Exploring formation scenarios for the exomoon candidate Kepler 1625b I

ABSTRACT If confirmed, the Neptune-size exomoon candidate in the Kepler 1625 system will be the first natural satellite outside our Solar system. Its characteristics are nothing alike we know for a satellite. Kepler 1625b I is expected to be as massive as Neptune and to orbit at 40 planetary radii around a ten Jupiter mass planet. Because of its mass and wide orbit, this satellite was first thought to be captured instead of formed in situ. In this work, we investigated the possibility of an in situ formation of this exomoon candidate. To do so, we performed N-body simulations to reproduce the late phases of satellite formation and use a massive circumplanetary disc to explain the mass of this satellite. Our setups started soon after the gaseous nebula dissipation, when the satellite embryos are already formed. Also for selected exomoon systems, we take into account a post-formation tidal evolution. We found that in situ formation is viable to explain the origin of Kepler 1625b I, even when different values for the star–planet separation are considered. We show that for different star–planet separations the minimum amount of solids needed in the circumplanetary disc to form such a satellite varies, the wider is this separation more material is needed. In our simulations of satellite formation, many satellites were formed close to the planet, this scenario changed after the tidal evolution of the systems. We concluded that if the Kepler1625 b satellite system was formed in situ, tidal evolution was an important mechanism to sculpt its final architecture.

Selection of compression test images using variance-based statistical method

In this research paper, we used a variance-based statistical method to select 20 test images, according to these latter types (natural, satellite and medical) among a sample of 300 images (100 natural, 100 satellite and 100 medical). The images selection has been done using parameters of image quality, namely PSNR, MSSIM and VIF, which were applied on three compression algorithms (DWT+SPIHT, JPEG, and JPEG2000).

The Caviar software package for the astrometric reduction of Cassini ISS images: description and examples

Aims. Caviar is a software package designed for the astrometric measurement of natural satellite positions in images taken using the Imaging Science Subsystem (ISS) of the Cassini spacecraft. Aspects of the structure, functionality, and use of the software are described, and examples are provided. The integrity of the software is demonstrated by generating new measurements of the positions of selected major satellites of Saturn, 2013–2016, along with their observed minus computed (O−C) residuals relative to published ephemerides. Methods. Satellite positions were estimated by fitting a model to the imaged limbs of the target satellites. Corrections to the nominal spacecraft pointing were computed using background star positions based on the UCAC5 and Tycho2 star catalogues. UCAC5 is currently used in preference to Gaia-DR1 because of the availability of proper motion information in UCAC5. Results. The Caviar package is available for free download. A total of 256 new astrometric observations of the Saturnian moons Mimas (44), Tethys (58), Dione (55), Rhea (33), Iapetus (63), and Hyperion (3) have been made, in addition to opportunistic detections of Pandora (20), Enceladus (4), Janus (2), and Helene (5), giving an overall total of 287 new detections. Mean observed-minus-computed residuals for the main moons relative to the JPL SAT375 ephemeris were − 0.66 ± 1.30 pixels in the line direction and 0.05 ± 1.47 pixels in the sample direction. Mean residuals relative to the IMCCE NOE-6-2015-MAIN-coorb2 ephemeris were −0.34 ± 0.91 pixels in the line direction and 0.15 ± 1.65 pixels in the sample direction. The reduced astrometric data are provided in the form of satellite positions for each image. The reference star positions are included in order to allow reprocessing at some later date using improved star catalogues, such as later releases of Gaia, without the need to re-estimate the imaged star positions.

Effects of the Moon on the Earth in the Past, Present and Future

The Moon has fascinated human civilization for millennia. Exploration of the lunar surface played a pioneering role in space exploration, epitomizing the heights to which modern science could bring mankind. In the decades since then, human interest in the Moon has dwindled. Despite this fact, the Moon continues to affect the Earth in ways that seldom receive adequate recognition. This paper examines the ways in which our natural satellite is responsible for the tides, and also produces a stabilizing effect on Earth’s rotational axis. In addition, phenomena such as lunar phases, eclipses and lunar libration will be explained. While investigating the Moon’s effects on the Earth in the past and present, it is hoped that human interest in it will be revitalized as it continues to shape life on our blue planet.