Astro2110 – The Solar System

“Out to sea, the calm lagoon waters were darkening, while the comets overhead glowed brighter, omens in the gloaming.” ― Julian May, Perseus Spur

A comet is an icy small body in the solar system that when passing close to the Sun, it produces a visible atmosphere or coma from a process called outgassing — Wikipedia. I always hope to see the comet steaming away into the space and passing the night sky with a beautiful tail. Although most people may not get the chance to witness their beauty themselves, some pictures and scientific facts about famous comets will help us understand more about those mysterious objects traveling in the solar system.

• HALLEY’S COMET

Halley’s Comet is probably the most famous comet in history. It was named after the astronomer Edmund Halley who found out its 76-year orbit. “Halley is the only known short-period comet that is regularly visible to the naked eye from Earth, and the only naked-eye comet that might appear twice in a human lifetime.” — Wikipedia. Comet Halley will return to the inner Solar System in the year 2061.

• COMET HALE-BOPP

Hale–Bopp was discovered on July 23, 1995 prior to it becoming naked-eye visible on Earth. One if its outstanding traits is its intense brightness, which is due to the exceptionally large size. Comet Hale-Bopp was estimated to have a nuclei about 40 km across, which is way larger than most comets. And Comet Hale-Bopp holds the record for a 19 months period of naked-eye visibility, which is amazing!

• COMET HYAKUTAKE

Comet Hyakutake was first discovered by an amateur astronomer called Yuji Hyakutake  from southern Japan on January 30, 1996 using a pair of binoculars. Then in the spring of that year, this small bright comet with a nucleus of 1.6 to 3,2 km made a close flyby of Earth — sporting one of the longest tails ever observed. — Wikipedia.

Everyone got some basic knowledge about planets, stars, and asteroids at school, but not many people actually know much about comets. How are these things formed? Why do they have tails? How big are they? Stay with me if you want to find out.

Our entire Solar System was created by the collapse of a giant, diffuse cloud of gas and gas 4.6 billion years ago, and comets are simply some leftovers from the formation of the planets. Comets mainly contain dust, ice (the temperature in space is cold enough to produce ice), carbon dioxide, ammonia, methane, and are often called “dirty snowballs” by scientists.

In the outer Solar System comets remain frozen, and it is impossible to see them from the Earth due to their small size. “As a comet approaches the inner Solar System, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them. The streams of dust and gas thus released form a huge, extremely tenuous atmosphere around the comet called the coma, and the force exerted on the coma by the Sun’s radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun,” – Wikipedia.

The solid nucleus of comets is usually less than 50 km, but the coma may be larger than the SUN! Comet’s tail might extend up to 3.8 astronomical units (570 Gm). A comet can lose its tail only if magnetic reconnection occurs. This means that if at some point where the ion tail is sufficient, and the magnetic field lines are squeezed together, the tail “disconnects”.

So, to sum up… Comets are “dirty snowballs” made of dust, ice and some gases, their bodies might be tiny for cosmos, but their tails are suuuuper long! We do not see them too often, and they still remain a bit mysterious… In Russia we say that you need to make a wish when you see a comet in the sky!