What environmental factor causes the extreme diurnal temperature swings on an asteroid's surface?

Direct exposure to unfiltered solar radiation and shadow

The surface of an airless body like an asteroid experiences drastic temperature fluctuations because it lacks a protective atmosphere to distribute heat or insulate the surface. When directly facing the Sun, surface materials absorb intense solar radiation, causing temperatures to soar to hundreds of degrees Celsius (e.g., $120^ ext{}^ ext{oC}$). Conversely, when the body rotates into shadow, the heat rapidly radiates away into the near-perfect vacuum of space, causing temperatures to plummet to hundreds of degrees below zero (e.g., $-170 ext{}^ ext{oC}$). This extreme thermal cycling makes maintaining stable conditions, especially for liquid water, impossible on the surface.