Why are Neptune’s moons dancing around each other?

The “Moon dance” of the inner satellites of the eighth planet enables them to avoid a collision

Faisal Khan
Jan 3 · 3 min read

We have come a long way in our understanding of the solar system and the Universe in the past couple of decades. The rate of discovery has picked up phenomenally with better technology to confirm our observations. Be it exoplanets, black holes, Interstellar objects, strange phenomena or Saturn becoming the “Moon King” with the discovery of 20 new moons recently. Saturn now has 82 satellites around its orbit — surpassing Jupiter’s 79.

The inner two gas giants of Jupiter & Saturn and their moons steal the limelight when it comes to studying them in detail, but that is going to change with better techniques and innovative technology being used to explore the outer reaches of the solar system. NASA researchers have recently reported a strange phenomenon taking place around two of the inner moons of Neptune.

A little hindsight first. William Lassell, an English amateur astronomer spotted the biggest moon of Neptune, Triton on Oct. 10, 1846 — just 17 days after a Berlin observatory discovered its parent planet. Astronomers since then have confirmed a total of 14 satellites orbiting Neptune. The second-largest moon Proteus & five other inner moons were only discovered when Voyager made a trip to Neptune in 1989 since they are so dark and orbit so close to the planet.

Triton is not only the largest moon of Neptune, but it is also one of the coldest objects in our solar system with a surface temperature of about -400 degrees Fahrenheit (-240 degrees Celsius). The other bizarre thing is the frosty plumes shooting up from its icy volcanoes. To top all of this, Triton is the only moon in our solar system that circles its planet in a retrograde orbit — opposite to the planet’s rotation.

“ We refer to this repeating pattern as a resonance. There are many different types of ‘dances’ that planets, moons, and asteroids can follow, but this one has never been seen before.” ~ Researcher Marina Brozovic

Naiad and Thalassa are two of the seven inner moons of the giant planet — measuring only about 60 miles (100 kilometers) in length. While it takes Neso (farthest moon of Neptune) 27 years to complete the elliptical orbit of 46 million miles (74 million kilometers) around the planet, the former two do so in a matter of hours. Goes to show the strong gravitational pull being exerted by these giant planets.

The unprecedented “dance of avoidance” by Naiad and Thalassa, in the meanwhile, has intrigued the researchers. The two satellites are orbiting the planet at only about 1,150 miles (1,850 kilometers) apart. This is not much of distance in planetary terms but even then they have managed to move in perfect harmony without colliding.

Naiad’s orbit is tilted and every time it passes the slower-moving Thalassa, the two are about 2,200 miles (3,540 kilometers) apart. Somebody sitting on Thalassa can see Naiad pass by in a zigzag pattern — twice from above & twice from below. This results in the latter gaining four laps on the former as both rotate around the planet in seven & seven and a half hours respectively.

The data from NASA’s Hubble Space Telescope also provided other valuable insights into the internal composition of the icy giant’s inner moons like calculating their masses & densities.

Detailed Research was published in the Journal Icarus.


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Faisal Khan

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Content Specialist in Cryptocurrencies | Blockchain | Financial Markets | Technology | Future | Science | Space

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