[求助] 一道逻辑题

yuyuwang

comets do not give off their own light but refelt 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 reflet. A satellite probe, however, has revealed that the material of which Haley's comet is composed reflets 60 times less light per unit of mass than had been previously thought.
The staments above, if truee, give the most support to which one of the following?

Answer: Previous estimates of the mass of Halley's comet which were based on its brightness were too low.

My question is: why not too high, but "too low" as the last two words in the Answer?

Thank you!

qww

LSAT上的一道题。因为从条件来看亮度越强，质量越大。哈勒彗星的亮度比实际的要小，所以实际质量要大于以前的。以前的太小。previous estimates of the mass of halley's comet which were based on its brightness were too low

yuyuwang

I see,thank you!