No abstract

No abstract

ABSTRACT. Three optical telescopes located at the San Pedro Mártir National Observatory were used for the first time to obtain multifilter defocused photometry of the transiting extrasolar planets WASP-39b and WASP-43b. We observed WASP-39b with the 2.12 m telescope in the U filter for the first time, and additional observations were carried out in the R and I filters using the 0.84 m telescope. WASP-43b was observed in V RI with the same instrument, and in the i filter with the robotic 1.50 m telescope. We reduced the data using different pipelines and performed aperture photometry with the help of custom routines in order to obtain the light curves. The fit of the light curves (1.5-2.5 mmag rms), and of the period analysis, allowed a revision of the orbital and physical parameters, revealing for WASP-39b a period (4:0552947 AE 9:65 × 10 À7 days) which is 3:084 AE 0:774 seconds larger than previously reported. Moreover, we find for WASP-43b a planet/star radius (0:1738 AE 0:0033) which is 0:01637 AE 0:00371 larger in the i filter with respect to previous works, and that should be confirmed with additional observations. Finally, we confirm no evidence of constant period variations in WASP-43b.

The orbital elements of comet Halley are known to a very high precision, suggesting that the calculation of its future dynamical evolution is straightforward. In this paper we seek to characterize the chaotic nature of the present day orbit of comet Halley and to quantify the timescale over which its motion can be predicted confidently. In addition, we attempt to determine the timescale over which its present day orbit will remain stable. Numerical simulations of the dynamics of test particles in orbits similar to that of comet Halley are carried out with the Mercury 6.2 code. On the basis of these we construct survival time maps to assess the absolute stability of Halley's orbit, frequency analysis maps, to study the variability of the orbit and we calculate the Lyapunov exponent for the orbit for variations in initial conditions at the level of the present day uncertainties in our knowledge of its orbital parameters. On the basis of our calculations of the Lyapunov exponent for comet Halley, the chaotic nature of its motion is demonstrated. The e-folding timescale for the divergence of initially very similar orbits is approximately 70 years. The sensitivity of the dynamics on initial conditions is also evident in the self-similarity character of the survival time and frequency analysis maps in the vicinity of Halley's orbit, which indicates that, on average, it is unstable on a timescale of hundreds of thousands of years. The chaotic nature of Halley's present day orbit implies that a precise determination of its motion, at the level of the present day observational uncertainty, is difficult to predict on a timescale of approximately 100 years. Furthermore, we also find that the ejection of Halley from the solar system or its collision with another body could occur on a timescale as short as 10,000 years.

a b s t r a c tIt has been suggested that the ejection of terrestrial crustal material to interplanetary space, accelerated in a large impact, may result in the interchange of biological material between Earth and other Solar System bodies.In this paper, we analyze the fate of debris ejected from Earth by means of direct numerical simulations of the dynamics of a large collection of test particles. This allows us to determine the probability and conditions for the collision of Earth ejecta with other planets of the Solar System. We also estimate the amount of particles falling back to Earth and colliding with the Moon as a function of time after being ejected.The Mercury-6 code is used to compute the dynamics of test particles under the gravitational effect of the planets in the Solar System and the Sun. A series of simulations are conducted with different ejection speeds, considering more than 10 5 particles in each case. We find that in general, the collision rates of Earth ejecta with Venus and the Moon, as well as the fall-back rates, are within an order of magnitude of results reported in the literature. By considering a larger number of particles than in all previous calculations we have also determined, on the basis of direct numerical simulations, the collision probability with Mars and, for the first time, computed collision probabilities with Jupiter and Saturn. We find that the collision probability with Mars is greater than values determined from collision cross section estimations previously reported.