Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

EXOPLANETS

A naked gas giant

Subjects

Nature 583, 39–42 (2020)

The existence of a ‘hot Neptune desert’ tells us that it is very rare to find Neptune-mass exoplanets orbiting very close to their star. In fact, such planets either lose their atmosphere — and thus most of their mass — very efficiently due to photoevaporation; or are destroyed by tidal forces; or migrate outward. TOI-849b, discovered by David Armstrong and colleagues, is a double rarity: not only is it fully in the hot Neptune desert, but it also has a density comparable to the Earth’s.

Credit: Springer Nature Ltd

TOI-849b is almost the same size as Neptune but has a mean density of \(5.2_{ - 0.8}^{ + 0.7}\) g cm–3, comparable with that of 5.51 g cm–3 for Earth. Such a high density is very unusual for such a big planet — the density of Neptune itself is barely 1.64 g cm–3 — meaning it has a very thin atmosphere, ~4% of its mass. It also orbits its star, a ~6.7 billion-year-old Sun twin, in less than one day, which makes it very hot. TOI-849b is clearly in an isolated sector of the mass–period diagram (pictured). How it could exist is therefore puzzling.

Armstrong et al. advance the hypothesis that TOI-849b might have been born as a standard hot Jupiter, but its gaseous envelope was very efficiently removed by tidal disruption or giant impacts, leaving its massive core behind. Alternatively, it might not have accreted a lot of gas to begin with owing to some local conditions like a gap in the protoplanetary disk. TOI-849b might thus offer us the chance to directly observe the core of a giant planet (albeit affected by billions of years of exposure to its star) without the usual thick atmosphere that encases it.

Author information

Affiliations

Authors

Corresponding author

Correspondence to Luca Maltagliati.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Maltagliati, L. A naked gas giant. Nat Astron 4, 728 (2020). https://doi.org/10.1038/s41550-020-1184-2

Download citation

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing