A closer look
We spent a billion dollars to punch a rock, only to find out we were fighting a giant space ballpit. When NASA sent a probe to collect samples from the asteroid Bennu, engineers expected the sampling arm to smack into a rigid, solid surface. Instead, the arm plunged nearly two feet straight down into the asteroid with virtually zero resistance. Bennu isn't a solid rock at all; it's a 'rubble pile' asteroid entirely composed of loose boulders and dust just barely clinging to each other through the weakest gravitational forces imaginable. Had the thrusters not fired, the probe would have sunk entirely.
