* Astronomy

Blobrana · L

RE: Oort Cloud

Blobrana · L

Title: Eight billion asteroids in the Oort cloud
Author: Andrew Shannon, Alan P. Jackson, Dimitri Veras, Mark Wyatt

The Oort cloud is usually thought of as a collection of icy comets inhabiting the outer reaches of the Solar system, but this picture is incomplete. We use simulations of the formation of the Oort cloud to show that ~4% of the small bodies in the Oort cloud should have formed within 2.5 au of the Sun, and hence be ice-free rock-iron bodies. If we assume these Oort cloud asteroids have the same size distribution as their cometary counterparts, the Large Synoptic Survey Telescope should find roughly a dozen Oort cloud asteroids during ten years of operations. Measurement of the asteroid fraction within the Oort cloud can serve as an excellent test of the Solar system's formation and dynamical history. Oort cloud asteroids could be of particular concern as impact hazards as their high mass density, high impact velocity, and low visibility make them both hard to detect and hard to divert or destroy. However, they should be a rare class of object, and we estimate globally catastrophic collisions should only occur about once per billion years.

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Blobrana · L

Title: Oort Cloud and Scattered Disc formation during a late dynamical instability in the Solar System
Authors: R. Brasser, A. Morbidelli

One of the outstanding problems of the dynamical evolution of the outer solar system concerns the observed population ratio between the Oort Cloud (OC) and the Scattered Disc (SD): observations suggest that this ratio lies between 100 and 1000 but simulations that produce these two reservoirs simultaneously consistently yield a value of the order of 10. Here we stress that the populations in the OC and SD are inferred from the observed fluxes of new Long Period Comets (LPCs) and Jupiter-family comets (JFCs), brighter than some reference total magnitude. However, the population ratio estimated in the simulations of formation of the SD and OC refers to objects bigger than a given size. There are multiple indications that LPCs are intrinsically brighter than JFCs, i.e. an LPC is smaller than a JFC with the same total absolute magnitude. When taking this into account we revise the SD/JFC population ratio from our simulations relative to Duncan and Levison (1997), and then deduce from the observations that the size-limited population ratio between the OC and the SD is 44 (-34)(+54). From simulations we obtain 12 ± 1 but the agreement cannot be rejected by the null hypothesis.

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Blobrana · L

Title: The Solar System's Post-Main Sequence Escape Boundary
Authors: Dimitri Veras, Mark C. Wyatt

The Sun will eventually lose about half of its current mass nonlinearly over several phases of post-main sequence evolution. This mass loss will cause any surviving orbiting body to increase its semimajor axis and perhaps vary its eccentricity. Here, we use a range of Solar models spanning plausible evolutionary sequences and assume isotropic mass loss to assess the possibility of escape from the Solar System. We find that the critical semimajor axis in the Solar System within which an orbiting body is guaranteed to remain bound to the dying Sun due to perturbations from stellar mass loss alone is approximately 1,000 AU - 10,000 AU. The fate of objects near or beyond this critical semimajor axis, such as the Oort Cloud, outer scattered disc and specific bodies such as Sedna, will significantly depend on their locations along their orbits when the Sun turns off of the main sequence. These results are applicable to any exoplanetary system containing a single star with a mass, metallicity and age which are approximately equal to the Sun's, and suggest that few extrasolar Oort Clouds could survive post-main sequence evolution intact.

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Blobrana · L

Our sun will throw many of its comets into interstellar space when it dies, according to new simulations.

In about 5 billion years, the sun will run out of hydrogen to burn in its core and will expand to become a red giant star. The red giant will blow off its atmosphere, leaving an ember-like core called a white dwarf.
It is generally accepted that planets inward of Earth and possibly Earth itself will be engulfed and incinerated during the red giant phase. But astronomers have paid little attention to more distant objects.
Now a study suggests that the sun's death throes will reverberate all the way to the vast swarm of comets called the Oort cloud, out beyond Pluto.
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Blobrana · L

Title: The Colours of Extreme Outer Solar System Objects
Authors: Scott S. Sheppard (Carnegie Institution of Washington)

Thirty-three objects with possible origins beyond the Kuiper Belt edge, very high inclinations, very large semi-major axes or large perihelion distances were observed to determine their surface colours. All three objects that have been dynamically linked to the inner Oort cloud (Sedna, 2006 SQ372, and 2000 OO67) were found to have ultra-red surfaces (S~25). Ultra-red material is generally associated with rich organics and the low inclination "cold" classical Kuiper Belt objects. The observations detailed here show very red material may be a more general feature for objects kept far from the Sun. The recently discovered retrograde outer Solar System objects (2008 KV42 and 2008 YB3) and the high inclination object (127546) 2002 XU93 show only moderately red surfaces (S~9), very similar to known comets. The extended or detached disk objects, which have large perihelion distances and large eccentricities, are found to have mostly moderately red colours (10 < S < 18). The colours of the detached disk objects, including the dynamically unusual 2004 XR190 and 2000 CR105, are similar to the scattered disk and Plutino populations. Thus the detached and scattered disk likely have a similar mix of objects from the same source regions. Outer classical belt objects, including 1995 TL8, were found to have very red surfaces (18 < S < 30). The "cold" classical belt, outer classical belt and inner Oort cloud appear to be dominated by ultra-red objects (S > 25) and thus don't likely have a similar mix of objects as the scattered disk, detached disk and Trojan populations. A possible trend was found for the detached disk and outer classical belt in that objects with smaller eccentricities have redder surfaces irrespective of inclinations or perihelion distances. There is also a clear trend that objects more distant appear redder.

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Blobrana · L

Solar system may be more compact than thought

The solar system may be significantly more compact than previously thought, according to a new computer simulation of the cloud of comets that enshrouds the solar system. The work suggests the cloud may not contain as much material as once suspected, which could resolve a long-standing problem in models of how the planets formed.
Long-period comets, which take longer than 200 years to orbit the sun, come from all directions in the sky, an observation that has long led scientists to believe that they were nudged out of a diffuse halo of icy objects surrounding the solar system - the Oort Cloud.
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Blobrana · L

Subtle variations in the cosmic microwave radiation left over from the Big Bang may finally reveal the distant Oort Cloud, thought to send comets hurtling into the Solar System.
Since the 1930s, astronomers have theorised that a spherical shell of icy objects surrounds the Solar System, 50,000 to 100,000 times further out from the Sun than the Earth.
The debris, called the Oort Cloud, is the source of so-called long period comets, which take millions of years to orbit the Sun.
Despite the theory, the cloud has never been spotted from Earth, because although it must be vast, the individual objects are too small and too far away to see.

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