Astronomy

So is there nothing like satellite anymore?

So is there nothing like satellite anymore?


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I just read this article. I don't know how credible it is, since I couldn't find any link to the original paper. But it says that pluto will be considered a planet again, along with more than 100 other celestial objects including our moon. So, if the definition given here is applied, then would there be anything as dwarf planet or satellite? I think even comets and asteriouds would come under this defintion. I am talking about this:

The paper, published in Lunar and Planetary Science, declares a planet as a round body that's never undergone fusion, and has less mass than a star. That's it. This means, Pluto would be planet again-- But it would also bring along Ceres, Eris, Makemake and Haumea… as well as 97 other objects.


This is really a question of Language rather than Astronomy. The meaning of words is defined by their use. The IAU has proposed one way of using the word "planet", this group of scientists have proposed another.

Anyone can propose a definition of any word. This group proposes that a "planet" is any astronomical body which 1) Does not have, and never has had sustained nuclear fusion in its core, and 2) Is large enough for gravity to pull it into an ellipsoidal shape.

The intention of this definition is to make a planet defined entirely by "what" a body is, not by "where" it is. Under this definition the classic 8 planets, Ceres, Pluto, Charon, the Moon, the larger moons of Jupiter, Saturn Uranus and Neptune, Eris, Sedna, and the larger Kuiper belt objects would all be "planets" - about 100 known in total. The exoplanets would also be "planets"

Asteroids (except Ceres), comets and other small solar system bodies are too small, and so would not be planets.

The advantage of this definition is that the usually where something is located is not part of the definition of what it is. However, it contradicts several hundred years of use by defining the larger moons as planets.

Unlike the 8 planet definition, this does not have the support of a large international body of astronomers (the IAU). If you wish to use this definition you are free to. I doubt that without the support of the IAU this definition is ever going to be widely used. Most people will either use the 8 planet definition or the 8+Pluto definition.


Small objects like comets and asteroids are generaly not round. The roundness of bigger bodies is a consequence of the body own gravity.

So, to answer your question, no, not all celestial bodies would become a planet with this definition as small objects like comets and asteroids doesn't have a sufficent mass to become round.


I doubt if the definition given above will actually be applied ever, but if it is applied then all the current natural satellites (moons) will not be considered as a planet. So is the case with dwarf planets, comets, asteroids, etc.

Asteroids and comets are not round in shape (even if some are, they are not round as a result of their own gravity), so they will not be considered as planets. Most of the moons in the solar system are not round in shape. For example, moons of Mars, Phobos and Demos, are not in round shape. They will continue to be considered as moons or natural satellites.

So, in short, all the natural satellites, dwarf planets, etc., will not become planets.