Philippe Lamy

Context. Constraining the plasma properties and energetics of coronal mass ejections (CMEs) in the inner corona is essential for understanding their early evolution, yet it remains challenging because of limited observations. Aims. We investigate the mass and density evolution as well as energy partitioning of two CMEs observed on 14 and 16 September 2025, and assess the potential of coordinated Proba-3/ASPIICS and Aditya-L1/VELC observations to constrain CME energetics in the low corona. Methods. We present the first coordinated observations of CMEs obtained simultaneously by Proba-3/ASPIICS and Aditya-L1/VELC. Using ASPIICS white-light observations, we estimated the CME mass, volume, number density, and the evolution of kinetic, thermal, and magnetic energies. Magnetic energies were estimated from observed CME properties using observationally constrained, physically motivated assumptions. Simultaneous VELC Fe XIV 5303 A observations provide independent estimates of the emission measure, electron number density, thermal energy, and CME lateral extent. Results. The electron number density evolves as n _e χ r ^-33 for the 14 September CME and as n _e ∝ r ⁻⁶ for the 16 September CME. The two events exhibit markedly different energy partitioning in the low corona. For the 14 September CME, the kinetic and magnetic energies are comparable, while the thermal energy remains nearly two orders of magnitude smaller, indicating limited plasma heating. In contrast, the 16 September CME exhibits a substantial thermal-energy enhancement, with thermal energy eventually becoming comparable to kinetic energy. For both CMEs, the estimated magnetic energy remains comparable to or exceeds the kinetic energy over the observed height. Conclusions. Our results demonstrate the scientific potential of synergetic ASPIICS and VELC observations for constraining the CME mass, density, and energetics in the inner corona, providing new observational constraints on the early evolution of CMEs.

We describe the scientific objectives and instrument design of the ASPIICS coronagraph aboard the Proba-3 mission of the European Space Agency launched on 5 December 2024. Proba-3 consists of two spacecraft in a highly elliptical orbit around the Earth. One spacecraft carries the telescope, and the external occulter is mounted on the second spacecraft. The two spacecraft fly in a precise formation during 6 hours of a 19.63 hour orbit, together forming a giant solar coronagraph called ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun). The very long distance between the external occulter and the telescope (around 144 m) represents an increase of two orders of magnitude compared to classical externally occulted solar coronagraphs. This allows the inner corona to be observed in eclipse-like conditions, i.e., close to the solar limb (down to 1.099 R _⊙ ) and with very little stray light. ASPIICS provides a new perspective on the inner solar corona that will help solve several outstanding problems in solar physics, such as the origin of the slow solar wind and the physical mechanism of coronal mass ejections.

Context . ASPIICS is a giant-baseline visible light solar coronagraph, which relies on the millimetric positioning performance of the precision formation flying Proba-3 mission of the European Space Agency. Proba-3 was launched on 5 December 2024, and since then ASPIICS has observed the solar corona with the field of view (1.1–3) R _⊙ . Aims . Diffraction, in particular diffraction of solar disk light on the external occulter, is known to provide a major source of stray light in coronagraphs. Our aims were to analyze diffracted light visible in ASPIICS images, to compare it with the analytical-numerical diffraction model reported earlier, and to fine-tune the model. Methods . We compared the diffraction effects visible in the ASPIICS data with simulated diffraction images; in particular, we compared the geometrical properties and the radiometric signal. The properties of the diffraction described in previous works suggest how to fine-tune the model in order to achieve a better correspondence with the observations. Results . Early ASPIICS observations, where diffraction is pronounced, fully confirm all the qualitative properties of diffracted light suggested by the model. After fine-tuning the model we found a quantitative correspondence of the level of 30–50%, depending on the configuration. Conclusions . The performed analysis allows us to validate our analytical-numerical model and justify the assumptions, and to estimate the contribution of the diffracted light in the ASPIICS images. Over most of the field of view the diffracted light is two orders of magnitude below the coronal signal.

We report on the detection of three icy cavities on the nucleus of comet 67P/Churyumov–Gerasimenko. They were identified on high-resolution anaglyphs built from images acquired by the Optical, Spectroscopic, and Infrared Remote Imaging System instrument aboard the Rosetta spacecraft on 2016 April 9 and 10. Visually, they appear as bright patches of typically 15 to 30 m across whose large reflectances and spectral slopes in the visible substantiate the presence of sub-surface water ice. Using a new high-resolution photogrammetric shape model, we determined the three-dimensional shape of these cavities whose depth ranges from 20 to 47 m. Spectral slopes were interpreted with models combining water ice and refractory dark material and the water ice abundances in the cavities were found to amount to a few per cent. The determination of the lifetime of the icy cavities was strongly biased by the availability of appropriate and favourable observations, but we found evidence of values of up to 2 yr. The icy cavities were found to be connected to jets well documented in past studies. A thermal model allowed us to track their solar insolation over a large part of the orbit of the comet and a transitory bright jet on 2015 July 18 was unambiguously linked to the brief illumination of the icy bottom of one of the cavities. These cavities are likely to be the first potential subsurface access points detected on a cometary nucleus and their lifetimes suggest that they reveal pristine sub-surface icy layers or pockets rather than recently recondensed water vapour.

There are few possibilities to put the in-situ measurements of the coronal electron density such as obtained by the Parker Solar Probe (PSP) in the context of the 3D configuration of the corona and its structure. One of them consists in using MHD models relying on synoptic maps of the photospheric magnetic field, but their accuracy is subject to questions, especially in the case of complex coronae of the maximum type. The 2D inversion of white-light coronagraphic images requires the simplified assumption of spherical symmetry of the corona which basically washes out the longitudinal variations. We will present preliminary results of a new method which makes use of the 3D time-dependent tomographic reconstruction of the coronal electron density based on accurately corrected and calibrated LASCO-C2 images of the polarized brightness of the corona. It is performed over a sliding window of 14 days (half a Carrington rotation) centered at the times of the PSP perihelion with a time interval of 4 days. The resulting “cubes” of the 3D electron density Ne are visualized from six different vantage points and with movies. The orbit of PSP is projected on a synoptic map of Ne extracted from the cubes at a heliocentric distance of 5.5 Rs; the track extends from Perihelion-5 days to Perihelion+5 days. The electron density at the heliocentric distances of PSP is extrapolated radially from the values at 5.5 Rs using an inverse square law and compared with the in-situ measurements collected by PSP/FIELDS. We will present results from the first PSP encounters.

The observations of the solar F-corona from space are reviewed emphasizing the 25 years of continuous monitoring achieved by the LASCO-C2 and C3 coronagraphs. Our work includes images obtained by the Clementine cameras, and the STEREO/SECCHI/HI-1A and PSP/WISPR heliospheric imagers. The characteristic radiance profiles along the equatorial and polar directions follow power laws in the 5{\deg}-50{\deg} range of elongation, with constant power exponents of -2.33 and -2.55. Both profiles connect extremely well to the corresponding standard profiles of the zodiacal light. The LASCO equatorial profile exhibits a shoulder implying a 17% decrease of the radiance within 10Rsun that may be explained by the disappearance of organic materials within 0.3 AU. LASCO detected for the first time a secular variation of the F-corona, an increase at a rate of 0.46% per year of the integrated radiance in the LASCO-C3 FoV. This is likely the first observational evidence of the role of collisions in the inner zodiacal cloud. A composite of C2 and C3 images produced the LASCO reference map of the radiance of the F-corona from 2 to 30Rsun and, by combining with ground-based measurements, the LASCO extended map from 1 to 6 Rsun. The plane of symmetry of the inner zodiacal cloud is strongly warped, its inclination increasing towards the planes of the inner planets and ultimately the solar equator. In contrast, its longitude of ascending node is found to be constant and equal to 87.6{\deg}. LASCO did not detect any small-scale structures such as putative rings occasionally reported during solar eclipses. The outer border of the depletion zone where interplanetary dust particles start to be affected by sublimation appears well constrained at 19Rsun. This zone extends down to 5Rsun, thus defining the boundary of the dust-free zone where the most refractory materials, likely moderately absorbing silicates, disappear.

We present a review of the observations of the solar F-corona from space with a special emphasis of the 25 years of continuous monitoring achieved by the LASCO-C2 and C3 coronagraphs. Our work includes images obtained by the navigation cameras of the Clementine spacecraft, the SECCHI/HI-1A heliospheric imager onboard STEREO-A, and the Wide Field Imager for Solar Probe onboard the Parker Solar Probe. The connection to the zodiacal light is considered based on ground- and space-based observations, prominently from the past Helios, IRAS, COBE, and IRAKI missions. The characteristic radiance profiles along the two symmetry axis of the “elliptically” shaped F-corona (aka equatorial and polar directions) follow power laws in the $5^{\circ }$ 5 ∘ – $50^{\circ }$ 50 ∘ range of elongation, with constant power exponents of −2.33 and −2.55. Both profiles connect extremely well to the corresponding standard profiles of the zodiacal light. The LASCO equatorial profile exhibits a shoulder implying a $\approx17\%$ ≈ 17 % decrease of the radiance within $\approx10~\text{R}_{\odot }$ ≈ 10 R ⊙ that may be explained by the disappearance of organic materials within 0.3 AU. LASCO detected for the first time a secular variation of the F-corona, an increase at a rate of 0.46% per year of the integrated radiance in the LASCO-C3 field of view. This is likely the first observational evidence of the role of collisions in the inner zodiacal cloud. The temporal evolution of the integrated radiance in the LASCO-C2 field of view is more complex suggesting possible additional processes. Whereas it is well established that the F-corona is slightly redder than the Sun, the spectral variation of its color index is not yet well established. A composite of C2 and C3 images produced the LASCO reference map of the radiance of the F-corona from 2 to $30~\text{R}_{\odot }$ 30 R ⊙ and, by combining with ground-based measurements, the LASCO extended map from 1 to $6~\text{R}_{\odot }$ 6 R ⊙ . An upper limit of $0.03~\text{R}_{\odot}$ 0.03 R ⊙ is obtained for the offset between the center of the Sun and that of the F-corona with a most likely value of zero. The flattening index of the F-corona starts from zero at an elongation of $0.5^{\circ }\pm0.01^{\circ }$ 0.5 ∘ ± 0.01 ∘ ( $1.9~\text{R}_{ \odot }$ 1.9 R ⊙ ) and increases linearly with the logarithm of the elongation to connect to that of the zodiacal light with however a small hump related to the shoulder in the equatorial profile. The shape of the isophotes is best described by super-ellipses with an exponent linked to the flattening index. An ellipsoid model of the spatial density of interplanetary dust is solely capable of reproducing this shape, thus rejecting other classical models such as fan, and cosine. The plane of symmetry of the inner zodiacal cloud is strongly warped, its inclination increasing towards the planes of the inner planets and ultimately the solar equator. In contrast, its longitude of ascending node is found to be constant and equal to $87.6^{ \circ }$ 87.6 ∘ . LASCO did not detect any small scale structures such as putative rings occasionally reported during solar eclipses. The outer border of the depletion zone where interplanetary dust particles start to be affected by sublimation appears well constrained at $\approx19~\text{R}_{\odot }$ ≈ 19 R ⊙ . This zone extends down to $\approx5~\text{R}_{\odot}$ ≈ 5 R ⊙ , thus defining the boundary of the dust-free zone where the most refractory materials – likely moderately absorbing silicates – disappear.