A/2017 U1: Our First Known Interstellar Visitor

A small, recently discovered asteroid -- or perhaps a comet -- appears to have originated from outside the solar system, coming from somewhere else in our galaxy. If so, it would be the first "interstellar object" to be observed and confirmed by astronomers.

This unusual object - for now designated A/2017 U1 - is less than a quarter-mile (400 meters) in diameter and is moving remarkably fast. Astronomers are urgently working to point telescopes around the world and in space at this notable object. Once these data are obtained and analyzed, astronomers may know more about the origin and possibly composition of the object.

A/2017 U1 was discovered Oct. 19 by the University of Hawaii's Pan-STARRS 1 telescope on Haleakala, Hawaii, during the course of its nightly search for near-Earth objects for NASA. Rob Weryk, a postdoctoral researcher at the University of Hawaii Institute for Astronomy (IfA), was first to identify the moving object and submit it to the Minor Planet Center. Weryk subsequently searched the Pan-STARRS image archive and found it also was in images taken the previous night, but was not initially identified by the moving object processing.

link.

Some are starting to call A/2017 U1 'Oumuamua.'

Is likely to find its next star in around a quadrillion, yes, quadrillion! years.  (get over the math envy, one friend said)

What is the rotation rate of A/2017 U1 and does it have a comet-like tail?

A/2017 U1 appears to be very red and lack absorption lines.

A/2017 U1 seems to have formed in a warm environment, not like the outer solar system.

A/2017 U1 is likely to be interstellar in origin.

Could A/2017 U1 have formed in a local stellar association?

What does A/2017 U1's detection mean about the universe?

What does A/2017 U1 imply about planetary formation?

Did Earth's Carbon Come From a Mercurcy Sized Protoplanetary Impact?

Research by Rice University Earth scientists suggests that virtually all of Earth's life-giving carbon could have come from a collision about 4.4 billion years ago between Earth and an embryonic planet similar to Mercury.

In a new study this week in Nature Geoscience, Rice petrologist Rajdeep Dasgupta and colleagues offer a new answer to a long-debated geological question: How did carbon-based life develop on Earth, given that most of the planet's carbon should have either boiled away in the planet's earliest days or become locked in Earth's core?

"The challenge is to explain the origin of the volatile elements like carbon that remain outside the core in the mantle portion of our planet," said Dasgupta, who co-authored the study with lead author and Rice postdoctoral researcher Yuan Li, Rice research scientist Kyusei Tsuno and Woods Hole Oceanographic Institute colleagues Brian Monteleone and Nobumichi Shimizu.

link.

Are There Trans Neptunian Objects in the Asteroid Belt?

CAPTURE OF TRANS-NEPTUNIAN PLANETESIMALS IN THE MAIN ASTEROID BELT

Authors:

Vokrouhlický et al

Abstract:

The orbital evolution of the giant planets after nebular gas was eliminated from the Solar System but before the planets reached their final configuration was driven by interactions with a vast sea of leftover planetesimals. Several variants of planetary migration with this kind of system architecture have been proposed. Here, we focus on a highly successful case, which assumes that there were once five planets in the outer Solar System in a stable configuration: Jupiter, Saturn, Uranus, Neptune, and a Neptune-like body. Beyond these planets existed a primordial disk containing thousands of Pluto-sized bodies, ~50 million D > 100 km bodies, and a multitude of smaller bodies. This system eventually went through a dynamical instability that scattered the planetesimals and allowed the planets to encounter one another. The extra Neptune-like body was ejected via a Jupiter encounter, but not before it helped to populate stable niches with disk planetesimals across the Solar System. Here, we investigate how interactions between the fifth giant planet, Jupiter, and disk planetesimals helped to capture disk planetesimals into both the asteroid belt and first-order mean-motion resonances with Jupiter. Using numerical simulations, we find that our model produces the right proportion of P- and D-type asteroids in the inner, central, and outer main belt, while also populating the Hilda and Thule regions in Jupiter's 3/2 and 4/3 resonances. Moreover, the largest observed P/D types in each sub-population are an excellent fit to our captured population results (within uncertainties). The model produces a factor of ~10 overabundance of diameter D > 10 km P/D types in the main belt, but this mismatch can likely be explained by various removal mechanisms (e.g., collision evolution over 4 Gyr, dynamical losses via Yarkovsky thermal forces over 4 Gyr, thermal destruction of the planetesimals en route to the inner solar system). Overall, our instability model provides a more satisfying match to constraints than that of Levison et al., and it provides us with strong supporting evidence that the five giant planet instability model is reasonable. Our results lead us to predict that D-type asteroids found in the near-Earth object population on low delta-V orbits with Earth are the surviving relics from the same source population that now make up the Kuiper Belt, the irregular satellites, and the Jupiter Trojans. The singular Tagish Lake meteorite, a primitive sample unlike other carbonaceous chondrite meteorites, is likely a fragment from a D-type asteroid implanted into the inner main belt. This would effectively make it the first known hand sample with the same composition as Kuiper Belt objects.

The Inclination of the Gas Giants in the Solar System Constrains Planet Nine

The inclination of the planetary system relative to the solar equator may be explained by the presence of Planet 9

Authors:

Gomes et al

Abstract:

We evaluate the effects of a distant planet, commonly known as planet 9, on the dynamics of the giant planets of the Solar System. We find that, given the large distance of planet 9, the dynamics of the inner giant planets can be decomposed into a classic Lagrange-Laplace dynamics relative to their own invariant plane (the plane orthogonal to their total angular momentum vector) and a slow precession of said plane relative to the total angular momentum vector of the Solar System, including planet 9. Under some specific configurations for planet 9, this precession can explain the current tilt of approximately 6 degrees between the invariant plane of the giant planets and the solar equator. An analytical model is developed to map the evolution of the inclination of the inner giant planets' invariant plane as a function of the planet 9's mass, inclination, eccentricity and semimajor axis, and some numerical simulations of the equations of motion of the giant planets and planet 9 are performed to validate our analytical approach. The longitude of the ascending node of planet 9 is found to be linked to the longitude of the ascending node of the giant planets' invariant plane, which also constrain the longitude of the node of planet 9 on the ecliptic. Some of the planet 9 configurations that allow explaining the current solar tilt are compatible with those proposed to explain the orbital confinement of the most distant Kuiper belt objects. Thus, this work on the one hand gives an elegant explanation for the current tilt between the invariant plane of the inner giant planets and the solar equator and, on the other hand, adds new constraints to the orbital elements of planet 9.

When did Mars Form a Crust and Mantle?

Lush Venus & Crispy Earth: Solar System Sister Planets Could Have 'Swapped' Climates

If conditions had been just a little different an eon ago, there might be plentiful life on Venus and none on Earth.

The idea isn't so far-fetched, according to a hypothesis by Rice University scientists and their colleagues who published their thoughts on life-sustaining planets, the planets' histories and the possibility of finding more in Astrobiology this month.

The researchers maintain that minor evolutionary changes could have altered the fates of both Earth and Venus in ways that scientists may soon be able to model through observation of other solar systems, particularly ones in the process of forming, according to Rice Earth scientist Adrian Lenardic.

link.

Asteroid 2016 HO3: A Near Moon

A small asteroid has been discovered in an orbit around the sun that keeps it as a constant companion of Earth, and it will remain so for centuries to come.

As it orbits the sun, this new asteroid, designated 2016 HO3, appears to circle around Earth as well. It is too distant to be considered a true satellite of our planet, but it is the best and most stable example to date of a near-Earth companion, or "quasi-satellite."

"Since 2016 HO3 loops around our planet, but never ventures very far away as we both go around the sun, we refer to it as a quasi-satellite of Earth," said Paul Chodas, manager of NASA's Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California. "One other asteroid -- 2003 YN107 -- followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity. This new asteroid is much more locked onto us. Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth's companion for centuries to come."

link.

One of the Biggest Mysteries About Mars: Why is it so Small?

The presence of water isn’t the only Mars mystery scientists are keen to probe. Another centers around a seemingly trivial characteristic of the Red Planet: its size. Classic models of solar system formation predict that the girth of rocky worlds should grow with their distance from the sun. Venus and Earth, for example, should exceed Mercury, which they do. Mars should at least match Earth, which it doesn’t. The diameter of the Red Planet is little more than half that of Earth (1, 2).

“We still don’t understand why Mars is so small,” says astronomer Anders Johansen, who builds computational models of planet formation at Lund University in Sweden. “It’s a really compelling question that drives a lot of new theories.”

link.

Are Saturns Moons, Rings Less Than 100 Million Years Old?

New research suggests that some of Saturn's icy moons, as well as itsfamous rings, might be modern adornments. Their dramatic birth may have taken place a mere hundred million years ago, more recent than the reign of many dinosaurs.

"Moons are always changing their orbits. That's inevitable," says Matija Cuk, principal investigator at the SETI Institute. "But that fact allows us to use computer simulations to tease out the history of Saturn's inner moons. Doing so, we find that they were most likely born during the most recent two percent of the planet's history.

"While Saturn's rings have been known since the 1600s, there's still debate about their age. The straightforward assumption is that they are primordial – as old as the planet itself, which is more than four billion years. However, in 2012, French astronomers found that tidal effects – the gravitational interaction of the inner moons with fluids deep in Saturn's interior – are causing them to spiral to larger orbital radii comparatively quickly. The implication, given their present positions, is that these moons, and presumably the rings, are recent phenomena.

Cuk, together with Luke Dones and David Nesvorny of the Southwest Research Institute, used computer modeling to infer the past dynamic behavior of Saturn's icy inner moons. While our own moon has its orbit around Earth to itself, Saturn's many satellites have to share space with each other. All of their orbits slowly grow due to tidal effects, but at different rates. This results in pairs of moons occasionally entering so-called orbital resonances. These occur when one moon's orbital period is a simple fraction (for example, one-half or two-thirds) of another moon's period. In these special configurations, even small moons with weak gravity can strongly affect each other's orbits, making them more elongated and tilting them out of their original orbital plane.

link.

paper link.

Is the Grand Tack Model Compatible with Our Asteroid Belt?

Is the Grand Tack model compatible with the orbital distribution of main belt asteroids?

Authors:

Deienno et al

Abstract:

The Asteroid Belt is characterized by the radial mixing of bodies with different physical properties, a very low mass compared to Minimum Mass Solar Nebula expectations and has an excited orbital distribution, with eccentricities and inclinations covering the entire range of values allowed by the constraints of dynamical stability. Models of the evolution of the Asteroid Belt show that the origin of its structure is strongly linked to the process of terrestrial planet formation. The Grand Tack model presents a possible solution to the conundrum of reconciling the small mass of Mars with the properties of the Asteroid Belt, including the mass depletion, radial mixing and orbital excitation. However, while the inclination distribution produced in the Grand Tack model is in good agreement with the one observed, the eccentricity distribution is skewed towards values larger than those found today. Here, we evaluate the evolution of the orbital properties of the Asteroid Belt from the end of the Grand Tack model (at the end of the gas nebula phase when planets emerge from the dispersing gas disk), throughout the subsequent evolution of the Solar System including an instability of the Giant Planets approximately 400 Myr later. Before the instability, the terrestrial planets were modeled on dynamically cold orbits with Jupiter and Saturn locked in a 3:2 mean motion resonance. The model continues for an additional 4.1 Gyr after the giant planet instability. Our results show that the eccentricity distribution obtained in the Grand Tack model evolves towards one very similar to that currently observed, and the semimajor axis distribution does the same. The inclination distribution remains nearly unchanged with a slight preference for depletion at low inclination; this leads to the conclusion that the inclination distribution at the end of the Grand Tack is a bit over-excited. Also, we constrain the primordial eccentricities of Jupiter and Saturn, which have a major influence on the dynamical evolution of the Asteroid Belt and its final orbital structure.

Limits to Planet Nine

Evolution and Magnitudes of Candidate Planet Nine

Authors:

Linder et al

Abstract:

Context.

Given the recently renewed interest in a possible additional major body in the outer Solar System, the thermodynamic evolution of such an object was studied, assuming that it is a smaller version of Uranus and Neptune. Aims. We have modeled the temporal evolution of the radius, temperature, intrinsic luminosity, and the black body spectrum of distant ice giants. The aim is to provide also estimates of the magnitudes in different bands to assess the object's detectability.

Methods.

Simulations of the cooling and contraction were conducted for ice giants with masses of 5, 10, 20, and 50 Mearth containing 10, 14, 21, and 37 % H/He in mass that are located at 280, 700, and 1120 AU from the Sun. The core composition was varied from purely rocky to purely icy as well as 50% rock and 50% ice. The atmospheric opacity was set to 1, 50, and 100 times solar metallicity.

Results.

We find for the nominal 10 Mearth planet at 700 AU at the current age of the Solar System an effective temperature of 47 K, much more than the equilibrium temperature of about 10 K, a radius of 3.7 Rearth, and an intrinsic luminosity of 0.006 Ljupiter. It has estimated apparent magnitudes of Johnson V, R, I, L, N, Q of 21.7, 21.2, 20.8, 20.1, 19.7, and 11.4, and WISE W1-W4 magnitudes of 20.1, 20.0, 19.5, and 10.4. The Q and W4 band and other observation longward of ~13 microns pick up the intrinsic flux.

Conclusions.

If candidate Planet 9 has a significant H/He layer and an efficient energy transport in the interior, then its luminosity is dominated by the intrinsic contribution, making it a self-luminous planet. At a likely position on its orbit near the aphelion, we estimate for a mass of 5, 10, 20, and 50 Mearth a V magnitude from the reflected light of 24.2, 23.7, 23.2, and 22.5 and a Q magnitude from the intrinsic radiation of 15.6, 12.4, 9.8, 6.2. The latter would probably have been detected by past surveys.

Is There a Hidden Neptune Class Planet Out Past the Kuiper Belt?

EVIDENCE FOR A DISTANT GIANT PLANET IN THE SOLAR SYSTEM

Authors:

Konstantin Batygin and Michael E. Brown

Abstract:

Recent analyses have shown that distant orbits within the scattered disk population of the Kuiper Belt exhibit an unexpected clustering in their respective arguments of perihelion. While several hypotheses have been put forward to explain this alignment, to date, a theoretical model that can successfully account for the observations remains elusive. In this work we show that the orbits of distant Kuiper Belt objects (KBOs) cluster not only in argument of perihelion, but also in physical space. We demonstrate that the perihelion positions and orbital planes of the objects are tightly confined and that such a clustering has only a probability of 0.007% to be due to chance, thus requiring a dynamical origin. We find that the observed orbital alignment can be maintained by a distant eccentric planet with mass gsim10 m⊕ whose orbit lies in approximately the same plane as those of the distant KBOs, but whose perihelion is 180° away from the perihelia of the minor bodies. In addition to accounting for the observed orbital alignment, the existence of such a planet naturally explains the presence of high-perihelion Sedna-like objects, as well as the known collection of high semimajor axis objects with inclinations between 60° and 150° whose origin was previously unclear. Continued analysis of both distant and highly inclined outer solar system objects provides the opportunity for testing our hypothesis as well as further constraining the orbital elements and mass of the distant planet.

pop sci link.

2nd link.

3rd link.

The Sun Dimmed .1% Between 1940s to 1960s

DIMMING OF THE MID-20TH CENTURY SUN

Authors:

Foukal et al

Abstract:

Area changes of photospheric faculae associated with magnetic active regions are responsible for the bright contribution to variation in total solar irradiance (TSI). Yet, the 102-year white light (WL) facular record measured by the Royal Greenwich Observatory between 1874 and 1976 has been largely overlooked in past TSI reconstructions. We show that it may offer a better measure of the brightening than presently used chromospheric proxies or the sunspot number. These are, to varying degrees, based on magnetic structures that are dark at the photosphere even near the limb. The increased contribution of the dark component to these proxies at high activity leads to an overestimate of solar brightening around peaks of the large spot cycles 18 and 19. The WL facular areas measure only the bright contribution. Our reconstruction based on these facular areas indicates that TSI decreased by about 0.1% during these two cycles to a 20th century minimum, rather than brightening to some of the highest TSI levels in four centuries, as reported in previous reconstructions. This TSI decrease may have contributed more to climate cooling between the 1940s and 1960s than present modeling indicates. Our finding adds to previous evidence that such suppression of solar brightening by an increased area of dark flux tubes might explain why the Sun is anomalously quiet photometrically compared to other late-type stars. Our findings do not change the evidence against solar driving of climate warming since the 1970s.

Solar System Asteroid Belt Best Explained as Remnants of Planetary Formation Collisions, not Pristine, Remnant Planetesimals

Erosive Hit-and-Run Impact Events: Debris Unbound

Authors:

Sarid et al

Abstract:

Erosive collisions among planetary embryos in the inner solar system can lead to multiple remnant bodies, varied in mass, composition and residual velocity. Some of the smaller, unbound debris may become available to seed the main asteroid belt. The makeup of these collisionally produced bodies is different from the canonical chondritic composition, in terms of rock/iron ratio and may contain further shock-processed material. Having some of the material in the asteroid belt owe its origin from collisions of larger planetary bodies may help in explaining some of the diversity and oddities in composition of different asteroid groups.

The Solar System Probably did NOT Have Another Gas Giant

TILTING SATURN WITHOUT TILTING JUPITER: CONSTRAINTS ON GIANT PLANET MIGRATION

Authors:

Brasser et al

Abstract:

The migration and encounter histories of the giant planets in our solar system can be constrained by the obliquities of Jupiter and Saturn. We have performed secular simulations with imposed migration and N-body simulations with planetesimals to study the expected obliquity distribution of migrating planets with initial conditions resembling those of the smooth migration model, the resonant Nice model and two models with five giant planets initially in resonance (one compact and one loose configuration). For smooth migration, the secular spin–orbit resonance mechanism can tilt Saturn's spin axis to the current obliquity if the product of the migration timescale and the orbital inclinations is sufficiently large (exceeding 30 Myr deg). For the resonant Nice model with imposed migration, it is difficult to reproduce today's obliquity values, because the compactness of the initial system raises the frequency that tilts Saturn above the spin precession frequency of Jupiter, causing a Jupiter spin–orbit resonance crossing. Migration timescales sufficiently long to tilt Saturn generally suffice to tilt Jupiter more than is observed. The full N-body simulations tell a somewhat different story, with Jupiter generally being tilted as often as Saturn, but on average having a higher obliquity. The main obstacle is the final orbital spacing of the giant planets, coupled with the tail of Neptune's migration. The resonant Nice case is barely able to simultaneously reproduce the orbital and spin properties of the giant planets, with a probability $\sim 0.15\%.$ The loose five planet model is unable to match all our constraints (probability less than 0.08%). The compact five planet model has the highest chance of matching the orbital and obliquity constraints simultaneously (probability ~0.3%).

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 Jupiter or Saturn Have Ejected a Fifth Giant Planet?

Could Jupiter or Saturn Have Ejected a Fifth Giant Planet?

Authors:

Cloutier et al

Abstract:

Models of the dynamical evolution of the early solar system following the dispersal of the gaseous protoplanetary disk have been widely successful in reconstructing the current orbital configuration of the giant planets. Statistically, some of the most successful dynamical evolution simulations have initially included a hypothetical fifth giant planet, of ice giant mass, which gets ejected by a gas giant during the early solar system's proposed instability phase. We investigate the likelihood of an ice giant ejection event by either Jupiter or Saturn through constraints imposed by the current orbits of their wide-separation regular satellites Callisto and Iapetus respectively. We show that planetary encounters that are sufficient to eject an ice giant, often provide excessive perturbations to the orbits of Callisto and Iapetus making it difficult to reconcile a planet ejection event with the current orbit of either satellite. Quantitatively, we compute the likelihood of reconciling a regular Jovian satellite orbit with the current orbit of Callisto following an ice giant ejection by Jupiter of ~ 42% and conclude that such a large likelihood supports the hypothesis of a fifth giant planet's existence. A similar calculation for Iapetus reveals that it is much more difficult for Saturn to have ejected an ice giant and reconcile a Kronian satellite orbit with that of Iapetus (likelihood ~ 1%), although uncertainties regarding the formation of Iapetus, on its unusual orbit, complicates the interpretation of this result.

The Ultimate Delta V Map of the Solar System

link.

Pluto, the Kupier Belt & the Early Compact Solar System

Salt key to Understanding Neptune and Uranus' Interiors?

The interiors of several of our Solar System's planets and moons are icy, and ice has been found on distant extrasolar planets, as well. But these bodies aren't filled with the regular kind of water ice that you avoid on the sidewalk in winter. The ice that's found inside these objects must exist under extreme pressures and high-temperatures, and potentially contains salty impurities, too.

New research from a team including Carnegie's Alexander Goncharov focuses on the physics underlying the formation of the types of ice that are stable under the paradoxical-seeming conditions likely to be found in planetary interiors. Their work, published by Proceedings of the National Academy of Sciences, could challenge current ideas about the physical properties found inside icy planetary bodies.

When water (H2O) freezes into ice, the molecules are bound together in a crystalline lattice held together by hydrogen bonds. Due to the versatility of these hydrogen bonds, ice reveals a striking diversity of at least 16 different crystalline structures. But most of these structures could not exist in the interiors of frozen planets and moons.

Under high pressures, the variety of possible ice structures shrinks, just as the space between its hydrogen-bonded oxygen atoms does as the ice grows denser. When pressure is increased to more than about 20,000 times Earth's atmosphere (2 gigapascals), this number of possible ice structures is reduced to just two -- ice VII and ice VIII. Ordinary ice has a hexagonal structure. Ice VII has a cubic structure. Ice VIII has a tetragonal structure.

As the pressure increases further, both forms of ice transform to another phase called ice X. This happens at pressures around 600,000 times Earth's atmosphere (60 gigapascals), which would be comparable to the pressure conditions found in the interior of an icy-cored planet, like Neptune or Uranus. Ice X has a whole new kind of symmetrical lattice structure. It's called non-molecular ice, because the water molecule is broken apart and the hydrogen atoms are shared between neighboring oxygens.

Under similar pressures but higher temperatures, it has been suggested that ice X could possibly transform into a phase of ice that can conduct electricity as hydrogen atoms move freely around the oxygen lattice. But how such ice would be formed at the temperatures found in planetary interiors has remained mysterious.

Because the interiors of icy planetary bodies might also be salty, due to interactions between the ice and the surrounding rocks or a liquid ocean, lead author Livia Eleonora Bove of the CNRS & Université Pierre et Marie Curie in France and the Ecole Polytechnique Federal de Lausanne in Switzerland and the rest of the team studied the effects of salts on the formation of the ice X from ice VII.

They found that the inclusion of salts in ice VII -- both ordinary sodium chloride (NaCl) that you have on your table and the similarly structured lithium chloride (LiCl) -- pushes the formation of ice X to occur at higher and higher pressures. Such salts could easily have been incorporated as impurities when matter accreted during the planetary formation process and be present in rocks or liquid water with which the core ice interacts.

'These findings could challenge our current thinking on the physics occurring in the interiors of icy planetary bodies,' Goncharov said. 'All of our current assumptions are based on the behavior of ice without any impurities.'

link.