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Thread: Exoplanet Stuff

  1. Top | #31
    Administrator lpetrich's Avatar
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    Simulations of Light Curves from Earth-like Exoplanets - Planetary Habitability Laboratory @ UPR Arecibo - contains simulations of Earth ones. Both present-day Earth and 500-million-year-old Earth.

    For the present day, the Sahara Desert makes the Earth look neutral-colored when it is in full view in its local midday. Otherwise, the Earth looks bluish - a pale blue dot.

    Earth Climate Models and the Search for Life on Other Planets - Astrobiology Magazine - applying climate-modeling software for exoplanets' possible atmospheres - going through a variety of possible atmospheres.

    Alternative Earths - Astrobiology Magazine
    NASA Astrobiology Institute - Alternative Earths: Explaining Persistent Inhabitation on a Dynamic Early Earth
    Earth’s own evolution used as guide to hunt exoplanets - Astrobiology Magazine
    noting journal paper
    High-resolution Transmission Spectra of Earth Through Geological Time - IOPscience

    Uses an underappreciated source of data: our planet's past states. I say underappreciated because our planet looked different in the past, and if one looks far enough, it had a very different atmosphere and biosphere. That journal paper discussed something that could be observable in transit observations: the Earth's apparent size as a function of light wavelength, its transmission spectrum. One would observe a planet's transit in different wavelength bands then work out the apparent size of the planet in each of them, giving its transmission spectrum.
    We chose atmosphere models representative of five geological epochs of Earth's history, corresponding to a prebiotic high CO2-world 3.9 billion years ago (Ga), an anoxic world around 3.5 Ga, and 3 epochs through the rise of oxygen from 0.2% to present atmospheric levels of 21%. Our transmission spectra show atmospheric spectral features, which would show a remote observer that Earth had a biosphere since about 2 billion years ago.
    The atmosphere parameters that they used:
    Time SlFx CO2 CH4 O2 O3 N2O
    Now 1.00 3.65e-4 1.65e-6 2.1e-1 3.00e-8 3.00e-7
    0.5 - 0.8 0.95 1.00e-2 4.15e-4 2.1e-2 2.02e-8 9.15e-8
    1.0 - 2.0 0.87 1.00e-2 1.65e-3 2.1e-3 7.38e-9 8.37e-9
    3.5 0.77 1.00e-2 1.65e-3 1.00e-13 2.55e-19 0
    3.9 0.75 1.00e-1 1.65e-6 1.00e-13 2.55e-19 0
    Time: billions of years before the present.
    SlFx: solar flux ("solar constant")
    Numbers: "chemical mixing ratios"
    Total pressure for all the times: 1 bar

    No discussion of atmospheric nitrogen or argon. Their present fractions are 0.78 N2 and 0.01 Ar - by volume.

  2. Top | #32
    Administrator lpetrich's Avatar
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    Another bit of past-Earth data is amount of continental crust. It has grown over the Earth's history, growing from nothing to about 70% of present volume at 3 Ga, then more slowly growing to its present volume. Rates of generation and growth of the continental crust - ScienceDirect

    Early continents were likely relatively small, about the size of present-day large islands like Madagascar.

    Reddit has r/exoplanets and also r/astrobiology and r/exolife

    The Weirdest Solar System We've Found So Far? You May Be In It – Exoplanet Exploration: Planets Beyond our Solar System
    Before we found the first exoplanets — planets orbiting other stars — it seemed reasonable to suppose that other planetary systems looked like ours: small, rocky planets close to a Sun-like star, a big Jupiter and a few other gas giants farther out.

    But after a quarter century of discovery revealing thousands of exoplanets in our galaxy, things look very different. In a word, we are “weird” — at least among the planetary systems found so far.
    There are plenty of planets that we've observed that have no Solar-System counterparts: Hot Jupiters, Super-Earths and Mini-Neptunes.

    "In all this variety, we’ve seen nothing yet that quite resembles our own setup: a Sun-like star with a retinue of rocky planets close in and more distant gas giants (including a domineering Jupiter)." - part of the problem is the difficulty of detecting similar planetary systems, a difficulty that the article did not mention.

  3. Top | #33
    Contributor skepticalbip's Avatar
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    Quote Originally Posted by lpetrich View Post
    Another bit of past-Earth data is amount of continental crust. It has grown over the Earth's history, growing from nothing to about 70% of present volume at 3 Ga, then more slowly growing to its present volume. Rates of generation and growth of the continental crust - ScienceDirect

    Early continents were likely relatively small, about the size of present-day large islands like Madagascar.

    Reddit has r/exoplanets and also r/astrobiology and r/exolife

    The Weirdest Solar System We've Found So Far? You May Be In It – Exoplanet Exploration: Planets Beyond our Solar System
    Before we found the first exoplanets — planets orbiting other stars — it seemed reasonable to suppose that other planetary systems looked like ours: small, rocky planets close to a Sun-like star, a big Jupiter and a few other gas giants farther out.

    But after a quarter century of discovery revealing thousands of exoplanets in our galaxy, things look very different. In a word, we are “weird” — at least among the planetary systems found so far.
    There are plenty of planets that we've observed that have no Solar-System counterparts: Hot Jupiters, Super-Earths and Mini-Neptunes.

    "In all this variety, we’ve seen nothing yet that quite resembles our own setup: a Sun-like star with a retinue of rocky planets close in and more distant gas giants (including a domineering Jupiter)." - part of the problem is the difficulty of detecting similar planetary systems, a difficulty that the article did not mention.
    Right. Exoplanets comparable in size and mass to our system's rocky planets are extremely difficult to detect in distant systems so the planets detected so far are primarily the larger, more massives bodies. This doesn't necessarily mean their are few small rocky planets in those systems, just that our current technology makes them damn hard to detect if they are there.

  4. Top | #34
    Administrator lpetrich's Avatar
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    I'll assess the observability of both Earth and Jupiter with exoplanet-detection methods.

    • Luminosity (absolute visual magnitude): S +4.83, E +29.15, +J 23.59
    • Luminosity (visual, Sun fraction): E: 1.9*10^(-10), J: 3.1*10^(-8)
    • Luminosity (10-mcm IR, Sun fraction): E: 1.5*10^(-6), J: 2.5*10^(-4)
    • Deviation (at 10 pc): E: 0.30 mcas, J: 0.50 mas
    • Radial Velocity: E: 0.089 m/s, J: 12.5 m/s
    • Transit Depth: E: 8.4*10^(-5), J: 9.9*10^(-3)
    • Transit Probability: E: 4.7*10^(-3), J: 8.9*10^(-4)
    • Period: E: 1 yr, J: 11.86 yr

    Sources: some Wikipedia articles, like
    Absolute magnitude - calculated for Earth and Jupiter at 90d phase angle
    The IR luminosity I estimated by multiplying the visual luminosity by (10 mcm (IR peak) / 0.5 mcm (visual peak) )^3
    mcm = micrometer, mas = milliarcsecond, mcas = microarcsecond

    So it's very difficult to observe the Solar System from across interstellar space, even with present-day exoplanet-observation systems.

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