I’ve often wondered what it would be like for one of the astronomers of the past to come alive today. What would it be like for them to see what we’ve been doing in physics, space and planetary exploration, biology, chemistry, and so on? It’s a great storytelling hook: bring somebody like Galileo, for example, to a modern time and let them marvel at what we’ve done.

In Galileo’s case, he’d likely understand planetary exploration pretty well. People have been looking at the planets for several thousand years and he took advantage of that. Yet, I think you could say that the true exploration of the solar system began with him. He pointed his homemade telescope at Jupiter in early 1610 and found the four largest moons, which astronomers later gratefully named “the Galileans” in his honor. That set off a mad dash of Earth-based observations that continues to this day. And, I bet he’d be enthused that a Jupiter exploration spacecraft was named for him: Galileo.

Planetary Exploration: What’s First?

So, what would Galileo think of the most recent planetary exploration efforts? Imagine that we could sit down with him for an afternoon and bring him up to speed. Where would we start? Probably the best approach is to take it in a linear timeline. That would give him the depth and breadth of humanity’s efforts at learning about the solar system in situ.

Planetary scientists began their spacecraft explorations in the early 1960s, with spacecraft sent to the Moon and Mars. After that came Venus and Mercury. Oh, and the Sun, let’s not forget that.

In the 1970s, they added Jupiter, Saturn, Uranus, and Neptune to the list of targets. Pluto didn’t get a visit until nearly five years ago, in 2015. And,the rest of the solar system objects (such as asteroids and comets), have been explored only beginning in the mid 1980s (with four spacecraft sent to Comet Halley). I’m sure I’m forgetting something, but this is the general trend of solar system exploration: select the targets and make spacecraft to explore them.

So, I can imagine telling Galileo, “Well, sir, we’ve looked at nearly everything now. You’re best remembered for those Galilean satellites you found, so we’ve sent several spacecraft out to explore Jupiter and its moons. In fact, we’re thinking of sending more spacecraft to explore Europa.”

And, then, he nods sagely in agreement. With a quirky smile and a glint in his eye, he raises his arms to the heavens and asks, “What about exoplanets? I’ve read about those? What are you doing about them?”

And, I say, “We’re still at the stage of merely detecting them from a distance. But soon, very soon, we should be able to point very complex instruments at them and learn much more about those distant worlds.”

He nods again. “Of course. Now, tell me more about the most-explored world!”

Would that Be Mars?

Of course, Earth is the world we know best. And, we explore it with spacecraft continually. There’s still much to learn about our home planet. But, our imaginary Galileo isn’t interested in that. He wants to know more about other planets. So, I choose Mars. “You know of Mars, the Red Planet, right?”

He nods, favors me with a gentle smile, and opens his hand to encourage me to tell him more. “Sì, per favore continua.”

I smile because I know he’s gonna LOVE the tale of Mars exploration.

“Well, we’ve sent dozens of spacecraft to explore Mars—about eighty, in fact. Not all of them made it safely, but the ones that have told us wondrous tales of the Red Planet,” I start out by saying.

I go on to tell him about my favorite spacecraft (of the moment): Mars Curiosity. “It’s a roving machine that landed on Mars in the year 2012. It has wheels and follows commands sent to it from Earth to roll around and study the rocks and sand that are on the surface. Curiosity is a rugged explorer and has taught us much.”

As I talk, I wonder if he’s understanding half of what I say. But, the alert, lively look in his eyes tells me that this whole story has piqued his curiosity. He nods in understanding, and bids me to go on.

Curiosity’s Summer of Planetary Exploration

When Curiosity landed on Mars, it settled down near a peak called Mount Sharp. It’s centered in Gale Crater, an impact feature that appears to also have been inundated with water sometime in the past. Curiosity has explored clay-rich regions and will soon begin to explore sendimentary rocks on the slopes of Mount Sharp. Every layer of rock will reveal some clue to Mars’s water-rich past.

To get to its target, Curiosity will have to steer around a sandy stretch of landscape. Controllers don’t want it to get stuck in the sand as one of its predecessors, the Spirit rover did. So, it has to move about a mile (about a kilometer and a half) around the sand pit. Once Curiosity arrives on the slope of Mount Sharp, then it will resume its study of topsoil and rocky layers.

“But, why study the rocks?” asks Galileo. I smile at him. It could be that he’s not completely aware of the relationship between rocks, water, and the possibility of life. So, I take a deep breath and explain more.

“Signore Galileo, rocks tell a tale of conditions on the planet. Here on Earth, some rocks erupt from volcanoes and flow onto the landscape. Other rocks form as layers of dirt and sand pile up on each other. The wind may deposit them. Or, water may move them into layers. Rocks that have been in contact with water have special characteristics and chemical elements. The same types of rock have formed on Mars. We look for sedimentary rocks, for example, in order to understand where and when the water existed on this planet. And, of course, life requires water. So, if Mars once had a lot of water, perhaps it supported life.”

Why Explore a Planet?

Galileo considers this for a while. In fact, he stays deep in thought for a long, long time. Then, he asks many questions about how the spacecraft does this. I tell him about Curiosity’s instruments and how they work. I mention that teams of scientists and technicians control the spacecraft and tell it what to do. Of course, I also tell him about the long distance between us and Mars. Finally, he asks, “What will you do with all this knowledge of Mars?”

A good question.

“Signore, among other things, we hope one day to GO to Mars,” I say, hoping that he understands the need for humans to explore. “To have people stand on its surface and explore it first-hand is a big step for all of us. These spacecraft we send are like the first explorers of your own time who sailed the seas of Earth to find new lands. In this case, however, we want to approach Mars with respect, and if it has life, we need to know what that life consists of. If it has no life, or if we decide to live there, we need to know about its characteristics. Spacecraft such as Curiosity send back valuable data so that we can plan future missions for more robotic missions, and eventually, for humans.”

The Future Through the Past

The first peek through a telescope that Galileo Galilei took may have been a baby step, but it provided humanity with a leap to the planets. What if Galileo had never looked through a telescope? Chances are that somebody else would have, eventually. The telescope existed in his time, and it only needed one person to use it for planetary exploration. So, somebody else would get the credit for first astronomy use of a scope. But, the story might not be as crucial to science as Galileo’s contributions came to be.

If Galileo lived today, I have no doubt he’d be heading up spacecraft missions, directing people to do everything they could to explore distant worlds. That’s because he was a curious person, just as we are today. His questions started revolutions of thought and science. Galileo’s influence may have begun in the past, but it pointed the way to a future of planetary exploration. The smallest acts reverberate throughout time. And so, we have Galileo peeking through a scope at distant worlds, and with that act, he inspired the exploration of places such as Mars.