Het Astronomie Topic #9

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Op donderdag 13 februari 2014 08:36 schreef ExperimentalFrentalMental het volgende:
14-02-2014

Oorzaak van ‘maanvloek’ ontdekt

De retroreflectors – panelen ter grootte van een koffer die precies op de aarde zijn gericht –

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Op woensdag 5 maart 2014 15:33 schreef Perrin het volgende:
Als de maan maar 1 pixel groot was

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Op donderdag 8 augustus 2013 10:45 schreef Perrin het volgende:

[..]

[ afbeelding ]

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Op dinsdag 25 maart 2014 13:10 schreef lipper het volgende:

[..]

wat een toffe foto. Wat is het? En waar vind je dit?

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<sup>This is an orbit diagram for the outer solar system. The Sun and Terrestrial planets are at the center. The orbits of the four giant planets, Jupiter, Saturn, Uranus and Neptune, are shown by purple solid circles. The Kuiper Belt, including Pluto, is shown by the dotted light blue region just beyond the giant planets. Sedna's orbit is shown in orange while 2012 VP113's orbit is shown in red.

Credit: Scott Sheppard</sup>


Date: March 26, 2014
Source: Carnegie Institution

Summary:
The Solar System has a new most-distant member, bringing its outer frontier into focus. New work reports the discovery of a distant dwarf planet, called 2012 VP113, which was found beyond the known edge of the Solar System. This is likely one of thousands of distant objects that are thought to form the so-called inner Oort cloud. The work indicates the potential presence of an enormous planet, not yet seen, but possibly influencing the orbit of inner Oort cloud objects.

The Solar System has a new most-distant member, bringing its outer frontier into focus.

New work from Carnegie's Scott Sheppard and Chadwick Trujillo of the Gemini Observatory reports the discovery of a distant dwarf planet, called 2012 VP113, which was found beyond the known edge of the Solar System. This is likely one of thousands of distant objects that are thought to form the so-called inner Oort cloud. What's more, their work indicates the potential presence of an enormous planet, perhaps up to 10 times the size of Earth, not yet seen, but possibly influencing the orbit of 2012 VP113, as well as other inner Oort cloud objects.

Their findings are published March 27 in Nature.

The known Solar System can be divided into three parts: the rocky planets like Earth, which are close to the Sun; the gas giant planets, which are further out; and the frozen objects of the Kuiper belt, which lie just beyond Neptune's orbit. Beyond this, there appears to be an edge to the Solar System where only one object, Sedna, was previously known to exist for its entire orbit. But the newly found 2012 VP113 has an orbit that stays even beyond Sedna, making it the furthest known in the Solar System.

"This is an extraordinary result that redefines our understanding of our Solar System," says Linda Elkins-Tanton, director of Carnegie's Department of Terrestrial Magnetism.

Sedna was discovered beyond the Kuiper Belt edge in 2003, and it was not known if Sedna was unique, as Pluto once was thought to be before the Kuiper Belt was discovered. With the discovery of 2012 VP113 it is now clear Sedna is not unique and is likely the second known member of the hypothesized inner Oort cloud, the likely origin of some comets.

2012 VP113's closest orbit point to the Sun brings it to about 80 times the distance of Earth from the Sun, a measurement referred to as an astronomical unit or AU. For context, the rocky planets and asteroids exist at distances ranging between .39 and 4.2 AU. Gas giants are found between 5 and 30 AU, and the Kuiper belt (composed of thousands of icy objects, including Pluto) ranges from 30 to 50 AU. In our solar system there is a distinct edge at 50 AU. Only Sedna was known to stay significantly beyond this outer boundary at 76 AU for its entire orbit.

"The search for these distant inner Oort cloud objects beyond Sedna and 2012 VP113 should continue, as they could tell us a lot about how our Solar System formed and evolved," says Sheppard.

Sheppard and Trujillo used the new Dark Energy Camera (DECam) on the NOAO 4 meter telescope in Chile for discovery. DECam has the largest field-of-view of any 4-meter or larger telescope, giving it unprecedented ability to search large areas of sky for faint objects. The Magellan 6.5-meter telescope at Carnegie's Las Campanas Observatory was used to determine the orbit of 2012 VP113 and obtain detailed information about its surface properties.

From the amount of sky searched, Sheppard and Trujillo determine that about 900 objects with orbits like Sedna and 2012 VP113 and sizes larger than 1000 km may exist and that the total population of the inner Oort cloud is likely bigger than that of the Kuiper Belt and main asteroid belt.

"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," says Sheppard.

Both Sedna and 2012 VP113 were found near their closest approach to the Sun, but they both have orbits that go out to hundreds of AU, at which point they would be too faint to discover. In fact, the similarity in the orbits found for Sedna, 2012 VP113 and a few other objects near the edge of the Kuiper Belt suggests that an unknown massive perturbing body may be shepherding these objects into these similar orbital configurations. Sheppard and Trujillo suggest a Super Earth or an even larger object at hundreds of AU could create the shepherding effect seen in the orbits of these objects, which are too distant to be perturbed significantly by any of the known planets.

There are three competing theories for how the inner Oort cloud might have formed. As more objects are found, it will be easier to narrow down which of these theories is most likely accurate. One theory is that a rogue planet could have been tossed out of the giant planet region and could have perturbed objects out of the Kuiper Belt to the inner Oort cloud on its way out. This planet could have been ejected or still be in the distant solar system today. The second theory is that a close stellar encounter could have put objects into the inner Oort cloud region. A third theory suggests inner Oort cloud objects are captured extra-solar planets from other stars that were near our Sun in its birth cluster.

The outer Oort cloud is distinguished from the inner Oort cloud because in the outer Oort cloud, starting around 1500 AU, the gravity from other nearby stars perturbs the orbits of the objects, causing objects in the outer Oort cloud to have orbits that change drastically over time. Many of the comets we see were objects that were perturbed out of the outer Oort cloud. Inner Oort cloud objects are not highly affected by the gravity of other stars and thus have more stable and more primordial orbits.

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Date: March 26, 2014
Source: European Southern Observatory - ESO

Summary:
Astronomers have made the surprise discovery that the remote asteroid Chariklo is surrounded by two dense and narrow rings. This is the smallest object by far found to have rings and only the fifth body in the Solar System after the much larger planets Jupiter, Saturn, Uranus and Neptune to have this feature. The origin of these rings remains a mystery, but they may be the result of a collision that created a disc of debris.


<sup>Artists impression of the rings around Chariklo.

Credit: ESO</sup>

Observations at many sites in South America, including ESO's La Silla Observatory, have made the surprise discovery that the remote asteroid Chariklo is surrounded by two dense and narrow rings. This is the smallest object by far found to have rings and only the fifth body in the Solar System -- after the much larger planets Jupiter, Saturn, Uranus and Neptune -- to have this feature. The origin of these rings remains a mystery, but they may be the result of a collision that created a disc of debris. The new results are published online in the journal Nature on 26 March 2014.

The rings of Saturn are one of the most spectacular sights in the sky, and less prominent rings have also been found around the other giant planets. Despite many careful searches, no rings had been found around smaller objects orbiting the Sun in the Solar System. Now observations of the distant minor planet [1] (10199) Chariklo [2] as it passed in front of a star have shown that this object too is surrounded by two fine rings.

"We weren't looking for a ring and didn't think small bodies like Chariklo had them at all, so the discovery -- and the amazing amountof detail we saw in the system -- came as a complete surprise!" says Felipe Braga-Ribas (Observatório Nacional/MCTI, Rio de Janeiro, Brazil) who planned the observation campaign and is lead author on the new paper.

Chariklo is the largest member of a class known as the Centaurs [3] and it orbits between Saturn and Uranus in the outer Solar System. Predictions had shown that it would pass in front of the star UCAC4 248-108672 on 3 June 2013, as seen from South America [4]. Astronomers using telescopes at seven different locations, including the 1.54-metre Danish and TRAPPIST telescopes at ESO's La Silla Observatory in Chile [5], were able to watch the star apparently vanish for a few seconds as its light was blocked by Chariklo -- an occultation [6].

But they found much more than they were expecting. A few seconds before, and again a few seconds after the main occultation there were two further very short dips in the star's apparent brightness [7]. Something around Chariklo was blocking the light! By comparing what was seen from different sites the team could reconstruct not only the shape and size of the object itself but also the shape, width, orientation and other properties of the newly discovered rings.

The team found that the ring system consists of two sharply confined rings only seven and three kilometres wide, separated by a clear gap of nine kilometres -- around a small 250-kilometre diameter object orbiting beyond Saturn.

"For me, it was quite amazing to realise that we were able not only to detect a ring system, but also pinpoint that it consists of two clearly distinct rings," adds Uffe Gråe Jørgensen (Niels Bohr Institute, University of Copenhagen, Denmark), one of the team. "I try to imagine how it would be to stand on the surface of this icy object -- small enough that a fast sports car could reach escape velocity and drive off into space -- and stare up at a 20-kilometre wide ring system 1000 times closer than the Moon." [8] Although many questions remain unanswered, astronomers think that this sort of ring is likely to be formed from debris left over after a collision. It must be confined into the two narrow rings by the presence of small putative satellites.

"So, as well as the rings, it's likely that Chariklo has at least one small moon still waiting to be discovered," adds Felipe Braga Ribas.

The rings may prove to be a phenomenon that might in turn later lead to the formation of a small moon. Such a sequence of events, on a much larger scale, may explain the birth of our own Moon in the early days of the Solar System, as well as the origin of many other satellites around planets and asteroids.

The leaders of this project are provisionally calling the rings by the nicknames Oiapoque and Chuí, two rivers near the northern and southern extremes of Brazil [9].

[1] All objects that orbit the Sun, which are too small (not massive enough) for their own gravity to pull them into a nearly spherical shape are now defined by the IAU as being small solar system bodies. This class currently includes most of the Solar System asteroids, near-Earth objects (NEOs), Mars and Jupiter Trojan asteroids, most Centaurs, most Trans-Neptunian objects (TNOs), and comets. In informal usage the words asteroid and minor planet are often used to mean the same thing.

[2] The IAU Minor Planet Center is the nerve centre for the detection of small bodies in the Solar System. The names assigned are in two parts, a number -- originally the order of discovery but now the order in which orbits are well-determined -- and a name.

[3] Centaurs are small bodies with unstable orbits in the outer Solar System that cross the orbits of the giant planets. Because their orbits are frequently perturbed they are expected to only remain in such orbits for millions of years. Centaurs are distinct from the much more numerous main belt asteroids between the orbits of Mars and Jupiter and may have come from the Kuiper Belt region. They got their name because -- like the mythical centaurs -- they share some characteristics of two different things, in this case comets and asteroids. Chariklo itself seems to be more like an asteroid and has not been found to display cometary activity.

[4] The event was predicted following a systematic search conducted with the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory and recently published.

[5] Besides the Danish 1.54-metre and TRAPPIST telescopes at ESO's La Silla Observatory, event observations were also performed by the following observatories: Universidad Católica Observatory (UCO) Santa Martina operated by the Pontifícia Universidad Católica de Chile (PUC); PROMPT telescopes, owned and operated by the University of North Carolina at Chapel Hill; Pico dos Dias Observatory from the National Laboratory of Astrophysics (OPD/LNA) -- Brazil; Southern Astrophysical Research (SOAR) telescope; Caisey Harlingten's 20-inch Planewave telescope, which is part of the Searchlight Observatory Network; R. Sandness's telescope at San Pedro de Atacama Celestial Explorations; Universidade Estadual de Ponta Grossa Observatory; Observatorio Astronomico Los Molinos (OALM) -- Uruguay; Observatorio Astronomico, Estacion Astrofisica de Bosque Alegre, Universidad Nacional de Cordoba, Argentina; Polo Astronômico Casimiro Montenegro Filho Observatory and Observatorio El Catalejo, Santa Rosa, La Pampa, Argentina.

[6] This is the only way to pin down the precise size and shape of such a remote body -- Chariklo is only about 250 kilometres in diameter and is more than a billion kilometres from Earth. Even in the best telescopic views such a small and distant object just appears as a faint point of light.

[7] The rings of Uranus, and the ring arcs around Neptune, were found in a similar way during occultations in 1977 and 1984, respectively. ESO telescopes were also involved with the Neptune ring discovery.

[8] Strictly speaking the car would have to be rather fast -- something like a Bugatti Veyron 16.4 or McLaren F1 -- as the escape velocity is around 350 km/hour!

[9] These names are only for informal use, the official names will be allocated later by the IAU, following pre-established rules.