Their target is a better reading of the extragalactic background light (EBL), which is essentially the total combined light pouring into our galaxy from other sources across the universe. It's like an optical tally of everything else that's out there. But from our vantage point, it's hard to get a good read on the EBL. Zodiacal light--sunlight reflected by grains of dust in the asteroid belt or light from grains that are radiating themselves--pollutes our view of the EBL. There's no good way to accurately extract that noise from data collected by telescopes on and around Earth, so our picture of the EBL remains blurry at best.