Abstract We present an XMM–Newton X-ray observation of TRAPPIST-1, which is an ultracool dwarf star recently discovered to host three transiting and temperate Earth-sized planets. We find the star is ...a relatively strong and variable coronal X-ray source with an X-ray luminosity similar to that of the quiet Sun, despite its much lower bolometric luminosity. We find LX/Lbol = 2–4 × 10−4, with the total XUV emission in the range LXUV/Lbol = 6–9 × 10−4, and XUV irradiation of the planets that is many times stronger than experienced by the present-day Earth. Using a simple energy-limited model, we show that the relatively close-in Earth-sized planets, which span the classical habitable zone of the star, are subjected to sufficient X-ray and EUV irradiation to significantly alter their primary and any secondary atmospheres. Understanding whether this high-energy irradiation makes the planets more or less habitable is a complex question, but our measured fluxes will be an important input to the necessary models of atmospheric evolution.
Variability in the super-Earth 55 Cnc e Demory, Brice-Olivier; Gillon, Michael; Madhusudhan, Nikku ...
Monthly notices of the Royal Astronomical Society,
01/2016, Letnik:
455, Številka:
2
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Considerable progress has been made in recent years in observations of atmospheric signatures of giant exoplanets, but processes in rocky exoplanets remain largely unknown due to major challenges in ...observing small planets. Numerous efforts to observe spectra of super-Earths, exoplanets with masses of 1–10 Earth masses, have thus far revealed only featureless spectra. In this paper, we report a 4σ detection of variability in the dayside thermal emission from the transiting super-Earth 55 Cancri e. Dedicated space-based monitoring of the planet in the mid-infrared over eight eclipses revealed the thermal emission from its dayside atmosphere varying by a factor of 3.7 between 2012 and 2013. The amplitude and trend of the variability are not explained by potential influence of star spots or by local thermal or compositional changes in the atmosphere over the short span of the observations. The possibility of large-scale surface activity due to strong tidal interactions possibly similar to Io, or the presence of circumstellar/circumplanetary material appear plausible and motivate future long-term monitoring of the planet.
Initiated in the sixteenth century, the Copernican revolution toppled our Earth from its theological pedestal, revealing it not to be the centre of everything but a planet among several others in ...orbit around one of the zillions of stars of our Universe. Already proposed by some philosophers at the dawn of this major paradigm shift, the existence of exoplanets, i.e. planets in orbit around stars other than our Sun, remained suspected but unconfirmed for centuries. It is only in the last decade of the twentieth century that the first of these extrasolar worlds were found. Their seminal discoveries initiated the development of more and more ambitious projects that led eventually to the detection of thousands of exoplanets, including a few dozen potentially habitable ones, i.e. terrestrial exoplanets that could harbour large amounts of liquid water – and maybe life – on their surfaces. Upcoming astronomical facilities will soon be able to probe the atmospheric compositions of some of these extrasolar worlds, maybe performing in the process the historical detection of chemical signs of life light-years away. But while the existence of extraterrestrial life remains pure speculation for now, it has been a major theme of science fiction for more than a century. By creating countless stories of encounters between humans and alien forms of life, science-fiction authors have pursued, in a sense, the Copernican revolution, confronting us with the idea that not only could life be widespread in the Universe, but also that our species may be far from the Cosmic pinnacle in matters of intelligence and technological development.
A rocky planet transiting a nearby low-mass star Berta-Thompson, Zachory K; Irwin, Jonathan; Charbonneau, David ...
Nature (London),
11/2015, Letnik:
527, Številka:
7577
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M-dwarf stars--hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun--are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent ...results have shown that M dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star. The nearest such planets known to transit their star are 39 parsecs away, too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.
One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. Recently, three Earth-sized planets were detected that transit (that ...is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away. The transiting configuration of these planets, combined with the Jupiter-like size of their host star-named TRAPPIST-1-makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the star and migrated inwards. Moreover, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces.
Many hypotheses have been raised to explain the famous Fermi paradox. One of them is that self-replicating probes could have explored the whole Galaxy, including our Solar System, and that they are ...still to be detected. In this scenario, it is proposed here that probes from neighboring stellar systems could use the stars they orbit as gravitational lenses to communicate efficiently with each other. Under this hypothesis, a novel SETI approach would be to monitor the solar focal regions of the most nearby stars to search for communication devices. The envisioned devices are probably not detectable by imagery or stellar occultation, but an intensive multi-spectral monitoring campaign could possibly detect some communication leakages. Another and more direct option would be to message the focal regions of nearby stars in an attempt to initiate a reaction.
•A novel SETI strategy is proposed, focusing on our own solar system.•It is assumed that the Galaxy has been colonized by self-replicating probes.•It is assumed that neighboring probes use stellar lensing for communication.•Under these assumptions, the position of the ET communication devices is known.
Search for an Alien Message to a Nearby Star Gillon, Michaël; Burdanov, Artem; Wright, Jason T.
The Astronomical journal,
11/2022, Letnik:
164, Številka:
5
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Abstract
If alien probes have colonized the whole galaxy, they could have formed an efficient galactic-scale communication network by establishing direct gravitationally lensed links between ...neighboring systems. Under this scenario, observing the positions opposite the nearest ecliptic stars represents a promising artifact SETI strategy that could make it possible to “eavesdrop” on the emission of local probes to one of these stars. In this context, we present here a first attempt to detect optical messages emitted from the solar system to the ecliptic star Wolf 359, the third-nearest stellar system, based on observations gathered by the TRAPPIST-South and SPECULOOS-South robotic telescopes. While sensitive enough to detect constant emission with emitting power as small as a few watts, this search led to a null result. We note that the putative alien probes could be emitting “off-axis” and be located much closer to the Sun than the start of the “solar gravitational line” at 550 au. We performed a search for such an off-axis emitter in our data, whose result turned out negative too.
Planet formation theories predict a large but still undetected population of short-period terrestrial planets orbiting brown dwarfs. Should specimens of this population be discovered transiting ...relatively bright and nearby brown dwarfs, the Jupiter-size and the low luminosity of their hosts would make them exquisite targets for detailed atmospheric characterization with JWST and future ground-based facilities. The eventual discovery and detailed study of a significant sample of transiting terrestrial planets orbiting nearby brown dwarfs could prove to be useful not only for comparative exoplanetology but also for astrobiology, by bringing us key information on the physical requirements and time-scale for the emergence of life. In this context, we present a search for transit-signals in archival time series photometry acquired by the Spitzer Space Telescope for a sample of 44 nearby brown dwarfs. While these 44 targets were not particularly selected for their brightness, the high precision of their Spitzer light curves allows us to reach sensitivities below Earth-sized planets for 75 per cent of the sample and down to Europa-sized planets on the brighter targets. We could not identify any unambiguous planetary signal. Instead, we could compute the first limits on the presence of planets on close-in orbits. We find that within a 1.28 d orbit, the occurrence rate of planets with a radius between 0.75 and 3.25 R... is ... < 67 plus or minus 1 per cent. For planets with radii between 0.75 and 1.25 R..., we place a 95 per cent confident upper limit of ... < 87 plus or minus 3 per cent. If we assume an occurrence rate of ... = 27 per cent for these planets with radii between 0.75 and 1.25 R..., as the discoveries of the Kepler-42b and TRAPPIST-1b systems would suggest, we estimate that 175 brown dwarfs need to be monitored in order to guarantee (95 per cent) at least one detection. (ProQuest: ... denotes formulae/symbols omitted.)
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