Search

On February 28, 2021, a fireball dropped $\sim0.6$ kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behaviour, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive ($\sim13$ kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure ($\sim0.6$ MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km/s). A near-catastrophic fragmentation at $\sim0.07$ MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region $\sim0.08$ Myr ago and it never had a perihelion distance smaller than $\sim0.7$ AU, while other CM2 meteorites with known orbits approached the Sun closer ($\sim0.5$ AU) and were heated to at least 100 K higher temperatures., Comment: Accepted for publication in MAPS

In meteor physics the luminous efficiency ${\tau}$ is used to convert the meteor's magnitude to the corresponding meteoroid's mass. However, lack of sufficiently accurate verification methods or adequate laboratory tests leave this parameter to be controversially discussed. In this work meteor/fireball data obtained by the Fireball Recovery and InterPlanetary Observation Network (FRIPON) was used to calculate the masses of the pre-atmospheric meteoroids which could in turn be compared to the meteor brightnesses to assess their luminous efficiencies. For that, deceleration-based formulas for the mass computation were used. We have found ${\tau}$-values, as well as the shape change coefficients, of 294 fireballs with determined masses in the range of $10^{-6}$ kg - $100$ kg. The derived ${\tau}$-values have a median of ${\tau}_{median}$ = 2.17 %. Most of them are on the order of 0.1 % - 10 %. We present how our values were obtained, compare them with data reported in the literature, and discuss several methods. A dependence of ${\tau}$ on the pre-atmospheric velocity of the meteor, $v_e$, is noticeable with a relation of ${\tau}=0.0023 \cdot v_e^{2.3}$. The higher luminous efficiency of fast meteors could be explained by the higher energy released. Fast meteoroids produce additional emission lines that radiate more efficiently in specific wavelengths due to the appearance of the so-called second component of higher temperature. Furthermore, a dependence of ${\tau}$ on the initial meteoroid mass, $M_e$, was found, with negative linear behaviour in log-log space: ${\tau}=0.48 \cdot M_e^{-0.47}$. This implies that the radiation of smaller meteoroids is more efficient.

We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by SOFIA with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 Aug 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 $\pm$ 0.0005 hours. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the New Horizons flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies., Comment: Submitted to Astronomical Journal (revised); 40 pages, 13 figures, 9 tables

This paper describes the path strewn with pitfalls encountered during the development of a large dynamic range and very fast radiometer designed to precisely observe the meteor light curves. A small series production of a finalized version of the current prototype should accompany some video cameras from the FRIPON network., Comment: To be published in the Proceedings of the International Meteor Conference, Bollmannsruh, Germany,3 to 6 October 2019

Small-scale waves were observed along the boundary between Jupiter's North Equatorial Belt and North Tropical Zone, ~16.5{\deg} N planetographic latitude in Hubble Space Telescope data in 2012 and throughout 2015 to 2018, observable at all wavelengths from the UV to the near IR. At peak visibility, the waves have sufficient contrast (~10%) to be observed from ground-based telescopes. They have a typical wavelength of about 1.2{\deg} (1400 km), variable-length wave trains, and westward phase speeds of a few m/s or less. New analysis of Voyager 2 data shows similar wave trains over at least 300 hours. Some waves appear curved when over cyclones and anticyclones, but most are straight, but tilted, shifting in latitude as they pass vortices. Based on their wavelengths, phase speeds, and faint appearance at high-altitude sensitive passbands, the observed NEB waves are consistent with inertia-gravity waves at the 500-mbar pressure level, though formation altitude is not well constrained. Preliminary General Circulation Model simulations generate inertia-gravity waves from vortices interacting with the environment and can reproduce the observed wavelengths and orientations. Several mechanisms can generate these waves, and all may contribute: geostrophic adjustment of cyclones; cyclone/anticyclone interactions; wind interactions with obstructions or heat pulses from convection; or changing vertical wind shear. However, observations also show that the presence of vortices and/or regions of convection are not sufficient by themselves for wave formation, implying that a change in vertical structure may affect their stability, or that changes in haze properties may affect their visibility., Comment: Astronomical Journal, accepted

The French FRIPON (Fireball Recovery and Interplanetary Observation Network) programme relies on a video cameras network associated to radio sensors running in a radar multistatic configuration to observe fireballs and to determine meteoroid accurate orbits and potential meteorites strewnfields. This paper focuses on some peculiar phenomena observed with radio means during the final phase of the meteors flight, Comment: International Meteor Conference 2017

The Ursid meteor shower is an annual shower that usually shows little activity. However, its Zenith Hourly Rate sometimes increases, usually either when its parent comet, 8P/Tuttle, is close to its perihelion or its aphelion. Outbursts when the comet is away from perihelion are not common and outburst when the comet is close to aphelion are extremely rare. The most likely explanation offered to date is based on the orbital mean motion resonances. The study of the aphelion outburst of December 2000 provided a means of testing that hypothesis. A new aphelion outburst was predicted for December 2014. The Spanish Meteor Network in collaboration with the French Fireball Recovery and InterPlanetary Observation Network set up a campaign to monitor this outburst and eventually retrieve orbital data that expands and confirms previous preliminary results and predictions. Despite unfavourable weather conditions over the South of Europe over the relevant time period precise trajectories from multi-station meteor data recorded over Spain were obtained, as well as orbital and radiant information for four Ursid meteors. The membership of these four meteors to the expected dust trails that were to provoke the outburst is discussed, and we characterize the origin of the outburst in the dust trail produced by the comet in the year 1392 A.D., Comment: 12 pages, 6 figures, 7 tables

Since the discovery of Sirius-B about 130 yr ago, there have been several claims of a possible second companion around the brightest star Sirius-A. Such a companion could, in particular, be responsible of the suspected colour change of the star, now strongly suggested from two independent historical sources. We reported here on a new observation of the sky region around Sirius, to search for such a companion, using a coronographic device. By comparison of the new stellar field with a similar image obtained by us $\sim$13 yr ago and using the Sirius proper motion, we are able to eliminate the most obvious companion candidates down to a magnitude m$_v$$\sim$17 in a field from 30 arcsec to 2.5 arcmin of the central star. None of the visible stars appears consistent in magnitude and colours with what expected from current theoretical models and observations of low-mass stars. From the study of the same field, it is also shown that the Sirius companion, consistently reported by observers during the years 1920-1930, is most probably an unrelated m$_g$$\simeq$12 background star, now $\sim$ 1 arcmin away but located precisely on the Sirius proper motion trajectory. The closest apparent conjunction with Sirius was realized in 1937 with a minimum angular distance of 6.9 arcsec, of the same order than the Sirius A-B binary separation. The reported observations do not eliminate the possibility of a second companion but now confined the search to the more central 30 arcsec region around Sirius. In particular, the existence of a long period companion cannot definitively be ruled out since the arbitrary orientation of the orbit can yield an observed projected position on sky inside this more central region., Comment: 6 pages, 4 figures, published in Astronomy and Astrophysics