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  • richardmitnick 2:53 pm on October 28, 2018 Permalink | Reply
    Tags: , , , , , Habitable Zone,   

    From JPL-Caltech: “Rocky? Habitable? Sizing up a Galaxy of Planets” 

    NASA JPL Banner

    From JPL-Caltech

    Oct. 25, 2018

    Calla Cofield
    Jet Propulsion Laboratory, Pasadena, Calif.
    626-808-2469
    calla.e.cofield@jpl.nasa.gov

    Alison Hawkes
    Ames Research Center, California’s Silicon Valley
    650-604-0281
    alison.hawkes@nasa.gov

    Written by Pat Brennan​

    1
    Artist’s concept of how rocky, potentially habitable worlds elsewhere in our galaxy might appear. Data gathered by telescopes in space and on the ground suggest that small, rocky planets are common. (Placing them so close together in a line is for illustrative purposes only.) Credits: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

    The planets so far discovered across the Milky Way are a motley, teeming multitude: hot Jupiters, gas giants, small, rocky worlds and mysterious planets larger than Earth and smaller than Neptune. As we prepare to add many thousands more to the thousands found already, the search goes on for evidence of life – and for a world something like our own.

    And as our space telescopes and other instruments grow ever more sensitive, we’re beginning to zero in.

    The discoveries so far inspire excitement and curiosity among scientists and the public. We’ve found rocky planets in Earth’s size range, at the right distance from their parent stars to harbor liquid water. While these characteristics don’t guarantee a habitable world – we can’t quite tell yet if these planets really do possess atmospheres or oceans – they can help point us in the right direction.

    Future space telescopes will be able to analyze the light from some of these planets, searching for water or a mixture of gases that resembles our own atmosphere. We will gain a better understanding of temperatures on the surface. As we continue checking off items on the habitability list, we’ll draw closer and closer to finding a world bearing recognizable signs of life.

    Among the most critical factors in the shaping and development of a habitable planet is the nature of its parent star. The star’s mass, size and age determine the distance and extent of its “habitable zone” – the region around a star where the temperature potentially allows for liquid water to pool on a planet’s surface.

    Star-mapping the Galaxy

    The European Space Agency’s Gaia satellite, launched in 2013, is becoming one of history’s greatest star mappers.

    ESA/GAIA satellite

    It relies on a suite of high-precision instruments to measure star brightness, distance, and composition. The ambitious goal is to create a three-dimensional map of our Milky Way galaxy. The chart so far includes the positions of about 1.7 billion stars, with distances for about 1.3 billion.

    That has prompted a reassessment of star sizes to learn whether some might be larger, smaller, dimmer or brighter than scientists had thought.

    It turns out that many of the stars were found to be brighter – and larger – than previous surveys estimated. For the team managing the explosion of planet finds from NASA’s Kepler space telescope, beginning in 2009, that also means a revision of sizes for the planets in orbit around them.

    NASA/Kepler Telescope

    If a star is brighter than we thought, it’s often larger than we thought as well. The planet in orbit around it, measured proportionally by the transit method, must also be larger.

    That means some of the planets thought to be of a size and temperature similar to Earth’s are really bigger – and usually, hotter.

    “Gaia has improved distances and has improved assessments of how bright a star is, and how big a planet is,” said Eric Mamajek, the deputy program chief scientist for NASA’s Exoplanet Exploration Program. “The whole issue has always been, how well do we understand the star? This is just another chapter of that ongoing story.”

    The latest scientific data from the Gaia space probe also is prompting a reassessment of the most promising “habitable zone” planets found by observatories around the world, as well as space-based instruments like NASA’s Kepler.

    Habitable planets Current Potential Planetary Habitability Laboratory U Puerto Rico Arecibo

    As scientists iron out both observations and definitions of what we consider a potentially habitable world, better data is bringing us closer to finding such a planet and – maybe just as important – finding our own planet’s place among them.

    Of the 3,700 exoplanets – planets around other stars – confirmed by scientists so far, about 2,600 were found by the Kepler space telescope. Kepler hunts for the tiny eclipse, or dip in starlight, as a planet crosses the face of its star.

    The most recent analysis of Kepler’s discoveries shows that 20 to 50 percent of the stars in the sky are likely to have small, potentially rocky planets in their habitable zones. Our initial estimate of near Earth-sized, habitable-zone planets from the Kepler spacecraft as of June 19, 2017, was 30. Preliminary analysis of newer data, on both those exoplanets and their host stars, shows that the number is likely smaller – possibly between 2 and 12.

    Much more data are needed, including a better understanding of how a planet’s size relates to its composition.

    “We’re still trying to figure out how big a planet can be and still be rocky,” said Jessie Dotson, an astrophysicist at NASA’s Ames Research Center in California’s Silicon Valley. She is also the project scientist for Kepler’s current, extended mission, known as K2.

    At first glance, the latest analysis might seem disappointing: fewer rocky, potentially habitable worlds among the thousands of exoplanets found so far. But that doesn’t change one of the most astonishing conclusions after more than 20 years of observation: Planets in the habitable zone are common.

    More and better data on these far distant planets means a more accurate demographic portrait of a universe of planets – and a more nuanced understanding of their composition, possible atmospheres and life-bearing potential.

    That should put us on more solid ground for the coming torrent of exoplanet discoveries from TESS (the Transiting Exoplanet Survey Satellite), and future telescopes as well. It brings us one step closer in our search for a promising planet among a galaxy of stars.

    “This is the exciting part of science,” Dotson said. “So often, we’re really portrayed as, ‘Now we know this story.’ But I have a theory: Scientists love it when we don’t know something. It’s the hunt that’s so exciting.”

    See the full article here .


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    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge, on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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  • richardmitnick 2:32 pm on May 3, 2016 Permalink | Reply
    Tags: , , Habitable Zone,   

    From SA: “Which Came First on Earth—Habitability or Life?” 

    Scientific American

    Scientific American

    May 3, 2016
    Shannon Hall

    One astronomer suggests that we cannot necessarily disentangle the two

    1
    These limestone cliffs along the English coastline are composed of calcium carbonate that formed when the skeletal remains of planktonic algae sank to the bottom of the ocean during the Cretaceous period. Credit: leo.wan/Flickr, CC BY 2.0

    The hunt for life on other planets is due for a makeover. Although it is often confined to planets orbiting in the so-called habitable zone where proximity to their host stars makes temperatures just right for liquid water, many astronomers are beginning to think outside the “Goldilocks” box. Some wonder if previously overlooked mechanisms—including life itself—could broaden the habitable zone well beyond its current definition. Colin Goldblatt, a planetary scientist at the University of Victoria in British Columbia, even argues that life’s ability to alter a planet’s climate poses a new paradox: A planet’s habitability could depend on whether life has already made itself at home there, a situation that would place habitability and life in a baffling chicken-or-egg scenario.

    Goldblatt has been looking beyond Earth-like atmospheres to see how different concentrations of nitrogen and carbon dioxide might tweak a planet’s habitability. Higher concentrations of carbon dioxide, for example, could keep a planet that is relatively far from its host star toasty whereas lower concentrations could keep a close-in planet chilly. Nitrogen is more complicated because higher concentrations both scatter sunlight (helping cool a planet) and make greenhouse gases absorb light more efficiently (keeping it warmer). At the fall 2015 American Geophysical Union meeting in San Francisco, Goldblatt argued these gases could help keep a planet habitable. He recently summarized his talk in a paper* published to the preprint server arXiv.

    NASA Orbiting Carbon Observatory 2, NASA JPL-Caltech
    NASA Orbiting Carbon Observatory 2, NASA JPL-Caltech

    “It’s a property of the planet that you’re living on.” Earth, for example, has a built-in temperature control system: the carbon–silicate cycle. Some 2.5 billion years ago the sun was so faint that the oceans should have been frozen—but they were not. The simple explanation is that Earth likely boasted an atmosphere thick with greenhouse gases. Then as the sun’s brightness grew, the planet counteracted the warming climate by scrubbing carbon dioxide from the air: Higher temperatures increased rainfall, which pulled the greenhouse gas from the atmosphere and carried it into the oceans, where plate tectonics eventually subducted it into Earth’s mantle. Today most of the world’s carbon dioxide is safely stored beneath Earth’s crust. Had the opposite occurred and the sun’s brightness waned, the planet might have counteracted the cooling climate by pumping more carbon dioxide into the air. Cooler temperatures would have slowed precipitation and increased volcanic eruptions, spewing the greenhouse gas out of the Earth’s mantle and back into the atmosphere.

    This balancing act has stabilized Earth’s climate for billions of years, letting the carbon dioxide swing up or down by more than 1,000 percent in order to keep the planet’s temperature steady and thereby increase the size of its habitable zone. And it is not just due to geochemistry; the carbon–silicate cycle depends on biology as well. Carbon dioxide is removed from the ocean when sea creatures convert it into the calcium carbonate they use to build their shells. After those creatures die they sink into the deep ocean where their shells are subducted into the mantle. For an example of this phenomenon, Goldblatt points to the White Cliffs of Dover. These limestone cliffs along the English coastline are composed of calcium carbonate that formed when the skeletal remains of planktonic algae sank to the bottom of the ocean during the Cretaceous period. It appears that levels of both carbon dioxide and nitrogen (which is similarly whipped between Earth’s mantle and atmosphere) can be subject to a planet’s biosphere. Life creates conditions that help sustain itself.

    “The existence of a biosphere actually increases the span of a habitable zone in a given solar system,” Crisp says. “The habitability of an environment is affected to a certain extent by whether or not it is inhabited by some life form.” Although this is generally agreed on, Goldblatt takes it a step further by saying that we cannot disentangle a habitable planet from the presence of life itself. “The thing that I want to push in this paper is a philosophical point—not a point of technical calculations,” Goldblatt says. “You can’t try to address whether a planet is suitable for life or not without considering whether there is already life on the planet.” Whereas most astronomers search for worlds that are suited to host life around other stars, Goldblatt does not think a planet can be called “habitable.” It is either inhabited, or it is not. If we find a lifeless Earth-like planet in the so-called habitable zone and we just plop an egg of life on that planet, there is no guarantee that life will take hold, Goldblatt says. “We have no idea what a planet at that [distance] without life would actually look like,” he says. “It would look nothing at all like the Earth.”

    Although this paradox might make the search for life look bleak, Goldblatt is hopeful we will find life in the galaxy. He simply thinks that astronomers should not confine themselves to such a strict definition of the habitable zone around stars. Life might exist within those bounds or it might exist well beyond them in ways that scientists have yet to imagine. To demonstrate his point he told me a story about Carl Sagan. When Cassini first arrived at Saturn, the spacecraft beamed images back to Earth where Sagan and other scientists could watch them first appear in a room at JPL. Most scientists attempted to interpret the results immediately, but Sagan remained quiet. He knew that the theoretical postulating was over. It was time to let the data speak for itself. “When we went out in the solar system we found things that we never expected,” Goldblatt says. “And when we go out to observe the atmospheres on planets, we’re going to find things that we don’t expect. We need to be ready to broaden our horizons.”

    *Science paper:
    The inhabitance paradox: how habitability and inhabitancy are inseparable

    See the full article here .

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  • richardmitnick 12:01 pm on April 20, 2016 Permalink | Reply
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    From AAS NOVA: “Choosing Stars to Search for Habitable Planets” 

    AASNOVA

    Amercan Astronomical Society

    20 April 2016
    Susanna Kohler

    1
    Artist’s illustration of an M-dwarf star surrounded by three planets. A recent study examines which stars make the best targets when searching for habitable exoplanets. [NASA/JPL-Caltech]

    M-dwarf stars are excellent targets for planet searches because the signal of an orbiting planet is relatively larger (and therefore easier to detect!) around small, dim M dwarfs, compared to Sun-like stars. But are there better or worse stars to target within this category when searching for habitable, Earth-like planets?
    Confusing the Signal

    Radial velocity campaigns search for planets by looking for signatures in a star’s spectra that indicate the star is “wobbling” due to the gravitational pull of an orbiting planet. Unfortunately, stellar activity can mimic the signal of an orbiting planet in a star’s spectrum — something that is particularly problematic for M dwarfs, which can remain magnetically active for billions of years. To successfully detect planets that orbit in their stars’ habitable zones, we have to account for this problem.

    In a recent study led by Elisabeth Newton (Harvard-Smithsonian Center for Astrophysics), the authors use literature measurements to examine the rotation periods for main-sequence, M-type stars. They focus on three factors that are important for detecting and characterizing habitable planets around M dwarfs:

    Whether the habitable-zone orbital periods coincide with the stellar rotation
    False planet detections caused by stellar activity often appear as a “planet” with an orbital period that’s a multiple of the stellar rotation period. If a star’s rotation period coincides with the range of orbital periods corresponding to its habitable zone, it’s therefore possible to obtain false detections of habitable planets.
    How long stellar activity and rapid rotation last in the star
    All stars become less magnetically active and rotate more slowly as they age, but the rate of this decay depends on their mass: lower-mass stars stay magnetically active for longer and take longer to spin down.
    Whether detailed atmospheric characterization will be possible
    It’s ideal to be able to follow up on potentially habitable exoplanets, and search for biosignatures such as oxygen in the planetary atmosphere. This type of detection will only be feasible for low-mass dwarfs, however, due to the relative size of the star and the planet.

    1
    Stellar rotation period as a function of stellar mass. The blue shaded region shows the habitable zone as a function of stellar mass. For M dwarfs between ~0.25 and ~0.5 solar mass, the habitable-zone period overlaps with the stellar rotation period. [Newton et al. 2016]

    An Ideal Range

    Newton and collaborators find that stars in the mass range of 0.25 to 0.5 solar mass (stellar class M1V-M4V) are non-ideal targets, because their stellar rotation periods (or a multiple thereof) coincide with the orbital periods of their habitable zones. In addition, atmospheric characterization will only be feasible in the near future for stars with mass less than ~0.25 solar mass.

    On the other hand, dwarfs with mass less than ~0.1 solar masses (stellar classes later than M6V) will retain their stellar activity and faster rotation rates throughout most of their lifetimes, making them non-ideal targets as well.

    When searching for habitable exoplanets, the best targets are therefore the mid M dwarfs in the mass range of 0.1 to 0.25 solar mass (stellar class M4V-M6V). Building a sample focused on these stars will reduce the likelihood that planets found in the stars’ habitable zones are false detections. This will hopefully produce a catalog of potentially habitable exoplanets that we can eventually follow up with atmospheric observations.
    Citation

    Elisabeth R. Newton et al 2016 ApJ 821 L19. doi:10.3847/2041-8205/821/1/L19

    Science paper:
    THE IMPACT OF STELLAR ROTATION ON THE DETECTABILITY OF HABITABLE PLANETS AROUND M DWARFS

    See the full article here .

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  • richardmitnick 1:32 pm on February 24, 2016 Permalink | Reply
    Tags: , , , CELESTA Catalogue, Habitable Zone   

    From AAS NOVA: “Where to Look for Habitability” 

    AASNOVA

    Amercan Astronomical Society

    24 February 2016
    Susanna Kohler

    Habitability zones of different types of stars
    Illustration of habitable zones around different types of stars. A recent study has generated a catalog, known as CELESTA, of the zones around nearby stars in which liquid water could exist on orbiting, hypothetical planets. [NASA/Kepler Mission/Dana Berry]

    One of the main goals of exoplanet surveys like the Kepler mission is to find potentially habitable planets orbiting other stars.

    NASA Kepler Telescope
    NASA/Kepler

    Finding planets in a star’s habitable zone, however, is easier when we know in advance where to look! A recent study has provided us with a starting point.

    Defining the Zone

    A habitable zone is defined as the range of distances from a star where liquid water could exist on an orbiting planet, given a dense enough planetary atmosphere. The habitable zone can be calculated from the star’s parameters, and the inner and outer edges of a habitable zone are set considering hypothetical planetary atmospheres of different composition.

    Knowing the parameters of the habitable zones around nearby stars is important for current and future exoplanet surveys, as this information allows them to identify stars with habitable zones that can be probed, given the survey’s sensitivity. To provide this target selection tool, a team of scientists led by Colin Chandler (San Francisco State University) has created a catalog of the habitable zones of roughly 37,000 nearby, main-sequence stars.

    Selecting for Sun-Like Stars

    The Catalog of Earth-Like Exoplanet Survey Targets, or CELESTA, was built starting with the Revised Hipparcos Catalog, a high-precision catalog of photometry and parallax measurements (which provides the star’s distance) for 117,955 bright, nearby stars. Chandler and collaborators combined these measurements with stellar models to determine parameters such as effective temperature, radius, and mass of the stars.

    The authors exclude giant stars and cool dwarfs, choosing to focus on main-sequence stars within the temperature range 2600–7200K, more similar to the Sun. They test their derived stellar parameters by comparing to observational data from the Exoplanet Data Explorer (EDE), where available, and confirm that their photometrically derived stellar parameters agree well with the parameters in EDE, typically measured spectroscopically.

    Providing Survey Targets

    The final CELESTA catalog details the habitable zones of 37,354 bright, main-sequence stars. The stars’ habitable-zone widths are generally under 5 AU, with the majority falling between 1 and 1.5 AU. The authors also provide an estimate of how many of these habitable zones current surveys (like Kepler) and upcoming surveys (like the Transiting Exoplanet Survey Satellite, or TESS) will be able to probe, based on the duration of the surveys’ typical campaigns.

    NASA TESS
    NASA/TESS

    Though a planet’s potential for habitability relies on additional factors besides the location of its orbit, cataloging the locations of stellar habitable zones for nearby, observable stars is an important start. CELESTA is an excellent reference for this, and it will provide a living resource that the authors plan to continue to update with additional stars, as well as with improved-accuracy stellar measurements, expected from upcoming astrometric missions.
    Citation

    Colin Orion Chandler et al 2016 AJ 151 59. doi:10.3847/0004-6256/151/3/59

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  • richardmitnick 9:31 am on March 18, 2015 Permalink | Reply
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    From Niels Bohr Institute: “Planets in the habitable zone around most stars, calculate researchers” 

    Niels Bohr Institute bloc

    Niels Bohr Institute

    18 March 2015
    Gertie Skaarup
    skaarup@nbi.dk

    Habitable planets

    Astronomers have discovered thousands of exoplanets in our galaxy, the Milky Way, using the Kepler satellite and many of them have multiple planets orbiting the host star.

    NASA Kepler Telescope
    NASA/Kepler

    By analysing these planetary systems, researchers from the Australian National University and the Niels Bohr Institute in Copenhagen have calculated the probability for the number of stars in the Milky Way that might have planets in the habitable zone. The calculations show that billions of the stars in the Milky Way will have one to three planets in the habitable zone, where there is the potential for liquid water and where life could exist. The results are published in the scientific journal, Monthly Notices of the Royal Astronomical Society.

    1
    Planets outside our solar system are called exoplanets. The Kepler satellite observes exoplanets by measuring the light curve of a star. When a planet moves in front of the star there is a small dip in brightness. If this little dip in brightness occurs regularly, there might be a planet orbiting the star and obscuring its light.

    Using NASA’s Kepler satellite, astronomers have found about 1,000 planets around stars in the Milky Way and they have also found about 3,000 other potential planets. Many of the stars have planetary systems with 2-6 planets, but the stars could very well have more planets than those observable with the Kepler satellite, which is best suited for finding large planets that orbit relatively close to their stars.

    Planets that orbit close to their stars would be too scorching hot to have life, so to find out if such planetary systems might also have planets in the habitable zone with the potential for liquid water and life, a group of researchers from the Australian National University and the Niels Bohr Institute at the University of Copenhagen made calculations based on a new version of a 250-year-old method called the Titius-Bode law.

    2
    Light curves of the five planets orbiting the star Kepler-62. The dip in the light curve occur when the planet moves in front of the host star, thereby dimming the light of the star. The dip in the light curve is proportional to the size of the planet. The two light curves at the bottom of the plot are of planets in the habitable zone.

    Calculating planetary positions

    The Titius-Bode law was formulated around 1770 and correctly calculated the position of Uranus before it was even discovered. The law states that there is a certain ratio between the orbital periods of planets in a solar system. So the ratio between the orbital period of the first and second planet is the same as the ratio between the second and the third planet and so on. Therefore, if you knew how long it takes for some of the planets to orbit around the Sun/star, you can calculate how long it takes for the other planets to orbit and can thus calculate their position in the planetary system. You can also calculate if a planet is ‘missing’ in the sequence.

    “We decided to use this method to calculate the potential planetary positions in 151 planetary systems, where the Kepler satellite had found between 3 and 6 planets. In 124 of the planetary systems, the Titius-Bode law fit with the position of the planets as good as or better than our own solar system. Using T-B’s law we tried to predict where there could be more planets further out in the planetary systems. But we only made calculations for planets where there is a good chance that you can see them with the Kepler satellite,” explains Steffen Kjær Jacobsen, PhD student in the research group Astrophysics and Planetary Science at the Niels Bohr Institute at the University of Copenhagen.

    In 27 of the 151 planetary systems, the planets that had been observed did not fit the T-B law at first glance. They then tried to place planets into the ‘pattern’ for where planets should be located. Then they added the planets that seemed to be missing between the already known planets and also added one extra planet in the system beyond the outermost known planet. In this way, they predicted a total of 228 planets in the 151 planetary systems.

    2
    The illustration shows the habitable zone for different types of stars. The distance to the habitable zone is dependent on how big and bright the star is. The green area is the habitable zone (HZ), where liquid water can exist on a planet’s surface. The red area is too hot for liquid water on the planetary surface and the blue area is too cold for liquid water on the planetary surface. (Credit: NASA, Kepler)

    “We then made a priority list with 77 planets in 40 planetary systems to focus on because they have a high probability of making a transit, so you can see them with Kepler. We have encouraged other researchers to look for these. If they are found, it is an indication that the theory stands up,” explains Steffen Kjær Jacobsen.

    Planets in the habitable zone

    Planets that orbit very close around a star are too scorching hot to have liquid water and life and planets that are far from the star would be too deep-frozen, but the intermediate habitable zone, where there is the potential for liquid water and life, is not a fixed distance. The habitable zone for a planetary system will be different from star to star, depending on how big and bright the star is.

    The researchers evaluated the number of planets in the habitable zone based on the extra planets that were added to the 151 planetary systems according to the Titius-Bode law. The result was 1-3 planets in the habitable zone for each planetary system.

    4
    Exoplanetary systems where the previously known planets are marked with blue dots, while the red dots show the planets predicted by the Titius-Bode law on the composition of planetary systems. 124 planetary systems in the survey – based on data from the Kepler satellite, fit with this formula.

    Out of the 151 planetary systems, they now made an additional check on 31 planetary systems where they had already found planets in the habitable zone or where only a single extra planet was needed to meet the requirements.

    “In these 31 planetary systems that were close to the habitable zone, our calculations showed that there was an average of two planets in the habitable zone. According to the statistics and the indications we have, a good share of the planets in the habitable zone will be solid planets where there might be liquid water and where life could exist,” explains Steffen Kjær Jacobsen.

    If you then take the calculations further out into space, it would mean that just in our galaxy, the Milky Way, there could be billions of stars with planets in the habitable zone, where there could be liquid water and where life could exist.

    He explains that what they now want to do is encourage other researchers to look at the Kepler data again for the 40 planetary systems that they have predicted should be well placed to be observed with the Kepler satellite.

    Out of the 151 planetary systems, they now made an additional check on 31 planetary systems where they had already found planets in the habitable zone or where only a single extra planet was needed to meet the requirements.

    “In these 31 planetary systems that were close to the habitable zone, our calculations showed that there was an average of two planets in the habitable zone. According to the statistics and the indications we have, a good share of the planets in the habitable zone will be solid planets where there might be liquid water and where life could exist,” explains Steffen Kjær Jacobsen.

    If you then take the calculations further out into space, it would mean that just in our galaxy, the Milky Way, there could be billions of stars with planets in the habitable zone, where there could be liquid water and where life could exist.

    He explains that what they now want to do is encourage other researchers to look at the Kepler data again for the 40 planetary systems that they have predicted should be well placed to be observed with the Kepler satellite.

    Article in Monthly Notices of the Royal Astronomical Society

    See the full article here.

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    Niels Bohr Institute Campus

    The Niels Bohr Institute (Danish: Niels Bohr Institutet) is a research institute of the University of Copenhagen. The research of the institute spans astronomy, geophysics, nanotechnology, particle physics, quantum mechanics and biophysics.

    The Institute was founded in 1921, as the Institute for Theoretical Physics of the University of Copenhagen, by the Danish theoretical physicist Niels Bohr, who had been on the staff of the University of Copenhagen since 1914, and who had been lobbying for its creation since his appointment as professor in 1916. On the 80th anniversary of Niels Bohr’s birth – October 7, 1965 – the Institute officially became The Niels Bohr Institute.[1] Much of its original funding came from the charitable foundation of the Carlsberg brewery, and later from the Rockefeller Foundation.[2]

    During the 1920s, and 1930s, the Institute was the center of the developing disciplines of atomic physics and quantum physics. Physicists from across Europe (and sometimes further abroad) often visited the Institute to confer with Bohr on new theories and discoveries. The Copenhagen interpretation of quantum mechanics is named after work done at the Institute during this time.

    On January 1, 1993 the institute was fused with the Astronomic Observatory, the Ørsted Laboratory and the Geophysical Institute. The new resulting institute retained the name Niels Bohr Institute.

     
  • richardmitnick 9:49 am on December 5, 2014 Permalink | Reply
    Tags: , , , , , , Habitable Zone   

    From Cornell: “Finding infant earths and potential life just got easier” 

    Cornell Bloc

    Cornell University

    Dec. 4, 2014
    Contact: Syl Kacapyr
    Phone: (607) 255-7701
    vpk6@cornell.edu

    Among the billions and billions of stars in the sky, where should astronomers look for infant Earths where life might develop? New research from Cornell University’s Institute for Pale Blue Dots shows where – and when – infant Earths are most likely to be found. The paper by research associate Ramses M. Ramirez and director Lisa Kaltenegger, The Habitable Zones of Pre-Main-Sequence Stars will be published in the Jan. 1, 2015, issue of Astrophysical Journal Letters.

    i

    m

    [Above from] Images and study: https://cornell.box.com/infantearths

    “The search for new, habitable worlds is one of the most exciting things human beings are doing today and finding infant Earths will add another fascinating piece to the puzzle of how ‘Pale Blue Dots’ work” says Kaltenegger, associate professor of astronomy in Cornell’s College of Arts and Sciences.

    The researchers found that on young worlds the Habitable Zone – the orbital region where water can be liquid on the surface of a planet and where signals of life in the atmosphere can be detected with telescopes – turns out to be located further away from the young stars these worlds orbit than previously thought.

    “This increased distance from their stars means these infant planets should be able to be seen early on by the next generation of ground-based telescopes,” says Ramirez. “They are easier to spot when the Habitable Zone is farther out, so we can catch them when their star is really young.”

    Moreover, say the researchers, since the pre-main sequence period for the coolest stars is long, up to 2.5 billion years, it’s possible that life could begin on a planet during its sun’s early phase and then that life could move to the planet’s subsurface (or underwater) as the star’s luminosity decreases.

    “In the search for planets like ours out there, we are certainly in for surprises. That’s what makes this search so exciting,” says Kaltenegger.

    To enable researchers to more easily find infant earths, the paper by Kaltenegger and Ramirez offers estimates for where one can find habitable infant Earths. As reference points, they also assess the maximum water loss for rocky planets that are at equivalent distances to Venus, Earth and Mars from our Sun.

    Ramirez and Kaltenegger also found that during the early period of a solar system’s development, planets that end up being in the Habitable Zone later on, when the star is older, initially can lose the equivalent of several hundred oceans of water or more if they orbit the coolest stars. However, even if a runaway greenhouse effect is triggered – when a planet absorbs more energy from the star than it can radiate back to space, resulting in a rapid evaporation of surface water – a planet could still become habitable if water is later delivered to the planet, after the runaway phase ends.

    “Our own planet gained additional water after this early runaway phase from a late, heavy bombardment of water-rich asteroids,” says Ramirez. “Planets at a distance corresponding to modern Earth or Venus orbiting these cool stars could be similarly replenished later on.”

    Ramirez and Kaltenegger’s research was supported by the Institute for Pale Blue Dots and the Simons Foundation.

    See the full article here.

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    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

     
  • richardmitnick 2:53 pm on August 7, 2014 Permalink | Reply
    Tags: , , , , , Habitable Zone   

    From Astrobiology Magazine: “Rotation of Planets Influences Habitability’ 

    Astrobiology Magazine

    Astrobiology Magazine

    Aug 7, 2014
    Amanda Doyle

    There are currently almost 2,000 extrasolar planets known to us, but most are inhospitable gas giants. Thanks to NASA’s Kepler mission, a handful of smaller, rockier planets have been discovered within the habitable zones of their stars that could provide a niche for alien life.

    NASA Kepler Telescope3
    NASA/Kepler

    Habitable planets Current Potential

    The habitable zone of a star is typically defined as the range from a star where temperatures would allow liquid water to exist on the surface of a planet. At the inner edge of this zone, the star’s blistering heat vaporizes the planet’s water into the atmosphere in a runaway greenhouse effect. At the outer edge of the habitable zone, temperatures are so cold that clouds of carbon dioxide form and the little solar energy that does arrive bounces off the clouds, turning the planet into a frozen wasteland.

    zones
    In astronomy, a habitable zone is a region of space around a star where conditions are favorable for life as it may be found on Earth. Planets and moons in these regions are the likeliest candidates to be habitable. Our sun has a temperature of about 5800K. For stars cooler than our sun (M dwarfs, also known as red dwarfs, at 3000-4000K) the region is closer in. For hotter stars (A dwarfs at 10,000K) the region is much farther out. Credit: NASA

    However, this concept is rather simple. In reality, many other factors come into play that could affect a planet’s habitability. New research has revealed that the rate at which a planet spins is instrumental in its ability to support life. Not only does rotation control the length of day and night, it can also tug on the winds that blow through the atmosphere and ultimately influence cloud formation.The paper has been accepted to Astrophysical Journal Letters and a preprint is available online at Arxiv.

    zones
    The traditional habitable zone is outlined in blue, showing that Venus is currently well outside of the zone. However, for slowly rotating planets under the right atmospheric conditions, this zone will be extended so that it is much closer to the star. Image Credit: NASA

    Air circulation and rotation rates

    The radiation that the Earth receives from the Sun is strongest at the equator. The air in this region is heated until it rises up through the atmosphere and heads towards the poles of the planet where it subsequently cools. This cool air falls through the atmosphere and is ushered back towards the equator. This process of atmospheric circulation is known as a Hadley cell.

    If a planet is rotating rapidly, the Hadley cells are confined to low latitudes and they are arranged into different bands that encircle the planet. Clouds become prominent at tropical regions, which are important for reflecting a proportion of the light back into space. However, for a planet in a tighter orbit around its star, the radiation received from the star is much more extreme.

    This will decrease the temperature difference between the equator and the poles and ultimately weaken the Hadley cells. The result is fewer clouds at the tropical regions available to protect the planet from the intense heat, and the planet becomes uninhabitable.

    If, on the other hand, the planet is a slow rotator, then the Hadley cells can expand to encompass the entire world. This is because the atmospheric circulation is enhanced due to the difference in temperature between the day and night side of the planet. The days and nights are very long, so that the half of the planet that is bathed in light from the star has plenty of time to soak up the Sun. In contrast, the night side of the planet is much cooler, as it has been shaded from the star for some time.

    hadley
    A Hadley cell is created when warm air rises at the equator and moves to the poles. The air then cools, sinks, and heads back towards the equator. Credit: Lyndon State College Atmospheric Sciences

    cell
    Vertical velocity at 500 hPa, July average in units of pascals per second. Ascent (negative values) is concentrated close to the solar equator; descent (positive values) is more diffuse.

    This difference in temperature is large enough to cause the warm air from the day side to flow to the night side, in a similar manner as opening a door on a cold day results in warm air fleeing from a room. The increased circulation causes more clouds to build up over the substellar point, which is the point on the planet where the star would be seen directly overhead, and where radiation is most intense. The clouds over the substellar point then create a shield for the ground below as most of the harmful radiation is reflected away.

    The high albedo clouds can allow a planet to remain habitable even at levels of radiation that were previously thought to be too high, so that the inner edge of the habitable zone is pushed much closer to the star.

    “Rotation can have a huge effect, and lots of planets that we previously thought were definitely not habitable now can be considered as candidates,” says Dorian Abbot of the University of Chicago, and a co-author on the paper.

    Earth in Venus’ orbit

    The study used computer simulations to show that a slowly rotating planet with the same atmospheric composition, mass, and radius of the Earth could potentially be habitable even at Venus’ distance from the Sun. Under the typical boundaries of a habitable zone, Venus is situated closer to the Sun than the inner edge of the zone. In the study, the simulated planet received almost twice as much radiation as the actual Earth did, and yet the surface temperature was cool enough for life to thrive due to the shielding clouds.

    Despite the slow rotation, Venus itself is actually a scorching hot planet with a atmosphere so dense that it would crush a person on the surface in seconds. This goes to show that just because a planet is rotating slowly does not automatically mean that it is habitable, rather it has the potential to be habitable if the right conditions exist.

    map
    A runaway greenhouse effect occurs when the stellar radiation becomes trapped in the atmosphere, the planet warms up, and the oceans evaporate. Credit: ESA

    For instance, it is possible that Venus used to spin much faster, giving shorter days than it has now. Venus’ atmosphere is enriched with deuterium, which indicates that an ocean might have once been present. Such a rapid rotation rate on a planet so close to the Sun would have led to a runaway greenhouse effect and the loss of the oceans. By the time the rotation of the planet slowed to its current rate the damage was irreversible.

    Finding the slow rotators

    While it is difficult to measure planetary rotation rates, future observations by the James Webb Space Telescope might be able to measure rotation if the right conditions were present. The James Webb Space Telescope is an infrared telescope due to launch in 2018, and it is capable of measuring the level of heat emitted by exoplanets.

    NASA Webb Telescope
    NASA/Webb

    The telescope would be able to measure the heat emitted from any high albedo clouds that are formed over the substellar point. An unusually low temperature at what is expected to be the hottest location on the planet could indicate that the planet is a potentially habitable slow rotator.

    “From space, Earth looks like it is between -70 and -50 degrees Celsius over large regions of the western tropical Pacific because of high clouds there, even though the surface is more like 30 degrees Celsius,” says Abbot.

    planet
    A slowly rotating planet is not guaranteed to be habitable, as is evident when looking at the inhospitable Venus. Credit: NASA/JPL/Caltech

    It is also known than many planets that orbit cool M dwarf stars are either tidally locked, meaning that the same side of the planet faces the star all the time, or they are slow rotators.

    This research emphasises the importance of looking beyond the traditional habitable zone for planets that could host life, and it turns out that planets we once thought were too hot might actually be just right for life.

    See the full article here.

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