From interstellar comets to alien clues: 2025’s top space discoveries

The past year delivered unprecedented discoveries in space. Astronomers uncovered clues about Mars, interstellar comets, exoplanets, and dark energy, captivating scientists and enthusiasts worldwide.

3I/ATLAS: An Interstellar Visitor
The highlight of late 2025 was comet 3I/ATLAS. The Chilean Asteroid Terrestrial-impact Last Alert System spotted it first. Observations began on July 1 near Sagittarius. Its trajectory was hyperbolic, confirming it came from interstellar space. The comet moved faster than any previously recorded, at 36 miles per second. NASA and ESA spacecraft monitored it during solar conjunction. Scientists found its chemistry largely resembled solar system comets. Slightly more nickel than iron revealed its star system origin. The comet also displayed a rare "anti-tail" pointing toward the Sun. Tracking continues into 2026 to understand its full composition.

Signs of Early Supermassive Black Holes
JWST deep images revealed unusual luminous red dots. These objects did not resemble stars or dwarf galaxies. Astronomers now identify them as forming black holes. The black holes emerged in dense gas clouds early in the universe. Their formation challenges previous assumptions about supermassive black hole growth.

Dark Energy Shows Unexpected Behaviour
DESI released data from over 13 million galaxies and quasars. Researchers observed dark energy weakening over the past 4.5 billion years. Previously, dark energy was thought constant across cosmic history. Findings suggest exotic "phantom dark energy" existed earlier, then weakened unexpectedly. The discovery could reshape cosmology and models of universal expansion.