Some interesting science from the New York Times.

A recent image taken by the Hubble Space Telescope of the planet Neptune, whose tally of moons has been upped to 14 in a new paper.

An image made by the Hubble Space Telescope in 2004, showing Neptune and some of its moons — including Hippocamp — at right. Hippocamp is also shown enlarged in the inset image top right.

Neptune Has a Newly Discovered Moon. What Else Is It Hiding?

There is much more to learn about the solar system’s eighth planet, which hasn’t been visited by a spacecraft for 30 years.

By Shannon Hall
Feb. 20, 2019

It’s time to add one more tiny moon to Neptune’s icy family tree. Astronomers using the Hubble Space Telescope have spied a previously undetected satellite around the solar system’s eighth planet, bringing its total number to 14.

The discovery, formally reported Wednesday in Nature, is a stark reminder that there is much more to be found in our own backyard, with implications for our understanding of worlds around other stars in our galaxy.

“I think people have the impression that we know everything there is to know about the moons of Jupiter, the moons of Saturn, the moons of Uranus and the moons of Neptune — but we don’t really,” said Anne Verbiscer, a planetary scientist at the University of Virginia, who was not involved in the recent discovery. “We haven’t found everything.”

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That’s especially true for Uranus and Neptune, which are known as the ice giants. While every other planet in our solar system has been poked and prodded by multiple spacecraft, these two remain largely unexplored. Voyager 2 did swing past Neptune 30 years ago — shooting images that revealed rings, six new moons and its dynamic blue globe. But the spacecraft was moving too fast and was limited by technology designed in the 1970s.

“What this paper shows is that you couldn’t learn everything with that one flyby,” said Heidi Hammel, a planetary astronomer and executive vice president at the Association of Universities for Research in Astronomy (AURA) in Washington, D.C., who was not involved in the study.

Mark Showalter, a researcher at the SETI Institute in Mountain View, Calif., did not set out to make this discovery. He was analyzing Neptune’s rings with a new technique to process old images that essentially twisted them while adding them together. That allowed him to better see the rings, which are both faint and quick-moving.

On a whim, he decided to apply that same technique to other parts of the image he produced. To his surprise, a tiny white dot appeared.

Further analyses have confirmed that it is a moon, and a rather odd one.

It’s both tiny (at roughly 20 miles in diameter, it’s nearly the north-to-south distance of Long Island) and its fast orbit may be a little tooclose to a larger moon called Proteus. Dr. Showalter’s team suspects that the new moon likely formed billions of years ago when an icy body from the outer solar system smashed into Proteus — tossing debris into orbit that later coalesced to form the small moon, which they named Hippocamp after a sea creature in Greek mythology.

“We’re basically seeing a chip off of Proteus itself,” Dr. Showalter said.

The findings highlight the challenges in making discoveries in the years since the Voyager flyby. “Uranus and Neptune have been neglected in the history of space exploration,” Dr. Showalter said. “There’s a big hole in our understanding of the outer solar system.”

When Voyager 2 zipped past Neptune in 1989, it revealed a dynamic world with winds that whip and churn through its atmosphere at speeds as high as 1,500 miles per hour. Its blue atmosphere was also marked by a dark blemish nicknamed the Great Dark Spot. And while it was reminiscent of Jupiter’s Red Spot, which has remained intact for hundreds of years, Neptune’s spot vanished roughly five years later. In the years since, other blemishes have come and gone — each a mystery.

As are Neptune’s rings and moons. From Earth, the rings appear to clump together into partial rings, or arcs, unseen elsewhere in the solar system and previously thought impossible (any such material in orbit around the planet should stretch into a continuous ring). But Neptune’s arcs persist and astronomers can’t say why.

And Neptune’s largest moon, Triton, is an oddity in more ways than one. It hosts geysers that hurtle nitrogen gas five miles into the atmosphere, and might be linked to a subsurface ocean. Its surface is constantly being remodeled, which hints at active geology. And Triton might not even be a native to Neptune at all — but a refugee from the Kuiper belt (that distant field of frozen fossils that is home to Pluto and the recently visited Ultima Thule).

Only a closer look could explain these mysteries.

Studying Neptune and Uranus could also have implications for our understanding of thousands of worlds detected in orbit around distant stars. Data from the Kepler Space Telescope suggests that ice giants might be the most common type of planet in the galaxy.

“It’s kind of ironic — the Neptune-like exoplanets are far more common than the Jupiter-like exoplanets, yet we’ve studied Jupiter here in our own solar system far more intensively than we have either Uranus or Neptune,” Dr. Verbiscer said.

Astronomers, however, think the tide is turning. In a survey produced every 10 years by an expert committee that ranks funding priorities for NASA, a mission to the ice giants was ranked third after missions that would return samples from Mars and visit Jupiter’s moon Europa. Given that scientists have made headway on the first two, a mission to these blue orbs might have good prospects in the near future.

“I’m hoping that it might be time to turn toward this gap in our knowledge and fill it in,” Dr. Hammel said.