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Physics and dynamics of planets and smal bodies in the Solar System

Questions related to the origin and evolution of the solar system are timeless themes. Today, in the context of fascinating discoveries of new extrasolar systems, these are different and more numerous. This happens, amongst others, because  we did not expect to discover bizarre planets, unlike either giant planets or terrestrial planets (for example such as Super-Earths), and often on orbits much closer to the parent star than Mercury.

We conduct multi-threaded research at the Centrum Badań Kosmicznych PAN (CBK PAN) related to studies of the Solar System and its planets and multiple types of minor objects (see also: Solar System Dynamics and Planetology Division).  A list of our research can be started from attempts to model the initial conditions necessary for the formation of our solar system, and as a result, receiving its currently existing populations as four giant planets, four terrestrial planets, main asteroid belt,  Kuiper belt, other transneptunian objects, short-period comets, long-period comets and the Oort Cloud. Other studies concern issues related to the dynamics and physics of real comet populations (short-period and long-period comets) or asteroids (for example the dynamics of NEOs – Near Earth Asteroids).  One of the most important line of our research is the analysis and interpretation of observations obtained from space missions such as Herschel (study of processes involving water in the cometary atmosphere, search for water in distant comets) and Rosetta (study of the surface, interior and atmosphere of comet 67P/Churyumov-Gerasimenko, including changes in the comet’s activity over several years of mission, conducted using various types of optical instruments, spectrometers in various wavelength ranges, mass spectrometers, radars or plasma instruments), or ExoMars (study of Mars surface focusing on the search for trace volatile substances and water) and BepiColombo (study of Mercury’s surface and its exosphere).

The Sun and its home star cluster

CBK PAN conducts dynamical and physical research of small bodies of the Solar System related to the early stages of evolution of the Solar System and populations of small bodies located in its various domains. Due to the recent steady increase in computational capabilities, these issues are attracting growing interest of scientists dealing not only with the formation of the Solar System, but more broadly the formation of planetary systems around stars similar to the Sun.  At CBK PAN, we have started work on analyzing the basic issues related to planet formation, including the role of star clusters in shaping newborn planetary systems and their dynamical evolution. A natural way to understand this issue is to study our Solar System and think about what we can learn about the star cluster in which the Sun may have formed. We can then use our knowledge of our solar system as a starting point when comparing various systems of observed exoplanets that are of major interest to the future ARIEL mission.

Water in comets and water on the Earth

Water played an important role in the formation and evolution of planets and comets. Thus, the study of its isotopes is a source of information about the evolution of solar system bodies. In this context, we are particularly interested in the origin of Earth’s water and, in particular, its possible connections with small bodies of the Solar System. One intriguing question is how likely it is that comets or asteroids supplied some of the water to the Earth in the early moments of its formation. Such research was made possible, among others, by the instruments aboard the Herschel space telescope. It seems that the isotope composition of comet water within the same comet population may be varied, and models predicting that Jupiter Family comets formed at further distances from the Sun than the long-period comets associated with the Oort Cloud must be verified. Perhaps large-scale mixing of comets and asteroids during the migration of giant planets at the beginning of the solar system may have played a greater role in the past.

Water on Mars?

We also deal with the problem of the existence and origin of water on Mars, as it is likely that there was formerly abundant water on Mars. Analyzing the water balance on young Mars, scientists from CBK PAN, in international cooperation, came to the conclusion that most of the water was delivered to this planet probably via stray planetesimals during the time before the Earth’s Moon-forming impact.  A corresponding resurfacing event of smaller scale on Mars, also causing an important loss of early water, is the still hypothetical Borealis-forming impact. Moreover, it was shown that the km-sized comets that would have populated the exterior disk until the LHB (Late Heavy Bombardement era) would not survive against collisional destruction – a conclusion in apparent conflict with the pristine nature of comets. The resolution of this dilemma likely consists of a revision of the timing of the planetary rearrangement in the Nice Model, the commonly accepted scenario for planet migration.

Dynamics of comets and other small bodies

Since the beginning of our Institute, CBK PAN has been developing detailed research on comet dynamics, taking into account the subtle effects associated with non-gravitational perturbations in their orbital motion, that is the non-gravitational acceleration caused by spherically asymmetric emission of volatile substances and the escape of dust from their surfaces. During the comet orbital motion, the solar heating  varies due to  the changing distance of the comet from the Sun. Thus, the rate of ice sublimation is also changing. It should be noted here that water ice is a significant component of the comet nucleus. The models of non-gravitational acceleration we build, take into account the physical properties of the nucleus, which is the source of observed changes in cometary activity. In some of our models, we use not only astrometric observations, but also photometric data and measurements of the rate of production of volatile substances as a result of ice sublimation.

Dozens of short-period comets were included in this type of investigations, and in recent years about 300 long-period comets were also examined. The latter study will soon result in a unique cometary database, constructed in cooperation with the IAO UAM from Poznań. Such a database can contribute to understanding the discrepancies that have been suspected for many years between observations and numerical simulations of the Oort Cloud formation and the  dynamical evolution of  long-period comets.

Missions to planets, comets and other bodies of the Solar System

For several decades, CBK PAN has been involved in research carried out as part of missions to planets and small bodies of the Solar System. Today, the Rosetta and Herschel missions, mentioned above, are formally completed, although  analysis of the wealth of data provided by these missions is still underway, and CBK PAN researchers are also working on it.

Some examples of activities that we currently carry out in the area of space missions are research in PFS projects on the Mars Express mission, CaSSIS on the ExoMars mission; VIRTIS on the Venus Express mission, projects VIRTIS and OSIRIS on the Rosetta mission to comet 67P/Churyumov-Gerasimenko and activity in two projects (MERTIS and SYMBIO-SYS) in the recently launched BepiColombo mission to Mercury.

The results are fascinating. Interpretation of data provided by instruments and numerical modeling and laboratory observations allowed, for example, to search for the presence of water on Mars and detect methane in its atmosphere, determine the shape of comet 67P and the structure of its dust-ice surface, and analysis of intensive gas-dust streams ejected from its nucleus. We hope that the results of the current mission to the relatively unexplored planet Mercury will provide new discoveries and solve many puzzles, for examples regarding the dark and icy regions on this planet.

Extensive Mars research. Methane on Mars?

Currently, CBK PAN is involved in the ExoMars mission, under which we make attempts at

This last issue requires modelling the transport of trace gases in the Mars atmosphere. The European-Russian ExoMars Trace Gas Orbiter (TGO) has been in scientific orbit since 2018. The orbiter (CaSSIS instrument) furnishes data on the abundance of trace gases, as well as colour and stereo images of the surface that are useful in characterizing sources and sinks of certain atmospheric trace gases. One of the most interesting subjects of investigation is the appearance and disappearance of methane (CH4) on short timescales. In our institute, to analyze the data sent back by the probe we have developed a model of the photochemistry in the atmosphere of Mars. The model follows a few dozen molecules that are present or expected to exist in the atmosphere due to a few hundred considered chemical and photochemical reactions. The model takes into account the role of dust, ice clouds as well as the densities and fluxes of considered gases at the surface as a result of their transport from subsurface/surface sources. This model will help us to better understand the origin and evolution of trace gases, especially CH4.

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