Jupiter’s atmosphere offers an indirect way to study faint cosmic gamma rays

Jupiter could offer astronomers an indirect way to study a faint background of high-energy radiation. Instead of measuring that radiation across the whole sky, researchers can look for photons scattered by the planet’s atmosphere. A new analysis tests this approach using archival observations, but finds no statistically significant emission from Jupiter.

Dimitris Tsatsis and colleagues describe the work in the preprint arXiv:2611.09488v1, submitted on 6 November 2026. Its arXiv record states that the paper has been accepted by Astronomy & Astrophysics.

Why look at Jupiter?

The cosmic gamma-ray background is radiation arriving from sources spread across the universe. At energies around a million electronvolts, or MeV, it is difficult to measure: radiation generated within a telescope and its spacecraft can overwhelm the faint celestial signal.

Jupiter offers a different observational target. Some incoming photons scatter in its atmosphere and escape toward an observer. Cosmic rays—energetic particles such as protons and electrons—can also strike the atmosphere and generate secondary photons. Together, these processes create what researchers call gamma-ray albedo: high-energy radiation emerging from an irradiated body.

The planet is not a simple mirror. Atmospheric interactions change the photons’ energies, so interpreting any signal requires a model of what enters the atmosphere and what escapes.

Following a moving target

The team searched 22 years of observations from SPI, the spectrometer aboard the INTEGRAL satellite. Most observations targeted other objects; Jupiter happened to fall within the instrument’s field of view.

After excluding regions around the Galactic centre and anticentre, where bright sources complicate the search, the researchers retained 1,527 telescope pointings. These provided 4.08 million seconds of observing time—about 47 days, accumulated across the archive rather than a continuous watch.

For each pointing, they calculated Jupiter’s position and the instrument’s response at that location. They also corrected for the changing Earth–Jupiter distance, because an otherwise identical source appears fainter when farther away. Their analysis fitted Jupiter’s possible contribution alongside instrumental background and other celestial sources. Recovering a spectrum consistent with previous measurements of the quasar 3C 273 provided a useful check, although it does not eliminate every possible systematic error.

Simulating the atmosphere

The researchers built a spherical atmospheric model extending 1,000 kilometres into Jupiter, divided into shells one kilometre thick. Its density and composition were based on Galileo probe measurements, with hydrogen and helium providing the main ingredients.

They then used Monte Carlo simulations: computer calculations that track many individual particles through interactions governed by physical probabilities. The simulations followed incoming photons, protons, electrons, positrons and alpha particles, recording the photons that escaped.

These calculations produced a mapping between incoming particle energy and outgoing photon energy. The team applied that mapping to proposed cosmic-background and cosmic-ray spectra, then passed the predicted emission through the telescope’s response. This allowed them to compare physical models with the observations rather than treating Jupiter as an unchanged reflection of the sky.

What the limits mean

Across 30 kiloelectronvolts to 8 MeV, the measured emission was consistent with zero within uncertainties. The team therefore reported two-sigma upper limits: statistical bounds on how bright a signal could be while remaining compatible with the data under their analysis assumptions. They are not measurements of zero emission.

The predicted reflected cosmic background is roughly 10,000 times fainter than the corresponding limit. The cosmic-ray-induced model could be scaled up by about 240 before reaching its limit. Thus, the observations do not yet test the expected brightness of either component closely.

A separate model gives an upper bound of roughly 10^18 ergs per second on Jupiter’s MeV bremsstrahlung luminosity—radiation emitted as energetic electrons slow down. This is a model-dependent ceiling, not a measured planetary power output.

Remaining uncertainties

The interpretation depends on assumed incident particle spectra and an atmospheric model. Instrumental background remains a major obstacle, and excluding crowded sky regions sacrifices exposure to reduce confusion.

The authors also combine SPI results with earlier Fermi-LAT data to constrain a particular dark-matter scenario involving particles that escape Jupiter before decaying. Those constraints are conditional: low-mass dark matter could escape Jupiter before annihilating, weakening the predicted signal.

Future instruments such as COSI, and analyses of additional Solar System bodies, could improve the prospects. For now, the work supplies a method and sensitivity benchmark—not a detection of reflected cosmic gamma rays or evidence for dark matter.