The Ongoing Decline in Activity of Comet 103P/Hartley 2

How the definition of a planet has changed over 250 years — and why the count may not be final

From 6 to 9 to 11 to 7 to 8: What 250 years has done to our solar system planet count.

How the definition of a planet has changed over 250 years — and why the count may not be final

From 6 to 9 to 11 to 7 to 8: What 250 years has done to our solar system planet count.

Interstellar Comet 3I/ATLAS Shows Rapid Brightening and Gas Emission Near Perihelion

Interstellar comet 3I/ATLAS has been approaching its 2025 October 29 perihelion while opposite the Sun from Earth, hindering ground-based op

Comets reflect on decade of growth

Comet 3I/ATLAS is older than the sun

At over 9 billion years old, the rare interstellar visitor is more than twice the sun's age. The post Comet 3I/ATLAS is older than the sun a

Study Suggests Interstellar Comet 3I/ATLAS Could Be 12 Billion Years Old

Based on the composition of gases spewed by the icy space rock, researchers estimate that our guest might be up to 12 billion years old—abou

Webb Telescope reveals surprising chemistry of interstellar Comet 3I/ATLAS

The third identified interstellar comet in human history has a surprising chemical makeup, raising questions as to how common, or unusual, c