arXiv subjects

Birgit Loibnegger

Publications and source records attributed to Birgit Loibnegger.

8 recordsLinked to original sources

arXiv2020

Theoretical Studies of Comets in the 55 Cancri System

We present orbital integrations for various Jupiter family comets (JFCs) in the 55 Cancri system. This star is known to possess (at least) five planets with masses ranging from super-Earth to Jupiter-type. Furthermore, according to observational constraints, there is a space without planets between ~0.8 au and ~5.7 au, offering the principal possibility of habitable terrestrial planets, including long-term orbital stability. Hence, there is a stark motivation for the study of comets in the 55 Cnc system noting that comets are viewed a viable candidate mechanism for the delivery of water to Earth-type planets located in stellar habitable zones. However, our study shows that the duration of stability of JFC analogs in the 55 Cnc system is much shorter compared to comets in the Solar System owing to profound differences in the planetary structure of the systems. For example, between planet 55 Cnc-f and 55~Cnc-d, the comets do not undergo close cometary encounters akin to Earth and Mars in the Solar System as the planetary masses in the 55 Cnc system are much larger than in the Solar System and therefore the comets are much less orbitally stable. Nevertheless, we expect an increased number of comet-planet encounters as well as cometary collisions in the 0.8 / 5.7 au gap. Future observations and additional theoretical studies are required to shed light on the possibility of habitable terrestrial planets in the 55 Cnc system, including the possible role(s) of exocomets in the facilitation of planetary habitability.

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arXiv2019

On the Dynamics of Comets in Extrasolar Planetary Systems

Since very recently, we acquired knowledge on the existence of comets in extrasolar planetary systems. The formation of comets together with planets around host stars now seems evident. As stars are often born in clusters of interstellar clouds, the interaction between the systems will lead to the exchange of material at the edge of the clouds. Therefore, almost every planetary system should have leftover remnants as a result of planetary formation in form of comets at the edges of those systems. These Oort clouds around stars are often disturbed by different processes (e.g., galactic tides, passing stars, etc.), which consequently scatter bodies from the distant clouds into the system close to the host star. Regarding the Solar System, we observe this outcome in the form of cometary families. This knowledge supports the assumption of the existence of comets around other stars. In the present work, we study the orbital dynamics of hypothetical exocomets, based on detailed computer simulations, in three star-planet systems, which are: HD~10180, 47~UMa, and HD~141399. These systems host one or more Jupiter-like planets, which change the orbits of the incoming comets in characteristic ways.

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arXiv2018

Stability of a rotating asteroid housing a space station

Today there are numerous studies on asteroid mining. They elaborate on selecting the right objects, prospecting missions, potential asteroid redirection, and the mining process itself. For economic reasons, most studies focus on mining candidates in the 100-500m size-range. Also, suggestions regarding the design and implementation of space stations or even colonies inside the caverns of mined asteroids exist. Caverns provide the advantages of confined material in near-zero gravity during mining and later the hull will shield the inside from radiation. Existing studies focus on creating the necessary artificial gravity by rotating structures that are built inside the asteroid. Here, we assume the entire mined asteroid to rotate at a sufficient rate for artificial gravity and investigate its use for housing a habitat inside. In this study we present how to estimate the necessary spin rate assuming a cylindrical space station inside a mined asteroid and discuss the implications arising from substantial material stress given the required rotation rate. We estimate the required material strength using two relatively simple analytical models and apply them to fictitious, yet realistic rocky near-Earth asteroids.

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arXiv2018

Exocomets in the 47 UMa System: Theoretical Simulations including Water Transport

Motivated by ongoing discoveries of features (most likely) attributable to exocomets in various systems, this study examines the dynamics of possible comets around 47 UMa. Based on the assumption that most systems hosting planets should also harbor leftovers from planet formation processes, comets are thus also expected to exist in the system of 47 UMa. This system is known to host three Jupiter-type planets; however, based on stability analyses, additional terrestrial planets in stable orbits might also be able to exist, including planets in 47 UMa's habitable zone. Furthermore, we also consider a possible 'Hilda'-planet. The aim of our study is to explore the interaction of exocomets with the Jupiter-type planets in the system and examine the probability of cometary collisions with the planets, including possible Earth-mass planets located in the habitable zone. Moreover, we investigate the transport of water onto the Earth-mass planets, including quantitative estimates. It is found that the Earth-mass planets would be able to receive some water, but much less than currently present on Earth. We also checked if the comets form families, but no families were found. Finally, the capture of comets in close orbits and the possibility of small clouds formed when comets come too close to the star and disintegrate are also part of our work.

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arXiv2017

Exocomets in the Proxima Centauri system and their importance for water transport

The scenario and efficiency of water transport by icy asteroids and comets are still amongst the most important unresolved questions of planetary systems. A better understanding of cometary dynamics in extrasolar systems shall provide information about cometary reservoirs and give an insight into water transport especially to planets in the habitable zone. The detection of Proxima Centauri-b (PCb), which moves in the habitable zone of this system, triggered a debate whether or not this planet can be habitable. In this work, we focus on the stability of an additional planet in the system and on water transport by minor bodies. We perform numerous N-body simulations with PCb and an outer Oort-cloud like reservoir of comets. We investigate close encounters and collisions with the planet, which are important for the transport of water. Observers found hints for a second planet with a period longer than 60 days. Our dynamical studies show that two planets in this system are stable even for a more massive second planet (~12 Earth masses). Furthermore, we perform simulations including exocomets, a second planet, and the influence of the binary Alpha Centauri. The studies on the dynamics of exocomets reveal that the outer limit for water transport is around 200 au. In addition we show that water transport would be possible from a close-in planetesimal cloud (1-4 au). From our simulations, based on typical M-star protoplanetary disks, we estimate the water mass delivered to the planets up to 51 Earth oceans.

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arXiv2017

Case Studies of Exocomets in the System of HD 10180

The aim of our study is to investigate the dynamics of possible comets in the HD 10180 system. This investigation is motivated by the discovery of exocomets in various systems, especially $\beta$ Pictoris, as well as in at least ten other systems. Detailed theoretical studies about the formation and evolution of star--planet systems indicate that exocomets should be quite common. Further observational results are expected in the foreseeable future, in part due to the availability of the Large Synoptic Survey Telescope. Nonetheless, the Solar System represents the best studied example for comets, thus serving as a prime motivation for investigating comets in HD 10180 as well. HD 10180 is strikingly similar to the Sun. This system contains six confirmed planets and (at least) two additional planets subject to final verification. In our studies, we consider comets of different inclinations and eccentricities and find an array of different outcomes such as encounters with planets, captures, and escapes. Comets with relatively large eccentricities are able to enter the inner region of the system facing early planetary encounters. Stable comets experience long-term evolution of orbital elements, as expected. We also tried to distinguish cometary families akin to our Solar System but no clear distinction between possible families was found. Generally, theoretical and observational studies of exoplanets have a large range of ramifications, involving the origin, structure and evolution of systems as well as the proliferation of water and prebiotic compounds to terrestrial planets, which will increase their chances of being habitable.

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arXiv2017

Dynamics of passing-stars-perturbed binary star systems

In this work, we investigate the dynamical effects of a sequence of close encounters over 200 Myr varying in the interval of 10000 -- 100000 au between a binary star system and passing stars with masses ranging from 0.1$M_{\odot}$ to 10$M_{\odot}$. We focus on binaries consisting of two Sun-like stars with various orbital separations $a_{\scriptscriptstyle 0}$ from 50 au to 200 au initially on circular-planar orbits. We treat the problem statistically since each sequence is cloned 1000 times. Our study shows that orbits of binaries initially at $a_{\scriptscriptstyle 0}$ = 50 au will slightly be perturbed by each close encounter and exhibit a small deviation in eccentricity (+0.03) and in periapsis distance (+1 and -2 au) around the mean value. However increasing $a_{\scriptscriptstyle 0}$ will drastically increase these variances: up to +0.45 in eccentricity and between +63 au and -106 au in periapsis, leading to a higher rate of disrupted binaries up to 50% after the sequence of close encounters. Even though the secondary star can remain bound to the primary, $\sim$20% of the final orbits will have inclinations greater than 10$^{\circ}$. As planetary formation already takes place when stars are still members of their birth cluster, we show that the variances in eccentricity and periapsis distance of Jupiter- and Saturn-like planets will inversely decrease with $a_{\scriptscriptstyle 0}$ after successive fly-bys. This leads to higher ejection rate at $a_{\scriptscriptstyle 0}$ = 50 au but to a higher extent for Saturn-likes (60%) as those planets' apoapsis distances cross the critical stability distance for such binary separation.

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arXiv2015

On the probability of the collision of a Mars-sized planet with the Earth to form the Moon

The problem of the formation of the Moon is still not explained satisfactorily. While it is a generally accepted scenario that the last giant impact on Earth between some 50 to 100 million years after the starting of the formation of the terrestrial planets formed our natural satellite, there are still many open questions like the isotopic composition which is identical for these two bodies. In our investigation we will not deal with these problems of chemical composition but rather undertake a purely dynamical study to find out the probability of a Mars-sized body to collide with the Earth shortly after the formation of the Earth-like planets. For that we assume an additional massive body between Venus and Earth, respectively Earth and Mars which formed there at the same time as the other terrestrial planets. We have undertaken massive n-body integrations of such a planetary system with 4 inner planets (we excluded Mercury but assumed one additional body as mentioned before) for up to tens of millions of years. Our results led to a statistical estimation of the collision velocities as well as the collision angles which will then serve as the basis of further investigation with detailed SPH computations. We find a most probable origin of the Earth impactor at a semi-major axis of approx. 1.16 AU.

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