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Papers by Antigona Segura
Encyclopedia of Astrobiology, 2015
In this presentation, we discuss the possibility for abiotic processes to produce O2 and O3, and ... more In this presentation, we discuss the possibility for abiotic processes to produce O2 and O3, and examine how to discriminate between false and true positives.
The Astrophysical Journal, 2014
Applied Physics Letters, 2006
The authors report on x-ray absorption measurements performed on Zn1-xMnxO (x=0.05,0.25) at the M... more The authors report on x-ray absorption measurements performed on Zn1-xMnxO (x=0.05,0.25) at the Mn K edge (6539 eV) under high pressure. Mn is found to substitute for Zn both in the low pressure wurtzite phase and in the high pressure rocksalt phase. The Mn-O bond length is determined to be 2.02+/-0.01 A˚ at ambient conditions, with a compressibility similar to
![Research paper thumbnail of Effects of high pressure on the optical absorption spectrum of scintillating PbWO[sub 4] crystals](https://attachments.academia-assets.com/54336640/thumbnails/1.jpg)
](Applied Physics Letters, 2006
Applied Physics Letters, 2006
In this study, the application of synchrotron radiation microprobe to the analysis of Co incorpor... more In this study, the application of synchrotron radiation microprobe to the analysis of Co incorporation in Zn1-xCoxO is reported. From the Co and Zn fluorescence line intensity ratio, the Co concentrations were deduced. A combination of fluorescence mapping with x-ray absorption spectroscopic techniques made possible to examine not only the uniform elemental distribution but also the short range structural order
Applied Physics Letters, 2011
Applied Physics Letters, 2003
On Earth, methane is produced mainly by life, and it has been proposed that, under certain condit... more On Earth, methane is produced mainly by life, and it has been proposed that, under certain conditions, methane
detected in an exoplanetary spectrum may be considered a biosignature. Here, we estimate how much methane
may be produced in hydrothermal vent systems by serpentinization, its main geological source, using the kinetic
properties of the main reactions involved in methane production by serpentinization. Hydrogen production by
serpentinization was calculated as a function of the available FeO in the crust, given the current spreading rates.
Carbon dioxide is the limiting reactant for methane formation because it is highly depleted in aqueous form
in hydrothermal vent systems. We estimated maximum CH4 surface fluxes of 6.8 · 108 and 1.3 · 109 molecules
cm- 2 s - 1 for rocky planets with 1 and 5 M4, respectively. Using a 1-D photochemical model, we simulated
atmospheres with volume mixing ratios of 0.03 and 0.1 CO2 to calculate atmospheric methane concentrations for
the maximum production of this compound by serpentinization. The resulting abundances were 2.5 and
2.1 ppmv for 1 M4 planets and 4.1 and 3.7ppmv for 5 M4 planets. Therefore, low atmospheric concentrations of
methane may be produced by serpentinization. For habitable planets around Sun-like stars with N2-CO2 atmospheres,
methane concentrations larger than 10 ppmv may indicate the presence of life.
The search for life on planets outside our solar system will use spectroscopic identification of ... more The search for life on planets outside our solar system will use spectroscopic identification of atmospheric
biosignatures. The most robust remotely detectable potential biosignature is considered to be the detection of
oxygen (O2) or ozone (O3) simultaneous to methane (CH4) at levels indicating fluxes from the planetary surface in
excess of those that could be produced abiotically. Here we use an altitude-dependent photochemical model with the
enhanced lower boundary conditions necessary to carefully explore abiotic O2 and O3 production on lifeless planets
with a wide variety of volcanic gas fluxes and stellar energy distributions. On some of these worlds, we predict
limited O2 and O3 buildup, caused by fast chemical production of these gases. This results in detectable abiotic O3
and CH4 features in the UV-visible, but no detectable abiotic O2 features. Thus, simultaneous detection of O3 and
CH4 by a UV-visible mission is not a strong biosignature without proper contextual information. Discrimination
between biological and abiotic sources of O2 and O3 is possible through analysis of the stellar and atmospheric
context—particularly redox state and O atom inventory—of the planet in question. Specifically, understanding
the spectral characteristics of the star and obtaining a broad wavelength range for planetary spectra should allow
more robust identification of false positives for life. This highlights the importance of wide spectral coverage
for future exoplanet characterization missions. Specifically, discrimination between true and false positives may
require spectral observations that extend into infrared wavelengths and provide contextual information on the
planet’s atmospheric chemistry.
Astrobiology, 2007
Stable, hydrogen-burning, M dwarf stars make up about 75% of all stars in the Galaxy. They are ex... more Stable, hydrogen-burning, M dwarf stars make up about 75% of all stars in the Galaxy. They are extremely long-lived, and because they are much smaller in mass than the Sun (between 0.5 and 0.08 MSun), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially habitable, wet planets that reside within their habitable zones, which are only about one-fifth to 1/50th of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone does not necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity or thermal and nonthermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life. This paper presents the summary conclusions of an interdisciplinary workshop (http://mstars.seti.org) sponsored by the NASA Astrobiology Institute and convened at the SETI Institute. Key Words: Planets-Habitability-M dwarfs-Stars. Astrobiology 7, 30-65. M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially habitable, wet planets that reside within their habitable zones, which are only about one-fifth to 1/50th of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone does not necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity or thermal and nonthermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life. This paper presents the summary conclusions of an interdisciplinary workshop (http://mstars.seti.org) sponsored by the NASA Astrobiology Institute and convened at the SETI Institute. Key Words: Planets-Habitability-M dwarfs-Stars. Astrobiology 7, 30-65.
Stable, hydrogen-burning, M dwarf stars comprise about 75% of all stars in the Galaxy. They are e... more Stable, hydrogen-burning, M dwarf stars comprise about 75% of all stars in the Galaxy. They are extremely long-lived and because they are much smaller in mass than the Sun (between 0.5 and 0.08 MSun), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially-habitable, wet planets residing within their habitable zones, which are only ~ 1/5 to 1/50 of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone doesn't necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity, or thermal and non-thermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life.
Encyclopedia of Astrobiology, 2015
In this presentation, we discuss the possibility for abiotic processes to produce O2 and O3, and ... more In this presentation, we discuss the possibility for abiotic processes to produce O2 and O3, and examine how to discriminate between false and true positives.
The Astrophysical Journal, 2014
Applied Physics Letters, 2006
The authors report on x-ray absorption measurements performed on Zn1-xMnxO (x=0.05,0.25) at the M... more The authors report on x-ray absorption measurements performed on Zn1-xMnxO (x=0.05,0.25) at the Mn K edge (6539 eV) under high pressure. Mn is found to substitute for Zn both in the low pressure wurtzite phase and in the high pressure rocksalt phase. The Mn-O bond length is determined to be 2.02+/-0.01 A˚ at ambient conditions, with a compressibility similar to
Applied Physics Letters, 2006
Applied Physics Letters, 2006
In this study, the application of synchrotron radiation microprobe to the analysis of Co incorpor... more In this study, the application of synchrotron radiation microprobe to the analysis of Co incorporation in Zn1-xCoxO is reported. From the Co and Zn fluorescence line intensity ratio, the Co concentrations were deduced. A combination of fluorescence mapping with x-ray absorption spectroscopic techniques made possible to examine not only the uniform elemental distribution but also the short range structural order
Applied Physics Letters, 2011
Applied Physics Letters, 2003
On Earth, methane is produced mainly by life, and it has been proposed that, under certain condit... more On Earth, methane is produced mainly by life, and it has been proposed that, under certain conditions, methane
detected in an exoplanetary spectrum may be considered a biosignature. Here, we estimate how much methane
may be produced in hydrothermal vent systems by serpentinization, its main geological source, using the kinetic
properties of the main reactions involved in methane production by serpentinization. Hydrogen production by
serpentinization was calculated as a function of the available FeO in the crust, given the current spreading rates.
Carbon dioxide is the limiting reactant for methane formation because it is highly depleted in aqueous form
in hydrothermal vent systems. We estimated maximum CH4 surface fluxes of 6.8 · 108 and 1.3 · 109 molecules
cm- 2 s - 1 for rocky planets with 1 and 5 M4, respectively. Using a 1-D photochemical model, we simulated
atmospheres with volume mixing ratios of 0.03 and 0.1 CO2 to calculate atmospheric methane concentrations for
the maximum production of this compound by serpentinization. The resulting abundances were 2.5 and
2.1 ppmv for 1 M4 planets and 4.1 and 3.7ppmv for 5 M4 planets. Therefore, low atmospheric concentrations of
methane may be produced by serpentinization. For habitable planets around Sun-like stars with N2-CO2 atmospheres,
methane concentrations larger than 10 ppmv may indicate the presence of life.
The search for life on planets outside our solar system will use spectroscopic identification of ... more The search for life on planets outside our solar system will use spectroscopic identification of atmospheric
biosignatures. The most robust remotely detectable potential biosignature is considered to be the detection of
oxygen (O2) or ozone (O3) simultaneous to methane (CH4) at levels indicating fluxes from the planetary surface in
excess of those that could be produced abiotically. Here we use an altitude-dependent photochemical model with the
enhanced lower boundary conditions necessary to carefully explore abiotic O2 and O3 production on lifeless planets
with a wide variety of volcanic gas fluxes and stellar energy distributions. On some of these worlds, we predict
limited O2 and O3 buildup, caused by fast chemical production of these gases. This results in detectable abiotic O3
and CH4 features in the UV-visible, but no detectable abiotic O2 features. Thus, simultaneous detection of O3 and
CH4 by a UV-visible mission is not a strong biosignature without proper contextual information. Discrimination
between biological and abiotic sources of O2 and O3 is possible through analysis of the stellar and atmospheric
context—particularly redox state and O atom inventory—of the planet in question. Specifically, understanding
the spectral characteristics of the star and obtaining a broad wavelength range for planetary spectra should allow
more robust identification of false positives for life. This highlights the importance of wide spectral coverage
for future exoplanet characterization missions. Specifically, discrimination between true and false positives may
require spectral observations that extend into infrared wavelengths and provide contextual information on the
planet’s atmospheric chemistry.
Astrobiology, 2007
Stable, hydrogen-burning, M dwarf stars make up about 75% of all stars in the Galaxy. They are ex... more Stable, hydrogen-burning, M dwarf stars make up about 75% of all stars in the Galaxy. They are extremely long-lived, and because they are much smaller in mass than the Sun (between 0.5 and 0.08 MSun), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially habitable, wet planets that reside within their habitable zones, which are only about one-fifth to 1/50th of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone does not necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity or thermal and nonthermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life. This paper presents the summary conclusions of an interdisciplinary workshop (http://mstars.seti.org) sponsored by the NASA Astrobiology Institute and convened at the SETI Institute. Key Words: Planets-Habitability-M dwarfs-Stars. Astrobiology 7, 30-65. M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially habitable, wet planets that reside within their habitable zones, which are only about one-fifth to 1/50th of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone does not necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity or thermal and nonthermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life. This paper presents the summary conclusions of an interdisciplinary workshop (http://mstars.seti.org) sponsored by the NASA Astrobiology Institute and convened at the SETI Institute. Key Words: Planets-Habitability-M dwarfs-Stars. Astrobiology 7, 30-65.
Stable, hydrogen-burning, M dwarf stars comprise about 75% of all stars in the Galaxy. They are e... more Stable, hydrogen-burning, M dwarf stars comprise about 75% of all stars in the Galaxy. They are extremely long-lived and because they are much smaller in mass than the Sun (between 0.5 and 0.08 MSun), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially-habitable, wet planets residing within their habitable zones, which are only ~ 1/5 to 1/50 of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone doesn't necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity, or thermal and non-thermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life.