I. P. Williams

Properties of the 67P/Churyumov-Gerasimenko interior revealed by CONSERT radar

The Philae lander provides a unique opportunity to investigate the internal structure of a comet nucleus, providing information about its formation and evolution in the early solar system. We present Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) measurements of the interior of Comet 67P/Churyumov-Gerasimenko. From the propagation time and form of the signals, the upper part of the “head” of 67P is fairly homogeneous on a spatial scale of tens of meters. CONSERT also reduced the size of the uncertainty of Philae’s final landing site down to approximately 21 by 34 square meters. The average permittivity is about 1.27, suggesting that this region has a volumetric dust/ice ratio of 0.4 to 2.6 and a porosity of 75 to 85%. The dust component may be comparable to that of carbonaceous chondrites.

Comet nucleus sounding experiment by radiowave transmission

Abstract We describe the radio science experiment proposed for the Rosetta cometary mission. The experiment consists in the transmission of electromagnetic waves between the landers and the orbiter through the comet to study its internal structure. In the paper, the electromagnetic model of the comet is presented and used to evaluate the potentiality of the experiment. Various modellings of the radio wave propagation are discussed. Finally, a description of the experiment and the instrument is made.

Observations of the Trans-Neptunian Objects 1993 SC and 1996 TL66 with the Infrared Space Observatory*

Observations at 90 μm of the trans-Neptunian objects (TNOs), 1993 SC and 1996 TL66, using the Infrared Space Observatory (ISO) are reported. Five individual observations of 1993 SC were acquired giving a 2.7 σ detection (a confidence level of 99.6%). The signal level of 11.46 ± 4.24 mJy has been modeled using a standard thermal model (STM) and gives an effective radius of 164 km and a geometric albedo of 0.022. Estimated radii and albedos using the fast rotator approximation and the thermophysical model are also presented. Two individual observations of 1996 TL66 are also reported. A clear signal of 39.77 ± 11.62 mJy at 90 μm was recorded. However, the position of the signal on the detector does not correspond to the position expected. A detailed investigation has not revealed a satisfactory explanation. Assuming that ISO was mispointed and that the origin of the signal is 1996 TL66, application of the STM gives an effective radius of 316 km and a geometric albedo of 0.030. This is in good agreement with expectations based on the assumption that the surfaces of TNOs are similar to those of cometary nuclei. The results for 1996 TL66 and 1993 SC indicate that TNOs are large, spherical, and very dark objects. A main-belt asteroid, 1997 SU15, was also detected giving an effective radius of 1.13 ± 0.04 km and a geometric albedo of 0.25 ± 0.02. An estimate of the relative dependence of the zodiacal light background in the ecliptic on elongation angle at 90 μm was also determined.

The 2011 October Draconids outburst – II. Meteoroid chemical abundances from fireball spectroscopy

We acknowledge support from the Spanish Ministry of Science and Innovation (projects AYA2009-13227, AYA2009-14000-C03-01 and AYA2011-26522), Junta de Andalucia (project P09-FQM-4555) and CSIC (grant # 201050I043).

Orbit and dynamic origin of the recently recovered Annama's H5 chondrite

We describe the fall of Annama meteorite occurred in the remote Kola Peninsula (Russia) close to Finnish border on April 19, 2014 (local time). The fireball was instrumentally observed by the Finnish Fireball Network. From these observations the strewnfield was computed and two first meteorites were found only a few hundred meters from the predicted landing site on May 29th and May 30th 2014, so that the meteorite (an H4-5 chondrite) experienced only minimal terrestrial alteration. The accuracy of the observations allowed a precise geocentric radiant to be obtained, and the heliocentric orbit for the progenitor meteoroid to be calculated. Backward integrations of the orbits of selected near-Earth asteroids and the Annama meteoroid showed that they rapidly diverged so that the Annama meteorites are unlikely related to them. The only exception seems to be the recently discovered 2014UR116 that shows a plausible dynamic relationship. Instead, analysis of the heliocentric orbit of the meteoroid suggests that the delivery of Annama onto an Earth-crossing Apollo type orbit occurred via the 4:1 mean motion resonance with Jupiter or the nu6 secular resonance, dynamic mechanisms that are responsible for delivering to Earth most meteorites studied so far.

Near-Earth asteroids among the Piscids meteoroid stream

It is now accepted that some near-Earth asteroids (NEAs) may be dormant or dead comets. One strong indicator of cometary nature is the existence of an associated meteoroid stream with its consequent observed meteor showers. We identify a complex of four NEAs (1997GL3, 2000PG3, 2002GM2, and 2002JC9) which have very similar orbits and a likely common progenitor. We also calculate the theoretical parameters for any meteor shower that may be associated with this complex. Finally we carried out of a search of existing catalogues of meteor showers and found that activity has been observed corresponding to each of the theoretically predicted showers. We conclude that the complex of four NEAs is the result of a cometary break-up.

Optical observations of water in Leonid meteor trails

[1] Two simultaneous filtered images (589 and 423 nm) of a meteor trail were recorded during the 2002 Leonid storm. The first image shows Na atoms and the second Ca and Fe atoms and signals at altitudes much higher than can give rise to ablation of metals, in agreement with other observations of high altitude visible trails [Spurný et al., 2000a; Spurný et al., 2000b]. Ablation models [McNeil et al., 1998] and analysis of the history of the 2002 Leonid meteoroids [McNaught and Asher, 1999] support the conclusion that the high altitude emissions are due to H 2 O + and H α,β,γ formed through the decomposition in the hyperthermal collision between H 2 O from meteoroid ice [Kresak, 1973] and atmospheric N 2 [Dressier et al., 1992].

Near-Earth asteroids among the Iota Aquariids meteoroid stream

It is shown that the near-Earth asteroids 2002JS2, 2002PD11, and 2003MT9 have very similar orbits to each other and probably a common origin. We investigate the orbital evolution of these asteroids under the perturbing action of the planets and calculated the theoretical shower parameters for any meteor shower that may be associated with these asteroids. Finally we searched the existing catalogues of meteor showers and fireballs, and found that activity has been observed corresponding to each of the theoretically predicted shower. We conclude that this asteroid-meteoroid complex is the result of a cometary break-up.

Meteoroid streams and the sporadic background

SummaryThere is a general agreement that meteoroid streams form through the ejection of dust grains, or meteoroids, up to a few centimeters in size from comets and possibly asteroids. After ejection these meteoroids are subject to forces arising from Solar radiation and the gravitational fields of the planets. Meteoroids may also break up into smaller ones through collisions and other effects. In many cases meteor showers have been observed for millennia, with material being fed into the stream throughout this period from the parent and material lost through the external effects mentioned. Much of the lost material forms the general sporadic background. This paper will review our state of knowledge of the processes involved above and will also aim to give some insight into the structure of the sporadic background

Near-Earth asteroids among the Scorpiids meteoroid complex

A group of near-Earth asteroids (NEAs) that moved on similar orbits to each other and where the orbits could be classed as cometary were identified by searching the “Near-Earth Objects Dynamic Site” database. Six NEAs were identified, 2003HP2, 2006WX29, 2007VH189, 2007WT3, 2007WY3, and 2008UM1. The orbits were integrated back over one complete cycle in the variation of the argument of perihelion to identify times when their nodal distance was 1 AU. Theoretical meteoroids were assumed to have been released at these times on an orbit identical to those of the NEAs. The characteristics of a meteor shower that would be formed when these meteoroids hit the Earth’s atmosphere were calculated. It was found that the showers produced from all six NEAs were identical and could be recognized as the nighttime χand δ-Scorpiids and the daytime βand σ-Librids, the latter two being named by us. It was also found that the orbital evolution of the Scorpiids was almost identical to the orbital evolution of the six NEAs. The similarity of the orbits, the nature of the orbit as cometary and the association of the Scorpiid meteoroid stream lead us to suggest that the origin of the whole complex was the fragmentation of some unknown comet several millennia ago.