We all remember the extraordinary success of the Rosetta mission and its Philae module with the comet 67P/Churioumov-Guérassimenko. But do we remember that its discoverers, Klim Ivanovitch Tchourioumov and Svetlana Ivanovna Guérassimenko, are of Ukrainian and that they observed thestar on photographic plates in 1969 while working at Kyiv University Astronomical Observatory ?
Today it is several of their colleagues and compatriots stationed at the Main Astronomical Observatory of the National Academy of Sciences of Ukraine (Main Astronomical Observatory of Academy of Science of Ukraine), also in Kyiv, who have just confirmed the existence of exocomets around the famous star Beta Pictoris by discovering five more stars of this type performing transits.
This sequence begins with a wide view of the southern sky and ends with the bright star Beta Pictoris in the constellation of Pictor (the artist’s easel). This young star is surrounded by a dusty disk with a large planet in orbit around it, which is the first exoplanet whose own rotation speed has been measured. It has an equatorial rotation speed of nearly 100,000 kilometers per hour, much faster than any of the planets in the Solar System. © ESO, Digitized Sky Survey 2, Nick Risinger (skysurvey.org), L. Calçada. Music: movetwo
Beta Pictoris, a laboratory for understanding the formation of the Solar System
It is indeed not the first time that exocomets have been discovered around Beta Pictoris, as Futura had explained on several occasions and in particular in the previous article below, also exposing some of the characteristics of this star. mythical studied for decades to understand young stars and planetary cosmogony.
The theory of stellar structure and evolution tells us that Beta Pictoris, with its mass 1.8 times that of Sun and located about 63 light years of the Earth, would be only about twenty million years old. This type star AT 5 so close is therefore a target of choice for astronomers who have been observing it for some time with the Transiting Exoplanet Survey Satellite (Tess).
Ukrainian astronomers were already aware of the detection of three transits that could be interpreted as those of exocomets, the discovery of which was announced in 2019 and already with Tess, and they had set themselves the task of finding some others by analyzing the data already collected by Tess which is available in the Mikulski Archive for Space Telescopes (MAST).
The orbital distances of the five newly discovered transiting exocomets are between 0.5 and 1.5 AUas the researchers explain in an article published in Astronomy & Astrophysicsfreely available at arXiv.
An artist’s impression of the exocomets around Beta Pictoris. © European Southern Observatory (ESO)
What you must remember
- The laws of physics suggest, and observations confirm, that the formation of planets must involve processes and stages that are broadly universal.
- We don’t yet understand them as well as we would like and it is for this reason that young stars with forming planets are studied.
- We see that these stars are surrounded not only by young exoplanets but also by young exocomets.
- This is the case around Beta Pictoris which therefore serves as a laboratory to understand the formation of the Solar System.
Three exocomets discovered around young star Beta Pictoris
Article of Laurent Sacco published on 01/06/2019
Over the past thirty years, indications and measurements have multiplied concerning the existence of a large number of exocomets in the debris disk of the very young star Beta Pictoris. These exocomets are becoming more and more perceptible using the transit method and this is the telescope Tess who has just achieved this great first with this star.
It has been almost 35 years since the star Beta Pictoris (β Pic) has been talked about in the field of the cosmogony of planetary systems. Indeed, in the mid-1980s, astronomers turned the barely available gaze infrared of the Iras satellite (Infrared Astronomical Satellite) to this very young white star, located at a distance of about 63 light-years from Solar system in the constellation austral of the Painter.
Iras revealed that around this sun present on the main sequence of the Hertzsprung-Russel diagram for approximately 23 million years, there existed a disc of debris strongly depleted in gas but still rich in dust to allow the formation ofexoplanetsas demonstrated by measurements taken at the start of the 21stand century. This debris disk contains dust resulting from the ongoing collisions between the embryos planetary or asteroids. It therefore gives us a view of what our solar system must have looked like more than 4.5 billion years ago.
With its proximity, it therefore constitutes an extraordinary window to understand the formation of the planets and since 1999, the astrophysicists French, Alain Lecavelier des Étangs, Alfred Vidal-Madjar and Roger Ferlet, had predicted that we would detect comets, exocomets therefore, in orbit around Beta Pictoris. This is indeed what happened. Hundreds have even been discovered using the famous harps spectrographfed with fiber from the foyer Cassegrain of the 3.6 meter telescopeESO, at the La Silla Observatory in Chile. The instrument is indeed famous for its detection of exoplanets by the radial velocity method.
Exocomets betrayed by their transits
Today, the existence ofexocomets around Beta Pictoris is confirmed by another method of detecting exoplanets, that of transits. It is the successor of the Kepler satellite, namely the Transiting Exoplanet Survey Satellite (in French, Satellite for the census of exoplanets in transit) which was used for this discovery. He is better known by his acronym TESS and was launched on April 18, 2018 by the Nasa.
It is an international team of astronomers from the universities of Innsbruck, Warwick and Leiden who have just made it known first via an open-access article on arXiv and by a press release from the University of Innsbruck, the first announcing the discovery of an exocomet, and the second explaining that it was finally three of these stars that were identified by the transit method and therefore by drops of the brightness in the Beta Pictoris light curve.
Tess has more powerful instruments than Kepler. However, we have just learned that analyzes of the archived data of Kepler had made it possible to identify exocomets, still by the transit method, in three other planetary systems. Tess should have done so far only inspecting the tip of an iceberg that the probe should reveal in more detail in the years to come.
It is expected that the number of exocomets will be all the lower as a star is old and it would be interesting to study how this decrease takes place over time because this would allow us to have keys to better understand the evolution of young planetary systems and therefore, ultimatelyto better understand what happened to the young solar system.
In the near future, it should even be possible to impose constraints on the composition of exocomets, according to the researchers.
Two types of exocomets around the young star Beta Pictoris
ESO article published on 26/10/2014
The Harps instrument, which equips the La Silla observatory in Chile, has made it possible to carry out the most complete census to date of comets orbiting the young star Beta Pictoris. A French team of astronomers, by carefully studying half a thousand of them, was able to discover that they belong to two distinct families.
Located about 63 light-years from the Sun, Beta Pictoris is a star only about twenty million years old, surrounded by a vast disc of matter. This is a very active young planetary system, whose gas and dust come from the evaporation of comets and collisions between asteroids.
Flavier Kiefer (IAP, CNRS, UPMC), lead author of this new study published in the October 23 issue of Naturesets the scene: “Beta Pictoris is a target of choice! The detailed observations of its exocomets provide us with keys to understanding the processes at work in this type of young planetary system.”.
For nearly 30 years, astronomers have observed subtle variations in intensity in the brightness of Beta Pictoriswhich they attributed to the passage of comets in front of the star. Comets are small bodies a few kilometers in diameter, rich in ice, which evaporate near their star, thus creating gigantic tails of gas and dust capable of partially absorbing the light which passes through them.
Nearly 500 exocomets and two families
To carry out the study of Beta Pictoris exocometsthe team analyzed more than a thousand observations made between 2003 and 2011 using the Harps instrument that equips the 3.6 m telescope of Eso, installed at the La Silla Observatory in Chile.
The researchers selected a sample of 493 distinct exocomets. Some of them were observed several times and for a few hours. A meticulous analysis made it possible to determine the speed as well as the size of the clouds gas. Some of the orbital properties of each of the exocomets, such as shape, trajectory and distance to the star, could also be deduced.
Such an analysis involving several hundredexocomets belonging to the same exoplanetary system is unique. It revealed the existence of two families: on the one hand, old exocomets whose orbits are controlled by the gravitational attraction of a massive planet and, on the other hand, exocomets probably resulting from the recent splitting of a or more larger objects. A distinction comparable to what is observed within our solar system.
The exocomets of the first family are characterized by a large diversity of orbits as well as low emissions gas and dust. This suggests that they have exhausted their ice reserves during their multiple passes near parent star Beta Pictoris.
The exocomets classified within the second family are much more active and describe similar orbits. This suggests their common origin: probably the splitting of a larger object whose debris now orbits near the star.
Flavien Kiefer concludes: “For the very first time, a statistical study has made it possible to determine the shape and orbit of a large number of exocomets. This work offers tremendous insight into the mechanisms at work in the Solar System shortly after its formation 4.6 billion years ago.”.
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