J/AJ/160/238ivo://CDS.VizieR/J/AJ/160/238doi:10.26093/cds/vizier.51600238CDSMayorga L.C.Charbonneau D.Thorngren D.P.2023-12-20T08:20:32Z2021-02-10T07:48:22ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frsolar-systemsolar-system-planetsphotometryvisible-astronomyFor terrestrial exoplanets with thin or no atmospheres, the surface contributes light to the reflected light signal of the planet. Measurement of the variety of disk-integrated brightnesses of bodies in the solar system and the variation with illumination and wavelength is essential for both planning imaging observations of directly imaged exoplanets and interpreting the eventual data sets. Here we measure the change in brightness of the Galilean satellites as a function of planetocentric longitude, illumination phase angle, and wavelength. The data span a range of wavelengths from 400 to 950nm and predominantly phase angles from 0{deg} to 25{deg}, with some constraining observations near 60{deg}-140{deg}. Despite the similarity in size and density between the moons, surface inhomogeneities result in significant changes in the disk-integrated reflectivity with planetocentric longitude and phase angle. We find that these changes are sufficient to determine the rotational periods of the moon. We also find that at low phase angles, the surface can produce reflectivity variations of 8%-36%, and the limited high phase angle observations suggest variations will have proportionally larger amplitudes at higher phase angles. Additionally, all of the Galilean satellites are darker than predicted by an idealized Lambertian model at the phases most likely to be observed by direct imaging missions. If Earth-sized exoplanets have surfaces similar to that of the Galilean moons, we find that future direct imaging missions will need to achieve precisions of less than 0.1ppb. Should the necessary precision be achieved, future exoplanet observations could exploit similar observation schemes to deduce surface variations, determine rotation periods, and potentially infer surface composition.2020AJ....160..238Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/160/238CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+A/532/A36 : Galilean satellites mutual events in 2009 (Zhang, 2011)J/A+A/572/A43 : Saturnian satellites Cassini ISS astrometry (Cooper+, 2014)J/A+A/575/A73 : Astrometry of Saturnian satellites 2004-12 (Tajeddine+, 2015)J/A+A/580/A76 : Positions of satellites of giant planets (Gomes-Junior+, 2015)J/A+A/582/A8 : Astrometry of the main satellites of Uranus (Camargo+, 2015)J/other/SoSyR/49.383 : Galilean satellites, Jupiter position (Narizhnaya, 2015)J/AJ/153/147 : The orbits of Jupiter's irregular satellites (Brozovic+, 2017)J/other/KFNT/33.70 : Topocentric positions Saturn moons (Yizhakevych+, 2017)J/A+A/610/A2 : Saturnian satellites Cassini ISS astrometry (Cooper+, 2018)J/other/SoSyR/53.368 : Observations of the Galilean moons (Narizhnaya+, 2019)J/AJ/159/129 : 21 saturnian small moons brightness with ISS (Hedman+, 2020)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/160/238https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/160/238http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/160/238https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/160/238https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/160/238http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/160/238GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/AJ/160/238/table3Tabulated reflectivity as a function of moon, filter, phase angle, and planetocentric longitudeImageImage nameobs.imagecharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMoonGalilean Satellite identification; Callisto, Europa, Ganymede and Iometa.id;meta.maincharFiltCassini/ISS Filter (1)meta.note;instr.filtercharPA[1.02/141] Phase angledegsrc.orbitaldoubleLON[-180/180] Planetocentric Longitudedegpos.earth.londoubleIF[0.0003/0.75] Reflectivity (2)phys.albedodouble