Do you know the difference between an asteroid and a comet? A comet characteristically has a tail and coma. This red streak is made of leftovers. Comet Siding Spring, discovered by Australian skywatchers in 2007, is -- like all comets -- believed to be made of materials that didn't attach to planets or the sun when the solar system formed. A comet's rocky, icy nucleus is surrounded by a cloud of gas called a coma and followed by a tail. It has no light of its own but reflects sunlight. This one, captured by NASA's Wide-field Infrared Survey Explorer (WISE) appears red for display purposes. In the next photo, discover an Oort Cloud.
Image Credit: NASA/JPL-Caltech/UCLA
Many of the known comets come from a region called the Kuiper Belt. This disc-shaped area surrounds the solar system beyond Neptune and includes Pluto, dwarf planets and other asteroids. Scientists believe this area, like all our solar system, is housed within the Oort Cloud, which contains billions of comets. Next up, see who discovered the Comet Kohoutek.
Image Credit: NASA/C. Veillet (CFHT)
In 1973, Czech astronomer Dr. Lubos Kohoutek discovered a comet called C/1973 E1, which is known to the world as Comet Kohoutek. Here he is shown early the next year at NASA's Mission Control Center in Houston talking to the crew of the Skylab space station.
Image Credit: NASA
NASA's Operation Kohoutek mobilized observation of the comet though Skylab, satellites, rockets, balloons and ground observatories. This 1974 image was captured with a 35 millimeter camera by a team at the University of Arizona. Can you name any artists that were inspired by Comet Kohoutek?
Image Credit: NASA
Comet Kohoutek inspired a wide range of artists, from the rock bands Journey and Pink Floyd to avant-garde jazz musician Sun Ra, folksinger Burl Ives and "Peanuts" creator Charles Schulz. Its influence has remained strong over the decades -- "The Simpsons" made a Kohoutek joke and R.E.M. has a song called "Kohoutek." These December 1973 sketches are by a man who got closer than most to his subject, Skylab 4 astronaut Edward Gibson.
Image Credit: NASA
Skywatchers have recorded sightings of Halley's Comet for more than 2,000 years. It passes Earth every 75 or 76 years, and it was the first comet to be observed up close. The European Space Agency probe Giotto was named for the Renaissance painter who observed Halley's Comet and included it in his depiction of the Nativity. The spacecraft Giotto came within about 370 miles (596 km) of the comet and took this picture of its nucleus. Up next, see amazing images captured by Hubble Space Telescope.
Image Credit: NASA
Comet Hale-Bopp passed through our Solar System in the mid-1990s. This is a series of false-color images from NASA's Hubble Space Telescope, in which the brightest areas are white and the different intensities are shown in varying reds, with the darkest areas black. The upper left picture captures a dust outburst from the comet just after passing Jupiter. Like Halley's Comet, Hale-Bopp reverberated through the culture. With a wink at modern jazz, American composer John Adams named a piano concerto movement "Hail Bop." And 39 members of the Heaven's Gate cult chose a moment when the comet shined brightly to commit mass suicide.
Image Credit: NASA Jet Propulsion Laboratory
NASA has called Hartley 2 "a weird little comet." This image of its nucleus was captured by the unmanned EPOXI mission between Nov. 3 and 4, 2010. "It was moving around the sky like a knuckleball and gave my navigators fits," EPOXI Project Manager Tim Larson of NASA's Jet Propulsion Laboratory has said. "And these new results show this little comet is downright hyperactive." Hartley 2 spins around one axis and tumbles around another, and spews out an unusual amount of water and carbon dioxide. See one of the best comet images to date in the next photo.
Image Credit: NASA/JPL-Caltech/UMD
NASA's unmanned Deep Space 1, which launched in 1998, acquired what were then the best comet images to date. It flew past Comet Borrelly in September 2001. The comet's nucleus is approximately 5 miles (8 kilometers) long. These colors represent intensities of light, with red being a tenth as bright as the nucleus, blue one one-hundredth and purple one one-thousandth. Next, see a magnificent portrait of a comet.
Image Credit: NASA/JPL
This portrait of Comet Wild 2 is a composite image from a January 2, 2004 flyby of unmanned spacecraft Stardust. A quick-exposure picture captured surface detail of the nucleus, which is approximately 3.1 miles (5 km) in diameter. The image was combined with a picture taken seconds later using a longer exposure to show the jets of dust and gas, which can trail millions of miles behind the comet.
Image Credit: NASA/JPL-Caltech
This is not a comet but a "shooting star," or meteor. It is just one tiny piece of the 100 tons (91 metric tons) of space rocks and other debris that falls toward Earth each day. When a piece of rubble or a boulder falls through the atmosphere, it heats up and releases gases that shine briefly in the night sky. The material left in the wake of a passing comet can continue to fall to Earth for centuries, as our planet orbits through the area each year.
Image Credit: NASA/Jimmy Westlake
Earth isn't the only planet to experience meteor showers. This picture, taken by NASA Mars Exploration Rover Spirit, shows meteors in the sky above the red planet. In the next photo, see the ingredients for cooking up your own comet.
Image Credit: NASA/JPL-Caltech/Cor nell/Texas A&M/SSI
While you can't -- and probably shouldn't -- have a comet delivered, NASA has assembled the ingredients for cooking up your own. This tongue-in-cheek recipe for comet soup includes (upper left) a cup of ice and (upper right) a cup of dry ice; (middle row from left to right) olivine, smectite clay, polycyclic aromatic hydrocarbons, spinel, metallic iron; (front, left to right) the silicate enstatite, the carbonate dolomite, and the iron sulfide marcasite. Combine, season to taste and hurl away from the body at hundreds of thousands of miles or kilometers per hour.
Image Credit: NASA/JPL-Caltech
Here we see comet 65/P Gunn. It orbits the sun inside the main asteroid belt between the orbits of Mars and Jupiter. It takes 6.79 years to complete one trip around the sun. When this picture was captured, the comet was 243 million miles (392 million kilometers) from Earth and its speed was around 4,800 miles per hour (7,700 kilometers per hour). Just in front of this comet is a fuzzy red line that makes 65/P Gunn look a bit like a swordfish. This "sword," a dust trail, is made of dust particles that have previously been shed by the comet as it orbits the sun. The dust is warmed by sunlight and glows in infrared light. Dust trails appear both ahead and behind the comet's nucleus. With time, the material in the debris trail can drift away from the comet's orbit and become clouds of debris that will be seen as meteor showers if Earth passes through them.
Image Credit: NASA/JPL-Caltech/UCLA
Earlier, we saw Comet Siding Spring. Here it is from another angle and image. This mass of ice and dust (imagine a giant snowball) orbited the deeply frozen Oort Cloud (a cloud of comets surrounding our solar system) for billions of years. It was, at some time, knocked out of this orbit and booted onto a course that brings it closer to the sun. In fact, on October 7, 2009, it passed to within 1.2 astronomical units from Earth and 2.25 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth). Here, the Siding Spring is leaving the relatively cozy, warmer area of the solar system and heading back out toward the much colder regions. Next, we'll visit a cosmic celebrity that makes paparazzi of amateur astronomers here on Earth.
Image Credit: NASA/JPL-Caltech/UCLA
NASA's Spitzer Space Telescope caught this wondrous image of the Helix nebula, which, thanks to its rather unsettling resemblance to a human eye, is often the target of photographs by amateur astronomers. The nebula is about 700 light years away, in the constellation Aquarius. It belongs to a class of objects astronomers call planetary nebulae -- the remains of stars that once looked like our sun. When sun-like stars die, they pump outward their outer, gaseous layers, like a balloon expanding. These layers are heated by the hot core of the dead star (called a white dwarf) and shine with infrared and visible colors. Our own sun will become a planetary nebula when it dies in about five billion years. The brighter red circle in the center of the image is the glow from a dusty disk circling the white dwarf (the disk is too small to be photographed clearly). This dust, discovered by Spitzer's infrared heat-seeking vision, was most likely kicked up by comets that survived the death of their star.
Image Credit: NASA/JPL-Caltech/Univ.of Ariz.
Sure, comets are neat. But this comet got to use exactly that for its name. The Kitt Peak National Observatory in Arizona was able to pluck from the night skies this image of Comet NEAT on May 7, 2004.
Image Credit: NASA
Here we catch a distant glimpse of comet 103P/Hartley 2 in a highly active state, approaching the sun. Hubble Space Telescope data showed it to be about 0.93 miles in diameter (1.5 kilometers), with a coma (which we learned earlier is the cloud of gas surrounding a comet) that was strikingly uniform, without jets outgassing from it.
Image Credit: NASA, ESA, and H. Weaver (The Johns Hopkins University/Applied Physics Lab)
The Chandra X-ray Observatory plucked from the cosmos this false-color image of comet Tempel 1. The 2005 picture showed Tempel 1 to be bright and condensed. The X-rays Chandra observes from comets are caused by the interaction between highly charged oxygen in the solar wind and neutral gases from the comet itself. In our next picture, we'll see Tempel 1 in a much different light.
Image Credit: NASA/CXC/C. Lisse and S. Wolk
This is comet Tempel 1 in 2011, as seen by NASA's Stardust-NExT (New Exploration of Tempel 1) mission, a low-cost initiative from NASA that is following up on earlier Tempel 1 observations made by the Deep Impact mission of 2005. Next up, we'll get contrasting views of comet Holmes, which has puzzled astronomers on two occasions.
Image Credit: NASA/JPL-Caltech/Cornell
NASA's Spitzer Space Telescope took the picture on the left of comet Holmes in February 2008, four months after the comet suddenly erupted and got brighter by a million times -- overnight! The picture on the right is an enhanced contrast version that helps show the anatomy of the comet. Holmes is a creature of habit, like most comets. Every six years, it zooms away from Jupiter and heads inward toward the sun, traveling the same route -- usually without any high drama. But twice in the last 116 years -- in November 1892 and October 2007 -- Holmes exploded as it approached the asteroid belt. Exactly why remains a mystery: Astronomers still do not know the cause of these eruptions. Next, we'll get an idea of what a comet rain storm looks like.
Image Credit: NASA/JPL-Caltech
Does anyone make galactic umbrellas? This artist's conception shows a kind of rain storm of comets around a star called Eta Corvi. The Spitzer Space Telescope's infrared detectors received indications that one or more comets had been torn to shreds after colliding with a rocky body. In this depiction, one of the giant comets is smashing into a rocky planet with a glowing red flash, hurling ice and carbon dust out into space, while at the same time slamming water and organic material into the surface of the planet. The yellow-white star Eta Corvi is shown to the left, with more comets streaming toward it.
Image Credit: NASA/JPL-Caltech
This picture shows how NASA's Wide-field Infrared Survey Explorer, or WISE, surveys asteroids and comets in the solar system. The perspective is one of looking down from high above the Earth's north pole, taking in a bird's eye view of the entire solar system. Planets are the sparsely seen, dark-blue dots, their orbits dashed lines. The great mass of black dots forming the circle consists of asteroids in the main belt, between Mars and Jupiter. The green dots show the known near-Earth objects -- both asteroids and comets -- spotted so far. Newly discovered near-Earth objects are the red dots. The turquoise dots are comets, and the yellow ones are newfound comets. WISE data such as this is used by project NEOWISE, which hunts for asteroids and comets, especially those that are near Earth.
Image Credit: NASA/JPL-Caltech/UCLA/JHU
These three pairs of images show that both a dust jet and gaseous carbon dioxide are being released at the same time from comet Hartley 2 (which we met earlier) -- and from the same location on the comet. The observations told researchers that the carbon dioxide is driving the dust jet and taking tiny grains with it as it spews out of the nucleus of the comet. It was the first time this type of jet had been observed. The top row consists of three images showing carbon dioxide gas being released by the comet at different points in time. The bottom row of images shows dust coming from a jet on the comet at the same three points in time. The presence of the jet told scientists that Hartley 2 is made of chunks that are rich in solid carbon dioxide, sort of like chocolate chip chunks in frozen cookie dough, as NASA described it. This variable nature of the comet's makeup implies that the ingredients for both comets and planets must have been mixed early on in the formation of the solar system. Without that mixing, comets would be either just "dough" or just the "chocolate chunks" but not both. Next, we'll see a comet fly too close to the sun and live to tell about it.
Image Credit: NASA/JPL-Caltech/UMD
Here we see comet Lovejoy, which in December 2011 skimmed across the sun's edge about 87,000 miles (140,000 kilometers) above the surface. It was the brightest sungrazing comet NASA had ever observed, and its nucleus was calculated to be almost two football fields across. Miraculously, it survived the close brush with the sun and came out from behind it hours later. Somewhere Icarus must be smiling.
Image Credit: NASA
The Hubble Space Telescope's advanced camera for surveys took images of this disintegration of Comet 73P/Schwassmann-Wachmann 3's fragment B. Back in the spring of 2006, there was rampant speculation that the comet and its 40 fragments might somehow cause harm to Earth, but scientists were quick to reassure people that this comet with the long name posed no threat.
Image Credit: NASA, ESA, H. Weaver (APL/JHU), M. Mutchler and Z. Levay (STScI)
This picture is of comet Lulin, courtesy of NASA's Swift satellite. Lulin was making it closest approach to Earth in February 2009 when the image was captured. Lulin is fairly new to the cometary stage, having been discovered in 2008 by astronomers at Taiwan's Lulin Observatory. Next, we'll learn about comet trails and tails.
Image Credit: NASA, Swift, Univ. Leicester, DSS (STScI/AURUA), Dennis Bodewits, et al.
Here an artist's illustration shows a comet's dust trail and its dust tail. The dust trail is made of tiny particles -- no bigger than grains of sand or pebbles. The particles are nonetheless large enough that they are not terribly affected by sunlight or solar wind. But the dust tail is made of even tinier stuff -- grains the size of smoke particles. The sun's light blows these grains out of the dust coma in a puff of diffusion near the comet nucleus.
Image Credit: NASA
This is Phoebe, Saturn's moon. You might be wondering what a moon is doing in a gallery about comets. Well, images captured of Phoebe by the Cassini probe when it drew near to Saturn indicate to scientists that the moon may actually have originated in the outer solar system. It has researchers speculating that Phoebe was once a comet. That's because its surface (irregular), retrograde (backward) orbit, dark surface, craters of varying sizes and low average density fit with the suspicion that Phoebe was once part of the Kuiper Belt of icy-cold comets out beyond Neptune, before it was pulled into orbit around Saturn.
Image Credit: NASA/ESA/JPL/SSI
We finish our gallery off with, appropriately enough, the pulverizing of a comet. This artist's conception depicts a comet being torn to pieces around a white dwarf (a dead star) called G29-3. The Spitzer Space Telescope noted a cloud of dust around this particular white dwarf that may have been generated by this type of comet's unfortunate dismemberment. In the illustration, part of the comet still exists as a chain of small clumps, while the rest has already dispersed into a dusty disk. Comet Shoemaker-Levy 9 famously broke apart similarly when it plunged into Jupiter in 1994, making world headlines along the way.
Now that you've seen our Fascinating Comet Pictures, take our Comets Quiz and see what you've learned!
Image Credit: NASA/JPL-Caltech
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