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Radiogenic heat production is fundamental to the energy budget of planets. Roughly half of the heat that Earth loses through its surface today comes from the three long-lived, heat-producing elements (potassium, thorium, and uranium). These three elements have long been believed to be highly lithophile and thus concentrate in the mantle of rocky planets. However, our study shows that they all become siderophile under the pressure and temperature conditions relevant to the core formation of large rocky planets dubbed super-Earths. Mantle convection in super-Earths is then primarily driven by heating from the core rather than by a mix of internal heating and cooling from above as in Earth. Partitioning these sources of radiogenic heat into the core remarkably increases the core-mantle boundary (CMB) temperature and the total heat flow across the CMB in super-Earths. Consequently, super-Earths are likely to host long-lived volcanism and strong magnetic dynamos.
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Formation of rocky super-earths from a narrow ring of planetesimals
The formation of super-Earths, the most abundant planets in the Galaxy, remains elusive. These planets have masses that typically exceed that of the Earth by a factor of a few, appear to be predominantly rocky, although often surrounded by H/He atmospheres, and frequently occur in multiples. Moreover, planets that encircle the same star tend to have similar masses and radii, whereas those belonging to different systems exhibit remarkable overall diversity. Here we advance a theoretical picture for rocky planet formation that satisfies the aforementioned constraints: building upon recent work, which has demonstrated that planetesimals can form rapidly at discrete locations in the disk, we propose that super-Earths originate inside rings of silicate-rich planetesimals at approximately ~1 au. Within the context of this picture, we show that planets grow primarily through pairwise collisions among rocky planetesimals until they achieve terminal masses that are regulated by isolation and orbital migration. We quantify our model with numerical simulations and demonstrate that our synthetic planetary systems bear a close resemblance to compact, multi-resonant progenitors of the observed population of short-period extrasolar planets.
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- Award ID(s):
- 2109276
- PAR ID:
- 10527768
- Publisher / Repository:
- Springer-Nature
- Date Published:
- Journal Name:
- Nature Astronomy
- Volume:
- 7
- Issue:
- 3
- ISSN:
- 2397-3366
- Page Range / eLocation ID:
- 330 to 338
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41550-022-01850-5
