Fascinating objects in the cosmos: Comets

A few days ago I wrote a bit about the Swift-Tuttle comet responsible for the Perseids meteor shower that is currently striking the Earth's atmosphere. I hope you could have seen some already. I didn't have the time to gaze the stars yet.

This is the Swift-Tuttle comet, it looks amazing! Comets always inspired men for millennia.

[NASA Image gallery. Photo by Gerald Rhemann]

But what are the comets made of, how are they formed, where do they come from??
Such interesting questions.

In general, comets like Swift-Tuttle, are fragile balls of dust, ice, frozen gases, rock, non volatile mix of grainy particles and dark organic material packed together in irregular shape, that's why they're also called "dirty snowballs".
To be more precise comets contain lots of stuff, including the following, discovered in other comets by spectrographic analysis:
Organic: C, C2, C3, CH, CN, CO, CO2, CS, HCN, CH3CN, HCO, H2CO
Inorganic: H, NH, NH2, O, OH, H2O, S, S2, NH3, NH4
Metals: Na, K, Ca, V, Mn, Fe, Co, Ni, Cu
Ions: C+, CH+, CO+, CO2+, N2+, O+, OH+, H2O+, H3O+, S+, S2+, H2S+, CS2+
Dust: silicates, organic compounds.

Scientists say this is only a fraction of what can be found in a comet.
It makes us wonder if all this compounds could create the spark of life. Probably we'll never know but it's a good theory!

They are formed along with stars but not all stars form this masses, only stars with planetary systems have comets.
They have very elliptical orbits that bring them close to the Sun and shoot them back to orbits well beyond that of Pluto.

Has they come close to the Sun and start heating up, the ices in the comet begin to sublimate bursting out from the interior as jets of gas carrying dust with them, developing a surrounding coma that will grow in size and brightness. This cloud of diffuse material expelled from the nucleus and the nucleus itself constitute the head of the comet and it can be 100000 kilometers wide.

ASTR 1210 (O'Connell) Study Guide

The particles expelled will form a long tail with millions of kilometers in length.
The sun will also induce a huge ionic tail and an hydrogen envelope 1000 times larger than the coma.
When the comet moves far away from the Sun's heat and charged particles influence it is a completely frozen object with almost no activity other than moving and reflecting Sun light.

Source

Distances on the solar system are often measured in Astronomical units.
Earth is about one Astronomical unit (1AU) from the sun (149 597 871 kilometers, roughly 150 million Km), making it a good comparison measure and easy to understand.

It is believed that comets come from two major different sites on the solar system: Oort Cloud and Kuiper Belt.
The Oort Cloud may harbor hundreds of billions, even trillions of icy bodies spread away from each other at least 1AU. It’s round like a ball, and huge! It completely envelops the sun and the rest of our solar system. Every now and then, if something disturbs one of these icy rocks it begins a long fall toward our sun. These comets, called long-period comets, have very large orbits of greater than 200 years.

Scientists believe that comets with orbits of 200 years or less, traveling in the ecliptic plane, come from the Kuiper Belt. Those comets with longer orbits, or that travel at angles to the ecliptic plane, come from the Oort Cloud.

The Kuiper Belt appears to be a flat disk of icy objects lying in the same plane as the orbits of the planets in the solar system (ecliptic plane). It begins past Neptune’s orbit and stretches to about eight billion km from the sun.

Hope you enjoyed learning something more about comets.

https://solarsystem.nasa.gov/planets/oort
NASA sources.