How do scientists know exoplanets are planets orbiting around other stars?

How do they know they are nearly round shaped and thus meet all three criterion of a planet by the iau

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  • 1 month ago
    Favorite Answer

    The objects have to be round, because ANYTHING that big and massive is going to be round. We know the strength of rock, of metal, and other things. They are not strong enough to be any other shape. Gravity pulls them into round shape.

  • Joe
    Lv 4
    1 month ago

    Your best answer only answered one of your two questions.   They know the planets are there because of measured gravity perturbations of the central star. 

  • 1 month ago

    They know exoplanets by how they affect their parent star.

    Every known planet formation is some manner of sphere, Physics sees to that. The IAU has no better clue of such planets criterion than you do.

    I don't think you will ever see a cube shaped planet.

  • 1 month ago

    They don't know their shapes, but based on the calculated masses of the objects they call them planets.  They may not have cleared their orbital paths of debris but we can't know that until we go there.

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  • jehen
    Lv 7
    1 month ago

    The laws of physics.  Gravity requires that any body becomes a sphere when it grows to sufficient size.   500 years ago the orbits of our visible planets were precisely described mathematically. That same math applies to other stars.  They pretty much know the mass, size and energy output of any star by the observable qualities.  Transit observations tell us about some of the planets around some of those stars, by which orbits, distance, and mass of those planets can be calculated.  Once the orbits and masses are known there ample evidence for whether the planet is likely gaseous or solid. It may be possible in our lifetime to image some of these exoplanets with a gravity lens telescope.  But without some new, as yet undiscovered physics, it will never be possible to travel to any in a thousand lifetimes.

  • 1 month ago

    "Exoplanet" is simply the word coined to distinguish whether one is discussing Solar System planets or planets around other stars.

    Exoplanets generally are discovered in two quite different ways.  The more massive ones are found from their gravitational effect causing their stars position in space appear to wobble as the exoplanet orbits it.  This method provides info on the exoplanet's mass and approximate orbit around its star, but little on composition.

    The other method can be used for most possible sizes, but requires precise positioning of the exoplanet's orbit.  It must pass in front of its star as seen from Earth.  The amount of light loss during this transit and the duration of the transit gives us the exoplanet's approximate size, and can provide some info on a possible atmosphere.  

    Any object more than approximately 250 miles/400 kilometers in diameter is forced by its own gravity into a roughly spherical shape.

    NOTE:  pizzas and hockey pucks are round (2D).  Planets and stars are approximately spherical (3D).

  • 1 month ago

    A body more than about 400 km in diameter is going to approach sphericality unless it's very tenuous such as a nebula or comet tail.  They are currently detected by the light they block out from the star when they orbit in front of it and the Doppler effect caused by movement of the star in response to the planet's gravitational pull.  Tabby's Star seems to have a number of associated objects cutting out the light, and this has been detected by a series of troughs but this doesn't usually occur, so these bodies will be round, will dominate their orbits and will be orbiting their stars, so they're planets.

  • Robert
    Lv 6
    1 month ago

    They don't know.

  • Andy C
    Lv 7
    1 month ago

    Terms.   The human population is obsessed with words instead of concepts. 

  • !
    Lv 7
    1 month ago

    They dont know of a certainty that the objects detected are planets, but based on what we know from the available data, thats what theyre most likely to be

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