Demonstration of gaps due to Jupiter in meteoroid streams. What happened with the 2003 Pi-Puppids ?

The original publication is available in Astronomy & Astrophysics at www.aanda.org.International audienceWe simulated the dynamics of the Pi-Puppid meteoroid stream. The evolution of such a short period stream is dominated by close encounters with Jupiter. The effect is so great that it can cause the stream to split into several parts and form gaps. The difference in period of each part leads to the possibility of a meteor outburst on Earth while the parent body is at aphelion. Past observations are linked to streams ejected in the 19th and 20th century. Sometimes there are overlaps between several streams ejected at different perihelion passages of the parent body, affecting the time of maximum meteor activity. Generally speaking, observations suffer from a lack of coverage. In the 1972 and 2003 cases, only radio observations are available, and they are not in accordance with our predictions. This can be due to the radio detectors' lack of sensivity or to the poor knowledge of the efficiency of this physical process

Survey of cometary CO2, CO, and particulate emissions using the Spitzer Space Telescope: Smog check for comets

We surveyed 23 comets using the Infrared Array Camera on the Spitzer Space Telescope in wide filters centered at 3.6 and 4.5 microns. Emission in the 3.6 micron filter arises from sunlight scattered by dust grains; these images generally have a coma near the nucleus and a tail in the antisolar direction due to dust grains swept back by solar radiation pressure. The 4.5 micron filter contains the same dust grains, as well as strong emission lines from CO2 and CO gas; these show distinct morphologies, in which cases we infer they are dominated by gas. Based on the ratio of 4.5 to 3.6 micron brightness, we classify the survey comets as CO2+CO "rich" and "poor." This classification is correlated with previous classifications by A'Hearn based on carbon-chain molecule abundance, in the sense that comets classified as "depleted" in carbon-chain molecules are also "poor" in CO2+CO. The gas emission in the IRAC 4.5 micron images is characterized by a smooth morphology, typically a fan in the sunward hemisphere with a radial profile that varies approximately as the inverse of projected distance from the nucleus, as would apply for constant production and free expansion. There are very significant radial and azimuthal enhancements in many of the comets, and these are often distinct between the gas and dust, indicating that ejection of solid material may be driven either by H2O or CO2. Notable features in the images include the following. There is a prominent loop of gas emission from 103P/Hartley 2, possible due to an outburst of CO2 before the Spitzer image. Prominent, double jets are present in the image of 88P/Howell. A prominent single jet is evident for 3 comets. Spirals are apparent in 29P and C/2006 W3; we measure a rotation rate of 21 hr for the latter comet. Arcs (possibly parts of a spiral) are apparent in the images of 10P/Tempel 2, and 2P/Encke.Comment: accepted for publication in Icaru

Encounters of the dust trails of comet 45P/Honda-Mrkos-Pajdusakova with Venus in 2006

The original publication is available in Astronomy & Astrophysics at www.aanda.org.International audienceAims. We aim to investigate the dynamical fate of meteoroids ejected during past perihelion passages of comet 45P/Honda-Mrkos-Pajdusakova that intersect the orbit of Venus. Of particular interest is the possibility, borne of previous work, that a significant flux of these particles will reach the planet during early June and late August 2006, when the Venus Express spacecraft will be operating in orbit around Venus. Methods. We have simulated the generation of meteoroid trails ejected by the comet at some past perihelion passages, and numericaly integrated them forward in time until they approach Venus in 2006. Results. On the inbound leg of the comet's path towards perihelion, we find a trail composed of dust particles ejected between 1943 and 1980 that encounters Venus on 9 June 2006 at a distance of 0.009 AU. On the outbound leg, we observe a dense trail of particles ejected between 1985 and 2001 that measures 3.4 × 10−4 AU (5 × 104 km) in half-width, and passes under the planet at a distance of 1.72 × 10−3 AU (2.6 × 105 km) on 30 August. Based on these results, we conclude that, on both occasions, the incident flux at Venus will likely be too low to allow for the detection of a shower by optical means. We discuss the circumstances under which Venus Express may encounter a significant flux of small particles detectable through impact ionization or disturbances in the interplanetary magnetic field

The population of natural Earth satellites

Peer reviewe

A new method to predict meteor showers. II. Application to the Leonids

The original publication is available in Astronomy & Astrophysics at www.aanda.org.International audienceOur model of meteor shower forecasting (described in Paper I) is applied to the Leonid shower. This model is based on the "dirty snowball" model of comets, and on heavy numerical simulation of the generation and evolution of meteoroid streams. The amount of dust emitted by comet 55P/Tempel-Tuttle is computed. A statistical weight is associated to each simulated particle. This weight represents the real amount of meteoroids released by the comet. Particles close to the Earth are examined. There is no unique set of initial conditions (velocity and angle of ejection) for them to reach the Earth at the time of the shower. The shape of the metoroid stream projected on the ecliptic is not elliptical, due to non-gravitational forces and ejection processes. The mixing of particles is revealed to be very efficient. A comparison between observations and predictions of Leonid meteor showers is done. The time of maximum is found to be very accurate, except for certain years (1999 in particular). This problem is common to all models. The level of the predicted shower is obtained through a fit of the size distribution index s = 2.4±0.1. This model provides a unique opportunity to derive cometary parameters from meteor shower observations. Leonid meteor shower forecasts are provided for years up to 2100. The next storm is expected in 2034

The Sporadic Meteoroid Complex and Spacecraft Risk

The meteoroid population in near-Earth space is typically broken down into two components: shower meteoroids which orbit in collimated streams, and the older sporadic meteoroids which have been dispersed into a much broader uncollimated distribution of orbits. The sporadic meteors dominate the meteoroid flux at Earth in the size range of those particles of the most of the risk to spacecraft (approximately 100 microns to 1 cm). We describe the results of numerical simulations of the sporadic meteoroid complex by full physical modeling of meteoroids from ejection from their parent body through their perturbation by planets and radiation forces though the end of their lives through collision or ejection from the solar system. This model together with comparison with optical and radar measurements of meteoroid fluxes in near Earth space will allow improved assessment of the risk to spacecraft in near-Earth space from the sporadic complex

The dust trail complex of comet 79P/du Toit-Hartley and meteor outbursts at Mars

The original publication is available in Astronomy & Astrophysics at www.aanda.org.International audienceAims. Meteoroid trails ejected during past perihelion passages of the Mars-orbit-intersecting comet 79P/du Toit-Hartley have the potential of generating meteor outbursts in the Martian atmosphere. Depending on timing and intensity, the effects of these outbursts may be detectable by instrumentation operating in the vicinity of Mars. We aim to generate predictions for meteor activity in the martian atmosphere related to that comet; to search for evidence, in planetary mission data, that such activity took place; and to make predictions for potentially detectable future activity. Methods. We have modelled the stream by integrating numerically the states of particle ensembles, each ensemble representing a trail of meteoroids ejected from the comet during 39 perihelion passages from 1803, and propagated them forward in time, concentrating on those particles that physically approach Mars in the recent past and near future. Results. We find several instances where meteor outbursts of low to moderate intensity may have taken place at Mars since 1997. A search through Mars Global Surveyor (MGS) radio science data during two periods in 2003 and 2005 when data coverage was available showed that a plasma layer did indeed form in the martian ionosphere for a period of a few hours in April 2003 as a direct consequence of the predicted outburst. The apparent failure to identify such an event in 2005 could be due to those meteoroids ablating lower in the atmosphere or that the cometary dust follows a different particle size distribution than what was assumed. Our study highlights the need for further theoretical modelling of the response of the martian ionosphere to a time-variable meteoroid flux, observations of the comet itself and, most importantly, regular monitoring of the martian ionosphere during future outbursts predicted by our model

Distribution and properties of fragments and debris from the split comet 73P/Schwassmann-Wachmann 3 as revealed by Spitzer Space Telescope

During 2006 Mar - 2007 Jan, we used the IRAC and MIPS instruments on the Spitzer Space Telescope to study the infrared emission from the ensemble of fragments, meteoroids, and dust tails in the more than 3 degree wide 73P/Schwassmann-Wachmann 3 debris field. We also investigated contemporaneous ground based and HST observations. In 2006 May, 55 fragments were detected in the Spitzer image. The wide spread of fragments along the comet's orbit indicates they were formed from the 1995 splitting event. While the number of major fragments in the Spitzer image is similar to that seen from the ground by optical observers, the correspondence between the fragments with optical astrometry and those seen in the Spitzer images cannot be readily established, due either to strong non-gravitational terms, astrometric uncertainties, or transience of the fragments outgassing. The Spitzer data resolve the structure of the dust comae at a resolution of 1000 km, and they reveal the infrared emission due to large (mm to cm size) particles in a continuous dust trail that closely follows the projected orbit. We detect fluorescence from outflowing CO2 gas from the largest fragments (B and C), and we measure the CO2:H2O proportion (1:10 and 1:20, respectively). Three dimensionless parameters to explain dynamics of the solid particles: alpha (sublimation reaction), beta (radiation pressure), and nu (ejection velocity). The major fragments have nu>alpha>beta and are dominated by the kinetic energy imparted to them by the fragmentation process. The small, ephemeral fragments seen by HST in the tails of the major fragments have alpha>nu>beta dominated by rocket forces. The meteoroids along the projected orbit have beta~nu>>alpha. Dust in the fragments' tails has beta>>(nu+alpha) and is dominated by radiation pressure.Comment: accepted 5/13/09 by Icaru

Explosion of Comet 17P/Holmes as revealed by the Spitzer Space Telescope

An explosion on comet 17P/Holmes occurred on 2007 Oct 23, projecting particulate debris of a wide range of sizes into the interplanetary medium. We observed the comet using the Spitzer spectrograph on 2007 Nov 10 and 2008 Feb 27, and the photometer, on 2008 Mar 13. The fresh ejecta have detailed mineralogical features from small crystalline silicate grains. The 2008 Feb 27 spectra, and the central core of the 2007 Nov 10 spectral map, reveal nearly featureless spectra, due to much larger grains that were ejected from the nucleus more slowly. We break the infrared image into three components (size, speed) that also explain the temporal evolution of the mm-wave flux. Optical images were obtained on multiple dates spanning 2007 Oct 27 to 2008 Mar 10 at the Holloway Comet Observatory and 1.5-m telescope at Palomar Observatory. The orientation of the leading edge of the ejecta shell and the ejecta blob, relative to the nucleus, do not change as the orientation of the Sun changes; instead, the configuration was imprinted by the orientation of the initial explosion. The kinetic energy of the ejecta >1e21 erg is greater than the gravitational binding energy of the nucleus. We model the explosion as being due to crystallization and release of volatiles from interior amorphous ice within a subsurface cavity; once the pressure in the cavity exceeded the surface strength, the material above the cavity was propelled from the comet. The size of the cavity and the tensile strength of the upper layer of the nucleus are constrained by the observed properties of the ejecta; tensile strengths on >10 m scale must be greater than 10 kPa. The appearance of the 2007 outburst is similar to that witnessed in 1892, but the 1892 explosion was less energetic by a factor of about 20.Comment: 51 pages. Some figures compressed (see real journal for full quality). accepted by Icaru

Monitoring Observations of the Jupiter-Family Comet 17P/Holmes during 2014 Perihelion Passage

We performed a monitoring observation of a Jupiter-Family comet, 17P/Holmes, during its 2014 perihelion passage to investigate its secular change in activity. The comet has drawn the attention of astronomers since its historic outburst in 2007, and this occasion was its first perihelion passage since then. We analyzed the obtained data using aperture photometry package and derived the Afrho parameter, a proxy for the dust production rate. We found that Afrho showed asymmetric properties with respect to the perihelion passage: it increased moderately from 100 cm at the heliocentric distance r_h=2.6-3.1 AU to a maximal value of 185 cm at r_h = 2.2 AU (near the perihelion) during the inbound orbit, while dropping rapidly to 35 cm at r_h = 3.2 AU during the outbound orbit. We applied a model for characterizing dust production rates as a function of r_h and found that the fractional active area of the cometary nucleus had dropped from 20%-40% in 2008-2011 (around the aphelion) to 0.1%-0.3% in 2014-2015 (around the perihelion). This result suggests that a dust mantle would have developed rapidly in only one orbital revolution around the sun. Although a minor eruption was observed on UT 2015 January 26 at r_h = 3.0 AU, the areas excavated by the 2007 outburst would be covered with a layer of dust (<~ 10 cm depth) which would be enough to insulate the subsurface ice and to keep the nucleus in a state of low activity.Comment: 25 pages, 6 figures, 2 tables, ApJ accepted on December 29, 201