Planetenring
.jpg)
.jpg)
.jpg)
.png){kind=spacer}
Ein Planetenring ist eine Ansammlung fester Partikel unterschiedlicher Größe (typischerweise von Staubkorngröße bis zu Durchmessern über zehn Meter), die einen planetenartigen Himmelskörper oder Asteroiden innerhalb eines abgrenzbaren Entfernungsintervalls nahe einer Ebene umkreisen und dabei zahlreich genug sind, um in ihrer Gesamtheit als ringscheibenförmiges Gebilde beschreibbar zu sein. Solche Ringe können unterschiedliche Ausmaße, Zusammensetzungen (beispielsweise aus Eis- oder Gesteinspartikeln), Flächen- und Gesamthelligkeiten aufweisen. Mehrere Ringe um einen Planeten bilden ein konzentrisches Ringsystem.
Entstehung
Die Entstehung eines Planetenrings ist bis heute nicht vollständig erklärt. Ein Ansatz ist, dass Ringe entstehen können, wenn ein kleiner Mond dem Planeten zu nahe kommt, sich also innerhalb der Roche-Grenze befindet, und dort durch die Gezeitenkräfte des Planeten auseinandergerissen und um den Planeten verteilt wird. Ein weiterer Ansatz im Zusammenhang mit der Roche-Grenze geht davon aus, dass die Ringe Überreste der Gasscheibe sind, aus denen sich der Planet geformt hat – innerhalb der Roche-Grenze konnte sich das restliche Gas aber zu keinen Monden formen.
Eine andere Theorie besagt, dass ein Planetenring entsteht, wenn der Planet von einem anderen Himmelskörper getroffen wird oder zwei kleine Körper kollidieren, so dass sie auseinanderbrechen und sich aufgrund der hohen Schwerkraft des Planeten nicht wieder zusammensetzen, sondern um den Planeten verteilt werden.
Planetenringe im Sonnensystem
Im Sonnensystem hat jeder der vier Gasplaneten ein Ringsystem. Deren Teilchen umlaufen den Planeten rechtläufig innerhalb bzw. sehr nahe dessen Äquatorebene und fast immer innerhalb der Roche-Grenze. Trotz der gemeinsamen Hauptmerkmale ist die Struktur der Ringe in allen vier Fällen sehr unterschiedlich.
Das bekannteste Planetenringsystem sind die Ringe des Saturn. Es ist das umfangreichste Ringsystem, besteht aus hellem Material und ist daher bereits mit einem guten Amateurteleskop sichtbar. Es besteht aus mehreren sogenannten Hauptringen, die wiederum aus vielen dünnen Ringen bestehen.
Nach Saturn am zweitstärksten sind im Sonnensystem die Ringe des Uranus ausgeprägt. Am schwächsten ist das Ringsystem des Jupiters. Es besteht aus äußerst dunklem Material, noch dazu ist es verschwindend unscheinbar, sodass es nur durch Raumsonden nachgewiesen werden konnte. Man nimmt an, dass Jupiters Ringe von winzigen innersten Monden mit neuem Material versorgt werden, während das alte Material stetig auf Jupiter herabrieselt. Uranus und Neptun haben ebenfalls äußerst dunkle Ringe. Bei Neptun glaubte man anfangs, dass seine Ringe nur unvollständige Ringbögen seien, also nicht in sich geschlossen wären.
Es sieht so aus, dass sich dichte Ringsysteme nur in einem Sonnenabstand zwischen 8 und 20 AE bei Oberflächentemperaturen von etwa 70 K bilden.[1]
Ringe um Asteroiden
2014 wurden von der Europäischen Südsternwarte (ESO) erstmals Ringe um einen Asteroiden entdeckt, nämlich um (10199) Chariklo.
Auch für (2060) Chiron wird in einer Veröffentlichung von 2015 ein Ringsystem vermutet.[2]
Anlässlich einer Sternbedeckung am 21. Januar 2017 wurde entdeckt, dass Haumea über einen 70 km breiten Ring von etwa 4.574 km Durchmesser verfügt.
Ringe um Exoplaneten
Da sämtliche Gasriesen des Sonnensystems Ringsysteme besitzen, kann die Existenz von Exoplaneten mit Planetenringen angenommen werden. Während Eispartikel (wie sie den Hauptbestandteil der Saturnringe bilden) nur bei Planeten außerhalb der Eislinie langfristig in Ringen vorhanden sein können, können innerhalb der Eislinie Planetenringe aus Gesteinsteilen langfristig stabil sein.[3] Nachgewiesen werden könnten solche Ringsysteme beispielsweise bei mit der Transitmethode beobachteten Planeten, wenn sie optisch dicht genug sind, um zusätzlichen Lichtabfall beim Zentralstern zu verursachen. Derzeit (Stand Januar 2015) sind solche Beobachtungen nicht bekannt.
„Super-Saturn“ J1407b
Eine Folge von Verfinsterungen des Sterns 1SWASP J140747.93-394542.6, die sich 2007 über 56 Tage hinzog, wurde in einer Veröffentlichung im August 2011[4] als Vorübergang des Ringsystems eines (nicht direkt beobachteten) substellaren Objekts (Exoplanet oder Brauner Zwerg) „J1407b“ interpretiert. Im Januar 2015 wurde diese Interpretation in einer erneuten Analyse der Daten bestätigt und präzisiert.[5] Auf die Bekanntgabe dieser Arbeit durch die University of Rochester[6] folgten Pressemeldungen über die damit erfolgte Entdeckung eines Super-Saturn.[7]
Das Ringsystem hat einen Radius von ca. 90 Millionen km (also etwa dem 200-fachen der Saturnringe). Das mit etwa 16 Millionen Jahren geringe Alter des Sternsystems deutet darauf hin, dass es sich eher um eine Struktur analog zu einer protoplanetaren Scheibe (bzw. tatsächlich um eine solche, falls J1407b für einen Planeten zu massereich ist) handelt, als um ein langfristig stabiles Ringsystem in einem ausentwickelten Planetensystem.
Siehe auch
Literatur
- Matthew S. Tiscareno, et al.: Planetary Ring Systems - Properties, Structure, and Evolution. Cambridge University Press, Cambridge 2018, ISBN 978-1-107-11382-4.
Weblinks
- USGS: Ring and Ring Gap Nomenclature (englisch)
Quellen
- ↑ M.M. Hedman: Why are dense planetary rings only found between 8 and 20 AU? arxiv:1502.07696 [astro-ph].
- ↑ J.L. Ortiz, R. Duffard, N. Pinilla-Alonso, A. Alvarez-Candal, P. Santos-Sanz, N. Morales, E. Fernández-Valenzuela, J. Licandro, A. Campo Bagatin, A. Thirouin:: Possible ring material around centaur (2060) Chiron. In: Astronomy & Astrophysics. 23. Januar 2015, arxiv:1501.05911 [astro-ph].
- ↑ Hilke E. Schlichting, Philip Chang: Warm Saturns: On the Nature of Rings around Extrasolar Planets that Reside Inside the Ice Line. In: Astrophysical Journal. 19. April 2011, arxiv:1104.3863.
- ↑ Eric E. Mamajek, Alice C. Quillen, Mark J. Pecaut, Fred Moolekamp, Erin L. Scott, Matthew A. Kenworthy, Andrew Collier Cameron, Neil R. Parley: Planetary Construction Zones in Occultation: Discovery of an Extrasolar Ring System Transiting a Young Sun-like Star and Future Prospects for Detecting Eclipses by Circumsecondary and Circumplanetary Disks. 19. August 2011, arxiv:1108.4070. Revidierte Fassung: Astronomical Journal, vol. 143, issue 3, article id. 72, 15 pp. (2012)
- ↑ Matthew A. Kenworthy, Eric E. Mamajek: Modeling giant extrasolar ring systems in eclipse and the case of J1407b: sculpting by exomoons? 22. Januar 2015, arxiv:1501.05652 (englisch).
- ↑ Leonor Sierra: Gigantic ring system around J1407b much larger, heavier than Saturn’s. University of Rochester, 26. Januar 2015, abgerufen am 1. Februar 2015 (englisch).
- ↑ Tilmann Althaus: Ein Super-Saturn beim Stern J1407. Spektrum der Wissenschaft, 27. Januar 2015, abgerufen am 27. Januar 2015.
Auf dieser Seite verwendete Medien
Hey Neptune. Did you ring? 👋
Webb’s latest image is the clearest look at Neptune's rings in 30+ years, and our first time seeing them in infrared light. Take in Webb's ghostly, ethereal views of the planet and its dust bands, rings and moons. (Some of these rings have not been detected since Voyager 2 flew by in 1989!)
In visible light, Neptune appears blue due to small amounts of methane gas in its atmosphere. Here, Webb’s NIRCam instrument observed Neptune at near-infrared wavelengths, so Neptune doesn’t look so blue!
Read more about Webb’s views of Neptune: www.nasa.gov/feature/goddard/2022/new-webb-image-captures...
Image description: In this Webb image, Neptune resembles a pearl with rings that look like ethereal concentric ovals around it. There are 2 thinner, crisper rings and 2 broader, fainter rings. A few extremely bright patches on the lower half of Neptune represent methane ice clouds. Six tiny white dots, which are six of Neptune’s 14 moons, are scattered among the rings. The background of the image is black.
Credits: NASA, ESA, CSA, STScI(c) NASA, ESA, CSA, STScI, J. DePasquale (STScI), CC BY 4.0
This zoomed-in image of Uranus, captured by Webb’s Near-Infrared Camera (NIRCam) on 6 February 2023, reveals stunning views of the planet’s rings. The planet displays a blue hue in this representative-colour image, made by combining data from two filters (F140M, F300M) at 1.4 and 3.0 microns, shown here as blue and orange, respectively.On the right side of the planet is an area of brightening at the pole facing the Sun, known as a polar cap. This polar cap is unique to Uranus because it is the only planet in the Solar System that is tilted on its side, which causes its extreme seasons. A new aspect of the polar cap revealed by Webb is a subtle brightening near the Uranian north pole.At the edge of the polar cap lies a bright cloud and a few fainter extended features can be seen just beyond the cap’s edge; a second very bright cloud is seen at the planet’s left limb. Such clouds are typical for Uranus at infrared wavelengths, and are likely connected to storm activity.[Image description: The planet Uranus on a black background. The planet appears light blue with a large, white patch on the right side. On the edge of that patch at the upper left is a bright white spot. Another white spot is located on the left side of the planet at the 9 o’clock position. Around the planet is a system of nested rings. The rings of Uranus are vertical.]
Autor/Urheber: Kevin Gill from Los Angeles, CA, United States, Lizenz: CC BY 2.0
Processed using orange and violet (as grayscale) images taken by Voyager 2 on July 11 1979 and grayscale images taken by Galileo on November 9 1997.
NASA/JPL-Caltech/Kevin M. GillOn July 19, 2013, in an event celebrated the world over, NASA's Cassini spacecraft slipped into Saturn's shadow and turned to image the planet, seven of its moons, its inner rings -- and, in the background, our home planet, Earth.
With the sun's powerful and potentially damaging rays eclipsed by Saturn itself, Cassini's onboard cameras were able to take advantage of this unique viewing geometry. They acquired a panoramic mosaic of the Saturn system that allows scientists to see details in the rings and throughout the system as they are backlit by the sun. This mosaic is special as it marks the third time our home planet was imaged from the outer solar system; the second time it was imaged by Cassini from Saturn's orbit; and the first time ever that inhabitants of Earth were made aware in advance that their photo would be taken from such a great distance.
With both Cassini's wide-angle and narrow-angle cameras aimed at Saturn, Cassini was able to capture 323 images in just over four hours. This final mosaic uses 141 of those wide-angle images. Images taken using the red, green and blue spectral filters of the wide-angle camera were combined and mosaicked together to create this natural-color view. A brightened version with contrast and color enhanced and an annotated version are also available.
This image spans about 404,880 miles (651,591 kilometers) across.
The outermost ring shown here is Saturn's E ring, the core of which is situated about 149,000 miles (240,000 kilometers) from Saturn. The geysers erupting from the south polar terrain of the moon Enceladus supply the fine icy particles that comprise the E ring; diffraction by sunlight gives the ring its blue color. Enceladus (313 miles, or 504 kilometers, across) and the extended plume formed by its jets are visible, embedded in the E ring on the left side of the mosaic.
At the 12 o'clock position and a bit inward from the E ring lies the barely discernible ring created by the tiny, Cassini-discovered moon, Pallene (3 miles, or 4 kilometers, across). (For more on structures like Pallene's ring, see PIA08328). The next narrow and easily seen ring inward is the G ring. Interior to the G ring, near the 11 o'clock position, one can barely see the more diffuse ring created by the co-orbital moons, Janus (111 miles, or 179 kilometers, across) and Epimetheus (70 miles, or 113 kilometers, across). Farther inward, we see the very bright F ring closely encircling the main rings of Saturn.
Following the outermost E ring counter-clockwise from Enceladus, the moon Tethys (662 miles, or 1,066 kilometers, across) appears as a large yellow orb just outside of the E ring. Tethys is positioned on the illuminated side of Saturn; its icy surface is shining brightly from yellow sunlight reflected by Saturn. Continuing to about the 2 o'clock position is a dark pixel just outside of the G ring; this dark pixel is Saturn's Death Star moon, Mimas (246 miles, or 396 kilometers, across). Mimas appears, upon close inspection, as a very thin crescent because Cassini is looking mostly at its non-illuminated face.
The moons Prometheus, Pandora, Janus and Epimetheus are also visible in the mosaic near Saturn's bright narrow F ring. Prometheus (53 miles, or 86 kilometers, across) is visible as a faint black dot just inside the F ring and at the 9 o'clock position. On the opposite side of the rings, just outside the F ring, Pandora (50 miles, or 81 kilometers, across) can be seen as a bright white dot. Pandora and Prometheus are shepherd moons and gravitational interactions between the ring and the moons keep the F ring narrowly confined. At the 11 o'clock position in between the F ring and the G ring, Janus (111 miles, or 179 kilometers, across) appears as a faint black dot. Janus and Prometheus are dark for the same reason Mimas is mostly dark: we are looking at their non-illuminated sides in this mosaic. Midway between the F ring and the G ring, at about the 8 o'clock position, is a single bright pixel, Epimetheus. Looking more closely at Enceladus, Mimas and Tethys, especially in the brightened version of the mosaic, one can see these moons casting shadows through the E ring like a telephone pole might cast a shadow through a fog.
In the non-brightened version of the mosaic, one can see bright clumps of ring material orbiting within the Encke gap near the outer edge of the main rings and immediately to the lower left of the globe of Saturn. Also, in the dark B ring within the main rings, at the 9 o'clock position, one can see the faint outlines of two spoke features, first sighted by NASA's Voyager spacecraft in the early 1980s and extensively studied by Cassini.
Finally, in the lower right of the mosaic, in between the bright blue E ring and the faint but defined G ring, is the pale blue dot of our planet, Earth. Look closely and you can see the moon protruding from the Earth's lower right. (For a higher resolution view of the Earth and moon taken during this campaign, see PIA14949.) Earth's twin, Venus, appears as a bright white dot in the upper left quadrant of the mosaic, also between the G and E rings. Mars also appears as a faint red dot embedded in the outer edge of the E ring, above and to the left of Venus.
For ease of visibility, Earth, Venus, Mars, Enceladus, Epimetheus and Pandora were all brightened by a factor of eight and a half relative to Saturn. Tethys was brightened by a factor of four. In total, 809 background stars are visible and were brightened by a factor ranging from six, for the brightest stars, to 16, for the faintest. The faint outer rings (from the G ring to the E ring) were also brightened relative to the already bright main rings by factors ranging from two to eight, with the lower-phase-angle (and therefore fainter) regions of these rings brightened the most. The brightened version of the mosaic was further brightened and contrast-enhanced all over to accommodate print applications and a wide range of computer-screen viewing conditions.
Some ring features -- such as full rings traced out by tiny moons -- do not appear in this version of the mosaic because they require extreme computer enhancement, which would adversely affect the rest of the mosaic. This version was processed for balance and beauty.
This view looks toward the unlit side of the rings from about 17 degrees below the ring plane. Cassini was approximately 746,000 miles (1.2 million kilometers) from Saturn when the images in this mosaic were taken. Image scale on Saturn is about 45 miles (72 kilometers) per pixel.
This mosaic was made from pictures taken over a span of more than four hours while the planets, moons and stars were all moving relative to Cassini. Thus, due to spacecraft motion, these objects in the locations shown here were not in these specific places over the entire duration of the imaging campaign. Note also that Venus appears far from Earth, as does Mars, because they were on the opposite side of the sun from Earth.
The Cassini Solstice Mission is a joint United States and European endeavor. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.
For more information about the Cassini Solstice Mission visit http://ciclops.org, http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.
The original NASA image has been modified by cropping at the sides and conversion from tif to jpg format. Some of the features in the image have been annotated in Wikimedia Commons.