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  • richardmitnick 10:33 am on March 20, 2017 Permalink | Reply
    Tags: , , , , , , , , Planet transits, Sardines in Space   

    From astrobites: “Sardines in Space: The Intensely Densely-Packed Planets Orbiting Kepler-11” 

    Astrobites bloc


    Title: A Closely-Packed System of Low-Mass, Low-Density Planets Transiting Kepler-11
    Authors: Jack J. Lissauer, Daniel C. Fabrycky, Eric B. Ford, et al.
    Lead Author’s Institution: NASA Ames Research Center, Moffett Field, CA, 94035, USA

    Status: Published in Nature 2011 [open access]

    The dawn of the Kepler Space Telescope data has unearthed a treasure trove of new and unusual celestial objects. Among these new discoveries is the planetary system Kepler-11. The system contains six transiting planets that are packed incredibly close around the Sun-like star, much like sardines are packed very closely in cans. The first five of these planets fall within the orbit of Mercury, and the sixth one falls well within the orbit of Venus. Few systems like this have been discovered; most planetary systems have a much larger separation between the planets, yet this system has its planets arranged in an extremely packed, yet extraordinarily still stable, way.

    Figure 1: This figure from the NASA website is a visual representation of the Kepler-11 system, overlaid with the orbits of Mercury and Venus.

    When a single planet orbits a star, its period follows Kepler’s Laws to a tee; however, when other planets are introduced in the system, the orbiting bodies tend to perturb each other’s orbits. Their periods differ slightly according to the gravitational perturbations, and this variation is called a transit timing variation (TTV). Since Kepler-11 has five planets orbiting in extreme proximity to one another, it is the perfect illustration of measurements from transit-timing variations.

    Planet transit. NASA/Ames

    The photometric Kepler data marked the discovery of this system. The transits for each of the planets appeared separately in the light curve of the system. The light curve is just a measurement of the brightness of the star over time, so when a planet passes in front of the star, the brightness decreases, causing the dip in the light curve. The shape varies with each planet based on differences in size of the planet and orbital radius. From this data, it is possible to measure the radius of the transiting planet. This team followed up their photometric data with spectroscopic analysis from the Keck I telescope. This additional data allowed for the precise measurements of transit-timing variations, which yielded mass measurements for the inner five planets.

    For the first five planets, the TTVs were successfully measured, and with this information, the research team found the densities of the inner five planets, which yielded a surprising result. These planets, despite being densely packed, are not made of very dense material. Kepler-11b is both closest to the Sun and densest, but only with an overall density of 3.31 g/cm3. For comparison, Earth has an overall density of about 5.5 g/cm3. The densities of the planets orbiting Kepler-11 are depicted in Figure 2.

    Figure 2: This shows the mass versus radius of the planets in the Kepler-11 system. The planets orbiting Kepler-11 are represented by the filled in circles. The other marking on the graph indicate planets in our solar system, shown for comparison. Figure 5 from today’s paper.

    While transit timing variations worked like a charm for the inner five planets, the sixth planet (Kepler-11g) was too distant from the others for this method to work well, so to confirm this planet, another method was employed. This team used several simulations to rule out alternate scenarios, which include chance alignment of the Kepler-11 system with and eclipsing star or with another star-planet system. This analysis successfully confirmed Kepler-11g , but because no TTVs could be measured for this particular planet, its mass and radius remain unknown.

    Even though this system has been more closely studied than most, the measurements have raised nearly as many questions as they have answered. The inner five have small inclinations and eccentricities, which implies some planetary migration process. However, since the periods of these planets are not in resonance, slow and convergent migration theories—which would naturally force the planets into resonant orbits—seem unlikely to be at play in this system. Formation of such a system is still a bit of a mystery. After all, such low-density planets are unusual and do not completely fit within the current understanding of planet formation.

    Kepler-11 continues to be one of the more intriguing planetary systems discovered, and its formation is not fully understood. Even though this system has been more closely studied than most, the measurements have raised nearly as many questions as they have answered. Systems like this extend our understanding of astrophysics, perhaps in a bit of an unexpected way; these closely packed planets have so much more to teach us about their system formation.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

  • richardmitnick 1:08 pm on December 22, 2016 Permalink | Reply
    Tags: , , LAMOST telescope, , Planet transits   

    From Kavli: “Revealing the Orbital Shape Distributions of Exoplanets with China’s LAMOST Telescope” 


    The Kavli Foundation


    Using data from China’s LAMOST telescope, a team of astronomers have derived how the orbital shapes distribute for extrasolar planets. The work is recently published in the journal Proceedings of the National Academy of Sciences of the United States of America” (PNAS). The lead authors are Prof. Jiwei Xie from Nanjing University and Prof. Subo Dong, a faculty member of the Kavli Institute of Astronomy & Astrophysics (KIAA) at Peking University.

    LAMOST telescope located in Xinglong Station, Hebei Province, China
    The Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST) telescope in Hebei, China. It is the most efficient spectroscopy machine in the world.

    Until two decades ago, the only planetary system known to mankind was our own solar system. Most planets in the solar system revolve around the Sun on nearly circular orbits, and their orbits are almost on the same plane within about 3 degrees on average (i.e., the averaged inclination angle is about 3 degrees). Astronomers use the parameter called eccentricity to describe the shape of a planetary orbit. Eccentricity takes the value between 0 and 1, and the larger the eccentricity, the more an orbit deviates from circular. The averaged eccentricity of solar system planets is merely 0.06. Hundreds of years ago, motivated by circular and coplanar planetary orbits, Kant and Laplace hypothesized that planets should form in disks, and this theory has developed into the “standard model” on how planets form.

    In 1995, astronomers discovered the first exoplanet around a Sun-like star 51 Pegasi with a technique called Radial Velocity, and this discovery started an exciting era of exoplanet exploration. At the beginning of the 21st Century, people had discovered hundreds of exoplanets with the Radial Velocity technique, and most of them are giant planets comparable in mass with the Jupiter. These Jovian planets are relatively rare, found around approximately one tenth of stars studied by the Radial Velocity technique. The shapes of their orbits were a big surprise: a large fraction of them are on highly eccentric orbits, and all the giant planets found by Radial Velocity have a mean eccentricity of about 0.3. This finding challenges the “standard model” of planet formation and raises a long-standing puzzle for astronomers – are the nearly circular and coplanar planetary orbits in the solar system common or exceptional?

    The Kepler satellite launched by NASA in 2009 has discovered thousands of exoplanets by monitoring tiny dimming in the brightness of stars when their planets happen to cross in the front (called “transit”).

    Planet transit. NASA/Ames
    Planet transit. NASA/Ames

    Many of the planets discovered by Kepler have sizes comparable to that of the Earth. Kepler’s revolutionary discoveries show that Earth-size planets are prevalent in our galaxy. However, data from the Kepler satellite alone cannot be used to measure the shape of a transiting exoplanet’s orbit. To do so, one way is to use the size of the planet host star as a “ruler” to measure against the length of the planet transit, while implementing this method needs precise information on the host star parameters such as size and mass. This method has previously been applied to the host stars characterized with the asteroseismology technique but the sample is limited to a relatively small number of stars with high-frequency, exquisite brightness information required by asteroseismology.

    With its innovative design, the LAMOST telescope in China can observe spectra of thousands of celestial objects simultaneously within its large field of view, and it is currently the most efficient spectroscopy machine in the world (Figure 1). In recent years, LAMOST has obtained tens of thousands of stellar spectra in the sky region where the Kepler satellite monitors planet transits, and they include many hundreds of stars hosting transiting exoplanets. By comparing with other methods such as asteroseismology, the research team finds that, high-accuracy characterization of stellar parameters can be reliably obtained from LAMOST spectra, and they can subsequently be used to measure the the orbital shape distributions of Kepler exoplanets.

    They analyze a large sample of about 700 exoplanets whose host stars have LAMOST spectra, and with the LAMOST stellar parameters and Kepler transit data, they measure the eccentricity and inclination angle distributions. They find that about 80% of the analyzed planet orbits are nearly circular (averaged eccentricity less than 0.1) like those in the solar system, and only about 20% of the planets are on relatively eccentric orbits that significantly deviate from circular (average eccentricity large than 0.3). They also find that the average eccentricity and inclination angle for the Kepler systems with multiple planets fit into the pattern of the solar system objects (Figure 2).

    Therefore, circular orbits are not exceptional for planetary systems, and the orbital shapes of most planets inside and outside the solar system appear to distribute in a similar fashion. This implies that the formation and evolution processes leading to the distributions of the orbital shapes of the solar system may be common in the Galaxy.

    See the full article here .

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    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

    • vegetarian dash diet meal pla 1:39 pm on December 22, 2016 Permalink | Reply

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      • richardmitnick 2:27 pm on December 22, 2016 Permalink | Reply

        Thanks, I am just glad my work is appreciated. I do it for the love of bringing this material which the press ignores to the public. I have about 800 readers in North America , Europe, East Asia, Africa, and the Middle East. No contests.


  • richardmitnick 3:48 pm on March 1, 2016 Permalink | Reply
    Tags: , , ET Search: Look for the Aliens Looking for Earth, , Planet transits,   

    From SA- “ET Search: Look for the Aliens Looking for Earth” 

    Scientific American

    Scientific American

    March 1, 2016
    Alexandra Witze

    Planet transit
    Light Curve of a Planet Transiting Its Star. NASA/Kepler

    By watching how the light dims as a planet orbits in front of its parent star, NASA’s Kepler spacecraft has discovered more than 1,000 worlds since its launch in 2009.

    NASA Kepler Telescope

    Now, astronomers are flipping that idea on its head in the hope of finding and talking to alien civilizations.

    Scientists searching for extraterrestrial intelligence should target exoplanets from which Earth can be seen passing in front of the Sun, says René Heller, an astronomer at the Max Planck Institute for Solar System Research in Göttingen, Germany. By studying these eclipses, known as transits, civilizations on those planets could see that Earth has an atmosphere that has been chemically altered by life. “They have a higher motivation to contact us, because they have a better means to identify us as an inhabited planet,” Heller says.

    About 10,000 stars that could harbour such planets should exist within about 1,000 parsecs (3,260 light years) of Earth, Heller and Ralph Pudritz, an astronomer at McMaster University in Hamilton, Canada, report in the April issue of Astrobiology. They argue that future searches for signals from aliens, such as the US$100-million Breakthrough Listen project, should focus on these stars, which fall in a band of space formed by projecting the plane of the Solar System out into the cosmos.

    Breakthough Listen
    Breakthrough Listen Project

    Breakthrough Listen currently has no plans to search this region; it is targeting both the centre and the plane of our galaxy, which is not the same as the plane of the Solar System, as well as stars and galaxies across other parts of the sky.

    The idea of searching for worlds whose inhabitants could see Earth transits dates back to at least the 1980s. But astronomers can now update and revise their ideas thanks to what they have learned from Kepler, Heller says.

    In the zone

    The zone of space in which Earth transits would be visible is a relatively narrow strip. It gets even narrower if restricted to geometries in which the Earth passes less than half a solar radius from the Sun’s centre—which gives a transit that should be easily visible, if aliens have a tool similar to Kepler.

    Heller and Pudritz went through a catalogue of stars compiled using data from the Hipparcos satellite and found 82 Sun-like stars in this zone that are within 1,000 parsecs of Earth. Because not all of the stars in this region of space have been discovered, Heller and Pudritz extrapolated the number of known stars to the number that probably exists and came up with roughly 10,000 candidate stars. If these stars have planets, and if the planets have intelligent life forms, they could have long ago spotted the blink of an Earth transit and begun beaming signals towards us, Heller says.

    One of the closest known stars in the zone is Van Maanen’s Star, only 4 parsecs away. It is a white dwarf star, the remains of a stellar explosion, and may or may not have planets orbiting it. But if they did exist, they would provide a ringside seat for watching Earth. “If any civilization survived the death of their star, they could see us transiting our own Sun,” says Heller.

    For four days in 2010, the Allen Telescope Array in northern California looked for signals coming from the region of space directly opposite the Sun, says Seth Shostak, an astronomer at the SETI (search for extraterrestrial intelligence) Institute in Mountain View, California.

    Allen Telescope Array
    Allen Telescope Array

    The goal was to test whether extraterrestrials might be timing any transmissions to reach Earth just as they see it transiting the Sun. No signs of aliens were found, and no follow-up is planned.

    “Unfortunately, there are more good ideas for SETI experiments than there are SETI experimenters to act on them,” says Andrew Siemion, an astronomer at the University of California, Berkeley.

    In the next five or so years, the European Space Agency’s Gaia satellite is likely to discover most of the nearby stars in the Earth transit zone, Heller says.

    ESA Gaia satellite

    Until then, he and Pudritz plan to use data from K2, the Kepler follow-on mission, to hunt directly for planets in the zone—and to look for aliens who might be looking for us.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

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