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Register a new userReconstructing Extreme Space Weather from Planet Hosting Stars
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Added by
Vladimir Airapetian
Publication date
2019
fields
Physics
and research's language is
English
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The field of exoplanetary science is making rapid progress both in statistical studies of exoplanet properties as well as in individual characterization. As space missions provide an emerging picture of formation and evolution of exoplanetary systems, the search for habitable worlds becomes one of the fundamental issues to address. To tackle such a complex challenge, we need to specify the conditions favorable for the origin, development and sustainment of life as we know it. This requires the understanding of global (astrospheric) and local (atmospheric, surface and internal) environments of exoplanets in the framework of the physical processes of the interaction between evolving planet-hosting stars along with exoplanetary evolution over geological timescales, and the resulting impact on climate and habitability of exoplanets. Feedbacks between astrophysical, physico-chemical atmospheric and geological processes can only be understood through interdisciplinary studies with the incorporation of progress in heliophysics, astrophysics, planetary, Earth sciences, astrobiology, and the origin of life communities. The assessment of the impacts of host stars on the climate and habitability of terrestrial (exo)planets and potential exomoons around them may significantly modify the extent and the location of the habitable zone and provide new directions for searching for signatures of life. Thus, characterization of stellar ionizing outputs becomes an important task for further understanding the extent of habitability in the universe. The goal of this white paper is to identify and describe promising key research goals to aid the theoretical characterization and observational detection of ionizing radiation from quiescent and flaring upper atmospheres of planet hosts as well as properties of stellar coronal mass ejections and stellar energetic particle events.
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It is currently unknown how common life is on exoplanets, or how long planets can remain viable for life. To date, we have a superficial notion of habitability, a necessary first step, but so far lacking an understanding of the detailed interaction between stars and planets over geological timescales, dynamical evolution of planetary systems, and atmospheric evolution on planets in other systems. A planet mass, net insolation, and atmospheric composition alone are insufficient to determine the probability that life on a planet could arise or be detected. The latter set of planetary considerations, among others, underpin the concept of the habitable zone (HZ), defined as the circumstellar region where standing bodies of liquid water could be supported on the surface of a rocky planet. However, stars within the same spectral class are often treated in the same way in HZ studies, without any regard for variations in activity among individual stars. Such formulations ignore differences in how nonthermal emission and magnetic energy of transient events in different stars affect the ability of an exoplanet to retain its atmosphere.In the last few years there has been a growing appreciation that the atmospheric chemistry, and even retention of an atmosphere in many cases, depends critically on the high-energy radiation and particle environments around these stars. Indeed, recent studies have shown stellar activity and the extreme space weather, such as that created by the frequent flares and coronal mass ejections (CMEs) from the active stars and young Sun, may have profoundly affected the chemistry and climate and thus habitability of the early Earth and terrestrial type exoplanets. The goal of this white paper is to identify and describe promising key research goals to aid the field of the exoplanetary habitability for the next 20 years.
To better understand how planets form, it is important to study planet occurrence rates as a function of stellar mass. However, estimating masses of field stars is often difficult. Over the past decade, a controversy has arisen about the inferred occurrence rate of gas-giant planets around evolved intermediate-mass stars -- the so-called `retired A-stars. The high masses of these red-giant planet hosts, derived using spectroscopic information and stellar evolution models, have been called into question. Here we address the controversy by determining the masses of eight evolved planet-hosting stars using asteroseismology. We compare the masses with spectroscopic-based masses from the Exoplanet Orbit Database that were previously adopted to infer properties of the exoplanets and their hosts. We find a significant one-sided offset between the two sets of masses for stars with spectroscopic masses above roughly 1.6Msun, suggestive of an average 15--20% overestimate of the adopted spectroscopic-based masses. The only star in our sample well below this mass limit is also the only one not showing this offset. Finally, we note that the scatter across literature values of spectroscopic-based masses often exceed their formal uncertainties, making it comparable to the offset we report here.
Stellar flares, winds and coronal mass ejections form the space weather. They are signatures of the magnetic activity of cool stars and, since activity varies with age, mass and rotation, the space weather that extra-solar planets experience can be very different from the one encountered by the solar system planets. How do stellar activity and magnetism influence the space weather of exoplanets orbiting main-sequence stars? How do the environments surrounding exoplanets differ from those around the planets in our own solar system? How can the detailed knowledge acquired by the solar system community be applied in exoplanetary systems? How does space weather affect habitability? These were questions that were addressed in the splinter session Cool stars and Space Weather, that took place on 9 Jun 2014, during the Cool Stars 18 meeting. In this paper, we present a summary of the contributions made to this session.
This article aims to measure the age of planet-hosting stars (SWP) through stellar tracks and isochrones computed with the textsl{PA}dova & Ttextsl{R}ieste textsl{S}tellar textsl{E}volutionary textsl{C}ode (PARSEC). We developed algorithms based on two different techniques for determining the ages of field stars: emph{isochrone placement} and emph{Bayesian estimation}. Their application to a synthetic sample of coeval stars shows the intrinsic limits of each method. For instance, the Bayesian computation of the modal age tends to select the extreme age values in the isochrones grid. Therefore, we used the isochrone placement technique to measure the ages of 317 SWP. We found that $sim6%$ of SWP have ages lower than 0.5 Gyr. The age distribution peaks in the interval [1.5, 2) Gyr, then it decreases. However, $sim7%$ of the stars are older than 11 Gyr. The Sun turns out to be a common star that hosts planets, when considering its evolutionary stage. Our SWP age distribution is less peaked and slightly shifted towards lower ages if compared with ages in the literature and based on the isochrone fit. In particular, there are no ages below 0.5 Gyr in the literature.
This section shows an overview of a recent development of the studies on great space weather events in history. Its discussion starts from the Carrington event and compare its intensity with the extreme storms within the coverage of the regular magnetic measurements. Extending its analyses back beyond their onset, this section shows several case studies of extreme storms with sunspot records in the telescopic observations and candidate auroral records in historical records. Before the onset of telescopic observations, this section shows the chronological coverages of the records of unaided-eye sunspot and candidate aurorae and several case studies on their basis.
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