APOD: Meteor in the Desert Sky (2010 Dec 11)

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Expand view Topic review: APOD: Meteor in the Desert Sky (2010 Dec 11)

Re: 3200 Phaethon: Asteroid or Dead Comet?

by neufer » Sun Dec 12, 2010 11:17 pm

http://astrobob.areavoices.com/2010/12/12/asteroid-switches-gears-becomes-comet/ wrote:
Asteroid switches gears, becomes comet Posted on December 12, 2010 by astrobob
<<Early yesterday morning, Steve Larson with the Catalina Sky Survey, photographed what was thought to be an ordinary asteroid, (596) Scheila, but when he examined the images, discovered it wore the guise of a comet. Instead of looking like a star-like point, the usual appearance of an asteroid, Scheila was surrounded by a vaguely spiral-shaped cloud of vapor.

See: http://www.universetoday.com/81576/aste ... -and-coma/

596 Scheila was discovered in February 1906 by German astronomer August Kopff and named after a student acquaintance. It orbits in the main belt of asteroids between Mars and Jupiter. Currently, Scheila is about 235 million miles from Earth. Nearly all the asteroids in the main belt are rocky bodies, but hidden among them is a newly emerging class of “sometimes asteroids-sometimes comets” called main belt comets.

The first one, 1979 OW7, was discovered in 1979 and designated as an asteroid based on its star-like appearance and orbit. When re-observed in 1996 by Eric Elst and Guido Pizarro, 1979 OW7 had sprouted a small coma (envelope of gas around the head of a comet) and a tail. Now known as Comet 133P/Elst-Pizarro, it was first thought the asteroid suffered an impact from another smaller asteroid, creating the dust tail. But Elst-Pizarro grew a new tail in 2002, making it more likely a dormant comet – one that comes back to life when its orbit brings it near enough to the sun that solar heat vaporizes lingering pockets of ice on or near the surface. Only four or five of these quick-change artists have been discovered to date; Scheila looks to be the most recent member in a rare class.

Most comets orbit the sun in highly elliptical or oblong orbits that take them beyond Jupiter and even Neptune into the frozen reaches of the solar system’s Kuiper Belt, a repository of icy asteroids and comets. Many more hail from a spherical halo called the Oort Cloud that’s even further away. Not only do main belt comets come from closer in, their orbits are like those of asteroids, which travel in more circular paths, compared to the stretched out, cigar-shaped orbits of comets.
[img3="Schelia's orbit takes it both above (light blue) the plane of Earth's orbit as well as below (dark blue). The number "596" refers to it being the 596th asteroid to have its orbit determined. Credit: JPL"]http://astrobob.areavoices.com/files/20 ... 00x209.jpg[/img3]
What’s so surprising about finding dormant comets in the asteroid belt is that logic implies all the ice from these bodies should have vaporized away because of their proximity to the sun’s heat. Yet here they are. Did they migrate there from a more distant, colder region? That’s not likely according to the latest studies, which suggest they’ve been there all along. Another question that scientists will try to answer in the coming days and weeks is what caused Scheila to turn comet in the first place. Was it chance vaporization of ice as in Elst-Pizarro’s case or did the 70-mile diameter asteroid/comet get whacked by another asteroid that happened to cross its path? An impact would release a cloud of water ice and dust that the sun’s light would push back into a tail. Perhaps an impact occurred much earlier and the freshly-exposed ice got jazzed by sunlight at a later date when conditions were right. If icy comets do inhabit the inner solar system, there’s speculation they might have been responsible for delivering water to Earth after our planet cooled down following it fiery hot formation. Catching Schelia in the act of swapping personalities may someday help us learn more about the water we use to make our daily coffee.

This morning I got up to have a look at 596 Schelia. To my amazement, I have all ten fingers left to prove I survived the fierce winds and -8 F temperature. The asteroid/comet, located in Leo the Lion, was a faint star of magnitude 14.3. Using a 15-inch telescope and magnification of 145x, I teased out a small puff of vapory light around it. Advanced amateur astronomers can locate the comet using JPL’s Small-Body Database Browser. Scroll down below the orbit diagram and input the asteroid’s orbital elements (numbers describing its orbit) into your planetarium software program. From there, you can create a personalized finder chart. If you don’t have a program that allows you to add or change asteroid elements, you can scroll down a bit further, click on the ephemeris link, select your location, time, etc. and then hand-plot Schelia’s position on a detailed star atlas.>>

Re: APOD: Meteor in the Desert Sky (2010 Dec 11)

by lenka » Sat Dec 11, 2010 5:02 pm

good excuse for bad images:) Fortunately, I live out of town so it will be very dark, unless I fall into the lake it will be dark wet and after midnight ..not good:)

Re: APOD: Meteor in the Desert Sky (2010 Dec 11)

by neufer » Sat Dec 11, 2010 3:40 pm

lenka wrote:
I am ready for Geminids and my camera too :)
Important instructions:
  • 1) Avoid bright lights.
    2) Don't get wet.
    3) Don't eat after midnight.
http://en.wikipedia.org/wiki/Gremlins wrote: [c]Gremlins (1984)[/c]
<<Randall "Rand" Peltzer (Hoyt Axton) is an inventor who is struggling to market his unusual and problem-plagued home appliances, including the handheld "Bathroom Buddy". While searching for a Christmas present for his teenage son Billy in an old antique store in Chinatown, Randy comes across a small furry creature called a Mogwai which he tries to buy for his son. The owner of the store, Mr. Wing, refuses to sell the Mogwai to Rand on the grounds that owning the Mogwai is too great a responsibility. As Randy is leaving the store, Mr. Wing's grandson tells Rand to meet him outside, where he sells Rand the creature because Mr. Wing was in need of money. The grandson reminds Rand to follow three important instructions: never expose the Mogwai to bright lights (especially sunlight, which will kill it), don't get it wet, and never feed it after midnight.>>

Re: APOD: Meteor in the Desert Sky (2010 Dec 11)

by lenka » Sat Dec 11, 2010 3:24 pm

Iam ready for Geminids and my camera too :)

Re: APOD: Meteor in the Desert Sky (2010 Dec 11)

by Chris Peterson » Sat Dec 11, 2010 3:01 pm

PacRim Jim wrote:I find it interesting that the luminosity of the meteor varies symmetrically, like a bell curve.
Most meteors show a more unsymmetrical light curve, building up slowly and then decaying quickly, but light curves like that seen in today's image are not all that uncommon.

Re: APOD: Meteor in the Desert Sky (2010 Dec 11)

by PacRim Jim » Sat Dec 11, 2010 8:22 am

I find it interesting that the luminosity of the meteor varies symmetrically, like a bell curve.

Re: APOD: Meteor in the Desert Sky (2010 Dec 11)

by mexhunter » Sat Dec 11, 2010 6:22 am

Congratulations to my friend Wally, this is another of those pictures that involve being in the right place at the right time.
Beautiful!!!
Greetings
César

Re: 3200 Phaethon: Asteroid or Dead Comet?

by bystander » Sat Dec 11, 2010 5:41 am

3200 Phaethon: Asteroid or Dead Comet?

by neufer » Sat Dec 11, 2010 5:32 am

http://astroprofspage.com/archives/498 wrote:
3200 Phaethon: Asteroid or Dead Comet?
Published on Dec 1, 2006 at 3:41 pm.

<<Comets are icy bodies that form in the outermost parts of the Solar System. Sometimes their orbits are disturbed, and they swing close to the Sun. When this happens, the ices (frozen water, frozen carbon dioxide, frozen methane, frozen ammonia, etc) begin to sublimate and shoot off, giving rise to a pretty blue tail. But, they are also composed of rocks and dust. Some of this dust is also blown out when the gases shoot away from the comet’s nucleus. The dust particles then are pushed back by light pressure to form a more yellowish dust tail. But, the larger dust and rock particles continue to orbit the Sun for a while with orbits not too dissimilar to the comet. Occasionally comets that swoop in towards the Sun from the outer Solar System pass too close to Jupiter or Saturn, and those giant planets’ gravity cause the comets’ orbits to shift so that they return to perihelion over and over again in only a few years. These are periodic comets. And, sometimes these comets have orbits that cross the orbit of the Earth. For a comet whose orbit passes near Earth’s orbit, and has done so for a very long time, the dust and rock particles moving along in orbits similar to that of the comet form a swarm of meteoroids that Earth tends to pass through at about the same time every year. These particles, when they strike Earth’s atmosphere, become meteors (we call them meteoroids when they are still traveling through space). When a bunch of meteoroids are striking Earth, then there are more than the normal number of meteors to be seen, and they appear to be coming from a particular direction in space. We call this a meteor shower. Several meteor showers can be directly associated with comets. For example, the Orionid meteors and the Eta Aquarid meteors are associated with Halley’s Comet. The Leonid meteors are associated with Comet Tempel-Tuttle, and the Perseid meteors are associated with Comet Swift-Tuttle.

Now, for the really new part. In a couple of weeks, the Geminid Meteors will peak. I’ll say more about them in a later post. Occurring near the middle of December every year, the Geminids are a pretty reliable meteor shower. So, what comet are the Geminids associated with? Well, as it turns out, none. The Geminids are associated with an asteroid: 3200 Phaethon. An asteroid? What’s going on? Well, obviously we need to take a closer look at Phaethon.

In 1983, Simon Green and John Davies were studying images from the IRAS satellite. They were looking for moving bodies, and they found one. This was the first asteroid discovered from a satellite, and it turned out to be quite an odd one! The newly found object was assigned a provisional designation of 1983 TB. Eventually, it was given a number and a name: 3200 Phaethon. With a perihelion of only 0.140 AU, Phaethon approaches closer to the Sun than just about any other asteroids, making its surface temperature at that point in excess of 1000K. Hence, the asteroid was named after Phaeton, the son of the Greek Sun god Helios. No one has really explained to me the difference in spelling, except that it may be an attempt to avoid confusion with Heinrich Olbers’ hypothetical planet that he called Phaeton that was supposedly between Mars and Jupiter and somehow blew up to form the asteroid belt. If that were the reason, then the strategy failed, because people regularly misspell the asteroid’s name as Phaeton instead of the correct spelling of Phaethon. With an aphelion of 2.403 AU, Phaethon is classified as an Apollo Asteroid (one whose orbit crosses that of the Earth). Phaethon will actually be passing fairly close to Earth just next year: December 10, 2007. On that date, it will be only about 0.121 AU away. In astronomical terms, that’s pretty close, but it is still far by human standards (a bit over 11 million miles).

But, none of this really explains the Geminid meteors. So, what else can we say about Phaethon besides its having a strange orbit? Well, for one thing, Phaethon is one of a rather rare category of asteroids that is carbonaceous (rich in carbon compounds). It is a Type-B asteroid (a subtype of Type-C carbonaceous asteroids with a slightly different UV spectrum and a slightly more bluish color). This is one clue.

There have been several other bodies discovered that were unusually rich in organic compounds for an asteroid. One of these was 2060 Chiron, and more recently 60558 Echeclus. Both of these bodies were found in the outer Solar System, beyond Saturn. They have another similarity, too. They were discovered and named as asteroids (though their location in the Solar System makes them clearly different from the asteroids of the main belt), but several years after discovery they were found to have cometary features (a coma and tail). Both have now also received cometary designations: 95P/Chiron and 174P/Echeclus (making them the only two comets that I know of that are named for other than the one who discovered them, unless you count Halley’s Comet, which he didn’t actually see himself). So, what are these things, comets or asteroids?

It gets more confusing. There are at least two comets that orbit in the asteroid belt that look and act just like asteroids when they are near perihelion. They have comet names, but they have also been assigned asteroid designations. They are 133P/Elst-Pizarro (7968 Elst-Pizarro), and 176P/LINEAR (118401 LINEAR). Upon discovery, and much of the time, they look like rather wimpy comets, but at aphelion they look more like very carbon-rich asteroids. Another comet, P/2005 U1, does something similar, but to my knowledge has not yet been assigned an asteroid designation. And then, there is another comet, 107P/Wilson-Harrington that was discovered in 1949. In 1979, an asteroid was found and given a provisional designation of 1979 VA. Upon closer analysis, it was found that 1979 VA had the same orbit as Comet Wilson-Harrington! So, the comet had apparently turned into an asteroid! It was eventually given an asteroid number, making it yet another body with dual asteroid/comet status: Comet 107P/Wilson-Harrington and Minor Planet 4015 Wilson-Harrington.

Now, we have more pieces of the puzzle. Comets can become asteroids. But, how is this possible? Well, remember that comets are a mixture of ices, frozen gases, rock, and dust. Once the icy part has mostly sublimated away, what is left is rocky material rich in organic molecules (originating from chemical reactions from the ammonia and methane that made up the comet). After comets have spent long enough and made enough passes by the Sun, the volatiles are mostly gone, and what is left looks pretty much like a carbon-rich asteroid. No doubt deep inside these bodies, there is still some ice and frozen gas, but it is buried under many layers of rock and can’t get out unless a major impact fractures the body. So, Phaethon, perhaps, is what is left of a comet that has run out of easily accessible volatiles. Before doing so, though, it would have been a comet spewing material into space like any other comet. Some of that material would have been dust and small rocks: the things that are the source of meteor showers. So, could Phaethon be a dead comet? That seems very likely. Now, that is not the only possible interpretation of the association of the Geminid meteors with Phaethon. Some have suggested that a major impact on the asteroid could have thrown a lot of material out into space in a similar orbit. But, that seems unlikely to me to be the source of a rather regular meteor shower. Such a thing suggests to me repeated events shedding material, like a comet would do. So, I rather think that Phaethon is more likely a dead comet than an asteroid. But, as we have seen, a comet might be a lot like an icy asteroid. It sort of depends on how you look at them.

And Phaethon is not the only dead comet out there. Other asteroids that have a great deal of similarities to Phaethon and to comets are 2101 Adonis and 2201 Oljato. And, the Geminid meteor shower is not the only meteor shower associated with an asteroid. The Arietid meteor shower, which comes in June each year, seems to be associated with the asteroid 1566 Icarus. So, I guess that just complicates the whole classification thing yet more. Hmm. Astronomy used to be so simple before we started finding out how complicated the universe is!>>

APOD: Meteor in the Desert Sky (2010 Dec 11)

by APOD Robot » Sat Dec 11, 2010 5:09 am

Image Meteor in the Desert Sky

Explanation: Created as planet Earth sweeps through dusty debris from mysterious, asteroid-like, 3200 Phaethon, the annual Geminid Meteor Shower should be the best meteor shower of the year. The Geminids are predicted to peak on the night of December 13/14, but you can start watching for Geminid meteors this weekend. The best viewing is after midnight in a dark, moonless sky, with the shower's radiant constellation Gemini well above the horizon - a situation that favors skygazers in the northern hemisphere. In this picture from the 2009 Geminid shower, a bright meteor with a greenish tinge flashes through the sky over the Mojave Desert near Barstow, California, USA. Recognizable in the background are bright stars in the northern asterism known as the Big Dipper, framing the meteor streak.

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