Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness: the greater a comet’s mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of light per unit of mass than had been previously thought.
What this question is testing
Setup
Scientists estimate how massive a comet is by how bright it looks. The brighter the reflection, the more mass — that's the assumption. New finding: the stuff Halley's comet is made of reflects 60 times less light per unit of mass than scientists assumed.
Evaluate
Picture two flashlights pointed at a wall. A bright wall means a strong flashlight, right? But what if the wall is way less reflective than you thought — the bright wall now actually means an even stronger flashlight than you originally guessed.
Same idea here. For Halley's observed brightness, the comet must contain way more mass than the old method gave it credit for. The old estimates were too low.
Goal
Find the answer that follows: previous mass estimates of Halley's comet were too low.
Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.