scholarly journals Photosynthesis on exoplanets and exomoons from reflected light

2019 ◽  
Vol 19 (3) ◽  
pp. 210-219 ◽  
Author(s):  
Manasvi Lingam ◽  
Abraham Loeb
Keyword(s):  
Carbon Fixation ◽  
Giant Planets ◽  
Oxygenic Photosynthesis ◽  
Late Type ◽  
M Dwarfs ◽  
Convenient Means ◽  
Reflected Light ◽  
Orbital Instability ◽  
Long Timescales ◽  
Physiological And Biochemical

AbstractPhotosynthesis offers a convenient means of sustaining biospheres. We quantify the constraints for photosynthesis to be functional on the permanent nightside of tidally locked rocky exoplanets via reflected light from their exomoons. We show that the exomoons must be at least half the size of Earth's moon in order for conventional oxygenic photosynthesis to operate. This scenario of photosynthesis is unlikely for exoplanets around late-type M-dwarfs due to the low likelihood of large exomoons and their orbital instability over long timescales. Subsequently, we investigate the prospects for photosynthesis on habitable exomoons via reflected light from the giant planets that they orbit. Our analysis indicates that such photosynthetic biospheres are potentially sustainable on these moons except those around late-type M-dwarfs. We conclude our analysis by delineating certain physiological and biochemical features of photosynthesis and other carbon fixation pathways, and the likelihood of their evolution on habitable planets and moons.

scholarly journals Giant planets around AF and M stars

2013 ◽  
Vol 8 (S299) ◽  
pp. 64-65
Author(s):  
Julien Rameau ◽  
Gaël Chauvin ◽  
Anne-Marie Lagrange ◽  
Philippe Delorme ◽  
Justine Lannier
Keyword(s):  
Giant Planets ◽  
Early Type ◽  
Late Type ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Planetary Mass ◽  
Nearby Stars ◽  
Low Mass ◽  
M Stars ◽  
The One

AbstractWe present the results of two three-year surveys of young and nearby stars to search for wide orbit giant planets. On the one hand, we focus on early-type and massive, namely β Pictoris analogs. On the other hand, we observe late type and very low mass stars, i.e., M dwarfs. We report individual detections of new planetary mass objects. According to our deep detection performances, we derive the observed frequency of giant planets between these two classes of parent stars. We find frequency between 6 to 12% but we are not able to assess a/no correlation with the host-mass.

scholarly journals Characteristics of aquatic biospheres on temperate planets around Sun-like stars and M dwarfs

2021 ◽  
Vol 503 (3) ◽  
pp. 3434-3448
Author(s):  
Manasvi Lingam ◽  
Abraham Loeb
Keyword(s):  
Primary Productivity ◽  
Large Scale ◽  
Carbon Fixation ◽  
Net Primary Productivity ◽  
Effective Rate ◽  
Environmental Variable ◽  
Oxygenic Photosynthesis ◽  
M Dwarfs ◽  
Earth Like Planets ◽  
Rocky Planets

ABSTRACT Aquatic biospheres reliant on oxygenic photosynthesis are expected to play an important role on Earth-like planets endowed with large-scale oceans insofar as carbon fixation (i.e. biosynthesis of organic compounds) is concerned. We investigate the properties of aquatic biospheres comprising Earth-like biota for habitable rocky planets orbiting Sun-like stars and late-type M dwarfs such as TRAPPIST-1. In particular, we estimate how these characteristics evolve with the available flux of photosynthetically active radiation (PAR) and the ambient ocean temperature (TW), the latter of which constitutes a key environmental variable. We show that many salient properties, such as the depth of the photosynthesis zone and the net primary productivity (i.e. the effective rate of carbon fixation), are sensitive to PAR flux and TW and decline substantially when the former is decreased or the latter is increased. We conclude by exploring the implications of our analysis for exoplanets around Sun-like stars and M dwarfs.

scholarly journals A Deep Large area Search for Low Luminosity Stars

1998 ◽  
Vol 11 (1) ◽  
pp. 435-435
Author(s):  
Hugh R.A. Jones ◽  
Mike R.S. Hawkins
Keyword(s):  
Spectral Type ◽  
Low Temperatures ◽  
Current Model ◽  
Brown Dwarfs ◽  
Evolutionary Models ◽  
Spectral Indices ◽  
Late Type ◽  
Brown Dwarf ◽  
Large Area ◽  
M Dwarfs

In a recent survey for faint red stars from a digital stack of Schmidt plates a number of candidate objects were identified. Parallax’s for three of these objects have been reported showing them to have luminosities which interpreted within the available evolutionary models indicate them to be good brown dwarf candidates. Here we examine spectra of these objects and others from the plate stack. Using standard spectral indices we find that for a given spectral type their spectra are more consistent with the Pleiades brown dwarfs (PPL 15, Teide 1 and Calar 3) than with standard late-type M dwarfs. Our interpretation is that this is due to their selection by RF IN colours which at values > 3 preferentially selects objects with relatively low gravities. For late-type M dwarfs and brown dwarfs low gravities are expected to be a reliable indication of youth. We also notice that the stack objects generally have strong FeH absorption for their spectral type. Current model atmospheres suggest that FeH strongly increases in strength toward lower metallicities and lower temperatures. We believe that this is not consistent with the available observational evidence from late-type M dwarfs. It is possible that solid Fe is forming inthe low temperature atmospheres relatively depleting FeH strengths toward lower temperatures. We find some evidence that for dwarfs at low temperatures dust formation is less prevalent in lower gravity objects suggesting that dwarfs at low temperatures stronger FeH may be an indication of youth. In addition to the spectral evidence the three stack objects whose parallax’s have been measured show small tangential velocities which is a further indication of youth.

scholarly journals Infrared Spectroscopy of Jupiter and Saturn

2002 ◽  
Vol 12 ◽  
pp. 96-98
Author(s):  
Pierre Drossart
Keyword(s):  
Remote Sensing ◽  
Infrared Spectroscopy ◽  
Thermal Emission ◽  
Temporal Evolution ◽  
Imaging Spectroscopy ◽  
Giant Planets ◽  
Infrared Range ◽  
Physical Parameters ◽  
Temperature Structure ◽  
Reflected Light

AbstractThe spectroscopy of giant planets in the infrared range gives access to a remote sensing of many physical parameters. The composition, pressure/temperature structure, and the cloud structure all contribute to the spectrum, in solar reflected light below 3 micrometer as well as thermal emission above, from atmospheric levels ranging from the mesosphere down to the troposphere. Imaging spectroscopy revealing the variability of the atmosphere gives access to spatial and temporal evolution of these parameters, constraining the meteorological evolution of the planets.

scholarly journals A FIRST LOOK AT ROTATION IN INACTIVE LATE-TYPE M DWARFS

2009 ◽  
Vol 693 (2) ◽  
pp. 1283-1289 ◽  
Author(s):  
Andrew A. West ◽  
Gibor Basri
Keyword(s):  
Late Type ◽  
M Dwarfs

scholarly journals Cryptic oxygen cycling in anoxic marine zones

2017 ◽  
Vol 114 (31) ◽  
pp. 8319-8324 ◽  
Author(s):  
Emilio Garcia-Robledo ◽  
Cory C. Padilla ◽  
Montserrat Aldunate ◽  
Frank J. Stewart ◽  
Osvaldo Ulloa ◽  
...  
Keyword(s):  
Surface Layer ◽  
Carbon Fixation ◽  
Nitrogen Loss ◽  
Biogeochemical Cycling ◽  
Oxygenic Photosynthesis ◽  
Nitrite Oxidation ◽  
Tight Coupling ◽  
Expression Of Genes ◽  
Aerobic Processes ◽  
Oxygen Cycling

Oxygen availability drives changes in microbial diversity and biogeochemical cycling between the aerobic surface layer and the anaerobic core in nitrite-rich anoxic marine zones (AMZs), which constitute huge oxygen-depleted regions in the tropical oceans. The current paradigm is that primary production and nitrification within the oxic surface layer fuel anaerobic processes in the anoxic core of AMZs, where 30–50% of global marine nitrogen loss takes place. Here we demonstrate that oxygenic photosynthesis in the secondary chlorophyll maximum (SCM) releases significant amounts of O2to the otherwise anoxic environment. The SCM, commonly found within AMZs, was dominated by the picocyanobacteriaProchlorococcusspp. Free O2levels in this layer were, however, undetectable by conventional techniques, reflecting a tight coupling between O2production and consumption by aerobic processes under apparent anoxic conditions. Transcriptomic analysis of the microbial community in the seemingly anoxic SCM revealed the enhanced expression of genes for aerobic processes, such as nitrite oxidation. The rates of gross O2production and carbon fixation in the SCM were found to be similar to those reported for nitrite oxidation, as well as for anaerobic dissimilatory nitrate reduction and sulfate reduction, suggesting a significant effect of local oxygenic photosynthesis on Pacific AMZ biogeochemical cycling.

scholarly journals PII-like signaling protein SbtB links cAMP sensing with cyanobacterial inorganic carbon response

2018 ◽  
Vol 115 (21) ◽  
pp. E4861-E4869 ◽  
Author(s):  
Khaled A. Selim ◽  
Florian Haase ◽  
Marcus D. Hartmann ◽  
Martin Hagemann ◽  
Karl Forchhammer
Keyword(s):  
Inorganic Carbon ◽  
Nucleotide Binding ◽  
Binding Pocket ◽  
Oxygenic Photosynthesis ◽  
Binding Modes ◽  
Signaling Protein ◽  
Evolutionarily Conserved ◽  
Photosynthetic Production ◽  
The Individual ◽  
Physiological And Biochemical

Cyanobacteria are phototrophic prokaryotes that evolved oxygenic photosynthesis ∼2.7 billion y ago and are presently responsible for ∼10% of total global photosynthetic production. To cope with the evolutionary pressure of dropping ambient CO2 concentrations, they evolved a CO2-concentrating mechanism (CCM) to augment intracellular inorganic carbon (Ci) levels for efficient CO2 fixation. However, how cyanobacteria sense the fluctuation in Ci is poorly understood. Here we present biochemical, structural, and physiological insights into SbtB, a unique PII-like signaling protein, which provides new insights into Ci sensing. SbtB is highly conserved in cyanobacteria and is coexpressed with CCM genes. The SbtB protein from the cyanobacterium Synechocystis sp. PCC 6803 bound a variety of adenosine nucleotides, including the second messenger cAMP. Cocrystal structures unraveled the individual binding modes of trimeric SbtB with AMP and cAMP. The nucleotide-binding pocket is located between the subunit clefts of SbtB, perfectly matching the structure of canonical PII proteins. This clearly indicates that proteins of the PII superfamily arose from a common ancestor, whose structurally conserved nucleotide-binding pocket has evolved to sense different adenyl nucleotides for various signaling functions. Moreover, we provide physiological and biochemical evidence for the involvement of SbtB in Ci acclimation. Collectively, our results suggest that SbtB acts as a Ci sensor protein via cAMP binding, highlighting an evolutionarily conserved role for cAMP in signaling the cellular carbon status.

scholarly journals AN ACTIVITY–ROTATION RELATIONSHIP AND KINEMATIC ANALYSIS OF NEARBY MID-TO-LATE-TYPE M DWARFS

2015 ◽  
Vol 812 (1) ◽  
pp. 3 ◽  
Author(s):  
Andrew A. West ◽  
Kolby L. Weisenburger ◽  
Jonathan Irwin ◽  
Zachory K. Berta-Thompson ◽  
David Charbonneau ◽  
...  
Keyword(s):  
Kinematic Analysis ◽  
Late Type ◽  
M Dwarfs

scholarly journals Age, Activity and Rotation in Mid and Late-Type M Dwarfs from MEarth

2013 ◽  
Vol 9 (S302) ◽  
pp. 176-179
Author(s):  
Andrew A. West ◽  
Kolby L. Weisenburger ◽  
Jonathan Irwin ◽  
David Charbonneau ◽  
Jason Dittmann ◽  
...  
Keyword(s):  
Dimensional Space ◽  
Large Fraction ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Rotating Stars ◽  
Late Type ◽  
M Dwarfs ◽  
Magnetic Field Generation ◽  
Rotation Periods ◽  
Wide Range

AbstractUsing spectroscopic observations and photometric light curves of 280 nearby M dwarfs from the MEarth exoplanet transit survey, we examine the relationships between magnetic activity (quantified by Hα emission), rotation period, and stellar age (derived from three-dimensional space velocities). Although we have known for decades that a large fraction of mid-late-type M dwarfs are magnetically active, it was not clear what role rotation played in the magnetic field generation (and subsequent chromospheric heating). Previous attempts to investigate the relationship between magnetic activity and rotation in mid-late-type M dwarfs were hampered by the limited number of M dwarfs with measured rotation periods (and the fact that vsini measurements only probe rapid rotation). However, the photometric data from the MEarth survey allows us to probe a wide range of rotation periods for hundreds of M dwarf stars (from less than one to over 100 days). Over all M spectral types we find that magnetic activity decreases with longer rotation periods, including late-type, fully convective M dwarfs. We find that the most magnetically active (and hence, most rapidly rotating) stars are consistent with a kinematically young population, while slow-rotators are less active or inactive and appear to belong to an older, dynamically heated stellar population.

scholarly journals PHOENIX model chromospheres of mid- to late-type M dwarfs

2005 ◽  
Vol 439 (3) ◽  
pp. 1137-1148 ◽  
Author(s):  
B. Fuhrmeister ◽  
J. H. M. M. Schmitt ◽  
P. H. Hauschildt
Keyword(s):  
Late Type ◽  
M Dwarfs
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