Image credit: NASA
In 1846, when European astronomers debated what to name a newly discovered eighth planet, they finally settled on Neptune, in honor of the Roman god of the sea. The name turned out to be perfect, because Neptune, as we know in much better detail now, is colored a deep ocean blue, with specks of white and deeper blues playing through its clouds.
Along with Uranus, astronomers classify Neptune as an “ice giant,” a large world, four times the diameter of Earth, with a thick atmosphere of mostly hydrogen and helium along with some water, ammonia, and other substances.
If Uranus appears to be far away 1.76 billion miles from the Sun, Neptune is another billion miles away about 30 times farther from the Sun than Earth. Studying Neptune is, as one might imagine, very difficult.
“Neptune is on the edge of our detection capabilities with ground-based telescopes, and so is [the] [space telescope] Hubble,” said Heidi Hammel, executive vice president of the Association of Universities for Research in Astronomy AURA, a nonprofit organization. based in Washington, DC
The only close-up look we’ve had of Neptune was in 1989, courtesy of a Voyager 2 flyby. The spacecraft’s investigation uncovered many enduring mysteries, including:
A hyperactive atmosphere
Astronomers expected Neptune to look rather dull as a featureless, weatherless world in deep freeze. Instead, Voyager revealed a turbulent atmosphere with lighter cloud ripples and raging storms, including a so-called Great Dark Spot. Surprisingly, the fastest winds ever recorded in the solar system rotates at Neptune, around 1,300 miles or 2,100 kilometers per hour.
The engine of this meteorological activity appears to be Neptune’s internal heat, which is possibly hotter than Uranus. “As you move away from the sun, Jupiter, Saturn and Uranus are getting colder in their upper atmosphere,” Hammel said. “But when you get to Neptune, it’s as hot as Uranus.” In relative terms, of course, both planets cool in the range of -355 degrees Fahrenheit -215 degrees Celsius.
Typical sources of planetary heat, including internal heat left over from the formation and decay of radioactive elements, could possibly explain Neptune’s temperature. Maybe Neptune is normal and Uranus is the weirdo. “It could be that Uranus is unusually cold,” Hammel said.
Neptune, like its sister giant planets Jupiter, Saturn, and Uranus, has a ring system. But instead of distinct hula hoop-shaped structures, Neptune’s rings are puzzling and thick, with chunks of material arcing around the outer ring. “These clumps are places where a lot of ring particles are stuck together.” Hammel said.
The gravitational influences of small moons can cause regular gumming of the rings. But observations by Hammel and his colleagues over the years show that this mechanism seems too orderly. “The locations of the arches relative to each other have changed in ways that I really don’t understand,” Hammel said.
When Voyager 2 detected a strange magnetic field on Uranus, scientists calculated that any collision that had struck that planet sideways had similarly altered its magnetic field production. However, when Voyager 2 measured Neptune’s field, it also originated in a region far from the heart of the world, and it also did not align with planetary rotation as other described magnetic fields do.
“No one expected these magnetic fields to drift off the center of the planet and tilt at these crazy angles,” Hammel said.
The best theory, Hammel said, is that the magnetic field is not generated in Neptune’s core like it is on Earth, Jupiter, and other planets. Rather, the field emanates from an electrically conductive layer between the core and the surface in a “blanket of salt water,” Hammel speculated, under extreme pressure and unlike any water here on Earth.
Of Neptune’s 13 moons, Triton is by far the largest and the only one massive enough to be spheroidal. Interestingly, Triton has a “retrograde” orbit, rotating in the opposite direction of the planet and other moons. Also, the orbit is at an angle rather than in the plane around the equator like typical satellites.
These features suggest that Triton did not form around Neptune. Instead, the planet’s gravity likely captured the rogue Triton, an icy, rocky body that passed the Kuiper Belt, a band of bodies that includes Pluto beyond the realm of Neptune. “The main theory is this capture.hypothesis,” said Candice Hansen, senior scientist at the Institute for Planetary Sciences in Tucson, Arizona.
When Voyager 2 passed over Neptune, Hansen was available to view the first images, including those of Triton, which turned out to have geyser-like eruptions on its surface. “We were surprised to see those active columns,” Hansen said. The Little Mysteries of Life.
What fuels those columns isn’t Triton’s only mystery. Its young surface is not as completely cratered as one might expect, which points to the geological activity that obliterated the first craters. Triton also has an intriguing and unique terrain textured like a melon.