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Neptune's radius is almost four times larger than Earth's, its surface has super intense storms, and we barely know anything else about it. It is time to send another orbiter out there.

Host: Caitlin Hofmeister

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Neptune is probably the most underrated planet in the solar system. I mean it’s almost four times larger than Earth, has super intense storms, and in a lot of ways, we barely know anything about it. We’ve only visited the planet once, when Voyager 2 did a flyby back in 1989, and because it’s too far to clearly see with telescopes, it’s still shrouded in mystery.

Like, scientists can tell us exactly what elements are chilling in some ancient lakebed on Mars, but they can’t tell us why Neptune is so blue. To figure this stuff out, we’d need to send an orbiter there, and there’s a pretty compelling case for why we should. And here are four big mysteries it could help solve.

If Neptune is famous for anything, it’s for being strikingly blue. Like Uranus, it gets its color from the little bit of methane in its atmosphere, which reflects the blue wavelengths of light coming from the Sun. Except, that’s not the whole story.

Neptune is actually too blue to be colored by methane alone. Uranus even has more methane in its atmosphere than Neptune does, about 2.3% compared to 1.5%. But it’s a much lighter color.

So, this suggests that there’s another component to Neptune’s atmosphere we don’t know about. But since the planet is so far away, it’s hard to take the measurements we need with telescopes. A new orbiter, with better instruments than we had during the Voyager 2 flyby, would almost definitely be able to figure it out, no problem.

Neptune has an extremely strong magnetic field, almost 30 times more powerful than Earth’s. It’s also misaligned. Compared to the axis the planet rotates on, its magnetic field is tilted about 47°, and we’re not sure why.

Uranus has the same problem, but they’re the only planets in the solar system that do. According to a 2004 study in the journal Nature, which was based on computer models, the tilt could happen if Neptune’s interior is different from most of the other planets. Specifically, if it has a liquid core instead of a solid one like Earth’s.

Solid cores don’t allow magnetic field lines to fluctuate as much, so if Neptune doesn’t have one, its field lines could get all tangled up and, ultimately, misaligned. But there’s also plenty of evidence that Neptune actually does have a solid core. And other, more recent models suggest that the magnetic field issues might really be caused by a special type of conductive hydrogen close to the planet’s surface.

We can keep building models and collecting data from Earth, but paying Neptune another visit would help pin down some real answers to our questions. Since Neptune is the farthest planet from the Sun, you’d think it would be the coldest … but it’s not. That honor actually goes to Uranus, where the temperature around its cloud tops is about -220°C.

Meanwhile, at Neptune, the temperatures are closer to -210°. Admittedly, that’s not a huge difference. But considering Neptune is around one and a half times as far from the Sun as Uranus, or more than 1.5 billion kilometers farther, it’s strange that the planet wouldn’t be colder.

When you combine that with infrared measurements taken by Voyager 2, which suggested the planet is radiating heat, it looks like something is warming Neptune’s interior. We just don’t know what it is. Over the years, papers have suggested it’s being heated by its moon Triton, which could pull on the planet and generate heat from friction.

And a 2017 paper in Nature Astronomy suggested the heat could be come from sinking diamonds, of all things. That idea says the pressure is so high inside Neptune that carbon atoms get compressed into diamonds. Then, as those heavy minerals sink toward the planet’s core, they generate friction that causes things to heat up.

And while that would be awesome, it’s hard to know for sure unless we take more measurements up close. Finally, Jupiter’s Great Red Spot might get credit as the most famous storm in the solar system, but Neptune has a pretty cool one, too. Or at least, it used to.

When Voyager 2 showed up in 1989, it took photos of the so-called Great Dark Spot. It was a huge, swirling storm roughly the size of Earth, and it had winds up to 2400 kilometers per hour or so. Except, when we observed Neptune again in the 1990s, this time using the Hubble Space Telescope, it had disappeared.

We weren’t able to confirm any new storms of that magnitude on Neptune until 2016, when Hubble spotted another one in its southern hemisphere. But there’s still not much we can do from Earth to study it. Since Neptune is so far, it’s difficult to observe these storms, let alone get data on them.

And Hubble also has lots of other things to study, so it’s not like we can train it on Neptune 24/7. So far, the most we can say is that storms on Neptune aren’t very consistent. They show up in different parts of the planet, drift in different ways, and come in all kinds of shapes and sizes.

With an orbiter, we’d be able to get much more detailed data, like how Juno can study Jupiter’s storms up close. But without one, we’ll just have to keep admiring these blurry features from a distance. Thanks to advances in telescopes, there’s a lot we can learn about other planets from Earth.

But when it comes to something as far as Neptune, detailed observations become really difficult. Our current telescopes won’t cut it, so to solve these mysteries, we’re just going to have to pay the planet another visit. All we need now is an orbiter.

So if you happen to have a rocket and a functional spacecraft at hand leave us a comment. Or maybe just call NASA. Or you could email NASA, but if you do, do it on a Virtual Private Network with NordVPN.

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