...that's a classic and iconic image from the Viking 1 orbiter in 1976 — one of the earliest clear views showing the surprisingly thin Martian atmosphere as a faint, hazy layer along the planet's limb (edge).This photo (often referred to in processed versions as showing the "thin atmosphere of Mars") was captured in violet light (image ID roughly 34A13 from the Viking Orbiter archive, dated around July 24, 1976). It beautifully reveals how tenuous Mars' atmosphere is — mostly carbon dioxide, with surface pressure only about 0.6% of Earth's (around 6 mbar on average). The haze is caused by suspended dust particles and sometimes thin ice clouds (CO₂ or water ice), scattering light and creating that delicate glow at the horizon.Key features in the image:Left/center: The prominent Galle crater (about 230 km / 143 miles in diameter), famously nicknamed the "Happy Face" or "smiley face" crater due to its curved mountain ridge "mouth" and two dark spots resembling "eyes." It's located on the eastern rim of the huge Argyre impact basin. Right side: The rugged Charitum Montes (Charitum Mountains), rising along the southern edge of the Argyre Planitia basin — a vast, ancient impact feature in Mars' southern hemisphere. This limb view was valuable for early studies of atmospheric structure, showing how dust can loft high into the thin air and how the atmosphere thins dramatically with altitude (scale height ~11 km, vs Earth's ~8 km).Here are some high-quality views and processed versions of this legendary Viking 1 photo, highlighting the atmospheric limb, Galle crater, and surrounding terrain: Modern orbiters like Mars Express, Mars Reconnaissance Orbiter, and others have imaged Galle crater in much higher detail (including its dune fields and frost patterns), but this 1976 Viking shot remains legendary for giving us one of our first glimpses of Mars' fragile atmosphere from orbit. It's a reminder of how alien — and yet hauntingly beautiful — the Red Planet's sky really is.