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| An image of TESS in orbit |
In a discovery that offers a rare glimpse into the turbulent adolescence of planetary systems, astronomers have confirmed the existence of a fascinating exoplanet located just 106 light-years away. This distant world, caught in a delicate state of cosmic transition, is providing crucial clues about how planets change—and sometimes, how they almost disappear entirely.
The planet, designated TOI-5734 b, orbits a modest K-type dwarf star (a star slightly cooler and smaller than our Sun) in the constellation of Mensa. While finding exoplanets has become almost routine, TOI-5734 b is special because it appears to be mid-transformation. It is a "hot sub-Neptune," a class of planet not found in our own solar system, and it is currently losing its primordial atmosphere at a significant rate.
A Planet on the Edge
So, what exactly is TOI-5734 b like? It occupies a unique middle ground in the cosmos. With a radius of about 2.1 times that of Earth and a mass of roughly 9.1 Earths, it is smaller than Neptune but significantly larger than our home planet. Its density is slightly lower than Earth’s, suggesting it is not a purely rocky world but rather possesses a thick, gaseous envelope.
This world hugs its star incredibly closely, completing one full orbit in just 6.18 days at a distance of a mere 0.06 AU (Astronomical Units). For context, Mercury takes 88 days to orbit the Sun at a distance of 0.4 AU. This extreme proximity scorches the planet's surface to an estimated temperature of roughly 688 K (about 415°C or 779°F) .
But the most intriguing detail about TOI-5734 b isn't just its size or heat—it’s where it sits on the cosmic size chart. It lies right at the edge of what astronomers call the "radius valley."
The Mystery of the Radius Valley
One of the most exciting recent discoveries in exoplanet science is the "radius valley." When plotting thousands of exoplanets by size, a curious gap appears: there is a distinct lack of planets between roughly 1.5 and 2.0 times the size of Earth. Planets tend to be either rocky super-Earths below this gap or gaseous mini-Neptunes above it.
TOI-5734 b, with its 2.1 Earth radii, sits right on the upper edge of this valley.
"This planet is in a very specific evolutionary phase," explains the team of astronomers behind the discovery. "It is a sub-Neptune that may be in the process of shedding its atmosphere to become a super-Earth."
The prevailing theory is that planets like this lose their atmospheres through a process called photoevaporation. The intense X-ray and ultraviolet radiation from their young host star heats the gaseous envelope of the planet, causing it to bleed off into space over hundreds of millions of years. Researchers estimate that TOI-5734 b may lose its entire primordial envelope in about 300 million years, leaving behind only its rocky core. Essentially, we are watching a potential super-Earth in the making.
The Detection: A TESS Discovery Confirmed by HARPS-N
Uncovering this celestial drama required a powerful, two-pronged approach using some of the most advanced planet-hunting technology available.
The story began with NASA’s Transiting Exoplanet Survey Satellite (TESS) . In 2022, TESS spotted a telltale sign around the star TOI-5734: a tiny, periodic dip in the star's brightness. This "transit" method is highly effective for determining a planet's physical size, which is exactly what TESS did, giving astronomers their first estimate of the planet's radius.
However, to truly understand the nature of the planet, astronomers needed to know its mass. For that, they turned to the HARPS-N (High Accuracy Radial velocity Planet Searcher for the Northern hemisphere) instrument, located on the Telescopio Nazionale Galileo in the Canary Islands. HARPS-N is a master of the radial velocity method, detecting the minuscule "wobble" in a star's motion caused by the gravitational tug of an orbiting planet. By combining the data from TESS and HARPS-N, the international team was able to calculate the planet's mass, density, and confirm its status.
The full details of this remarkable observation have been published on the preprint server arXiv, offering the scientific community a detailed look at this cosmic work in progress. You can read the full study here:
Astronomers Confirm a Young Hot Sub-Neptune on the Edge of the Radius Valley
Why This Matters
The discovery of TOI-5734 b is more than just another addition to the exoplanet catalog, which now numbers in the thousands. It serves as a critical laboratory for testing theories of planetary evolution.
By studying this planet now, while it is still massive enough to hold onto its atmosphere, astronomers can measure the rate of atmospheric loss and refine their models of how planetary climates and compositions change over time. The star itself, TOI-5734, is a young and active K-type dwarf with about 72% of the Sun's mass and 64% of its radius. Its youth and high-energy output are precisely what drive the evaporation seen on its planet.
In a universe where we usually see static snapshots of distant worlds, TOI-5734 b offers a rare moving picture—a planet caught in the act of becoming something else. As we continue to peer deeper into the cosmos, worlds like this remind us that even on astronomical timescales, change is the only constant.
For further reading and the source of this discovery, you can visit the original article published via Phys.org here.