Yes and no. Yes, in that planets do not emit radiation in visible light (they can emit infrared if they are warmed by a parent star. They also reflect light that is incident on them if they have a large enough albedo. But if the planet is a rogue planet, i.e. does not orbit a star, could it be an answer to our dark matter question?
No, in that planets cannot make up a significant amount of dark matter. Just look at our solar system. Yes, Jupiter is a large planet, but even so, it is 1047 times less massive than the Sun. In our solar system, the Sun accounts for over 99.8% of all the mass including all the planets, dwarf planets, asteroid, comets, satellites, everything. Now imagine that all planetary systems are similar in this nature. Even if all planetary system had 10 planets, remember that those planets would only account for 0.2% of the mass of that system. That is not a lot of mass, especially considering what the curve looks like.
Could rogue planets then be the answer? Rogue planets had to form around a star. That is the definition of a planet - it formed from the stellar cloud that a star formed in. It become rogue only when the star supernovae or possibly a passing body (star, brown dwarf) pulled on the planet to eject it from the system. Rogue planets are out there, however the total mass they contain is not enough to give a significant dent to the dark matter issue.
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