Uv Surface Environment of Earth-Like Planets Orbiting FGKM Stars Through Geological Evolution

Rugheimer, Sarah; Segura, Antígona; Kaltenegger, Lisa; Sasselov, Dimitar

doi:10.1088/0004-637x/806/1/137

Cited by 126 publications

(261 citation statements)

References 58 publications

Supporting

Mentioning

253

Contrasting

Order By: Relevance

“…We do not consider photochemistry here, however the stellar type, stellar activity, and atmospheric oxygen concentration are all critical for determining the UV radiation hazard for the planet surface, and have been studied elsewhere (Segura et al 2003;Rugheimer et al 2015). For each planet, we assume Earth-like orbital characteristics, with an orbital period of 1 Earth year, zero eccentricity, and 23.5° obliquity.…”

Section: Methodsmentioning

confidence: 99%

Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model

Wolf

Shields

Kopparapu

et al. 2017

ApJ

117

View full text Add to dashboard Cite

Conventional definitions of habitability require abundant liquid surface water to exist continuously over geologic timescales. Water in each of its thermodynamic phases interacts with solar and thermal radiation and is the cause for strong climatic feedbacks.Thus, assessments of the habitable zone require models to include a complete treatment of the hydrological cycle over geologic time. Here, we use the Community Atmosphere Without long timescale regulation of non-condensable greenhouse species at Earth-like temperatures and pressures, such as CO 2 , habitability can be maintained for an upper limit of ~2.2, ~2.4 and ~4.7 Gyr around F-, G-and K-dwarf stars respectively due to main sequence brightening.

show abstract

Section: Methodsmentioning

confidence: 99%

Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model

Wolf

Shields

Kopparapu

et al. 2017

ApJ

117

View full text Add to dashboard Cite

show abstract

“…Assuming cloudless skies, an upper limit on the early Earth integrated UV flux from 200-250 nm is ∼0.4 W m −2 [35,60]. UV wavelengths < 200 nm would be completed attenuated by CO 2 and H 2 O in the early atmosphere [35].…”

Section: Uv Photodissociationmentioning

confidence: 99%

Origin of the RNA world: The fate of nucleobases in warm little ponds

Pearce

Pudritz

Semenov

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

170

222

View full text Add to dashboard Cite

Prior to the origin of simple cellular life, the building blocks of RNA (nucleotides) had to form and polymerize in favourable environments on the early Earth. At this time, meteorites and interplanetary dust particles delivered organics such as nucleobases (the characteristic molecules of nucleotides) to warm little ponds whose wet-dry cycles promoted rapid polymerization. We build a comprehensive numerical model for the evolution of nucleobases in warm little ponds leading to the emergence of the first nucleotides and RNA. We couple Earth's early evolution with complex prebiotic chemistry in these environments. We find that RNA polymers must have emerged very quickly after the deposition of meteorites (< a few years). Their constituent nucleobases were primarily meteoritic in origin and not from interplanetary dust particles. Ponds appeared as continents rose out of the early global ocean but this increasing availability of "targets" for meteorites was offset by declining meteorite bombardment rates. Moreover, the rapid losses of nucleobases to pond seepage during wet periods, and to UV photodissociation during dry periods means that the synthesis of nucleotides and their polymerization into RNA occurred in just one to a few wet-dry cycles. Under these conditions, RNA polymers likely appeared prior to 4.17 billion years ago.Significance: There are currently two competing hypotheses for the site at which an RNA world emerged: hydrothermal vents in the deep ocean and warm little ponds. Because the former lacks wet and dry cycles, which are well known to promote polymerization (in this case, of nucleotides into RNA), we construct a comprehensive model for the origin of RNA in the latter sites. Our model advances the story and timeline of the RNA world by constraining the source of biomolecules, the environmental conditions, the timescales of reaction, and the emergence of first RNA polymers.Keywords: life origins | astrobiology | planetary science | meteoritics | RNA worldOne of the most fundamental questions in science is how life first emerged on the Earth. Given its ubiquity in living cells and its ability to both store genetic information and catalyze its own replication, RNA probably formed the basis of first life [1]. RNA molecules are made up of sequences of 4 different nucleotides, the latter of which can be formed through reaction of a nucleobase with a ribose and a reduced phosphorous (P) source [2,3]. The evidence suggests that first life appeared earlier than 3.7 Gyr ago (Ga) [4,5] and thus the RNA world would have developed on a violent early Earth undergoing meteoritic bombardment at a rate of ∼1-1000 ×10 12 kg/yr [6], which is approximately 8-11 orders of magnitude greater than today [7]. At this time, the atmosphere was dominated by volcanic gases, and dry land was scarce as continents were rising out of the global ocean. [8,9], the answer to these questions are largely unknown.As to the sources of nucleobases, the early Earth's atmosphere was likely dominated by CO 2 , N 2 , SO 2 , and H 2 O [10...

show abstract

“…Extensive work has been done to explore mechanisms that might protect surface life from the UV output of Mdwarfs in quiescence and in flare, such as ozone layers (Segura et al 2005(Segura et al , 2010Rugheimer et al 2015), oceans (Kiang et al 2007), and bioflourescence (O'Malley-James & Kaltenegger 2016). Overall, these works show that UV irradiance at the surface of modern-Earth-analog M-dwarf planets should be suppressed to levels below those of modern Earth itself, because oflower M-dwarf near-UV (NUV) output and because offavorable ozone-generating atmospheric photochemistry.…”

Section: Background: Previous Studies Of M-dwarf Planet Uvmentioning

confidence: 99%

The Surface UV Environment on Planets Orbiting M Dwarfs: Implications for Prebiotic Chemistry and the Need for Experimental Follow-up

Ranjan

Wordsworth

Sasselov

2017

ApJ

Self Cite

132

134

View full text Add to dashboard Cite

Potentially habitable planets orbiting Mdwarfs are of intense astrobiological interest because they are the only rocky worlds accessible to biosignature search over the next 10+ years because ofa confluence of observational effects. Simultaneously, recent experimental and theoretical work suggests that UV light may have played a key role in the origin of life on Earth, especially the origin of RNA. Characterizing the UV environment on M-dwarfplanets is important for understanding whether life as we know it could emerge on such worlds. In this work, we couple radiative transfer models to observed M-dwarf spectra to determine the UV environment on prebiotic Earth-analog planets orbiting Mdwarfs. We calculate dose rates to quantify the impact of different host stars on prebiotically important photoprocesses. We find that M-dwarf planets have access to 100-1000 times less bioactive UV fluence than the young Earth. It is unclear whether UV-sensitive prebiotic chemistry that may have been important to abiogenesis, such as the only known prebiotically plausible pathways for pyrimidine ribonucleotide synthesis, could function on M-dwarf planets. This uncertainty affects objects like the recently discovered habitable-zone planets orbiting Proxima Centauri, TRAPPIST-1, and LHS 1140. Laboratory studies of the sensitivity of putative prebiotic pathways to irradiation level are required to resolve this uncertainty. If steadystate M-dwarf UV output is insufficient to power these pathways, transient elevated UV irradiation due to flares may suffice; laboratory studies can constrain this possibility as well.

show abstract

Uv Surface Environment of Earth-Like Planets Orbiting FGKM Stars Through Geological Evolution

Cited by 126 publications

References 58 publications

Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model

Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model

Origin of the RNA world: The fate of nucleobases in warm little ponds

The Surface UV Environment on Planets Orbiting M Dwarfs: Implications for Prebiotic Chemistry and the Need for Experimental Follow-up

Contact Info

Product

Resources

About