Comets: Dirty Snowballs


Florida Tech has plenty of tech majors and one of the courses we are required to take is Scientific and Technical Communication.

As future scientists and engineers, we need to take special efforts to ensure that our work is accessible and understandable to a general audience. I’d like to share some of the things I’ve learned in that class through the speech I presented last week.

Choosing the topic was fun. Each one of us listed five interesting topics on a piece of paper and circulated it in class. Everyone marked the topics they were keen on hearing about, and I chose to speak about comets.

The first outline I drafted for the speech was more like an essay than a speech. So I watched TED talks and recollected the various scientific talks and public lectures I had attended. That helped me remember some of the things that help speakers get their point across in the least amount of words possible like:

  • Pictures: An informative picture, or even a neat diagram can instantly help the audience to grasp the concept you’re trying to explain
  • Analogies: Give examples that they can relate to. What is important is that the idea is put across effectively. For example, if the sun were to be considered as having a diameter as big as a normal-sized door, the earth would be as big as a marble, while a comet would just be a tiny speck of dust. As you can see, examples need not be super precise.
  • Focus on the important and the interesting: I had six minutes and had to make the most efficient use of them. So I chose to talk about something that would capture my friends’ imaginations.
  • Practice: I didn’t get a lot of time to practice my speech beforehand. However, I felt pretty confident as far as delivering the content was concerned. What I could have done better was shorten my speech so that I finished talking in less than six minutes. I remember being under pressure while I was talking just so I could get the speech done as fast as possible. That is not a good idea. Talking clearly and slowly is very important, for the audience might be hearing some concepts or technical terms for the first time.
  • Body language: It’s important to look at everyone in the room during the course of your talk, have a straight posture and enjoy yourself while you talk. Confidence and a cheerful countenance greatly enhance any speech.
  • The beginning and the end: Start with an exciting attention-grabber: an anecdote, a quote, a related joke or even a question that you might answer later during your talk. The end could also be any of the above or a profound thought that stays with the audience long after they have heard the speech.

With that done, let’s talk about comets now!

Comet 2P/Encke Image Source: NASA, Gerald Rhemann

So, what are comets? During the formation of the solar system from a hot cloud of gas and dust, many small bodies, comets and asteroids, did not aggregate into planets. Composed primarily of frozen gas and dust, comets are often called ‘dirty snowballs’. Comets orbit the Sun in two main regions, the Kuiper belt, and the Oort cloud. If the Earth-Sun distance is considered to be 1 unit, (called an Astronomical Unit, abbreviated as AU) the Kuiper belt is about 50 AU from the sun whereas the Oort cloud is 10000 AU away from the sun. This helps classify comets into two broad categories: short period comets — those coming from the Kuiper belt, with orbital periods less than 200 years and long period comets: those originating from the Oort cloud, with periods greater than 200 years.

The chunk of dust and ice form the nucleus of the comet. A comet forms a tail only when it nears the sun. The frozen gases on the comet sublimate due to the heat of the sun, and begin to glow, producing a fuzzy, luminous ball called a coma that’s typically a million kilometers in diameter. This is huge compared to the diameter of the comet’s nucleus, which is about 10 kilometers. There are two types of tails formed. An ion tail is formed due to charged particles from the sun (solar wind) interacting with the gases in the comet, a dust tail is primarily composed of dust particles from the comet trailing behind it due to light pressure from the sun.

Here’s an interesting video:

The debris from comets lie suspended in the comet’s orbit. If the earth were to intersect these debris, these particles would enter the earth’s atmosphere, creating a meteor shower, which is an amazing phenomenon!

Here’s more information about comets.

During the early years of the formation of the earth, the planet was constantly bombarded with asteroids and comets. Present day comets are leftovers from that same period and studying comets and their composition can help us understand the formation of our planet better.

The NASA Stardust mission collected samples from the dust trailing behind comet “Wild-2” in January 2004 and discovered the presence of complex organic compounds like amino acids. These compounds are essential constituents of life processes and it might be true comets delivered water and the building blocks of life to our planet! Isn’t that exciting?

Source: Halley Multicolor Camera Team, Giotto Project, ESA Published: 26 November 2010 In 1986, the European spacecraft Giotto became one of the first spacecraft ever to encounter and photograph the nucleus of a comet, passing and imaging Halley’s nucleus as it receded from the sun. Data from Giotto’s camera were used to generate this enhanced image of the potato shaped nucleus that measures roughly 15 km across. Some surface features on the dark Every 76 years Comet Halley returns to the inner solar system and each time the nucleus sheds about a 6-m deep layer of its ice and rock into space. This debris shed from Halley’s nucleus eventually disperses into an orbiting trail responsible for the Orionids meteor shower, in October of every year, and the Eta Aquarids meteor shower every May.



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