Comet C/2021 A1 (Leonard), 2021’s brightest comet, has just passed its closest approach to earth, at a distance of 34 million kilometres from our planet on December 12. The comet has continued on its approach towards the sun, passing a mere 4.2 million kilometres from Venus on the night between December 17 and 18, making this the closest cometary approach to Venus ever observed. It is expected to round the sun at its orbit’s perihelion on January 3, 2022, at a distance of 90 million kilometres from the sun.
Orbital calculations for the comet have shown that its estimated orbital period is of around 80,000 years. It is also a very fast-moving comet, moving at a speed of over 70 kilometres per second relative to earth on a path which will most likely see it ejected from the solar system.
Such long-period comets normally originate from the outer reaches of the solar system, well past the Kuiper belt at large distances away from the sun. Indeed, on its 40,000 year approach from aphelion – the furthest point from the sun in its orbit – the comet is estimated to have travelled some 3,700 astronomical units, or approximately 550 billion kilometres!
Comets are normally huge chunks of rock and ice, with several different volatile compounds being frozen on its surface in the frigid outer reaches of the solar system and thus forming its icy surface content.
As a comet traverses into the inner solar system on its highly elliptical path, it will rapidly heat up as it approaches the sun at gathering speed.
This typically results in comets exhibiting tails of material, with a dust and gas tail both pointing away from the sun.
The dust tail results from the release of dust particles previously locked inside volatile ices on the comet’s surface. As the volatile ice sublimes and forms the gas tail, dust is released to form a trailing dust tail as well.
Since the dust particles are driven out of the comet’s coma more slowly than the gaseous particles, some of the forward motion of the comet itself is retained, and the dust tail thus exhibits a more curved, wider appearance than the gas tail.
While the comet might brighten up enough to be visible with the naked eye, the use of binoculars from dark skies is advised to assist in observations. Short exposure images should easily reveal the comet, with the comet’s coma and tail easily visible in small telescopes.
Josef Borg completed a PhD in Astronomy at the Institute of Space Sciences and Astronomy, University of Malta, and is currently a researcher at the Faculty of Health Sciences at the University of Malta. He is also Malta’s representative on the European Astrobiology Network Association (EANA) council.
Sound Bites
• James Webb Space Telescope finally set for launch!: It has taken the better part of three decades for the James Webb telescope to finally be ready for launch, making it through its design phase and its fair share of delays, issues, setbacks and even cancellation threats. The telescope will now launch from the Kourou Space Centre in French Guiana on a ESA Ariane 5 rocket no earlier than December 24.
https://skyandtelescope.org/astronomy-news/james-webb-space-telescope-science/
• NASA’s Parker Solar Probe has touched the sun’s corona in daring mission milestone: The Parker Space Probe, which has spent three years winding its way by planets, finally reached the atmosphere of the sun. The aim of the mission is to learn more about the origin of the solar wind, which pushes charged particles outwards across the solar system, and thus assist in solar weather prediction.
https://www.space.com/parker-solar-probe-touches-sun-atmosphere
For more sound bites listen to Radio Mocha every Saturday at 7.30pm on Radju Malta and the following Monday at 9pm on Radju Malta 2 https://www.fb.com/RadioMochaMalta/.
DID YOU KNOW?
• Comets can have short periods, with some observed and recorded frequently across history! One of the more famous comets in our solar system, Halley’s Comet, completes one orbit around the sun in approximately 75.32 earth years. The comet is indeed depicted in the famous Bayeaux tapestry, and first recorded observations of the comet date back over 2,000 years!
• Comet Shoemaker-Levy 9 was observed to collide with Jupiter in July 1994! The comet’s collision with Jupiter marked the first-ever observation of the collision of two extraterrestrial solar system objects. Twenty-one separate comet fragments hit Jupiter’s atmosphere, providing a unique window of opportunity for astronomers to learn more about Jupiter itself.
• Crashing comets and asteroid were more common in the early solar system. During the Late Heavy Bombardment, early on in the formation history of the solar system, earth was likely bombarded by a number of comets and asteroids when it had not yet cleared its orbit. Indeed, incoming comets are estimated to have contributed to around 10 per cent of all of earth’s water!
For more trivia, see: www.um.edu.mt/think.