AR12860, made at Bucharest Solar Observatory on 01.01.2021. This region has the greatest activity at the beginning of the 25th solar cycle, with an M4.7 class and several C1-C9 class eruptions. Instrumentation used: Zeiss refractor 110mm F/15, Halpha Baader Solar Spectrum 0.3A, 0.4X reducer, camera ASI290MM mono. Processed in AutoStakkert 3 and gimp. In this image different features of the solar activity in the chromosphere region can be seen: sun dark spots, plages (bright regions of very hot plasma), flares, filaments of cold plasma, fibriles, prominences, and spicules at the limb. Author: scientific researcher Octavian Blagoi. Annotated colorized image in full resolution available here.

Chromospheric solar image, Bucharest Astronomical Observatory
At the end of the tour, on the stairs of Bosianu House

A group from Nicolae Bălcescu Youth Cultural Center visited AIRA

Members of „Nicolae Bălcescu” Youth Cultural Center and a group of 18 students from several Bucharest high schools were welcomed today at the Astronomical Institute of the Romanian Academy. Their visit was joined by the B1 TV crew which made interviews and a news report. During the event, the AIRA team was represented by our Director, Dr. Mirel Bîrlan, and by historian Sorin Marin. The astronomy promoter Daniel Berteșteanu from Bucharest Astroclub, was also invited and took part in the event.

The participants had the chance to attend several science presentations as they observed the Sun through a refractory telescope using an H-alpha filter, astronomy lessons in the Planetarium Hall and didactic laboratory demonstrations with projector support and various specialized hardware and software.

All these were followed by a relaxing guided tour which included: the Ecuatorial Dome - where it is preserved the largest refractory telescope in Romania, the marvels of Meridian Hall, Bosianu House, Sun Dome, and Telescope Building. While walking towards Bosianu House, a neo-gothic architectural jewell, the students learned they were walking on the footsteps of Prince Alexander John Cuza, who was present in the same house before the 1859 Union, and who later became the first monarch of modern Romania. They have also been told about Constantin Bosianu, Doctor in Law at Sorbonne University in Paris and the owner of the house and its surrounding property for a few decades in the XIXthC., who dreamed with his mind, believed with his heart, and worked day after day for the unification of the Romanian Principalities Moldova and Walachia and the creation of modern Romania.

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