The Hubble Space Telescope observed three Jovian moons orbiting across Jupiter’s surface in a photograph captured on Jan. 24, 2015. On Thursday, NASA released the images to the public indicating that such an event is a rare occurrence. The three moons observed in the photograph(s) are Europa, Io and Callisto.

The rare satellite transit occurs only once or twice in a decade, according to NASA. Europa has received attention lately due to the White House’s 2016 fiscal year budget proposals. The budget proposals included funding for NASA wherein a portion of the space agency’s total budget will be allocated toward anticipated missions to Europa. The fuss over budget allocations and subsequent missions to the Jovian moon is primarily due to the fact that Europa has a vast potential for scientific discoveries, according to sources.

Exobiologists have been interested with Europa because of its potential for harboring microorganisms in the moon’s subsurface layer. The suspected ocean of liquid water that may exist beneath the subsurface layer might act as a substrate wherein potential microorganisms could exist, according to sources. The implications of scientific discoveries that may or may not be found on Europa affect NASA’s finalized budget allocation. Finalization of the 2016 fiscal year budget will occur in Oct. 2015.

Aside from budget allocations, the famous Europa and, the perhaps lesser known, Io and Callisto are seen in NASA’s Hubble image. The image was captured in a 42-minute time span wherein the famous telescope fired off a series of snapshots. The images of the snapshots revealed the three Jovian moons celestially-walking across Jupiter. In addition, the moons’ shadows are seen to be casted across the surface. The Hubble image was taken by the telescope’s Wide Field Camera 3 (WFC3) in visible-light conditions.

The aforementioned Jovian moons are more commonly referred to as ‘Galilean’ moons. The term Galilean is attributed to the moons because of their discoverer, Galileo Galilei, whom observed of their existence in the 17th century. There are four Galilean moons in total, missing from the Hubble photograph is Ganymede which was not in view at the time of the photo. Coincidently, the Galilean moons represent the largest of the 16 total satellites orbiting Jupiter.

Trivial as it may seem, the occurrence of three moons photographed in one shot represents Hubble’s dynamic usage and diverse capabilities. For example, last Jan. Hubble photographed the largest, most-detailed, high-defintion panoramic ever captured of the Milky Way’s galactic neighbor, Andromeda (M31). The panoramic of the Andromeda galaxy was able to resolve over 100 million stars, whose distance from Earth is over two million light-years away. For perspective, this is the equivalent of photographing an entire beach and being able to resolve individual grains of sand, according to NASA.