H₃⁺ is a small but extraordinarily important ion in hydrogen-rich atmospheres. It forms when hydrogen molecules are ionized by energetic solar radiation or by particles accelerated within a planet’s magnetic environment. In Jupiter’s auroral regions, intense electron precipitation provides an especially efficient source of ionization. Once produced, H₃⁺ radiates strongly in the infrared, making it a valuable tracer of atmospheric temperature, energy deposition and ionospheric dynamics. Its emissions have long allowed researchers to study Jupiter’s polar atmosphere from afar, but those observations could not directly determine how much H₃⁺ was present at particular altitudes or whether it was moving away from the planet.

The new study changes that picture by detecting H₃⁺ plasma in situ, directly within the auroral region rather than through infrared light integrated along a distant line of sight. That distinction is crucial. Remote observations combine emissions from broad regions of the atmosphere, making it difficult to separate structures at different heights or to follow the motion of individual plasma populations. An in situ measurement can identify the ions themselves and determine how their density and velocity vary within the surrounding space plasma. The result is direct evidence that H₃⁺ exists as a mobile, dynamically important component of Jupiter’s polar environment.

The measurements also revealed intermittent bursts of H₃⁺ flowing upward from the ionosphere. These outflows reached velocities greater than Jupiter’s escape speed, meaning that at least part of the ion population possesses enough kinetic energy to overcome the planet’s powerful gravitational field. Rather than rising briefly and falling back into the atmosphere, these ions can be carried outward into the magnetosphere and, in the fastest events, escape Jupiter altogether. The finding identifies H₃⁺ as a previously overlooked vehicle for removing both mass and energy from the Jovian atmosphere.

The estimated loss rate is on the order of 10²⁶ H₃⁺ ions per second. In planetary terms, that is a substantial flow, even though H₃⁺ represents only a trace component of Jupiter’s overwhelmingly hydrogen-dominated atmosphere. The escape does not imply that Jupiter is rapidly losing its atmosphere or that the planet’s structure is threatened. Jupiter is enormously massive, and its atmospheric reservoir is vast. Instead, the result reveals a persistent form of coupling between the ionosphere and magnetosphere, in which a chemically distinctive ion can transport atmospheric material into the surrounding plasma environment.

The researchers propose that the outflow begins in regions associated with upward electric currents above the auroral ionosphere. Jupiter’s aurora is powered by the interaction between the planet’s rapidly rotating magnetic field, its magnetosphere and charged particles moving along magnetic field lines. In these regions, electromagnetic energy can be transferred into the upper atmosphere through particle precipitation, electric fields and plasma waves. Plasma-wave interactions may first disturb and energize H₃⁺ near the ionosphere. The ions can then be accelerated further by electric potential structures that develop above the atmosphere, producing the observed high-speed outflows.

This mechanism illustrates why H₃⁺ is more than an infrared thermometer. As a molecular ion, it participates in the chemistry and electrical conductivity of the upper atmosphere. The abundance and distribution of H₃⁺ influence how easily electric currents can flow through the ionosphere, while the currents themselves help shape the electric fields that govern charged-particle motion. In this way, H₃⁺ may form part of a feedback system: auroral energy creates the ions, the ions alter ionospheric conductance, and the resulting electrodynamic environment helps regulate their transport into the magnetosphere.

The discovery also helps resolve a long-standing observational problem in planetary science. Jupiter’s auroral emissions are among the brightest and most complex in the Solar System, but infrared brightness alone cannot reveal the complete three-dimensional structure of the plasma above the clouds. A bright signal may represent dense plasma, high temperature, enhanced excitation or a combination of these factors. Direct detection of escaping H₃⁺ provides a physical link between the remote-sensing signatures and the actual movement of atmospheric ions. It gives researchers a way to test models of auroral heating, ionospheric conductivity and atmospheric escape against measurements made in the plasma itself.

Jupiter may not be unique. Other planets and moons with hydrogen-rich atmospheres, strong magnetic fields and infrared aurorae could host related processes. The same general chain—ion production, wave-driven energization, electric acceleration and eventual escape—could operate wherever auroral currents connect an atmosphere to a powerful magnetosphere. The new result therefore extends beyond a single planet. It suggests that molecular ions can serve as active messengers between atmospheric chemistry and space plasma physics, carrying energy and material from a planetary ionosphere into its magnetospheric surroundings. For Jupiter, the aurora is now shown to be not only a spectacular light display, but also an engine of atmospheric escape.

Subject of Research: Direct in situ detection and atmospheric escape of trihydrogen cations (H₃⁺) from Jupiter’s polar auroral regions.

Article Title: Ionospheric escape of H₃⁺ from Jupiter’s polar regions

Article References: Wang, Jz., Bagenal, F., Szalay, J.R. et al. Ionospheric escape of H₃⁺ from Jupiter’s polar regions. Nature Astronomy (2026). https://doi.org/10.1038/s41550-026-02950-2

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41550-026-02950-2

Keywords: Jupiter, H₃⁺, trihydrogen cations, aurora, atmospheric escape, ionosphere, magnetosphere, plasma physics, planetary science, space weather

The search for atmospheres on rocky planets has been notoriously difficult. While gas giants often show clear spectral fingerprints, habitable-zone super-Earths produce extremely subtle signals. Even with powerful observatories such as NASA’s James Webb Space Telescope, previous observations frequently suggested airless or weakly buffered worlds, leaving open the key question of whether they can hold onto atmospheres long enough to be habitable.

Red dwarf stars offer a practical advantage: their small size makes planetary transits more detectable. By measuring periodic dips in starlight as a planet passes in front of its host star, researchers can perform transmission spectroscopy—splitting the starlight into a spectrum and reading which atmospheric constituents absorb particular wavelengths. In this study, the team targeted a more accessible atmospheric layer by searching for helium in the upper atmosphere.

LHS 1140 b orbits an older, cool red dwarf every 24.7 days. With a mass about 5.6 times Earth’s and a radius roughly 1.7 Earth radii, the planet is consistent with a rocky composition. It receives about 42% of the radiation Earth gets from the Sun, placing it in a temperature range where liquid water could exist, though the presence of an Earth-like surface remains unknown.

Using the WINERED spectrograph on the Magellan Clay telescope at Las Campanas Observatory in Chile, the researchers observed the planet in 2024 and detected spectral evidence of helium escaping from its atmosphere. The result indicates an active gaseous envelope, challenging assumptions that many rocky habitable-zone planets rapidly lose volatiles.

The data show that heating from stellar X-rays and extreme ultraviolet radiation likely drives the escape. In 2025, however, the team found no escaping helium, implying the atmospheric outflow is variable rather than constant. This short-timescale change provides rare real-time evidence that an exoplanet’s atmosphere can evolve quickly under changing stellar forcing.

By combining the observations with models of exoplanet evolution, the team interpreted the atmosphere as highly layered: a helium-dominated, hydrogen-poor upper region, with heavier species such as water trapped at lower altitudes nearer the surface. Such stratification helps explain both the detectability of helium and the lack of signals from deeper atmospheric layers.

The group also examined a second planet in the same system, LHS 1140 c, which is smaller and more strongly irradiated. No atmospheric evidence was found there, suggesting the planets may lie on opposite sides of the “cosmic shoreline,” where some worlds retain atmospheres for billions of years while others lose them quickly.

The study was conducted by scientists across Harvard and Carnegie, including Shreyas Vissapragada, Collin Cherubim, and multiple Carnegie co-authors, and involved prior observations and advanced interpretation. Together, these results strengthen the case that at least some rocky habitable-zone exoplanets can maintain atmospheres—and that helium escape spectroscopy can reveal them.

Subject of Research:
Not applicable

Article Title:
Helium escaping from the atmosphere of a nearby rocky exoplanet orbiting in a habitable zone

News Publication Date:
16-Jul-2026

Web References:
http://dx.doi.org/10.1126/science.aea9708

References:
10.1126/science.aea9708

Image Credits:
Melissa Weiss/Center for Astrophysics | Harvard & Smithsonian

Keywords

exoplanets; rocky worlds; habitable zone; atmospheric escape; helium; transmission spectroscopy; red dwarf stars; LHS 1140 b; WINERED; James Webb Space Telescope