A glow in Jupiter’s night could be the signal for dark matter

Somewhere, somewhere in the universe, there is a lot of matter that we have not yet been able to find.

And it’s not a trivial amount, either. About 70 to 80 percent of all mass is thought to be the mysterious stuff known as dark matter. Normal matter is the minority. That’s all we can detect — all the stars, planets, black holes, dust, gas, moons, people.

So where is all this dark matter? Well, we don’t know. But there are ways we can detect it, and one of them is right here in the solar system.

On Jupiter’s nightside, an infrared glow high in the atmosphere could be produced by an interaction with this shadowy material.

There, charged hydrogen ions called trihydrogen cations (H₃⁺) are found in abundance. And while there are several cosmic processes that can produce H₃⁺ In Jupiter’s atmosphere, an interaction with dark matter could produce an excess beyond what we would expect.

‘We point out that dark matter is an additional source of H₃⁺ in planetary atmospheres,” write physicists Carlos Blanco of Princeton University and Stockholm University, and Rebecca Leane of the Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory and Stanford University.

“This occurs when dark matter is scattered and captured by planets, and then annihilates, producing ionizing radiation.”

Although we can’t detect dark matter directly, and although it doesn’t seem to interact with normal matter in ways that we can detect indirectly, there is one way in which it does manifest itself. Objects in the universe appear to move as if they were under the influence of much more gravity than is produced by normal matter.

Once we subtract the normal matter contribution, the remaining gravity is attributed to dark matter. This way we know something is there and we can measure how much of it is there.

There are many different theoretical candidates for what dark matter might be. Many of these candidates have properties that can be detected in different ways.

One idea is that dark matter self-destructs. When two dark matter particles collide, they sweep each other away, producing a small burst of heat or light or both.

Blanco and Leane propose that this destruction could occur high in the atmosphere of planets, in the layer known as the ionosphere. The dark matter particles are captured by the planet’s gravity and sucked into the ionosphere, where they risk mutual destruction.

Jupiter would be the best place to look for this process, the researchers reasoned. It is the largest non-solar body in the solar system, with a relatively cool core, so it would be the most efficient dark matter trapper locally available.

When Saturn’s Cassini spacecraft flew by Jupiter more than two decades ago, it was equipped with an instrument called the Visual and Infrared Mapping Spectrometer (VIMS), which might have detected the signature of the supposed annihilation of dark matter.

Now, it’s not the little cloud of radiation from the destruction itself that we would expect, but the product of it. That radiation could be ionizing—that is, it knocks electrons loose from atoms in the ionosphere. This results in positively charged H₃⁺whose infrared glow was detectable by VIMS.

The problem is that there are many ionizing processes going on in the solar system. Solar radiation can be ionizing. Jupiter has huge, powerful auroras at its poles that H₃⁺also. So Blanco and Leane looked at measurements of Jupiter’s equatorial region at night, for three hours either side of Jupiter’s midnight, where the influence of the aurora is minimal and no sunlight can disturb the ionosphere.

While there is no excess H₃⁺ was detected, the results allowed researchers to place constraints on how this particular type of dark matter should behave, providing crucial information for the detection of dark matter on other planets outside the solar system.

“We have shown for the first time that dark matter can produce ionizing radiation in planetary atmospheres, which can be detected via an irrefutable excess of atmospheric trihydrogen cations,” Blanco and Leane write.

‘Atmospheric ionization of dark matter could be detected in Jupiter-like exoplanets using future high-precision measurements of planetary spectra.’

The research was published in Physical Assessment Letters.