October 10 – Triton

Discovered on October 10th 1846 by William Lassell, (who was living and working at that time in West Derby, Liverpool), the Solar System’s biggest retrograde moon Triton, aka Neptune I, is, at 1,353 km radius (approx) the largest satellite of Neptune.

Triton from Voyager 2 (image: NASA)
Triton from Voyager 2 (image: NASA)

Lassell wasn’t daft.  The massive Neptune itself had only been discovered 17 days previously, so where else was he going to be looking for moons?

Current thinking is that Triton is a captured Kuiper Belt Object.  It has a thin atmosphere of mostly nitrogen, with a little methane mixed in, and is, like our own Moon, locked in a synchronous orbit, meaning it always keeps the same face pointing toward its parent (or possibly in this case “adoptive parent”).

Triton (image credit: NASA/JPL-Caltech)
Triton (image credit: NASA/JPL-Caltech)

1868  –  Discovery of asteroid 106 Dione by J C Watson.  Not to be confused with the Saturnian moon of the same name, this Dione is a main belt, G-type asteroid of around 147 km diameter.  The name is a reference to a titaness of Greek mythology, whom some sources call the mother of Aphrodite.

1874  –  Discovery of asteroid 139 Juewa, also by J C Watson.  This main belt asteroid of about 160km wide was discovered by Watson during a visit to China.  He was there to view the transit of Venus on December 9th, but couldn’t resist bagging an asteroid while he waited.  The name was chosen by Prince Gong (or Kung), son of the Emperor.

Prince Gong of the Qing Dynasty.
Prince Gong/Kung of the Qing Dynasty.

The photograph shows a 40-ish year old Gong, looking about 60. It was taken by the Scottish photographer John Thomson.