Skip to content

Find habitable zone boundaries

8. Find habitable zone boundaries (How-to)

Goal

Compute habitable zone (HZ) boundary orbital distances (AU) as a function of stellar mass and age using mors.aOrbHZ.

Prerequisites

Install MORS and download stellar evolution data:

pip install fwl-mors
mors download all

Units: Mstar in M☉, Age in Myr, returned distances in AU.

Citation note: If you use these HZ boundaries in research, cite Kopparapu et al. (2013) (HZ prescription) and Spada et al. (2013) (stellar parameters used).

Step 1: Compute HZ boundaries for a single star mass

By default, aOrbHZ uses stellar parameters at 5000 Myr if you don’t specify Age.

import mors

hz = mors.aOrbHZ(Mstar=1.0)

The returned dictionary contains these keys: - RecentVenus - RunawayGreenhouse - MoistGreenhouse - MaximumGreenhouse - EarlyMars - HZ

Print them:

for k in ["RecentVenus", "RunawayGreenhouse", "MoistGreenhouse",
          "MaximumGreenhouse", "EarlyMars", "HZ"]:
    print(k, hz[k])

HZ is defined (Johnstone et al. 2020) as the average of the RunawayGreenhouse and MoistGreenhouse orbital distances.

Step 2: Specify a stellar age

import mors
hz_1gyr = mors.aOrbHZ(Mstar=1.0, Age=1000.0)  # Myr
print(hz_1gyr["HZ"])

Step 3: Compute HZ boundaries for multiple masses

If you pass an array of masses, you get arrays back in the dictionary:

import numpy as np
import mors

masses = np.array([0.3, 0.5, 0.8, 1.0])
hz = mors.aOrbHZ(Mstar=masses, Age=5000.0)

print(hz["HZ"])              # array of AU
print(hz["RunawayGreenhouse"])

Common pitfalls

  • Age is in Myr (not years).
  • When passing arrays for Mstar, each returned dict entry becomes an array of the same length.