What scientific observation is made about asteroid 6478 Gault?

• A. The singular nature of impact ejection makes it untenable as an account of multiple loss episodes of similar duration over several years.
• B. Gault's mass loss is fully explained by a single impact event.
• C. Mass loss episodes occur only at perihelion.
• D. The mass loss is caused by internal geological activity.

Answer: (A)

The main idea here is that when a small body shows several bursts of activity over years, the cause isn’t a single collision. A one-time impact would eject material in one instant, and you wouldn’t expect repeated ejections of similar duration over a long timescale.

For asteroid 6478 Gault, observations show multiple episodes of dust emission spanning years, with each episode lasting a similar amount of time. That pattern points to a process that can recur, not a solitary hit. A single impact can’t account for repeated mass loss like this, so the explanation that mass loss is due to a one-off event isn’t compatible with the data.

A mechanism that fits better is rotational shedding: the asteroid spins up over time due to solar radiation effects, reaching a point where surface material peels away in bursts. This naturally produces episodic activity that can recur as the body’s rotation evolves, matching the observed repeated episodes.

The other possibilities don’t line up as well. If mass loss came only at perihelion, you’d expect the activity to synchronize tightly with the closest Sun approach, which isn’t what’s seen. And internal geological activity is unlikely for such a small body, which rarely harbors the heat or conditions needed to drive ongoing volcanism or similar processes.