NEW STUDY REVEALS BIG COMPOSITIONAL SHIFT IN SMALL NEAR-EARTH ASTEROIDS

Findings improve understanding of meteorite origins and impact‑risk models.

FLAGSTAFF, Ariz., April 24, 2026 /PRNewswire/ -- A new study has highlighted a striking, size-dependent trend in the compositions of near-Earth asteroids (NEAs). By analyzing 189 NEAs, an international team of planetary scientists led by Dr. Nick Moskovitz of Lowell Observatory found that the smallest asteroids approaching Earth differ significantly from their larger counterparts. The discovery offers fresh insight into meteorite origins, asteroid-family evolution, and the materials most likely to reach Earth's atmosphere—key information for planetary defense.

The research draws on more than a decade of data, from 2014 to 2025, collected by the Mission Accessible Near-Earth Object Survey (MANOS). Observations were made using three major 4-meter-class telescopes: the Lowell Discovery Telescope in Arizona, the SOAR Telescope in Chile, and the Mayall Telescope at Kitt Peak National Observatory.

These facilities enabled the team to classify the asteroids based on how they reflect sunlight at four different wavelengths of light, which provides a measure of the surface colors of the objects.
The team devoted special attention to understanding and correcting for how rotational brightness variations—changes in an asteroid's brightness as it spins–can influence the measured colors. These corrections proved essential for accurate color measurements. "If you don't account for how an asteroid brightens and dims as it spins, you can end up with misleading colors," says Moskovitz. "For individual objects, the effect can be dramatic, and for population studies, it can introduce subtle but important biases."

After classifying the objects, the researchers combined their results with other similar surveys to build a comprehensive dataset of colors across a wide range of NEA sizes. A clear pattern emerged: S-complex asteroids—those most similar to the most common type of meteorites, known as ordinary chondrites—dominate the population at kilometer scales but become far less common among smaller objects.

According to the study, S-complex NEAs represent roughly 65% of kilometer-scale objects, but only one-third of objects smaller than 50 meters. The team evaluated several potential explanations for this trend, including heating from the Sun, tidal resurfacing during near-Earth encounters, and the size of the grains of material that cover the surfaces of asteroids. None could fully account for the observed shift. Instead, the results align with recent models showing that small NEAs originate from a handful of young asteroid families in the Main Belt, whose compositions differ from the broader population feeding larger NEAs.

"This is one of the clearest pieces of evidence yet that the smallest NEAs come from a different mix of sources," Moskovitz says. "It helps explain why the meteorites that land on Earth don't perfectly match what we see among larger asteroids."

Beyond scientific insight, the findings have practical importance. "Understanding what small NEAs are made of is essential for impact-risk assessment," Moskovitz notes. "These are the objects most likely to reach Earth's atmosphere, so knowing their compositions helps us model how they behave if they were to enter the atmosphere and to inform any risk posed by an object large enough to reach the ground."

The study was published on April 23 in The Planetary Science Journal (Volume 7, Issue 4).

About Lowell Observatory
Founded in 1894, Lowell Observatory in Flagstaff, Arizona, is a renowned nonprofit research institution. It is the site of historic and groundbreaking discoveries, including the first evidence of the expanding universe and the discovery of Pluto. Today, Lowell's astronomers utilize global ground-based and space telescopes, along with NASA spacecraft, for diverse astronomical and planetary science research. The observatory hosts more than 100,000 visitors annually for educational tours, presentations, and telescope viewing through a suite of world-class public telescopes.

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SOURCE Lowell Observatory