What is a comet?
At its core, a comet is a chunk of ice, rock, and gas captured in a neat orbit by Jupiter, then flung out of the planet’s pull. How can comets possibly outshine the sun? In a word: comets are tiny. Comets orbit at the outer edges of the solar system — far, far beyond Jupiter’s orbit and the orbit of Neptune. On average, comets are some 2,000 to 10,000 years old, compared to the age of the sun at 4.6 billion years.
In other words, comets are ice balls that come out of the same planetary formation as the planets. At the moment of their birth, they are in a circumstellar disc around their parent star. Like most objects in the solar system, comets orbit the Sun. They usually stay in the circumstellar disc for millions of years. The Sun (or another star) eventually ionizes the ice in the comet’s disc, heating the particles and causing them to shed mass. In an effort to escape the Sun’s intense heat and get farther out into the Solar System, comets are propelled out of the circumstellar disc. When a comet gets close enough to the Sun, it ionizes and burns up in the atmosphere.
Comets are full of “heavy chemical elements” such as carbon, oxygen, and nitrogen that form in the presence of liquid water. You can “see” comets as you’re looking at the sun, as they appear to be glowing or shimmering, according to NASA. Comets are also known as “shooting stars” because they “seem to move with considerable speed,” according to NASA.
How many comets are out there and do they pose a danger to Earth?
As NASA noted, “Comets are icy balls of rock, ice, and dust that are constantly bombarded by the solar wind (a stream of charged particles emanating from the Sun).” Some comets undergo intense warming as they pass close to the Sun and many eventually break up. Others experience more dramatic transformations, as they are heated up by the Sun’s energy.
When did we discover comets?
Using telescopes, astronomers have found over 7,000 comets. They typically orbit around the sun in more or less elliptical orbits, which allow the comets to make regular trips around the solar system. Comets began forming about 4.6 billion years ago and represent a primitive form of the solar system, NASA says. The first examples of asteroids (which orbit around the sun in a regular path) came later. When did comets become established as a large group of celestial objects? Comets are like the monsoons of the solar system. Before comets formed, it was extremely chaotic in the solar system. As a result, the Earth was subject to frequent and random impacts, including meteor showers. When we find them today, they are leftover from that violent early period of our solar system.
What makes a comet different from an asteroid?
They’re both tiny bits of rocky debris, but comets are the term astronomers use for large chunks of these rocky bodies. How do comets get so bright? Comets are made of frozen, carbon-rich gases. As the rock is exposed to ultraviolet rays from the sun, some gases are stripped away, giving us the comet’s distinctive tail and beauty. Moreover, comets appear bright in the night sky as they travel across our sky. What makes comets so interesting? Some comets have tails that stretch thousands of miles into space.
How far away from us can comets get?
Comets are relatively close to Earth — so close that they’re actually considered planets. Most visible comets, including Comet ISON, are between 0.1 and 1 kilometer across. Did you know that sunlight is the only thing that helps them shine? It’s actually a complex mixture of dust, ice, rock, and other particles.
What is it like on a comet?
Comets are wispy orbs of frozen dust and ice that orbit the sun. “They are icy balls that have been here since the dawn of the solar system,” David Levy, author of “Comet Over Broadway,” told FoxNews.com. But what makes comets different from other celestial bodies? Unlike rocky planets or icy moons, comets aren’t likely to have a surface. Furthermore, when these big rocks are exposed to the sun, they become very heated. Cornell astronomer David Jewitt described it as “like sticking your hand in a kettle of boiling water.” Jewitt is the lead scientist on NASA’s Deep Impact project, which in 2007 delivered a space probe close to Comet Hartley 2.
Who was the first person to make contact with a comet or land on one?
Francois-Marie Arouet, better known as Chevalier de Wittert, was an amateur astronomer in the late 1700s who noticed something unusual about an object he observed. (Fun fact: he came up with the term “comet” after the constellation Pisces, which the object was moving through at the time).
Comets in our solar system (and what they’re made of)
In the 1950s and ’60s, astronomers began observing comets outside the solar system using infrared telescopes. One, designated C/1961 Y1, had a very distinct morphology — “pretty close to the shape of a Christmas tree,” University of Maryland astronomer Bruce McClure told TIME — and when it flew too close to the sun, its coma started to expand and a tail was visible. This was the first example of what is now called a comet. In 1972, astronomers detected a large tail and identified the comet as Comet Kohoutek. It was dubbed the “Comet of the Century” because it was the brightest comet ever seen, shining brighter than Venus for the vast majority of the time it was visible from Earth. In 1979, the comet brightened significantly again, until it faded away for good in 1985.
Are comets dangerous to Earth?
A comet does not pose a threat to us or any other planet, as long as you stay away from its nucleus. As long as the comet is well away from the sun, it burns up in our atmosphere. The comet nucleus is more like dust and gas, as a large piece of rock. However, comets sometimes break up into smaller pieces, which can survive the journey to Earth. And some comets can cause major damage to our environment. The Helix Nebula (the most brilliant star-forming nebula in the entire Milky Way) was formed by a massive comet that crashed into our galaxy and was filled with gas and dust, transforming it into one of the Milky Way’s most beautiful and important astronomical sites.
There are different types of comets.
Comets tend to be frozen, dirty snowballs covered with craters and gas. They are a little bit like space rocks. This type of comet has a dry atmosphere, but sometimes the atmosphere gets stirred up and snow turns to gas. Comets are made of ice. They consist of about a third of water, with just enough to keep it from melting, but not much more. In a frozen comet, water can be packed into spheres up to 2,500 times thicker than water molecules. Comets have been found in every phase of their lives. They can begin as a ball of ice, and as they spiral around the sun they grow older. This releases more of the gas and dust that causes them to re-grow into a comet that can be detected. As comets orbit the sun, they see flares of sunlight. These flares go deep into the coma.
An interesting fact about comets: comets can be black.
They can be white. They can be anywhere in between. And they can have lots and lots of tails. But the tail that stands out, the one you see in the movies, is always green. That’s because comet tails form when dust or water vapor condenses on the comet’s surface. When these gases fall back to the surface, they glow like the tail of a neon sign, a green glow as opposed to a yellowish glow in a typical comet. Comets have lived inside the solar system for hundreds of millions of years. Over the eons, these tiny planets like Earth orbited the sun while the gas and dust that formed the planets were continually eaten away. Occasionally, one of the giant planets crashed into a comet, vaporizing much of the water and dust that made up the comet, leaving a snowball of ice and rock.
An interesting fact about comets: a comet has not hit the Earth for over 100 years.
Some comets have even been estimated to be as wide as Mars. Comets are divided into two main types: Neutron Stars: These are ancient rocky bodies that are very massive, ranging from three to 200 miles in diameter. Astronomers think they formed when a dying star collapsed into a black hole. Comets: These are rocky bodies like asteroids, which range from one to several miles in diameter. They are relatively rare, but some of them have been spectacularly bright. The next comet to be visible to the naked eye from Earth is asteroid 2012 DA14.
Comet Fact: The majority of comets orbit the sun in the Oort Cloud.
Of the 4,000 knowns, there are perhaps 2,000 or so that are in a long-term orbit that takes them within 1,500 astronomical units of the sun (2,500 times the distance from the Earth to the sun)—sometimes even closer. These are called periodic comets. The only periodic comet observed over the past 60 years is Hale-Bopp.
Over the past 40 years, astronomers have discovered hundreds of new periodic comets — but it is likely that there are hundreds more, and they may not be where astronomers have found them yet. For example, the New Horizons spacecraft that was recently sent to Pluto discovered a comet. After it zoomed past the dwarf planet, the team looked for another one, but couldn’t find one. Maybe it was hiding and they just couldn’t see it.
Interesting Comet Fact: The Kuiper Belt is an area beyond the planets’ outer edges where small icy objects, such as Pluto, orbit.
This is the first asteroid we’ve seen from the sun, and it is one of the last in this region of the solar system. This might be the only Earth-like world in the Kuiper Belt. Not many have been found so far, but these things are out there, and the odds are slim that our planet is the only one in the solar system that is inhabited. The more that is discovered, the greater the chances we have of finding another, maybe Earth-like, one. The Yarkovsky effect in the solar wind causes the coma and tail of a comet to extend out further than the orbit of the sun. Not all comets create tails, however, and those that do are named after the comets that created them.
