How Much Of The Space Has Been Explored

When we gaze at the night sky, it’s easy to feel as though we’ve conquered the cosmos. We’ve landed on the Moon, rovers crawl across Mars, and telescopes peer into the dawn of the universe. Yet the true answer to “how much of space has been explored?” is a humbling lesson in scale. The short answer is: an infinitesimally small fraction. The longer answer reveals a fascinating story of what we have touched, what we’ve seen, and the overwhelming majority that remains a profound mystery.

To grasp this, we must first redefine “explored.” In the context of space, exploration exists on a spectrum. At one end is direct physical exploration—sending humans or robots to touch, sample, and measure. At the other is remote observation—using telescopes across the electromagnetic spectrum to study objects light-years away. Most of our “exploration” falls into the latter category, a form of cosmic archaeology from a distance.

The Cosmic Scale: A Shoreline in an Infinite Ocean

Imagine all of space as Earth’s entire ocean. Our direct exploration is akin to wading in the shallowest, warmest waters right at the beach, while the vast, dark, pressurized depths—the abyssal plains, the trenches, the open ocean—remain completely unknown. The observable universe is estimated to be 93 billion light-years in diameter. A single light-year is nearly 6 trillion miles. Within that sphere, there are over 2 trillion galaxies, each containing billions of stars and countless planets.

Our physical presence is confined to a single, tiny speck: Earth. Our robotic probes have ventured only as far as the edge of our own Sun’s influence, a bubble called the heliosphere. The farthest human-made object, Voyager 1, is about 15 billion miles away—a staggering achievement, yet it has only just exited the heliosphere and entered interstellar space. Compared to the distance to the next star (over 25,000 years away at Voyager’s speed), we have not even left our solar system’s front yard.

The Realm of Direct Physical Exploration: Our Solar System’s Surface

This is where we have made the most tangible progress, but even here, the explored area is miniscule.

1. Human Exploration: A Single Celestial Body

• The Moon: Twelve astronauts have walked on the lunar surface during the Apollo missions (1969-1972), exploring sites within a few hundred miles of each other. They brought back 842 pounds of rocks. The total area traversed on foot is less than 100 square miles. The Moon’s surface area is about 14.6 million square miles. We have directly explored far less than 0.001% of another world’s surface with human boots.
• Low Earth Orbit (LEO): The International Space Station (ISS) has been continuously inhabited for over two decades, making it humanity’s longest-running outpost. Hundreds of astronauts have lived and worked there, conducting experiments in microgravity. This represents a permanent human presence in a very specific orbital zone, about 250 miles above Earth. It is exploration of an environment, not a planetary surface.

2. Robotic Exploration: A Scattering of Landers and Rovers Our robotic emissaries have been far more ambitious, yet their footprint is still a collection of dots on a vast canvas.

• Mars: We have successfully landed eight missions on Mars. Rovers like Sojourner, Spirit, Opportunity, Curiosity, and Perseverance have traversed a combined total of less than 50 miles across the Martian surface. The planet’s land area is roughly equivalent to Earth’s dry land. Our rovers have explored a few select sites—craters and plains—representing a vanishingly small percentage of the planet’s geology.
• Other Worlds: We have soft-landed probes on Venus (Soviet Venera missions), Titan (Saturn’s moon, via Huygens), and a comet (Rosetta’s Philae). Each mission studied its immediate landing zone for hours, days, or months. The asteroid Bennu and the Ryugu asteroid were sampled by orbiters (OSIRIS-REx and Hayabusa2), providing pristine material from a single location on each rock.
• Flybys: Missions like Voyager, Pioneer, New Horizons (which flew past Pluto), and Juno (orbiting Jupiter) have conducted grand tours, imaging and measuring planets, moons, and rings from space. They have mapped these worlds in unprecedented detail, but they are snapshots from a passing train, not ground-level exploration.

In total, the number of celestial bodies (planets, moons, asteroids, comets) that have been directly touched by a human-made object is fewer than 20. There are over 200 known moons in our solar system alone, millions of asteroids, and countless comets. The percentage of objects we have physically interacted with is statistically zero.

The Realm of Remote Observation: Mapping the Unreachable

This is the true powerhouse of cosmic exploration, accounting for nearly all of our knowledge. Here, “explored” means “characterized from afar.”

• Our Solar System: Space telescopes like Hubble and ground-based observatories have mapped the surfaces of planets and moons in incredible detail. We have cataloged hundreds of thousands of asteroids and comets by their reflected sunlight. We have studied the atmospheres of gas giants and even detected water vapor on some moons. We have, in essence, remotely explored the entire solar system through observation, but without physical contact.
• Exoplanets: Since the 1990s, we have confirmed over 5,500 planets orbiting other stars. We have not imaged most of them directly; we infer their existence by the wobble they induce in their star (radial velocity) or the dimming caused when they transit across its face (photometry). For a tiny fraction, we have begun to characterize their atmospheres using spectroscopy.