Lead astronomers have discovered two exoplanets orbiting the sun-like star HD 35843, aka TOI 4189. This unexpected discovery, published in this week’s Nature study, informs one aspect of the still-mysterious picture of planetary systems around stars with high and low metallicity. HD 35843 is about 2.5 billion years old. Photo credit: Daniel Kordan Its unusual features may provide deep insights into more generalized processes that govern exoplanet formation and evolution.
HD 35843 is a cool, albeit metal-poor, G-dwarf star. It has a mass just below that of the Sun, and a radius about 0.9 times Solar. The temperature of this star is 5,666 K, and the metallicity is -0.27. These properties are key for determining the conditions under which its exoplanets were formed.
The two newly discovered exoplanets, HD 35843 b and HD 35843 c, have quite different properties. HD 35843 b is a super-Earth exoplanet and HD 35843 c is a sub-Neptune exoplanet. HD 35843 b completes one orbit around its host star every 9.9 days. That makes it super close, at only 0.088 AU away, which likely helped earn it the classification of a super-Earth!
HD 35843 c has an orbital period of 46.7 days. It orbits the star at a distance of 0.25 AU. This planet is twice the size of Earth, about 2.5 times its diameter. It has a mass that is about 11.3 times greater than that of our home planet. The equilibrium temperature of HD 35843 c is approximately 479 K. This means that its atmosphere may be very different from the planets we have in our own solar system.
In a recent paper, researchers Katharine Hesse and her colleagues emphasized the importance of this finding.
“We report the discovery and confirmation of two planets orbiting the metal-poor sun-like star, HD 35843 (TOI 4189),” – Katharine Hesse et al, arXiv (2025).
The discovery of these two exoplanets provides valuable information about the diversity of planetary systems and their potential to harbor life. As astronomers continue to study HD 35843 and its planets, further discoveries may reveal additional details about how such systems evolve over time, particularly around stars with low metallicity.