Xena (Eris) and other Extraordinary KBOs

 

The planet, officially designated 2003 UB313, was found by Dr Mike Brown and colleagues using the Samuel Oschin Telescope at Palomar Observatory near San Diego. It is currently about 97 times farther from the Sun than Earth, or 97 Astronomical Units, and is at least as large as Pluto (3).   It is the most distant object ever to be directly located in the solar system. You can appreciate the approximate distances involved from the artistic image I have created above (5).  All of the other Kuiper Belt Objects discovered so far have been found within 50 AU, although some of these have eccentric orbits which take them way beyond that distance.

 

The new tenth planet has not yet been given a name, but a suggestion has been put forward by Mike Brown to the official body sanctioned with making the historic decision of naming the tenth planet (4).  Dr Mike Brown would like the planet to be called 'Xena', after the fictional warrior princess played by the TV actress Lucy Lawless (2).  I would have thought something like 'Vulcan' would be more appropriate for this object, although it appears that the astronomical use of this Roman God of Fire has been reserved exclusively for a planet within Mercury's orbit!

[Update: Xena was officially named 'Eris' in 2006 by the IAU].

One researcher with a particular interest in a distant tenth planet going by the name 'Vulcan' is Barry Warmkessel.  Vulcan's existence is tied in with writings by Theosophists like Madame Blavatsky.  Barry Warmkessel suggests that the steeply inclined orbital path of 'Xena' can be explained by the presence of an as yet undiscovered planet the the general vicinity of this new planet.  Vulcan, he suggests, has an inclination in the region of about 50 degrees, and its presence far off the ecliptic would help to explain two things; how many of the Edgeworth-Kuiper Belt objects have anomalous orbits, and why this sizeable planet has so far escaped detection. 

Saying that, Barry is quite convinced that Vulcan has already been discovered, citing the lengthy passage of time taken for information about these newly discovered minor worlds to be released to the public (8).  Might astronomers be keeping information about a 'real' tenth planet secret right now?

 


Such considerations are actually far from fanciful, but the issue is admittedly a rather complex one.  Whilst the Edgeworth-Kuiper Belt is essentially a flat disc of objects beyond Neptune, many of them vary in inclination: Pluto is an obvious example.  The early conditions of the Solar System are still shrouded in mystery, to a certain extent, with many new theories about planetary interaction and migration emerging all the time to explain various anomalies.  The existence of one or more major planets beyond Neptune is one such theory among many.  Other theories include external gravitational influences, like passing stars or Gigantic Molecular Clouds in interstellar space.  So we cannot state with total confidence that anomalous orbits have to be related to larger bodies yet to be discovered, although this theory is certainly one of the best available!

Releasing information about the discovery of new EKBOs is also fraught with difficulties.  Spotting new dots of light on CCD camera images, and capturing enough data to actually specify orbits and sizes of new objects are two entirely separate things.  So an object might be initially classified in 2003, but it may take a couple of years of painstaking work to establish enough factual data to allow other scientists, and the general public, to recognise this object as a new planet. Scientists who rush this kind of process are liable to find egg on their faces.  So they must shroud their on-going work in secrecy to prevent other workers from stealing their discoveries while they work to confirm them properly.  As it turns out, this is pretty much what happened in the case of Xena, as I will discuss in a moment!
 

 

The name eventually attributed to 2003 UB313 ill depend upon whether it is actually classified as a major or minor planet.  Given that it is larger than Pluto, that should be incontrovertible.  Pluto, after all, doggedly remains a 'major planet'. However, this discovery may be the first among many.  If every round chunk of rock and ice larger than Pluto in the Edgeworth-Kuiper Belt were to be classified as a major planet, then one could imagine a situation where the science books need to list literally dozens of planets in the solar system in a just few years time! 

Indications of the orbit of 'Xena' are not entirely clear at this stage, nor even its size, which is probably between 2200 and 3000km in diameter (1).  Dr Brown says that the planet's perihelion is about 38 Astronomical Units, and its perihelion is 97 AU, which presumably means that it currently lies at or near its furthest point from the Sun.  This makes its orbit quite eccentric, bringing it close to Pluto  for much of the time.

NASA's artistic rendering of the tenth planet

 

For those interested in the more esoteric aspects of Planet X research, it is important to state that this is not Nibiru.  The planet is a rocky, icy world similar to Pluto, and it is certainly not a big player in the evolution of the Solar System!  Instead, it is one of many such worlds lying in the Edgeworth-Kuiper Belt, albeit being a particularly large example.   

Xena currently lies in the middle of the constellation of Cetus and has a highly inclined orbit:

"The object, designated 2003 UB313 ... is a scattered-disk object, meaning that at some point in its history Neptune probably flung it into its highly inclined (44°) orbit. It's currently glowing at magnitude 18.9 in the constellation Cetus. Its high inclination is the only reason it wasn't discovered years ago; no one was looking for planets so far from the plane of the solar system." (6)

Xena appears to share many characteristics with Pluto.  It has a highly reflective surface, which may indicate a layer of ice.  This contrasts with Sedna, and some of the other outer planetary bodies, which has reddish surfaces.  I wonder whether these two diverse sets of minor planetary bodies (some white, some red) may tell us something about their origins?  It has been speculated that the reddish appearance of Sedna may have resulted from collisional activity early in the life of the Solar System, or even that Sedna is a captured object.  Whatever the truth of this, Xena does not appear to have the same controversial surface characteristics, despite its eccentric orbit. Mike Brown writes:

"Pluto and the new planet are not completely identical, however. While Pluto's surface is moderately red, the new planet appears almost grey. We are only now beginning to try to understand why the colours differ so." (4)

My opinion on this is that the reddish coloured minor planets of the Edgeworth-Kuiper Belt have been affected more or less directly by the Dark Star at some point.  Some of them may even have resonant orbits with it.  The whiter planetoids escaped whatever interaction took place to create this effect early in the life of the Solar System.

 

Xena's discovery was made on 8th January 2005, but was kept secret whilst astronomers attempted to confirm the finding with other telescopes, and to give time for an official name to be given to it. However, technical information about 'Xena' was being held on telescope databases used by Dr Brown's team. This 'secure' data was actually available over the internet and someone with an astronomical background had accessed this information clandestinely. This forced the team to release the news in a hasty manner (2).

Without an official name, the impact of this story amongst the public, and mainstream media, has been somewhat muted.  This is a shame, particularly for Mike Brown's pioneering team.  However, if the new planet (which I can't imagine for 5 minutes will actually end up being called 'Xena' officially!) is classified as a major planet, then Dr Brown's place in history books is assured.

This announcement came on the same day as release of the news that a minor planetary body larger than Sedna was discovered by a group led by Jose-Luis Ortiz, of the Sierra Nevada Observatory in Spain.  This object, whose angle of inclination to the ecliptic is also significant, has the official designation 2003 EL61. (7)

Astronomers who, only a few years ago, were arguing adamantly that there would be no tenth planet to be found have been proven wrong!  There is a lot of undiscovered territory out there, with many more discoveries to be made.  I am quite convinced that one of those discoveries will be an actual binary companion to the Sun, which I call the Dark Star, in the form of a sub-brown dwarf.  It is likely to be 5-10 times as far away as this new planet.  As interest in outer solar system increases among astronomers, the probability of a discovery in the near future must be steadily improving.

I explain all about this in my new book, "The Dark Star" (published 2005).  I will also devote a complete web-page to this planet once an official name has been designated.  Time has been allotted for the Hubble Space Telescope to take a closer look at Xena, so hopefully a more detailed picture will emerge regarding its exact size and surface conditions.

 

If the name 'Xena' stood little or no chance of being recognised officially by the International Astronomical Union, then the latest nicknames to be applied to newly discovered 'mini-planets' are entirely doomed to failure (9). Mike Brown's team have announced the discovery of two more objects of Pluto-sized proportions. Both of them are located at high angles to the ecliptic, although they reside within the Edgeworth-Kuiper Belt at about 52AU.

They have been given nicknames to mark the times of their discoveries; Santa and the Easterbunny! Santa (2003 EL61), an elongated object about the size of Pluto, even has a little moon, called Rudolph (10).

Easterbunny  (2005 FY9) exhibits a surface of frozen methane ice, similar to Pluto, Sedna and Xena. There seems to be a pattern emerging, then, with this set of Pluto-sized objects. Perhaps this suggests a common origin for these particularly large Edgeworth-Kuiper Belt objects, with their uncommonly inclined orbits. Dr Brown suspects that they formed closer to the Sun and were flung into the Edgeworth-Kuiper Belt by gravitational interactions with the giant planets (10). But he has no idea why they are all covered in methane, or why methane should be showing up so much in the Solar System in general (11). 

The dwarf planet formerly known as 2005 FY9, or "Easterbunny", was given the name 'Makemake' by the International Astronomical Union in July 2008.

The red methane-covered dwarf planet orbits beyond Neptune, and has been designated the third plutoid in the solar system.  It is named after a Polynesian creator of humanity and god of fertility.  This artist's illustration shows the dwarf planet as it is believed to look:

 

'Buffy' Keeps her Distance

 

Another Edgeworth-Kuiper Belt Object has created profound difficulties for astronomers.  The discovery of 'Buffy', designated 2004 XR190, has led to a rash of speculation amongst scientists. 

 

This object is not one of the largest objects so far discovered, but it has a puzzling orbit: 

It is highly inclined to the ecliptic, at 47 degrees.

It has a roughly circular orbit, rather than the usual elongated variety.

Its orbital diameter is always greater than 50AU, meaning that it is part of the extended Scattered Disk, lying beyond Neptune's influence. (12)

 

 

Other objects have been discovered which show one or two of these characteristics.  Sedna, for instance, had a very distance orbit which is entirely removed from the influence of Neptune.  What is remarkable, and perhaps more difficult to explain, about Buffy is that it shows all three of these attributes.  That shouldn't have happened, at least according to theory. 

Orbits of such objects can expand, and become tilted, through the repeated influence of Neptune's resonances.  (Many of the objects in the outer solar system are held in these resonant orbits by Neptune).  But the influence seems too small to have created such a distant orbit as Buffy's.  Furthermore, this influence tends to elongate the orbits of the Edgeworth-Kuiper Belt Objects.  Buffy's orbit is too circular to fit into this theoretical picture:

 

"2004 XR190, however, follows a nearly circular path. And it is too distant to have come into direct contact with Neptune, travelling between 52 and 62 AU from the Sun. Its orbit is also too circular - and too small - to have been tilted by a passing star, says Lynne Allen of the University of British Columbia in Vancouver, Canada, who first spotted the object in observations made with the Canada-France-Hawaii Telescope in December 2004." (13)

The last few years have produced more questions than answers about the Edgeworth-Kuiper Belt.  I suspect that the study of the Belt is a bit like watching a juggler at work, and realising that some of the balls are moving around without ever touching his hands!  Something seems to be creating an invisible influence, or at least may have done so in the past.  The possibility of a passing star disturbing the Belt in the distant past is cited by some as an explanation, but appears to be the 'nuclear option', in that it would have profoundly affected the composition of the outer solar system. 

Of course, I'm inclined to think that the influence was that of a smaller 'sub-brown dwarf', in a relatively distant orbit around the Sun.  Some astronomers consider this possible too, and have discussed it, like Mike Brown, Alice Quillen and Hal Levison, although they would argue that this object must have left the influence of the Sun a very long time ago.  Even with that proviso they have reservations:

"Hal Levison, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, US, says he and others have produced objects like Buffy using models of such special resonances. "However, I do have some problems with the idea," he admits.

"He points out that this object was found when it happened to be passing through the plane of the solar system - where it spends just 2% of its orbit. That suggests many more such objects remain undiscovered, tilted at orbits where most surveys do not search for them. "I just don't think these mechanisms can deliver that much stuff," Levison told New Scientist.

"He ventures another possible explanation - that the Sun had a twin and that both stars followed circular orbits around each other. "That could excite inclinations without exciting the eccentricities," he says. "However, this idea creates more problems than it solves, by far."" (13)

But to even be thinking about this idea gives the reader some indication of the highly anomalous nature of the Edgeworth-Kuiper Belt.  Where general members of the public might consider the 'binary theory' to be right out of the ball-park, and into the fringe, the actual astronomers studying the outer solar system are having to consider such possibilities. On the whole, they may remain sceptical, but they seem deeply troubled by what they have found, and continue to find, out there.

 

Amateurs Glimpse Planet X

 

Xena was discovered using electronic scanning equipment linked by computers to the telescopes.  A series of CCD images are taken by astronomers of a particular portion of the night sky, then analysed by computer.  Discrepancies between the images are then checked out to see if a new object has been discovered. this is how Xena was found, but Dr Mike Brown's team haven't actually 'seen' the object 2003 UB313 themselves.

Instead, it has fallen to a small team of enthusiastic, and highly skilled amateurs, to actually spot the object through a telescope, in this case, the 2.1-meter (82-inch) Otto Struve Telescope at McDonald Observatory (14). Xena is a very difficult object to see, being only of luminosity magnitude 19.  Fuzzy, indistinct objects like this, seen through a telescope, are very difficult to distinguish at all when directly looked at.  Instead, by averting one's eye slightly, the object becomes apparent in the peripheral vision, which is more attuned to such visual minutae.  To even be able to set the telescope up to peer at the correct portion of the sky is a technical feat in itself, let alone glimpse Xena's dull light.

There are some issues here about how astronomers 'look' for objects in the sky. Professional astronomers don't really look at the sky in the traditional way anymore, but leave such traditional sky-watching to the amateurs, making use of the University telescopes in 'public access' time. This is an important issue when considering comet-hunting and the search for Planet X proper...Comets are often first seen by amateurs, and are thus often named after fairly obscure astronomers.  That's not always the case, of course, but it indicates a pattern.  Professional astronomers focus on deep space objects, like galaxies and distant star clusters.  They effectively see through everything in between.  This is another point to consider when pondering how Planet X objects have thus far evaded detection.

 

The Mystery Brightens

 

Hubble pictures taken of Xena in December 2005 have allowed Mike Brown's team to discovery the planet's actual size.  It turns out to be smaller than previously thought, being much the same size as Pluto.  But this finding has created fresh controversy.  The answer to this mystery is as plain as day to me, but it has got the astronomers stumped.

 

For Xena to be the size it is, but also as bright as it is, its surface must be extraordinarily reflective.  So reflective, in fact, that it is matched only by the Saturnian moon Enceladus, which we now know is spewing out liquid water onto its surface due to the gravitational pull of Saturn (15). 

For Xena to be this reflective, it must also be renewing its surface relatively frequently. 

 

This is how the enigma was reported by "New Scientist"

"Xena's surface is brighter than Antarctica - but astronomers do not know what is resurfacing it… The fact that Xena is smaller than initially thought means it must reflect about 86% of the light that falls on it - making it about as bright as fresh snow and brighter than every other solar system body except Saturn's moon Enceladus. Spectral observations suggest its surface is covered with frozen methane, like Pluto. .
 
""When we made the size measurement, we were thoroughly shocked," Brown told New Scientist. "Such a high albedo is simply unprecedented other than the very odd Enceladus."Richard Binzel, a planetary scientist at the Massachusetts Institute of Technology in Cambridge, US, agrees. "Space is a dirty place," he says, explaining that particles from the solar wind alter the structure of ices, darkening them over time. "It's very hard to keep a surface bright and white - it requires some process to keep the surface fresh."
 
"Brown suggests two possible mechanisms, working together, for the resurfacing. Xena moves in a very elongated orbit that stretches from 38 to 97 astronomical units (1 AU is the distance between the Sun and Earth). When it is near the Sun in its 560-year orbit, it may have a gaseous atmosphere. But when it moves away, it receives so little sunlight that any atmosphere would freeze onto Xena's surface, leaving it fresh and white. But a similar freeze-thaw cycle occurs on Pluto, which moves from 30 to 50 AU over about 250 years, says Binzel. And it does not have a blindingly bright surface. But a similar freeze-thaw cycle occurs on Pluto, which moves from 30 to 50 AU over about 250 years, says Binzel. And it does not have a blindingly bright surface. "So it may also be that fresh methane is leaking out of the surface," suggests Brown. "It would be more like a picture of a steam vent in Antarctica, where the steam instantly freezes onto the surface," he says.
 
"But he and other astronomers had thought that Xena's interior was made of rock and ice. For gaseous methane to survive within the planet, "you have to have an energy source", says Binzel. Brown agrees: "The real question is: Why would methane leak out of the surface?" Some objects are heated when they are gravitationally stretched and compressed by massive objects nearby. But though Xena has a moon that might be a tenth its size, it is too small to gravitationally deform and heat Xena, says Brown. Similarly, the decay of radioactive isotopes could not provide the necessary heat, says Binzel: "It's a wonderful mystery."" (15)
 

Yet, this small world is apparently alone in the outer solar system; no massive planet comes close to it, or it to them.  Without such a gravitational tug, there is no mechanism whereby Xena could be active in any way.  Even a small moon accompanying Xena could not be providing the gravitational tug sufficient to cause Xena to spew its contents out onto its surface.

 

 

It seems to me, and to anyone else who has followed my theories at all, that Xena does indeed have such an opportunity.  If Xena's orbit took it close to the dark companion of the Sun, then this periodic proximity to the Dark Star would absolutely provide the right conditions for Xena to act like a comet!  You see, if this little world runs a gauntlet between two stars, the Sun and its dark companion, then it could be highly active when passing close to this Dark Star.

The evidence from Hubble suggests that Xena has a remarkably bright surface.  Such surfaces are associated with close proximity to massive planets.  Yet, Xena is not close to such a planet.  It must be meeting up with a massive planet at some stage, or its surface could not be getting renewed as observed.  Such an explanation is simple and straightforward; that periodic encounters with the Sun's binary companion refashion the surface of Xena.  Xena, a minor planet the size of Pluto, may be acting as a planet-sized comet as it nears the Dark Star. Such an outburst of inner material would be sufficient to refashion the minor planet's surface. 

 

This is a remarkable possibility.  Xena may in reality be a planet-sized comet!  Only, it doesn't take on its comet-like appearance when it nears the Sun; it simply doesn't get close enough for the volatiles on and below its surface to burst out into space.  Instead, that activity only occurs when it is far away from the Sun; much further than it is now.  The comet-like appearance occurs when the minor planet Xena comes close to the Dark Star, whose own significant magnetosphere and heat output is enough to activate the frozen little world.  This activity causes the re-surfacing of Xena, and subsequently its anomalously bright surface.

My bet is that certain astronomers are toying with this very idea...In which case I'd like to invite them to a hold of a copy of my book and start reading! 

Indeed, Dr Mike Brown has also publicly contemplated the idea that a massive companion once existed circling the Sun.  This new observation adds more evidence to suggest that this is so.  However, this new data suggests that the Dark Star object MUST still be out there, awaiting discovery!  Why?  Because, otherwise, how can one explain Xena's refashioned surface? If the Dark Star object is no longer present beyond Pluto, then Xena should be a dull object like Pluto.  That is not what has been observed.

 

Santa's Surprise Collision

 

That Kuiper Belt is doing its strange stuff again.  Dr Mike Brown, that leading discoverer of outer solar system planets, has found a KBO shaped like a rugby ball.

 

It may be on its way towards a close encounter with Neptune in the future, which may divert its path into the inner solar system. One can just imagine the god Neptune booting 2003 EL61 towards the rest of his team-mates in about 2 million years time.  It would be quite something to score a drop-kick from the back of the pitch!  Also, quite a kick is needed by Neptune: 2003 EL61 is about the same size as Pluto. (16)

 

 

This unusual orbital behaviour is matched by the bizarre shape of this object.  Speculation in the astronomical community is growing that 2003 EL61 (initially nicknamed 'Santa') was subject to a violent collision sometime in the past (17).  The odds of such an event occurring in the Edgeworth-Kuiper Belt as it is known to exist today are very long indeed.  The objects in the belt are simply too scattered to present any kind of risk to one another. 

 

 

Yet, this object appears to have taken a big knock, and may be on of a number of such objects in the belt. 

"Flanked by two moonlets, 2003 EL61 measures some 1,500 kilometers (950 miles) across, tumbling over and over at a prodigious rate and pursuing a weird egg-shaped orbit inclined at nearly 30 degrees to the plane at which almost all of the Solar System's objects travel.

"[Dr Michael] Brown's team found five other rocks, measuring between 10 and 400 kilometers (six and 250 miles) across, that they believe were smashed away from 2003 EL61 in the distant past. The cluster shares the same colour and the light they reflect has a signature that suggests they are covered with surface water ice." (17)

The astronomers speculate that the collision which sheared all of these smaller objects from 'Santa' took place around the time of the Earth's formation.  Interesting, don't you think?  It has to be said that the likelihood of that having happened is not very high...unless the Edgeworth-Kuiper Belt contained a great many more objects 4+ billion years ago.  Add in a Dark Star to the equation and the whole scenario then makes much more sense... 

 

 

Eris's Surface is Changing, But Why?

 

We've already seen how reflective the surface of Eris (the KBO formally known as Xena) is.  Scientists have been able to study the surface, which is largely made up of methane ice, and some trace nitrogen ice.  They have discovered that it has changed, in just two years (18).

When Eris is at the closest point of its elongated 560 year orbit, the ices exposed to the sun are probably able to vaporise to create a small, temporary atmosphere.  This would then condense out onto the dark side of the dwarf planet, which rotates every 26 hours. This would then change the surface of the planet over time.

However, the changes to the surface - which have been noted through complex studied carried out by different astrophysics teams - are taking place when Eris is at its most distant point from the Sun.  Theoretically, it should be too cold for the ices to evaporate off at the moment, even in the sun-exposed areas.  So how is the change occurring?  This is yet another mystery posed by Eris. 

Planetary scientists have speculated that volcanic activity may have discharged material out onto the surface of Eris. But the dwarf planet seem rather small, and cold to have allowed this kind of activity, known as 'cryovulcanism'. Perhaps Eris is warmer than previously thought.  Astronomers have been shocked before by some of the unexpected activity in the solar system involving liquid water...Enceladus, the water-spouting moon of Saturn, is a case in point.  In my opinion the Kuiper Belt and beyond guard a wealth of secrets, the clues to which are only just starting to come to light.

 

 

Written by Andy Lloyd, 30 July - 4 August 2005, updated 16/9/05, 14/12/05, 6/3/06, 16-18/4/06, 20/3/07, 22/7/08, & 11/11/08

author of 'The Dark Star' (2005), 'Ezekiel One' (2009), 'The Followers of Horus' (2010) and 'Darker Stars' (2019)

Published by Timeless Voyager Press

 

    Darker Stars

 

References:

1) David Whitehouse "Astronomers detect '10th planet'" 30 July 2005

news.bbc.co.uk news

2) Robin McKie "The Little Rock Causing a Galactic Storm" The Observer 31 July 2005

3) NASA "New Tenth Planet Discovered" 29 July 2005

science.nasa.gov article

4) Michael Brown, Caltech "Astronomers at Palomar Observatory Discover a 10th Planet Beyond Pluto" With thanks to Mattia Galiazzo

gps.caltech.edu article

5) Caltech Astronomy: Images of the Samuel Oschin Telescope

astro.caltech.edu article

6) David Tytell "Astronomers Discover "Tenth Planet"" Sky and Telescope, 29 July 2005 (article on longer available online)

7) R. Britt "Large New World Discovered Beyond Neptune" 29 July 2005 with thanks to David Pearson

space.com article

8) For more information on Barry Warmkessel's hunt for Vulcan see

barry.warmkessel.com/

9)  D. Perlman "Astronomers discover 2 more oddball objects" San Francisco Chronicle, 9 September 2005, with thanks to Peter Gersten

sfgate.com article

10) Caltech News Release "Work Continues on the Solar System's Three Recently Discovered Objects" 8 September 2005, (article on longer available online)

11)  L. Moulton Howe " "Planet X" and the Kuiper Belt's Oddballs, "Santa" and "Easterbunny" - Interview with Dr Mike Brown,  with thanks to David Pearson earthfiles.com news

12) CFEPS Press Release 13 December 2005 with thanks to David Pearson (article on longer available online)

minorplanetcenter.net article

13) Maggie McKee "Strange new object found at edge of Solar System" 13 December 2005 with thanks to David Pearson and Shad Bolling

New Scientist article

14)  "Amateur astronomers make first sighting of ‘10th planet’ through eyepiece of Mcdonald Observatory telescope" 4 March 2006, with thanks to David Pearson

mcdonaldobservatory.org news

15)   New Scientist "Tenth planet as bright as fresh snow" 11 April 2006, with thanks to David Pearson

newscientist.com article

16)  Paul Rincon "Dwarf planet 'becoming a comet': An unusual dwarf planet discovered in the outer Solar System could be en route to becoming the brightest comet ever known"   17 January 2007, with thanks to Paul Wood

bbc.co.uk news

17)  Caltech "Kuiper-belt Object Was Broken up by Massive Impact 4.5 Billion Years Ago, Study Shows"  14 March 2007, with thanks to David Pearson

physorg.com news

18) Rachel Courtland, New Scientist "Mysterious changes seen on distant dwarf planet" 10th Nov 2008, with thanks to David Pearson

newscientist.com article

 

 Xena y otros EKBOs Extraordinarios