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Now technically, according to the International Astronomical Union, these bodies can't be planets since they don't orbit the sun: https://www.iau.org/static/res

by rlanday 10y ago

Now technically, according to the International Astronomical Union, these bodies can't be planets since they don't orbit the sun: https://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf https://www.iau.org/static/resolutions/Resolution_GA26-5-6.p... "1. A planet is a celestial body that (a) is in orbit around the Sun" Makes me wonder how much this definition of a planet was motivated by the desire to be able to give elementary schoolers a nice small set of things to memorize. Edit: actually I might be incorrect about this, the resolution is titled "Definition of a Planet in the Solar System", I'm not sure the IAU actually has a definition of what a "planet" would be outside the solar system, but they may be open to the idea that they exist :)

hughes 10y ago
Are you saying that they don't orbit their star because some of them gravitationally influence each other? Or are you saying that nothing outside of our solar system can be a planet? Either way, NASA should schedule another press release about taking celestial pedantry to a new level.
- rlanday 10y ago
  My understanding is that according to the IAU definition, a "planet" must orbit the sun and not any other star. Kind of reminds me of when people thought the solar system was the center of the universe.
  - acqq 10y ago
    The word planet comes from the ancient Greek word for "wanderer" which they used to refer to the wandering stars, the only stars that moved across the sky in relation the all other stars, only five of them visible, assigned to the gods and one goddess: Hermes, Aphrodite, Ares, Zeus and Cronus. Since then, the definition of the planet had to be modified as there are a lot of bodies orbiting the Sun known today. According to the latest precise definition, even Pluto isn't a planet anymore (but a dwarf planet). In this light, I don't see the problem in making the difference between the planets (orbiting our Sun) and the exoplanets (orbiting other stars, see my other post here). These guys however would like to remove the International Astronomical Union's definition from 2006 and to introduce the new with which even the moons(!) of the planets would be called "planets": https://arstechnica.com/science/2017/02/how-positively-peeved-pluto-people-plan-to-pluck-back-plutos-planethood/ https://arstechnica.com/science/2017/02/how-positively-peeve... As the reporter cleverly summarized, their definition could be simpler stated as, "round objects in space that are smaller than stars." Then there would be around 110 such "planets" around the Sun, and the exoplanets would also be, of course, just "planets." Their reasoning: "In the mind of the public, the word “planet” carries a significance lacking in other words used to describe planetary bodies. In the decade following the supposed “demotion” of Pluto by the International Astronomical Union (IAU) [1], many members of the public, in our experience, assume that alleged “non-planets” cease to be interesting enough to warrant scientific exploration, though the IAU did not intend this consequence [1]. To wit: a common question we receive is, “Why did you send New Horizons to Pluto if it’s not a planet anymore?” To mitigate this unfortunate perception, we propose a new definition of planet, which has historical precedence [e.g., 2,3]. In keeping with both sound scientific classification and peoples’ intuition, we propose a geophysically-based definition of “planet” that importantly emphasizes a body’s intrinsic physical properties over its extrinsic orbital properties."
acqq 10y ago
NASA therefore uses the term "exoplanets": https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around/ https://www.nasa.gov/press-release/nasa-telescope-reveals-la... Also: https://en.wikipedia.org/wiki/Exoplanet https://en.wikipedia.org/wiki/Exoplanet "An exoplanet or extrasolar planet is a planet that orbits a star other than the Sun. The first scientific detection of an exoplanet was in 1988." Nature did their own clickbaiting with "alien worlds" in the title which was at least here on HN corrected with "planets" whereas the technical term would be "exoplanets."

by rlanday 10y ago

hughes 10y ago

Are you saying that they don't orbit their star because some of them gravitationally influence each other? Or are you saying that nothing outside of our solar system can be a planet? Either way, NASA should schedule another press release about taking celestial pedantry to a new level.

rlanday 10y ago
My understanding is that according to the IAU definition, a "planet" must orbit the sun and not any other star. Kind of reminds me of when people thought the solar system was the center of the universe.
- acqq 10y ago
  The word planet comes from the ancient Greek word for "wanderer" which they used to refer to the wandering stars, the only stars that moved across the sky in relation the all other stars, only five of them visible, assigned to the gods and one goddess: Hermes, Aphrodite, Ares, Zeus and Cronus. Since then, the definition of the planet had to be modified as there are a lot of bodies orbiting the Sun known today. According to the latest precise definition, even Pluto isn't a planet anymore (but a dwarf planet). In this light, I don't see the problem in making the difference between the planets (orbiting our Sun) and the exoplanets (orbiting other stars, see my other post here). These guys however would like to remove the International Astronomical Union's definition from 2006 and to introduce the new with which even the moons(!) of the planets would be called "planets": https://arstechnica.com/science/2017/02/how-positively-peeved-pluto-people-plan-to-pluck-back-plutos-planethood/ https://arstechnica.com/science/2017/02/how-positively-peeve... As the reporter cleverly summarized, their definition could be simpler stated as, "round objects in space that are smaller than stars." Then there would be around 110 such "planets" around the Sun, and the exoplanets would also be, of course, just "planets." Their reasoning: "In the mind of the public, the word “planet” carries a significance lacking in other words used to describe planetary bodies. In the decade following the supposed “demotion” of Pluto by the International Astronomical Union (IAU) [1], many members of the public, in our experience, assume that alleged “non-planets” cease to be interesting enough to warrant scientific exploration, though the IAU did not intend this consequence [1]. To wit: a common question we receive is, “Why did you send New Horizons to Pluto if it’s not a planet anymore?” To mitigate this unfortunate perception, we propose a new definition of planet, which has historical precedence [e.g., 2,3]. In keeping with both sound scientific classification and peoples’ intuition, we propose a geophysically-based definition of “planet” that importantly emphasizes a body’s intrinsic physical properties over its extrinsic orbital properties."

acqq 10y ago

NASA therefore uses the term "exoplanets": https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around/ https://www.nasa.gov/press-release/nasa-telescope-reveals-la... Also: https://en.wikipedia.org/wiki/Exoplanet https://en.wikipedia.org/wiki/Exoplanet "An exoplanet or extrasolar planet is a planet that orbits a star other than the Sun. The first scientific detection of an exoplanet was in 1988." Nature did their own clickbaiting with "alien worlds" in the title which was at least here on HN corrected with "planets" whereas the technical term would be "exoplanets."