Six hundred retrograde jovian irregular moons discovered around Jupiter; the gas giant is a "solar system" of its own.
Of all the planets in the solar system, Jupiter is one of my favorites.
Not just because of its behemoth size and the fact that it technically doesn’t orbit the sun, but because it is a planet that I’ve had the opportunity to observe up-close through my telescope, seeing with my own eyes what a beautiful planet the gas giant is.
I’ve also had the opportunity to photograph Jupiter and some of its largest moons a few months ago. It is a striking experience, and I can’t wait to observe it again.
The Gas Giant is our solar system’s largest planet. Many astronomers refer to it as the protector of our solar system, mostly because a plethora of space debris from the outer parts of the solar system crash into it, which means that Jupiter protects the inner planets of the solar system from potentially catastrophic asteroids and comet impacts.
Jupiter, a solar system of its own
In its journey through the solar system, Jupiter is not alone. The confirmed number of Jovian moons has grown to 79 in recent years, which means that there are many moons around Jupiter we’ve clearly not been able to observe.
While 79 new moons may sound a pretty huge number for ONE planet, a new study says there may be 600 small irregular moons orbiting Jupiter. This is mindboggling and begs to question of how many more unseen moons exist in the solar system beyond the orbit of Mars?
But did we directly observe and photograph the moons? Not entirely. Astronomers pored over 2010 archival data from the Canada-France-Hawaii Telescope. They looked for a small area of the sky in that data, about one-degree square, and found four dozen small, irregular moons were constantly circling the gas giant. Based on that, they extrapolated the number of small moons that should be orbiting Jupiter, which comes just at over 600.
It is noteworthy to explain a few things. These moons vary in size, and there are two categories; irregular and regular.
Regular moons are formed by accumulating material, in the same way, that planets do, and irregular moons are captured objects. In this study, the researchers found a large number of small irregular moons, objects captured by the powerful gravity of Jupiter.
For example, the moons of Mars, Phobos, and Deimos are considered irregular moons because they are believed to have been “captured” by the red planet in the distant past.
Earth’s Moon, on the other hand, is a regular moon because it actually formed there.
But for years have astronomers speculated that there are many more moons around Jupiter.
Back in 2017, astronomers published a study announcing the discovery of 12 irregular moons orbiting Jupiter. Before this new research, the number of known Jovian irregulars was 71.
Scientists have speculated for years that Jupiter has an undiscovered population of smaller moons. Some astronomers have said that the great giants have the same number of satellites, despite the differences in their masses. It’s just that they’re hard to see; some are too far away, too dark, or obscured by other cosmic bodies, which makes them especially hard to observe directly.
How the moons were found
To make the discovery, The Canada France Hawaii Telescope on Mauna Kea played a central role. The telescope has a powerful digital camera called the MegaCam, making the job so much easier for astronomers.
The so-called MegaCam is a 340-megapixel wide-field imager that sees in the optical and near-infrared, allowing astronomers to explore the solar system in an unprecedented way. In the study, astronomers focused on 60 exposures of 140 seconds each of a region near Jupiter.
Astronomers found 52 objects in their images that they identified as irregular moons. The objects had magnitudes up to 25.7, which corresponds to objects with diameters of about 800 meters.
Of those 52, seven of the brightest were known irregular moons. While those seven are prograde moons, the other 45 are most likely retrograde moons, which means that they orbit in the opposite direction to Jupiter’s direction of rotation.
Unlike Jupiter’s largest moons, such as Io, Europa, and Ganymede, many even host primitive forms of life–the irregular moons did not form by accretion. Instead, these objects were likely once independent objects traveling through the solar system and were captured by the gravity of Jupiter.
This is fascinating because it also tells us that planets such as Saturn, Neptune, and Uranus could still hide many of their moons from us.
In the future, more powerful telescopes and missions to the outer planets of the solar system could help reveal and confirm many moons and astronomical objects of interest.
Until then, Ad Astra.
Reference: Europlanet Science Congress 2020 Sky and Telescope
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