Thomas Widemann
A5033245498- Planetary Science and Exploration
- Astro and Planetary Science
- Space Exploration and Technology
- Solar and Space Plasma Dynamics
- Stellar, planetary, and galactic studies
- Atmospheric Ozone and Climate
- Space exploration and regulation
- Space Science and Extraterrestrial Life
- Spaceflight effects on biology
- Astronomical Observations and Instrumentation
- Isotope Analysis in Ecology
- Astronomy and Astrophysical Research
- History and Developments in Astronomy
- Scientific Research and Discoveries
- Atmospheric and Environmental Gas Dynamics
- Gamma-ray bursts and supernovae
- Spacecraft Design and Technology
- Geomagnetism and Paleomagnetism Studies
- Geophysics and Gravity Measurements
- Historical Astronomy and Related Studies
- Geology and Paleoclimatology Research
- Spacecraft and Cryogenic Technologies
- Adaptive optics and wavefront sensing
- Astrophysics and Star Formation Studies
- Ionosphere and magnetosphere dynamics
Laboratoire d’études spatiales et d’instrumentation en astrophysique
2015-2024
Observatoire de Paris
2013-2024
Sorbonne Paris Cité
2019-2024
Université Paris Cité
2014-2024
Centre National de la Recherche Scientifique
2014-2024
Université Paris Sciences et Lettres
2019-2024
Université de Versailles Saint-Quentin-en-Yvelines
2012-2024
Université Paris-Saclay
2020-2024
Délégation Paris 7
2011-2024
Sorbonne Université
2014-2024
Abstract Surface geologic features form a detailed record of Venus’ evolution. Venus displays profusion volcanic and tectonics features, including both familiar exotic forms. One challenge to assessing the role these in evolution is that there are too few impact craters permit age dates for specific or regions. Similarly, without surface water, erosion limited cannot be used evaluate age. These same observations indicate has, on average, very young (150–1000 Ma), with most recent deformation...
We present results derived from the first multi-chord stellar occultations by transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, a single-chord occultation October 15. If timing of five chords obtained in were correct, then Quaoar would possess topographic features (crater or mountain) that be too large for body this mass. An alternative model consists applying time shifts to some account possible errors. Satisfactory elliptical fits are possible, yielding an...
On 5-6 June 2012, Venus will be transiting the Sun for last time before 2117. This event is an unique opportunity to assess feasibility of atmospheric characterisation Earth-size exoplanets near habitable zone with transmission spectroscopy technique and provide invaluable proxy atmosphere such a planet. In this letter, we theoretical spectrum that could tested spectroscopic observations during 2012 transit. done using radiative transfer across Venus' atmosphere, inputs from in-situ missions...
Abstract In this work we discuss various selected mission concepts addressing Venus evolution through time. More specifically, address investigations and payload instrument supporting scientific goals open questions presented in the companion articles of volume. Also included are their related (observations & modeling) discussion which measurements future data products needed to better constrain Venus’ atmosphere, climate, surface, interior habitability A new fleet missions has been...
Surface rocks on Venus are exposed to a dense atmosphere, primarily composed of CO₂ (96.5%) and N₂ (3.5%), with trace amounts H₂O sulfur compounds like SO₂ H₂SO₄, surface temperatures around 460°C pressures ⁓ 90 times that Earth. Understanding surface-atmosphere interactions is essential for interpreting data from NASA VERITAS DAVINCI ESA EnVision mission. Collaborative research between the Planetary Spectroscopy...
In 1985 the VEGA 1 and 2 spacecraft dropped two descent probes into nightside of Venus. Onboard was French‐Russian ISAV ultraviolet spectroscopy experiment, consisting a UV light source absorbed by atmospheric constituents circulating freely tube attached outside pressurized modules. generated wealth absorption spectra in 220‐ to 400‐nm range with an unprecedented vertical resolution (60–170 m) from 62 km altitude down ground. On basis known instrument properties careful examination curves...
We analyze two multi-chord stellar occultations by Pluto observed on July 18th, 2012 and May 4th, 2013, monitored respectively from five six sites. They provide a total of fifteen light-curves, twelve them being used for simultaneous fit that uses unique temperature profile, assuming clear (no-haze) pure N_2 atmosphere, but allowing possible pressure variation between the dates. find solution fits satisfactorily (i.e. within noise level) all providing atmospheric constraints ~1,190 km...
Some of the most outstanding questions about evolution and present-day state Venus involve current level volcanic activity its surface composition, both directly linked to amount differentiation that our neighbor experienced through time. Several observations indicate was volcanically active in recent past magmatic may still be ongoing [e.g., 1,2,3,4,5].While there is growing evidence a geologically world, information composition needed. Three missions (ESA’s EnVision...
EnVision is the fifth Medium-class mission in ESA’s Science Program, selected June 2021 and adopted January 2024. an ESA-led partnership with NASA, where NASA provides Synthetic Aperture Radar payload support. The launch scheduled for 2031; science operations at Venus will start early 2035 following cruise aerobraking phase to achieve a low polar orbit. scientific objective of provide holistic view planet from its inner core upper atmosphere, studying planet's long-term history,...
We report the observation of two stellar occultations by Titan on 14 November 2003, using stations in Indian Ocean, southern Africa, Spain, and northern Americas. These probed altitudes between ∼550 250 km (∼1 to μ bar) Titan's upper stratosphere. The light curves reveal a sharp inversion layer near 515 ± 6 altitude (1.5 bar pressure level), where temperature increases 15 K only km. This is close an observed fourteen months later Huygens HASI instrument during entry probe atmosphere January...
We have been using the TEXES high-resolution imaging spectrometer at NASA Infrared Telescope Facility to map sulfur dioxide and deuterated water over disk of Venus. Observations took place on January 10–12, 2012. The diameter Venus was 13 arcsec, with an illumination factor 80%. Data were recorded in 1344–1370 cm-1 range (around 7.35 μm) a spectral resolving power 80 000 spatial resolution about 1.5 arcsec. In this range, emission comes from above cloud top (z = 60–80 km). Four HDO lines...
We present results derived from four stellar occultations by the plutino object (208996) 2003~AZ$_{84}$, detected at January 8, 2011 (single-chord event), February 3, 2012 (multi-chord), December 2, 2013 (single-chord) and November 15, 2014 (multi-chord). Our observations rule out an oblate spheroid solution for 2003~AZ$_{84}$'s shape. Instead, assuming hydrostatic equilibrium, we find that a Jacobi triaxial with semi axes $(470 \pm 20) \times (383 10) (245 8)$~km % axis ratios $b/a= 0.82...
Context. Pluto's tenuous nitrogen (N2) atmosphere undergoes strong seasonal effects due to high obliquity and orbital eccentricity, has been recently (July 2015) observed by the New Horizons spacecraft. Goals are (i) construct a well calibrated record of evolution surface pressure on Pluto (ii) constrain structure lower using central flash in 2015. Method: eleven stellar occultations between 2002 2016 used retrieve atmospheric profiles (density, pressure, temperature) $\sim$5 km $\sim$380...
Since January 2012 we have been monitoring the behavior of sulfur dioxide and water on Venus, using Texas Echelon Cross-Echelle Spectrograph (TEXES) imaging spectrometer at NASA InfraRed Telescope Facility (IRTF, Mauna Kea Observatory). We present here observations obtained between 2016 September 2018. As in case our previous runs, data were recorded around 1345 cm −1 (7.4 μ m). The molecules SO 2 , CO HDO (used as a proxy for H O) observed, cloudtop Venus was probed an altitude about 64 km....
This paper presents the only space-borne optical-imaging observations of 2004 June 8 transit Venus, first such visible from Earth since AD 1882. The high-resolution, high-cadence satellite images we arranged NASA's Transition Region and Coronal Explorer (TRACE) reveal onset visibility Venus's atmosphere give further information about black-drop effect, whose causes previously demonstrated TRACE a Mercury. is gradually revealed before second contact after third contact, resulting changing...
We present the analysis of a four-year observational campaign using TEXES high-resolution imaging spectrometer at NASA Infrared Telescope Facility to map sulfur dioxide and deuterated water over disk Venus. Data have been recorded in two spectral ranges around 1345 cm-1 (7.4 μm) 530 (19 order probe cloudtop an altitude about 64 km (SO2 HDO 7.4 few kilometers below 19 μm). Observations took place during six runs between January 2012 2016. The diameter Venus ranged 12 33 arcsec. were with...