Universe Today

We reported earlier that on January 6, 2010, ground-based observatories may have spotted evidence that two asteroids had collided in the asteroid belt. Now, the Hubble Space Telescope has taken a look at the mysterious X-shaped debris pattern and trailing streamers of dust. With Hubble's sharp vision, astronomers believe a head-on collision between two asteroids has actually occured. Astronomers have long thought the asteroid belt is being ground down through collisions, but such a smashup has never been seen before.
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Here are some cool pictures of comets.

This is an artist's illustration of comets orbiting around a newly forming solar system. Because of the intense solar wind coming from the newborn star, the comets are blasted by radiation and form long tails. It's thought that a process like this might have delivered water to the rocky inner solar system.

This is a mosaic of images taken of the Shoemaker-Levy 9 impact into Jupiter in 1994. When the impact happened, were were fortunate to have the powerful Hubble Space Telescope at our disposal, capturing images of the impacts as they happened, leaving dark bruises on the surface of Jupiter.

This is a picture of Comet 73P/Schwassmann-Wachmann, a long period comet in the process of disintegrating as it moves through the Solar System. This is an image of the comet captured by the Spitzer Space Telescope, which sees in the infrared spectrum.

Here's a photo of comet Hale-Bopp, which blazed through the skies in 1997. This was one of the brightest comets of the century, visible in the skies for several weeks.

Did you know that the most successful comet hunter is actually a spacecraft? NASA's SOHO spacecraft, designed to study the Sun and its environment has actually discovered more comets than any person or other spacecraft. That's because it sees comets as they crash into the Sun, or make close passes around it. The comet in this image didn't survive the trip.

We've written many articles about comets for Universe Today. Here's an article about comets posing as asteroids, and here's an article about where comets come from.

If you'd like more info on comets, check out NASA's World Book on Comets, and here's a link to the asteroids and comets page.

We've also recorded an episode of Astronomy Cast all about comets. Listen here, Episode 19: Comets, Our Icy Friends from the Outer Solar System.

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Are we ready to act if an asteroid or comet were to pose a threat to our planet? No, says a new report from the National Research Council. Plus, we don't have the resources in place to detect all the possible dangerous objects out there. The report lays out options NASA could follow to detect more near-Earth objects (NEOs) that could potentially cross Earth's orbit, and says the $4 million the U.S. spends annually to search for NEOs is insufficient to meet a congressionally mandated requirement to detect NEOs that could threaten Earth. "To do what Congress mandated NASA to do is going to take new technology, bigger telescopes with wider fields," said Don Yeomans, Manager of NASA's Near Earth Object Program Office, speaking at the American Geophysical Union conference last month.
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Here are some amazing comet pictures.

This is a photograph of Comet Holmes, taken in March 2008. This was after the comet suddenly broke up into pieces, drifting apart, and eventually becoming one of the largest objects in the Solar System. Holmes makes its closest approach every 6 years or so.

This is an image of Comet Hyakutake, taken by the Hubble Space Telescope. This photo shows the inner regions of the comet's nucleus. Hyakutake brightened in the sky in 1998, becoming one of the biggest and brightest comets in recent memory.

This picture, taken by the Hubble Space Telescope, shows the heart of Comet Hale-Bopp. You can see how the nucleus of the comet has changed between the two images, and how it appears that jets from the comet have caused it to spin, spewing out material in a pinwheel shape.

When Shoemaker-Levy 9 crashed into Jupiter in 1994, astronomers were fortunate enough to have the incredible Hubble Space Telescope at their disposal to watch the cosmic collision. You can see the huge bruises at the bottom of Jupiter, where fragments of the comet plunged into Jupiter's atmosphere.

This image shows the region around the nucleus of Comet Hyakutake. It shows how dust is being produced on the sunward side of the comet, and not the side of the comet in shadow. This whole image only measures about 3,340 km across.

We've written many articles about comets for Universe Today. Here's an article about how comets might pose as asteroids, and here's an article about mini-comets ejected from Comet Holmes after it broke up.

If you'd like more information on comets, check out NASA's World Book on Comets, and here's a link to NASA's Asteroid and Comets page.

We've also recorded an episode of Astronomy Cast all about comets. Listen here, Episode 19: Comets, Our Icy Friends from the Outer Solar System.

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A strange comet-like object discovered on January 6, 2010 may actually be the result of a collision between two asteroids. Lincoln Near-Earth Asteroid Research (LINEAR) sky survey in New Mexico spotted an object in the asteroid belt, called P/2010 A that looked "fuzzy," with a tail like a comet rather than a speck of light like a normal asteroid. But comets don't normally reside in the asteroid belt, and the object's orbit is all wrong for a comet. While the asteroid belt is made up of debris from the "leftovers" of our solar system, and like the remains of early crashes between giant rocks, astronomers haven't witnessed a collision before.
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Asteroids are rocky bodies which belong between Mars and Jupiter. Comets are icy bodies that belong way out beyond Pluto. So what are comet-like objects doing in the asteroid belt?

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Title this one "Rich Blue Crescent" (as opposed to Pale Blue Dot.) This spectacular image of our home planet was captured by the OSIRIS instrument on ESA's Rosetta comet chaser today (November 12) at 12:28 GMT from about 633,000 km as the spacecraft approached Earth for the third and final swingby. Closest approach is due at 07:45 GMT, on November 13. You can follow Rosetta's progress at ESA's Rosetta site and the Rosetta Blog.

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Comets in space are among the most fascinating bodies in the Universe. They are classified as Small Solar System Bodies or SSSBs, the term used to define objects in the Solar System that are not planets or even dwarf planets. When a comet makes a fly-by near Earth, it generally arouses the interest of the general public (not just astronomers).

In extreme cases, some groups portray them as harbingers of doom.

Comets in space are usually confused with asteroids. However, if you paid attention to the movies Deep Impact and Armageddon (where both of them got to play the role of the villain), you should know the difference by now. Otherwise, you'd still be classifying them both as huge rocks that may come to a collision course with planet Earth.

Actually, the term 'rock' is more suitable for asteroids, being largely made of metals and, yes, rocks. Comets in space, on the other hand, are composed of rocks, dust, and lots of ice. The presence of ice and other frozen gases is the reason why comets are accompanied by a stream of material.

Basically, comets in space are made up of three main parts: the nucleus, the coma, and the tail. As the comet approaches the Sun, some of the frozen materials vaporize and form a stream, known as the tail, pointing away from the Sun. This is due to the radiation pressure and solar wind coming from the Sun. The atmosphere of vaporized dust surrounding the comet's core, the nucleus, is called the coma.

Recent studies have shown that the comet's core is very similar to an asteroid. They both have irregular shapes because their gravitational forces are too low to mold them into a spherical form. This was confirmed when NASA's Deep Space 1 was sent to probe Comet Borrelly.

Because of the size of their orbits, most comets in space have to travel long distances before they can come back for a fly-by. Majority of the comets having long orbital periods are believed to be originating from the Oort Cloud, while those with short orbital periods come from Kuiper Belt.

Only a few comets are visible through the naked eye. We were lucky enough to have witnessed the fly by of Hale Bopp in 1997, which was visible to the naked eye for a long time. Unfortunately, most comets will require telescopes for you to observe them.

So the next time you're asked by your little kid to draw an asteroid, don't include a tail – that's supposed to be a comet in space.

We've got some cool articles about comets in space here in Universe Today. Here are two of them:
What Are Comets?
What is the Difference Between Asteroids and Comets

Here are two more from NASA:

Comet
A Bright Comet Is Coming

Tired eyes? Listen to a couple of episodes from Astronomy Cast:

Comets, Our Icy Friends From the Outer Solar System
Asteroid Belt

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Deep Impact is the name of a NASA space mission whose primary objective was to study Comet Tempel 1 (a.k.a. 9P/Tempel). It was launched on 12 January, 2005, and the smart impactor crashed into the comet on 4 July, 2005.

Oh, and yes, Deep Impact is also the name of a movie … but the two have no connection (the science team came up with their name independently of the Hollywood studio), other than that they both concern a comet!

Comets had been the focus of several space probes before Deep Impact, perhaps the most famous of which is the ESA's Giotto flyby of Comet Halley. However, flybys could not, and cannot, tell us much about what's beneath the cometary surface; in particular, what the relative amounts of ices and dust is, how porous the comet body is, and so on. The Deep Impact mission was designed to address many of these unknowns.

The space probe consisted of two parts, a 370 kg copper Smart Impactor – that smashed into the comet – and the Flyby section, which watched the impact from a safe distance. In addition, many ground-based telescopes – including those of thousands of amateurs – and some space-based ones, watched the event from an even safer distance.

The mission was a great success in that the heavy copper section did, in fact, smash into the comet, and the other section did observe the impact up-close-and-personal, but safely. A great deal was learned about this comet – its composition and mechanical strength, etc – and comets in general. However, the plume which resulted from the impact was much denser than expected, so the Flyby did not get any images of the impact crater itself.

After the encounter with Comet Tempel 1, an extended mission for the Flyby was designed and implemented, called EPOXI, after its two objectives: the Extrasolar Planet Observation and Characterization (EPOCh) and the Deep Impact Extended Investigation (DIXI) … hence Extrasolar Planet Observation and Deep Impact Extended Investigation. The former uses the larger telescope on the space probe to look for exoplanet transits; the latter is a flyby of another comet, Hartley 2, now expected on 11 October, 2010.

There are several official Deep Impact websites, including NASA's, JPL's (Jet Propulsion Laboratory), and the University of Maryland's on EPOXI.

The Deep Impact mission resulted in lots of Universe Today stories, far too many to mention here. Some of the best are Deep Impact Smashes into Temple 1, What the Ground Telescopes Saw During Deep Impact, Deep Impact Turns Up Cometary Ice, and Deep Impact Begins Searching for Extrasolar Planets.

Comets, our Icy Friends from the Outer Solar System is a good Astronomy Cast episode which gives a good background on comets.

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Meteor showers are usually caused by debris coming from comets flying by the Sun. In the case of the Leonid Meteor Shower, the debris is shed by the Comet Tempel-Tuttle.

Every time a comet passes by the Sun, part of the comet vaporizes and is shed off as debris. This debris forms a stream that follows the comet's trajectory. If the Earth happens to pass through this stream, the debris enters our planet's atmosphere. They then ignite and are seen as meteor showers.

Comet Tempel-Tuttle's orbit almost intersects the Earth's. That is why streams of debris coming from the comet easily interact with our planet. The high density of the debris or meteoroids is the reason why the Leonid meteor shower is one of the most magnificent showers we observe on a yearly basis.

The superlative storm of 1833 is one of the most spectacular in recorded history. Estimates are putting the shower rate at more than 100,000 meteors per hour. Spectacular Leonid storms were also observed in 1866, 1867, 1996, and 1998.

As the 1998 event was approaching, airborne observations were arranged so as to implement the modern observing techniques designed by NASA Ames Research Center's Peter Jenkins. As an offshoot, magnificent images were captured in 1999, 2001, and 2002.

Meteor showers don't get their names from their parent body, like Comet Tempel-Tuttle. Instead, each meteor shower is named after the constellation from where they are perceived to be coming from as viewed on Earth. This apparent point of origin is known as the shower's radiant. For example, since the Leonid Meteor Shower appears to be coming from the constellation Leo, Leo is its radiant and hence the name '(Leo)nid'.

The Leonid meteor shower can be seen yearly every November. This year, the shower is expected to peak in a 1 hour duration on November 17, 2009.

The great thing about meteor showers is that you can appreciate their beauty even without a telescope. Just look for a dark open field far from all the city glow. A public park with a vast track of land will usually suffice. For as long as the sky has minimal to zero cloud cover and especially if there is no moon, it will be difficult not to spot them.

Allow us to share previous announcements here at Universe Today regarding the Leonid Meteor Shower:

Leonid Meteor Shower: November 19, 2006
See the Leonids Tonight!

There's a nifty tool from NASA that will calculate the shower rate for a given location and date. You may even choose the name of the shower, e.g. Leonids, Perseids, Geminids, Orionids, and so on.

More about the Leonid Meteor Shower at NASA.

Tired eyes? Let your ears help you learn for a change. Here are some episodes fromAstronomy Cast that just might suit your taste:

Meteor Showers. Yes, the sky is falling.
Getting Started in Amateur Astronomy

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In the movie “Deep Impact” the chance of a comet hitting Earth is explored. The world is saved when a spacecraft is built to deliver a system of destroying the comet before an Extinction Level Event(ELE) could happen. Is this pure science fiction or is there a chance of a comet hitting Earth? The fact is that there are comets and other solar debris hitting the Earth on a yearly basis. The most recent was in 2008 when a small asteroid hit our atmosphere. It burned up immediately and left nothing to hit the ground, but it goes to show that these events happen on a yearly basis. The chances of an ELE are very rare and only happen many millions of years apart.

Small objects hit the Earth with an amazing regularity. Astronomers have even gone to the trouble to predict these comet hitting Earth events. Objects with a 1 km diameter impact the Earth every 500,000 years on average. Large collisions with five kilometer objects happen approximately once every ten million years. Objects with diameters of 5-10 m impact the Earth's atmosphere approximately once per year, but break up and most of the material is vaporized in the upper atmosphere. Objects of diameters of over 50 meters strike the Earth approximately once every thousand years. It is easy to believe these numbers when you take into account the millions of objects that are out there, then couple that with gravity anomalies, etc. The surprise is actually that you would expect more frequent impact events.

A comet hitting Earth helps us to learn many new things about solar objects, but could be very dangerous for the peoples of the world if we are caught off guard. The complexity of the SENTRY and NEAT programs will prevent any unexpected strikes and will help us to defend any threatened cities. The movies have embellished on what might happen to prevent an impact, but they might not be too far off from the truth.

NASA has a good article about monitoring near Earth objects here. Here on Universe Today there are two good articles on the topic. One is about meteors hitting the Earth and the other is about the Tunguska event being caused by a comet hitting Earth. Astronomy Cast offers a good episode about destruction in our solar system.

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A comet coma is like a comet's atmosphere. It is made up of the heated gases and dust that makes up the comet's nucleus. The nucleus of a comet is a ball of ice and rocky dust particles that resembles a dirty ice ball. The ice consists mainly of frozen water but may include other frozen substances, such as ammonia, carbon dioxide, carbon monoxide, and methane. Scientists believe the nucleus of some comets may be fragile because several comets have split apart for no apparent reason.

As a comet nears the inner solar system, heat from the sun vaporizes some of the ice on the surface of the nucleus, spewing gas and dust particles into space. This gas and dust forms the comet's coma. Radiation from the sun pushes dust particles away from the coma. These particles form a tail called the dust tail. At the same time, the solar wind — that is, the flow of high-speed electrically charged particles from the sun-converts some of the comet's gases into ions (charged particles). These ions also stream away from the coma, forming an ion tail. Because comet tails are pushed by solar radiation and the solar wind, they always point away from the sun.

Scientists learned much about comets by studying Comet Halley as it passed near Earth in 1986. Five spacecraft flew past the comet and gathered information about its appearance and chemical composition. Several probes flew close enough to study the nucleus, which is normally concealed by the comet coma. The spacecraft found a roughly potato-shaped nucleus measuring about15 kilometers long. The nucleus contains equal amounts of ice and dust. About 80 percent of the ice is water ice, and frozen carbon monoxide makes up another 15 percent. Much of the remainder is frozen carbon dioxide, methane, and ammonia. Scientists believe that other comets are chemically similar.

There are interesting articles about comet coma here and here. We have a couple of great articles here on Universe Today. One covers comets in general and the other talks about some interesting facts about comets. Astronomy Cast has a good episode about losing contact with rovers and shooting lasers into space.

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A comet nucleus is the solid, central part of the comet. Some people refer to it as the dirty snowball aspect of a comet, but it is really rock, dust, and frozen gases that are covered by a shallow crust. NASA sent the space probe Deep Space 1 closer to Comet Borrelly than any probe had ever been. The probe found that a comet's nucleus can have mountains, valleys, and smooth plains. Many of the materials in a comet have different reflective properties. They look similar to asteroids when viewed close up.

When a comet nucleus is heated by the Sun, the gases transition for solid to gas without a liquid state and produce a temporary atmosphere surrounding the nucleus called the coma. The forces exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun. A typical comet nucleus has an albedo of 0.04. Cometary nuclei are among the darkest objects known to exist in the solar system. Some comet nuclei reflect less than 4% of the light that falls on them. Blacktop(asphalt) reflects 7% of the light that falls on it. It is thought that complex organic compounds make up the dark surface material. Solar heating drives off volatile compounds leaving behind heavy long-chain organics that tend to be very dark. The very darkness of cometary surfaces allows them to absorb the heat necessary to drive their outgassing.

Most cometary nuclei are thought to be no more than about16 km across. But cometary nuclei up to 40km across are known to exist. The shapes of comets is very inconsistent. Comets lack the needed gravity to become spherical, so the are often irregular, somewhat potato shaped in appearance.

NASA has a short page about comet nucleus here. There is an in depth article on the topic here. Here on Universe Today we have an article about the interesting facts about comets that has a lot of info on the nucleus and another on an asteroid/comet hybrid.

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A comet tail does not appear on a comet until it approaches the Sun. As the Sun's radiation heats up the dust and gases there are actually two tails formed. The dust forms the anititail and the gases form the true tail. In the outer solar system, comets remain frozen and are extremely difficult or impossible to detect from Earth due to their small size. As a comet approaches the inner solar system, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them. The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the sun.

The streams of dust and gas each form their own distinct tail, pointing in slightly different directions. The tail of dust is left behind in the comet's orbit so that it often forms a curved tail called the antitail. At the same time, the ion tail, made of gases, always points directly away from the Sun. This gas is more strongly affected by the solar wind than dust and follows magnetic field lines instead of an orbital trajectory. Parralax viewing from the Earth may sometimes mean the tails appear to point in opposite directions.

Ion tails have been observed to extend 1 AU (150 million km) or more. The observation of antitails contributed significantly to the discovery of solar wind. The ion tail is formed as a result of solar ultra-violet radiation acting on particles in the coma. Once the particles have been ionized, they attain a net positive electrical charge which in turn gives rise to an induced magnetosphere around the comet. The comet and its induced magnetic field form an obstacle to outward flowing solar wind particles. As the relative orbital speed of the comet and the solar wind becomes supersonic, a bow shock is formed upstream of the comet, in the flow direction of the solar wind. In this bow shock, large concentrations of cometary ions congregate and act to load the solar magnetic field with plasma, such that the field lines drape around the comet forming the ion tail.

There is a good article about the comet tail here. Here on Universe Today we have an article about the strange acting Comet Lulin. Astronomy Cast has a good episode about space dust in general.

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On January 30, 1996, Comet Hyakutake was discovered using 25×150 binoculars. The comet was designated Comet C/1996 B2 (Hyakutake). As subsequent observations of the new comet were obtained, the IAU Central Bureau was able to compute the comet's orbital elements, and these computations indicated that the comet passed as close as 0.10 AU from the Earth on March 25, 1996! The comet became a bright unaided-eye object and remained so in March, April and May in 1996. The comet had exceeded expectations, becoming the brightest comet since Comet West in 1976. A long tail of up to 100 degrees was reported, and small fragments have been observed to break off the main nucleus. Comet Hyakutake was indeed the Great Comet of 1996.

Comet Hyakutake led to several scientific discoveries. Most surprising to cometary scientists was the first discovery of X-rays being emitted from a comet. They are believed to have been caused by ionized solar wind particles interacting with neutral atoms in the coma of the comet. The Ulysses spacecraft unexpectedly crossed the comet's tail at a distance of more than 500 million km from the nucleus, showing that Comet Hyakutake had the longest tail known for a comet. Hyakutake is a long period comet. Its orbital period was 17,000 years, but the gravitational influences of the large planets this trip through the inner solar system have extended that to every 100,000 years.

Comet Hyakutake became visible to the naked eye in early March 1996. By mid-March, the comet was still fairly unremarkable, shining at 4th magnitude with a tail about 5 degrees long. As it neared its closest approach to Earth, it rapidly became brighter, and its tail grew in length. After its close approach to the Earth, the comet faded to about 2nd magnitude. It reached perihelion on May 1, 1996, brightening again and exhibiting a dust tail in addition to the gas tail seen as it passed the Earth. By this time, however, it was close to the Sun and was not seen as easily. It was observed passing perihelion by the SOHO Sun-observing satellite, which also recorded a large coronal mass ejection being formed at the same time. Its distance from the Sun at perihelion was 0.23 AU, well inside the orbit of Mercury.

There are many good images and some good information on the JPL page for Comet Hyakutake. Here is a good article about the comet. Here on Universe Today there is more information about the X-rays that Hyakutake emitted. Astronomy Cast offers an episode about what the Christmas Star may have been. Possibly a comet?

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