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Register a new userA revolution is brewing: observations of TRAPPIST-1 exoplanetary system fosters a new biomarker
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The recent discovery of seven potentially habitable Earth-size planets around the ultra-cool star TRAPPIST-1 has further fueled the hunt for extraterrestrial life. Current methods focus on closely monitoring the host star to look for biomarkers in the transmission signature of exoplanets atmosphere. However, the outcome of these methods remain uncertain and difficult to disentangle with abiotic alternatives. Recent exoplanet direct imaging observations by THIRSTY, an ultra-high contrast coronagraph located in La Trappe (France), lead us to propose a universal and unambiguous habitability criterion which we directly demonstrate for the TRAPPIST-1 system. Within this new framework, we find that TRAPPIST-1g possesses the first unambiguously habitable environment in our galaxy, with a liquid water percentage that could be as large as $sim~90~%$. Our calculations hinge on a new set of biomarkers, CO$_2$ and C$_{x}$H$_{2(x+1)}$O (liquid and gaseous), that could cover up to $sim~10~%$ of the planetary surface and atmosphere. THIRSTY and TRAPPIST recent observations accompanied by our new, unbiased habitability criterion may quench our thirst for the search for extraterrestrial life. However, the search for intelligence must continue within and beyond our Solar System.
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The nearby (d = 12 pc) M8 dwarf star TRAPPIST-1 (2MASS J23062928-0502285) hosts a compact system of at least seven exoplanets with sizes similar to Earth. Given its importance for testing planet formation and evolution theories, and for assessing the prospects for habitability among Earth-size exoplanets orbiting the most common type of star in the Galaxy, we present a comprehensive assessment of the age of this system. We collate empirical age constraints based on the color-absolute magnitude diagram, average density, lithium absorption, surface gravity features, metallicity, kinematics, rotation, and magnetic activity; and conclude that TRAPPIST-1 is a transitional thin/thick disk star with an age of 7.6$pm$2.2 Gyr. The stars color-magnitude position is consistent with it being slightly metal-rich ([Fe/H] $simeq$ +0.06), in line with its previously reported near-infrared spectroscopic metallicity; and it has a radius (R = 0.121$pm$0.003 R$_{odot}$) that is larger by 8-14% compared to solar-metallicity evolutionary models. We discuss some implications of the old age of this system with regard to the stability and habitability of its planets.
TRAPPIST-1 is a fantastic nearby (~39.14 light years) planetary system made of at least seven transiting terrestrial-size, terrestrial-mass planets all receiving a moderate amount of irradiation. To date, this is the most observationally favourable system of potentially habitable planets. Since the announcement of the discovery of TRAPPIST-1 planets in 2016, a growing number of techniques and approaches have been used and proposed to reveal its true nature. Here we have compiled a state-of-the-art overview of all the observational and theoretical constraints that have been obtained so far using these techniques and approaches. The goal is to get a better understanding of whether or not TRAPPIST-1 planets can have atmospheres, and if so, what they are made of. For this, we surveyed the literature on TRAPPIST-1 about topics as broad as irradiation environment, orbital architecture, transit observations, density measurements, stellar contamination, and numerical climate and escape models. Each of these topics adds a brick to our understanding of the likely atmospheres of the seven planets. We show that (i) HST transit observations, (ii) density measurements, (iii) atmospheric escape modelling, and (iv) gas accretion modelling altogether offer solid evidence against the presence of H2-dominated atmospheres around TRAPPIST-1 planets. This means they likely have either (i) a high molecular weight atmosphere or (ii) no atmosphere at all. There are several key challenges ahead to characterize the bulk compositions of the atmospheres (if present) of TRAPPIST-1 planets. The main one so far is characterizing and correcting for the effects of stellar contamination. Fortunately, a new wave of observations with the James Webb Space Telescope and near-infrared high-resolution ground-based spectrographs on very large telescopes will bring significant advances in the coming decade.
Stellar variability studies are now reaching a completely new level thanks to ESAs Gaia mission, which enables us to locate many variable stars in the Hertzsprung-Russell diagram and determine the various instability strips/bands. Furthermore, this mission also allows us to detect, characterise and classify many millions of new variable stars thanks to its very unique nearly simultaneous multi-epoch survey with different instruments (photometer, spectro-photometer, radial velocity spectrometer). An overview of what can be found in literature in terms of mostly data products by the Gaia consortium is given. This concerns the various catalogues of variable stars derived from the Gaia time series and also the location and motion of variable stars in the observational Hertzsprung-Russell diagram. In addition, we provide a list of a few thousands of variable white dwarf candidates derived from the DR2 published data, among them probably many hundreds of new pulsating white dwarfs. On a very different topic, we also show how Gaia allows us to reveal the 3D structures of and around the Milky Way thanks to the RR Lyrae stars.
Understanding the human brain remains one of the most significant challenges of the 21st century. As theoretical studies continue to improve the description of the complex mechanisms that regulate biological processes, in parallel numerous experiments are conducted to enrich or verify these theoretical predictions and with the aim of extrapolating more accurate models. In the field of magnetometers for biological application, among the various sensors proposed for this purpose, NV centers have emerged as a promising solution due to their perfect biocompatibility and the possibility of being positioned in close proximity and even inside the cell, allowing a nanometric spatial resolution. There are still many difficulties that must be overcome in order to obtain both spatial resolution and sensitivity capable of revealing the very weak biological electromagnetic fields generated by neurons (or other cells). However, over the last few years, significant improvements have been achieved in this direction, thanks to the use of innovative techniques, which allow us to hope for an early application of these sensors for the measurement of fields such as the one generated by cardiac tissue, if not, in perspective, for the nerve fibers fields. In this review, we will analyze the new results regarding the application of NV centers and we will discuss the main challenges that currently prevent these quantum sensors from reaching their full potential.
We study the evolution of protoplanetary discs that would have been precursors of a Trappist-1 like system under the action of accretion and external photoevaporation in different radiation environments. Dust grains swiftly grow above the critical size below which they are entrained in the photoevaporative wind, so although gas is continually depleted, dust is resilient to photoevaporation after only a short time. This means that the ratio of the mass in solids (dust plus planetary) to the mass in gas rises steadily over time. Dust is still stripped early on, and the initial disc mass required to produce the observed $4,M_{oplus}$ of Trappist-1 planets is high. For example, assuming a Fatuzzo & Adams (2008) distribution of UV fields, typical initial disc masses have to be $>30,$per cent the stellar (which are still Toomre $Q$ stable) for the majority of similar mass M dwarfs to be viable hosts of the Trappist-1 planets. Even in the case of the lowest UV environments observed, there is a strong loss of dust due to photoevaporation at early times from the weakly bound outer regions of the disc. This minimum level of dust loss is a factor two higher than that which would be lost by accretion onto the star during 10 Myr of evolution. Consequently even in these least irradiated environments, discs that are viable Trappist-1 precursors need to be initially massive ($>10,$per cent of the stellar mass).
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