![\"Photosynthetic](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/02\/Photosynthetic-Exergy.png\")
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\n Spectral flux and exergy at the top of the atmosphere for three blackbody models, all normalized to the same bolometric flux \ud835\udc39bol = 1361 W m2.Solid curves show \ud835\udc39TOA,\ud835\udf06 and dashed curves \ud835\udf02ex\ud835\udc39TOA,\ud835\udf06. The vertical line marks a PSII-like threshold at \ud835\udf06thr = 690 nm, illustrating how the shortwavelength band available for high-\u0394\ud835\udc3a photochemistry shrinks for M-type hosts. \u2014 astro-ph.EP <\/p>\n
Photosynthesis is central to Earth\u2019s biosphere and a prime candidate for sustaining complex life on habitable exoplanets, yet a thermodynamically consistent treatment of the work potential of stellar radiation at planetary surfaces is still lacking.<\/p>\n
We develop a radiative-thermodynamic framework that quantifies the maximum useful work extractable for a given star-planet configuration and yields exergy-based bounds on photosynthetic power and long-wavelength absorption cutoffs.<\/p>\n
From these we derive kinetically constrained red limits for high-\u0394G photochemistry and apply them to Earth-like planets receiving the same bolometric flux from FGK and M blackbody hosts, computing thresholded photon supplies and truncated exergy fluxes below a photosystem II red limit.<\/p>\n
For such planets the constraints confine single-photon oxygenic photosynthesis to near-infrared bands around Solar-type stars and to somewhat bluer wavelengths around late M dwarfs. Integrated over the stellar spectrum, the thresholded photon supply and truncated exergy available to drive a photosystem water-oxidation step are larger by factors \u223c5 around FGK hosts than around T\u22c6\u22483000~K M dwarfs.<\/p>\n
For the Solar-Earth system, the exergy-based upper bound on O2 production exceeds the observed O2 throughput by several orders of magnitude, consistent with Earth\u2019s photosynthetic efficiencies. Cool M dwarfs suffer a double penalty: fewer photons above threshold and a lower shortwave exergy fraction, yielding systematically tighter ceilings on high-\u0394G photosynthesis than around FGK stars.<\/p>\n
Our framework provides upper limits on photosynthetically harvestable power on habitable-zone planets and enables comparisons of photosynthetic potential across exoplanetary systems, and can be extended to multi-band photosystems.<\/p>\n
Giovanni Covone, Amedeo Balbi<\/p>\n
Comments: 10 pages, 3 figures. Submitted to MNRAS Astrobiology,<\/p>\n Explorers Club Fellow, ex-NASA Space Station Payload manager\/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na\u2019Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he\/him) \ud83d\udd96\ud83c\udffb<\/p>\n","protected":false},"excerpt":{"rendered":"Spectral flux and exergy at the top of the atmosphere for three blackbody models, all normalized to the…\n","protected":false},"author":2,"featured_media":303882,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[162684,40915,5964,2288,57302,166453,166454,111,139,69,166455,65008,166456,147],"class_list":{"0":"post-303881","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-science","8":"tag-astro-ph-ep","9":"tag-biochemistry","10":"tag-exoplanet","11":"tag-genomics","12":"tag-habitability","13":"tag-habotable-zone","14":"tag-m-dwarf","15":"tag-new-zealand","16":"tag-newzealand","17":"tag-nz","18":"tag-oxygenic-photosynthesis","19":"tag-photochemistry","20":"tag-photosynthesis","21":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/303881","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=303881"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/303881\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/303882"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=303881"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=303881"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=303881"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2602.20789 [astro-ph.EP] (or arXiv:2602.20789v1 [astro-ph.EP] for this version)
https:\/\/doi.org\/10.48550\/arXiv.2602.20789<\/a>
Focus to learn more
Submission history
From: Giovanni Covone
[v1] Tue, 24 Feb 2026 11:28:42 UTC (463 KB)
https:\/\/arxiv.org\/abs\/2602.20789<\/a><\/p>\n![\"\"\/](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2025\/09\/keith_cowing.jpg\")
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