Caloris

Caloris, officially the Caloris Basin, is a colossal impact basin on the planet Mercury. It is among the largest confirmed impact structures in the Solar System, with a diameter of about 1,550 kilometers (960 miles). It was first detected from Mariner 10 images in the 1970s and was later mapped in greater detail by the MESSENGER mission (2008–2015).

Geology and morphology: Caloris is a complex, multi-ring basin. It comprises a broad, rugged rim set by concentric mountain belts, a floor that includes regions of smooth plains and disrupted terrain, and evidence of ejecta blankets. The interior is faulted and shows geomorphological units whose exact layering remains debated.

Formation: The basin formed when a large asteroid or comet collided with Mercury early in its history, likely around 3.8 to 4.0 billion years ago during the Late Heavy Bombardment. The impact released enough energy to generate substantial seismic effects and reshape the nearby crust.

Antipodal effects: The impact's seismic energy produced notable deformation on the opposite side of Mercury, an effect associated with the so-called “weird terrain,” which is used to study the planet's crustal response to massive impacts.

Naming and designation: The name Caloris is Latin for warmth or heat, and the term was formalized by the International Astronomical Union for this feature.

Observations and significance: Caloris serves as a key landmark for understanding Mercury's crust, impact history, and the evolution of its surface. Data from MESSENGER have refined measurements of its size, structure, and composition.