Astronomy - Tale of the Comet

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Comets can eject particles that are between the size of a grain of sand and the size of a pebble (Bennett). These particles that get ejected form an invisible tail because they are too big to be affected by solar wind or sunlight. This means that they remain on the comet’s orbital plane (“comets”). It is these particles that are the reason for most meteors and meteor showers seen on Earth (Bennett). On Earth, meteors are seen lighting up in the sky due to one of these particles burning up in the Earth’s atmosphere. The particles themselves can’t be seen from Earth because they are way too small. What is being observed on Earth is the air surrounding the particle glowing with heat because of the extremely high speed that the particle enters the Earth’s atmosphere with. This glowing of the air surrounding the particle is what is observed on Earth as the flash of a meteor. The particles become vaporized by the heat resulting from the high speeds at which they enter the Earth’s atmosphere. Some particles manage to avoid being burned up completely and have been collected by aircraft in the Earth’s atmosphere at very high altitudes (“comets”). However, the particles never reach the Earth’s surface (Bennett). Meteor showers occur when the Earth crosses a comet’s orbit. The dust left behind from the tail of the comet rains down on the Earth as it passes through the orbit of the comet. Meteor showers are recurring events because the Earth crosses the orbits of different comets at about the same time each year.

How do Comets Die?

There are multiple ways in which a comet’s life can end. Comets can undergo outbursts, which are substantial losses of mass (Fernandez). Comets can also split, which is a process that not only includes an outburst, but the nucleus itself splits into two or more easily identifiable pieces. Since the comet’s nucleus has a low density and internal strength because it is made up of weakly-bonded particles, it is very fragile and therefore it doesn’t take much for outbursts and splitting to occur. Most of these splitting and outburst incidents occur when a comet is near the Sun. This happens due to the Sun’s tidal force causing cracks in the comet to form. The comet will eventually split thanks to “… thermal stress, rapid rotation or sublimation” (Fernandez 255). These fragmented comets could continue on and survive for a decent period of time, or they don’t survive this splitting process and eventually dissipate (Fernandez). Comets can also collide with planets during their passage through the solar system. It is possible for comets to collide with the Sun, the moon and even satellites (Brandt). Another way in which the life of the comet can cease is that it can turn into an asteroid. Comets have a limited life due to the fact that once the materials that they contain have sublimated, they don’t get replenished. When this occurs, eventually the materials will be gone and the body will die, becoming completely inactive. Once it is inactive, it is considered an asteroid. What makes a comet different from an asteroid is the object’s orbit as well as its chemical attributes (“comets”). All of these events are ways in which the life of a comet can end.

A rare example of the way in which a comet can die is the life of Comet Lovejoy. On December 16th, 2011, Comet Lovejoy passed within 200000 km of the Sun’s surface (Bortle). When a comet passes near the Sun’s surface, it usually ends up splitting or just dissipating from the intense heat that is imposed on it by the Sun. Sungrazers, or comets that pass very close to the Sun, are believed to be remnants of a very large comet that broke apart millennia ago. Usually, with each passing of the Sun, sungrazers break into smaller and smaller pieces, until they no longer exist. Pygmy sungrazers are the end result of repeated breakups of larger comets. These sungrazers are extremely fragile and can be rather small. As they are unable to withstand the Sun’s heat and gravity, pygmy sungrazers usually vaporize as they approach the Sun. However, Comet Lovejoy’s journey didn’t end as this evidence of sungrazers suggests it should have ended. Lovejoy’s approach to the Sun was thought to be a plummet to its death; but astonishingly, after it disappeared behind the Sun, it emerged again on the other side. Unlike most sungrazers, Comet Lovejoy survived its initial passing of the Sun fully intact. On December 20th, Lovejoy’s head began to produce a tail-like ray instead of what the head is supposed to be- a compact central object. This ray was formed by debris that moved at a fast pace outward toward its tail. The ray grew longer and longer each day as the comet’s heat became slightly weaker and more diffused. Eventually, Comet Lovejoy was essentially just a tail, a tail that survived the Sun to return again when other sungrazers couldn’t.

It is quite clear that astronomers’ knowledge of comets has increased substantially since Newton’s first simple idea of the physical attributes of a comet. Astronomers now know that comets are simply made up of a nucleus, and can include a coma, a plasma tail, and a dust tail if the comet is in close proximity of the Sun. Astronomers have also concluded that comets originate from the Oort cloud and the Kuiper belt out in the outer solar system and can visit the inner solar system never, once, or many times. The process by which comet tails are formed, and the two different types of comet tails are now known. It has also been discovered that meteors and meteor showers are a direct result of the Earth passing through the orbit of a comet in which dust particles left behind from the comet rain down on the Earth and burn up it its atmosphere. And finally, there have been multiple ways discovered in which a comet’s life can end. All of these discoveries have drastically changed the outdated seventeenth century’s generally accepted view of comets.

Works Cited

Bennett, Jeffrey, et al. The Essential Cosmic Perspective. 6th ed. Boston: Addison- Wesley, 2012. Print.

Bortle, John E. “The Remarkable Case of Comet Lovejoy.” Sky & Telescope. May 2012: 36-40. Print.

Brandt, John C. “Physics and Chemistry of Comets.” Encyclopedia of the Solar System. 2nd ed. 2007. Print.

Cochran, Anita L. “Comets.” Encyclopedia of Space Science and Technology. 2003 ed. Print.

“comet.” Encyclopedia Britannica. Encyclopedia Britannica Online School Edition. Encyclopedia Britannica, Inc., 2012. Web. 7 Nov. 2012.

Fernandez,