My latest (and likely last!) paper is up on arXiv today! As the title says, it's about the "Relative Habitability of Exoplanet Systems with Two Giant Planets".

Go check it out ➡️ arxiv.org/abs/2205.02777

Or for a TL;DR, continue ⬇️

The basic idea is, given an exoplanet system with 2 giant planets, what can we say—from a dynamical perspective—about its ability to host a habitable Earth-like planet?

We focus here on whether the system would be stable and how the exo-Earth's eccentricity would be changed.

Unstable systems (planets ejecting or colliding): not habitable. Easy enough, except the question of whether an arbitrary 3-planet system is stable is, um, HARD. In this case, I used a bunch of different predictive techniques that have been developed by other scientists.

The question of whether an Earth-like planet is habitable and a given semi-major axis and eccentricity is likewise HARD. I (intentionally) use a very simple model here based on existing work in the field. This framework is very adaptable with other habitability models!

Relative Habitability of Exoplanet Systems with Two Giant Planets

The architecture of a planetary system can influence the habitability of a planet via orbital effects, particularly in the areas of stability and eccentricity. Some of these effects are readily apparent, particularly when they occur on short timescales that are easily numerically calculable. However, the appearance and evolution of life can take place on gigayear timescales, long enough that secular effects become important. These effects are difficult to investigate, as a direct integration requires significant computational time. In this paper, we apply a semi-analytic framework in conjunction with N-body integrations and predictive techniques to determine the relative habitability for an Earth-like planet in a system with two giant companions over a multidimensional parameter space. Relative habitability quantifies the integrated habitability probability compared to a system containing only a single Earth-like planet. We find trends with mass, eccentricity, location, spacing, inclination, and alignment of the giant planets, including configurations where the system is more habitable due to the giant planets. As long as the system remains stable, a moderate eccentricity excitation of the terrestrial planet can be beneficial by increasing the outer boundary of the habitable zone through higher mean irradiance. In our simulations, the median ($\pm 1 σ$) habitable planet has an eccentricity of 0.11 (+0.16, -0.08), though it started circular. Low-mass, widely separated, and moderately eccentric perturbing giants can accomplish this, an "ultra-habitable" configuration of companions.

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In general, as the exo-Earth's eccentricity increases, it gets more sunlight from its star, making it less habitable in the inner regions and more habitable in the outer regions.

For each giant planet pair, we consider 80 different locations of the exo-Earth. At each of these locations, we find the stability and habitability probabilities. Then we can integrate over the exo-Earth locations to find a relative habitability for the giant planet pair.

A couple trends we saw:

• Mass of the giant planets ↑, relative habitability ↓
• Very low relative habitability when the giant planets are in the habitable zone
• Eccentricity of the giant planets ↑, relative habitability ↓
• Secular resonances can have big effects

While in general the presence of the giant planets reduces the relative habitability compared to a system with just an exo-Earth, there are some cases where the giant planets make the system "ultra-habitable":

@norasguidetothegalaxy congrat for this ! it's really cool you can do a PhD defense _and_ a great learning video in one shot ... I enjoyed it all ;)

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