[T0T0R0]

Exoplanets are dark matter. They do not emit light, so they are dark. You can't see an exoplanet, you have to look for stars that wobble.

Asteroid belts are also dark matter. If a remote star has an asteroid belt, it wouldn't be easily detectable, since it probably wouldn't elicit the kepler-style wobbles and flickers, or if it did, perhaps less obvious/detectable events.

Based on this, the astronomical fad terminology is flawed, since it seems to claim that only stars matter because only stars are matter (and the luminous gas of nebulae too, of course). The layperson finds intrigue in the term Dark Matter, because journalists are trying to sell a story.

[LeifCarrotson]

I am pretty sure this is satire. But this is the internet, so it is hard to tell.

To be clear: to an astrophysicist, "dark" means "does not interact with electromagnetic radiation except through the curvature of space-time by gravity". It only interacts with normal matter in that it affects gravity. It is otherwise completely transparent.

It does no mean "is not currently reflecting or producing visible light". Your closet does not contain dark matter when you close the door.

[logfromblammo]

Well... it might.

Your closet probably has the same concentration of dark matter in it as everywhere else on the surface of Earth. But that quantity is unmeasurable at our current technology level, because any signal we might get is completely obscured by all the noise from bright matter around here.

Dark matter is not matter that does not emit light. A rogue asteroid far from any star is a dark object, but it is not dark matter. If you aimed a radar beam at it, the signal would bounce off, and you could detect the reflected/absorbed/re-emitted signal when it gets back to you. If you somehow found an aggregation of dark matter, your radar beam would not bounce. It would pass right through, like a flashlight beam shining through a crystal ball. Your beam might refract slightly due to the gravity, but it would not reflect. It would be similar to aiming a neutrino beam at the regular asteroid. Most of the beam just passes straight through without interacting.

Not even black holes are dark matter (or if they ever were, they aren't any more), because they absorb light. If one eclipses a known light source, you can see the black spot, along with the lensing around the outside. They interact with light.

[zuminator]

A couple comments here are somewhat conflating dark matter, in general, with non-baryonic matter, which is what we presume to be the primary component of dark matter. Dark matter theories arose because the Milky Way and other galaxies are much heavier than they appear to be based upon the mass of objects in them that we can detect. Therefore we know there's something else out there that has mass, and is spread fairly evenly throughout the galaxy but is otherwise currently undetectable to us. We don't know enough to definitively say what that stuff is or isn't. Part of that mysterious stuff may be MACHOs (massive compact halo objects), which are just made of normal baryonic matter that's aggregated in bodies too small and dark for us to individually detect through existing means, such as small rocky objects which would be perfectly visible if we could get a spotlight on them, and also black holes, neutron stars, dwarf stars, and other dark objects. However, it's currently thought that the majority of dark matter is non-baryonic, which fits the exotic description of invisible and completely non-interacting except through gravitational attraction. MACHOs have the problem that if they're plentiful enough to account for the missing mass, we really ought to be able to detect them through other means. (And furthermore that if baryonic matter were the primary form of dark matter, it would be too abundant for our well-established theories of structure formation and nucleosynthesis to work.) But the bigger problem is that none of the theories of non-baryonic matter are in any way substantiated either, except for garden variety neutrinos, which don't have enough mass and are too energetic to account for the bulk of dark matter. This leaves the door open to even more exotic speculations such as tweaking the theory of gravitation. In a sense, the real darkness to "dark" matter lies in our understanding more than anything else.

[T0T0R0]

Just going to point out that science is filled with garbage theories, and "Dark Matter" certainly feels like one of them.

Why not just go back to calling it The Æther? Or mayhap a form of non-luminiferous aether, if I may be so bold?

https://en.wikipedia.org/wiki/Aether_theories

  a space-filling substance or field, thought 
  to be necessary as a transmission medium for 
  the propagation of [...] gravitational forces.

You say tomato, I say Tomato. Aether. Why not?

[Retra]

Because that would be the kind of 'garbage theory' that would make you look incompetent rather than clever.

[oldmanjay]

If there's one thing I've learned from the internet, it's that people sure prize the appearance of being clever.

[mikeash]

I thought it just meant that it can't (yet?) be detected with electromagnetic radiation, not that it necessarily doesn't interact. For example, MACHOs have fallen out of favor, but were once a decent theory to explain dark matter, and they're just normal matter in a form and location that makes them hard to see.

[mikeash]

Exoplanets and asteroids don't explain the discrepancies. There aren't enough of them. Our galaxy appears to have about 20x more dark matter than regular matter, yet our solar system has about 99.9% of its mass concentrated in its star. There's no indication other star systems with planets are radically different in that respect. If there was enough of this stuff to make up the discrepancy, there would be enough of it to see it.

There's also apparently decent evidence, based on things like irregularities in the cosmic microwave background, that most dark matter isn't any form of baryonic matter.

[zig]

How do you rectify these numbers?

The sun is 99.86% of the mass of our solar system and is quite average. [1]

Dark matter is ~27% of the mass of the observable universe. [2]

Are you claiming that exoplanets and asteroids represent 27% of the mass of the universe when a typical G-type star (not particularly massive, by any means) is almost 100% of the mass of our entire solar system?

I'm confused by your assertion - you either have some data I am lacking, have entirely made up your post, or are, yourself, confused.

[1] https://en.wikipedia.org/wiki/Sun [2] https://en.wikipedia.org/wiki/Dark_matter

[mikeash]

Note that 27% is of the total mass and energy, where ~68% consists of dark energy. If you ignore dark energy and just look at matter, dark matter is about 85% of the total. Which is pretty crazy! We have no real idea what 5/6ths of the stuff in the universe actually is!

[fizx]

We're kind of out on the edge of the galaxy. As you might suspect, dark matter tends to be more dense in the middle of the galaxy.

I'll let someone else be more precise:

http://cdms.berkeley.edu/Education/DMpages/FAQ/question36.ht...

[netcraft]

im pretty sure this isnt true - if any of those things were massive enough to substitute for the gravitational effects that have been observed they would emit infrared radiation at least.

[T0T0R0]

So go ahead and observe this all-too-obvious infrared, that exoplanets must surely emit.

Meanwhile, their gravity is now well known to induce wobble on their parent stars, which are much more luminous, and probably outshines any exoplanet in the infrared.

[GFK_of_xmaspast]

On the other hand, this has already been done: https://en.wikipedia.org/wiki/List_of_directly_imaged_exopla...

[T0T0R0]

  This method works best for 
  young planets *that emit infrared 
  light* and are far from the glare 
  of the star.

In other words, if they are still swirling balls of liquid magma. So, NOT dark matter.

[GFK_of_xmaspast]

You originally claimed that "Exoplanets are dark matter. They do not emit light, so they are dark", which goes against the cited link.

Furthermore, are you aware that you yourself are emitting infrared light right at this moment and are presumably not a swirling ball of liquid magma?

[T0T0R0]

  are you aware that you yourself are emitting 
  infrared light right at this moment [...] ?

WHAAATTT???!!!1one

The hell you say!

Come on, man. You and I both know that exoplanets are a recent discovery (1988 being the earliest verified potential candidate for the real thing), and thus hard to detect in the visible spectrum. No one is looking at them with an ordinary telescope, tuned into the visible spectrum.

Last time I checked, anything not emitting visible light is commonly referred to as "dark." But wait, let me just check with my specialized visible light emission instrument.

Gee, when I turn off this incandescant light bulb, it goes... dark! Hypothesis verified! Is it still hot? Why yes! Yes, it is still hot. But also dark. Weird!

But hey, while we're being pedantic nerds, I'll just take a moment to correct you, regarding your correction of me.

Most of the examples in the impeccably cited link are measured in multiples of Jupiter's mass, which, you know, pretty much means they're certainly gas giants, and damn near brown dwarf classification, lending to their thermal activity.

So, the heat would likely not be owing to lava or magma.