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The article discusses the potential consequences and likelihood of the appearance of centaurs, giant comets from the trans-Neptunian region that reach the inner solar system via short-term, in the Earth. Topics include assessments of the risk posed by near-Earth objects (NEO) and the enhancement of their population, the disintegration of centaurs, and stratigraphic studies of craters in Earth.

Asteroids and comets have collided with the Earth in the past and will do so again in the future. Throughout Earth׳s history these collisions have played a significant role in shaping Earth׳s biological and geological histories. The planetary defense community has been examining a variety of options for mitigating the impact threat of asteroids and comets that approach or cross Earth׳s orbit, known as near-Earth objects (NEOs). This paper discusses the preliminary study results of selecting small (100-m class) NEO targets and mission analysis and design trade-offs for validating the effectiveness of a Hypervelocity Asteroid Intercept Vehicle (HAIV) concept, currently being investigated for a NIAC (NASA Advanced Innovative Concepts) Phase 2 study. In particular this paper will focus on the mission analysis and design for single spacecraft direct impact trajectories, as well as several mission types that enable a secondary rendezvous spacecraft to observe the HAIV impact and evaluate it׳s effectiveness. [ABSTRACT FROM AUTHOR]

A recrystallized band of pale feldspathic impact melt in a gneissic impact breccia from the approximately 10 km Paasselkä impact structure in southeast Finland was dated via 40Ar/39Ar step-heating. The newly obtained plateau age of 228.7 ± 1.8 (2.2) Ma (2σ) ( MSWD = 0.32; p = 0.93) is equal to the previously published pseudoplateau age of 228.7 ± 3.0 (3.4) (2σ) for the impact event. According to the current international chronostratigraphic chart and using the most recent published suggestions for the K decay constants, a Carnian (Late Triassic) age for the Paasselkä impact structure of 231.0 ± 1.8 (2.2) Ma (2σ) is calculated and considered the most precise and accurate age for this impact structure. The new plateau age for Paasselkä confirms the previous dating result but is, based on its internal statistics, much more compelling. [ABSTRACT FROM AUTHOR]

The strong 14C increase in the year AD 774/5 detected in one German and two Japanese trees was recently suggested to have been caused by an impact of a comet onto Earth and a deposition of large amounts of 14C into the atmosphere (Liu et al. 2014). The authors supported their claim using a report of a historic Chinese observation of a comet ostensibly colliding with Earth's atmosphere in AD 773 January. We show here that the Chinese text presented by those authors is not an original historic text, but that it is comprised of several different sources. Moreover, the translation presented in Liu et al. is misleading and inaccurate. We give the exact Chinese wordings and our English translations. According to the original sources, the Chinese observed a comet in mid January 773, but they report neither a collision nor a large coma, just a long tail. Also, there is no report in any of the source texts about 'dust rain in the daytime' as claimed by Liu et al. (2014), but simply a normal dust storm. Ho (1962) reports sightings of this comet in China on AD 773 Jan 15 and/or 17 and in Japan on AD 773 Jan 20 (Ho 1962). At the relevant historic time, the Chinese held that comets were produced within the Earth's atmosphere, so that it would have been impossible for them to report a 'collision' of a comet with Earth's atmosphere. The translation and conclusions made by Liu et al. (2014) are not supported by the historical record. Therefore, postulating a sudden increase in 14C in corals off the Chinese coast precisely in mid January 773 (Liu et al. 2014) is not justified given just the 230Th dating for AD 783 ± 14. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A kinetic impactor spacecraft is a viable method to deflect an asteroid which poses a threat to the Earth. The technology to perform such a deflection has been demonstrated by the Deep Impact (DI) mission, which successfully collided with comet Tempel 1 in July 2005 using an onboard autonomous navigation system, called AutoNav, for the terminal phase of the mission. In this paper, we evaluate the ability of AutoNav to impact a wider range of scenarios that a deflection mission could encounter, varying parameters such as the approach velocity, phase angle, size of the asteroid, and the attitude determination accuracy. In particular, we evaluated the capability of AutoNav to impact 100–300 m size asteroids at speeds between 7.5 and 20 km/s at various phase angles. Using realistic Monte Carlo simulations, we tabulated the probability of success of the deflection as a function of these parameters and find the highest sensitivity to be due to the spacecraft attitude determination error. In addition, we also specifically analyzed the impact probability for a proposed mission (called ISIS) which would send an impactor to the asteroid 1999RQ36. We conclude with some recommendations for future work. [ABSTRACT FROM AUTHOR]

A large and sudden increase in radiocarbon (14C) aroundAD773 are documented in coral skeletons from the South China Sea. The 14C increased by ~15%during winter, and remain elevated for more than 4 months, then increased and dropped down within two months, forming a spike of 45%high in late spring, followed by two smaller spikes. The 14C anomalies coincide with an historic comet collision with the Earth's atmosphere on 17 January AD 773. Comas are known to have percent-levels of nitrogen by weight, and are exposed to cosmic radiation in space. Hence they may be expected to contain highly elevated 14C/12C ratios, as compared to the Earth's atmosphere. The significant input of 14C by comets may have contributed to the fluctuation of 14C in the atmosphere throughout the Earth's history, which should be considered carefully to better constrain the cosmic ray fluctuation. [ABSTRACT FROM AUTHOR]

review of the current state of investigations into the complex global problem of asteroid-comet hazard (ACH) is presented. Main attention is drawn to a comprehensive analysis of prospects of developing the intra-Russia cooperation of studies on the ACH problem and initiating a working program of solving this problem on the national basis. Special space projects are briefly discussed, aimed to investigate and solve the ACH problem, in particular, the project of a mission of spacecraft with an onboard transponder to a hazardous asteroid (conventionally, asteroid Apophis is chosen as a target). [ABSTRACT FROM AUTHOR]

Based on elevated concentrations of a set of "impact markers" at the onset of the Younger Dryas stadial from sedimentary contexts across North America, Firestone, Kennett, West, and others have argued that 12.9 ka the Earth experienced an impact by an extraterrestrial body, an event that had devastating ecological consequences for humans, plants, and animals in the New World [Firestone RB, et al. (2007) Proc. Natl. Acad. Sd. USA 104:16016- 16021]. Herein, we report the results of an independent analysis of magnetic minerals and microspherules from seven sites of similar age, including two examined by Firestone et al. We were unable to reproduce any results of the Firestone et al. study and find no support for Younger Dryas extraterrestrial impact. [ABSTRACT FROM AUTHOR]

The article provides a discussion on the study of near-earth objects (NEOs). NEOs include comets and asteroids which have the possibility of crashing into earth. NEOs that pass 7.5 million kilometers within the Earth's orbit must be detected immediately. On December 2004, the asteroid Apophis was estimated to collide with Earth on April 2029. Additional studies moved the date to April 13, 2036. The incident prompted the development of measures to track NEOs including the completion of the Panoramic Survey Telescope and Rapid Response System. An overview of efforts to track NEOs is provided.

Based on the model concepts of destruction of the substance of a celestial body in the shock wave initiated by a strong explosion of weak penetration, the radius of the destroyed region, the ejected mass, and the recoil momentum have been evaluated. The values of the charges necessary for destroying completely bodies of different size and composition or withdrawing bodies from the Earth for a required distance have been determined. The efficiencies of the explosion and sublimation methods of changing orbits for the case where the hazardous bodies are comets have been compared. Problems on improving the efficiency of the explosion method of action on a hazardous body due to the high relative velocity of impact of this body with the charge-carrying rocket have been discussed. [ABSTRACT FROM AUTHOR]

On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics. [ABSTRACT FROM AUTHOR]

Using the cometary nucleus model developed by Espinasse et al., we calculate the thermodynamical evolution of Comet 9P/Tempel 1 over a period of 360 yr. Starting from an initially amorphous cometary nucleus which incorporates an icy mixture of H2O and CO, we show that, at the time of Deep Impact collision, the crater is expected to form at depths where ice is in its crystalline form. Hence the subsurface exposed to space should not be primordial. We also attempt an order-of-magnitude estimate of the heating and material ablation effects on the crater activity caused by the 370-kg projectile released by the Deep Impact spacecraft. We thus show that heating effects play no role in the evolution of crater activity. We calculate that the CO production rate from the impacted region should be about 300–400 times higher from the crater resulting from the impact with a 35-m ablation than over the unperturbed nucleus in the immediate post-impact period. We also show that the H2O production rate is decreased by several orders of magnitude at the crater base just after ablation. [ABSTRACT FROM AUTHOR]

Time variation in impact probability is studied by assuming that the periodic flux of the Oort Cloud comets within 15 au arises from the motion of the Sun with respect to the Galactic mid-plane. The periodic flux clearly shows up in the impact rate of the captured Oort Cloud cometary population, with a phase shift caused by the orbital evolution. Depending on the assumed flux of comets and the size distribution of comets, the impact rate of the Oort Cloud comets of 1 km in diameter or greater is from 5 to 700 impacts Myr[sup -1] on the Earth and from 0.5 to 70 impacts per 1000 yr on Jupiter. The relative fractions of impacts are 0.09, 0.11, 0.26 and 0.54 for long-period comets, Halley type comets, Jupiter family comets and near-Earth objects, respectively. For Jupiter, the corresponding fractions in the first three categories are 0.18, 0.31 and 0.51. If we consider physical fading of comet activity that is compatible with the observations, then the impact rates of active comets are two orders of magnitude smaller than the total impact rates by all kinds of comets and cometary asteroids of size 1 km or greater. [ABSTRACT FROM AUTHOR]

The article discusses organic matter existing inside glass created by comet and asteroid debris impact discovered in Argentina by a research team from Brown University, led by geologist Pete Schultz. Details related to the soil of eastern Argentina, the results of the chemical analysis performed on glass samples, and the natural preservation of the impact glass are provided.

The article discusses a study by Dartmouth College Earth science professors Jason Moore and Mukul Sharma that suggests a high-velocity comet, not an asteroid, caused the extinction of the dinosaurs. Information is provided on the history of the asteroid impact theory, which began from discoveries by physicist Luis Alvarez. Particular attention is given to Moore and Sharma's focus on iridium and osmium levels at the impact site, known as Chicxulub.

Reports on cratering which has taken place on the Earth. Various craters on the Earth's surface; Iron meteorite craters of Wabar, Saudi Arabia; The importance of major impacts on the evolution of life on Earth; Mechanisms of planetary impact; Obstacles to a greater understanding of the mechanisms.

Presents research which presented evidence for a multiple impact event that occurred on Earth and formed a linear crater chain. How crater chains are formed; Five terrestrial impact structures in linear crater chain; Where the structures are; Plotting structures on a tectonic reconstruction of the North American and Eurasian plates; Dating of impact; Impact by a fragmented comet or asteroid.