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  • richardmitnick 6:38 am on August 21, 2020 Permalink | Reply
    Tags: "The Impact of Land on an Ocean World’s Habitability", , , , , , , Proxima Centauri b   

    From AAS NOVA: “The Impact of Land on an Ocean World’s Habitability” 


    From AAS NOVA

    19 August 2020
    Susanna Kohler

    Artist’s illustration of the view from a water-covered exoplanet. [David A. Aguilar/CfA]

    Which habitable-zone planets can actually support life? A recent study uses a nearby planet — Proxima Centauri b — to examine how the presence and size of a land mass impacts the habitability of an ocean world.

    A Target for Potential Life

    In our galaxy, roughly 80% of stars are cool, dim M dwarfs — and one in six of these is thought to host an Earth-sized planet in its habitable zone. But being in a star’s habitable zone doesn’t guarantee a planet’s habitability! M-dwarf habitable-zone planets present valuable targets for observations and models to better understand which of these worlds can support life.

    Most habitable-zone planets around M dwarfs are likely tidally locked: one side of the planet experiences constant day; the other, constant night. Nominally, this would cause only one region of the planet to be heated — the point closest to the star — and the rest of the planet would be locked in darkness and ice. But if the planet is covered in a dynamic ocean, heat can be transported around the planet via ocean currents, affecting the potential habitability of the world.

    Do continents get in the way of this heat transport? And how do land masses affect the circulation of nutrients in the ocean, critical for sustaining ocean-based photosynthetic life? A new study explores the particular case of a tidally locked ocean planet with a continent — and it uses the nearby Proxima Centauri b as a model to do so.

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    Modeling a Nearby World

    At just 4.2 light-years away, Proxima b is the closest known exoplanet and presents an excellent target for future follow-up observations. This habitable-zone M-dwarf planet is probably tidally locked, and estimates of its density have led to speculation that the planet is covered in a large ocean.

    Possible depiction of Proxima Centauri b. Credit: ESO M. Kornmesser

    Ocean heat transport in the authors’ models for varying continent size; from top to bottom, continents (noted as the white rectangle in the figure) cover 0%, 4%, 22%, and 39% of the planet surface. Continents at the substellar point inhibit ocean heat transport. [Adapted from Salazar et al. 2020]

    In a recent publication led by Andrea Salazar, a team of scientists from the University of Chicago has used a general circulation model to explore how heat and nutrients are transported on an ocean-covered, tidally locked Proxima b — both with and without the presence of a land mass in the ocean.

    Salazar and collaborators placed a continent at the point on the planet closest to the star — because land masses are thought to migrate to the planet–star axis over time — and tested a range of continent sizes, covering from 0 to 40% of the total planet surface.

    Promising Outcomes

    The authors find that the presence of a continent decreases how efficiently heat and nutrients are transported from the dayside to the nightside of the planet — the larger the continent, the less efficient the transport. Nonetheless, in all cases, an ice-free ocean is maintained on the planetary dayside, and nutrients are circulated and delivered to the layer of the ocean where photosynthesis is viable, providing ideal conditions for photosynthetic marine life.

    This work suggests that the presence of both a dynamic ocean and continents won’t decrease the habitability prospects of tidally locked planets like Proxima b. This is good news as we prepare for future observations with the James Webb Space Telescope, which may provide further insight into this nearby, potentially habitable world and others like it.


    “The Effect of Substellar Continent Size on Ocean Dynamics of Proxima Centauri b,” Andrea M. Salazar et al 2020 ApJL 896 L16.

    See the full article here .


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    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
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  • richardmitnick 2:24 pm on February 1, 2020 Permalink | Reply
    Tags: , , , Centauri star system, , , National Institute of Astrophysics, Possible Proxima Centauri C, Proxima Centauri b   

    From National Institute of Astrophysics via EarthSky: “Is there a 2nd planet orbiting Proxima Centauri?” 

    From National Institute of Astrophysics




    January 27, 2020
    Paul Scott Anderson

    Proxima Centauri, the closest star to our sun, may have a second planet, according to researchers from the National Institute of Astrophysics.

    Centauris Alpha Beta Proxima , 27 February 2012. Skatebiker

    If confirmed, it would be an ideal candidate for direct imaging by new upcoming space telescopes.

    Artist’s concept of Proxima Centauri b, an Earth-sized exoplanet orbiting the nearest star to our sun, Proxima Centauri. Now researchers think there is a second, larger planet also orbiting the star. Image via ESO/ M. Kornmesser/

    In 2016, astronomers announced the discovery of an exoplanet orbiting the closest star to our solar system, Proxima Centauri . Exciting, since the planet appeared to be close to the same size as Earth and not too far away, cosmically-speaking, at 4.2 light-years. Could there be other planets in this nearby system? On January 15, 2020, another research team published its evidence for a second, larger planet orbiting Proxima Centauri. At this point, this second object is still considered a candidate. It is not confirmed. But researchers do make a compelling case for its existence.

    The potential discovery was announced by Mario Damasso of the National Institute of Astrophysics and his colleagues on January 15. The new peer-reviewed paper appeared in Science Advances on the same day.

    The planet – dubbed Proxima Centauri c – is a fair bit larger than the first planet, Proxima Centauri b, and is about six times more massive than Earth. This would make it a super-Earth, planets that are significantly larger and more massive than Earth but smaller and less massive than Neptune. It is estimated to orbit its star every 5.2 years. Proxima Centauri b, by comparison, is only about 1.3 times Earth’s mass.

    Even though Proxima Centauri is the closest star, part of the Alpha Centauri three-star system, it has been difficult to detect planets orbiting it. That’s because most exoplanets discovered so far have been glimpsed via the transit method; that is, they’re detected because they lie edge-on to our line-of-sight to their host stars, and astronomers can detect a minute dip in the host star’s light when the planet crosses in front of it.

    Planet transit. NASA/Ames

    No such dip in brightness has been seen for Proxima Centauri.

    Instead, to find this star’s planets, astronomers have had to use a second planet-hunting technique, called the radial velocity method.

    Radial velocity Image via SuperWasp http:// http://www.superwasp.org/exoplanets.htm

    Radial Velocity Method-Las Cumbres Observatory

    Radial velocity refers to a slight wobble in the star’s motion as seen from Earth, caused by the gravity of unseen planets tugging on it. This is how Proxima Centauri b was found, and now, seemingly, Proxima Centauri c.

    Two European Southern Observatory (ESO) telescope instruments, the High Accuracy Radial velocity Planet Searcher (HARPS) and the Ultraviolet and Visual Echelle Spectrograph (UVES), were used to obtain the data from Proxima Centauri.

    ESO 3.6m telescope & HARPS at Cerro LaSilla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO/HARPS at La Silla

    UVES spectrograph mounted on the VLT at the Nasmyth B focus of UT2

    2009 ESO VLTI Interferometer image, Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level, • ANTU (UT1; The Sun ),
    KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).

    Damasso and his team analyzed the star’s light spectrum data, going back 17.5 years, to see if a previously reported light spectrum signal really was from a second planet. If the spectrum oscillates between the red and blue radial velocity, that typically means the star is moving slightly closer to and then farther away from Earth, due to the gravitational pull of a planet or planets. The researchers did find such a signal, occurring over a 1,900-day period. That would mean it is unlikely to be due only to other cyclical shifts in the star’s magnetic field. It would be more consistent with a second planet orbiting the star.


    So, could either of these planets be habitable?

    At this point, we just don’t know enough about them to answer that question. Proxima Centauri b is almost the same size as Earth, and is thought to have similar temperatures, but it orbits very close to its star, which is a red dwarf. Red dwarfs are known for being very active, emitting powerful solar flares. The radiation from those flares could strip away the atmosphere of any close-in planets. Proxima Centauri c is farther out, but may be too cold for life as we know it. It also may be more like Neptune, with a deep gaseous atmosphere and no real solid surface, rather than a super-Earth, which is rocky like Earth, but larger. We just don’t know yet.

    Another exciting aspect of Proxima Centauri c, however, is that it is far enough from the glare of its star that it should be able to be photographed directly by upcoming space telescopes. So far, only a handful of planets that are much larger than this have been successfully photographed, and even then, they are still just blobs of light.

    If scientists can learn more about both Proxima Centauri c and b, including direct imaging for at least c (b would be a lot more difficult), then that should give them a better idea of what both Earth-sized and super-Earth exoplanets are actually like, in particular ones that orbit red dwarf stars. That would then help them figure how many could be potentially habitable, and what conditions would make that possible, an exciting endeavor.

    See the full article here .

    Please help promote STEM in your local schools.

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