What To Know
- Although modest in size, with an axis of only 250 kilometres long and a narrowest point of 128 km, Amalthea fascinates scientists because of its irregular shape and intriguing composition.
- Juno’s recent observation, made during the 59th close flyby of Jupiter, revealed Amalthea as a small black dot moving through the giant planet’s dark red cloud belts, then transiting the Great Red Spot The perspective of Juno, which flies past Jupiter every 53 Earth days, offers an impressive view of this rare event, highlighting the incredible scale of the Great Red Spot, an anticyclonic storm spanning 12,500 km.
- In fact, this moon is considered to be the reddest body in the solar systemalthough the origin of this color remains a mystery.
NASA’s Juno spacecraft recently captured a rare and fascinating view of Jupiter’s fifth moon, Amalthea, transiting the giant planet’s Great Red Spot. The observation offers astronomers a unique opportunity to study this small, often overlooked natural satellite more closely amid its famous Galilean siblings.
A very discreet moon
Discovered in 1892 by American astronomer Edward Emerson Barnard, Amalthea currently ranks fifth in size among the 95 known moons of Jupiter. It also has the distinction of having the third shortest orbit of any of the planet’s moons, orbiting it every 0.5 Earth days, putting it on an inward trajectory relative to Io’s volcanic orbit. Although its magnitude is relatively small (+14), its proximity to Jupiter makes it difficult to detect. Barnard’s initial discovery is therefore a testament to his expertise and tenacity. Although modest in size, with an axis of only 250 kilometres long and a narrowest point of 128 km, Amalthea fascinates scientists because of its irregular shape and intriguing composition. Each observation thus offers a unique opportunity to unravel its mysteries and better understand it. Juno’s recent observation, made during the 59th close flyby of Jupiter, revealed Amalthea as a small black dot moving through the giant planet’s dark red cloud belts, then transiting the Great Red Spot The perspective of Juno, which flies past Jupiter every 53 Earth days, offers an impressive view of this rare event, highlighting the incredible scale of the Great Red Spot, an anticyclonic storm spanning 12,500 km.
Amalthea seen in two images of Jupiter captured by NASA’s Juno spacecraft on March 7, 2024. Credits: NASA/JPL-Caltech/SwRI/MSSS. Image processing by Gerald Eichstäd
Still many questions
Previous observations by space probes like Voyager 1, Voyager 2, and Galileo have revealed several intriguing features of Amalthea, including bright spots and craters on its surface, as well as a unique reddish coloration. In fact, this moon is considered to be the reddest body in the solar systemalthough the origin of this color remains a mystery. Another enigma surrounding Amalthea concerns its production of additional heat compared to what it receives from the Sun. Several theories have been proposed to explain this phenomenon, including the influence of Jupiter’s radiation and magnetic field, as well as tidal stresses and induced electrical currents in its core. These complex mechanisms add to the charm and appeal of this small, often overlooked moon. In short, Juno’s observation of Amalthea provides a valuable opportunity to deepen our understanding of this intriguing little moon and its interaction with Jupiter’s dynamic environment. While the famous Galilean satellites (Io, Euroe, Ganymede and Callisto) often capture attention, Amalthea reminds us that even the most modest of moons can harbor fascinating mysteries and deserve to be studied closely.
