59 research outputs found
Detectability of Earth-like Planets in Circumstellar Habitable Zones of Binary Star Systems with Sun-like Components
Given the considerable percentage of stars that are members of binaries or
stellar multiples in the Solar neighborhood, it is expected that many of these
binaries host planets, possibly even habitable ones. The discovery of a
terrestrial planet in the alpha Centauri system supports this notion. Due to
the potentially strong gravitational interaction that an Earth-like planet may
experience in such systems, classical approaches to determining habitable
zones, especially in close S-Type binary systems, can be rather inaccurate.
Recent progress in this field, however, allows to identify regions around the
star permitting permanent habitability. While the discovery of alpha Cen Bb has
shown that terrestrial planets can be detected in solar-type binary stars using
current observational facilities, it remains to be shown whether this is also
the case for Earth analogues in habitable zones. We provide analytical
expressions for the maximum and RMS values of radial velocity and astrometric
signals, as well as transit probabilities of terrestrial planets in such
systems, showing that the dynamical interaction of the second star with the
planet may indeed facilitate the planets detection. As an example, we discuss
the detectability of additional Earth-like planets in the averaged, extended,
and permanent habitable zones around both stars of the alpha Centauri system.Comment: accepted for publication in The Astrophysical Journa
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 to
10. We focus on binaries consisting of two Sun-like stars with
various orbital separations 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 = 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
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,
20% of the final orbits will have inclinations greater than 10.
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
after successive fly-bys. This leads to higher
ejection rate at = 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.Comment: Accepted for publication (MNRAS
An Analytic Method to determine Habitable Zones for S-Type Planetary Orbits in Binary Star Systems
With more and more extrasolar planets discovered in and around binary star
systems, questions concerning the determination of the classical Habitable Zone
arise. Do the radiative and gravitational perturbations of the second star
influence the extent of the Habitable Zone significantly, or is it sufficient
to consider the host-star only? In this article we investigate the implications
of stellar companions with different spectral types on the insolation a
terrestrial planet receives orbiting a Sun-like primary. We present time
independent analytical estimates and compare these to insolation statistics
gained via high precision numerical orbit calculations. Results suggest a
strong dependence of permanent habitability on the binary's eccentricity, as
well as a possible extension of Habitable Zones towards the secondary in close
binary systems.Comment: submitted to ApJ, status: accepte
Circumstellar Habitable Zones of Binary Star Systems in the Solar Neighborhood
Binary and multiple systems constitute more than half of the total stellar
population in the Solar neighborhood (Kiseleva-Eggleton and Eggleton 2001).
Their frequent occurrence as well as the fact that more than 70 (Schneider et
al. 2011) planets have already been discovered in such configurations - most
noteably the telluric companion of alpha Centauri B (Dumusque et al. 2012) -
make them interesting targets in the search for habitable worlds. Recent
studies (Eggl et al. 2012b, Forgan 2012) have shown, that despite the
variations in gravitational and radiative environment, there are indeed
circumstellar regions where planets can stay within habitable insolation limits
on secular dynamical timescales. In this article we provide habitable zones for
19 near S-Type binary systems from the Hipparchos and WDS catalogues with
semimajor axes between 1 and 100 AU. Hereby, we accounted for the combined
dynamical and radiative influence of the second star on the Earth-like planet.
Out of the 19 systems presented, 17 offer dynamically stable habitable zones
around at least one component. The 17 potentially habitable systems contain 5
F, 3 G, 7 K and 16 M class stars. As their proximity to the Solar System (d <
31 pc) makes the selected binary stars exquisite targets for observational
campaigns, we offer estimates on radial velocity, astrometric and transit
signatures produced by habitable Earth-like planets in eccentric circumstellar
orbits
Conditions of Dynamical Stability for the HD 160691 Planetary System
The orbits in the HD 160691 planetary system at first appeared highly
unstable, but using the MEGNO and FLI techniques of global dynamics analysis in
the orbital parameter space we have found a stabilizing mechanism that could be
the key to its existence. In order to be dynamically stable, the HD 160691
planetary system has to satisfy the following conditions: (1) a 2:1 mean motion
resonance, combined with (2) an apsidal secular resonance in (3) a
configuration where the two apsidal lines are
anti-aligned, and (4) specific conditions on the respective sizes of the
eccentricities (high eccentricity for the outer orbit is in particular the most
probable necessary condition). More generally, in this original orbital
topology, where the resonance variables and librate
about while librates about , the HD
160691 system and its mechanism have revealed aspects of the 2:1 orbital
resonances that have not been observed nor analyzed before. The present
topology combined with the 2:1 resonance is indeed more wide-ranging than the
particular case of the HD 160691 planetary system. It is a new theoretical
possibility suitable for a stable regime despite relatively small semi-major
axes with respect to the important masses in interactions.Comment: 21 pages, 8 figures, 1 table, accepted version to ApJ (31 Jul 2003
Water delivery in the early Solar System
As part of the national scientific network 'Pathways to Habitable Worlds' the delivery of water onto terrestrial planets is a key question since water is essential for the development of life as we know it. After summarizing the state of the art we show some first results of the transport of water in the early Solar System for scattered main belt objects. Hereby we investigate the questions whether planetesimals and planetesimal fragments which have gained considerable inclination due to the strong dynamical interactions in the main belt region around 2 AU can be efficient water transporting vessels. The Hungaria asteroid group is the best example that such scenarios are realistic. Assuming that the gas giants and the terrestrial planets are already formed, we monitor the collisions of scattered small bodies containing water (in the order of a few percent) with the terrestrial planets. Thus we are able to give a first estimate concerning the respective contribution of such bodies to the actual water content in the crust of the Earth
Origin and evolution of the atmospheres of early Venus, Earth and Mars
We review the origin and evolution of the atmospheres of Earth, Venus and Mars from the time when their accreting bodies were released from the protoplanetary disk a few million years after the origin of the Sun. If the accreting planetary cores reached masses â„0.5 MEarth before the gas in the disk disappeared, primordial atmospheres consisting mainly of H2 form around the young planetary body, contrary to late-stage planet formation, where terrestrial planets accrete material after the nebula phase of the disk. The differences between these two scenarios are explored by investigating non-radiogenic atmospheric noble gas isotope anomalies observed on the three terrestrial planets. The role of the young Sunâs more efficient EUV radiation and of the plasma environment into the escape of early atmospheres is also addressed. We discuss the catastrophic outgassing of volatiles and the formation and cooling of steam atmospheres after the solidification of magma oceans and we describe the geochemical evidence for additional delivery of volatile-rich chondritic materials during the main stages of terrestrial planet formation. The evolution scenario of early Earth is then compared with the atmospheric evolution of planets where no active plate tectonics emerged like on Venus and Mars. We look at the diversity between early Earth, Venus and Mars, which is found to be related to their differing geochemical, geodynamical and geophysical conditions, including plate tectonics, crust and mantle oxidation processes and their involvement in degassing processes of secondary N2 atmospheres. The buildup of atmospheric N2, O2, and the role of greenhouse gases such as CO2 and CH4 to counter the Faint Young Sun Paradox (FYSP), when the earliest life forms on Earth originated until the Great Oxidation Event â 2.3 Gyr ago, are addressed. This review concludes with a discussion on the implications of understanding Earthâs geophysical and related atmospheric evolution in relation to the discovery of potential habitable terrestrial exoplanets.PostprintPeer reviewe
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