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posted by charon on Thursday May 18 2017, @03:34AM   Printer-friendly
from the just-like-earth dept.

[N]ew models increasingly suggest that the closest Earth-like planet to our solar system could be habitable. Researchers first started playing a bit of "fantasy exoplanet" with the rocky world—dubbed Proxima b—last year after scientists discovered it orbiting our nearest neighbor star, Proxima Centauri. With knowledge only of the luminosity of the star (1/600 that of the sun), the mass of the planet (1.3 times that of Earth), and the length of its orbit (11.2 days), the team was able to predict that, with a variety of possible atmospheres, it would be possible for Proxima b to harbor liquid water on its surface.

Now, another team has upped the level of detail by taking a climate model designed for Earth—the Unified Model developed by the United Kingdom's Met Office—and pasted it onto Proxima b.

[...] As the team reports today in Astronomy & Astrophysics, it found an even wider range of circumstances in which Proxima b could have liquid water than the earlier study. The fact that the two very different models agree so closely is "somewhat remarkable," the team writes.

Source: Daniel Clery at sciencemag.org


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Dust Belts and Possible Additional Exoplanet Spotted Around Proxima Centauri 11 comments

The Atacama Large Millimeter Array (ALMA) has reported the detection of a dust belt around 1-4 astronomical units (AU) from Proxima Centauri, as well as a possible outer belt 30 AU away and an "unknown source" (possible exoplanet) about 1.6 AU away from the star. The data also show "a hint of warmer dust closer to the star".

Proxima b is 0.05 AU from Proxima Centauri, and is considered to be in the star's "habitable zone". The 1-4 AU belt on the other hand has a characteristic temperature of about 40 K, while the 30 AU outer belt would have a temperature of about 10 K. Neptune's moon Triton is roughly 30 AU from the Sun with a temperature of 38 K.

The 1-4 AU belt is estimated to contain 0.01 Earth masses of asteroids (primarily?) up to 50 km in diameter. By comparison, our main asteroid belt (including Ceres) is estimated to contain 4% of the Moon's mass, or about 0.000492 Earth masses (Ceres is about 0.00015 Earth masses, roughly a third of the main asteroid belt). A minimum estimate for the Kuiper belt's mass is 20x that of the main asteroid belt, or the equivalent of this newly detected dust belt around Proxima Centauri.

Astronomy Magazine has an interview with one of the co-authors, who noted another possible exoplanet at 0.5 AU:

An Earth-Like Atmosphere May Not Survive the Radiation in Proxima b's Orbit 2 comments

Another study has cast doubt on the habitability of an Earth-like exoplanet in the "habitable zone" of a red dwarf, in this case Proxima Centauri specifically:

At only four light-years away, Proxima b is our closest known extra-solar neighbor. However, due to the fact that it hasn't been seen crossing in front of its host star, the exoplanet eludes the usual method for learning about its atmosphere. Instead, scientists must rely on models to understand whether the exoplanet is habitable.

One such computer model considered what would happen if Earth orbited Proxima Centauri, our nearest stellar neighbor and Proxima b's host star, at the same orbit as Proxima b. The NASA study, published on July 24, 2017, in The Astrophysical Journal Letters [DOI: 10.3847/2041-8213/aa7eca], suggests Earth's atmosphere wouldn't survive in close proximity to the violent red dwarf.

[...] In Proxima Centauri's habitable zone, Proxima b encounters bouts of extreme ultraviolet radiation hundreds of times greater than Earth does from the sun. That radiation generates enough energy to strip away not just the lightest molecules — hydrogen — but also, over time, heavier elements such as oxygen and nitrogen.

The model shows Proxima Centauri's powerful radiation drains the Earth-like atmosphere as much as 10,000 times faster than what happens at Earth.

Previously: "Earth-Like" Exoplanet Found in Habitable Zone of Proxima Centauri
Proxima b May Have Oceans
Researchers Suffocate Hopes of Life Support in Red Dwarf "Habitable Zones"
Proxima B Habitability Study Adds Climate Model

Related: MAVEN Results Find Solar Wind and Radiation Responsible for Stripping the Martian Atmosphere


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  • (Score: 2) by Bot on Thursday May 18 2017, @06:08AM (1 child)

    by Bot (3902) Subscriber Badge on Thursday May 18 2017, @06:08AM (#511555)

    If the study were good, the researcher would have thrown it out the window and done something else.

    Planet is habitable, meatbags settle in, make it unhabitable, bots settle in.

    Unless the study was by an AI, but then it would have been like a one liner what I just wrote.

    • (Score: 0) by Anonymous Coward on Thursday May 18 2017, @06:32AM

      by Anonymous Coward on Thursday May 18 2017, @06:32AM (#511560)

      Time for the B Ship to leave? After you, Mr Hawking...

  • (Score: 3, Interesting) by Anonymous Coward on Thursday May 18 2017, @10:19AM (2 children)

    by Anonymous Coward on Thursday May 18 2017, @10:19AM (#511621)

    I get this for the pressure-temperature profile of an earth like planet with the same Insolation as proxima B: http://i.imgur.com/FrpIdXr.png [imgur.com]

    Compare to figure 5 of the paper (https://arxiv.org/abs/1702.08463) and you'll see theirs is too hot by 10- 20 K.

    Here is my model in R:

    ## Stefan Boltzmann Law for two planets with different insolation
    # T_s1 = (S_1*(1-a)/(eps*sigma)^0.25
    # T_s2 = (S_2*(1-a)/(eps*sigma)^0.25

    ## Solve for surface temperature of planet 2 as a function of T_s1
    # T_s2 = T_1s*(S_2/S_1)^0.25
    # where:
    # S_2/S_1 = 0.646
    # T_s1    = 288

    # This yields
    T_s1 = 288
    T_s2 = 258.1967

    ## 1976 US standard Atmosphere constants
    p0 = 1013.25
    R  = 0.00831432
    g0 = 9.80665
    m0 = 0.0289644
    Le = -6.5

    # Aggregate Constant
    Ce = (g0*m0)/(R*Le)

    ## Calulate temperature for pressures from 1000 to 200 mbar, which
    #  corresponds to Earth troposphere pressures
    p   = seq(1000, 200, length = 1000)
    t_1 = T_s1/(p/p0)^(1/Ce)
    t_2 = T_s2/(p/p0)^(1/Ce)

    ## Initialize plot and plot Earth Pressure-Temp profile
    plot(t_1, p, type = "l", lwd = 2,
        xlab = "Temperature (K)",  ylab = "Pressure (mBar)",
        xlim = range(c(t_1, t_2)), ylim = rev(range(p)),
        log  = "y",
        panel.first = grid())

    ## Plot Proxima B profile
    lines(t_2, p, col = "Blue", lwd = 2)

    ## Add legend
    legend("topright", legend = c("Earth", "Proxima B"),
        col = c("Black", "Blue"),
        lwd = 3)

    • (Score: 1, Interesting) by Anonymous Coward on Thursday May 18 2017, @10:36AM (1 child)

      by Anonymous Coward on Thursday May 18 2017, @10:36AM (#511626)

      Actually I'm seeing their dayside for the tidally locked model (fig 5 still) matches Earth's mean profile almost exactly. This is kind of a strange coincidence.

      • (Score: 3, Interesting) by Anonymous Coward on Thursday May 18 2017, @10:55AM

        by Anonymous Coward on Thursday May 18 2017, @10:55AM (#511629)

        This is all same AC still. Now that I looked at the earlier paper[1] I see that one must be wrong too. If you check Fig 7 you see their model allows a troposphere above 0.1 bar. This is not seen for any planets/moons in the solar system, so is likely non-physical:[2]

        A minimum atmospheric temperature, or tropopause, occurs at a pressure of around 0.1 bar in the atmospheres of Earth, Titan, Jupiter, Saturn, Uranus and Neptune, despite great differences in atmospheric composition, gravity, internal heat and sunlight. In all these bodies, the tropopause separates a stratosphere with a temperature profile that is controlled by the absorption of shortwave solar radiation, from a region below characterised by convection, weather, and clouds.

        [1] https://www.aanda.org/articles/aa/abs/2016/12/aa29577-16/aa29577-16.html [aanda.org]
        [2] https://arxiv.org/abs/1312.6859 [arxiv.org]

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