https://phys.org/news/2020-06-billion-earth-like-planets-galaxy.html As many as six billion Earth-like planets in our galaxy, according to new estimates: To be considered Earth-like, a planet must be rocky, roughly Earth-sized and orbiting Sun-like (G-type) stars. It also has to orbit in the habitable zones of its star—the range of distances from a star in which a rocky planet could host liquid water, and potentially life, on its surface. "My calculations place an upper limit of 0.18 Earth-like planets per G-type star," says UBC researcher Michelle Kunimoto, co-author of the new study in The Astronomical Journal. "Estimating how common different kinds of planets are around different stars can provide important constraints on planet formation and evolution theories, and help optimize future missions dedicated to finding exoplanets." According to UBC astronomer Jaymie Matthews: "Our Milky Way has as many as 400 billion stars, with seven percent of them being G-type. That means less than six billion stars may have Earth-like planets in our Galaxy." Previous estimates of the frequency of Earth-like planets range from roughly 0.02 potentially habitable planets per Sun-like star, to more than one per Sun-like star. Typically, planets like Earth are more likely to be missed by a planet search than other types, as they are so small and orbit so far from their stars. That means that a planet catalog represents only a small subset of the planets that are actually in orbit around the stars searched. Kunimoto used a technique known as 'forward modeling' to overcome these challenges. more at link.................................. the paper: https://iopscience.iop.org/article/10.3847/1538-3881/ab88b0 Searching the Entirety of Kepler Data. II. Occurrence Rate Estimates for FGK Stars: Abstract We present exoplanet occurrence rates estimated with approximate Bayesian computation for planets with radii between 0.5 and 16 R ⊕ and orbital periods between 0.78 and 400 days orbiting FGK dwarf stars. We base our results on an independent planet catalog compiled from our search of all ~200,000 stars observed over the Kepler mission, with precise planetary radii supplemented by Gaia DR2-incorporated stellar radii. We take into account detection and vetting efficiency, planet radius uncertainty, and reliability against transit-like noise signals in the data. By analyzing our FGK occurrence rates as well as those computed after separating F-, G-, and K-type stars, we explore dependencies on stellar effective temperature, planet radius, and orbital period. We reveal new characteristics of the photoevaporation-driven "radius gap" between ~1.5 and 2 R ⊕, indicating that the bimodal distribution previously revealed for P < 100 days exists only over a much narrower range of orbital periods, above which sub-Neptunes dominate and below which super-Earths dominate. Finally, we provide several estimates of the "eta-Earth" value—the frequency of potentially habitable, rocky planets orbiting Sun-like stars. For planets with sizes 0.75–1.5 R ⊕ orbiting in a conservatively defined habitable zone (0.99–1.70 au) around G-type stars, we place an upper limit (84.1th percentile) of <0.18 planets per star.
Supplementary: https://phys.org/news/2020-06-life.html If there is life out there, can we detect it? Instruments aboard future space missions are capable of detecting amino acids, fatty acids and peptides, and can even identify ongoing biological processes on ocean moons in our solar system. These are the exciting conclusions reached by two studies from an international team led by scientists of the Planetary Sciences research group at Freie Universität Berlin. The two studies were published in the peer-reviewed scientific journal Astrobiology. Enceladus, one of Saturn's moons, is known to emit plumes of gas and ice grains formed from the moon's subsurface ocean, located beneath an ice crust, into space. A similar phenomenon is suspected to occur on Jupiter's moon Europa. The compositions of ice grains emitted from such water worlds can be sampled by spacecraft intercepting the particles, using so-called impact ionization mass spectrometers. Scientists at Freie Universität Berlin have undertaken unique laboratory experiments that accurately simulate the mass spectra of ice grains measured in space. more at link.............. the paper: https://www.liebertpub.com/doi/10.1089/ast.2019.2188 Discriminating Abiotic and Biotic Fingerprints of Amino Acids and Fatty Acids in Ice Grains Relevant to Ocean Worlds: Abstract Identifying and distinguishing between abiotic and biotic signatures of organic molecules such as amino acids and fatty acids is key to the search for life on extraterrestrial ocean worlds. Impact ionization mass spectrometers can potentially achieve this by sampling water ice grains formed from ocean water and ejected by moons such as Enceladus and Europa, thereby exploring the habitability of their subsurface oceans in spacecraft flybys. Here, we extend previous high-sensitivity laser-based analog experiments of biomolecules in pure water to investigate the mass spectra of amino acids and fatty acids at simulated abiotic and biotic relative abundances. To account for the complex background matrix expected to emerge from a salty Enceladean ocean that has been in extensive chemical exchange with a carbonaceous rocky core, other organic and inorganic constituents are added to the biosignature mixtures. We find that both amino acids and fatty acids produce sodiated molecular peaks in salty solutions. Under the soft ionization conditions expected for low-velocity (2–6 km/s) encounters of an orbiting spacecraft with ice grains, the unfragmented molecular spectral signatures of amino acids and fatty acids accurately reflect the original relative abundances of the parent molecules within the source solution, enabling characteristic abiotic and biotic relative abundance patterns to be identified. No critical interferences with other abiotic organic compounds were observed. Detection limits of the investigated biosignatures under Enceladus-like conditions are salinity dependent (decreasing sensitivity with increasing salinity), at the μM or nM level. The survivability and ionization efficiency of large organic molecules during impact ionization appears to be significantly improved when they are protected by a frozen water matrix. We infer from our experimental results that encounter velocities of 4–6 km/s are most appropriate for impact ionization mass spectrometers to detect and discriminate between abiotic and biotic signatures.
