Is Oumuamua Really a Comet?

The first-known visitor from outside the Solar System, an object dubbed ‘Oumuamua, is an icy comet rather than a rocky asteroid. New measurements help to confirm early guesses as to the composition of the interstellar interloper, and could also aid researchers in their hunt for similar objects in our Solar System.

Careful observations of ‘Oumuamua’s orbit showed that as the object flew through space, something continually nudged it a tiny bit farther from the Sun than expected. That something was probably ice that warmed up and sprayed gas into space. This process is characteristic of a comet, rather than an asteroid, even though ‘Oumuamua never displayed the glorious tail of gas and dust that accompanies most comets.

“It’s an unusual comet, and that’s pretty exciting,” says Karen Meech, an astronomer at the University of Hawaii in Honolulu. She and her colleagues, led by astronomer Marco Micheli of the European Space Agency in Frascati, Italy, report the discovery on 27 June in Nature.

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2015 BZ509: A Retrograde Asteroid From Another Solar System

A new study has discovered the first known permanent immigrant to our Solar System. The asteroid, currently nestling in Jupiter's orbit, is the first known asteroid to have been captured from another star system. The work is published in Monthly Notices of the Royal Astronomical Society: Letters.

The object known as 'Oumuamua was the last interstellar interloper to hit the headlines in 2017. However it was just a tourist passing through, whereas this former exo-asteroid - given the catchy name (514107) 2015 BZ509 - is a long-term resident.

All of the planets in our Solar System, and the vast majority of other objects as well, travel around the Sun in the same direction. However 2015 BZ509 is different - it moves in the opposite direction in what is known as a 'retrograde' orbit.

"How the asteroid came to move in this way while sharing Jupiter's orbit has until now been a mystery," explains Dr Fathi Namouni, lead author of the study. "If 2015 BZ509 were a native of our system, it should have had the same original direction as all of the other planets and asteroids, inherited from the cloud of gas and dust that formed them."

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pop sci link.

A/2017 U1 Oumuamua: Just a bit More Info

Implications of the interstellar object 1I/'Oumuamua for planetary dynamics and planetesimal formation.

Interstellar object 'Oumuamua as an extinct fragment of an ejected cometary planetesimal.

Oumuamua is likely from a binary star system.

What can Oumuamua teach us?

The Greenbank Radio Telescope listened to Oumuamua for the OH 18 cm emission line.

An Australian radio telescope listened for SETI signals from Oumuamua.

Oumuamua is in an excited spin state.

The effects of tidal torques on Oumuamua.

2004 EW95: A C Type Asteroid Found in Kuiper Belt

2004 EW95: A phyllosilicate bearing carbonaceous asteroid in the Kuiper Belt

Authors:

Seccull et al

Abstract:

Models of the Solar System's dynamical evolution predict the dispersal of primitive planetesimals from their formative regions amongst the gas-giant planets due to the early phases of planetary migration. Consequently, carbonaceous objects were scattered both into the outer asteroid belt and out to the Kuiper Belt. These models predict that the Kuiper Belt should contain a small fraction of objects with carbonaceous surfaces, though to date, all reported visible reflectance spectra of small Kuiper Belt Objects (KBOs) are linear and featureless. We report the unusual reflectance spectrum of a small KBO, (120216) 2004 EW95, which exhibits a large drop in its near-UV reflectance and a broad shallow optical absorption feature centered at ~700 nm. These features, confirmed through multiple epochs of spectral photometry and spectroscopy, have respectively been associated with ferric oxides and phyllosilicates. The spectrum bears striking resemblance to those of some C-type asteroids, suggesting that those objects may share a common origin with 2004 EW95. 2004 EW95 orbits the Sun in a stable mean motion resonance with Neptune, at relatively high eccentricity and inclination, suggesting it may have been emplaced there by some past dynamical instability. These results appear consistent with the aforementioned model predictions and are the first to show a reliably confirmed detection of silicate material on a small KBO.

A/2017 U1 Oumuamua: Even More Information on our First Interstellar Visitor

Breakthrough Listen observed Oumuamua with a radio telescope and released its data to the public.  Oumuamua was radio silent.

Oumuamua is a natural, not made object.

Oumuamua could be a binary contact asteroid.

Oumuamua might be left over from a star that died.

How common and where do interstellar 'roids like Oumuamua come from?

Can we backtrack Oumuamua to its origin? 

Oumuamua appears to have a carbon rich crust.

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.

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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?

What Kind of Asteroids Impacted the Earth During the PaleoProterozoic?

Chromium isotope evidence in ejecta deposits for the nature of Paleoproterozoic impactors

Authors:

Mougel et al

Abstract:

Non-mass dependent chromium isotopic signatures have been successfully used to determine the presence and identification of extra-terrestrial materials in terrestrial impact rocks. Paleoproterozoic spherule layers from Greenland (Graenseso) and Russia (Zaonega), as well as some distal ejecta deposits (Lake Superior region) from the Sudbury impact (1,849 +/- 0.3 Ma) event, have been analyzed for their Cr isotope compositions. Our results suggest that 1) these distal ejecta deposits are all of impact origin, 2) the Graenseso and Zaonega spherule layers contain a distinct carbonaceous chondrite component, and are possibly related to the same impact event, which could be Vredefort (2,023 +/- 4 Ma) or another not yet identified large impact event from that of similar age, and 3) the Sudbury ejecta record a complex meteoritic signature, which is different from the Graenseso and Zaonega spherule layers, and could indicate the impact of a heterogeneous chondritic body.

Were Major Impacts on Moon, Mercury & Mars Caused by Protoplanets?

Around 3.8 billion years ago, an asteroid more than 150 miles across, roughly equal to the length of New Jersey, slammed into the Moon and created the Imbrium Basin -- the right eye of the fabled Man in the Moon. This new size estimate, published in the journal Nature, suggests an Imbrium impactor that was two times larger in diameter and 10 times more massive than previous estimates.

"We show that Imbrium was likely formed by an absolutely enormous object, large enough to be classified as a protoplanet," said Pete Schultz, professor of earth, environmental and planetary sciences at Brown University. "This is the first estimate for the Imbrium impactor's size that is based largely on the geological features we see on the Moon."

Previous estimates, Schultz said, were based solely on computer models and yielded a size estimate of only about 50 miles in diameter.

These new findings help to explain some of the puzzling geological features that surround the Imbrium Basin. The work also suggests -- based on the sizes of other impact basins in the Moon, Mars and Mercury -- that the early solar system was likely well stocked with protoplanet-sized asteroids.

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Hektor is a Strange D-Type Member of Jovian Trojan Asteroids

Hektor - an exceptional D-type family among Jovian Trojans

Authors:

Rozehnal et al

Abstract:

In this work, we analyze Jovian Trojans in the space of suitable resonant elements and we identify clusters of possible collisional origin by two independent methods: the hierarchical clustering and a so-called "randombox". Compared to our previous work (Bro\v{z} and Rozehnal 2011), we study a twice larger sample. Apart from Eurybates, Ennomos and 1996RJ families, we have found three more clusters --- namely families around asteroids (20961)~Arkesilaos, (624)~Hektor in the L4 libration zone and (247341)~2001UV209 in L5. The families fulfill our stringent criteria, i.e. a high statistical significance, an albedo homogeneity and a steeper size-frequency distribution than that of background. In order to understand their nature, we simulate their long term collisional evolution with the Boulder code (Morbidelli et al. 2009) and dynamical evolution using a modified SWIFT integrator (Levison and Duncan, 1994). Within the framework of our evolutionary model, we were able to constrain the the age of the Hektor family to be either 1 to 4 Gyr or, less likely, 0.1 to 2.5 Gyr, depending on initial impact geometry. Since (624) Hektor itself seems to be a bilobed--shape body with a satellite (Marchis et al. 2014), i.e. an exceptional object, we address its association with the D--type family and we demonstrate that the moon and family could be created during a single impact event. We simulated the cratering event using a Smoothed Particle Hydrodynamics (SPH, Benz and Asphaug, 1994). This is also the first case of a family associated with a D--type parent body.

NASA Declines to SEnd Dawn Spacecraft to Another Asteroid

A senior review of NASA’s planetary science missions has concluded the Dawn spacecraft should remain in orbit around the dwarf planet Ceres rather than venture to another asteroid as project officials proposed.

NASA announced July 1 the outcome of a review of extended planetary science missions, including the approval of plans to send New Horizons past a distant Kuiper Belt object and the extension of seven other missions at the moon and Mars.

Dawn, which completed its primary mission June 30, had proposed an extended mission where the spacecraft would leave its current orbit around Ceres and travel to another asteroid. Project officials declined to name that asteroid, saying that they would identify it if NASA approved the extended mission.

However, in a mission update posted to the Dawn web site late June 30, only to be removed within minutes, the mission did identify that destination: the asteroid 145 Adeona, a main belt asteroid about 150 kilometers across that Dawn would fly by in May 2019. The NASA statement July 1 about the mission extension confirmed the planned target was Adeona.

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Ceres, we Knew you not

The asteroid belt hides lots of mysteries of the solar system’s past, but perhaps no place holds more mysteries than Ceres. It’s an oddball place — a dwarf planet in the midst of our solar system’s belt of smaller debris. And it’s an ancient world possibly left over from the era when the planets first came together.

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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."

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What's the Risk of an Asteroid Impact for Each Nation Through 2100?

On the influence of impact effect modelling for global asteroid impact risk distribution

Authors:

Rumpf et al

Abstract:

The collision of an asteroid with Earth can potentially have significant consequences for the human population. The European and United States space agencies (ESA and NASA) maintain asteroid hazard lists that contain all known asteroids with a non-zero chance of colliding with the Earth in the future. Some software tools exist that are, either, capable of calculating the impact points of those asteroids, or that can estimate the impact effects of a given impact incident. However, no single tool is available that combines both aspects and enables a comprehensive risk analysis. The question is, thus, whether tools that can calculate impact location may be used to obtain a qualitative understanding of the asteroid impact risk distribution. To answer this question, two impact risk distributions that control for impact effect modelling were generated and compared. The Asteroid Risk Mitigation Optimisation and Research (ARMOR) tool, in conjunction with the freely available software OrbFit, was used to project the impact probabilities of listed asteroids with a minimum diameter of 30 m onto the surface of the Earth representing a random sample (15% of all objects) of the hazard list. The resulting 261 impact corridors were visualised on a global map. Furthermore, the impact corridors were combined with Earth population data to estimate the “simplified” risk (without impact effects) and “advanced” risk (with impact effects) associated with the direct asteroid impacts that each nation faces from present to 2100 based on this sample. The relationship between risk and population size was examined for the 40 most populous countries and it was apparent that population size is a good proxy for relative risk. The advanced and simplified risk distributions were compared and the alteration of the results based on the introduction of physical impact effects was discussed. Population remained a valid proxy for relative impact risk, but the inclusion of impact effects resulted in significantly different risks, especially when considered at the national level. Therefore, consideration of physical impact effects is essential in estimating the risk to specific nations of the asteroid threat.

Looking at Ceres

At last week's Lunar and Planetary Science Conference, I enjoyed a large number of talks about Ceres, which Dawn is now orbiting at an altitude of merely 385 kilometers. Several sessions worth of talks considered a wealth of new data that has been acquired since the last time I attended scientific sessions on Dawn, at lower altitudes and hence more detail. All that freshly acquired data made for talks bursting with pretty pictures and data but relatively thin on interpretation and with little coordination (yet) across data sets, which makes them a bit hard to summarize briefly. Deputy principal investigator Carol Raymond summed the situation up well at the press briefing: "Clearly, we have a lot of work to do to put together a self-consistent story among all these different data sets."

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Impacts by Comets and Asteroids Since the Noachian Probably NOT the Cause of Martian Atmospheric Loss

Scenarios of atmospheric mass evolution on Mars influenced by asteroid and comet impacts since the late Noachian

Authors:

Pham et al

Abstract:

Early in its history, Mars probably had a denser atmosphere and higher surface temperatures to sustain the presence of stable liquid water or saline solution at the surface. Impacts by asteroids and comets could affect the atmospheric evolution of a planet, by removing part of its atmosphere and by delivering into it material and volatiles. In this study we investigate the atmospheric loss and delivery of volatiles between the end of the Noachian and present, with the help of a semi-analytic model. Our results suggest that impacts alone can hardly remove a significant amount of atmospheric mass over this period. Contribution of additional factors such as outgassing and non-thermal escape processes can not explain neither the presence of surface pressure larger than few hundreds of mbars 3.9 Gyr ago, unless parameter values outside of their expected range are considered. Based on extreme case scenarios, maximum surface pressures at the end of the Noachian, could be as much as 0.25 bar or 1.9 bar, with and without CO2 storage into carbonate reservoirs, respectively.

To Fly Over Ceres

The Double Impact From Dapingian/Floian Ordovician Sweden

Around 470 million years ago, what is now central Sweden was covered in a shallow, ancient sea inhabited by tiny, plankton-like organisms. The placid scene would soon be scarred by one of the largest cataclysms in the last billion years, scientists reported Monday.

That's because far away, trouble was brewing. In the main asteroid belt, between Mars and Jupiter, two space rocks were about to collide. When they slammed together, the collision shattered a 200-kilometer-wide asteroid, sending fragments ricocheting through space—some of which headed right for planet Earth.

As they traveled through the inner solar system, a portion of these pulverized bits and pieces re-congealed, forming what's known as a rubble pile asteroid—a type of space object that is exactly what it sounds like. But this rocky swarm wasn't like most of the others: It had a small, orbiting companion.

And when that twosome finally plowed into the ancient Swedish sea after a 12-million-year journey, it left a distinctive double crater. Or rather, a double crater that would have been distinctive had the smaller of the two punches not remained hidden until just a few years ago.

"We are quite convinced that the two craters were formed at the same time," says Erik Sturkell of the University of Gothenburg, who presented the story Monday at the American Geophysical Union's annual meeting.

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The Fate of Asteroids in a Migrating Jupiter Scenario

THE EVOLUTION OF ASTEROIDS IN THE JUMPING-JUPITER MIGRATION MODEL

Authors:

Roig et al

Abstract:

In this work, we investigate the evolution of a primordial belt of asteroids, represented by a large number of massless test particles, under the gravitational effect of migrating Jovian planets in the framework of the jumping-Jupiter model. We perform several simulations considering test particles distributed in the Main Belt, as well as in the Hilda and Trojan groups. The simulations start with Jupiter and Saturn locked in the mutual 3:2 mean motion resonance plus three Neptune-mass planets in a compact orbital configuration. Mutual planetary interactions during migration led one of the Neptunes to be ejected in less than 10 Myr of evolution, causing Jupiter to jump by about 0.3 AU in semimajor axis. This introduces a large-scale instability in the studied populations of small bodies. After the migration phase, the simulations are extended over 4 Gyr, and we compare the final orbital structure of the simulated test particles to the current Main Belt of asteroids with absolute magnitude H less than 9.7. The results indicate that, in order to reproduce the present Main Belt, the primordial belt should have had a distribution peaked at ~10° in inclination and at ~0.1 in eccentricity. We discuss the implications of this for the Grand Tack model. The results also indicate that neither primordial Hildas, nor Trojans, survive the instability, confirming the idea that such populations must have been implanted from other sources. In particular, we address the possibility of implantation of Hildas and Trojans from the Main Belt population, but find that this contribution should be minor.

Where are Near Earth Asteroids Likely to Impact on Earth?

The global impact distribution of Near-Earth objects

Authors:

Rumpf et al

Abstract:

Asteroids that could collide with the Earth are listed on the publicly available Near-Earth object (NEO) hazard web sites maintained by the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). The impact probability distribution of 69 potentially threatening NEOs from these lists that produce 261 dynamically distinct impact instances, or Virtual Impactors (VIs), were calculated using the Asteroid Risk Mitigation and Optimization Research (ARMOR) tool in conjunction with OrbFit. ARMOR projected the impact probability of each VI onto the surface of the Earth as a spatial probability distribution. The projection considers orbit solution accuracy and the global impact probability. The method of ARMOR is introduced and the tool is validated against two asteroid-Earth collision cases with objects 2008 TC3 and 2014 AA. In the analysis, the natural distribution of impact corridors is contrasted against the impact probability distribution to evaluate the distributions’ conformity with the uniform impact distribution assumption. The distribution of impact corridors is based on the NEO population and orbital mechanics. The analysis shows that the distribution of impact corridors matches the common assumption of uniform impact distribution and the result extends the evidence base for the uniform assumption from qualitative analysis of historic impact events into the future in a quantitative way. This finding is confirmed in a parallel analysis of impact points belonging to a synthetic population of 10,006 VIs. Taking into account the impact probabilities introduced significant variation into the results and the impact probability distribution, consequently, deviates markedly from uniformity. The concept of impact probabilities is a product of the asteroid observation and orbit determination technique and, thus, represents a man-made component that is largely disconnected from natural processes. It is important to consider impact probabilities because such information represents the best estimate of where an impact might occur.

Good Grief: Comets and Asteroids Brought 15N Enriched Ammonia to Earth?!

THE PATH OF REDUCED NITROGEN TOWARD EARLY EARTH: THE COSMIC TRAIL AND ITS SOLAR SHORTCUTS

Authors:

Pizzarello et al

Abstract:

Large isotopic anomalies are found in meteoritic insoluble organic materials (IOMs) and, for nitrogen, show 15N-excesses up to ${\delta }^{15}$N ~ 5000‰. These 15N-enrichments are commonly ascribed to presolar origins, but the attribution seems contradicted by available data on N-isotopes' cosmic distribution. We report here that 15N hotspots in several IOMs are reduced by hydrothermal treatment and their loss correlates with 15N values of ammonia released upon treatment. Because released ammonia's 15N-enrichments also relate with meteorites' mineralogy, i.e., asteroidal processes, and no current models offer plausible explanations for the finding, we account for our data with a novel scenario whereby 15N-enriched ammonia produced in the solar nebula is incorporated by carbonaceous materials and delivered to early Earth by comets and meteorites. The proposal also implies that abundant reduced nitrogen, a required element in origins of life theories, could reach our nascent planet and other planetary systems affecting their habitability.