Identification of carbon dioxide in an exoplanet atmosphere

Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (that is, elements heavier than helium, also called ‘metallicity’), and thus the formation processes of the primary atmospheres of hot gas giants. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science programme. The data used in this study span 3.0–5.5 micrometres in wavelength and show a prominent CO2 absorption feature at 4.3 micrometres (26-sigma significance). The overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiative–convective–thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 micrometres that is not reproduced by these models

Physical map of five candidate genes that were mutated in <i>Tgm9</i>-insertion mutants.

<p>Flanking molecular markers from the genetic linkage maps for <i>y20 Mdh1-n</i>, <i>ms9</i>, <i>Fsp2</i>, <i>Fsp3</i> and <i>Fsp5</i> were placed on the physical map along with <i>Tgm9</i>-insertion sites identified in these mutants [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0180732#pone.0180732.ref029" target="_blank">29</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0180732#pone.0180732.ref031" target="_blank">31</a>]. Scale is represented in million base pairs (Mb) of DNA.</p

Physical map of the <i>Tgm9</i> insertion sites among 105 mutants.

<p>Green arrows represent locations of <i>Tgm9</i> in genes (exons and introns) and red arrows show <i>Tgm9</i> insertions in other genomic regions. A purple arrow shows the location of <i>Tgm9</i> in <i>W4</i> on Chromosome 17. Centromeres (black rectangles) and heterochromatic regions (grey areas) are shown on individual chromosomes. Scale is represented in million base pairs (Mb) of DNA.</p

Display of <i>Tgm9</i>-induced mutants in the SoyBase genome browser.

<p>The track for <i>Tgm9</i>-insertion lines shows the location of two <i>Tgm9</i>-induced insertions (T91200307 and T91200364) on Chromosome 15. Note that in the T91200307 mutant, the <i>Tgm9</i> insertion site is located in the inter-genic region, and in T91200364, the insertion site is in the 2^nd exon of <i>Glyma</i>.<i>15G033300</i>. (<a href="http://soybase.org/gb2/gbrowse/gmax2.0x/?start=1;stop=56831624;ref=Gm01;width=1024;version=100;flip=0;grid=1;id=28f86f22137273c155fe3e1756259be0;l=tgm9-gene_models_wm82_a2_v1-pericentromere:overview" target="_blank">http://soybase.org/gb2/gbrowse/gmax2.0x/?start=1;stop=56831624;ref=Gm01;width=1024;version=100;flip=0;grid=1;id=28f86f22137273c155fe3e1756259be0;l=tgm9-gene_models_wm82_a2_v1-pericentromere:overview</a> {Please use user name: Bhatt; password: tgm9#}).</p

Percent distribution of the type of <i>Tgm9</i>-induced mutants.

<p>The observed frequency of <i>Tgm9</i> insertions in exonic and intronic sequences were calculated from 105 <i>Tgm9</i> insertion loci (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0180732#pone.0180732.s007" target="_blank">S3 Table</a>). The expected frequency of <i>Tgm9</i> is based on random insertion of the element in the exonic and intronic sequences calculated from the soybean genome sequences mapped to chromosomes (Soybase). The χ² value (1.7752 at df = 1) calculated for observed <i>Tgm9</i> insertion frequencies and expected frequencies of random <i>Tgm9</i> insertions in exon and intron sequences is statistically non-significant at <i>p</i> = 0.05.</p

Genetically mapped soybean mutants identified by screening germinal revertants of the mutable line, T322 (<i>w4-m</i>).

<p>Genetically mapped soybean mutants identified by screening germinal revertants of the mutable line, T322 (<i>w4-m</i>).</p