Welcome to the April episode of Comet Watch featuring special guest, Michelle Thaller Ph.D  . My thanks, as always to my co-host Neil Norman!   Mary McIntyre is unwell and will be joining us again next month.

BAA Comet Section Visual Observations Page

Comet Lexell was discovered by Charles Mesier on June 14th,1770.

At this one and only apparition, it passed by Earth on its way to a August 14th perihelion, at a distance of 0.015 AU’s or 1,400,000 miles.

The comet was a member of the Jupiter family comets and originally had a perihelion distance of beyond 2 AU’s, but a close Jupiter approach by the comet in 1767 lead to its perihelion distance being radically changed . Comet Lexell holds the distinctions of being the first known JFC and also first NEO.

The comet again approached close to Jupiter in 1779 and the perihelion distance was increased greatly to some 3.3 AU’s.

The comet is today considered lost, but many still speculate that the comet was eventually expelled from the Solar System by Jupiter.

The debate continues………..

D/1770 L1 (Lexell)  http://cometography.com/pcomets/1770l1.html

Finding long lost Lexell’s comet: the fate of the first discovered near-earth object   https://arxiv.org/pdf/1802.08904.pdf

Evolution of orbit of Lexell’s Comet   https://vimeo.com/58118316

The Late Heavy Bombardment (abbreviated LHB and also known as the lunar cataclysm) is an event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth.

Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets  https://www.nature.com/articles/nature03676

http://www.pbs.org/wgbh/nova/blogs/secretlife/space-science/michelle-thaller/

Spacewatch  https://spacewatch.lpl.arizona.edu/

Asteroid Day   https://asteroidday.org/

Neoshield     http://www.neoshield.eu/

NEOShield Official Youtube channel