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  • richardmitnick 4:42 pm on March 18, 2016 Permalink | Reply
    Tags: , , , SFSU   

    From SFSU: “Most eccentric planet known flashes astronomers with reflected light” 

    SFSU bloc

    San Fransisco State University

    March 16, 2016
    University Communications

    An artist's rendering shows the planet HD 20782, the most eccentric planet ever known. Credit NASA
    An artist’s rendering shows the planet HD 20782, the most eccentric planet ever known. Credit NASA

    Led by SF State astronomer Stephen Kane, a team of researchers has spotted an [exoplanet] about 117 light-years from earth that boasts the most eccentric orbit yet seen.

    What’s more, Kane and his colleagues were able to detect a signal of reflected light from the planet known as HD 20782* — a “flash” of starlight bouncing off the eccentric planet’s atmosphere as it made its closest orbital approach to its star. The discovery was announced online Feb. 28 in The Astrophysical Journal.

    In this case, “eccentric” doesn’t refer to a state of mind, but instead describes how elliptical a planet’s orbit is around its star. While the planets in our solar system have nearly circular orbits, astronomers have discovered several extrasolar planets with highly elliptical or eccentric orbits.

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    This graphic shows the orbit of the planet HD 20782 relative to the inner planets of our solar system. HD 20782’s orbit more closely resembles that of a comet, making it the most eccentric planet ever known. No image credit.

    HD 20782 has the most eccentric orbit known, measured at an eccentricity of .96. This means that the planet moves in a nearly flattened ellipse, traveling a long path far from its star and then making a fast and furious slingshot around the star at its closest approach.

    HD 20782 offers “a particularly lucrative observing opportunity” for studying the planetary atmosphere of an eccentric-orbit planet — a type not seen in our own solar system, the scientists say in the journal article. By studying the reflected light from HD 20782, astronomers may learn more about the structure and composition of a planetary atmosphere that can withstand a brief but blistering exposure to its star.

    At the furthest point in its orbit, the planet is separated from its star by 2.5 times the distance between the sun and Earth. At its closest approach, it ventures as close as .06 of that same Earth-sun distance — much closer than Mercury orbits the sun, said Kane, an assistant professor of physics and astronomy. “It’s around the mass of Jupiter, but it’s swinging around its star like it’s a comet.”

    An earlier observation of HD 20782 suggested that the planet might have an extremely eccentric orbit. Kane and his colleagues were able to confirm its extreme eccentricity and the rest of its orbital parameters as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS), a project led by Kane to detect extrasolar planets as they pass in front of their stars.

    Using these new parameters to time their observations, the scientists also used a satellite-based telescope to collect light data from the planet as it orbited closest to its star. They were able to detect a change in brightness that appears to be a signal of reflected light bouncing off the planet’s atmosphere.

    CSA MOST
    CSA/MOST

    The reflected light could tell researchers more about how the atmosphere of a planet like HD 20782 responds when it spends most of its time far away from its star, “but then has a very close approach where it’s flash-heated by the star,” Kane said.

    The percentage of light reflected from a planet, or how bright it appears in the sky, is determined in part by the composition of its atmosphere. Planets shrouded in clouds full of icy particles, like Venus and Jupiter, for instance, are very reflective. But if a planet like Jupiter were to move too close to the sun, the heat would remove the icy material in its clouds.

    In some of the extrasolar, Jupiter-sized planets that tread short, circular orbits, Kane explained, this phenomenon does appear to strip the atmospheres of reflective particles, making the planets appear “dark.” But in the case of HD 20782, “the atmosphere of the planet doesn’t have a chance to respond,” he said. “The time it takes to swing around the star is so quick that there isn’t time to remove all the icy materials that make the atmosphere so reflective.”

    Astronomers can’t determine the exact makeup of HD 20782’s atmosphere yet, but this newest observation does suggest that it might have an atmosphere with Jupiter-like, highly reflective cloud cover.

    Extrasolar planets like HD 20782 contain a wealth of questions for astronomers, Kane said. “When we see a planet like this that is in an eccentric orbit, it can be really hard to try and explain how it got that way,” he explained. “It’s kind of like looking at a murder scene, like those people who examine blood spatter patterns on the walls. You know something bad has happened, but you need to figure out what it was that caused it.”

    There are few possible “suspects” in the case of HD 20782, Kane noted. It could be that there was originally more than one planet in the system, and one planet developed an unstable orbit that brought the two planets too close together. This collision or near-collision might have ejected one planet from the system entirely and pushed HD 20782 on its eccentric path. The planet is in a binary star system, so it might also be the case that the second star in the binary made a close approach that threw HD 20782 off a more circular orbit.

    Kane is a member of the science team for two upcoming satellite missions — NASA’s Transiting Exoplanet Survey Satellite (TESS) and the European Space Agency’s Characterizing ExOPLanet Satellite (CHEOPS) — that will have HD 20782 in their sights after they launch in 2018.

    NASA/TESS
    NASA/TESS

    ESA/CHEOPS
    ESA/CHEOPS

    Evidence for reflected light from the most eccentric exoplanet known by Stephen R. Kane, Robert A. Wittenmyer (University of New South Wales), Natalie R. Hinkel (Arizona State University), Arpita Roy and Suvrath Mahadevan (Pennsylvania State University), Diana Dragomir (Las Cumbres Observatory Global Telescope Network), Jaymie M. Matthews (University of British Columbia), Gregory W. Henry (Tennessee State University), Abhijit Chakraborty (Physical Research Laboratory, Navrangpura), Tabetha S. Boyajian (Yale University), Jason T. Wright (Pennsylvania State University), David R. Ciardi (Caltech), Debra A. Fischer (Yale University), R. Paul Butler (Carnegie Institution of Washington), C.G. Tinney (University of New South Wales), Brad D. Carter (University of Southern Queensland), Hugh R.A. Jones (University of Hertfordshire), Jeremy Bailey (University of New South Wales) and Simon J. O’Toole (Australian Astronomical Observatory) was published online on Feb. 28.

    • This is the designation of the star around which this planet orbits.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    SFSU Campus

    San Francisco State University (commonly referred to as San Francisco State, SF State and SFSU) is a public comprehensive university located in San Francisco, California, United States. As part of the 23-campus California State University system, the university offers 118 different Bachelor’s degrees, 94 Master’s degrees, 5 Doctoral degrees including two Doctor of Education, a Doctor of Physical Therapy, a Ph.D in Education and Doctor of Physical Therapy Science, along with 26 teaching credentials among six academic colleges.

     
  • richardmitnick 8:45 am on May 7, 2015 Permalink | Reply
    Tags: , , SFSU,   

    From SFSU: Venus 

    SFSU bloc

    San Fransisco State University

    Why is Venus interesting?

    Venus is often referred to as Earth’s “sister planet”. This is because it is relatively close and is of similar size and mass as the Earth. It also has a substantial cloudy atmosphere which is effective at reflecting sunlight, giving it a bright appearance in our morning and evening skies. Any similarities to Earth end there. Venus has a mean surface temperature of 462°C (863°F), the result of a runaway greenhouse in its primarily carbon dioxide atmosphere. With a surface atmospheric pressure 92 times that on Earth and clouds of sulfuric acid, Venus can be aptly described as the epitome of uninhabitable.

    How is Venus related to the search for habitable planets?

    The search for exoplanets is largely motivated by answering the question: Is our solar system common? Venus and Earth formed under very similar conditions and probably had water delivered to their surfaces in the same way. However, at some point in their histories, the evolution of their surfaces and atmospheres diverged dramatically! To understand the history of the Earth, we must also understand the tenuous gap that separates the Earth from a runway greenhouse, such as that which exists on Venus. That understanding will come from determining the frequency of Venus-like planets as well as possible habitable planets like the Earth.

    Could we mistake a “Venus” for an “Earth”?

    The main method that is currently used to detect terrestrial-size planets is the transit method, mostly using data from NASA’s Kepler telescope.

    NASA Kepler Telescope
    Kepler

    The main property of an exoplanet we measure using these data is the size of the exoplanet. Since Venus and Earth are approximately the same size (Venus is only 5% smaller), we cannot distinguish between Venus and Earth based solely on size. However, we do know that Venus receives almost twice the amount of energy from the Sun than the Earth does. We can use this information to define a new region where we can hunt for potential analogs to the Venus in our solar system.

    1

    What is the “Venus Zone”?

    In the same way that the “Habitable Zone” is the region around a star where a planet similar to Earth could have liquid water on the surface, the Venus Zone is the region around a star where the atmosphere of a planet like Earth would likely be pushed into a runaway greenhouse producing surface conditions similar to those found on Venus. The below figure shows the Venus Zone (red) and Habitable Zone (blue) for stars of different temperatures. The outer boundary of the Venus Zone is the “Runaway Greenhouse” line which is calculated using climate models of Earth’s atmosphere. The inner boundary (red dashed line) is estimated based on where the stellar radiation from the star would cause the atmosphere of the planet to erode and disappear relatively quickly. The pictures of Venus shown in this region represent planet candidates detected by NASA’s Kepler space telescope.

    3

    How common are Venus-type planets?

    Our analysis of Kepler data detected 43 planets in their star’s Venus Zone. These planets have sizes that are between 50% and 140% the size of the Earth. Using all of the available Kepler data and our knowledge of how many stars have planets, we estimate that approximately 32% of small low-mass stars have terrestrial planets that are potentially like Venus. For stars like our Sun, this number rises to 45%. This is the first estimate for how common our sister-planet is in the universe.

    How can we know for certain if these planets are like Venus?

    Unfortunately it is presently beyond our reach to know for sure if indeed these planets have a runaway greenhouse type of atmosphere. That will require a detailed spectroscopic analysis of the atmospheres to determine the molecular abundances present, such as the dominance of the carbon dioxide spectral lines that we see for Venus’s atmosphere. The transit detection method is far more sensitive to short period-planets than long-period planets, meaning that we can detect a Venus-analog much easier than an Earth-analog. Upcoming space telescopes, such as the Transiting Exoplanet Survey Satellite (TESS) will be efficient Venus detectors in the same way that Kepler is. However, the host stars of planets detected via TESS will be significantly brighter than those found with Kepler, enabling detailed follow-up observations with the James Webb Space Telescope (JWST) due to be launched in 2018. Thus there is a strong chance that we will have our first confirmation of a runaway greenhouse atmosphere on an exoplanet within the next 10 years.

    NASA TESS
    TESS

    NASA James Webb Telescope
    Webb

    Where can I find the scientific publication and related data?

    The science paper On the Frequency of Potential Venus Analogs from Kepler Data has been accepted for publication in the Astrophysical Journal Letters and can be found here.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    SFSU Campus

    San Francisco State University (commonly referred to as San Francisco State, SF State and SFSU) is a public comprehensive university located in San Francisco, California, United States. As part of the 23-campus California State University system, the university offers 118 different Bachelor’s degrees, 94 Master’s degrees, 5 Doctoral degrees including two Doctor of Education, a Doctor of Physical Therapy, a Ph.D in Education and Doctor of Physical Therapy Science, along with 26 teaching credentials among six academic colleges.

     
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