Nobody can sniff a vacuum. But after a spacewalk, astronauts describe a strange odor clinging to their suits and the airlock: hot metal, welding fumes, seared steak. Its origin is still debated; one idea is highly reactive oxygen atoms stuck to surfaces, which react once air flows back in.
A large share of Earth's water molecules formed in the interstellar cloud that existed before the Sun was even born, more than 4.6 billion years ago. You are literally drinking a cosmic fossil.
By day, the Martian sky looks butterscotch because of fine dust hanging in the air. But at dusk, those same grains scatter blue light forward, creating a bluish glow around the Sun. Rovers have photographed these blue sunsets: the exact reverse of what we see on Earth.