Astronomical specifications:
| Discovery | 1610 by Galileo |
| Orbital characteristics: | |
| Distance from Jupiter | 421,600 km |
| Perihelion | (106 km) |
| Aphelion | (106 km) |
| Inclination | deg |
| Eccentricity | 0.0041 |
| Orbital periode round Jupiter | 1.769 days |
| Orbital speed | 17.34 km/s |
| Inclination to Sun equator | 0.04 deg |
| Rings | No |
| Physical characteristics: | |
| Radius | 1,815 km |
| Surface area | 41,910,000 km² |
| Volume | 2.53 x 1010 km³ |
| Mass | 8.94 x 1022 kg |
| Density | 3.528 g/cm³ |
| Equatorial gravity | 1.796 m/s² |
| Escape velocity | 2.56 km/s |
| Rotation period | 1.769 days |
| Axial tilt | 0 deg |
| Surface temperature | 130 K |
| Atmospheric composition | SO2 |
Galileo spacecraft acquired its highest resolution images of Jupiter's moon Io on 3 July 1999