Shaping of the inner Oort cloud by Planet Nine

Shaping of the inner Oort cloud by Planet Nine

Authors:

Michaely et al

Abstract:

We present a numerical calculation of the dynamical interaction between the proposed Planet Nine and an initially thin circular debris disk around the Sun for 4Gyr, accounting the secular perturbation of the four giant planets. We show that Planet Nine governs the dynamics in between 1000-5000AU and forms spherical structure in the inner part (~1000AU) surrounded by an inclined disk aligned to its orbital plane. This structure is the outcome of mean motion resonances and secular interaction with Planet Nine. We compare the morphology of this structure with the outcome from a fly-by encounter of a star with the debris disk and show distinct differences between the two scenarios. We predict that this structure serves as a source of comets and calculate the resulting comet production rate to be detectable.

The Upper Limits For Oort Cloud Comets Based on X Ray Astronomy Observations

Upper limits to the number of Oort Cloud Objects based on serendipitous occultation events search in X-rays

Authors:

Chang et al

Abstract:

Using all the RXTE archival data of Sco X-1 and GX 5-1, which amount to about 1.6 mega seconds in total, we searched for possible occultation events caused by Oort Cloud Objects. The detection efficiency of our searching approach was studied with simulation. Our search is sensitive to object size of about 300 m in the inner Oort Cloud, taking 4000 AU as a representative distance, and of 900 m in the outer Oort Cloud, taking 36000 AU as the representative distance. No occultation events were found in the 1.6 Ms data. We derived upper limits to the number of Oort Cloud Objects, which are about three orders of magnitude higher than the highest theoretical estimates in the literature for the inner Oort Cloud, and about six orders higher for the outer Oort Cloud. Although these upper limits are not constraining enough, they are the first obtained observationally, without making any model assumptions about comet injection. They also provide guidance to such serendipitous occultation event search in the future.

V774104: a Dwarf Planet Half the Diameter of Pluto at 103 AU, end of the Kuiper Belt or Beginning of the Oort Cloud?

Newly discovered small Solar System body V774104 may seem just another tiny, cold and remote world beyond Neptune but this is an important discovery as its mere existence suggests that the wastes of the outer Solar System are considerably more populous than we thought a couple of decades ago.

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Finding the Comets Knocked Into the Inner Solar System by Past StellarEncounters

Finding the imprints of stellar encounters in long-period comets

Authors:

Feng et al

Abstract:

The Solar system's Oort cloud can be perturbed by the Galactic tide and by individual passing stars. These perturbations can inject Oort cloud objects into the inner parts of the Solar system, where they may be observed as the long-period comets (periods longer than 200 yr). Using dynamical simulations of the Oort cloud under the perturbing effects of the tide and 61 known stellar encounters, we investigate the link between long-period comets and encounters. We find that past encounters were responsible for injecting at least 5 per cent of the currently known long-period comets. This is a lower limit due to the incompleteness of known encounters. Although the Galactic tide seems to play the dominant role in producing the observed long-period comets, the non-uniform longitude distribution of the cometary perihelia suggests the existence of strong – but as yet unidentified – stellar encounters or other impulses. The strongest individual future and past encounters are probably HIP 89825 (Gliese 710) and HIP 14473, which contribute at most 8 and 6 per cent to the total flux of long-period comets, respectively. Our results show that the strength of an encounter can be approximated well by a simple proxy, which will be convenient for quickly identifying significant encounters in large data sets. Our analysis also indicates a smaller population of the Oort cloud than is usually assumed, which would bring the mass of the solar nebula into line with planet formation theories.

Could Schloz's Star(s) Passed Within 20,000 AU of the Sun 70,000 Years Ago?

The Closest Known Flyby of a Star to the Solar System

Authors:

Mamajek et al

Abstract:

Passing stars can perturb the Oort Cloud, triggering comet showers and potentially extinction events on Earth. We combine velocity measurements for the recently discovered, nearby, low-mass binary system WISE J072003.20-084651.2 ("Scholz's star") to calculate its past trajectory. Integrating the Galactic orbits of this ∼0.15 M⊙ binary system and the Sun, we find that the binary passed within only 52+23−14 kAU (0.25+0.11−0.07 parsec) of the Sun 70+15−10 kya (1σ uncertainties), i.e. within the outer Oort Cloud. This is the closest known encounter of a star to our solar system with a well-constrained distance and velocity. Previous work suggests that flybys within 0.25 pc occur infrequently (∼0.1 Myr−1). We show that given the low mass and high velocity of the binary system, the encounter was dynamically weak. Using the best available astrometry, our simulations suggest that the probability that the star penetrated the outer Oort Cloud is ∼98%, but the probability of penetrating the dynamically active inner Oort Cloud (<20 among="" be="" binary="" blockquote="" caused="" cloud="" comets="" discovery="" dynamically="" flux="" flyby="" highlights="" impact="" important="" is="" kau="" likely="" long-period="" lurking="" may="" nearby="" negligible="" of="" on="" oort="" perturbers="" recent="" stars.="" system="" that="" the="" this="" while="">

8 Billion Asteroids may Lurk in the Oort Cloud

Eight billion asteroids in the Oort cloud

Authors:

Shannon et al

Abstract:

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.

Did Large Retrograde Centaurs Originate in the Oort Cloud?

Large retrograde Centaurs: visitors from the Oort cloud?

Authors:

de la Fuente Marcos et al

Abstract:

Among all the asteroid dynamical groups, Centaurs have the highest fraction of objects moving in retrograde orbits. The distribution in absolute magnitude, H, of known retrograde Centaurs with semi-major axes in the range 6-34 AU exhibits a remarkable trend: 10% have H less than 10 mag, the rest have H greater than 12 mag. The largest objects, namely (342842) 2008 YB3, 2011 MM4 and 2013 LU28, move in almost polar, very eccentric paths; their nodal points are currently located near perihelion and aphelion. In the group of retrograde Centaurs, they are obvious outliers both in terms of dynamics and size. Here, we show that these objects are also trapped in retrograde resonances that make them unstable. Asteroid 2013 LU28, the largest, is a candidate transient co-orbital to Uranus and it may be a recent visitor from the trans-Neptunian region. Asteroids 342842 and 2011 MM4 are temporarily submitted to various high-order retrograde resonances with the Jovian planets but 342842 may be ejected towards the trans-Neptunian region within the next few hundred kyr. Asteroid 2011 MM4 is far more stable. Our analysis shows that the large retrograde Centaurs form an heterogeneous group that may include objects from various sources. Asteroid 2011 MM4 could be a visitor from the Oort cloud but an origin in a relatively stable closer reservoir cannot be ruled out. Minor bodies like 2011 MM4 may represent the remnants of the primordial planetesimals and signal the size threshold for catastrophic collisions in the early Solar System.

Do Halley-type Comets Come From the Oort Cloud?

An Oort cloud origin of the Halley-type comets

Authors:

Wang et al

Abstract:

The origin of the Halley-type comets (HTCs) is one of the last mysteries of the dynamical evolution of the Solar System. Prior investigation into their origin has focused on two source regions: the Oort cloud and the Scattered Disc. From the former it has been difficult to reproduce the non-isotropic, prograde skew in the inclination distribution of the observed HTCs without invoking a multi-component Oort cloud model and specific fading of the comets. The Scattered Disc origin fares better but suffers from needing an order of magnitude more mass than is currently advocated by theory and observations. Here we revisit the Oort cloud origin and include cometary fading. Our observational sample stems from the JPL catalogue. We only keep comets discovered and observed after 1950 but place no a priori restriction on the maximum perihelion distance of observational completeness. We then numerically evolve half a million comets from the Oort cloud through the realm of the giant planets and keep track of their number of perihelion passages with perihelion distance q less than 2.5AU, below which the activity is supposed to increase considerably. We can simultaneously fit the HTC inclination and semi-major axis distribution very well with a power law fading function of the form m^-k, where m is the number of perihelion passages with q less than 2.5 AU and k is the fading index. We match both the inclination and semi-major axis distributions when k~1 and the maximum imposed perihelion distance of the observed sample is q~1.8AU. The value of k is higher than the one obtained for the Long-Period Comets (LPCs), with k~0.7. This increase in k is most likely the result of cometary surface processes. We argue the HTC sample is now most likely complete for q less than 1.8AU. We calculate that the steady-state number of active HTCs with diameter D greater than 2.3km and q less than 1.8AU is of the order of 100.

Using Cherenkov Telescopes for Outer Solar System Science

On the Use of Cherenkov Telescopes for Outer Solar System Body Occultations

Authors:

Lackey et al

Abstract:

Imaging Atmosphere Cherenkov Telescopes (IACT) are arrays of very large optical telescopes that are well-suited for rapid photometry of bright sources. I investigate their potential in observing stellar occultations by small objects in the outer Solar System, Transjovian Objects (TJOs). These occultations cast diffraction patterns on the Earth. Current IACT arrays are capable of detecting objects smaller than 100 meters in radius in the Kuiper Belt and 1 km radius out to 5000 AU. The future Cherenkov Telescope Array (CTA) will have even greater capabilities. Because the arrays include several telescopes, they can potentially measure the speeds of TJOs without degeneracies, and the sizes of the TJOs and background stars. I estimate the achievable precision using a Fisher matrix analysis. With CTA, the precisions of these parameter estimations will be as good as a few percent. I consider how often IACTs can observe occultations by members of different TJO populations, including Centaurs, Kuiper Belt Objects (KBOs), Oort cloud objects, and satellites and Trojans of Uranus and Neptune. The great sensitivity of IACT arrays means that they likely detect KBO occultations once every O(10) hours when looking near the ecliptic. IACTs can also set useful limits on many other TJO populations.

Do Most Comets Originate in the Oort Cloud?

A model for the common origin of Jupiter family and Halley type comets

Authors:

Emel'yanenko et al

Abstract:

numerical simulation of the Oort cloud is used to explain the observed orbital distributions and numbers of Jupiter-family and Halley-type short-period comets. Comets are given initial orbits with perihelion distances between 5 and 36 AU, and evolve under planetary, stellar and Galactic perturbations for 4.5 Gyr. This process leads to the formation of an Oort cloud (which we define as the region of semimajor axes a greater than 1000 AU), and to a flux of cometary bodies from the Oort cloud returning to the planetary region at the present epoch. The results are consistent with the dynamical characteristics of short-period comets and other observed cometary populations: the near-parabolic flux, Centaurs, and high-eccentricity trans-Neptunian objects. To achieve this consistency with observations, the model requires that the number of comets versus initial perihelion distance is concentrated towards the outer planetary region. Moreover, the mean physical lifetime of observable comets in the inner planetary region (q less than 2.5 AU) at the present epoch should be an increasing function of the comets' initial perihelion distances. Virtually all observed Halley-type comets and nearly half of observed Jupiter-family comets come from the Oort cloud, and initially (4.5 Gyr ago) from orbits concentrated near the outer planetary region. Comets that have been in the Oort cloud also return to the Centaur (5 less than q less than 28 AU, a less than 1000 AU) and near-Neptune high-eccentricity regions. Such objects with perihelia near Neptune are hard to discover, but Centaurs with characteristics predicted by the model (e.g., large semimajor axes, above 60 au, or high inclinations, above 40 degrees) are increasingly being found by observers. The model predicts that the mean physical lifetime of all comets in the region q less than