Two low-density planets confirmed orbiting the bright star HD 148797

Star system: HD 148797 | Distance from the Sun: 562 light years

The bright F-type star HD 148797 hosts two moderate-period planets, classified as sub-Jovian worlds with unusually low density. These planets reside in a region of space known as the Neptunian savanna, a classification for planets with specific ranges of size and orbital distance. The findings provide insights into how such systems form and evolve, suggesting they often develop in dynamically stable environments rather than through violent orbital shifts.

The planets, designated HD 148797 b and c, were studied using photometric data from the TESS and CHEOPS space telescopes. These instruments track the slight dip in light when a planet passes in front of its host star, a process called a transit. By measuring these dips over time, researchers determined the orbital periods and physical sizes of both planets.

Researchers detected transit-timing variations, which are tiny fluctuations in the predicted arrival times of transits caused by the gravitational interaction between the two planets. By analyzing these variations, the team calculated the mass and overall density of each planet. Both worlds exhibit a low density of roughly 0.38 grams per cubic centimeter, which is very light for their size.

Key findings
- HD 148797 b and c have orbital periods of 42.1 days and 68.2 days, respectively.
- Both planets have radii of approximately 8.3 times that of Earth.
- The calculated mass for both planets is roughly 39 times that of Earth.
- Their low density places them firmly within the Neptunian savanna population.
- The orbital layout suggests a stable, disk-driven formation history.

Scientific study

HD 148797: A bright F-type star with two moderate-period low-density sub-Jovian planets. Compact multi-planet architectures are common in the Neptunian savanna (external link)