Prevalence of Earth-size planets orbiting Sun-like stars

Petigura, Erik A.; Howard, Andrew W.; Marcy, Geoffrey W.

doi:10.1073/pnas.1319909110

Cited by 762 publications

(766 citation statements)

References 111 publications

(216 reference statements)

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“…This is consistent with some theoretical predictions of planet migration in circumbinary disks (Pierens & Nelson 2013). Furthermore, the detection of Kepler planets around single stars is biased toward those with a short period ( < ∼ 200 d, Petigura et al 2013). But the different distribution of circumbinary planets in Fig.…”

Section: Discussionsupporting

confidence: 90%

Effects of X-ray and extreme UV radiation on circumbinary planets

Sanz-Forcada

Desidera

Micela

2014

A&A

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Context. Several circumbinary planets have recently been discovered. The orbit of a planet around a binary stellar system poses several dynamic constraints. In addition to these constraints, the effects that radiation from the host stars may have on the planet atmospheres must be considered. We here evaluate these effects. Because of the configuration of a close binary system, these stars have a high rotation rate, even for old stars. The fast rotation of close, tidally locked binaries causes a permanent state of high stellar activity and copious XUV radiation. The accumulated effects are stronger than for normal exoplanets around single stars and cause a faster evaporation of their atmospheres. Aims. We evaluate the effects that stellar radiation has on the evaporation of exoplanets around binary systems and on the survival of these planets. Methods. We considered the X-ray and EUV spectral ranges (XUV, 1-912 Å) to account for the photons that are easily absorbed by a planet atmosphere that is mainly composed of hydrogen. A more complex atmospheric composition is expected to absorb this radiation more efficiently. We used direct X-ray observations to evaluate the energy in the X-rays range and coronal models to calculate the (nondetectable) EUV part of the spectrum. Results. We considered in this problem different configurations of stellar masses, and a resonance of 4:1 and 3:1. The simulations show that exoplanets orbiting close binary systems in a close orbit will suffer strong photoevaporation that may cause a total loss of atmosphere in a short time. We also applied our models to the best real example, Kepler-47 b, to estimate the current mass-loss rates in circumbinary planets and the accumulated effects over the time. Conclusions. A binary system of two solar-like stars will be highly efficient in evaporating the atmosphere of the planet (less than 6 Gyr in our case). These systems will be difficult to find, even if they are dynamically stable. Still, planets may orbit around binary systems of low mass stars for wider orbits. Currently known circumbinary planets are not substantially affected by thermal photoevaporation processes, unless Kepler-47 b has an inflated atmosphere. The distribution of the orbital periods of circumbinary planets is shifted to much longer periods than the average of Kepler planets, which supports a scenario of strong photoevaporation in close-in circumbinary planets.

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Section: Discussionsupporting

confidence: 90%

Effects of X-ray and extreme UV radiation on circumbinary planets

Sanz-Forcada

Desidera

Micela

2014

A&A

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“…The exact value of the boundary we use here is not tailored to the latest Kepler results, but it does produce terrestrial planets for a large fraction of star systems, which generally speaking is thought to be the case given the Kepler dataset (Petigura, Howard & Marcy, 2013). Above Neptune masses, the metallicity correlation is stronger, so we assume that the probability of giant planet formation is governed by:…”

Section: Calculating Habitabilitymentioning

confidence: 99%

Evaluating galactic habitability using high-resolution cosmological simulations of galaxy formation

Forgan

Dayal

Cockell

et al. 2016

International Journal of Astrobiology

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We present the first model that couples high-resolution simulations of the formation of Local Group galaxies with calculations of the galactic habitable zone (GHZ), a region of space which has sufficient metallicity to form terrestrial planets without being subject to hazardous radiation. These simulations allow us to make substantial progress in mapping out the asymmetric three-dimensional GHZ and its time evolution for the Milky Way (MW) and Triangulum (M33) galaxies, as opposed to works that generally assume an azimuthally symmetric GHZ.Applying typical habitability metrics to MW and M33, we find that while a large number of habitable planets exist as close as a few kiloparsecs from the galactic centre, the probability of individual planetary systems being habitable rises as one approaches the edge of the stellar disc. Tidal streams and satellite galaxies also appear to be fertile grounds for habitable planet formation.In short, we find that both galaxies arrive at similar GHZs by different evolutionary paths, as measured by the first and third quartiles of surviving biospheres. For the Milky Way, this interquartile range begins as a narrow band at large radii, expanding to encompass much of the galaxy at intermediate times before settling at a range of 2-13kpc. In the case of M33, the opposite behaviour occurs -the initial and final interquartile ranges are quite similar, showing gradual evolution. This suggests that galaxy assembly history strongly influences the time evolution of the GHZ, which will affect the relative time lag between biospheres in different galactic locations. We end by noting the caveats involved in such studies and demonstrate that high resolution cosmological simulations will play a vital role in understanding habitability on galactic scales, provided that these simulations accurately resolve chemical evolution.

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“…Further work has demonstrated that such planets are often found within the Habitable Zone (HZ) of their host star. Recent analyses of the Kepler data showed (Petigura et al, 2013) that about 20% of all solar-type stars have small, approximately Earth-sized planets orbiting within their HZ. Observational uncertainties and false-positive detections (Foreman-Mackey, Hogg and Morton, 2014;Farr, Mandel and Stroud, 2014) may significantly reduce this figure (down to 2-4%, however with a large uncertainty), yet it still implies a significant fraction and a huge number of stars with Earth-size habitable planets.…”

Section: Prevalence Of Earthlike Planets Outside Of the Solar Systemmentioning

confidence: 99%

The potential of planets orbiting red dwarf stars to support oxygenic photosynthesis and complex life

Gále

Wandel

2016

International Journal of Astrobiology

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We review and reassess the latest findings on the existence of extra-solar system planets and their potential of having environmental conditions that could support Earth-like life. Within the last two decades, the multi-millennial question of the existence of extra-Solarsystem planets has been resolved with the discovery of numerous planets orbiting nearby stars, many of which are Earth-sized (and some even with moderate surface temperatures).Of particular interest in our search for clement conditions for extra-solar system life are planets orbiting Red Dwarf (RD) stars, the most numerous stellar type in the Milky Way galaxy. We show that including RDs as potential life supporting host stars could increase the probability of finding biotic planets by a factor of up to a thousand, and reduce the estimate of the distance to our nearest biotic neighbor by up to 10. We argue that multiple star systems need to be taken into account when discussing habitability and the abundance of biotic exoplanets, in particular binaries of which one or both members are RDs. Early considerations indicated that conditions on RD planets would be inimical to life, as their Habitable Zones (where liquid water could exist) would be so close as to make planets tidally locked to their star. This was thought to cause an erratic climate and expose life forms to flares of ionizing electro-magnetic radiation and charged particles. Moreover, it has been argued that the lesser photon energy of the radiation of the relatively cool RDs would not suffice for Oxygenic Photosynthesis (OP) and other related energy expending reactions. Recent calculations show that these negative factors are less severe than originally thought. Numerous authors suggest that OP on RD planets may evolve to utilize photons in the infrared. We however argue, by analogy to the evolution of OP and the environmental

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Prevalence of Earth-size planets orbiting Sun-like stars

Cited by 762 publications

References 111 publications

Effects of X-ray and extreme UV radiation on circumbinary planets

Effects of X-ray and extreme UV radiation on circumbinary planets

Evaluating galactic habitability using high-resolution cosmological simulations of galaxy formation

The potential of planets orbiting red dwarf stars to support oxygenic photosynthesis and complex life

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