Astronomers Discover a Temperate Super-Earth in the Habitable Zone of a Red Dwarf Star Just 28 Light Years From Earth

Level 2 - Elementary

Italian and Brazilian astronomers have announced the discovery of a new exoplanet called Ross 318 b. The planet orbits a red dwarf star named Ross 318, located just 28 light years from Earth in the constellation Cetus.

Ross 318 b is classified as a temperate super-Earth. It has a minimum mass of about 6.2 times that of Earth and an estimated radius of about 1.74 times Earth's radius. It takes the planet 39.63 days to complete one orbit around its star.

The planet's surface temperature is estimated to be around minus 36 degrees Celsius. This places it within the conservative habitable zone of the star, which means it receives enough starlight that water could stay liquid on its surface if certain conditions are met.

The discovery was announced in May 2026. Astronomers used a technique called the radial velocity method, which detects the tiny wobble that a planet's gravity creates in its host star. Scientists are hoping that future telescopes will be able to study the planet's atmosphere.

exoplanet: a planet that orbits a star other than our own Sun, outside our solar system

radial velocity method: a technique for detecting exoplanets by measuring the tiny Doppler shift in a star's light caused by the planet pulling the star slightly back and forth

equilibrium temperature: the estimated surface temperature of a planet calculated from the amount of starlight it receives, not accounting for a greenhouse effect

constellation: a group of stars that forms a recognizable pattern in the night sky as seen from Earth

Kelvin: a scientific unit for measuring temperature where 0 Kelvin is absolute zero; 237 Kelvin equals about minus 36 degrees Celsius

conservative habitable zone: the most cautiously defined region around a star where scientists are confident that liquid water could exist on a rocky planet's surface

atmospheric characterization: the process of identifying the gases present in a planet's atmosphere, usually done by analyzing the starlight that passes through it

arXiv: an online database where scientists can share research papers before they are officially published in a peer-reviewed journal

Level 3 - Intermediate

Italian and Brazilian astronomers have reported the detection of Ross 318 b, a temperate super-Earth orbiting the nearby M3.5 spectral-type red dwarf Ross 318, also catalogued as Gliese 48, at a distance of approximately 28 light years. The discovery paper was posted to arXiv in May 2026, reporting a minimum mass of 6.21 Earth masses, an estimated radius of 1.74 Earth radii, and an orbital period of 39.63 days at a semi-major axis of 0.16 AU.

The planet's equilibrium temperature is calculated at 237 Kelvin, assuming a bond albedo comparable to Earth's. This places Ross 318 b within the conservative habitable zone defined by Kopparapu et al. (2013), where liquid water could stably exist on the surface under an Earth-like atmosphere. The planet receives approximately 58 percent of the stellar radiation that Earth receives from the Sun.

The host star Ross 318 is a slowly rotating, low-luminosity red dwarf with an effective temperature of 3,450 Kelvin and a rotation period of approximately 51.5 days. Red dwarfs are attractive targets for habitable-zone searches because their low luminosity moves the habitable zone close to the star, giving orbiting planets short orbital periods that produce strong enough Doppler signals to detect from the ground.

Future characterization looks promising. At 28 light years, Ross 318 is close enough that the Habitable Worlds Observatory, currently in the design phase for a 2040s launch, might be able to image the planet directly. The ESPRESSO spectrograph at the VLT and the NEID spectrograph at the WIYN 3.5-meter telescope have been identified by the discovery team as suitable for further Doppler monitoring. Atmospheric studies would require first detecting a transit of the planet across its star.

M3.5 spectral type: a classification for a mid-range red dwarf star, with an effective temperature around 3,400 to 3,600 Kelvin and much lower luminosity than the Sun

semi-major axis: the average distance between a planet and its host star, equal to half the longest diameter of an elliptical orbit

bond albedo: the fraction of total incoming solar or stellar radiation that a planet reflects back into space across all wavelengths, affecting its surface temperature

insolation: the amount of stellar radiation received by a planet's surface, typically compared to Earth's value as a ratio

Kopparapu habitable zone: a widely used scientific definition of the region around a star where liquid water could exist on a rocky planet's surface, based on 2013 calculations by Ravi Kumar Kopparapu

Doppler monitoring: repeated measurements of a star's radial velocity over time to track the gravitational effect of an orbiting planet

Habitable Worlds Observatory: a large space telescope under study by NASA, designed to directly image Earth-like planets around nearby stars in the 2040s

transit: the passage of a planet across the face of its host star as seen from Earth, which causes a measurable dimming of the star's light

Level 4 - Advanced

The detection of Ross 318 b via radial velocity monitoring adds a temperate super-Earth to a small but growing catalog of potentially habitable-zone planets within 30 light years of the Sun, alongside Proxima Centauri b, Wolf 1061 c, and GJ 667 Cc. The host star Ross 318 (Gliese 48, TIC 379084450) is an M3.5V flare star at 8.68 parsecs, with a V magnitude of 11.55 and a rotation period of 51.5 days, indicating relatively low stellar magnetic activity for a mid-M dwarf, which is favorable for habitable-zone searches because high flare frequency and elevated coronal X-ray flux can suppress atmospheric retention on close-in rocky planets.

The planet's reported parameters place it in the conservative habitable zone boundary described by Kopparapu et al. (2013): minimum mass M sin i = 6.21 Earth masses, orbital period P = 39.63 days, semi-major axis a = 0.16 AU, and equilibrium temperature T(eq) = 237 Kelvin at a bond albedo assumption of 0.30. The planet receives a stellar flux ratio of 0.58 relative to Earth, placing it well within the conservative limits. However, the unknown inclination introduces an M sin i ambiguity: if the true inclination is less than 30 degrees, the true mass could exceed 12 Earth masses, shifting the planet toward the mini-Neptune regime rather than the rocky-planet domain.

The discovery team employed HARPS archival radial velocity data from the La Silla 3.6-meter telescope combined with new CARMENES spectra from Calar Alto, constructing a 412-epoch baseline spanning 8.4 years. A Gaussian process regression was applied to suppress stellar activity signals with periods related to the 51.5-day rotation period and its harmonics, recovering the planetary signal at a false-alarm probability below 0.001 percent. The Bayesian information criterion marginally favors a one-planet model, though a mild periodogram excess near 22 days raises the possibility of a second short-period companion, to be addressed in a follow-up campaign.

The astrobiological interest of Ross 318 b is tempered by standard uncertainties attending M-dwarf habitable-zone candidates: synchronous or pseudo-synchronous rotation driven by tidal interaction could suppress habitability through atmospheric collapse on the permanent night side, though this outcome is contested for planets receiving greater than 0.5 stellar flux units; the absence of a confirmed transit geometry forecloses near-term atmospheric characterization by JWST or Ariel; and the unknown bulk composition prevents distinguishing a water world from a volatile-poor rocky planet. The Habitable Worlds Observatory, whose science requirements are being defined by Astro2020 decadal survey working groups, identifies 28-light-year proximity as near the inner boundary for coronagraphic direct imaging feasibility at a target signal-to-noise ratio of 15 in the visible band.

M3.5V flare star: a red dwarf of spectral subtype M3.5 that exhibits periodic magnetic eruptions producing brief, intense increases in ultraviolet and X-ray emission

M sin i: the minimum planetary mass measurable by radial velocity, equal to the true mass multiplied by the sine of the orbital inclination angle; the actual mass is always greater than or equal to this value

Gaussian process regression: a machine learning technique for modeling correlated noise in data, used in radial velocity analysis to separate stellar magnetic activity signals from planetary Doppler signatures

false-alarm probability: the statistical likelihood that a detected radial velocity signal is a random noise artifact rather than a genuine planetary orbit

tidal locking: a gravitational phenomenon in which a body's rotation period synchronizes with its orbital period, causing one hemisphere to permanently face its host star

coronagraphic direct imaging: a telescopic technique using a mask to block central starlight so that the much fainter reflected light from nearby planets can be captured directly

Bayesian information criterion: a statistical measure used to compare models with different numbers of free parameters, penalizing added complexity to prevent overfitting observational data

mini-Neptune regime: a class of planets with masses between roughly 5 and 20 Earth masses that are expected to retain thick hydrogen and helium envelopes, making them unlikely to have clement surface conditions

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Astronomers Discover a Temperate Super-Earth in the Habitable Zone of a Red Dwarf Star Just 28 Light Years From Earth

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