NASA telescope detects higher-frequency X-rays from Jupiter

According to the new study, the answer to Ulysses' nondetection mystery lies in the mechanism that produces the high-energy X-rays.

New observations by NASA's Nuclear Spectroscopic Telescope Array have revealed that auroras near Jupiter's north and south poles emit high-energy X-rays. The light, in the form of X-rays that NuSTAR can detect, is also the highest-energy light ever detected from a solar system planet other than Earth, says a new study.

The new observations have helped scientists solve a decades-old mystery: Why did the Ulysses mission fail to detect X-rays when it flew past Jupiter in 1992? According to NASA, Ulysses was capable of sensing higher-energy X-rays than NuSTAR.

Our X-ray telescopes usually focus on the universe outside the @NASASolarSystem, but sometimes they make discoveries within it! 🛰️ NuSTAR recently observed the highest-energy light ever detected from Jupiter and helped solve a decades-old mystery: https://t.co/hL34uPOuj3 pic.twitter.com/FzCXQWe71s

— NASA Universe (@NASAUniverse) February 10, 2022

Auroras - stunning light shows in a planet's atmosphere - are produced when high-energy particles hit a planet's atmosphere near its magnetic poles. Jupiter grabs charged particles from its surroundings including those within the solar wind as well as the one thrown into space by its volcanically active moon Io. The planet's powerful magnetic field accelerates these particles and funnels them toward its poles, where they collide with its atmosphere and release energy in the form of light.

According to the new study, the answer to Ulysses' nondetection mystery lies in the mechanism that produces the high-energy X-rays. While there are multiple mechanisms that can cause particles to produce light, finding out which mechanism is responsible requires direct observation of the light that the particles emit.

The researchers developed a new model that includes something called bremsstrahlung emission - the culprit in this case. When speedy electrons meet charged atoms in Jupiter' atmosphere, they attract like magnets, causing the electrons to slow and lose energy in the form of high-energy X-rays.

Using established studies of bremsstrahlung light profiles, they showed that the X-rays should get significantly fainter at higher energies, including in Ulysses' detection range.

"If you did a simple extrapolation of the NuSTAR data, it would show you that Ulysses should have been able to detect X-rays at Jupiter. But we built a model that includes bremsstrahlung emission, and that model not only matches the NuSTAR observations, it shows us that at even higher energies, the X-rays would have been too faint for Ulysses to detect," explains Shifra Mandel, a Ph.D. student in astrophysics at Columbia University and a co-author of the new study.

Observing Jupiter's auroras would require an X-ray instrument close to the gas giant with greater sensitivity than those carried by Ulysses in the 1990s, the researchers concluded.

The findings are published in the journal Nature Astronomy. More information can be found here.