Holmström et al. reply

Holmström, Mats; Ekenbäck, A.; Selsis, F.; Penz, T.; Lämmer, H.; Würz, Peter

doi:10.1038/nature07403

Cited by 50 publications

(78 citation statements)

References 3 publications

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“…However, if one applies comparative aeronomy between "Hot Jupiters" and Solar System planets, a different picture appears. Holmström et al (2008) and Ekenbäck et al (2010) applied for the first time a plasma flow model which was developed for the study of Energetic Neutral Atom (ENA) production around Mars, Venus and comets (e.g., Barabash et al 2002;Gunell et al 2005Gunell et al , 2006Futaana et al 2006aFutaana et al , 2006b to the case of HD 209458b and discovered that most of the "observed" hydrogen atoms may represent ENAs which originated from the stellar wind plasma after charge exchange and not form the outward flowing planetary atmosphere. We point out that this finding makes observations such as that of Vidal-Madjar et al (2003) or Lecavelier Des Etangs et al (2010) even more important, because a careful analysis of the data together with modeling efforts will give us an idea on the stellar wind environment around the exoplanet, the planetary obstacle which is linked to a possible magnetosphere and the thermosphereexosphere structure.…”

Section: Upper Atmosphere Structure Of "Hot Jupiters"mentioning

confidence: 99%

Hydrogen ENA-cloud observation and modeling as a tool to study star-exoplanet interaction

Lämmer

Kislyakova

Holmström

et al. 2011

Astrophys Space Sci

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International audienceDuring the previous years spacecraft observations of so-called Energetic Neutral Atoms (ENAs) have become an important remote-sensing technique in planetary science for analyzing the solar wind plasma flow around the upper atmospheric environments of Solar System bodies. ENAs are produced whenever solar or stellar wind protons interact via charge exchange with a neutral particle from a planetary atmosphere so that their signals constrain both, ion distributions and neutral gas densities. The observation of ENAs which have been generated due to charge exchange with stellar wind plasma have been used for the indirect mass loss and stellar wind property estimation of Sun-like stars by observing the interaction regions carved out by the collisions between stellar winds and the interstellar medium. In this work we review ENA-observations and data interpretations at Solar System planets and recent hydrogen-cloud observations in UV Lyman-α absorption around hydrogen-rich extra-solar gas giants. We discuss the production of stellar wind related hydrogen ENA-clouds around close-in exoplanets and show how a detailed analysis of attenuation spectra obtained for transiting hydrogen-rich close-in gas giants can be used for the study of the upper atmosphere structure, the planet's magnetosphere and to obtain information on stellar wind properties. Finally, we discuss how future hydrogen cloud observations around exoplanets by space observatories like the Russia-led World Space Observatory-UV (WSO-UV) together with ESAs planned PLATO mission can be used for the reconstruction of the solar wind history or the test of magnetosphere evolution hypotheses

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Section: Upper Atmosphere Structure Of "Hot Jupiters"mentioning

confidence: 99%

Hydrogen ENA-cloud observation and modeling as a tool to study star-exoplanet interaction

Lämmer

Kislyakova

Holmström

et al. 2011

Astrophys Space Sci

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“…In agreement with this hypothesis, we reveal that overexpressing ARMS in melanoma cells suppresses ERK phosphorylation, activates procaspase-3, and leads to mitochondrial depolarization, which in turn results in apoptosis. Other possible mechanisms proposed for ERK in protecting tumor cells from apoptosis include activation of antiapoptotic Bcl-2 proteins, inhibition of proapoptotic factors such as Bim EL or Bad, or prevention of cytosolic Bax from translocation to mitochondria (32)(33)(34)(35). Our microarray analysis between ARMS-RNAi cells and control-transfected cells reveals no differential expression of transcripts of Bcl-2 superfamily or other apoptosis-related molecules (data not shown).…”

Section: Discussionmentioning

confidence: 99%

ARMS Depletion Facilitates UV Irradiation–Induced Apoptotic Cell Death in Melanoma

2007

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Tumor cells often aberrantly reexpress molecules that mediate proper embryonic development for advantageous growth or survival. Here, we report that ankyrin repeat-rich membrane spanning (ARMS), a transmembrane protein abundant in the developing and adult neural tissues, is overexpressed in melanoma, a tumor ontogenetically originating from neural crest. Immunohistochemical study of 79 melanocytic lesions showed significantly increased expression of ARMS in primary malignant melanomas (92.9%) and metastatic melanoma (60.0%) in comparison with benign nevocellular nevi (26.7%). To investigate the role of ARMS in melanoma formation, murine B16F0 melanoma cells with stable knockdown of ARMS were established by RNA interference. Downregulation of ARMS resulted in significant inhibition of anchorage-independent growth in soft agar and restrictive growth of melanoma in severe combined immunodeficient mice. Importantly, depletion of ARMS facilitated UVB-induced apoptosis in melanoma cells through inactivation of mitogenactivated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK. Addition of MEK inhibitor PD98059 further sensitized ARMS-depleted melanoma cells to UVBinduced apoptosis, whereas constitutively active MEK rescued ARMS-depleted cells from apoptosis. We further showed that BRAF, a downstream signaling molecule of ARMS in ERK pathway, is not mutated as a constitutively active form in acral lentiginous melanoma; in contrast, BRAF T1799A mutation, which leads to constitutive activation of ERK signaling, was detected in 57.1% of superficial spreading melanoma. Our study suggests that overexpression of ARMS per se serves as one mechanism to promote melanoma formation by preventing stress-induced apoptotic death mediated by the MEK/ERK signaling pathway, especially in acral lentiginous melanoma, most of which does not harbor BRAF mutation. [Cancer Res 2007;67(24):11547-56]

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“…Given that the evaporating planets sustaining this system-wide hydrogen cloud would be in different relative positions at a given epoch, the structure of the cloud and its absorption signature would be highly variable over time, which could explain why it was not detected in Visit 1. We note, though, that the hydrogen cloud would still have to be accelerated to very high velocities away from the star (possibly through charge exchange with the stellar wind; Holmström et al 2008;Ekenbäck et al 2010;Bourrier et al 2016b) to explain the velocity range of the measured absorption.…”

Section: The Mysterious Shape Of the Trappist-1 Lyα Linementioning

confidence: 99%

Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets

et al. 2017

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The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could harbor liquid water on their surfaces. Ultraviolet observations are essential to measuring their high-energy irradiation and searching for photodissociated water escaping from their putative atmospheres. Our new observations of the TRAPPIST-1 Lyα line during the transit of TRAPPIST-1c show an evolution of the star emission over three months, preventing us from assessing the presence of an extended hydrogen exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape. However, TRAPPIST-1e to h might have lost less than three Earth oceans if hydrodynamic escape stopped once they entered the habitable zone (HZ). We caution that these estimates remain limited by the large uncertainty on the planet masses. They likely represent upper limits on the actual water loss because our assumptions maximize the X-rays to ultraviolet-driven escape, while photodissociation in the upper atmospheres should be the limiting process. Late-stage outgassing could also have contributed significant amounts of water for the outer, more massive planets after they entered the HZ. While our results suggest that the outer planets are the best candidates to search for water with the JWST, they also highlight the need for theoretical studies and complementary observations in all wavelength domains to determine the nature of the TRAPPIST-1 planets and their potential habitability.

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Holmström et al. reply

Cited by 50 publications

References 3 publications

Hydrogen ENA-cloud observation and modeling as a tool to study star-exoplanet interaction

Hydrogen ENA-cloud observation and modeling as a tool to study star-exoplanet interaction

ARMS Depletion Facilitates UV Irradiation–Induced Apoptotic Cell Death in Melanoma

Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets

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