The night sky is a shared wilderness. On a dark night, away from the city lights, you can see the stars in the same way as your ancestors did centuries ago. You can see the Milky Way and the constellations associated with stories of mythical hunters, sisters and journeys.

But like any wilderness, the night sky can be polluted. Since Sputnik 1 in 1957, thousands of satellites and pieces of space junk have been launched into orbit.

For now, satellites crossing the night sky are largely a curiosity. But with the advent of satellite constellations—containing hundreds or thousands of satellites—this could change.

The recent launch of BlueWalker 3, a prototype for a satellite constellation, raises the prospect of bright satellites contaminating our night skies. At 64 square meters, it's the largest commercial communications satellite in low Earth orbit—and very bright.

Pollution of the night sky

When it comes to "on the ground" exploration of Mars, rovers make pretty good advance scouts. From Pathfinder to Perseverance, we've watched as these semi-autonomous robots do what human explorers want to do in the future. Now, engineers are studying ways to expand rover exploration on Mars. One thing they're thinking about: communication satellite constellations for Mars surface navigation.

The current generation of Mars rovers landed in easily accessible places. Other Martian regions, such as the poles, or Valles Marineris, remain pretty much untouched. That's partly because they're difficult to reach and their weather conditions present challenges. The poles hold a lot of clues to the Martian climate system. Although one cap is known to be mostly water ice, both caps could contain (or be hiding) additional water either in underground lakes or frozen beneath the caps.