Written by Dr Melvin Chen, NTU-USP Faculty Member

The comet of the century is getting brighter as it makes its closest pass by Earth this week: C/2023 A3. The two facilities that detected C/2023 A3, Tsuchinshan (紫金山) Observatory and the ATLAS (Asteroid Terrestrial-impact Last Alert System) system, yield its longer, double-barrelled name: Tsuchinshan-ATLAS. Tsuchinshan-ATLAS may be spotted this weekend in Singapore’s skies, without the aid of binoculars or telescopes.

Comet C/2023 A3, or Tsuchinshan-ATLAS, was pictured about 99.4 million miles away from Earth by NASA astronaut Matthew Dominick using long-duration photography on a camera programmed for high sensitivity aboard the International Space Station.

Carl Sagan once remarked that if you wish to make an apple pie from scratch, you must first invent the universe. In a similar vein, if you wish to gaze at the Tsuchinshan-ATLAS comet this weekend, it may be helpful to understand its cosmic context. The Oort Cloud, a cloud representing the gravitational edge of our solar system and far beyond the orbit of Neptune, is thought to contain billions, or even trillions, of icy bodies such as comets. Like all comets, Tsuchinshan-ATLAS consists of frozen remnants from the birth and early formation of our solar system 4.6 billion years ago. Astronomers sometimes refer to comets as dirty snowballs or icy dirtballs. Unlike comets, asteroids are typically rocky or metallic bodies that hail from the asteroid belt within the inner solar system, between the orbits of Mars and Jupiter. Meteorites are fragments of comets or asteroids after they have landed on the surface of a planet.

taken in Australia, CC BY-SA 2.0

As stargazers look forward to the double bill of C/2023 A3 (Tsuchinshan-ATLAS) this weekend and C/2024 S1 (ATLAS) toward the end of this month, it is tempting to wax philosophical about humanity’s enduring interest in small solar system bodies. According to the panspermia hypothesis, life may have originated elsewhere in the universe and emerged on Earth as a result of microbes or seeds brought by asteroids, comets, or meteorites. The Black Stone (al-Ḥajar al-Aswad) of Mecca, a Muslim relic dating back, according to tradition, to the time of Adam and Eve, has been described as a meteorite. When it famously appeared in 1066 (the year of the Norman conquest), Halley’s comet, which passes by Earth roughly once every 80 years, was interpreted as a bad omen for King Harold II of England. King Harold II was eventually defeated and killed by William the Conqueror at the Battle of Hastings. The Bayeux tapestry, an embroidered cloth depicting the events leading up to the Norman conquest, features Halley’s comet at the centre of one of its scenes. Last but not least, according to the Alvarez hypothesis, the impact of a large asteroid on Earth resulted in the Cretaceous-Tertiary (K-T) mass extinction event 65 million years ago. This asteroid impact is believed to have created the Chicxulub crater in the Yucatán Peninsula in Mexico.

C/2023 A3 (Tsuchinshan-ATLAS) on 10 June 2024 as seen from an 8-inch reflector f/4 telescope. 59 30 seconds frames were stacked with DSS and edited in SIRIL.

Whether we regard them as bringers of life, loci of splendour and mystery, auguries and portents, fit subjects for great art, or harbingers and bringers of doom, there is no denying their allure. In ‘Auguries of innocence’, William Blake speaks of seeing a world in a grain of sand. I would like to extend a philosophical challenge to stargazers this weekend: the challenge of seeing the universe and our place in it in a 4.6 billion-year-old dirty snowball.

The writer of this blog post is incidentally an NTU-USP faculty member who is currently pivoting toward big philosophy in terms of his research interests. Big philosophy aims to understand how things in the broadest possible sense of the term hang together in the broadest possible sense of the term, from the Big Bang to the present. Tsuchinshan-ATLAS provides the perfect big-philosophical context for meditating on the nature of the universe and our place in it. A big philosophy component has been incorporated into the NTU-USP core course SP0001 (‘Writing & Reasoning’).