TOI-1846b

A Super-Earth in the Radius Valley

A fascinating water-rich world, 154 light-years away, challenging our understanding of how planets are born and evolve.

Found by a Flicker of Starlight

TOI-1846b was first detected as a "TESS Object of Interest" (TOI) by NASA's Transiting Exoplanet Survey Satellite (TESS). In March 2025, TESS recorded faint, periodic dips in the brightness of the star TOI-1846, the tell-tale sign of a planet passing in front of it—a method known as transit photometry.

The discovery, led by Abderahmane Soubkiou from Morocco's Oukaimeden Observatory, was confirmed through a global effort involving ground-based telescopes. These follow-up observations validated the planet's existence and helped pin down its characteristics.

Artist's impression of a water-rich super-Earth with a steamy atmosphere

A World of Extremes

Classified as a super-Earth, TOI-1846b is larger than Earth but smaller than gas giants like Neptune. Its density suggests a composition rich in water, which, given the planet's scorching temperatures, likely exists as high-pressure ice or a supercritical vapor in a dense, steamy atmosphere.

TOI-1846b Planetary Data
Radius	1.79 Earth Radii
Mass	~4.4 Earth Masses
Density	4.2 g/cm³
Orbital Period	3.93 Days
Equilibrium Temperature	~568 K (~295°C / 563°F)
Distance from Star	0.036 AU (Very Close)

Artist's concept of TRAPPIST-1 system with red dwarf star

An Ancient Host

The host star, TOI-1846, is an M-type red dwarf located 154 light-years away in the Lyra constellation. These stars are the most common type in the Milky Way.

TOI-1846 is smaller, cooler, and dimmer than our Sun. Crucially, it's estimated to be around 7.2 billion years old, making it significantly older than our 4.6-billion-year-old Sun. This great age provides a long timeline for planetary evolution, making the system a key laboratory for studying long-term atmospheric loss processes.

The Mystery of the Radius Valley

TOI-1846b's most significant feature is its size. With a radius of ~1.8 Earth radii, it falls directly within a curious statistical gap known as the "Radius Valley" or "Radius Gap."

Astronomers have found plenty of rocky planets smaller than 1.5 Earth radii and many gaseous planets larger than 2.5 Earth radii, but very few in between. This valley is thought to be a dividing line in planetary evolution. Planets born in this size range either have their thick primordial atmospheres stripped away by stellar radiation (becoming rocky super-Earths) or they are massive enough to hold onto their gas and become mini-Neptunes. TOI-1846b is a rare resident of this valley, offering a perfect test case to understand this critical phase of a planet's life.

A Note on "Mysterious Signals"

Recent media headlines have mentioned a "mysterious signal" from TOI-1846b. It's important to clarify what this means in an astronomical context.

The "signal" is not a message or an artificial transmission. It is the standard, periodic dip in the star's light caused by the planet's transit. This is the very signal astronomers use to detect thousands of exoplanets. The discovery is scientifically significant, but reports of unusual or mysterious communications are a misinterpretation of the standard detection method.

The Road Ahead

While much has been learned, key questions remain. The planet's mass needs to be measured more precisely to confirm its density and composition. Instruments like the MAROON-X spectrograph are slated for this task.

The ultimate goal is to study its atmosphere. Although challenging due to its suboptimal Transmission Spectroscopy Metric (TSM), the James Webb Space Telescope (JWST) may be able to detect key molecules like water vapor or methane, providing a direct glimpse into the nature of this super-Earth's steamy atmosphere.

James Webb Space Telescope deep field image

Frequently Asked Questions

Is TOI-1846b habitable?

No. With a surface temperature of around 295°C (563°F), it is far too hot for liquid water or life as we know it.

Why is it called a "water world" if it's so hot?

Its density suggests a significant fraction of its mass is water. At its high temperatures and pressures, this water would not be liquid but could exist as a dense, steamy atmosphere or as exotic forms of high-pressure ice deep within the planet.

Is TOI-1846b the same as Kepler-186f?

No, they are different planets in different systems. TOI-1846b is a hot super-Earth. Kepler-186f is a more famous, Earth-sized planet in its star's habitable zone. The "TOI" and "Kepler" prefixes denote the different discovery missions.