This Week in History: June 21-27

Ice and Stone 2020: Week 26 Content

Jim Christy points to the photographic plate on which he and U.S. Naval Observatory colleague Robert Harrington discovered Pluto’s largest moon, Charon, in 1978. Courtesy U.S. Naval Observatory.

JUNE 22, 1978: U.S. Naval Observatory astronomer James Christy discovers Charon, Pluto’s first-known moon. Charon, the discovery of which would be confirmed with a series of transit and occultation events between it and Pluto that began in 1995, provided a major step in our understanding of Pluto’s size and physical nature. Pluto, its system of moons, and the New Horizons flyby through this system are the topic of a future “Special Topics” presentation. 

JUNE 22, 2019: The ATLAS survey program based in Hawaii discovers a tiny asteroid, designated 2019 MO, that entered Earth’s atmosphere over the Caribbean Sea and disintegrated a little less than twelve hours later. This is the fourth, and thus far most recent, event of this nature that has been detected; these are discussed in a future “Special Topics” presentation. 

JUNE 25, 2020: Comet 2P/Encke, the comet with the shortest-known orbital period, will pass through perihelion at a heliocentric distance of 0.337 AU. Around the beginning of July it becomes accessible from the southern hemisphere and may briefly be bright enough to detect with binoculars. It is this week’s “Comet of the Week.” 

JUNE 26, 1927: Comet 7P/Pons-Winnecke passes 0.039 AU from Earth, the second-closest confirmed cometary approach to Earth during the 20th Century. For a few days it was bright enough to detect with the unaided eye. Close comet approaches to Earth are the subject of a previous “Special Topics” presentation. 

JUNE 26, 2012: A team of astronomers led by Mark Showalter discovers Pluto’s fifth known moon, Styx, in images taken with the Hubble Space Telescope. Pluto and its system of moons are discussed in a future “Special Topics” presentation. 

JUNE 26, 2014: American astronomer Marc Buie discovers the Kuiper Belt asteroid now formally known as (486958) Arrokoth with the Hubble Space Telescope. Arrokoth was encountered by the New Horizons spacecraft at the beginning of 2019. The Kuiper Belt, and the New Horizons mission, are discussed in future “Special Topics” presentations. 

JUNE 27, 1949: German-American astronomer Walter Baade discovers the asteroid now known as (1566) Icarus from Palomar Observatory in California. With a perihelion distance of 0.19 AU, Icarus had the smallest perihelion distance of any known asteroid for over three decades. It makes close approaches to Earth on occasion, and in 1968 it became the first asteroid to be detected via radar. 

JUNE 27, 1997: The main-belt asteroid (253) Mathilde is encountered by NASA’s Near-Earth Asteroid Rendezvous (NEAR) spacecraft – later renamed NEAR Shoemaker – while en route to its final destination of the near-Earth asteroid (433) Eros. The NEAR Shoemaker mission is discussed in a future “Special Topics” presentation. 

JUNE 27, 2018: JAXA’s Hayabusa2 spacecraft arrives at its destination, the near-Earth asteroid (162173) Ryugu. Hayabusa2 left Ryugu late last year and is expected to return to Earth, with collected samples, this coming December. The Hayabusa2 mission is discussed in detail in a future “Special Topics” presentation. 

More from Week 26:

Comet of the Week    Special Topic    Free PDF Download    Glossary

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