Each of Jupiter 's four great satellites reaches its sunny side in January . That 's rare ; it has happened only twice in the last 100 years . Jupiter 's images are primarily for aesthetic purposes , a gift to the world .
Three of Jupiter 's four great moons crossed its sunny side in January . That 's rare ; it has happened only twice in the last 15 years . Hubble 's images are primarily for aesthetic purposes , a gift to the public .