How do astronomers classify planets?

Answer 1

So far, we can lump the planets in our Solar System into two major groups; "terrestrial" planets that have a solid surface, and "gas giants", larger planets entirely shrouded by an atmosphere with thick clouds.

The "terrestrial" planets are Mercury, Venus, Earth and Mars; the "gas giants" are Jupiter, Saturn, Neptune and Uranus.

We don't know enough about the thousands of extra-solar planets ("exoplanets", which orbit other stars) to determine if we'll need to come up with additional categories; I think it almost certain that after we have examined a hundred or so additional planets, we'll need a dozen categories to group them.

Answer 2

Astronomers classify planets based on their composition, size, and location in the solar system. They categorize planets as terrestrial (rocky) or gas giants, as well as by their distance from the Sun (inner or outer planets). Additionally, astronomers use criteria like whether a planet orbits a star, is spherical in shape, and has cleared its orbital path to distinguish planets from other celestial bodies.

Answer 3

The only trees on small bodies in our solar system are "imaginary".

Trees grow on Earth, and noplace else. I'm sure we will eventually plant some in space habitats, but that will be a while yet.

Answer 4

There are many ways of dividing up the solar system into three parts.

1. The Sun.
2. Jupiter
3. Everything else

The Sun is over 99% of the mass of the entire solar system, and Jupiter is more than half of the remainder, so the other planets, all the asteroids and comets, and all of the assorted debris in the Kuiper Belt and the Oort Cloud all together is less massive than Jupiter.

Here is another possible division;

1. The Sun
2. The Earth, covered with life
3. All the other dead planets and space rocks

But this isn't particularly accurate, since while we don't know of any life elsewhere in the solar system, we cannot rule out the possibility of exotic forms of life on Mars, on Europa or on Titan - or elsewhere.


What your teacher is probably looking for is something like this;

1. The Sun
2. The Planets
3. The Asteroids and space junk.

Answer 5

Why dwarf planets are not planets.In 2006, the International Astronomical Union (IAU) defined a Solar System planet: "A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit." The new definition allows the four terrestrial planets--meaning planets with rock and metal compositions--Mercury, Venus, Earth, and Mars, and the two gas and two ice giants, Jupiter, Saturn, Uranus, and Neptune, respectively, to be called planets. The IAU classifies the icy Pluto as a dwarf planet. It is roughly 1000 kilometers across (620 miles), which makes it relatively miniscule to the Solar System, and it does not have size enough or gravitational strength enough to create its own cleared path around the Sun. Rather, it lies within a path among other Kuiper belt objects (pronounced like viper but with a K) in its revolution. Pluto neither combines the belt's other ice objects nor sends them off from their orbits, so the IAU classifies it as a dwarf planet, which means that it possesses other aspects of Solar planets while not being one. Pluto is a binary system.Most of what astronomers know about Pluto has been discovered since the turn of the millennium due to rapidity in the evolution of optics and computer technology. Note, if Pluto were classified as a planet by the IAU, it might be a binary one, because Pluto's gravitational center--called a "barycenter"--is not located within itself, but instead lies between itself and another Solar object: Charon. Pluto is not a satellite of Charon, nor is Charon a satellite of Pluto. This is because, in order for a Solar object to be a satellite of another Solar object, the center of gravity must be located within the other body itself. Hence, Charon does not possess the distinction of being a satellite around Pluto, because their collective center of gravitational pull is not within Pluto, but between the two objects, which makes them binary objects--they revolve around each other in their orbit around the Sun. For instance, the moon is a satellite of Earth, because the collective gravitational pull between the moon and Earth is located within Earth. If their collective gravitational pull were instead located between the Earth and the moon, the Earth and moon would be a binary system, rather than a planetary object and its satellite. However, the fact that Pluto and Charon are binary objects may have nothing to do with the IAU's definition of a planet. The IAU might define Pluto and Charon as a binary planet if their size were larger and their gravitational pull were strong enough to consume other objects or fling them into another path. But, the IAU has not formally recognized a term for binary Solar objects. The IAU, despite the facts, recognizes Charon as a satellite of Pluto. Pluto is in the Kuiper belt.Pluto resides in the Kuiper belt. The Kuiper belt is the belt of ice objects whose average revolutions around the Sun are beyond Neptune. And, like the terrestrial asteroid belt, it mingles among other objects in its belt path. Farther beyond the Kuiper belt lies the Oort cloud, a cloud of stagnant ice objects representing the twilight of the Solar system's gravitational pull that are not in a normal plane around the Sun. Astronomers have discovered only ice dwarves and other small Solar System bodies (SSSBs) of ice compositions in both the Kuiper belt and the Oort cloud, such as Pluto and Charon. The difference between them from Uranus and Neptune is the mammoth size of those two planets--ice giants. In relation to the Earth, all the terrestrial planets, and Earth's moon, are roughly the same size. The gas giants Jupiter and Saturn are thousands of times larger than the terrestrial planets and so large and similar to the Sun in composition that some theorists believe that they may have been failed stars. While Uranus and Neptune are not as large as them, they are still significantly massive enough to be comparatively referred to as giants. Objects of the Kuiper belt and Oort cloud are significantly smaller than Earth or its terrestrial sisters, with Pluto only being less than 2000 km at its longest diameter, though astronomers are still unsure of the exact size of Pluto and Charon. Remember "Planet X?"Imagine if, every time astronomers found another miniscule ice object floating past Pluto, humanity exclaimed that it had found a tenth, eleventh, twelfth, thirteenth, or twenty-ninth planet. The human race would be excitedly discovering a few more planets every decade. (Remember "Planet X?") Then, the relevance of that excitement would soon fade. That these ice objects are so small makes them rather insignificant compared to, not only what astronomers are discovering in this most recent decade, but especially, what astronomers have known about the Solar system for hundreds or even thousands of years. Hence, the IAU refers to Pluto as a "dwarf planet," a "plutoid." A dwarf planet is not a planet. It is its own category of Solar body. Any solar bodies not planets, dwarf planets, or moons are SSSBs according to the IAU.

Answer 6

Definition of planetoids are :-

• Star - A celestial body that is sufficiently massive to undergo extensive nuclear fusion in its core. (Above 0.075 solar masses)
• Brown Dwarf - A celestial body that is not massive enough to undergo extensive nuclear fusion but sufficiently massive enough to undergo limited fusion in its core. (between 80 Jovian masses (0.075 solar masses) and 13-14 Jovian masses)
• Planet - A celestial body that is orbits a star, not massive enough to undergo any fusion in its core but large enough to be rounded by gravity. Also it must have cleared its orbital neighbourhood of other planetoids (except in Lagrangian Points)
• Dwarf planet - A celestial body that orbits a star, massive enough to be rounded by gravity but has not cleared its orbital neighbourhood of other planetoids.
• Asteroid - A celestial body that orbits a star, is not sufficiently massive enough to be rounded due to gravity. Generally objects larger than a boulder sized. Generally contain more rock and dust than ice.
• Meteoroid - A celestial body that orbits a star, ranging from dust to boulder in size.
• Comet - A body that orbits a star, can be the size of an asteroid or meteoroid but is mainly made up of ice rather than rock and dust.
• A moon or satelite - A body that orbits another planetoid.

Answer 7

At the present time, planets fall into four very rough categories. From large to small: 1) Gas giants, like Jupiter and Saturn; 2) Ice giants, (which are still mostly gas) like Uranus and Neptune; 3) Rocky worlds, or terrestrial planets, like Earth, Venus, Mars and Mercury; and 4) Dwarf planets, like Pluto, Ceres, Eris and Quoadar. Smaller than these, and the bodies are called "asteroids," "planetoids," "planetesimals" or "KBOs" (Kuiper Belt Objects). Bigger, and they become "Planetars," "Brown dwarfs" or "PMOs" (Planetary Mass Objects). Bigger still, and they become stars.

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Until about 2006, there was no formal definition of a "planet". But faced with the discovery of several objects out in the Kuiper Belt beyond the orbit of Neptune, and the near certainty that more such objects would be found as our telescopes improved, the International Astronomical Union (IAU) proposed three criteria that any planet must meet.

1. A planet must orbit a sun.

2. A planet must have reached hydrostatic equilibrium; in other words, its mass is great enough that its own internal gravity has crushed it into a spherical shape.

3. A planet must have cleared its orbit of other objects, meaning that there are no other objects in similar orbits. For example, the asteroid Ceres is not a planet even though it meets the first two criteria, because there are thousands of other objects in the same general orbital area.

Objects like Ceres and Pluto which meet the first two criteria but not the third are called "dwarf planets".

Please note that astronomers are still divided on some of these issues, and the definition of "planet" may be modified by later meetings of the IAU.

Answer 8

the three types of celestial bodies in the solar system are stars,comets and planets

Answer 9

A planet has to be a large object that:

1. orbits a star,

2. is sphere-shaped ,

3. clears the neighborhood around its orbit.

Answer 10

Scientists classify galaxies by their shape.