Planets In Binaries Research Articles

Planet dispersal in binary systems during transient multiple star phases

Aims. If a significant fraction of binary star systems spent some time as inclined triple systems, either during their formation process or as the outcome of several close dynamical encounters in a crowded stellar environemnt, then the number of planets in binaries would be significantly lower than around single stars. The stellar chaotic phase preceding the instability of the triple system and the wide oscillations in eccentricity and inclination of the companion star due to the high mutual inclination between the companion and the singleton would quickly eject planets orbiting the binary in S-type orbits. Methods. We perform numerical simulations of the dynamical evolution of hierarchical triple star systems with planets hosted around the primary star of the inner binary. Different values of mutual inclination, binary separation and singleton initial semimajor axis are explored in a statistical way. Results. We find that a significant mutual inclination i m between the singleton and the binary is a key factor for instability of the planetary system. When i m is larger than ~$40^{\circ}$ the fraction of planets in the binary surviving the chaotic phase of the triple declines dramatically. The combination of eccentricity and inclination oscillations of the binary companion induced by the secular perturbations of the singleton and the sequence of close encounters preceding the ejection of one star fully destabilize a planetary system extending beyond 1 AU from the star. For i m around $90^{\circ}$ the percentage of surviving planets is lower than 20% for all binaries with a semimajor axis smaller than 200 AU. Conclusions. The frequency of planets in binaries with low separation may be strongly reduced by the residence of the pair in the past in a temporary inclined hierarchical triple.

The frequency of planets in multiple systems

Context. The frequency of planets in binaries is an important issue in the field of extrasolar planet studies, because of its relevance in estimating of the global planet population of our Galaxy and the clues it can give to our understanding of planet formation and evolution. However, only preliminary estimates are available in the literature. Aims. We analyze and compare the frequency of planets in multiple systems to the frequency of planets orbiting single stars. We also try to highlight possible connections between the frequency of planets and the orbital parameters of the binaries (such as the periastron and mass ratio.) Methods. A literature search was performed for binaries and multiple systems among the stars of the sample with uniform planet detectability defined by Fischer & Valenti (2005, ApJ, 622, 1102), and 202 of the 850 stars of the sample turned out to be binaries, allowing a statistical comparison of the frequency of planets in binaries and single stars and a study of the run of the planet frequency as a function of the binary separation.Results. We found that the global frequency of planets in the binaries of the sample is not statistically different from that of planets in single stars. Even conservatively taking the probable incompleteness of binary detection in our sample into account, we estimate that the frequency of planets in binaries can be no more than a factor of three lower than that of planets in single stars. There is no significant dependence of planet frequency on the binary separation, except for a lower value of frequency for close binaries. However, this is probably not as low as required to explain the presence of planets in close binaries only as the result of modifications of the binary orbit after the planet formation.

Habitable Planet Formation in Binary Planetary Systems

Recent radial velocity observations have indicated that Jovian-type planets can exist in moderately close binary star systems. Numerical simulations of the dynamical stability of terrestrial-class planets in such environments have shown that, in addition to their giant planets, these systems can also harbor Earth-like objects. In this paper, we study the late stage of terrestrial planet formation in such binary-planetary systems, and present the results of the simulations of the formation of Earth-like bodies in their habitable zones. We consider a circumprimary disk of Moon- to Mars-sized objects and numerically integrate the orbits of these bodies at the presence of the Jovian-type planet of the system and for different values of the mass, semimajor axis, and orbital eccentricity of the secondary star. Results indicate that, Earth-like objects, with substantial amounts of water, can form in the habitable zone of the primary star. Simulations also indicate that, by transferring angular momentum from the secondary star to protoplanetary objects, the giant planet of the system plays a key role in the radial mixing of these bodies and the water contents of the final terrestrial planets. We will discuss the results of our simulation and show that the formation of habitable planets in binary-planetary systems is more probable in binaries with moderate to large perihelia.

Detecting companions to extrasolar planets using mutual events

We investigate a new approach to the detection of companions to extrasolar planets beyond the transit method. We discuss the possibility of the existence of binary planets. We develop a method based on the imaging of a planet-companion as an unresolved system (but resolved from its parent star). It makes use of planet-companion mutual phenomena, namely mutual transits and mutual shadows. We show that companions can be detected and their radius measured down to lunar sizes.

Impact of Stellar Dynamics on the Frequency of Giant Planets in Close Binaries

Hostile tidal forces may inhibit the formation of Jovian planets in binaries with semimajor axes of ≾50 AU, binaries that might be called in this context. As an alternative to in situ planet formation, a binary can acquire a giant planet when one of its original members is replaced in a dynamical interaction with another star that hosts a planet. Simple scaling relations for the structure and evolution of star clusters, coupled with analytic arguments regarding binary-single and binary-binary scattering, indicate that dynamical processes can deposit Jovian planets in <1% of close binaries. If ongoing and future exoplanet surveys measure a much larger fraction, it may be that giant planets do somehow form frequently in such systems.

Detectability of Planets in Wide Binaries by Ground-Based Relative Astrometry with AO

AbstractMany planet candidates have been detected by radial-velocity variations of the primary star; they are planet candidates, because of the unknown orbit inclination. Detection of the wobble in the two other dimensions, to be measured by astrometry, would yield the inclination and, hence, true mass of the companions. We aim to show that planets can be confirmed or discovered in a close visual stellar binary system by measuring the astrometric wobble of the exoplanet host star as a periodic variation of the separation, even from the ground. We test the feasibility with HD 19994, a visual binary with one radial velocity planet candidate. We use the adaptive optics camera NACO at the VLT with its smallest pixel scale (∼ 13 mas) for high-precision astrometric measurements. The separations measured in 120 single images taken within one night are shown to follow white noise, so that the standard deviation can be divided by the square root of the number of images to obtain the precision. In this paper we present the first results and investigate the achievable precision in relative astrometry with adaptive optics. With careful data reduction it is possible to achieve a relative astrometric precision as low as 50 μ as for a 0″.6 binary with VLT/NACO observations in one hour, the best relative astrometric precision ever achieved with a single telescope from the ground. The relative astrometric precision demonstrated here with AO at an 8-m mirror is sufficient to detect the astrometric signal of the planet HD 19994 Ab as periodic variation of the separation between HD 19994 A and B.

Neptune's capture of its moon Triton in a binary–planet gravitational encounter

Triton is Neptune's principal satellite and is by far the largest retrograde satellite in the Solar System (its mass is approximately 40 per cent greater than that of Pluto). Its inclined and circular orbit lies between a group of small inner prograde satellites and a number of exterior irregular satellites with both prograde and retrograde orbits. This unusual configuration has led to the belief that Triton originally orbited the Sun before being captured in orbit around Neptune. Existing models for its capture, however, all have significant bottlenecks that make their effectiveness doubtful. Here we report that a three-body gravitational encounter between a binary system (of approximately 10(3)-kilometre-sized bodies) and Neptune is a far more likely explanation for Triton's capture. Our model predicts that Triton was once a member of a binary with a range of plausible characteristics, including ones similar to the Pluto-Charon pair.

Charon's size and an upper limit on its atmosphere from a stellar occultation

Pluto and its satellite, Charon (discovered in 1978; ref. 1), appear to form a double planet, rather than a hierarchical planet/satellite couple. Charon is about half Pluto's size and about one-eighth its mass. The precise radii of Pluto and Charon have remained uncertain, leading to large uncertainties on their densities. Although stellar occultations by Charon are in principle a powerful way of measuring its size, they are rare, as the satellite subtends less than 0.3 microradians (0.06 arcsec) on the sky. One occultation (in 1980) yielded a lower limit of 600 km for the satellite's radius, which was later refined to 601.5 km (ref. 4). Here we report observations from a multi-station stellar occultation by Charon, which we use to derive a radius, R(C) = 603.6 +/- 1.4 km (1sigma), and a density of rho = 1.71 +/- 0.08 g cm(-3). This occultation also provides upper limits of 110 and 15 (3sigma) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere.

A gravitational-tidal mechanism for the Earth’s polar oscillations

Perturbed, rotational-oscillational motions of the Earth induced by the gravitational torques exerted by the Sun and Moon are studied using a linear mechanical model for a viscoelastic rigid body. A tidal mechanism is identified for the excitation of polar oscillations, i.e., for oscillations of the angular-velocity vector specified in a fixed coordinate frame, attributed to the rotational-progressive motion of the barycenter of the Earth-Moon “binary planet” about the Sun. The main features of the oscillations remain stable and do not change considerably over time intervals significantly exceeding the precessional period of the Earth’s axis. A simple mathematical model containing two frequencies, namely, the Chandler and annual frequencies, is constructed using the methods of celestial mechanics. This model is adequate to the astrometric measurements performed by the International Earth Rotation Service (IERS). The parameters of the model are identified via least-squares fitting and a spectral analysis of the IERS data. Statistically valid interpolations of the data for time intervals covering from several months to 15–20 yr are obtained. High-accuracy forecasting of the polar motions for 0.5–1 yr and reasonably trustworthy forecasting for 1–3 yr demonstrated by observations over the last few years are presented for the first time. The results obtained are of theoretical interest for dynamical astronomy, geodynamics, and celestial mechanics, and are also important for astrometrical, navigational, and geophysical applications.

A Celestial Mechanics Model of Oscillations of the Poles of a Deformable Earth

The problem of Chandler motion of the Earth's poles is studied in the context of the model of a viscoelastic body. The Earth-Moon system is considered as a binary planet rotating around their barycenter. Numerical values of the period and amplitudes of oscillations of the poles are obtained by estimating the elastic deformation of the Earth and the variation of its inertia tensor, and they agree well with observational data. An evolution model of the Earth-Moon-Sun system is constructed by taking into account tidal forces of dissipation character. By means of the method of averaging, the qualitative properties of motion on asymptotically large intervals of time (comparable and essentially longer than the period of precession of the Earth's axis) are established and commented on.

Planets in Multiple-Star Systems: Properties and Detections

AbstractOrbital properties of extra-solar planets are briefly recalled and compared with equivalent features of stellar binaries. Similarities and differences are discussed. Among the more than 115 extra-solar planets discovered to date, 19 are orbiting a component of a binary system. We discuss the properties of this subsample and compare them with the equivalent characteristics of planets around single stars. Differences in the mass-period-eccentricity distributions are observed: exoplanets with m2 sin i &gt; 2 MJup and P≤ 40-100 days are in binaries and present low eccentricities. In the context of the migration scenario, these characteristics are tentatively explained in the light of recent simulations of planet-disk interactions showing an increased accretion and migration rates of planets in case an additional perturbing close stellar companion is present in the system. Finally, different observational approaches to find planets in long-period spectroscopic binaries aiming to improve the still poor available statistics are presented. An important result is the detection of a planetary companion in the HD 41004 triple system.

Timing Detection of Eclipsing Binary Planets and Transiting Extrasolar Moons

We investigate the improved detection of extrasolar planets around eclipsing binaries using eclipse minima timing and extrasolar moons around transiting planets using transit timing offered by the upcoming COROT (ESA, 2005), Kepler (NASA, 2007), and Eddington (ESA 2008) spacecraft missions. Hundreds of circum-binary planets should be discovered and a thorough survey of moons around transiting planets will be accomplished by these missions.

NASA plans Pluto‐Kuiper Belt Mission

The trans‐Neptunian region, which contains the binary planet Pluto‐Charon and the myriad planetary embryos of the Kuiper Belt, is a scientific and intellectual frontier. In recent years, the Pluto‐Charon system has become recognized as a key element for understanding the origin of the outer solar system. So, too, it has become apparent that Pluto‐Charon is a scientific wonderland offering insights into exotic dynamics, the nature of primitive organic material, complex volatile transport processes, and hydrodynamic atmospheric escape, as well as rich surface and atmospheric chemistry. Pluto's size, density albedo, surface composition, and atmosphere also make it a key comparator to Triton, Neptune's large and complex icy satellite.

Evolution of Motion of a Binary Planet

A model of a binary planet, consisting of a material point of small mass and a deformable viscoelastic sphere, is suggested. The center of mass of the binary planet moves in the gravitational field of a central body in the plane, which contains planets forming the binary planet. A deformable spherical planet rotates around the axis orthogonal to the plane of planetary motion. Planet deformations are described by the linear theory of viscoelasticity. It is shown that with an appropriate approximation of the gravitational potential, there is a class of quasicircular orbits, when the eccentricities of an orbit of the center of mass of a binary planet and an orbit, describing mutual planet motion, are equal to zero. The further evolution of motion is investigated in this class of orbits with the use of the canonical Poincare–Andoyer variables. Corresponding averaged equations are found, and phase pictures are constructed; the stability of stationary solutions is investigated on the basis of equations in variations. For the Solar system planets with their satellites, forming binary planets, the application of the presented model allows us to conclude that satellites sooner or later will fall on the corresponding planets.

Pluto and Charon: Ice Worlds on the Ragged Edge of the Solar System

New Frontier. First Facts. A Distant Dance. Another Snow. Building a Binary Planet. Icefields and Ice Dwarfs. Everest. Postscript: Where No One Has Gone Before. A Chronology of Major Events in the Exploration of Pluto. Suggested Readings. Index.

The Formation of Binary and Single Nuclei of Planetary Nebulae

We model the evolution of binary systems and explore the possibilities of formation of single and binary planetary nebula nuclei (PNNs). Under the assumption that all stars are born in binary systems, we obtain a Galactic rate of PNN formation of 0.87 yr -1 . The model suggests that about 20% of all PNNs are single, while 66% are CO white dwarfs accompanied by main-sequence stars. Our results are consistent with the observations of close binary PNNs. However, a direct comparison is difficult due to poor statistics and selection effects which bias the observed sample. We used the obtained results to place constraints on parameters of common envelope evolution

Formation and Evolution of Binary Planetary Nebula Nuclei and Related Objects

A study is made of the evolution of close binaries in which the primary first fills its Roche lobe after the exhaustion of helium at its center and before the onset of thermal pulses. Initial masses are in the range 3-6 M<SUB>0</SUB>. Also examined is the evolution of a 1 M<SUB>sun</SUB> model which fills its Roche lobe on the first giant branch when the mass of its helium degenerate core reaches 0.4 M<SUB>0</SUB>. In all cases, a common envelope scenario is assumed, and mass is removed from the model primary on a timescale shorter than the initial thermal timescale of the envelope of the primary until the model contracts within a final Roche lobe of predetermined size. After the removal of the common envelope, systems are very close binaries in which the evolved remnant has either a carbon-oxygen (CO) core and a helium-burning shell (progenitor of mass 2.3-8 M<SUB>sun</SUB>) or a helium core and a hydrogen-burning shell (progenitor of mass 1-2.3 M<SUB>sun</SUB>). The more massive remnants fill their Roche lobes for an extended period, transferring first hydrogen-rich material at a rate ∼10<SUP>-8±1</SUP> M<SUB>sun</SUB> yr<SUP>-1</SUP> for up to 10<SUP>6</SUP> yr, and then helium at a rate ∼10<SUP>-6±1</SUP> M<SUB>sun</SUB> yr<SUP>-1</SUP> for (1-4) × 10<SUP>5</SUP> yr. As much as ∼0.4 M<SUB>sun</SUB> of nearly pure helium can be transferred to an accretor. <P />A possible real analog of the hydrogen-transferring models is U Sco, although, in many instances, a hydrogen-transferring episode may be bypassed or considerably shortened if the hot remnant blows a strong enough wind. Possible observational analogs of helium transferring models are bright ultrasoft X-ray sources like CAL 83 and CAL 87 in the Large Magellanic Cloud and some classes of supernova precursors. Our models help to explain the number and properties of hot helium OB subdwarfs. <P />A method for estimating initial orbital periods of binary planetary nebula nuclei is introduced and used to infer the initial characteristics of binary systems which have produced close binary central stars, precataclysmic variables, and related systems. Using existing estimates of their current masses, we find that the initial primaries of V477 Lyr, UU Sge, KV Vel, and MT Ser (all central stars of planetary nebulae) filled their Roche lobes during the early asymptotic giant branch (EAGB) stage. As EAGB stars, these primaries had a small, degenerate CO nucleus, a massive helium shell, and an extended hydrogen-rich envelope. Most of the hydrogen-rich envelope was ejected in a common envelope event, and the planetary nebula now around the system is the ejected common envelope. The ionizing remnants of the primaries have a small, but growing, CO nucleus and a massive (≲0.2 M<SUB>sun</SUB>) helium shell. The progenitor of the primary component of V651 Mon, another central star of a common envelope planetary nebula, probably filled its Roche lobe during the first red giant phase, after the mass of its degenerate helium core reached ∼0.4 M<SUB>sun</SUB>. Wind mass loss may be responsible for the fact that the hot central star lies well within its Roche lobe. <P />An examination and interpretation of the properties of several precataclysmic systems and binaries with components having peculiar surface compositions provide further insight into the consequences of mass loss and mass transfer in close binaries. Included in the study are systems containing helium supergiants, helium subdwarf O stars, S stars, Ba stars, and main-sequence carbon stars.

The Moon and SETI

Many studies lead to the expectation that millions of planets in the galaxy are suitable for life. Studies of interstellar travel and migration show that the entire galaxy could be colonized in a few million years. Our 4-billion-year old solar system should have been colonized by other civilizations by now. This leads to Fermi's Paradox: where are the extraterrestrials? To answer that question, this paper focuses on the obvious but often overlooked observation that the Earth and the Moon constitute a unique “double planet.” Some evidence suggests that the moon was captured early in the history of the solar nebula and profoundly affected Earth's evolution. The Earth may have ended as a frozen, one-plate Mars or a runaway-greenhouse Venus if it had not enjoyed the presence of the Moon. Because of the expected rarity of double planets, we may be alone in our galaxy, and the search for extraterrestrial intelligence (SETI) may be more successful in nearby galaxies than in the Milky Way.

The unique lunar composition and its bearing on the origin of the Moon

The noble gas abundance patterns of Earth, Venus and Mars suggest that accretion of the terrestrial planets took place after the loss of H and He from the inner solar nebula. Since most meteorites also have noble gas patterns which differ from “solar” abundances, such dispersal must have occurred close to T0 (4.55 Ae). An initial depletion of volatile elements, as shown by low KU ratios of the inner planets, is ascribed to the same time. This depletion of volatiles occurred out to a “snow line” around 5 A.U. Formation of the inner planets, through accretion of planetesimals in a gas-free environment, occurred on timescales of 107–108 years. Large bodies (100 Moon-sized, 10 Mercury-sized and several Mars-sized objects) characterised the later stages of planetesimal sweep-up. Over 50% of the mass of the Earth may have previously existed and have undergone metal-silicate fractionation in these large precursor objects. Evidence for the existence of massive planetesimals comes from the obliquities of the planets and the slow retrograde motion of Venus. The Moon has a unique composition among satellites and planets. It is strongly depleted in the very volatile elements (e.g. Bi, Tl) by factors of several hundred relative to the solar nebula. FeO values of 13% in the bulk moon contrast with 36% in CI and 8% in the terrestrial mantle. Trace siderophile elements are depleted in order of their metal-silicate partition coefficients, consistent with their removal into a small lunar core. There is a probable enrichment of refractory elements (e.g. Ca, Al, Ti, REE, U, Th) based on geochemical balance considerations, heat flow, the presence of a thick aluminous crust, and the need to satisfy seismic velocity profiles. A major part of the Moon was molten shortly after accretion, followed by extensive differentiation. Capture, fission or double planet hypotheses for the origin of the Moon all fail to account for the chemical and dynamical problems, including the anomalously high angular momentum of the Earth-Moon system. Only the impact of a massive Mars-sized (>0.1 Earth mass) planetesimal appears adequate to account for both chemical and dynamical aspects. Ejection of a portion of the mantle of the impactor at least partly in a vapor phase accounts for the extreme depletion in volatile elements. The large impactor hypothesis appears to be the only current hypothesis which accounts for the singular composition of the Moon and the unique nature of the Earth-Moon system.

A new binary planetary nebula

A new binary planetary nebula