53 research outputs found
Galactic cosmic ray induced radiation dose on terrestrial exoplanets
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,
falling 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. Theoretical
calculations also suggest that close-in exoplanets are more likely to have
weaker planetary magnetic fields, especially in 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, which 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 sub-surface 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 explore the dependence of
the GCR induced radiation dose on the strength of the planetary magnetic field
and its atmospheric depth, finding that the latter is the decisive factor for
the protection of a planetary biosphere.Comment: Accepted for publication in Astrobiolog
Biomarker Response to Galactic Cosmic Ray-Induced NOx and the Methane Greenhouse Effect in the Atmosphere of an Earthlike Planet Orbiting an M-Dwarf Star
Planets orbiting in the habitable zone (HZ) of M-Dwarf stars are subject to
high levels of galactic cosmic rays (GCRs) which produce nitrogen oxides in
earthlike atmospheres. We investigate to what extent this NOx may modify
biomarker compounds such as ozone (O3) and nitrous oxide (N2O), as well as
related compounds such as water (H2O) (essential for life) and methane (CH4)
(which has both abiotic and biotic sources) . Our model results suggest that
such signals are robust, changing in the M-star world atmospheric column by up
to 20% due to the GCR NOx effects compared to an M-star run without GCR effects
and can therefore survive at least the effects of galactic cosmic rays. We have
not however investigated stellar cosmic rays here. CH4 levels are about 10
times higher than on the Earth related to a lowering in hydroxyl (OH) in
response to changes in UV. The increase is less than reported in previous
studies. This difference arose partly because we used different biogenic input.
For example, we employed 23% lower CH4 fluxes compared to those studies. Unlike
on the Earth, relatively modest changes in these fluxes can lead to larger
changes in the concentrations of biomarker and related species on the M-star
world. We calculate a CH4 greenhouse heating effect of up to 4K. O3
photochemistry in terms of the smog mechanism and the catalytic loss cycles on
the M-star world differs considerably compared with the Earth
The extreme physical properties of the CoRoT-7b super-Earth
International audienceâș Here, we discuss the extreme physical properties possible for the first characterized rocky super-Earth, CoRoT-7b ( = 1.58 , = 5.7 ). âș We make the working hypothesis that the planet is rocky with no volatiles in its atmosphere, and derive the physical properties that result. âș The dayside is very hot (2500 K at the sub-stellar point) while the nightside is very cold (⌠50 K). The sub-stellar point is as hot as the tungsten filament of an incandescent bulb, resulting in the melting and distillation of silicate rocks and the formation of a lava ocean. âș These possible features of CoRoT-7b should be common to many small and hot planets, including Kepler-10b. They define a new class of objects that we propose to name ''Lava-ocean planets''
The search for radio emission from giant exoplanets
International audienceThe intensity of Jupiter's auroral radio emission quickly gave rise to the question whether a comparable coherent emission from the magnetosphere of an extrasolar planet could be detectable. A simple estimation shows that exoplanetary auroral radio emission would have to be at least 1000 times more intense than Jupiter's emission to be detectable with current radio telescopes. Theoretical models suggest that, at least in certain cases, the radio emission of giant exoplanets may indeed reach such an intensity. At the same time, in order to generate such an emission, an exoplanet would need to have a sufficiently strong intrinsic planetary magnetic field. Extrasolar planets are indeed expected to have a magnetic field, but to date, their magnetic field has never been detected. As discussed elsewhere [Griessmeier et al., 2015], the most promising technique to unambiguously observe exoplanetary magnetic fields is to search for the planetary auroral radio emission. The detection of such an emission would thus constitute the first unambiguous detection of an exoplanetary magnetic field. We review recent theoretical studies and discuss their results for the two main parameters, namely the maximum emission frequency and the intensity of the radio emission. The predicted values indicate that detection should be possible using modern low-frequency radio telescopes. We also review past observation attempts, and compare their sensitivity to the predicted emission
The search for radio emission from the exoplanetary systems 55 Cnc, Upsilon Andromedae, and Tau Boötis using LOFAR beam-formed observations
International audienceThe detection of planetary auroral radio emission is the only method to unambiguously observe exoplanetary magnetic fields. Over the past few decades, a number of observational campaigns searching for exoplanetary radio emission have been performed and none have been successful. Observations of an exoplanet's magnetic field would allow constraints on planetary properties difficult to study such as their interior structure (composition and thermal state), atmospheric escape, the physics of star-planet interactions, and even habitability. In this study, we present the detection of the most conclusive exoplanetary radio signal to date from the hot Jupiter Tau Bootis. If confirmed, this detection would be the birth of a brand new field of observational exoplanet research
Radioastronomy with Lofar
International audienceLOFAR is the first radiotelescope of a new generation, which can be described as "software telescopes". Observing between 15 and 240 MHz, the main complexity of LOFAR does not lie in the receivers (crossed, active dipoles), but in the hierarchical organisation of a large number of antennae (almost 50000) and in the analysis of the incoming data in a large computing facility. Rather than mechanically steering the telescope, pointing occurs fully numerically, and all observations are pre-processed on the fly to obtain a reasonable data volume. LOFAR will be 10 to 100 times more sensitive than the current instruments in the same frequency range. It will achieve sub-arcsecond resolution, which is 10 to 100 times better than the resolution of existing low-frequency instruments. It is also one of the most flexible instruments, making it interesting for a large number of scientific fields
The search for radio emission from exoplanets using LOFAR beam-formed observations
International audienceThe detection of exoplanetary magnetic fields is one of the most elusive hunts in exoplanet science today. Observing the magnetic field of an exoplanet will give valuable information to constrain their interior structure, atmospheric escape, and the nature of any star-planet interactions. Additionally, the magnetic fields on Earth-like exoplanets might help contribute to their sustained habitability by deflecting energetic stellar wind particles. The most promising method to detect exoplanet magnetic fields is radio emission observations since this method is not susceptible to false positives. All the magnetized planets and moons in our Solar System emit in the radio using the Cyclotron Maser Instability (CMI) mechanism. To date, many ground-based observations conducted to find exoplanet radio emission have resulted in non-detections. In this talk, we discuss our ongoing observational campaign searching for exoplanetary radio emissions using beam-formed observations with the Low Band of the Low-Frequency Array (LOFAR). To date we have observed three exoplanetary systems: 55 Cnc, Upsilon Andromedae, and Tau Boötis. These planets were selected according to theoretical predictions, which indicated them as among the best candidates for an observation. Data analysis is currently ongoing. In order to test, validate, and quantify the sensitivity reached with our LOFAR pipeline, we apply it to a LOFAR observation of Jupiter's magnetospheric radio emission in which the signal from Jupiter is attenuated. The idea is simple: we observe Jupiter, divide its signal by a fixed factor before adding it to an observation of sky background, thereby creating an artificial dataset best described as "Jupiter as an exoplanet". We then run our pipeline and check whether the (attenuated) radio signal from Jupiter is detected. The maximum factor by which we can divide Jupiter's signal and still achieve a detection gives the sensitivity of our setup. We find that circularly polarized exoplanetary radio bursts can be detected up to a distance of 20 pc assuming the level of emission is 105 times stronger than the peak flux of Jupiter's decametric burst emission
Interstellar medium studies below 200 MHz: LOFAR single stations and NenuFAR
International audienceInternational LOFAR stations, equipped with powerful backends, can be used as individual telescopes, and provide data sets complementary to those obtained with the LOFAR Core. Such ``local mode'' observations are particularly adapted to monitoring observations, where the advantage of having a high observing cadence (one observation per week) outweighs the reduced sensitivity of a single station when compared to the full array. With such observations, it is possible to monitor the temporal evolution of the pulsars' behaviour via its dispersion, scattering, intensity, and profile shape. We present recent studies performed in the LOFAR low band (10-90 MHz)
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