Introduction
Near-Earth Objects (NEOs) are asteroids and comets with perihelia less than 1.3 AU. The catalog of known NEOs is essential to planetary defence: an unknown impact-class NEO cannot be deflected. The U.S. Congress has mandated cataloguing of all NEOs larger than 140 m diameter (an impact-class threshold roughly equivalent to a regional-scale damage event). Current ground-based and planned space-based surveys are progressively reducing the catalog gap. This report reviews the survey landscape, completeness statistics, and the principal remaining gaps.
The catalog as of 2026
The Minor Planet Center (MPC) catalogue lists approximately 35,000 NEOs as of early 2026. Of these, approximately 11,000 are larger than 140 m diameter (the congressional-mandate threshold), against a total estimated population of approximately 25,000 in this size range - giving completeness of approximately 44 percent. For the larger 1 km size class, completeness is approximately 95 percent of the estimated 1,000-object population. For the smaller 30 m size class, completeness is below 5 percent of the estimated population approaching 1 million.
Ground-based surveys
Three ground-based surveys dominate current NEO discovery:
Catalina Sky Survey (CSS) at Mount Lemmon Observatory uses three telescopes operating since 2003. CSS has produced the largest cumulative discovery count of NEOs.
Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) at Haleakala uses two 1.8 m telescopes operating since 2010. Pan-STARRS produces the deepest survey at the largest sky-area cadence.
ATLAS (Asteroid Terrestrial-impact Last Alert System) uses four 0.5 m telescopes (in Hawaii, Chile, and South Africa) optimised for short-warning detection of small impacting NEOs. ATLAS specialises in last-minute warning rather than survey completeness.
Several other surveys (the ESA Flyeye telescope, the Korean SOAR network, China's STA programme) provide complementary coverage. The combined ground-based programme is estimated to take approximately 30 years to reach 90 percent completeness at the 140 m level under current cadence.
The dark-NEO gap
Ground-based optical surveys are sensitive to NEO reflected sunlight. Dark NEOs (geometric albedo less than 0.05) are under-detected because the apparent brightness of a given NEO depends on size and albedo together. The dark-NEO population is estimated at approximately 30 percent of the total but is under-represented in the catalogue by a factor of 2-3. The bias is most severe for the smaller size classes where survey detection is at the magnitude limit.
Space-based survey advantage
Space-based infrared surveys detect NEOs by their thermal emission, which is approximately independent of albedo. Infrared surveys therefore close the dark-NEO gap and have higher completeness for a given mission lifetime than equivalent ground-based optical surveys. Two infrared mission classes are relevant:
Repurposed missions: NASA's NEOWISE used the WISE infrared satellite for NEO discovery from 2013 to early 2024. NEOWISE produced approximately 1,000 NEO discoveries plus albedo-and-diameter measurements for approximately 30,000 NEOs.
Dedicated missions: NEO Surveyor (formerly NEOCam), planned for 2027 launch by NASA, is a dedicated infrared survey telescope at the Sun-Earth L1 Lagrange point. NEO Surveyor is designed to reach 90 percent completeness at the 140 m size class within approximately 10 years of operation, dramatically faster than ground-based completeness extrapolation.
Vera C. Rubin Observatory contribution
The Vera C. Rubin Observatory (LSST) begins full operation in 2026 and is expected to dramatically increase NEO discovery cadence. Rubin's wide-field, deep-imaging survey will detect approximately 100,000 new NEOs in its first decade, including most of the remaining 140 m-class population. The Rubin survey is optical and therefore subject to the dark-NEO bias, but the deep imaging will identify many smaller NEOs that ATLAS-class surveys miss.
Planetary defence integration
NASA's Planetary Defense Coordination Office, established in 2016, integrates NEO catalogue data with impact-risk assessment and deflection planning. The DART mission (2022) demonstrated kinetic-impactor deflection of asteroid Dimorphos, validating the principal active-defence technique. Combined with the catalogue completeness investment, the planetary-defence framework is now mature enough to handle most realistic impact scenarios with adequate warning. The remaining vulnerability is short-warning impacts from previously-undetected NEOs, particularly in the dark-NEO and small-size populations.
Outlook
The NEO Surveyor launch (2027) and Vera C. Rubin Observatory full operations (2026) together constitute a step-change in NEO catalogue completeness. The 90 percent completeness goal at the 140 m size class is expected to be reached in the early 2030s. Beyond that, the smaller-size populations remain a long-term completeness challenge that will be addressed by continued ground-based and space-based survey investment.