This episode is brought to you by Squarespace. [♩INTRO] It might seem like we know a ton about the solar system, but we’ve really only learned most of what we know in the last 60 years or so.

Before that, we didn’t even know much about our closest neighbors: Mercury, Venus and Mars. And then the Mariner program came along.

When you think about space exploration in the 1960s, the Apollo landings are probably the first things that come to mind. But the Mariner probes made huge leaps in how we understand the solar system today -- and especially how we understand Mars. Starting in 1962, the Mariner missions explored the inner solar system, in NASA’s first program that resembled what we think of today as planetary science.

There were ten missions in all, with only three failures — which was pretty impressive for early spaceflight. One of the reasons the Mariner program was so successful was because of a new feature called three-axis stabilization. It allowed engineers to control the spacecraft’s orientation in three dimensions, so scientists could point its instruments wherever they liked -- which was important for getting those older cameras to take clear pictures.

Other spacecraft were stabilized by spinning like a top, which could be useful in some situations — just not this one. It also helped that NASA’s Jet Propulsion Laboratory built each spacecraft with a common design. The electronics were kept in a central hexagonal or octagonal housing called the “bus,” with pairs of solar panels attached to the sides.

Reusing basic pieces allowed them to refine components in an era when more than half of all missions could fail. Which is what happened to Mariner 1 in 1962. But later that year, its twin, Mariner 2, visited Venus and became the first spacecraft to fly past another planet!

Among other things, it taught us that Venus doesn’t have a powerful magnetic field like Earth does. Then, two years later, with Mariner 3, NASA set its sights on Mars … but its solar panels didn’t work, so the mission failed. Thankfully, everything went okay for Mariner 4, and in 1965, it became the first spacecraft to visit Mars!

It sent back only 5.2 million bits of data, or about 650 kilobytes, which is probably less than it takes to store half a second’s worth of the video you’re watching right now. But at the time, that was enough to include about 20 images, plus other observations, like surface temperature and pressure. Along with the news that Mars also doesn’t have much of a magnetic field.

And Mariner 4 properly disproved an idea that had been popular decades earlier: that Mars was crisscrossed by a series of enormous canals, which were built by an advanced civilization in a last-ditch effort to save their dying home. By the time the Mariner missions launched, most scientists didn’t agree with that, but other people still believed it. And with no sign of canals or other evidence of life, those first images were also proof that Mars was a dead world, at least on a large scale.

The computers in the ‘60s didn’t transmit or process data very quickly, though, so it took a while for those pictures to pop up on computers back home. It took so long that by assigning colors to the numbers Mariner sent back, the first image from Mars was colored by hand faster than it could be rendered on screen! So, yeah, the very first pictures we saw from a Mars probe were essentially coloring pages for scientists.

Sounds like my kind of coloring book. These days, we receive data from probes around Mars tens of thousands of times faster, so we’ve made plenty of progress. A few years later in 1969, just days after Apollo 11 landed on the moon, Mariners 6 and 7 arrived at Mars as the first successful dual mission.

Mariner 6 launched and arrived first, which allowed scientists to study broad images of the surface. The wanted a closer look at Mars’ south pole, so they used the camera on Mariner 7 to make more detailed observations five days later. Sending two probes together was so useful that NASA did this for other exploration missions, too, like the Voyager trips to Jupiter and Saturn.

Still, even with that one-two punch model, Mariners 6 and 7 only managed to image about 20% of the Martian surface. Clearly, just flying by wasn’t good enough, so Mariners 8 and 9 aimed to fix that! 8 was destroyed in a launch malfunction, which is a nice way of saying that after liftoff it came right back down and landed in the Atlantic Ocean. But in 1971, Mariner 9 became the first spacecraft to orbit another planet!

Nature almost threw a wrench in its plans, though. When the orbiter arrived, it found a global dust storm on Mars obscuring all but the tallest mountains. But just like Mariner 7, Mariner 9 was flexible and could receive new tasks from Earth, so NASA had it wait to start start seriously taking pictures until the storm settled in January.

Whereas two Soviet probes that arrived just weeks after Mariner 9 couldn’t accept new input from Earth, so they took a lot of pictures of dust. In the end, Mariner 9 imaged 85% of the Martian surface, taking more than 7300 pictures, which was way more than the other missions. It also taught us more about Mars’ atmosphere and surface.

So this whole orbiting thing worked out great! After the Mariner program wrapped up at Mars, Mariner 10 went on to be the first spacecraft to fly by Mercury. And two missions that were originally supposed to be Mariners 11 and 12 became Voyagers 1 and 2, which were among the first few spacecraft to explore the outer solar system.

The Mariner design was also adapted for the Viking orbiters that reached Mars in 1976, and it’s been used as recently as the Cassini mission, which is just now finishing up at Saturn after 20 years in space. To honor the Mariner program’s research at Mars, the solar system’s largest canyon system, Valles Marineris, carries their name. Their real legacy, though, is what they taught us about the inner solar system.

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