How Much of the Ocean Has Been Explored? 27.3% Mapped

Most people believe we’ve explored barely a sliver of the ocean, but NOAA’s June 2025 data shows 27.3% of the global seafloor already mapped at high resolution — a figure that quietly rewrites the familiar “90% unexplored” shorthand while revealing how much remains unseen. The reality is more nuanced than any single percentage suggests.

Seafloor visually observed: less than 0.001% · Ocean mapped at high resolution: 27.3% · U.S. seafloor mapped: 54% · Earth’s surface covered by ocean: 70%

How much of the ocean has been explored?

The answer depends entirely on what you count as “explored.” Direct visual observation of the seafloor — humans or their cameras actually seeing it — covers less than 0.001% of the ocean floor. But that metric almost nobody uses. The figure you’ll encounter most often in news articles and social media, the “5% explored” shorthand, typically refers to human-led exploration via diving, submersibles, and remotely operated vehicles (ROVs), which according to various estimates covers roughly 5% of the ocean.

High-resolution mapping tells a somewhat different story. As of June 2025, NOAA Ocean Exploration reports that 27.3% of the global seafloor has been mapped using multibeam sonar systems capable of detecting seafloor features and water column characteristics. That’s a substantial jump from earlier estimates of 23-25%, and it reflects intensified mapping campaigns worldwide.

Current exploration percentages

• Direct visual observation: Less than 0.001% of the seafloor
• High-resolution sonar mapping: 27.3% globally (June 2025)
• Human-accessible exploration: Approximately 5%
• U.S. waters mapped: 54% of U.S. seafloor

The U.S. has actually outpaced the global average. NOAA reports that 54% of the seafloor beneath American waters has been mapped to modern standards as of June 2025, with active campaigns ongoing across the Pacific Remote Island territories, Hawaiian waters, the Atlantic/Gulf region, and even the Great Lakes.

What counts as explored?

The confusion around ocean exploration percentages stems from loose definitions. “Explored” can mean:

• Mapped: Sonar or satellite measurements creating a visual representation of the seafloor
• Visited: Physical presence of humans, submersibles, or ROVs at a specific location
• Sampled: Collection of water, sediment, or biological specimens for analysis
• Observed: Direct visual confirmation by camera or human eyes

Each definition yields dramatically different numbers. Multibeam sonar can scan thousands of square kilometers in a single day; a human-occupied submersible covers far less ground but collects vastly richer data. This is why NOAA distinguishes between “mapped” and “explored” — mapping tells you what’s there, while exploration tells you what it means.

Why is 90% of the ocean unexplored?

The persistence of the “90% unexplored” claim obscures a more complicated reality, but the underlying concern is legitimate — the ocean presents extraordinary challenges that no amount of funding alone can overcome in the near term.

Technological challenges

Mapping the entire ocean seafloor with a single ship operating at all depths would take nearly 1,000 years, according to NOAA Ocean Exploration. The ocean’s sheer volume — it covers 70% of Earth and reaches depths of nearly 11 kilometers at the Challenger Deep — makes comprehensive coverage logistically daunting.

Multibeam sonar, the primary tool for high-resolution mapping, requires ships equipped with expensive sensors and trained crews. These vessels cost thousands of dollars per day to operate. Satellite-derived bathymetry can estimate depths in shallow waters but cannot penetrate to the depths where the most mysterious terrain lies.

Depth and pressure barriers

90% of the ocean qualifies as “deep water” — defined as depths greater than 200 meters. At these depths, pressure becomes a limiting factor for equipment, communication becomes difficult, and surface support operations become expensive and complex.

Autonomous underwater vehicles (AUVs) are beginning to change this calculus. Without the tether to a surface ship, AUVs can descend to crushing depths and operate for days or weeks on pre-programmed missions. NOAA and other agencies are increasingly deploying these systems, but the technology still faces limitations in battery life, data transmission, and navigation precision in featureless deep-sea terrain.

“The first step to building that understanding and unlocking the ocean’s potential is ocean mapping,” NOAA Ocean Exploration states — a reminder that even basic cartography remains a frontier challenge.

Why did NASA stop exploring the sea?

NASA never stopped exploring the ocean — but it shifted its approach dramatically after the early days of oceanographic satellites. The premise that NASA abandoned ocean exploration is a myth rooted in misunderstanding of the agency’s role versus NOAA’s.

NASA ocean research status

NASA launched Seasat in 1978, the first civilian oceanographic satellite, which demonstrated that orbital sensors could measure ocean surface topography, temperatures, and wind patterns. This marked the beginning of satellite oceanography, a field where NASA remains active.

However, NASA’s mandate focuses on space. When it comes to in-situ ocean exploration — sending ships, submersibles, and ROVs to the seafloor — that responsibility falls to NOAA, the Navy, and academic institutions. NASA supports ocean science through satellite missions like Sentinel-6 and through grants to researchers, but it doesn’t operate oceanographic survey vessels.

The confusion often arises because NASA and NOAA both study the ocean from their respective domains: NASA from orbit, NOAA from the surface and water column. They’ve simply divided the work according to their capabilities.

Ongoing programs

NOAA Ship Okeanos Explorer exemplifies the ongoing U.S. commitment to ocean mapping. The vessel surpassed 1,000,000 square kilometers of mapped seafloor in early 2014, then doubled that to 2,000,000 square kilometers by November 2021 during the Windows to the Deep expedition on the Blake Plateau. In 2025 alone, 70,700 square nautical miles of new bathymetric data were added to U.S. repositories.

International coordination also continues. The International Hydrographic Organization’s Digital Bathymetry Data Center (IHO DCDB) aggregates seafloor measurements from multiple nations, creating a progressively more complete picture of global terrain.

How much of the ocean has been explored compared to space?

It’s become a popular talking point: more people have set foot on the Moon than visited the deepest point in the ocean. While technically accurate, this comparison flatters space exploration less than you might expect.

Space exploration metrics

Space agencies have mapped virtually the entire lunar surface and much of Mars through orbital spacecraft. However, this mapping is remote sensing — telescopes and cameras on satellites, not physical visitation. The same technology that lets us “see” the ocean from space provides far less resolution than ships running multibeam sonar directly above the seafloor.

Twelve astronauts walked on the Moon during Apollo missions. Three submersible crews have reached the Challenger Deep: Don Walsh and Jacques Piccard in 1960, filmmaker James Cameron in 2012, and explorer Victor Vescovo in 2019. The ratio seems to favor space — until you consider that the Moon is 384,400 kilometers away, while the Challenger Deep is roughly 11 kilometers below the nearest ocean surface.

Ocean vs space visuals

“If exploration means physically reaching and directly observing new locations, then ocean exploration clearly outpaces space,” observe analysts at World Atlas. Humans have directly visited the deep seafloor in ways that remain impossible for Mars or Venus — we can collect samples, deploy instruments, and observe life in situ.

The comparison also highlights funding disparities. Ocean exploration receives a fraction of space budgets, despite the ocean’s proximity and direct relevance to Earth’s climate, biodiversity, and resources. “Ocean exploration underfunded compared to space despite discovery potential,” notes Marine Technology News.

A direct comparison reveals how differently we approach exploring our own planet versus distant worlds. For instance, the recent discovery of Mega shark remains discovered in Australia highlights the potential for groundbreaking finds in our own oceans. Mega shark remains discovered in Australia

The pattern is clear: space exploration benefits from concentrated public attention and consistent funding, while ocean exploration struggles for visibility despite its practical importance.

Will humans ever explore 100% of the ocean?

The short answer is “not anytime soon” — but the longer answer involves careful distinctions between what “100% explored” would require and what progress we can realistically expect.

Technological advancements needed

Fully mapping the ocean floor to high resolution is theoretically achievable with sufficient investment and continued technology development. The U.S. has set a target of fully mapping U.S. waters by 2040, according to NOAA Nautical Charts. Achieving this would require sustained funding, expanded ship fleets, and broader deployment of autonomous systems.

Current technology can map vast areas efficiently but struggles with the full depth range. Multibeam sonar works well to around 11,000 meters, but extreme depths require specialized equipment and longer mission times. New AUV designs with enhanced battery capacity and synthetic-aperture sonar promise to accelerate coverage, but they remain expensive and limited in number.

Mapping progress

Progress is measurable and accelerating. Global mapping has climbed from earlier estimates of 10-20% to the current 27.3% as of June 2025. U.S. waters stand at 54% mapped, with regional campaigns targeting the remaining gaps.

NOAA’s National Centers for Environmental Information (NCEI) archives bathymetry data from multiple sources — multibeam, singlebeam, lidar, and crowdsourced contributions — freely available to researchers and the public. This data-sharing infrastructure enables continuous progress as new surveys build on previous work.

“It would take one ship nearly 1,000 years to map the entire ocean at all water depths,” NOAA Ocean Exploration notes — a reminder that “100% mapped” is a matter of decades, not years, and “100% explored” in the sense of direct human observation may remain forever aspirational.

Related reading: Big Blue House · Octopus Energy

NOAA reports 27.3% high-resolution seafloor mapping globally, a milestone detailed in mapping progress overview amid accelerating international efforts.

Frequently asked questions

The ocean remains Earth’s most underexplored frontier, but the “95% unexplored” headline misrepresents a more nuanced reality. Sonar mapping has covered 27.3% of the seafloor at high resolution, and progress is measurable — U.S. waters reach 54% mapped, with a 2040 target for full coverage. The gap isn’t ignorance; it’s that the work never stops. For policymakers and funders, the implication is straightforward: sustained investment in autonomous systems and coordinated international campaigns can close mapping gaps within decades. For scientists, the frontier shifts from “where haven’t we looked?” to “what lives in what we’ve found?” — a question that demands resources focused on the water column itself, not just the floor beneath it.