Could the scarcity of small, dark NEOs be caused by some physical process that preferentially produces small, highly reflective asteroids?
"There could be some physical process, but there's no solid evidence one way or the other right now."
Visible vs. Infrared Surveys This bias against finding small dark asteroids could be the Achilles Heel of visible light surveys and needs to be considered before arriving at any definitive conclusion as to the population of small NEOs. But, as Mainzer pointed out, visible light surveys are highly complementary to NEOWISE-like infrared surveys.
"If you have infrared surveys alone, you get a pretty good idea of diameters," she added. "But you can't say anything about the reflectivity of the surfaces in visible light. So you need a combination of visible light plus infrared together to really nail down the reflectivity, which gives you an important clue as to the asteroid composition."
All of the objects studied by Mainzer's team were classified as NEOs, a number of which are also potentially hazardous asteroids (PHAs). PHAs are objects that make a minimum orbital approach to Earth's orbit of 0.05 AU (astronomical units; where 1 AU is the average distance between the sun and Earth).