Dark Matter detection in Jupiter

 

Although our findings consistently indicate that Dark Matter (DM) exceeds normal matter by a ratio of five to one throughout the cosmos, we remain uncertain about its composition due to the absence of direct detection. Based on our views of the cosmos, it is evident that dark matter must engage with gravity, as it lacks any interaction with light, meaning it does not emit, reflect, or absorb light. Furthermore, due to their exclusive interaction through gravitational forces, the probability of their colliding with each other is highly improbable. The mass and interaction properties of the enigmatic Dark Matter particle remain unknown, posing challenges in its detection and exploration. Particle physicists have constructed expansive subterranean Dark Matter detectors such as LUX (The Large Underground Xenon experiment) with the aim of detecting Dark Matter particles when they interact with other particles.

According to a recent study, Jupiter has the potential to serve as a means of detecting Dark Matter. The recent publication by Blanco and Leane (2024) aimed to identify the trihydrogen cation, also known as H3 plus, has garnered significant attention. A hydrogen atom consists of a positively charged proton located in its centre, with a negatively charged electron orbiting around it. Trihydrogen, also known as H3+, is a molecule consisting of three hydrogen atoms bound together in a triangular configuration. However, the term "cation" indicates that this molecule carries a positive charge. This implies that one of the electrons is absent. Trihydrogen consists of three protons that are bound together, sharing just two electrons. This trihydrogen cation is quite prevalent across the entire cosmos.

 

The trihydrogen cation has remarkable stability under conditions of low temperatures and low density. Molecular hydrogen (H2) in the interstellar medium is highly stable and serves as the building block for star formation. However, when a high-energy event such as a cosmic ray from a supernova collides with a hydrogen molecule, it can ionise the molecule by removing one of its electrons, resulting in the formation of a dihydrogen cation.

The dihydrogen cation is likely in close proximity to another H₂ molecule, with which it undergoes a reaction to generate the trihydrogen cation, also known as protonated molecular hydrogen.

It is not only cosmic rays that can initiate this response.  Any process that involves high energy, such as the emission of extreme ultraviolet light from stars, lightning in a planet's atmosphere, or the release and subsequent acceleration of high energy electrons by a star's magnetic field towards a planet's poles (like aurora), is more probable to generate trihydrogen cation in a planet's atmosphere. The abundance of trihydrogen cations in the atmospheres of gas giants has been thoroughly investigated due to their emission of infrared light. By analysing the detected infrared light, we can accurately determine the quantity of trihydrogen cations present in the atmosphere of a certain planet. Blanco and Leane proposed an alternative mechanism for the formation of trihydrogen cations in the atmosphere of a gas giant. If two dark matter particles were to collide within a planet's atmosphere and undergo annihilation, a substantial amount of energy would be released. This energy would be sufficient to ionise H2 molecules, which would then react with another H2 molecule to form trihydrogen cations. The question at hand is how to distinguish between trihydrogen cations produced by Aurora and those resulting from potential Dark Matter Annihilation. Blanco and Leane argued that by directing our search to the appropriate location, we can find a large number of trihydrogen cations on Jupiter. These cations are mostly generated by high-energy particles that create the Aurora phenomenon. Due to the influence of Jupiter's magnetic field, these cations tend to accumulate towards the planet's poles. Additionally, a significant number of trihydrogen cations will be generated by intense ultraviolet radiation emitted by the sun, and these cations will be concentrated exclusively on the illuminated side of Jupiter.  The authors suggest observing trihydrogen cations in the nocturnal hemisphere of Jupiter, notably in the equatorial regions facing away from the Sun. Discovering a signal would indicate that the process of dark matter Annihilation is capable of generating sufficient energy to form detectable trihydrogen cations at those specific latitudes on Jupiter. As of yet, we are unaware of any alternative sources that may account for their presence in that location.

An inherent challenge in observing Jupiter's night side is its perpetual orientation away from the Sun. Whenever we observe Jupiter using a telescope, we are specifically observing its illuminated side, known as the day side, which is directly exposed to sunlight.  In December 2000, the Cassini spacecraft was equipped with the necessary tools to detect the infrared light emitted by trihydrogen cations during its flyby of Jupiter. The data was gathered in the wavelength range of around 3 to 5 microns. A comprehensive investigation on the emission from trihydrogen cations was published by Stallard et al., in 2015. They observed the absence of infrared emission from trihydrogen cations on the nocturnal hemisphere of Jupiter at close proximity to the equator. Can this lack of detection provide any insights into the nature of Dark Matter? Blanco and Leane argue that a limited quantity of trihydrogen cations would result in insufficient light emission, rendering it too dim for Cassini to detect.  Cassini's instruments possess a high level of sensitivity, enabling them to determine the maximum amount of trihydrogen cations that might potentially emit light but remain too dim for detection by Cassini. By establishing this threshold, one can calculate the amount of energy required to generate a specific number of trihydrogen cations. This information can then be correlated with the models to determine the energy emitted by the annihilation of dark matter particles. The energy output is contingent upon the mass of the dark matter particle.

 

The Annihilation process is dependent upon the cross section, which provides information on the probability of collision between two dark matter particles resulting in their annihilation. By determining the maximum number of undetected trihydrogen cations, we can establish constraints on both the mass and cross-section of a dark matter particle.  The following diagram illustrates the displayed information.

 

 The absence of detection in the Cassini data suggests that the dark region in the graph should be excluded from consideration. Due to the ambiguous nature of their boundaries, the shaded region in yellow is one that they are relatively confused about. In a study conducted by Stallard and colleagues (2015), it was discovered that the dark side of Jupiter did not show any indications of trihydrogen cations. Blanco and Leanne emphasised that it provides valuable insights into the characteristics of dark matter, which will aid particle physicists in narrowing down their search to ultimately uncover the true nature of dark matter.

 

References

Blanco, C. and Leane, R.K., 2024. Search for Dark Matter Ionization on the Night Side of Jupiter with Cassini. Physical Review Letters, 132(26), p.261002.

Stallard, T.S., Melin, H., Miller, S., Badman, S.V., Baines, K.H., Brown, R.H., Blake, J.S., O'Donoghue, J., Johnson, R.E., Bools, B. and Pilkington, N.M., 2015. Cassini VIMS observations of H₃⁺ emission on the nightside of Jupiter. Journal of Geophysical Research: Space Physics, 120(8), pp.6948-6973.