Galaxy, Universe

A Strange Waltz Around A Blue Ice Giant

Within the dark darkness of the outer Solar System, odd events happen. Four gigantic planets in this faraway region entice observers on Earth with their terrifying treasure trove of delightful, shocking, strange, and wildly wonderful mysteries. The banded, majestic, and blue ice giant Neptune is both our Sun’s most distant alien planet and the smallest outer gaseous universe quartet. Yet also by the outer Solar System ‘s strange norms, in this crowd of weird balls, certain oddities stick out. The strange waltz of avoidance performed by the innermost duo of Neptune’s icy moons is such an outstanding oddity. Astronomers revealed in November 2019 that the tiny Neptunian moons, Naiad and Thalassa, are in orbits taking them just about 1,150 miles from each other — but the two moons can not get near enough to move.

Orbital dynamics experts refer to this strange performance as a “dance of avoidance” The two little moons are close to each other but still manage to stay far enough away to avoid a close encounter. This is because the orbit of Naiad is tilted, and timed perfectly. Each time the slower-moving Thalassa passes this little moon, the duo is about 2,200 miles apart.

Naiad twirls around his parent-planet every seven hours while this unusual dance of the moons is being done. Meanwhile, it takes seven and a half hours for Thalassa to dance along the outside road. If an Earthling stands on Thalassa and gazed up in awe at his mysterious alien moon, it would appear that the orbit of Naiad forms a peculiar and crazy zigzag pattern — passing from above twice and then from below again. This very unusual performance happens frequently when Naiad acquires four loops on his wife Thalassa.

While this distant dance may seem weird, it serves a definite purpose. This keeps the little moons’ orbits stable.

“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 was never seen before,” Dr. Marina Brozovic commented in a press release from the NASA Jet Propulsion Laboratory (JPL) on November 14, 2019. Dr. Brozovic is the lead author of the paper that outlines this study, released in the Icarus journal on 13 November 2019.

In The Distant Domain Of The Giant Planets

The planets themselves are the primary causes of gravity in the vast realms of the quartet of giant planets, miles from our Star’s strong grasp. The gaseous quartet jointly boasts myriads of predominantly ice moons, and several of those moons were born at the same time as their parent-planet — never moving away from their birthplace. By contrast, some of the other moons were later snared in the history of their planet and then locked into orbits controlled by their parent-planets. Many of such planets circle in the direction of movement of their world, while others swap paths with each other as though to prevent a disastrous smash-up.

Jupiter, Jupiter, Uranus, and Neptune are the four major planets in the Outer Solar System. Neptune and Uranus are all ice-giants, while Jupiter and Saturn are gas giants. The two ice giants are blanketed by dense gaseous atmospheres which are much thinner than the ones held by the much larger gas-giant pair, though. Uranus and Neptune also contain larger solid cores than Jupiter and Saturn, and both are smaller in size than the huge gas giants.

Neptune was discovered by Galileo Galilei (1564-1642) on 28 December 1612. Galileo used his simplistic “spyglass,” one of the first astronomical-purpose telescopes, to explore the outermost known giant planet in our Solar System. On 27 January 1613, he observed Neptune again for the second time. Perhaps Galileo mistook this alien universe on all times for a fixed star similar to the planet Jupiter. Galileo is generally not associated with Neptune’s detection regardless of this tragic instance of historical mistaken identification.

NASA’s Voyager 2 spacecraft whizzed by the much larger greenish-blue ice mass, Uranus, in 1989, bringing back to Earth some fascinating Neptune pictures that showed a stunning blue-banded planet of sapphires. Neptune ‘s early photographs often revealed spot-like whirling storms hauntingly close to Earth’s hurricanes. The lines and bands of Neptune are different colors of gray, which were created as a consequence of ambient methane — not oxygen. Many of the hurricanes in Neptune look like light blowing marshmallows.

Voyager 2 was also the first spacecraft to detect the Great Dark Spot at Neptune back in 1989. The Great Dark Spot was an anti-cyclonic storm extending 19,000 x 6,000 kilometers, and astronomers on Earth immediately noticed the similarity between this distant Neptunian storm and the Great Red Spot of Jupiter. Several years later, though, on 2 November 1994, the Hubble Space Telescope (HST) could not find the Great Dark Spot — which seemingly had disappeared. Instead, in the northern hemisphere of Neptune, HST encountered a new earthquake, which was quite close to the Great Dark Area.

Neptune itself is not apparent to the unassisted human eye, so it is the only planet in our Solar System to have been found by statistical inference rather than actual observation. Unanticipated changes in Uranus ‘orbit led French astronomer Alexis Bouvard (1767-1843) to mathematically determine that the gravitational jostling of an undiscovered planet influenced Uranus’ orbit. As a result, the German astronomer Johann Galle (1812-1911) discovered Neptune with a telescope on 23 September 1846. Not long after the discovery of Neptune, its greatest moon, Triton, has been discovered. There was no telescopic observation of any of the few identified planets on the earth until the 20th century.

The distance from our planet by Neptune makes it appear small in Earth’s sky, making it difficult for astronomers to observe it with Earth-based telescopes. The HST space telescope, together with large telescopes on the ground, recently provided a treasure trove of detailed observations from far away, using the adaptive optics technique. Adaptive optics is a technique that corrects temperature, water, and mechanical stress distortions by deforming a mirror to account for the distortion.

Like the other giant gaseous planets that dwell in the outer solar system, Neptune has many moons and a gossamer ring system. Neptune ‘s rings are fragmented and very slender and are called arcs. The arcs were first observed in 1982 and later verified by the spacecraft Voyager 2.

Neptune possesses 14 known moons. Neso is its parent planet’s farthest Neptunian object, and its orbit forms a curious elliptical path that brings it to 46 million miles from Neptune. It takes 27 years for Neso to enter one orbit.

A Bizarre Celestial Waltz

Naiad and Thalassa are very small moon-worlds of “Tic Tacs” shape. Both tiny bodies have a range of just around 60 miles. As two of the seven inner moons of Neptune, Naiad and Thalassa are members of a heavily populated system intermingled intricately with Neptune’s faint arc rings.

How winded up this strange duo so close yet so far apart? Astronomers suggest that when Neptune ‘s powerful gravitational pull snatched its large moon, Triton, the original moon system was disrupted. The consequence was the formation of the inner moons and rings from the fragments of debris left in the aftermath of this ancient calamity.

Triton orbits Pluto the wrong direction. Typically this means an entity observed that was not raised at its present location. Triton may be a disgruntled wanderer from the Kuiper belt who migrated too nearly to the gravitational grasp of Neptune and thereby becoming a satellite of one of the main planets in our solar system. The Kuiper belt is an area outside Neptune that hosts a varied size population of ice bodies and is considered home to frozen comet nuclei. Triton ‘s orbit is expected to fall in the future to the extent that it plunges into its parent-planet adopted.

“We believe that an earlier encounter with one of Neptune’s other inner moons pushed Naiad into its inclined orbit. Only afterward, after its orbital inclination was identified, could Naiad settle into this peculiar resonance with Thalassa,” Dr. Brozovic clarified in the November 14, 2019, JPL Press Release.

Dr. Brozovic and her colleagues found the unusual orbital chaos by studying HST observations. Their work also gives the first indication of the internal composition of the inner moons of Neptune. The scientists used the measurements to measure their mass, and thereby assess their densities — which have been discovered to be close to water ice.

Dr. Mark Showalter, a planetary astronomer at the SETI Institute in Mountain View, California, and the co-author of the study told the press that “Naiad and Thalassa were presumably stuck together in this arrangement for a very long time, as it allows their orbits more secure.

The Sky at Night – Ice Giants