Astrophysicists from the Federal University of the Far East (FEFU) have joined the international research team to explain the difference in the observation results for comet 41P / Tuttle – Giacobini – Kresak.
The researchers believe that the data obtained by three independent teams are complementary and that its complex analysis allows to unravel the mystery of the chemical composition of the dust of comet 41P and other enigmas of the Universe. A related article appears in Astronomy and astrophysics.
The activity of comets is more complex than it seems, according to one of the research results. The chemical composition of a cometary coma (dusty gaseous environment of the nucleus) is capable of changing very quickly, literally during the day. This is because the Sun affects the nucleus of an approaching comet.
Researchers around the world are trying to obtain data on the chemical composition of comets through analyzes of the light refracted by its dust particles. However, the information on the color spectrum of comets differs each time, depending on the different observation times and the different phase angles (Earth-comet-Sun angle).
This research paper postulates that the controversial data sets obtained due to different sets of photometric filters and that the search areas (apertures) are stable.
“At least three groups of researchers who observed comet 41P in 2017 had different results. The color of the comet ranged from red to blue. We explained in detail why this happened, ”says Anton Kochergin,“ one of the study’s authors, a young scientist from FEFU. “Usually, the final color is normalized taking into account the different bandwidths of the photometric filters applied. However, in many studies the color of celestial bodies is interpreted independently of a particular set of photometric filters. We show that this is not valid for all cases. The reason why the color of the comet differs is exactly from the sets of different photometric filters. In addition, the choice of the size of the calculation area, i.e. the opening, is of great importance. This is a certain radius around the cometary coma on images from observatories, which scientists define as an area of research. After deciding on the aperture, they analyze only the signal inside that field.
The choice of aperture determines the processes and outcomes included in the analysis. For example, a gas from a diatomic carbon (C2) molecule: there are parent molecules (called CHON particles in the literature), which become a source of C2 during photodissociation. This dissociation occurs at a certain distance from the nucleus of the comet, which in turn depends on the distance of the comet from the Sun. With the correct aperture chosen, we can exclude most of the signals that C2 molecules give by focusing on analyzes of the dust component of the coma.
Dr Kochergin pointed out that the opposing data on the color of the comet, collected by different groups using different sets of photometric filters, only benefits researchers. It is impossible to give a thorough description of the color (the color is directly related to the chemical composition of the dust of a cometary coma), and the chemical composition after a single observation. It is necessary to observe and determine the characteristics of the dynamics. The more measurements, the more precise the conclusions.
“In practice, this allows us to probe the microphysical properties of cometary dust, and the processes take place in a cometary coma. With such information, we will illuminate the evolutionary processes of the solar system. Many scientific groups around the world are working in this fundamental field, ”explains Anton Kochergin.
Scientists were able to model the results of color measurements of comet 41P, receiving almost simultaneously through different photometric filters at different locations. Although the color blue was acquired in one case and the color red in the other, the researchers found that both results were consistent with the actual behavior of comet dust particles in a 41P coma. These results can be copied by simulating light scattering by dust particles of the mineral pyroxene. Pyroxene is a silicate material that is part of lunar soil and was also delivered by the asteroid Itokawa and discovered in comet 81P / Wild 2. Pyroxenes are part of cometary matter and are well studied in the laboratory.
Researchers need to cooperate more to observe celestial bodies from different places on Earth. The routine makes it possible to catch up with the studied object in the event of unfavorable weather conditions at the location of one of the observatories. It also provides additional data in the case of different sets of filters applied by different teams. In the observation calendar of international collaborators, all the comets and asteroids that their equipment is able to trace.
The current results became possible thanks to the collaboration of scientists from the Astronomical Observatory, Kyiv National Taras Shevchenko University, Humanitas College, Kyung Hee University (South Korea), Institute of Science (USA), Astronomical Institute of the Slovak Academy of Sciences, Main Astronomical Observatory of the National Academy of Sciences, School of Natural Sciences, Federal University of the Far East, Ussuriysk Observatory of the Institute of Applied Astronomy from the Russian Academy of Sciences.
Previously, FEFU astrophysicists teamed up with Russian and foreign colleagues to observe comet ATLAS, which disintegrated as it approached the Sun. They concluded that the carbon found in the comet’s nucleus would help determine the age of comets in the solar system.
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