Using Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have taken a new, detailed look at the very early stages of planet formation around a binary star. Embedded in the outer reaches of a double star's protoplanetary disk, the researchers discovered a striking crescent-shape region of dust that is conspicuously devoid of gas. This result provides fresh insights into the planet-forming potential of a binary system. https://www.sciencedaily.com/releases/2016/02/160213185704.htm
Not too long ago I was told that there are no stable orbits for planets in binary systems. Then, planets have been discovered in such systems, and the now we even see planets forming in such a system. If we ever will find that famous planet who drives an 8-shaped orbit around two suns, and never has night? Such a planet sees the one sun rise when the other sets. I always wondered about sky colors and their daily change if the suns are of different colors - as far as I know white, yellow, orange and red suns are known to form stable binary systems, bown dwarves are common, too (and there is an article that say they are actually magenta, and were wrongly named brown). Source: https://en.wikipedia.org/wiki/Brown_dwarf We just had valentines day. But no brown dwarf to give us pink sky ... yet Please Register or Log in to view the hidden image!
I came up with a figure-8 shaped orbit too. But it's not stable. BTW, there's no reason it would not have night. Day/night is determined by the planet's rotation on its axis. It would have plenty of day/night cycles at each end of its orbit.
Right, I only thought of the locations between the suns. A pity that those orbits are not stable. Such a planet surely would have an interesting yearly pattern of seasson.
http://io9.gizmodo.com/weve-discovered-a-binary-star-system-whose-planet-is-in-1599753945 We've Discovered a Binary Star System Whose Planet Is in Stable Orbit It may not be anything like Tatooine of Star Wars, but this discovery is still incredible. We've found a frozen, rocky planet orbiting one of its two parent binary stars in a stable Earth-like orbit. This significantly expands our sense of where life can emerge in the galaxy. Binary star systems are quite common. So common, in fact, that they may account for as many as 50% of all stellar systems, though more conservative estimates place the figure at about a third. Regardless, the presence of so many binary stars likely imposes a profound constraint on galactic habitability; gravitational perturbations from a companion star can interfere in the formation and long-term stability of planets. Prior to this study, all the planets discovered thus far in binary systems have been gas giants, including a binary system with more than one planet. It's possible, of course, that the moons of these exoplanets are habitable, but astronomers have no idea if rocky Earth-like planets in stable Earth-like orbits can form in these systems
http://arxiv.org/pdf/1401.1006v3.pdf ABSTRACT A general formulation to compute habitable zones around binary stars is presented. A habitable zone in this context must satisfy two separate conditions: a radiative one and one of dynamical stability. For the case of single stars, the usual concept of circumstellar habitable zone is based on the radiative condition only, as the dynamical stability condition is taken for granted (assuming minimal perturbation from other planets). For the radiative condition, we extend the simple formulation of the circumstellar habitable zone for single stars, to the case of eccentric stellar binary systems, where two sources of luminosity at different orbital phases contribute to the irradiance of their planetary circumstellar and circumbinary regions. Our approach considers binaries with eccentric orbits and guarantees that orbits in the computed habitable zone remain within it at all orbital phases. For the dynamical stability condition, we use the approach of invariant loops developed by Pichardo et al. (2005) to find regions of stable, non-intersecting orbits, which is a robust method to find stable regions in binary stars, as it is based in the existence of integrals of motion. We apply the combined criteria to calculate habitable zones for 64 binary stars in the solar neighborhood with known orbital parameters, including some with discovered planets. Formulae and interpolating tables are provided, so the reader can compute the boundaries of the habitable zones for an arbitrary binary system, using the stellar flux limits they prefer. Together with the formulae provided for stable zones, these allow the computation of both regions of stability and habitability around any binary stellar system. We found 56% of the cases we consider can satisfy both restrictions, this is a very important constriction to binary systems. Nevertheless, we conclude that these systems where a dynamical and radiative safe zone exists, must be considered strong candidates in the search for habitable planets. 5 DISCUSSION AND CONCLUSIONS In this work we have constructed a straightforward and clear formulation to calculate regions for habitable planets in binary stellar systems. To this purpose, we search for two general restrictions assuming in principle Earth-like planets: a) the planet must be located in a region of orbital stability (and approximately circular orbit), and b) the planet is located at a position, such as it reaches the correct host star energy, to permit the existence of liquid water on its surface Kopparapu et al. (2013). Some other particular restrictions, as the ones proper of the intrinsic characteristics of the planet for example, can readily be addressed to this formulation as multiplicative factors. Regarding the fundamental test for orbital stability to develop life, in this paper we employ the criteria of Pichardo et al. (2005) and Pichardo et al. (2009) for stable orbits in binary systems. This stability method results better in searching habitable regions for planets. Indeed, although the empirical approximation of Holman & Wiegert was an excellent and fundamental first approximation to the stability problem, their method is rather based on a detailed trial and error approximation, that overestimates by construction, the available stable regions since their stability criteria depends on a given time of integration that particles keep in orbit (about 104 periods), which results on a relaxed criteria when looking for strict stability, needed for life emergency and developing. Instead, we have employed the invariant loops method that searches for the exact solution for stable orbits in binary systems at all binary eccentricities. On the other hand, invariant loops show in the circumbinary discs cases, that there is a shift of the geometric center of the stable region (disk) that can be considerable for high eccentricities, compromising the intersection between stable regions for planets and habitable regions in the simple sense of the irradiance (as is the case, for example of Kepler 16). The shift can not be detected with other method than the exact solution provided by the invariant loops tool, this was detected theoretically and presented in Pichardo et al. 2008 paper, we are considering this for planets in circumbinary disks in our calculations for binaries of the solar neighborhood. It is worth mentioning that in our approach to calculate habitable zones in binary stars, for different life likelihood considerations, such as orbital stability and irradiation, we are not considering multiple stars, or stars out of their main sequence or planets on highly eccentric orbits. In the case of multiple stars, although an extension of this work to any multiple star systems would be straightforward for the irradiance calculations, in the majority of cases these systems result in unstable ones, unless they are hierarchical (v.g. triple systems where a very close binary star with a far companion as Alpha Centauri and Proxima, or a double binary where both binary systems act like single stars in one larger binary system). On the other hand, there is no straightforward method to find stable orbital zones in multiple stellar systems, needed to calculate formally habitable zones. Although our method is aplicable to all kind of stars, we only calculated habitable zones for the solar neighborhood main sequence stars, since stars out of this life stage would likely be inhospitable for life. In the case of planets on very eccentric orbits (e&0.3), the probability of survival is diminished due to the presence of the companion that reduces severely the available phase space for planets to settle down (this is a detailed study that will be presented in a future work). On the other hand, what induces eccentricity on a planet in a binary star?, external factors are stellar encounters, but to affect a very small disc (truncated by the binary), a very close stellar encounter (with a third star) must be taking place (∼3 times the disk radius at least, Jimenez-Torres et al. (2011)), ´ likely affecting the binary stability itself, this results in a non stable situation for habitability. Or an internal factor, for example a resonance that is able to induce secularly eccentricity in the planetary orbits, however that is also an unstable situation for planets, since resonances tend to increase rapidly eccentricities on orbiting bodies, wiping out entire disk regions. Other possibility, a giant planet on eccentric orbit that induces eccentricity in terrestrial planets, a clearly difficult situation in terms of stability. Regarding irradiance zones. We have defined three zones where the binary star provides the necessary energy for habitability: (I) the zone around each star, (III) the zone around the hole binary or (II) in a mixture of this two zones. In this work, we consider a “habitable environment”, the intersection of one of these zones and the allowed dynamical zone for stable orbits. Taking into account both restrictions, from a binary sample of main sequence stars, with known orbital parameters of the solar neighborhood (64), we have selected 36 candidates (56 % of our original sample), as plausible candidates to host habitable planets. We present this table together with three particular and interesting examples in detail: HIP 1995, HIP 80346 and HIP 76852. We find, from our sample of candidates, that none allows planets inside the BHZ defined by the configuration II (circumbinary discs). This is because in all cases, the system allows habitability too close to the binary, where the stability restriction becomes very important, making impossible for all cases in our sample, to host a planet there. Although a greater sample is necessary to produce a final conclusion on the solar neighborhood, this small first sample is useful to statistically elucidate the possibilities of finding habitability on binaries of the solar neighborhood, and the possibilities for circumbinary discs seem reduced. Programming our formulation for habitable zones (from the irradiance point o view) is rather simple, however software to compute numerically the size of habitable zones for binary systems is available from the authors. We thank the anonymous referee for a very throrough review of our manuscript and suggestions that resulted in a clearer and deeper exposition. We acknowledge financial support from UNAM/DGAPA through grant IN114114.
Where's that from? [astro-ph/9809315] Long-Term Stability of Planets in Binary Systems Matthew Holman, Paul Wiegert 1998 There are three stable regions, one near each star, and one around both stars. For equal-mass stars in a circular orbit, the inner stable region has planet / stars major-axis ratio < 0.262 (a little greater than 1/4), while the outer stable region has it > 2.278. Inner region: ap/a < ((0.464±0.006) + (0.380±0.010)*μ + (0.631±0.034)*e + (0.586±0.061)*μ*e + (0.150±0.041)*e^2+ (-0.198±0.074)*μ*e^2) Outer region: ap/a > ((1.60±0.04) + (5.10±0.05)*e + (-2.22±0.11)*e^2 + (4.12±0.09)*μ + (-4.27±0.17)*μ*e + (-5.09±0.11)*μ^2 + (4.61±0.36)*μ^2*e^2) ap = semimajor axis of planet's orbit (initially circular and coplanar) a = semimajor axis of binary-star orbit e = eccentricity of binary-star orbit μ = (mass of other star)/(combined mass of both stars)
I have forgotten. Since planets have been discovered in binary systems, there was no need anymore to remember the source; it's been shown to be obsolete, even wrong. My guess is, that I read it somewhere in a popular science magazine that was having an article about solar systems ... can well have been 20 or 30 years ago.
