The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
David Charbonneau - One of the best experts on this subject based on the ideXlab platform.
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a precise water abundance measurement for the hot jupiter wasp 43b
arXiv: Earth and Planetary Astrophysics, 2014Co-Authors: Laura Kreidberg, David Charbonneau, Adam P. Showman, Jonathan J. Fortney, Nikku Madhusudhan, Michael R Line, Jacob L Bean, Jeanmichel Desert, Kevin B Stevenson, P R McculloughAbstract:The water abundance in a Planetary Atmosphere provides a key constraint on the planet's primordial origins because water ice is expected to play an important role in the core accretion model of planet formation. However, the water content of the Solar System giant planets is not well known because water is sequestered in clouds deep in their Atmospheres. By contrast, short-period exoplanets have such high temperatures that their Atmospheres have water in the gas phase, making it possible to measure the water abundance for these objects. We present a precise determination of the water abundance in the Atmosphere of the 2 $M_\mathrm{Jup}$ short-period exoplanet WASP-43b based on thermal emission and transmission spectroscopy measurements obtained with the Hubble Space Telescope. We find the water content is consistent with the value expected in a solar composition gas at Planetary temperatures (0.4-3.5x solar at 1 $\sigma$ confidence). The metallicity of WASP-43b's Atmosphere suggested by this result extends the trend observed in the Solar System of lower metal enrichment for higher planet masses.
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a precise water abundance measurement for the hot jupiter wasp 43b
The Astrophysical Journal, 2014Co-Authors: Laura Kreidberg, David Charbonneau, Adam P. Showman, Jonathan J. Fortney, Nikku Madhusudhan, Michael R Line, Jacob L Bean, Jeanmichel Desert, Kevin B Stevenson, P R McculloughAbstract:The water abundance in a Planetary Atmosphere provides a key constraint on the planet’s primordial origins because water ice is expected to play an important role in the core accretion model of planet formation. However, the water content of the Solar System giant planets is not well known because water is sequestered in clouds deep in their Atmospheres. By contrast, short-period exoplanets have such high temperatures that their Atmospheres have water in the gas phase, making it possible to measure the water abundance for these objects. We present a precise determination of the water abundance in the Atmosphere of the 2 MJup short-period exoplanet WASP-43b based on thermal emission and transmission spectroscopy measurements obtained with the Hubble Space Telescope. We nd the water content is consistent with the value expected in a solar composition gas at Planetary temperatures (0:4 3:5 solar at 1 condence). The metallicity of WASP-43b’s Atmosphere suggested by this result extends the trend observed in the Solar System of lower metal enrichment for higher planet masses. Subject headings: planets and satellites: Atmospheres | planets and satellites: composition | planets and satellites: individual: WASP-43b
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detection of atmospheric haze on an extrasolar planet the 0 55 1 05 μm transmission spectrum of hd 189733b with the hubble space telescope
Monthly Notices of the Royal Astronomical Society, 2008Co-Authors: F Pont, Ronald L Gilliland, C. Moutou, Heather Knutson, David CharbonneauAbstract:The nearby transiting planet HD 189733b was observed during three transits with the Advanced Camera for Surveys of the Hubble Space Telescope in spectroscopic mode. The resulting time-series of 675 spectra covers the 550–1050 nm range, with a resolution element of ∼8 nm, at extremely high accuracy (signal-to-noise ratio up to 10 000 in 50-nm intervals in each individual spectrum). Using these data, we disentangle the effects of limb darkening, measurement systematics and spots on the surface of the host star, to calculate the wavelength dependence of the effective transit radius to an accuracy of ∼50 km. This constitutes the ‘transmission spectrum’ of the Planetary Atmosphere. It indicates at each wavelength at what height the Planetary Atmosphere becomes opaque to the grazing stellar light during the transit. In this wavelength range, strong features due to sodium, potassium and water are predicted by Atmosphere models for a planet like HD 189733b, but they can be hidden by broad absorption from clouds or hazes higher up in the Atmosphere. We observed an almost featureless transmission spectrum between 550 and 1050 nm, with no indication of the expected sodium or potassium atomic absorption features. Comparison of our results with the transit radius observed in the near and mid-infrared (2–8 μm), and the slope of the spectrum, suggest the presence of a haze of submicrometre particles in the upper Atmosphere of the planet.
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detection of atmospheric haze on an extrasolar planet the 0 55 1 05 micron transmission spectrum of hd189733b with the hubble space telescope
arXiv: Astrophysics, 2007Co-Authors: F Pont, Heather A. Knutson, Ronald L Gilliland, C. Moutou, David CharbonneauAbstract:The nearby transiting planet HD 189733b was observed during three transits with the ACS camera of the Hubble Space Telescope in spectroscopic mode. The resulting time series of 675 spectra covers the 550-1050 nm range, with a resolution element of ~8 nm, at extremely high accuracy (signal-to-noise ratio up to 10,000 in 50 nm intervals in each individual spectrum). Using these data, we disentangle the effects of limb darkening, measurement systematics, and spots on the surface of the host star, to calculate the wavelength dependence of the effective transit radius to an accuracy of ~50 km. This constitutes the ``transmission spectrum'' of the Planetary Atmosphere. It indicates at each wavelength at what height the Planetary Atmosphere becomes opaque to the grazing stellar light during the transit. In this wavelength range, strong features due to sodium, potassium and water are predicted by Atmosphere models for a planet like HD 189733b, but they can be hidden by broad absorption from clouds or hazes higher up in the Atmosphere. We observed an almost featureless transmission spectrum between 550 and 1050 nm, with no indication of the expected sodium or potassium atomic absorption features. Comparison of our results with the transit radius observed in the near and mid-infrared (2-8 microns), and the slope of the spectrum, suggest the presence of a haze of sub-micron particles in the upper Atmosphere of the planet.
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a new search for carbon monoxide absorption in the transmission spectrum of the extrasolar planet hd 209458b
The Astrophysical Journal, 2005Co-Authors: Drake Deming, David Charbonneau, Timothy M Brown, Joseph Harrington, Jeremy L RichardsonAbstract:We have revisited the search for carbon monoxide absorption features in transmission during the transit of the extrasolar planet HD 209458b. In 2002 August-September we acquired a total of 1077 high-resolution spectra (λ/δλ ~ 25,000) in the K-band (2 μm) wavelength region using NIRSPEC on the Keck II telescope during three transits. These data are more numerous and of better quality than the data analyzed in an initial search by Brown et al. Our analysis achieves a sensitivity sufficient to test the degree of CO absorption in the first-overtone bands during transit on the basis of plausible models of the Planetary Atmosphere. We analyze our observations by comparison with theoretical tangent geometry absorption spectra, computed by adding height-invariant ad hoc temperature perturbations to the model Atmosphere of Sudarsky et al. and by treating cloud height as an adjustable parameter. We do not detect CO absorption. The strong 2-0 R-branch lines between 4320 and 4330 cm-1 have depths during transit less than 1.6 parts in 104 in units of the stellar continuum (3 σ limit) at a spectral resolving power of 25,000. Our analysis indicates a weakening similar to that found in the case of sodium, suggesting that a general masking mechanism is at work in the Planetary Atmosphere. Under the interpretation that this masking is provided by high clouds, our analysis defines the maximum cloud-top pressure (i.e., minimum height) as a function of the model atmospheric temperature. For the relatively hot model used by Charbonneau et al. to interpret their sodium detection, our CO limit requires cloud tops at or above 3.3 mbar, and these clouds must be opaque at a wavelength of 2 μm. High clouds comprised of submicron-sized particles are already present in some models but may not provide sufficient opacity to account for our CO result. Cooler model Atmospheres, having smaller atmospheric scale heights and lower CO mixing ratios, may alleviate this problem to some extent. However, even models 500 K cooler than the Sudarsky et al. model require clouds above the 100 mbar level to be consistent with our observations. Our null result therefore requires clouds to exist at an observable level in the Atmosphere of HD 209458b, unless this planet is dramatically colder than current belief.
Jeanmathias Griesmeier - One of the best experts on this subject based on the ideXlab platform.
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galactic cosmic rays on extrasolar earth like planets i cosmic ray flux
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: Jeanmathias Griesmeier, F Tabatabavakili, A Stadelmann, John Lee Grenfell, Dimitra AtriAbstract:(abridged abstract) Theoretical arguments indicate that close-in terrestial exoplanets may have weak magnetic fields, especially in the case of planets more massive than Earth (super-Earths). Planetary magnetic fields, however, constitute one of the shielding layers that protect the planet against cosmic-ray particles. In particular, a weak magnetic field results in a high flux of Galactic cosmic rays that extends to the top of the Planetary Atmosphere. We wish to quantify the flux of Galactic cosmic rays to an exoPlanetary Atmosphere as a function of the particle energy and of the Planetary magnetic moment. We numerically analyzed the propagation of Galactic cosmic-ray particles through Planetary magnetospheres. We evaluated the efficiency of magnetospheric shielding as a function of the particle energy (in the range 16 MeV $\le$ E $\le$ 524 GeV) and as a function of the Planetary magnetic field strength (in the range 0 ${M}_\oplus$ $\le$ {M} $\le$ 10 ${M}_\oplus$). Combined with the flux outside the Planetary magnetosphere, this gives the cosmic-ray energy spectrum at the top of the Planetary Atmosphere as a function of the Planetary magnetic moment. We find that the particle flux to the Planetary Atmosphere can be increased by more than three orders of magnitude in the absence of a protecting magnetic field. For a weakly magnetized planet (${M}=0.05\,{M}_{\oplus}$), only particles with energies below 512 MeV are at least partially shielded. For a planet with a magnetic moment similar to Earth, this limit increases to 32 GeV, whereas for a strongly magnetized planet ($M=10.0\,{M}_{\oplus}$), partial shielding extends up to 200 GeV. We find that magnetic shielding strongly controls the number of cosmic-ray particles reaching the Planetary Atmosphere. The implications of this increased particle flux are discussed in a companion article.
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galactic cosmic rays on extrasolar earth like planets i cosmic ray flux
Astronomy and Astrophysics, 2015Co-Authors: Jeanmathias Griesmeier, F Tabatabavakili, A Stadelmann, John Lee Grenfell, Dimitra AtriAbstract:Context. Theoretical arguments indicate that close-in terrestial exoplanets may have weak magnetic fields, especially in the case of planets more massive than Earth (super-Earths). Planetary magnetic fields, however, constitute one of the shielding layers that protect the planet against cosmic-ray particles. In particular, a weak magnetic field results in a high flux of Galactic cosmic rays that extends to the top of the Planetary Atmosphere. Aims. We wish to quantify the flux of Galactic cosmic rays to an exoPlanetary Atmosphere as a function of the particle energy and of the Planetary magnetic moment. Methods. We numerically analyzed the propagation of Galactic cosmic-ray particles through Planetary magnetospheres. We evaluated the efficiency of magnetospheric shielding as a function of the particle energy (in the range 16 MeV ≤ E ≤ 524 GeV) and as a function of the Planetary magnetic field strength (in the range 0 M ⊕ ≤ M ≤ 10 M ⊕). Combined with the flux outside the Planetary magnetosphere, this gives the cosmic-ray energy spectrum at the top of the Planetary Atmosphere as a function of the Planetary magnetic moment. Results. We find that the particle flux to the Planetary Atmosphere can be increased by more than three orders of magnitude in the absence of a protecting magnetic field. For a weakly magnetized planet (M = 0.05 M ⊕), only particles with energies below 512 MeV are at least partially shielded. For a planet with a magnetic moment similar to that of Earth, this limit increases to to 32 GeV, whereas for a strongly magnetized planet (M = 10.0 M ⊕), partial shielding extends up to 200 GeV. Over the parameter range we studied, strong shielding does not occur for weakly magnetized planets. For a planet with a magnetic moment similar to that of Earth, particles with energies below 512 MeV are strongly shielded, and for strongly magnetized planets, this limit increases to 10 GeV. Conclusions. We find that magnetic shielding strongly controls the number of cosmic-ray particles reaching the Planetary Atmosphere. The implications of this increased particle flux are discussed in a companion article.
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galactic cosmic ray induced radiation dose on terrestrial exoplanets
Astrobiology, 2013Co-Authors: Dimitra Atri, B Hariharan, Jeanmathias GriesmeierAbstract:This past decade has seen tremendous advancements in the study of extrasolar planets. Observations are now made with increasing sophistication from both ground- and space-based instruments, and exoplanets are characterized with increasing precision. There is a class of particularly interesting exoplanets that reside in the habitable zone, which is defined as the area around a star where the planet is capable of supporting liquid water on its surface. Planetary systems around M dwarfs are considered to be prime candidates to search for life beyond the Solar System. Such planets are likely to be tidally locked and have close-in habitable zones. Theoretical calculations also suggest that close-in exoplanets are more likely to have weaker Planetary magnetic fields, especially in the case of super-Earths. Such exoplanets are subjected to a high flux of galactic cosmic rays (GCRs) due to their weak magnetic moments. GCRs are energetic particles of astrophysical origin that strike the Planetary Atmosphere and produce secondary particles, including muons, which are highly penetrating. Some of these particles reach the Planetary surface and contribute to the radiation dose. Along with the magnetic field, another factor governing the radiation dose is the depth of the Planetary Atmosphere. The higher the depth of the Planetary Atmosphere, the lower the flux of secondary particles will be on the surface. If the secondary particles are energetic enough, and their flux is sufficiently high, the radiation from muons can also impact the subsurface regions, such as in the case of Mars. If the radiation dose is too high, the chances of sustaining a long-term biosphere on the planet are very low. We have examined the dependence of the GCR-induced radiation dose on the strength of the Planetary magnetic field and its atmospheric depth, and found that the latter is the decisive factor for the protection of a Planetary biosphere. Key Words: RadiationRadiation physicsHabitabilityHabitable zonePlanetary Atmospheres.
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response of atmospheric biomarkers to nox induced photochemistry generated by stellar cosmic rays for earth like planets in the habitable zone of m dwarf stars
Astrobiology, 2012Co-Authors: John Lee Grenfell, H Lammer, Jeanmathias Griesmeier, Philip Von Paris, Beate A C Patzer, Barbara Stracke, Stefanie Gebauer, Franz Schreier, H RauerAbstract:Abstract Understanding whether M dwarf stars may host habitable planets with Earth-like Atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N2), which leads to production of nitrogen oxides (NOx) in the Planetary Atmosphere, hence affecting biomarkers such as ozone (O3). We apply a stationary model, that is, without a time dependence; hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared...
John Lee Grenfell - One of the best experts on this subject based on the ideXlab platform.
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galactic cosmic rays on extrasolar earth like planets i cosmic ray flux
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: Jeanmathias Griesmeier, F Tabatabavakili, A Stadelmann, John Lee Grenfell, Dimitra AtriAbstract:(abridged abstract) Theoretical arguments indicate that close-in terrestial exoplanets may have weak magnetic fields, especially in the case of planets more massive than Earth (super-Earths). Planetary magnetic fields, however, constitute one of the shielding layers that protect the planet against cosmic-ray particles. In particular, a weak magnetic field results in a high flux of Galactic cosmic rays that extends to the top of the Planetary Atmosphere. We wish to quantify the flux of Galactic cosmic rays to an exoPlanetary Atmosphere as a function of the particle energy and of the Planetary magnetic moment. We numerically analyzed the propagation of Galactic cosmic-ray particles through Planetary magnetospheres. We evaluated the efficiency of magnetospheric shielding as a function of the particle energy (in the range 16 MeV $\le$ E $\le$ 524 GeV) and as a function of the Planetary magnetic field strength (in the range 0 ${M}_\oplus$ $\le$ {M} $\le$ 10 ${M}_\oplus$). Combined with the flux outside the Planetary magnetosphere, this gives the cosmic-ray energy spectrum at the top of the Planetary Atmosphere as a function of the Planetary magnetic moment. We find that the particle flux to the Planetary Atmosphere can be increased by more than three orders of magnitude in the absence of a protecting magnetic field. For a weakly magnetized planet (${M}=0.05\,{M}_{\oplus}$), only particles with energies below 512 MeV are at least partially shielded. For a planet with a magnetic moment similar to Earth, this limit increases to 32 GeV, whereas for a strongly magnetized planet ($M=10.0\,{M}_{\oplus}$), partial shielding extends up to 200 GeV. We find that magnetic shielding strongly controls the number of cosmic-ray particles reaching the Planetary Atmosphere. The implications of this increased particle flux are discussed in a companion article.
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galactic cosmic rays on extrasolar earth like planets i cosmic ray flux
Astronomy and Astrophysics, 2015Co-Authors: Jeanmathias Griesmeier, F Tabatabavakili, A Stadelmann, John Lee Grenfell, Dimitra AtriAbstract:Context. Theoretical arguments indicate that close-in terrestial exoplanets may have weak magnetic fields, especially in the case of planets more massive than Earth (super-Earths). Planetary magnetic fields, however, constitute one of the shielding layers that protect the planet against cosmic-ray particles. In particular, a weak magnetic field results in a high flux of Galactic cosmic rays that extends to the top of the Planetary Atmosphere. Aims. We wish to quantify the flux of Galactic cosmic rays to an exoPlanetary Atmosphere as a function of the particle energy and of the Planetary magnetic moment. Methods. We numerically analyzed the propagation of Galactic cosmic-ray particles through Planetary magnetospheres. We evaluated the efficiency of magnetospheric shielding as a function of the particle energy (in the range 16 MeV ≤ E ≤ 524 GeV) and as a function of the Planetary magnetic field strength (in the range 0 M ⊕ ≤ M ≤ 10 M ⊕). Combined with the flux outside the Planetary magnetosphere, this gives the cosmic-ray energy spectrum at the top of the Planetary Atmosphere as a function of the Planetary magnetic moment. Results. We find that the particle flux to the Planetary Atmosphere can be increased by more than three orders of magnitude in the absence of a protecting magnetic field. For a weakly magnetized planet (M = 0.05 M ⊕), only particles with energies below 512 MeV are at least partially shielded. For a planet with a magnetic moment similar to that of Earth, this limit increases to to 32 GeV, whereas for a strongly magnetized planet (M = 10.0 M ⊕), partial shielding extends up to 200 GeV. Over the parameter range we studied, strong shielding does not occur for weakly magnetized planets. For a planet with a magnetic moment similar to that of Earth, particles with energies below 512 MeV are strongly shielded, and for strongly magnetized planets, this limit increases to 10 GeV. Conclusions. We find that magnetic shielding strongly controls the number of cosmic-ray particles reaching the Planetary Atmosphere. The implications of this increased particle flux are discussed in a companion article.
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response of atmospheric biomarkers to nox induced photochemistry generated by stellar cosmic rays for earth like planets in the habitable zone of m dwarf stars
Astrobiology, 2012Co-Authors: John Lee Grenfell, H Lammer, Jeanmathias Griesmeier, Philip Von Paris, Beate A C Patzer, Barbara Stracke, Stefanie Gebauer, Franz Schreier, H RauerAbstract:Abstract Understanding whether M dwarf stars may host habitable planets with Earth-like Atmospheres and biospheres is a major goal in exoplanet research. If such planets exist, the question remains as to whether they could be identified via spectral signatures of biomarkers. Such planets may be exposed to extreme intensities of cosmic rays that could perturb their atmospheric photochemistry. Here, we consider stellar activity of M dwarfs ranging from quiet up to strong flaring conditions and investigate one particular effect upon biomarkers, namely, the ability of secondary electrons caused by stellar cosmic rays to break up atmospheric molecular nitrogen (N2), which leads to production of nitrogen oxides (NOx) in the Planetary Atmosphere, hence affecting biomarkers such as ozone (O3). We apply a stationary model, that is, without a time dependence; hence we are calculating the limiting case where the atmospheric chemistry response time of the biomarkers is assumed to be slow and remains constant compared...
Dimitra Atri - One of the best experts on this subject based on the ideXlab platform.
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galactic cosmic rays on extrasolar earth like planets i cosmic ray flux
arXiv: Earth and Planetary Astrophysics, 2015Co-Authors: Jeanmathias Griesmeier, F Tabatabavakili, A Stadelmann, John Lee Grenfell, Dimitra AtriAbstract:(abridged abstract) Theoretical arguments indicate that close-in terrestial exoplanets may have weak magnetic fields, especially in the case of planets more massive than Earth (super-Earths). Planetary magnetic fields, however, constitute one of the shielding layers that protect the planet against cosmic-ray particles. In particular, a weak magnetic field results in a high flux of Galactic cosmic rays that extends to the top of the Planetary Atmosphere. We wish to quantify the flux of Galactic cosmic rays to an exoPlanetary Atmosphere as a function of the particle energy and of the Planetary magnetic moment. We numerically analyzed the propagation of Galactic cosmic-ray particles through Planetary magnetospheres. We evaluated the efficiency of magnetospheric shielding as a function of the particle energy (in the range 16 MeV $\le$ E $\le$ 524 GeV) and as a function of the Planetary magnetic field strength (in the range 0 ${M}_\oplus$ $\le$ {M} $\le$ 10 ${M}_\oplus$). Combined with the flux outside the Planetary magnetosphere, this gives the cosmic-ray energy spectrum at the top of the Planetary Atmosphere as a function of the Planetary magnetic moment. We find that the particle flux to the Planetary Atmosphere can be increased by more than three orders of magnitude in the absence of a protecting magnetic field. For a weakly magnetized planet (${M}=0.05\,{M}_{\oplus}$), only particles with energies below 512 MeV are at least partially shielded. For a planet with a magnetic moment similar to Earth, this limit increases to 32 GeV, whereas for a strongly magnetized planet ($M=10.0\,{M}_{\oplus}$), partial shielding extends up to 200 GeV. We find that magnetic shielding strongly controls the number of cosmic-ray particles reaching the Planetary Atmosphere. The implications of this increased particle flux are discussed in a companion article.
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galactic cosmic rays on extrasolar earth like planets i cosmic ray flux
Astronomy and Astrophysics, 2015Co-Authors: Jeanmathias Griesmeier, F Tabatabavakili, A Stadelmann, John Lee Grenfell, Dimitra AtriAbstract:Context. Theoretical arguments indicate that close-in terrestial exoplanets may have weak magnetic fields, especially in the case of planets more massive than Earth (super-Earths). Planetary magnetic fields, however, constitute one of the shielding layers that protect the planet against cosmic-ray particles. In particular, a weak magnetic field results in a high flux of Galactic cosmic rays that extends to the top of the Planetary Atmosphere. Aims. We wish to quantify the flux of Galactic cosmic rays to an exoPlanetary Atmosphere as a function of the particle energy and of the Planetary magnetic moment. Methods. We numerically analyzed the propagation of Galactic cosmic-ray particles through Planetary magnetospheres. We evaluated the efficiency of magnetospheric shielding as a function of the particle energy (in the range 16 MeV ≤ E ≤ 524 GeV) and as a function of the Planetary magnetic field strength (in the range 0 M ⊕ ≤ M ≤ 10 M ⊕). Combined with the flux outside the Planetary magnetosphere, this gives the cosmic-ray energy spectrum at the top of the Planetary Atmosphere as a function of the Planetary magnetic moment. Results. We find that the particle flux to the Planetary Atmosphere can be increased by more than three orders of magnitude in the absence of a protecting magnetic field. For a weakly magnetized planet (M = 0.05 M ⊕), only particles with energies below 512 MeV are at least partially shielded. For a planet with a magnetic moment similar to that of Earth, this limit increases to to 32 GeV, whereas for a strongly magnetized planet (M = 10.0 M ⊕), partial shielding extends up to 200 GeV. Over the parameter range we studied, strong shielding does not occur for weakly magnetized planets. For a planet with a magnetic moment similar to that of Earth, particles with energies below 512 MeV are strongly shielded, and for strongly magnetized planets, this limit increases to 10 GeV. Conclusions. We find that magnetic shielding strongly controls the number of cosmic-ray particles reaching the Planetary Atmosphere. The implications of this increased particle flux are discussed in a companion article.
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galactic cosmic ray induced radiation dose on terrestrial exoplanets
Astrobiology, 2013Co-Authors: Dimitra Atri, B Hariharan, Jeanmathias GriesmeierAbstract:This past decade has seen tremendous advancements in the study of extrasolar planets. Observations are now made with increasing sophistication from both ground- and space-based instruments, and exoplanets are characterized with increasing precision. There is a class of particularly interesting exoplanets that reside in the habitable zone, which is defined as the area around a star where the planet is capable of supporting liquid water on its surface. Planetary systems around M dwarfs are considered to be prime candidates to search for life beyond the Solar System. Such planets are likely to be tidally locked and have close-in habitable zones. Theoretical calculations also suggest that close-in exoplanets are more likely to have weaker Planetary magnetic fields, especially in the case of super-Earths. Such exoplanets are subjected to a high flux of galactic cosmic rays (GCRs) due to their weak magnetic moments. GCRs are energetic particles of astrophysical origin that strike the Planetary Atmosphere and produce secondary particles, including muons, which are highly penetrating. Some of these particles reach the Planetary surface and contribute to the radiation dose. Along with the magnetic field, another factor governing the radiation dose is the depth of the Planetary Atmosphere. The higher the depth of the Planetary Atmosphere, the lower the flux of secondary particles will be on the surface. If the secondary particles are energetic enough, and their flux is sufficiently high, the radiation from muons can also impact the subsurface regions, such as in the case of Mars. If the radiation dose is too high, the chances of sustaining a long-term biosphere on the planet are very low. We have examined the dependence of the GCR-induced radiation dose on the strength of the Planetary magnetic field and its atmospheric depth, and found that the latter is the decisive factor for the protection of a Planetary biosphere. Key Words: RadiationRadiation physicsHabitabilityHabitable zonePlanetary Atmospheres.
Nikku Madhusudhan - One of the best experts on this subject based on the ideXlab platform.
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a precise water abundance measurement for the hot jupiter wasp 43b
arXiv: Earth and Planetary Astrophysics, 2014Co-Authors: Laura Kreidberg, David Charbonneau, Adam P. Showman, Jonathan J. Fortney, Nikku Madhusudhan, Michael R Line, Jacob L Bean, Jeanmichel Desert, Kevin B Stevenson, P R McculloughAbstract:The water abundance in a Planetary Atmosphere provides a key constraint on the planet's primordial origins because water ice is expected to play an important role in the core accretion model of planet formation. However, the water content of the Solar System giant planets is not well known because water is sequestered in clouds deep in their Atmospheres. By contrast, short-period exoplanets have such high temperatures that their Atmospheres have water in the gas phase, making it possible to measure the water abundance for these objects. We present a precise determination of the water abundance in the Atmosphere of the 2 $M_\mathrm{Jup}$ short-period exoplanet WASP-43b based on thermal emission and transmission spectroscopy measurements obtained with the Hubble Space Telescope. We find the water content is consistent with the value expected in a solar composition gas at Planetary temperatures (0.4-3.5x solar at 1 $\sigma$ confidence). The metallicity of WASP-43b's Atmosphere suggested by this result extends the trend observed in the Solar System of lower metal enrichment for higher planet masses.
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a precise water abundance measurement for the hot jupiter wasp 43b
The Astrophysical Journal, 2014Co-Authors: Laura Kreidberg, David Charbonneau, Adam P. Showman, Jonathan J. Fortney, Nikku Madhusudhan, Michael R Line, Jacob L Bean, Jeanmichel Desert, Kevin B Stevenson, P R McculloughAbstract:The water abundance in a Planetary Atmosphere provides a key constraint on the planet’s primordial origins because water ice is expected to play an important role in the core accretion model of planet formation. However, the water content of the Solar System giant planets is not well known because water is sequestered in clouds deep in their Atmospheres. By contrast, short-period exoplanets have such high temperatures that their Atmospheres have water in the gas phase, making it possible to measure the water abundance for these objects. We present a precise determination of the water abundance in the Atmosphere of the 2 MJup short-period exoplanet WASP-43b based on thermal emission and transmission spectroscopy measurements obtained with the Hubble Space Telescope. We nd the water content is consistent with the value expected in a solar composition gas at Planetary temperatures (0:4 3:5 solar at 1 condence). The metallicity of WASP-43b’s Atmosphere suggested by this result extends the trend observed in the Solar System of lower metal enrichment for higher planet masses. Subject headings: planets and satellites: Atmospheres | planets and satellites: composition | planets and satellites: individual: WASP-43b
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water vapor in the spectrum of the extrasolar planet hd 189733b i the transit
The Astrophysical Journal, 2014Co-Authors: Drake Deming, Peter R Mccullough, N Crouzet, Nikku MadhusudhanAbstract:We report near-infrared spectroscopy of the gas giant planet HD 189733b in transit. We used the Hubble Space Telescope Wide Field Camera 3 (HST WFC3) with its G141 grism covering 1.1 μm to 1.7 μm and spatially scanned the image across the detector at 2'' s{sup –1}. When smoothed to 75 nm bins, the local maxima of the transit depths in the 1.15 μm and 1.4 μm water vapor features are, respectively, 83 ± 53 ppm and 200 ± 47 ppm greater than the local minimum at 1.3 μm. We compare the WFC3 spectrum with the composite transit spectrum of HD 189733b assembled by Pont et al., extending from 0.3 μm to 24 μm. Although the water vapor features in the WFC3 spectrum are compatible with the model of non-absorbing, Rayleigh-scattering dust in the Planetary Atmosphere, we also re-interpret the available data with a clear Planetary Atmosphere. In the latter interpretation, the slope of increasing transit depth with shorter wavelengths from the near infrared, through the visible, and into the ultraviolet is caused by unocculted star spots, with a smaller contribution of Rayleigh scattering by molecular hydrogen in the planet's Atmosphere. At relevant pressures along the terminator, our model Planetarymore » Atmosphere's temperature is ∼700 K, which is below the condensation temperatures of sodium- and potassium-bearing molecules, causing the broad wings of the spectral lines of Na I and K I at 0.589 μm and 0.769 μm to be weak.« less