This code produces period–radius diagrams with the population-based boundaries of the exo-Neptunian landscape as derived in
Castro-González et al. (2024). It also generates plots showing the density–period trend for
super-Neptunes/sub-Saturns presented in the follow-up study by
Castro-González et al. (2024b).
No installation is required. Simply download this repository and run nep_des.ipynb. You can prepare the User configuration cell, run the (collapsed) cells in the main code block, and execute any of the plotting cells. In the following, we show examples covering the three types of plots that can be generated. The configuration cells for each example can be found here. For issues/suggestions, please feel free to contact me.
In the left panel (example#1), we contextualize several unusually short-period planets located within the core of the Neptunian desert. In the right panel (example#2), we place a sub-Saturn within the broader exo-Neptunian landscape (desert, ridge, and savanna) and highlight it with a text box.
In this two-panel plot (example#3), we contextualize several planets along the density trend for super-Neptunes and sub-Saturns presented in Castro-González et al. (2024b). Planets in the savanna show low densities, typically below 1 g/cm³, whereas planets in the ridge and the desert can reach densities of ~2 g/cm³. The density transition aligns closely with the planet-occurrence break between the ridge and the savanna (at Porb ~ 6 days), suggesting that desert and ridge planets may share common formation and/or evolutionary pathways distinct from those of Neptunes in the savanna (see the papers for further discussion).
This plotting option also uses an MCMC approach to assess the significance of the trend. At present, without including the (duplicated) user-plotted planets (include_user_planets_in_density_stats = False):
We obtain a KS p-value of 0.0065 for the (DESERT + RIDGE) vs. SAVANNA comparison, which is slightly better than the original value reported by Castro-González et al. 2024b (KS p-value = 0.0092). This result confirms that the density distributions of the desert+ridge and savanna populations are statistically different. Remarkably, there is no evidence of a density difference between the desert and ridge planets (p-value = 0.27), which is somewhat expected given the very small desert sample (N_desert = 6). Still, the Cliff’s delta remains high (0.38), which suggests a potentially meaningful effect that current sample sizes are not sufficient to confirm. In this line, we note that relatively low-density super-Neptunes exist in the ridge but not in the desert, an intriguing feature consistent with the proposed density brink (Bourrier et al. 2025).
Finally, we can generate the exact KDE-derived desert boundaries from Castro-González et al. (2024). These boundaries are broadly consistent with the approximate ones shown in the previous examples. However, they are especially valuable for contextualizing sub-Neptunes located near the opening of the radius valley, a region that is less well captured by straight-line approximations. For this format, the background is drawn from the Kepler DR25 catalogue (Thompson et al. 2018), to which the Inverse Detection Efficiency Method (IDEM) was applied to derive the corresponding bias-corrected boundaries.
In the left panel (example #4), we illustrate how to contextualize a desert planet. In the right panel (example #5), we show how to contextualize multiple desert planets with legend labels. We also demonstrate how to draw the classical desert boundaries of Mazeh et al. (2016) using the option show_mazeh_boundaries = True, which can be activated for any of the nep-des plot types.
If you use our population-based mapping of the exo-Neptunian landscape, please give credit to this work:
@ARTICLE{2024A&A...689A.250C,
author = {{Castro-Gonz{\'a}lez}, A. and {Bourrier}, V. and {Lillo-Box}, J. and {Delisle}, J. -B. and {Armstrong}, D.~J. and {Barrado}, D. and {Correia}, A.~C.~M.},
title = "{Mapping the exo-Neptunian landscape: A ridge between the desert and savanna}",
journal = {\aap},
keywords = {planets and satellites: atmospheres, planets and satellites: dynamical evolution and stability, planets and satellites: formation, planets and satellites: gaseous planets, planets and satellites: physical evolution, Astrophysics - Earth and Planetary Astrophysics},
year = 2024,
month = sep,
volume = {689},
eid = {A250},
pages = {A250},
doi = {10.1051/0004-6361/202450957},
archivePrefix = {arXiv},
eprint = {2409.10517},
primaryClass = {astro-ph.EP},
adsurl = {https://ui.adsabs.harvard.edu/abs/2024A&A...689A.250C},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}If you also use the super-Neptune / sub-Saturn density trend, please give credit to this work:
@ARTICLE{2024A&A...691A.233C,
author = {{Castro-Gonz{\'a}lez}, A. and {Lillo-Box}, J. and {Armstrong}, D.~J. and {Acu{\~n}a}, L. and {Aguichine}, A. and {Bourrier}, V. and {Gandhi}, S. and {Sousa}, S.~G. and {Delgado-Mena}, E. and {Moya}, A. and {Adibekyan}, V. and {Correia}, A.~C.~M. and {Barrado}, D. and {Damasso}, M. and {Winn}, J.~N. and {Santos}, N.~C. and {Barkaoui}, K. and {Barros}, S.~C.~C. and {Benkhaldoun}, Z. and {Bouchy}, F. and {Brice{\~n}o}, C. and {Caldwell}, D.~A. and {Collins}, K.~A. and {Essack}, Z. and {Ghachoui}, M. and {Gillon}, M. and {Hounsell}, R. and {Jehin}, E. and {Jenkins}, J.~M. and {Keniger}, M.~A.~F. and {Law}, N. and {Mann}, A.~W. and {Nielsen}, L.~D. and {Pozuelos}, F.~J. and {Schanche}, N. and {Seager}, S. and {Tan}, T.-G. and {Timmermans}, M. and {Villase{\~n}or}, J. and {Watkins}, C.~N. and {Ziegler}, C.},
title = "{TOI-5005 b: A super-Neptune in the savanna near the ridge}",
journal = {\aap},
keywords = {techniques: photometric, techniques: radial velocities, planets and satellites: composition, planets and satellites: detection, planets and satellites: individual: TOI-5005 b, stars: individual: TOI 5005 (TIC 282485660), Earth and Planetary Astrophysics},
year = 2024,
month = nov,
volume = {691},
eid = {A233},
pages = {A233},
doi = {10.1051/0004-6361/202451656},
archivePrefix = {arXiv},
eprint = {2409.18129},
primaryClass = {astro-ph.EP},
adsurl = {https://ui.adsabs.harvard.edu/abs/2024A&A...691A.233C},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}If you make use of nep_des to implement the exo-Neptunian boundaries in your research, please also copy-paste the following sentence within the acknowledgements section:
This research made use of \texttt{nep-des} (available in \url{https://github.com/castro-gzlz/nep-des})
Please also give credit to the catalogue(s) used: Nasa Exoplanet Archive (Akeson et al. 2013; Christiansen et al. 2025), Exoplanet.eu (Schneider et al. 2011), and/or Kepler DR25 (Thompson et al. 2018).