[1FreeAmerican]

Heat is the product of the interaction between radiation and any molecule that can absorb it. Since in space there are no molecules to absorb it the temperature is very cold but you will still get cooked without something to reflect or absorb the energy. There is more energy outside our atmosphere than inside it hence the conclusion that that the earth does not radiate any energy into space - it can only absorb energy. Therefore greenhouse gases do not make our planet warmer because they prevent warm air from escaping into the cooler atmosphere.
Im no physics guy though - just an electrician.

[Telepathic Intruder]

The writer of the article almost gets it right when he says "heat is the kinetic energy of an object". It's actually the thermal kinetic energy--the jiggling of the atoms in matter. Kinetic energy is just how fast the object is moving. The difference is whether the atoms are moving with the same or different vectors.

In space there is very little motion of atoms, since there are very few atoms, comparatively. Hence no heat transfer via conduction or convection. That leaves only radiation. Anything with heat becomes a black body radiator, so the earth radiates away heat while empty space does not. When the sun is down, the earth radiates its heat away.