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Tenth_Planet-00.jpgThe 10th Planet? (1)53 visiteDa "NASA - Picture of the Day", del 31 Luglio 2005:"Is that a Tenth Planet? A faint, slowly moving dot discovered by computer shows clear signs of being a deep Solar System object at least as large as Pluto. The object, designated 2003 UB313, is currently situated nearly 100 times the Earth-Sun distance - over twice the average Pluto-Sun distance. That far out, the only way a single round object could be as bright as 2003 UB313 would be if it is at least as large as Pluto and completely reflective.
Since 2003 UB313 is surely not completely reflective, it could be substantially larger. One of the discovery frames is shown above digitally expanded and artificially brightened. 2003 UB313 was identified initially on frames taken by the automated 1.2-meter Samuel Oschin Telescope at Palomar Observatory in California, USA".
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Tenth_Planet-01.jpgThe 10th Planet? (2)53 visitePerchè escludere a priori, come fa la NASA, che il Decimo Pianeta abbia una superficie TOTALMENTE RIFLETTENTE?
Scusateci la provocazione, ma sarebbe sufficiente ipotizzare - per assurdo, se volete - che questo ipotetico Decimo Pianeta sia:
1) una sfera costituita prevalentemente di ghiaccio (un'eventualità tutt'altro che remota);
2) un corpo capace di emanare luce propria (una piccola stella?);
3) una sfera metallica (ossìa, per esempio, una gigantesca astronave che si trova "parcheggiata" ai confini del Sistema Solare).
Stupidaggini "Cosmiche"? Fantascienza di basso livello? Forse.
Ma se ci pensate (e se conoscete almeno un poco la storia del Sistema Solare e delle meccaniche - per lo più teoriche - che ci hanno permesso di stimarne le dimensioni complessive), l'ipotesi più improbabile (molto in voga negli anni '60/'70 ma poi ritenuta inverosimile ed abbandonata) è proprio quella che immagina il Decimo Pianeta come un corpo roccioso di dimensioni medio-grandi!
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Tenth_Planet-03.jpgThe 10th Planet? (3)53 visiteDa "NASA - Picture of the Day", del 1mo Agosto 2005:"Has a tenth planet been discovered? A newly discovered object, designated 2003 UB313 and located more than twice the distance of Pluto, is expected to be at least as large as Pluto and probably larger, given current measurements. 2003 UB313's dimness and highly tilted orbit (44°) prevented it from being discovered sooner. Many astronomers speculate that numerous other icy objects larger than Pluto likely exist in the Kuiper Belt of the far distant Solar System. If so, and if some are found closer in than 2003 UB313, it may be premature to call 2003 UB313 the tenth planet. Illustrated above is an artist's drawing showing what 2003 UB313 might look. The unusually bright star on the right is the Sun. Much of the world eagerly await the decision by the International Astronomical Union on whether 2003 UB313 will be designated a planet or given a name without subscripts".
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Xena.jpgXena: another "Tenth Planet"? (2003 UB313)55 visiteNASA's Hubble Space Telescope has resolved the Tenth Planet, now nicknamed Xena, for the first time and has found that it is only just a little larger than Pluto.
Though previous ground-based observations suggested that Xena was about 30% greater in diameter than Pluto, Hubble observations taken on Dec. 9 and 10, 2005, yield a diameter of 1.490 miles (with an uncertainty of 60 miles) for Xena. Pluto's diameter, as measured by Hubble, is 1.422 miles. Xena is the large object at the bottom of this artist's concept. A portion of its surface is lit by the Sun, located in the upper left corner of the image. Xena's companion, Gabrielle, is located just above and to the left of Xena.
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ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-Ultima_Thule_-_1.jpgUltima Thule91 visiteThe New Horizons team used the Hubble Space Telescope to search for its post-Pluto, Kuiper Belt flyby target. Using observations made with Hubble on June 26, 2014, the science team (led by co-investigator Marc Buie) discovered an object that New Horizons could reach with its available fuel. The object was subsequently designated 2014 MU69, given the minor planet number 485968 and, with public input, nicknamed "Ultima Thule" (which means "beyond the known world").
MU69 is located in the Kuiper Belt, beyond the orbit of Neptune. At 12:33 a.m. (EST) on January 1, 2019, New Horizons flew just 2,200 miles (3,500) kilometers from the object's surface, when it was about 4 billion miles (6.6 billion kilometers) from the Sun -- the most distant planetary flyby in history and the first close-up look at a solar system object of this type.
Ultima Thule is the first unquestionably primordial contact binary ever explored. Approach pictures hinted at a strange, snowman-like shape, but further analysis of images, taken near closest approach, uncovered just how unusual the KBO's shape really is. At 22 miles (35 kilometers) long, the binary consists of a large, flat lobe (nicknamed "Ultima") connected to a smaller, rounder lobe (nicknamed "Thule").
This strange shape was the biggest surprise of the flyby. Nothign like it has been anywhere in the solar system -- sending the planetary science community back to the drawing board to understand how planetesimals (the building blocks of the planets) form.
Because it is so well preserved, MU69 offered our clearest look back to the era of planetesimal accretion and the earliest stages of planetary formation. Apparently the two lobes once orbited each other, like many so-called binary worlds in the Kuiper Belt, until something brought them together in a "gentle" merger.
In color and composition, New Horizons data revealed that MU69 resembles many other objects found in its region of the Kuiper Belt. Consistent with pre-flyby observations from the Hubble Telescope, Ultima Thule is very red – redder even than Pluto, which New Horizons flew past on the inner edge of the Kuiper Belt in 2015 – and about the same color as many other so-called "cold classical" KBOs. ("Cold" referring not to temperature but to the circular, uninclined orbits of these objects; "classical" in that their orbits have changed little since forming, and represent a sample of the primordial Kuiper Belt.)
New Horizons scientists have also seen evidence for methanol, water ice and organic molecules on the surface -- a spectrum similar to some of the most extreme objects we've seen in the outer solar system.
Flyby data transmission continues, with all data expected on the ground by late summer 2020.MareKromium
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ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-Ultima_Thule_2-flyby.gifUltima Thule (Fly-By)67 visiteOriginal Caption:"Mission scientists created this "departure movie" from 14 different images taken by the New Horizons Long Range Reconnaissance Imager (LORRI) shortly after the spacecraft flew past the Kuiper Belt object nicknamed Ultima Thule (officially named 2014 MU69) on Jan. 1, 2019".MareKromium
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ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-ZZ-Arrokoth.pngArrokoth ("Sky" - ex "Ultima Thule")101 visiteOver a year ago, the New Horizons spacecraft flew by a strange object at the edge of our solar system. Just a hazy form resembling a snowman on the day of the spacecraft’s closest approach, Arrokoth is now taking shape to be a fascinating and revelatory member of the region of the solar system beyond Neptune's orbit known as the Kuiper Belt. Untouched by the usual turmoil and impacts of most small objects, this pristinely preserved world could tell us about the earliest years of our solar system's formation.
New research published in a series of papers in Science begins to reveal Arrokoth's mysteries, including its formation, geography, composition, various basic properties and more. Scientists from NASA's Ames Research Center in California's Silicon Valley worked alongside researchers from across the world to provide a comprehensive first look at this object.
Also known as MU69, the object consists of two lobes connected by a thin "neck" and has days that run almost 16 hours, while a full orbit around the solar system takes 298 years. Its orbit lies 44 times further away from the Sun than our own Earth, and based on the craters we see across its surface, Arrokoth is estimated to be about 4 billion years old.
"Arrokoth is a time capsule for our solar system's origins," said Orkan Umurhan, a research scientist at Ames and collaborator on the three Science papers. "MU69, and objects like it, can give us a look four billion years into the past and insight into where our cosmic home came from."
A Cold, Red and Smooth Surface
The images from the New Horizon's flyby reveal a complex world, rich not only in its geology, but in color and temperature as well.
The surface of Arrokoth is all red, but new analysis shows there's more variation in the color than originally thought, with the smaller lobe slightly redder than the larger one. That red coloring is often an indicator of a type of chemical compound known as tholins – organics seen on many objects in the outer solar system, including Pluto and Saturn’s moon Titan. Though we don't know if this is the case for certain on Arrokoth, Titan-like tholins would match the data we do have on the object.
Though we can't measure the object's temperature as we traditionally think of it, we can find a value for the temperature based on the object's radiation by looking at its brightness. This "brightness temperature" varies around the object, with the poles of each lobe reaching temperatures below -350 degrees Fahrenheit, decreasing further about each lobe’s equator. The neck connecting the lobes is relatively warmer than the rest of the object by up to 6 degrees Fahrenheit.
Arrokoth is a world with complex geological features across its surface, and no rings or other smaller objects in its orbit. Though littered with light craters, each about half a mile or less across, the object's surface is mostly smooth – with the exception of a larger crater nicknamed Maryland on the smaller lobe.
Maryland is most likely an impact crater, with its rim stretching more than four miles across and less than half a mile deep. Between the crater and the neck connecting the two lobes is a series of troughs, similar to those found on the asteroid Eros or Mars’ moon Phobos.
The larger lobe is even flatter than its counterpart. Besides a section marked off by a chain of pits, there are no large craters at all. That so much of Arrokoth's surface is very lightly disturbed or not at all tells a story about its formation – one not filled with collisions and violence, but gentler and slower impacts.
The Origins of Arrokoth
Arrokoth's two lobes appear to have once been separate objects, orbiting each other in synchronicity until merging together at a very slow speed – no more than a couple meters per second, perhaps even slower.
Those objects were likely formed in the very early years of our solar system, over four billion years ago. Then, the solar system was a nebulous swirl of gas and dust. Microscopic dust particles began to stick together into larger and larger chunks. Soon, those chunks become pebble-sized clouds that continue to collapse together, creating larger objects. In some cases, such as Arrokoth's, those objects formed in pairs, leading to a binary system.
This could also explain certain aspects of Arrokoth's chemical compositions, with possible methanol ices and complex organics that were also present in the early solar system nebula seen on the object as well. However, those organics could have emerged after Arrokoth had formed through chemical processes spurred on by cosmic radiation affecting methane on its surface. Unlike many similar objects, there is an absence of water ice, which appears to have been depleted or is obscured from our view.
Because Arrokoth's formation was so benign, with no major collisions or aberrations apparent on its surface, the object can give us insight into this early phase of the solar system when planets and other objects were still forming. Its interior is likely preserved as well, leaving the same mixture of ices, organics and dust from the nebula of materials that created our solar system.
New Horizons has given us not only a new in-depth look into Arrokoth, but that of other Kuiper Belt objects and the larger solar system as well. This small and oddly shaped world contains aspects of our own history that can be uncovered almost nowhere else. It is a rare and pristine record of the early solar system, a time capsule of our origins that has many truths yet to unveil.MareKromium
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