09-17-2025, 06:26 PM
Today a preprint about the star system Eta Cassiopeiae (specifically the A component, or Achird) appears on arXiv. It does not detect a planet signature, and also failed to detect a candidate previously proposed by a preceding paper.
The gist is that the paper finds that a combination of radial velocity measurements and dynamical stability studies suggest the lack of giant planets in this system. Figure 3 shows the RV detection completeness, while Figure 4 shows the survivability of a planet orbiting at a given distance from star A, as well as (maximum) eccentricity induced by the companion star. Note that the binary orbit from Giovinazzi et al. (2025), a previous paper that investigated this system, finds inclination of ~35 degrees, implying that if its planetary system is coplanar to this binary orbit, then the true mass of any planet around these stars would be almost twice the mass found from RV.
As for my thoughts...while the combination of this work, planet occurrence rates in binary systems, and our understanding of giant planet formation would point to this system likely not having a giant planet, it is good to keep in mind that Gamma Cephei A b and Nu Octantis A b exist, and even Alpha Centauri A might be orbited by a giant planet as well (though I personally doubt), so it is not perfectly settled in stone. That said, I'd be comfortable with us removing any giant planet from this system, though what should orbit around these two stars is anyone's guess.
The gist is that the paper finds that a combination of radial velocity measurements and dynamical stability studies suggest the lack of giant planets in this system. Figure 3 shows the RV detection completeness, while Figure 4 shows the survivability of a planet orbiting at a given distance from star A, as well as (maximum) eccentricity induced by the companion star. Note that the binary orbit from Giovinazzi et al. (2025), a previous paper that investigated this system, finds inclination of ~35 degrees, implying that if its planetary system is coplanar to this binary orbit, then the true mass of any planet around these stars would be almost twice the mass found from RV.
As for my thoughts...while the combination of this work, planet occurrence rates in binary systems, and our understanding of giant planet formation would point to this system likely not having a giant planet, it is good to keep in mind that Gamma Cephei A b and Nu Octantis A b exist, and even Alpha Centauri A might be orbited by a giant planet as well (though I personally doubt), so it is not perfectly settled in stone. That said, I'd be comfortable with us removing any giant planet from this system, though what should orbit around these two stars is anyone's guess.