This week’s Lite bulletin is (admittedly tentatively) to the previous AITN bulletin in that it discusses other objects in the Solar System, beyond planets and moons, but that’s the end of the link! It is an article from April about the largest comet ever discovered, with the article discussed linked here:
This comet, thankfully, won’t cause any concern for Earth (since it won’t get within a billion miles of us at its closest approach, however, it is a behemoth. This comet is 85 miles across and is 50 times larger than usual, weighing in at a mass of 500 trillion tonnes (5 x1014 kg). Now this mass doesn’t compare to that of Earth or the Moon (6 x1024 kg and 7 x1022 kg, respectively) but it is still very large.
The discovery of this object, and its size, was confirmed using the Hubble Space Telescope, but it was initially observed by the Dark Energy Survey, a survey that is trying to observe galaxies to determine the nature of dark energy in the Universe. This survey would also pick up near-by objects, and this comet would have left a trail on the images, indicating something close and fast moving, relative to the Earth!
As alluded to above, comets are different to asteroids, mainly due to the presence of an atmosphere surrounding the central body (nucleus). This nucleus, made of rock, dust, ice and other frozen molecules, is surrounded by a very thin atmosphere. When the comet makes its way towards the Sun, this atmosphere is heated by the radiation pressure of the star, causing a “coma” or tail (which points away from the Sun) and this is what makes comets look so spectacular in the sky. This tail is made up of water and dust.