Weekly Space Hangout – March 28, 2014: Uwingu & New Dwarf Planet News

Host: Fraser Cain
Astrojournalists: Morgan Rehnberg, David Dickinson

Special Guest: Dr. Alan Stern, Principle Investigator of New Horizons, Founder of Uwingu
Continue reading “Weekly Space Hangout – March 28, 2014: Uwingu & New Dwarf Planet News”

Discovery! Possible Dwarf Planet Found Far Beyond Pluto’s Orbit

What is a dwarf planet? Some astronomers have been asking that question after Pluto was demoted from planethood almost a decade ago, partly due to discoveries of other worlds of similar proportions.

Today, astronomers announced the discovery of 2012 VP113, a world that, assuming its reflectivity is moderate, is 280 miles (450 kilometers) in size and orbiting even further away from the sun than Pluto or even the more distant Sedna (announced in 2004). If 2012 VP113 is made up mostly of ice, this would make it large (and round) enough to be a dwarf planet, the astronomers said.

Peering further into 2012 VP113’s discovery, however, brings up several questions. What are the boundaries of the Oort Cloud, the region of icy bodies where the co-discoverers say it resides? Was it placed there due to a sort of Planet X? And what is the definition of a dwarf planet anyway?

First, a bit about 2012 VP113. Its closest approach to the Sun is about 80 astronomical units, making it 80 times further from the Sun than Earth is. This puts the object in a region of space previously known only to contain Sedna (76 AU away). It’s also far away from the Kuiper Belt, a region of rocky and icy bodies between 30 and 50 AU that includes Pluto.

The discovery images of 2012 VP113. Each one was taken about two hours apart on Nov. 5, 2012. Behind the object, you can see background stars and galaxies that remained still (from Earth's perspective) in the picture frame. Credit: Scott S. Sheppard: Carnegie Institution for Science
The discovery images of 2012 VP113. Each one was taken about two hours apart on Nov. 5, 2012. Behind the object, you can see background stars and galaxies that remained still (from Earth’s perspective) in the picture frame. Credit: Scott S. Sheppard: Carnegie Institution for Science

“The detection of 2012 VP113 confirms that Sedna is not an isolated object; instead, both bodies may be members of the inner Oort Cloud, whose objects could outnumber all other dynamically stable populations in the Solar System,” the authors wrote in their discovery paper, published today in Nature.

The Oort cloud (named after the Dutch astronomer Jan Oort, who first proposed it) is thought to contain a vast number of smallish, icy bodies. This NASA web page defines its boundaries as between 5,000 and 100,000 AUs, so 2012 VP113 obviously falls short of this measure.

The astronomers hypothesize that 2012 VP113 is part of a collection of “inner Oort cloud objects” that make their closest approach at a distance of more than 50 AU, a boundary that is thought to avoid any “significant” interference from Neptune. Orbits of these objects would range no further than 1,500 AU, a location hypothesized as part of the “outer Oort cloud” — the spot where “galactic tides start to become important in the formation process,” the team wrote.

“Some of these inner Oort cloud objects could rival the size of Mars or even Earth. This is because many of the inner Oort cloud objects are so distant that even very large ones would be too faint to detect with current technology,” stated Scott Sheppard, co-author of the paper and a solar system researcher at the Carnegie Institution for Science. (The lead author is the Gemini Observatory’s Chadwick Trujillo, who co-discovered several dwarf planets with the California Institute of Technology’s Mike Brown.)

The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA
The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA

One large question is how 2012 VP113 and Sedna came to be. And of course, with only two objects, it’s hard to draw any definitive conclusions. Theory 1 supposes that the gas giant planets beyond Earth ejected a “rogue” planet (or planets) that in turn threw objects from the Kuiper Belt to the more distant inner Oort Cloud. “These planet-sized objects could either remain (unseen) in the Solar System or have been ejected from the Solar System during the creation of the inner Oort Cloud,” the researchers wrote.

(Planet X hopers: Note that NASA just released results from its Wide-Field Infrared Survey Explorer that found nothing Saturn’s size (or bigger) as far as 10,000 AU, and nothing bigger than Jupiter at 26,000 AU.)

Theory 2 postulates that a passing star moved objects closer to the Sun into the inner Oort cloud. The last, “less-explored” theory is that these objects are “extrasolar planetesimals” — small worlds from other stars — that happened to be close to the Sun when it was born in a field of stars.

However these objects came to be, the astronomers estimate there are 900 objects with orbits similar to Sedna and 2012 VP113 that have diameters larger than 620 miles (1,000 kilometers). How do we know which are dwarf planets, however, given their distance and small size?

Artist's impression of Makemake, a dwarf planet about two-thirds Pluto's size. Credit: ESO/L. Calçada/Nick Risinger (skysurvey.org)
Artist’s impression of Makemake, a dwarf planet about two-thirds Pluto’s size. Credit: ESO/L. Calçada/Nick Risinger (skysurvey.org)

The International Astronomical Union’s definition of a dwarf planet doesn’t mention how big an object has to be to qualify as a dwarf planet. It reads: “A dwarf planet is an object in orbit around the Sun that is large enough (massive enough) to have its own gravity pull itself into a round (or nearly round) shape. Generally, a dwarf planet is smaller than Mercury. A dwarf planet may also orbit in a zone that has many other objects in it. For example, an orbit within the asteroid belt is in a zone with lots of other objects.”

That same page mentions there are only five recognized dwarf planets: Ceres, Pluto, Eris, Makemake and Haumea. Brown led the discovery of the last three dwarf planets in this list, and calls himself “the man who killed Pluto” because his finds helped demote Pluto from planethood to dwarf planet status.

It’s hard for official bodies to keep up with the pace of discovery, however. Brown’s webpage lists 46 “likely” dwarf planets, which under this definition would give him 15 discoveries.

“Reality … does not pay much attention to official lists kept by the IAU or by anyone else,” he wrote on that page. “A more interesting question to ask is: how many round objects are there in the solar system that are not planets? These are, by the definition, dwarf planets, whether or not they ever make it to any offiicially sanctioned list. If the category of dwarf planet is important, then it is the reality that is important, not the official list.”

Artist's impression of the dwarf planet Haumea and its moons, Hi'aka and Namaka. Credit: NASA
Artist’s impression of the dwarf planet Haumea and its moons, Hi’aka and Namaka. Credit: NASA

His analysis (which focuses on Kuiper Belt objects) notes that most objects are too faint for us to notice if they are round or not, but you can get a sense of how round an object is by its size and composition. The asteroid belt’s Ceres (at 560 miles or 900 km) is the only known round, rocky object.

For icier objects, he suggested looking to icy moons to understand how small an object can be and still be round. Saturn’s moon Mimas is round at 250 miles (400 km), which he classifies as a “reasonable lower limit” (since observed satellites of 125 miles/200 km are not round).

Discovery of 2012 VP113 came courtesy of the new Dark Energy Camera (DECam) at the National Optical Astronomy Observatory’s 4-meter telescope in Chile. The orbit was determined with the Magellan 6.5-meter telescope at Carnegie’s Las Campanas Observatory, also in Chile.

The paper, called “A Sedna-like body with a perihelion of 80 astronomical units”, will soon be available on Nature’s website.

Mysterious and Well-Preserved Oort Cloud Object Heading Into Our Solar System

What if we could journey to the outer edge of the Solar System – beyond the familiar rocky planets and the gas giants, past the orbits of asteroids and comets – one thousand times further still – to the spherical shell of icy particles that enshrouds the Solar System. This shell, more commonly known as the Oort cloud, is believed to be a remnant of the early Solar System.

Imagine what astronomers could learn about the early Solar System by sending a probe to the Oort cloud! Unfortunately 1-2 light years is more than a little beyond our reach. But we’re not entirely out of luck. 2010 WG9 – a trans-Neptunian object — is actually an Oort Cloud object in disguise. It has been kicked out of its orbit, and is heading closer towards us so we can get an unprecedented look.

But it gets even better! 2010 WG9 won’t get close to the Sun, meaning that its icy surface will remain well-preserved. Dr. David Rabinowitz, lead author of a paper about the ongoing observations of this object told Universe Today, “This is one of the Holy Grails of Planetary Science – to observe an unaltered planetesimal left over from the time of Solar System formation.”

Now you might be thinking: wait, don’t comets come from the Oort Cloud? It’s true; most comets were pulled out of the Oort cloud by a gravitational disturbance. But observing comets is extremely difficult, as they are surrounded by bright clouds of dust and gas. They also come much closer to the Sun, meaning that their ices evaporate and their original surface is not preserved.

So while there is a surprisingly high number of Oort cloud objects hanging out within the inner solar system, we needed to find one that is easy to observe and whose surface is well preserved. 2010 WG9 is just the object for the job! It is not covered by dust or gas, and is believed to have spent most of its lifetime at distances greater than 1000 AU. In fact, it will never approach closer than Uranus.

Astronomers at Yale University have observed 2010 WG9 for over two years, taking images in different filters. Just as coffee filters allow ground coffee to pass through but will block larger coffee beans, astronomical filters allow certain wavelengths of light to pass through, while blocking all others.

Recall that the wavelength of visible light relates to color. The color red, for example, has a wavelength of approximately 650 nm. An object that is very red will therefore be brighter in a filter of this wavelength, as opposed to a filter of, say, 475 nm, or blue. The use of filters allow astronomers to study specific colors of light.

Astronomers observed 2010 WG9 with four filters: B, V, R, and I, also known as blue, visible, red, and infrared wavelengths. What did they see? Variation – a change in color over the course of just days.

The likely source is a patchy surface. Imagine looking at the Earth (pretend there’s no atmosphere) with a blue filter. It would brighten when an ocean came into view, and dim when that ocean left the field of view. There would be a variation in color, dependent on the different elements located on the surface of the planet.

The dwarf planet Pluto has patches of methane ice, which also show up as color variations on its surface. Unlike Pluto, 2010 WG9 is relatively small (100 km in diameter) and cannot hold on to its methane ice. It’s possible that part of the surface is newly exposed after an impact. According to Rabinowitz, astronomers are still unsure what the color variations mean.

Rabinowitz was very keen to explain that 2010 WG9 has an unusually slow rotation. Most trans-Neptunian objects rotate every few hours. 2010 WG9 rotates on the order of 11 days! The best reason for this discrepancy is that it exists in a binary system. If 2010 WG9 is tidally locked to another body — meaning that the spin of each body is locked to the rate of rotation — then 2010 WG9 will be slowed down in its rotation.

According to Rabinowitz, the next step will be to observe 2010 WG9 with larger telescopes — perhaps the Hubble Space Telescope — in order to better measure the color variation. We may even be able to determine if this object is in a binary system after all, and observe the secondary object as well.

Any future observations will help us further understand the Oort cloud. “Very little is known about the Oort cloud – how many objects are in it, what are its dimensions, and how it formed,” Rabinowitz explained.  “By studying the detailed properties of a newly arrived member of the Oort cloud, we may learn about its constituents.”

2010 WG9 will likely hint at the origin of the Solar System in helping us further understand its own origin: the mysterious Oort cloud.

Source: Rabinowitz, et al. AJ, 2013

Comet Pan-STARRS Wows Over Holland

Comet Pan-STARRS thrills Dutch observers of the Night Sky on March 14, 2013 shortly after sunset- note the rich hues. Shot with a Canon 60D camera and Canon 100/400 mm lens, exposure time 2 seconds, ISO 800. Credit: Rob van Mackelenbergh
See viewing guide and sky maps below
Update – see readers photo below[/caption]

Comet Pan-STARRS (C/2011 L4) is exciting amateur astronomers observing the night sky worldwide as it becomes visible in the northern latitudes after sunset. And now it’s wowing crowds in Europe and all over Holland – north to south.

Check out the beautiful, richly hued new photos of Comet Pan-STARRS captured on March 14, 2013 by Dutch astrophotographer Rob van Mackelenbergh.

“I took these photos in the southern part of the Netherlands on Thursday evening, March 14, at around 7:45 pm Dutch time with my Canon 60 D camera.”

“I was observing from the grounds of our astronomy club – “Sterrenwacht Halley” – named in honor of Halley’s Comet.”

Comet Pan-STARRS is a non-periodic comet from the Oort Cloud that was discovered in June 2011 by the Pan-STARRS telescope located near the summit of the Hawaiian Island of Maui.

The comet just reached perihelion – closest approach to the Sun – on March 10, 2013. It passed closest to Earth on March 5 and has an orbital period of 106,000 years.

Comet Pan-STARRS from Holland on March 15, 2013 at about 7:45 PM, shortly after sunset - Canon 60D camera, Canon 100/400 mm lens, exposure time 15 seconds, ISO 300.   Credit: Rob van Mackelenbergh
Comet Pan-STARRS from Holland on March 14, 2013 at about 7:45 PM, shortly after sunset – Canon 60D camera, Canon 100/400 mm lens, exposure time 2 seconds, ISO 800. Credit: Rob van Mackelenbergh

“Over 30 people were watching with me and they were all very excited, looking with binoculars and cameras. People were cheering. They were so excited to see the comet. But it was very cold, about minus 2 C,” said Mackelenbergh.

The “Sterrenwacht Halley” Observatory was built in 1987 and houses a Planetarium and a Celestron C14 Schmidt-Cassegrain telescope. It’s located about 50 km from the border with Belgium, near Den Bosch – the capitol city of southern Holland.

Comet Pan-STARRS was photographed from Sterrenwacht Halley - or 'Halley Observatory' in Holland.  Credit: Rob van Mackelenbergh
Comet Pan-STARRS was photographed from Sterrenwacht Halley – or ‘Halley Observatory” in Holland. Credit: Rob van Mackelenbergh

“It was hard to see the comet with the naked eye. But we were able to watch it for about 45 minutes altogether in the west, after the sun set.”

“The sky was completely clear except for a few scattered clouds near the horizon. After the comet set, we went inside the observatory for a general lecture about Comets and especially Comets Pan-STARRS and ISON because most of the people were not aware about this year’s pair of bright comets.”

“So everyone was lucky to see Comet Pan-STARRS because suddenly the sky cleared of thick clouds!”

Comet Pan-STARRS from Holland on March 15, 2013 at about 7:45 PM, shortly after sunset - Canon 60D camera, Canon 100/400 mm lens, exposure time 15 seconds, ISO 300.   Credit: Rob van Mackelenbergh
Comet Pan-STARRS from Holland on March 14, 2013 at about 7:45 PM, shortly after sunset – Canon 60D camera, Canon 100/400 mm lens, exposure time 2 seconds, ISO 800. Credit: Rob van Mackelenbergh

“In the past I also saw Comet Halley and Comet Hale-Bopp, but these are my first ever comet photos and I’m really excited !”

“I hope to see Comet Pan-STARRS again in the coming days when the sky is clear,” Mackelenbergh told me.

Over the next 2 weeks or so the sunset comet may grow in brightness even as it recedes from Earth into darker skies. Right now it’s about magnitude 0.2.

So keep looking with your binoculars; look west for up to 1 to 2 hours after sunset – and keep your eyes peeled.

And report back here !

Ken Kremer


See a readers photo of sunset Comet Pan-STARRS below

Comet Pan-STARRS viewing graphic from NASA
Comet Pan-STARRS viewing graphic from NASA
Comet Pan-Starrs Sky Map. Viewing guide to find the comet low in the horizon after sunset.Credit: Space Weather.com
Comet Pan-Starrs Sky Map. Viewing guide to find the comet low in the horizon after sunset.Credit: Spaceweather.com

Best Evidence Yet That Comets Delivered Water for Earth’s Oceans

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The idea isn’t new that Earth’s oceans originated from comets bombarding our planet back in its early days. But astronomers have now found the best evidence yet for this scenario. The Herschel infrared space observatory detected that comet Hartley 2, which originates from the distant Kuiper Belt, contains water with the same chemical signature as Earth’s oceans.

“Our results with Herschel suggest that comets could have played a major role in bringing vast amounts of water to an early Earth,” said Dariusz Lis, senior research associate in physics at the California Institute of Technology in Pasadena and co-author of a new paper in the journal Nature, published online on Oct. 5. “This finding substantially expands the reservoir of Earth ocean-like water in the solar system to now include icy bodies originating in the Kuiper Belt.”

Previous looks at various other comets showed water content different from Earth, with deuterium levels around twice that of Earth’s oceans, but those comets came from the Oort Cloud. Scientists theorized that if comets of this kind had collided with Earth, they could not have contributed more than a few percent of Earth’s water.

The Deep Impact spacecraft successfully flew past Comet Hartley 2 in November 2010 and is an example of the type of comet that the UCLA scientists describe in their research. Image: UPI/NASA/JPL-Caltech/UMD.

But Herschel’s observations of Hartley 2 are the first in-depth look at water in a comet from the Kuiper Belt — home of icy, rocky bodies that includes dwarf planets and innumerable comets — and it showed a surprising difference.

Using HIFI, a highly sensitive infrared spectrometer, Herschel peered into the comet’s coma, or thin, gaseous atmosphere, and found that Hartley 2 possessed half as much “heavy water” as other comets analyzed to date. In heavy water, one of the two normal hydrogen atoms has been replaced by the heavy hydrogen isotope known as deuterium. The ratio between heavy water and light, or regular, water in Hartley 2 is the same as the water on Earth’s surface.

“Comet Hartley’s deuterium-to-hydrogen ratio is almost exactly the same as the water in Earth’s oceans,” says Paul Hartogh, Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany, who led the international team of astronomers in this study.

The amount of heavy water in a comet is related to the environment where the comet formed, and by comparing the deuterium to hydrogen ratio found in the water in Earth’s oceans with that in extraterrestrial objects, astronomers were hoping to identify the origin of our water.

Astronomers know Hartley 2 comes from the Kuiper Belt, since they can track its path as it swoops into Earth’s neighborhood in the inner solar system every six-and-a-`half years. The five comets besides Hartley 2 whose heavy-water-to-regular-water ratios have been obtained all came from the Oort Cloud, an even more distant region in the solar system. This region is 10,000 times farther away than the Kuiper Belt, and is home to the most documented comets.

The team is now using Herschel to look at other Kuiper Belt comets to see whether they, too, carry the same type of water.

“Thanks to this detection made possible by Herschel, an old, very interesting discussion will be revived and invigorated,” said Göran Pilbratt, ESA Herschel Project Scientist. “It will be exciting to see where this discovery will take us.”

Paper: “Ocean-like Water in the Jupiter-family Comet 103P Hartley”

Sources: JPL, ESA

About that Giant Planet Possibly Hiding in the Outer Solar System…

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An old story got new legs this week as word went viral of a possible new 9th planet in our solar system – a gas giant bigger than Jupiter – which could be hiding somewhere in the Oort Cloud, just waiting to be found.

An article this week in The Independent suggested the new planet, called Tyche, had already been found among data from the WISE mission. This prompted the WISE team to post a rebuttal on their Facebook page: “Not true. A pair of scientists published a paper stating that if such a big planet exists in the far reaches of the Solar System, then WISE should have seen it. That is true. But, analysis over the next couple of years will be needed to determine if WISE has actually detected such a world or not.”

To make sense of this all, Universe Today sought out a scientist who has looked at the outer solar system as much as anyone, if not more: Mike Brown, of Eris, Haumea and Makemake fame – to get his take on Tyche.

“Yes,” said Brown, “this is all getting pretty funny these days!”

The story starts at least a decade ago. For years John Matese of the University of Louisiana at Lafayette and colleague Daniel Whitmire have been trying to figure out why many of the comets that originate from way out in the distant-most part of our solar system — the Oort Cloud — have strange orbits that don’t jive with theories of how comets should behave. The two scientists first suggested that the gravitational influence from a dark companion to the Sun — a dim brown-dwarf or red-dwarf star — was sending comets careening towards the inner solar system. They called it Nemesis, (another thing that went viral), but the Nemesis idea has widely been refuted.

Last year, Matese and Whitmire suggested that possibly a large planet four times the mass of Jupiter in the Oort Cloud could explain why long-period comets appear to be clustered in a band inclined to the ecliptic instead of coming from random directions. (Here’s their paper.)

Then came a revival of their theory with several articles about it this week, reporting it as seemingly fact.

Could there possibly be a giant planet 500 times as distant as Neptune?

“Absolutely,” Brown said. “Many people have speculated about such possibilities for a long time. It’s an intriguing idea because, well, it would be fun, to say the least.”

But beyond fun and excitement, is there actually any evidence for it?

The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA

“Well, the quality of the data that Matese and Whitmire have to work with is pretty crummy –no fault of their own — it’s just the historical record of where comets have come from,” Brown said in an email. “I don’t believe that anyone understands the ins and outs of the data set well enough to really draw a robust conclusion. But, Matese and Whitmire did the best they could and think the data point to something out there.”

Does Brown think there is really something out there?

“Well,” he said, “if I had to bet one way or another I’d bet no. The data don’t convince me, and there is no other hint anywhere that such a thing is real. So I’m pretty skeptical.”

That being said, however, Brown believes WISE really does have a good chance of detecting this type of object way out there – if it exists — even if the predictions have nothing to do with the real object.

“This is something that people will absolutely be looking for when the data are released,” Brown said, “and, indeed, the WISE team is undoubtedly already looking for — not because of the prediction, but simply because it’s the right way to search this unknown region of the solar system!”

So don’t worry about the International Astronomical Union having to confirm or name a new planet in our solar system, at least for now.

Astronomy Without A Telescope – Coloring In The Oort Cloud

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It’s possible that if we do eventually observe the hypothetical objects that make up the hypothetical Oort cloud, they will all be a deep red color. This red coloring will probably be a mix of ices, richly laced with organic compounds – and may represent remnants of the primordial material from which the solar system was formed.

Furthermore, the wide range of colors found across different classes of trans-Neptunian objects may help to determine their origins.

The current observable classes of trans-Neptunian objects includes Pluto and similar objects called plutinos, which are caught in a 2:3 orbital resonance with Neptune towards the inner edge of the Kuiper belt. There are other Kuiper belt objects caught in a range of different resonant orbital ratios, including two-tinos – which are caught in a 1:2 resonance with Neptune – and which are found towards the outer edge of the Kuiper belt.

Otherwise, the majority of Kuiper belt objects (KBOs) are cubewanos (named after the first one discovered called QB1), which are also known as ‘classical’ KBOs. These are not obviously in orbital resonance with Neptune and their solar orbits are relatively circular and well outside Neptune’s orbit. There are two fairly distinct populations of cubewanos – those which have little inclination and those which are tilted more than 12 degrees away from the mean orbital plane of the solar system.

Beyond the Kuiper belt is the scattered disk – which contains objects with very eccentric elliptical orbits. So, although it may take hundreds of years for them to get there, the perihelions of many of these objects’ orbits are much closer to the Sun – suggesting this region is the main source of short period comets.

The trans-Neptunian landscape. Classical Kuiper belt objects have relatively circular orbits that never stray within the orbit of Neptune (yellow circle) - while plutinos and scattered disk objects have eccentric orbits that may. Classical objects with low inclinations (see ecliptic view) tend to have the deepest red coloration. Objects with higher inclination - and those with eccentric solar orbits which take them closer to the Sun - appear faded.

Now, there are an awful lot of trans-Neptunian objects out there and not all of them have been observed in detail, but surveys to date suggest the following trends:

  • Cubewanos with little inclination or eccentricity are a deep red color; and
  • Plutinos, scattered disk objects and highly inclined cubewanos are much less red.

Beyond the scattered disk are detached objects, that are clearly detached from the influence of the major planets. The best known example is Sedna – which is… yep, deep red (or ultra-red as the boffins prefer to say).

Sedna and other extreme outer trans-Neptunian objects are sometimes speculatively referred to as inner Oort cloud objects. So if we are willingly to assume that a few meager data points are representative of a wider (and hypothetical) population of Oort cloud objects – then maybe, like Sedna, they are all a deep red color.

And, looking back the other way, the ‘much less red’ color of highly inclined and highly eccentric trans-Neptunian objects is consistent with the color of comets, Centaurs (comets yet to be) and damocloids (comets that once were).

On this basis, it’s tempting to suggest that deep red is the color of primordial solar system material, but it’s a color that fades when exposed to moderate sunlight – something that seems to happen to objects that stray further inward than Neptune’s orbit. So maybe all those faded objects with inclined orbits used to exist much nearer to the Sun, but were flung outward during the early planetary migration maneuvers of the gas giants.

And the primordial red stuff? Maybe it’s frozen tholins – nitrogen-rich organic compounds produced by the irradiation of nitrogen and methane. And if this primordial red stuff has never been irradiated by our Sun, maybe it’s a remnant of the glowing dust cloud that was once our Sun’s stellar nursery.

Ah, what stories we can weave with scant data.

Further reading: Sheppard, S.S. The colors of extreme outer solar system objects.

Where Do Asteroids Come From?

[/caption]Where do asteroids come from? Most of them are grouped in the main belt, but that is not the only asteroid field in the solar system. There are actually four sets of asteroids grouped into different fields: the main belt, Trojans, scattered disc, and the Kuiper belt. To understand where do asteroids come from, you need to know the theory on how they were formed.

Most scientists agree that all of the asteroids are the result of the the big bang. After the initial turmoil, large asteroids collided together and through the process known as accretion planets and dwarf planets were formed. The planets and dwarfs grew large enough to develop gravity and became rounded and able to sustain their own gravity. Asteroids continued to collide and destroy each other until we have the elliptical and other odd shaped, pock-marked solar objects that we have today. Here is a little information to help you understand where do asteroids come from today.

The asteroid field known as the main belt is a large collection of objects that are in orbit between Jupiter and Mars. The largest known asteroid in the belt is Ceres which accounts for 27% of the belts’ total mass. Ceres is also the only asteroid in the belt that is classified as a dwarf planet. Vesta, Hygeia, and Pallas are the other of the four largest bodies in the asteroid field. There have been several space missions that have crossed the field. The asteroids are far enough apart that traversing it is easily done. The Dawn space mission to the next to visit the main belt and will visit two of the largest bodies, hopefully it will be able to help reclassify Vesta as a dwarf planet.

The Kuiper belt is populated with thousands of icy bodies. The only one that is currently designated as a dwarf planet is the former planet Pluto. That may change in the near future since there are at least two bodies in the belt that are larger than Pluto. Our ability to send spacecraft that far out is what is holding us back right now.

The Trojans asteroid field, originally referred to the Trojan asteroids, orbits around Jupiter’s 4th and 5th Lagrangian points. Subsequently objects have been found orbiting the same Lagrangian points of Neptune and Mars. The word Trojan, in astronomy, refers to a natural satellite that shares an orbit with a larger planet or moon, but does not collide with it because it orbits around one of the two Lagrangian points of stability.

The scattered disc asteroid field is a subset of the Kuiper belt. Because their orbits take them well beyond 100AU from the Sun they are the coldest objects in the Solar System. Due to its unstable nature, astronomers now consider the scattered disc to be the place of origin for most periodic comets. Many of the objects in the Oort cloud are thought to have originated in the scattered disc.

Answering the question: ”Where do asteroids come from?” is pretty easy, but it is ambiguous at the same time. What we have are mostly theories and few definite facts. Things get even more blurry as you study different asteroids and find that some from different belts have somehow inter-mixed. Ah, the beauty of astronomy!

There is some good info on the asteroid belt here. NASA has a good piece on KBO’s. Here on Universe Today there is an article on the possibility of an alien asteroid belt and the Milky Ways’ own asteroid belts.

Reference:
Wikipedia