HomeDiscussion ForumEarth fits the classical definition of dark matter because?

Earth fits the classical definition of dark matter because?

A) made of exotic material
b) earth does not have an internal source of energy
c) earth is mostly covered with water
thanks guys, i was redoing this question from a test. Some of my teachers questions aren’t exactly correct at all.


  1. Earth does not emit a lot of energy; it would therefore appear ‘dark’.
    However, as long as it is heated by the sun, it does not fit the classical definition. At around 300 K, it does emit infrared radiation and would, therefore, be detectable (albeit, one would have to be very, very close). Also, it does have a bit of internal heat (from radioactivity and from gravitational sinking of heavy elements). Not much, but still it is around 11 TW (Terawatts) — compared to 110,000 TW received from the Sun.
    However, in a planetary system where one planet is overwhelmingly massive compared to others, the smaller planets do get ejected (it may take billions of years).
    One possible kind of ‘dark matter’ could be rogue planets that are drifting between star. They would be as cold as the universe (below 3K) and would be undetectable by their light. With the billions of planetary systems that could exist in the Galaxy, there could be a lot of rogue planets out there.
    This has the advantage that we do not need to invent a new type of exotic matter. Planet are made of ordinary matter.

  2. I disagree. The earth does not classify as dark matter. The theory hasn’t been around long enough to have a “classic” definition.
    The kind of matter, like the earth, was already estimated in attempts to figure out the mass of the universe. Somebody came up with the bright idea of “dark matter” which is supposed to have a gravitational effect but is not visible or in any way interactive with normal matter. IOW, they have no idea what it is made of. We most certainly do know what the earth is made of and it is normal matter. Not dark matter. Some astronomers now seem to be backing off of that idea and simply say it’s things like planets and black holes and dim stars. But that means they would be counting these things TWICE if they plan to add that to the estimated mass of the universe.
    Short story: the earth does not meet ANY of the conditions of “dark matter” and any attempt to include it in that category is essentially intellectual dishonesty.

  3. Dark matter is a blanket term for any type of matter that can only be detected by its gravitational field. We actually know very little about it other than it does not participate in the usual electromagnetic interactions that ordinary matter does. That is, it neither absorbs nor emits photons, which makes it a real pain for astronomers to detect. But they know its there since the structure of galaxies and galactic clusters tells them it must be, gluing them all together.
    Earth and everything on it is made of plain, ordinary matter. If there is dark matter anywhere on this planet, we wouldn’t really know since gravity is such a weak force, we would not detect it in such a small amounts. At any rate, Earth does not fit the classical definition of dark matter, therefore all three answers are wrong.


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