68 research outputs found
The Impact of the Temporal Distribution of Communicating Civilizations on their Detectability
We use a statistical model to investigate the detectability (defined by the
requirement that they are in causal contact with us) of communicating
civilizations within a volume of the universe surrounding our location. If the
civilizations are located in our Galaxy, the detectability requirement imposes
a strict constraint on their epoch of appearance and their communicating
lifespan. This, in turn, implies that the fraction of civilizations of which we
can find any empirical evidence strongly depends on the specific features of
their temporal distribution. Our approach shed light on aspects of the problem
that can escape the standard treatment based on the Drake equation. Therefore,
it might provide the appropriate framework for future studies dealing with the
evolutionary aspects of the search for extraterrestrial intelligence (SETI).Comment: 17 pages, 1 figure. Accepted for publication in Astrobiolog
Cosmology from Planck
I briefly review some of the main scientific outputs expected from the
upcoming Planck mission. Planck will map the CMB sky with 5' resolution and
K sensitivity, with minimal foreground contribution and superb control on
systematics. It will collect the entire information enclosed in the temperature
primary anisotropy signal and will also get a good measurement of the polarized
component of the CMB. This will have profound implications on our knowledge of
the physics of the early universe and on the determination of cosmological
parameters.Comment: Proceedings of the Francesco Melchiorri Memorial Conference (Rome,
Italy, April 12-14 2006). To appear in New Astron. Re
Neutrinos and dark energy constraints from future galaxy surveys and CMB lensing information
We explore the possibility of obtaining better constraints from future
astronomical data by means of the Fisher information matrix formalism. In
particular, we consider how cosmic microwave background (CMB) lensing
information can improve our parameter error estimation. We consider a massive
neutrino scenario and a time-evolving dark energy equation of state in the
CDM framework. We use Planck satellite experimental specifications
together with the future galaxy survey Euclid in our forecast. We found
improvements in almost all studied parameters considering Planck alone when CMB
lensing information is used. In this case, the improvement with respect to the
constraints found without using CMB lensing is of 93% around the fiducial value
for the neutrino parameter. The improvement on one of the dark energy parameter
reaches 4.4%. When Euclid information is included in the analysis, the
improvements on the neutrino parameter constraint is of approximately 128%
around its fiducial value. The addition of Euclid information provides smaller
errors on the dark energy parameters as well. For Euclid alone, the FoM is a
factor of 29 higher than that from Planck alone even considering CMB
lensing. Finally, the consideration of a nearly perfect CMB experiment showed
that CMB lensing cannot be neglected specially in more precise future CMB
experiments since it provided in our case a 6 times better FoM in respect to
the unlensed CMB analysis .Comment: Accepted for publication in PR
The Oxygen Bottleneck for Technospheres
On Earth, the development of technology required easy access to open air
combustion, which is only possible when oxygen partial pressure, P(O), is
above 18\%. This suggests that only planets with significant atmospheric oxygen
concentrations will be capable of developing ``advanced'' technospheres and
hence detectable technosignatures.Comment: 10 pages, 2 figure
Quantifying the information impact of future searches for exoplanetary biosignatures
One of the major goals for astronomy in the next decades is the remote search
for biosignatures (i.e.\ the spectroscopic evidence of biological activity) in
exoplanets. Here, we adopt a Bayesian statistical framework to discuss the
implications of such future searches, both in the case when life is detected,
and when no definite evidence is found. We show that even a single detection of
biosignatures in the vicinity of our stellar system, in a survey of similar
size to what will be obtainable in the next two decades, would affect
significantly our prior belief on the frequency of life in the universe, even
starting from a neutral or pessimistic stance. In particular, after such
discovery, an initially agnostic observer would be led to conclude that there
are more than inhabited planets in the galaxy with a probability
exceeding \%. However, this conclusion would be somewhat weakened by the
viability of transfer of biological material over interstellar distances, as in
panspermia scenarios. Conversely, the lack of significant evidence of
biosignatures would have little effect, leaving the assessment of the abundance
of life in the galaxy still largely undetermined.Comment: Published on PNA
The habitability of the Milky Way during the active phase of its central supermassive black hole
During the peak of their accretion phase, supermassive black holes in
galactic cores are known to emit very high levels of ionizing radiation,
becoming visible over intergalactic distances as quasars or active galactic
nuclei (AGN). Here, we quantify the extent to which the activity of the
supermassive black hole at the center of the Milky Way, known as Sagittarius A*
(Sgr A*), may have affected the habitability of Earth-like planets in our
Galaxy. We focus on the amount of atmospheric loss and on the possible
biological damage suffered by planets exposed to X-ray and extreme ultraviolet
(XUV) radiation produced during the peak of the active phase of Sgr A*. We find
that terrestrial planets could lose a total atmospheric mass comparable to that
of present day Earth even at large distances (~1 kiloparsec) from the galactic
center. Furthermore, we find that the direct biological damage caused by Sgr A*
to surface life on planets not properly screened by an atmosphere was probably
significant during the AGN phase, possibly hindering the development of complex
life within a few kiloparsecs from the galactic center.Comment: 6 pages, 2 figures. Published in Scientific Reports:
http://rdcu.be/zYD
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