First Analysis of Jupiter in Gamma Rays and a New Search for Dark Matter

We present the first dedicated $\gamma$-ray analysis of Jupiter, using 12 years of data from the Fermi Telescope. We find no robust evidence of $\gamma$-ray emission, and set upper limits of $\sim {10}^{-9}\mathrm{GeV}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ on the Jovian $\gamma$-ray flux. We point out that Jupiter is an advantageous dark matter (DM) target due to its large surface area (compared with other solar system planets), and cool core temperature (compared with the Sun). These properties allow Jupiter to both capture and retain lighter DM, providing a complementary probe of sub-GeV DM. We therefore identify and perform a new search for DM-sourced $\gamma$-rays in Jupiter, where DM annihilates to long-lived particles, which can escape the Jovian surface and decay into $\gamma$ rays. We consequently constrain DM-proton scattering cross sections as low as about ${10}^{-40}{\mathrm{cm}}^2$, showing Jupiter is up to 10 orders of magnitude more sensitive than direct detection. This sensitivity is reached under the assumption that the mediator decay length is sufficient to escape Jupiter, and the equilibrium between DM capture and annihilation; sensitivities can be lower depending on the DM model. Our work motivates follow-up studies with upcoming MeV telescopes such as AMEGO and e-ASTROGAM.

Figure 1

Schematic of DM annihilation to long-lived particles in Jupiter. The long-lived particles can decay outside the Jovian surface, producing a new source of $\gamma$ rays.

Figure 2

Fermi-LAT $\gamma$-ray data utilized in our analysis. For the visualization of this figure, we combine all energy bins between 1–3.16 GeV, and smear all results with a 1° Gaussian, choices that are not made in the analysis of our data. Left: Counts map produced by all events recorded within 45° of the position of Jupiter. Middle: The background map, which is produced from observations of events calculated by examining identical regions in $\mathrm{RA}/\mathrm{DEC}$ when Jupiter is not present. Right: The residual calculated by subtracting the model from our data.

Figure 3

The $\gamma$-ray flux from Jupiter obtained in our analysis. The blue horizontal line depicts no $\gamma$-ray flux. The significant energy dispersion (especially at low energies) makes the flux in nearby energy bins highly correlated. Through most of the energy range, we find no evidence for Jovian $\gamma$-ray emission. In the inset (green region), we enlarge to show the bright emission in the lowest energy bins.

Figure 4

95% C.L. DM-proton scattering cross section limits as a function of DM mass $m_{\chi }$, arising from DM annihilation to long-lived particles, from our new Jovian $\gamma$-ray search. We show complementary constraints from direct detection [60, 61, 62, 63], as well as DM annihilation to long-lived particles in the Sun [44, 46], and brown dwarfs in the Galactic Center [32].