These gases can consist of a mixture of ammonia, carbon dioxide, and water vapor. The atmosphere of vaporized gases that forms around the nucleus is called the coma. When it is heated by the Sun, the gases sublimate and produce an atmosphere surrounding the nucleus. Scientists call it a “dirty snowball” due to its composition. It is composed of frozen gases, dust, and rocky materials, ranging from about 6 to 62 miles in diameter. The Oort Cloud’s existence has not yet been proven.Ī comet’s nucleus is its solid head. Long-period comets that take more than 200 years to orbit the Sun are believed to come from the Oort Cloud, which may contain trillions of comets. The Oort Cloud is named after Danish astronomer Jan Oort, who proposed that comets reside in a huge cloud far beyond the orbit of Pluto. It’s thought to be a spherical shell of icy matter, rock, and dust. The second region, called the Oort Cloud, is located farther out from the Kuiper Belt (up to 100,000 astronomical units from the Sun). It’s believed that short-period comets that orbit the Sun at least every 200 years are Kuiper Belt objects. The Kuiper Belt, named after Gerard Kuiper, a Dutch-born astronomer, is a ring-shaped region beyond Neptune’s orbit where many asteroids, comets, and other smaller bodies of icy material reside. They are believed to primarily originate from two regions: the Kuiper Belt, and the theorized Oort Cloud. Asteroids, which are composed of rock and metal, are much larger than comets and are also known to suppress water ice, so perhaps water-rich asteroids and comets both contributed to making regular water deliveries when they impacted Earth during its infancy.Ĭomets spend most of their orbital journeys at great distances from the Sun in the far reaches of the Solar System. These two tails can stretch for over 620,000 miles (1 million km) out in space.īecause comets are known to contain water ice, some believe comets may have originally brought some water and organic molecules to Earth, but not enough of it to fill Earth’s oceans. This gives comets their signature appearance of a glowing coma with dust and gas (ion) tails pointing away from the Sun. As comets begin to heat up from the Sun’s energy, their nucleus spews volatile materials such as dust and gas, which sublimate and escape (outgassing). Scientists often describes comets as “dirty snowballs” due to their composition. Some comets plunge into Sun while others break up entirely during this close encounter. Comets are pulled in faster as they move closer to the Sun, then slingshot around its backside before heading back out into space. They are relatively small objects that travel through space in highly elliptical orbits that resemble a long, fat cigar. Some planetary scientists believe they may be leftovers from materials that initially formed the Solar System about 4.6 billion years ago.
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With the next “ghostly wanderer” on its way for a possible end-of-year encounter with the Sun, now is a good time to learn more about comets and how to observe them.Ĭomets are a mixture of frozen gases, dust, rock, and water ice. Comets are now one of the most sought-after objects for sky-watchers whenever they appear-especially when they are bright enough to be seen with the naked eye from the city. Comets no longer instill fear, but instead generate excitement and opportunities for people to observe, photograph, and to study these beautiful celestial visitors. Today, astronomers have a better understanding of comets. So, comets-especially the brighter ones-lit up the sky in all their wondrous glory, making them even more intimidating. In those days, the sky was dark and pristine without manmade light pollution. A comet could appear suddenly without warning, grow in size, eventually form a glowing nucleus and a formidable tail, and remain visible for several weeks before fading and heading back out into the abyss. It’s easy to see why ancient peoples feared them. Comets were once thought to be omens of disaster or messengers from the gods bearing bad news. These visitors from the far reaches of the Solar System have intrigued humans for thousands of years. Comets are among the most spectacular and mysterious objects to appear in our skies.
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