Astronomy & Telescopes

Observation Uncertainty Effects On The Precision Of Interior Planetary Parameters

By Keith Cowing
Status Report
May 10, 2024
Filed under , , , , , , ,
Observation Uncertainty Effects On The Precision Of Interior Planetary Parameters
Summary of error effects for water abundant planets: water-poor (top panel) and water-rich (bottom panel). We use different priors for the rocky assumptions: fixed to Fe/Mg = 1.7 (1 st column), similar to stars with typical stellar error Fe/Mg ∼ N (1.7, 0.4) (2 nd column), similar to stars with an error that spans all stars Fe/Mg ∼ N (1.7, 0.7) (3 rd column) and completely unconstrained cmf ∼ U (0, 1) (4 th columns). We report wmf error for all cases, note the colorbar for top and bottom panel has different scale. The minor differences between the different stellar prior assumptions, show that stars with chemical measurements are accurate enough to constraint the wmf. However, without any priors, the wmf is highly unconstrained. — astro-ph.EP

Determining compositions of low-mass exoplanets is essential in understanding their origins. The certainty by which masses and radius are measured affects our ability to discern planets that are rocky or volatile rich.

In this study, we aim to determine sound observational strategies to avoid diminishing returns. We quantify how uncertainties in mass, radius and model assumptions propagate into errors in inferred compositions of rocky and water planets. For a target error in a planet’s iron-mass fraction or water content, we calculate the corresponding required accuracies in radius and mass.

For instance, a rocky planet with a known radius error of 2% (corresponding to TESS detection best errors) demands mass precision to be at 5-11% to attain a 8 wt% precision in iron-mass fraction, regardless of mass. Similarly, a water world of equal radius precision requires 9-20% mass precision to confine the water content within a 10 wt% margin.

Lighter planets are more difficult to constrain, especially water-rich versus water-poor worlds. Studying Earth as an exoplanet, we find a ∼±5 point “error floor” in iron-mass fraction and ∼±7 in core-mass fraction from our lack of knowledge on mineralogy. The results presented here can quickly guide observing strategies to maximize insights into small exoplanet compositions while avoiding over-observing.

Mykhaylo Plotnykov, Diana Valencia

Comments: 13 pages, 8 figures, published in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2405.03860 [astro-ph.EP] (or arXiv:2405.03860v1 [astro-ph.EP] for this version)
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Submission history
From: Mykhaylo Plotnykov
[v1] Mon, 6 May 2024 21:18:27 UTC (379 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻