(An undated handout of an artists impression released by Nasa to illustrate the extent of the largest ring around Saturn, discovered by Nasa's Spitzer Space Telescope. Stunned astronomers have discovered that a small, distant moon of Saturn has the largest ring in the Solar System)
The Spitzer Space Telescope has discovered the biggest but never-before-seen ring around the planet Saturn, Nasa's Jet Propulsion Laboratory announced late Tuesday(06.10.2009)
The thin array of ice and dust particles lies at the far reaches of the Saturnian system and its orbit is tilted 27 degrees from the planet's main ring plane, the laboratory said.
JPL spokeswoman Whitney Clavin said the ring is very diffuse and doesn't reflect much visible light but the infrared Spitzer telescope was able to detect it.
Although the ring dust is very cold minus 316 degrees Fahrenheit it shines with thermal radiation.
No one had looked at its location with an infrared instrument until now, Clavin said.
thebulk of the ring material starts about 3.7 million miles from the planet and extends outward about antother 7.4 million miles.
the newly found ring is so huge it would take 1 billion Earths to fill it, JPL said.
Before the discovery Saturn was known to have seven main rings named A through E and several faint unnamed rings.
"This is one supersized ring," said one of the authors, Anne Verbiscer, an astronomer at the University of Virginia in Charlottesville. Her co-authors are Douglas hamilton of the Unviersity of Maryland, College park, and Michael Skrutskie, also of the University of Virginia.
Saturn's moon Phoebe orbits within the ring and is believed to be the source of the material.
The Singularities of Gravitational Collapse andCosmology
Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences, Volume 314, Issue 1519, pp. 529-548
A new theorem on space-time singularities is presented which largely incorporates and generalizes the previously known results. The theorem implies that space-time singularities are to be expected if either the universe is spatially closed or there is an 'object' undergoing relativisticgravitational collapse (existence of a trapped surface) or there is a point p whose past null cone encounters sufficient matter that the divergence of the null rays through p changes sign somewhere to the past of p (i.e. there is a minimum apparent solid angle, as viewed from p for small objects of given size). The theorem applies if the following four physical assumptions are made: (i) Einstein's equations hold (with zero or negative cosmological constant), (ii) the energy density is nowhere less than minus each principal pressure nor less than minus the sum of the three principal pressures (the 'energy condition'), (iii) there are no closed timelike curves, (iv) every timelike or null geodesic enters a region where the curvature is not specially alined with the geodesic. (This last condition would hold in any sufficiently general physically realistic model.) In common with earlier results, timelike or null geodesic incompleteness is used here as the indication of the presence of space-time singularities. No assumption concerning existence of a global Cauchy hypersurface is required for the present theorem.
