arXiv subjects

Laurent Lamy

Publications and source records attributed to Laurent Lamy.

23 records · Page 2Linked to original sources

arXiv2015

Cassini in situ observations of long-duration magnetic reconnection in Saturn's magnetotail

Magnetic reconnection is a fundamental process in solar system and astrophysical plasmas, through which stored magnetic energy associated with current sheets is converted into thermal, kinetic and wave energy. Magnetic reconnection is also thought to be a key process involved in shedding internally produced plasma from the giant magnetospheres at Jupiter and Saturn through topological reconfiguration of the magnetic field. The region where magnetic fields reconnect is known as the diffusion region and in this letter we report on the first encounter of the Cassini spacecraft with a diffusion region in Saturn's magnetotail. The data also show evidence of magnetic reconnection over a period of 19 h revealing that reconnection can, in fact, act for prolonged intervals in a rapidly rotating magnetosphere. We show that reconnection can be a significant pathway for internal plasma loss at Saturn. This counters the view of reconnection as a transient method of internal plasma loss at Saturn. These results, although directly relating to the magnetosphere of Saturn, have applications in the understanding of other rapidly rotating magnetospheres, including that of Jupiter and other astrophysical bodies.

astro-ph.EP↗

arXiv2015

The Auroral Planetary Imaging and Spectroscopy (APIS) service

The Auroral Planetary Imaging and Spectroscopy (APIS) service, accessible online, provides an open and interactive access to processed auroral observations of the outer planets and their satellites. Such observations are of interest for a wide community at the interface between planetology and magnetospheric and heliospheric physics. APIS consists of (i) a high level database, built from planetary auroral observations acquired by the Hubble Space Telescope (HST) since 1997 with its mostly used Far-UltraViolet spectro-imagers, (ii) a dedicated search interface aimed at browsing efficiently this database through relevant conditional search criteria and (iii) the ability to interactively work with the data online through plotting tools developed by the Virtual Observatory (VO) community, such as Aladin and Specview. This service is VO compliant and can therefore also been queried by external search tools of the VO community. The diversity of available data and the capability to sort them out by relevant physical criteria shall in particular facilitate statistical studies, on long-term scales and/or multi-instrumental multi-spectral combined analysis.

astro-ph.IM↗

arXiv2013

Building galaxies, stars, planets and the ingredients for life between the stars. A scientific proposal for a European Ultraviolet-Visible Observatory (EUVO)

The growth of luminous structures and the building blocks of life in the Universe began as primordial gas was processed in stars and mixed at galactic scales. The mechanisms responsible for this development are not well understood and have changed over the intervening 13 billion years. To follow the evolution of matter over cosmic time, it is necessary to study the strongest (resonance) transitions of the most abundant species in the Universe. Most of them are in the ultraviolet (UV; 950A-3000A) spectral range that is unobservable from the ground. A versatile space observatory with UV sensitivity a factor of 50-100 greater than existing facilities will revolutionize our understanding of the Universe. Habitable planets grow in protostellar discs under ultraviolet irradiation, a by-product of the star-disk interaction that drives the physical and chemical evolution of discs and young planetary systems. The electronic transitions of the most abundant molecules are pumped by the UV field, providing unique diagnostics of the planet-forming environment that cannot be accessed from the ground. Earth's atmosphere is in constant interaction with the interplanetary medium and the solar UV radiation field. A 50-100 times improvement in sensitivity would enable the observation of the key atmospheric ingredients of Earth-like exoplanets (carbon, oxygen, ozone), provide crucial input for models of biologically active worlds outside the solar system, and provide the phenomenological baseline to understand the Earth atmosphere in context. In this white paper, we outline the key science that such a facility would make possible and outline the instrumentation to be implemented.

astro-ph.IM↗

arXiv2012

OSS (Outer Solar System): A fundamental and planetary physics mission to Neptune, Triton and the Kuiper Belt

The present OSS mission continues a long and bright tradition by associating the communities of fundamental physics and planetary sciences in a single mission with ambitious goals in both domains. OSS is an M-class mission to explore the Neptune system almost half a century after flyby of the Voyager 2 spacecraft. Several discoveries were made by Voyager 2, including the Great Dark Spot (which has now disappeared) and Triton's geysers. Voyager 2 revealed the dynamics of Neptune's atmosphere and found four rings and evidence of ring arcs above Neptune. Benefiting from a greatly improved instrumentation, it will result in a striking advance in the study of the farthest planet of the Solar System. Furthermore, OSS will provide a unique opportunity to visit a selected Kuiper Belt object subsequent to the passage of the Neptunian system. It will consolidate the hypothesis of the origin of Triton as a KBO captured by Neptune, and improve our knowledge on the formation of the Solar system. The probe will embark instruments allowing precise tracking of the probe during cruise. It allows to perform the best controlled experiment for testing, in deep space, the General Relativity, on which is based all the models of Solar system formation. OSS is proposed as an international cooperation between ESA and NASA, giving the capability for ESA to launch an M-class mission towards the farthest planet of the Solar system, and to a Kuiper Belt object. The proposed mission profile would allow to deliver a 500 kg class spacecraft. The design of the probe is mainly constrained by the deep space gravity test in order to minimise the perturbation of the accelerometer measurement.

gr-qc↗

arXiv2011

Variability of southern and northern periodicities of Saturn Kilometric Radiation

Among the persistent questions raised by the existence of a rotational modulation of the Saturn Kilometric Radiation (SKR), the origin of the variability of the 10.8 hours SKR period at a 1% level over weeks to years remains intriguing. While its short-term fluctuations (20-30 days) have been related to the variations of the solar wind speed, its long-term fluctuations (months to years) were proposed to be triggered by Enceladus mass-loading and/or seasonal variations. This situation has become even more complicated since the recent identification of two separated periods at 10.8h and 10.6h, each varying with time, corresponding to SKR sources located in the southern (S) and the northern (N) hemispheres, respectively. Here, six years of Cassini continuous radio measurements are investigated, from 2004 (pre-equinox) to the end of 2010 (post-equinox). From S and N SKR, radio periods and phase systems are derived separately for each hemisphere and fluctuations of radio periods are investigated at time scales of years to a few months. Then, the S phase is used to demonstrate that the S SKR rotational modulation is consistent with an intrinsically rotating phenomenon, in contrast with the early Voyager picture.

astro-ph.EP↗