Many of the hotter stars in the visible image have faded in the near-infrared image. The near-infrared image shows cooler, reddish stars which do not appear in the visible light view. These stars are primarily red dwarfs and red giants, many of which are too cool to be detected by optical telescopes. These observations require the use of special cooled detectors containing crystals like germanium whose electrical resistance is very sensitive to heat. As we enter the mid-infrared region of the spectrum, the cool stars begin to fade out and cooler objects such as planets, comets and asteroids come into view.
Planets absorb light from the sun and heat up.
They then re-radiate this heat as infrared light. This is different from the visible light that we see from the planets which is reflected sunlight. The planets in our solar system have temperatures ranging from about 53 to 573 degrees Kelvin. Objects in this temperature range emit most of their light in the mid-infrared. For example, the Earth itself radiates most strongly at about 10 microns.