Kepler-90h

Lore & Background

Kepler-90h is a gas giant with no solid surface, with an equilibrium temperature of 292 K. It is around 0.64 times as massive and around 1.01 times as large as Jupiter, making it very similar to Jupiter in terms of mass and radius. It orbits its host star about every 331.6 days at a distance of 1.01 astronomical units, very similar to Earth's orbital distance from the Sun. The planet resides in the circumstellar habitable zone of its parent star, but with a radius of 1.01 times Jupiter's, it is too large to be rocky, and because of this the planet itself may not be habitable. Hypothetically, large enough moons, with a sufficient atmosphere and pressure, may be able to support liquid water and potentially life. For a stable orbit, the ratio between the moon's orbital period around its primary and that of the primary around its star must be less than 1/9; simulations suggest that a moon with an orbital period less than about 45 to 60 days will remain safely bound to a massive giant planet or brown dwarf that orbits 1 AU from a Sun-like star. In the case of Kepler-90h, this would be practically the same to have a stable orbit. Tidal effects could also allow the moon to sustain plate tectonics, which would cause volcanic activity to regulate the moon's temperature and create a geodynamo effect that would give the satellite a strong magnetic field. To support an Earth-like atmosphere for about 4.6 billion years, the moon would have to have a Mars-like density and at least a mass of 0.07 Earth masses. One way to decrease loss from sputtering is for the moon to have a strong magnetic field that can deflect stellar wind and radiation belts; NASA's Galileo measurements hint that large moons can have magnetic fields, as Jupiter's moon Ganymede has its own magnetosphere even though its mass is only 0.025 Earth masses.

Reader's Guide

Kepler-90h is notable as the outermost of eight planets discovered by NASA's Kepler spacecraft in the Kepler-90 system, which is one of the most compact multi-planet systems known. Its discovery, announced on November 12, 2013, was based on transit observations taken between 13 May 2009 and 17 March 2012. The planet's orbital period of roughly 331 days and its distance of 1.01 AU place it within the habitable zone of its host star, a region where liquid water could exist on a suitable surface. Although Kepler-90h itself is a gas giant and not habitable, its position in the habitable zone raises the possibility that large moons orbiting it could potentially support life if they have sufficient atmosphere, pressure, and a magnetic field. The star Kepler-90 is an F-type star, 1.2 times as massive and 1.2 times as large as the Sun, with an estimated age of 2 billion years and a surface temperature of 6080 K. The star's apparent magnitude is 14, too dim to be seen with the naked eye. The Kepler-90 system provides a valuable comparison to the inner solar system, as illustrated by an artist's concept showing the system's layout alongside the inner solar system.

Did You Know?

• Kepler-90h is the outermost of eight planets in the Kepler-90 system.
• Its equilibrium temperature is 292 K, similar to Earth's average temperature.
• The planet orbits its star at 1.01 AU, nearly the same distance as Earth orbits the Sun.
• Hypothetically, large moons around Kepler-90h could support liquid water if they have a sufficient atmosphere and magnetic field.

Place in the Kepler Mission Catalogue

Kepler-90h occupies a position within the dedicated catalogue of planets identified by the Kepler space telescope, one of several specialized registries maintained for exoplanet research. This particular list sits alongside companion catalogues for the K2 mission and the TESS mission, reflecting the layered history of space-based transit detection that has shaped our growing inventory of worlds beyond the Solar System. The existence of separate Kepler and K2 lists underscores how the spacecraft's operational phases produced distinct cohorts of discoveries, each requiring its own tracking. For a planet bearing the Kepler designation, its entry in this mission-specific registry signals that its detection relied on the photometric transit method as executed by that particular instrument, distinguishing it from worlds found through radial velocity surveys, direct imaging, or other techniques. The catalogue structure also means that Kepler-90h is cross-referenced with broader thematic lists, ensuring researchers can locate it whether they are searching by discovery method, by system architecture, or by physical characteristics.

Membership in a Multiplanetary System

The designation Kepler-90h encodes a critical piece of structural information: the letter suffix indicates this is one component of a larger planetary family, and as such it belongs to the curated registry of multiplanetary systems. That list gathers every confirmed arrangement of two or more worlds orbiting a single star, and Kepler-90h's presence there signals that its host star is not a solitary planet host but the gravitational anchor for a collection of orbiting bodies. This multiplanetary context matters because the dynamics, formation history, and long-term stability of each member are shaped by the presence of its siblings. In the broader taxonomy of exoplanet research, multiplanetary systems are tracked separately from single-planet detections precisely because they offer richer constraints on planetary formation models. The catalogue also includes specialized sub-lists for circumbinary planets and for planetary debris around giant stars and white dwarfs, illustrating the diversity of multi-body configurations that researchers now recognize. Kepler-90h's slot within its parent system thus connects it to a wider conversation about how planetary architectures assemble and evolve.

Position in the Discovery Timeline

The year-by-year breakdown of confirmed exoplanet discoveries provides the temporal backdrop against which Kepler-90h's confirmation must be understood. The annual tallies reveal a highly uneven rhythm: some years, such as 2014 with 869 entries and 2016 with 1498, saw massive influxes of new worlds, while others like 2017 (152) or 2015 (144) registered far fewer. These fluctuations reflect the cadence of survey data releases, the time required for independent confirmation, and the shifting emphasis between different detection techniques. Kepler-90h's placement within this sequence means it arrived during a period when the exoplanet inventory was already substantial, and its addition contributed to the steady growth visible across the full span from the 31 planets known before 2000 to the 238 confirmed in 2025 and the 283 already logged for 2026. The existence of a dedicated annual list for each year, stretching back to the pre-2000 era, shows that the field has maintained continuous record-keeping, and each new entry—regardless of how many others appear in the same year—represents a discrete addition to humanity's catalogue of distant worlds.

Classification and the Broader Taxonomy

Within the exoplanet catalogue, Kepler-90h is subject to a web of thematic classifications that go far beyond a simple name-and-number entry. Researchers maintain dedicated lists for the hottest and coldest worlds, the largest and smallest, transiting planets, and those with proper names, among many others. Additional specialized registries track extrasolar candidates for liquid water, terrestrial exoplanet candidates suitable for atmosphere detection, and potentially habitable worlds. There are also lists for exoplanets and planetary debris orbiting giant stars and white dwarfs, as well as a registry of extrasolar planetary collisions. A critical technical note applies to any planet whose mass was derived solely from radial velocity measurements: the listed value represents only a lower limit, not the true mass, a distinction that affects how such planets are compared across the catalogue. For Kepler-90h, which entered the inventory through the Kepler space telescope's photometric programme, its classification is anchored in transit-based detection, yet it remains eligible for inclusion in any thematic list where its measured or inferred properties qualify. This multi-axis filing system ensures that no single property defines the planet's research relevance.