535 research outputs found
Radioactive nuclei from cosmochronology to habitability
In addition to long-lived radioactive nuclei like U and Th isotopes, which
have been used to measure the age of the Galaxy, also radioactive nuclei with
half-lives between 0.1 and 100 million years (short-lived radionuclides, SLRs)
were present in the early Solar System (ESS), as indicated by high-precision
meteoritic analysis. We review the most recent meteoritic data and describe the
nuclear reaction processes responsible for the creation of SLRs in different
types of stars and supernovae. We show how the evolution of radionuclide
abundances in the Milky Way Galaxy can be calculated based on their stellar
production. By comparing predictions for the evolution of galactic abundances
to the meteoritic data we can build up a time line for the nucleosynthetic
events that predated the birth of the Sun, and investigate the lifetime of the
stellar nursery where the Sun was born. We then review the scenarios for the
circumstances and the environment of the birth of the Sun within such a stellar
nursery that have been invoked to explain the abundances in the ESS of the SLRs
with the shortest lives - of the order of million years or less. Finally, we
describe how the heat generated by radioactive decay and in particular by the
abundant 26Al in the ESS had important consequences for the thermo-mechanical
and chemical evolution of planetesimals, and discuss possible implications on
the habitability of terrestrial-like planets. We conclude with a set of open
questions and future directions related to our understanding of the
nucleosynthetic processes responsible for the production of SLRs in stars,
their evolution in the Galaxy, the birth of the Sun, and the connection with
the habitability of extra-solar planets.Comment: Review published in Progress in Particle and Nuclear Physics. The
article is being published Open Access, access to the full article is not
restricted in any way. Please download the final version of the paper at
https://doi.org/10.1016/j.ppnp.2018.05.00
Infrared spectral analys is and paleo-environment reconstruction on Mars
Connecting surface imaging and topography with IR spectral mineral identification provides better possibility for paleo-environment reconstruction. A project to compile a database of such indicators is started, the system’s background is outlined
Possibility for albedo estimation of exomoons: Why should we care about M dwarfs?
Occultation light curves of exomoons may give information on their albedo and
hence indicate the presence of ice cover on the surface. Icy moons might have
subsurface oceans thus these may potentially be habitable. The objective of our
paper is to determine whether next generation telescopes will be capable of
albedo estimations for icy exomoons using their occultation light curves. The
success of the measurements depends on the depth of the moon's occultation in
the light curve and on the sensitivity of the used instruments. We applied
simple calculations for different stellar masses in the V and J photometric
bands, and compared the flux drop caused by the moon's occultation and the
estimated photon noise of next generation missions with 5 confidence.
We found that albedo estimation by this method is not feasible for moons of
solar-like stars, but small M dwarfs are better candidates for such
measurements. Our calculations in the J photometric band show that E-ELT
MICADO's photon noise is just about 4 ppm greater than the flux difference
caused by a 2 Earth-radii icy satellite in a circular orbit at the snowline of
an 0.1 stellar mass star. However, considering only photon noise underestimates
the real expected noise, because other noise sources, such as CCD read-out and
dark signal become significant in the near infrared measurements. Hence we
conclude that occultation measurements with next generation missions are far
too challenging, even in the case of large, icy moons at the snowline of small
M dwarfs. We also discuss the role of the parameters that were neglected in the
calculations, e.g. inclination, eccentricity, orbiting direction of the moon.
We predict that the first albedo estimations of exomoons will probably be made
for large icy moons around the snowline of M4 -- M9 type main sequence stars.Comment: 13 pages, 6 figures, accepted for publication in A&
Analysing high resolution digital Mars images using machine learning
The search for ephemeral liquid water on Mars is an ongoing activity. After
the recession of the seasonal polar ice cap on Mars, small water ice patches
may be left behind in shady places due to the low thermal conductivity of the
Martian surface and atmosphere. During late spring and early summer, these
patches may be exposed to direct sunlight and warm up rapidly enough for the
liquid phase to emerge. To see the spatial and temporal occurrence of such ice
patches, optical images should be searched for and checked. Previously a manual
image analysis was conducted on 110 images from the southern hemisphere,
captured by the High Resolution Imaging Science Experiment (HiRISE) camera
onboard the Mars Reconnaissance Orbiter space mission. Out of these, 37 images
were identified with smaller ice patches, which were distinguishable by their
brightness, colour and strong connection to local topographic shading. In this
study, a convolutional neural network (CNN) is applied to find further images
with potential water ice patches in the latitude band between -40{\deg} and
-60{\deg}, where the seasonal retreat of the polar ice cap happens. Previously
analysed HiRISE images were used to train the model, where each image was split
into hundreds of pieces (chunks), expanding the training dataset to 6240
images. A test run conducted on 38 new HiRISE images indicates that the program
can generally recognise small bright patches, however further training might be
needed for more precise identification. This further training has been
conducted now, incorporating the results of the previous test run. To retrain
the model, 18646 chunks were analysed and 48 additional epochs were ran. In the
end the model produced a 94% accuracy in recognising ice, 58% of these images
showed small enough ice patches on them. The rest of the images was covered by
too much ice or showed CO2 ice sublimation in some places
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