Production and fate of the G ring arc particles due to Aegaeon (Saturn LIII) [EPA]

http://arxiv.org/abs/1801.04652


The G ring arc hosts the smallest satellite of Saturn, Aegaeon, observed with a set of images sent by Cassini spacecraft. Along with Aegaeon, the arc particles are trapped in a 7:6 corotation eccentric resonance with the satellite Mimas. Due to this resonance, both Aegaeon and the arc material are confined to within sixty degrees of corotating longitudes. The arc particles are dust grains which can have their orbital motions severely disturbed by the solar radiation force. Our numerical simulations showed that Aegaeon is responsible for depleting the arc dust population by removing them through collisions. The solar radiation force hastens these collisions by removing most of the 10$~\mu$m sized grains in less than 40 years. Some debris released from Aegaeon’s surface by meteoroid impacts can populate the arc. However, it would take 30,000 years for Aegaeon to supply the observed amount of arc material, and so it is unlikely that Aegaeon alone is the source of dust in the arc.

Read this paper on arXiv…

G. Madeira, R. Sfair, D. Mourao, et. al.
Tue, 16 Jan 18
23/79

Comments: N/A

Planetary Engulfment in the Hertzsprung–Russell Diagram [SSA]

http://arxiv.org/abs/1801.04274


Planets accompany most sun-like stars. The orbits of many are sufficiently close that they will be engulfed when their host stars ascend the giant branch. This Letter compares the power generated by orbital decay of an engulfed planet to the intrinsic stellar luminosity. Orbital decay power is generated by drag on the engulfed companion by the surrounding envelope. As stars ascend the giant branch their envelope density drops and so does the power injected through orbital decay, scaling approximately as $L_{\rm decay} \propto R_^{-9/2}$. Their luminosity, however, increases along the giant branch. These opposed scalings indicate a crossing, where $L_{\rm decay}= L_$. We consider the engulfment of planets along isochrones in the Hertzsprung-Russell (H-R) diagram. We find that the conditions for such a crossing occur around $L_\approx 10^2$~$L_\odot$ (or $a\approx 0.1$~au) for Jovian planetary companions. The consumption of closer-in giant planets, such as hot Jupiters, leads to $L_{\rm decay}\gg L_$, while more distant planets such as warm Jupiters, $a\approx 0.5$~au, lead to minor perturbations of their host stars with $L_{\rm decay} \ll L_*$. Our results map out the parameter space along the giant branch in the H-R Diagram where interaction with planetary companions leads to significant energetic disturbance of host stars.

Read this paper on arXiv…

M. MacLeod, M. Cantiello and M. Soares-Furtado
Tue, 16 Jan 18
33/79

Comments: 7 pages, 4 figures, accepted for publication in ApJL

Improving Orbit Prediction Accuracy through Supervised Machine Learning [EPA]

http://arxiv.org/abs/1801.04856


Due to the lack of information such as the space environment condition and resident space objects’ (RSOs’) body characteristics, current orbit predictions that are solely grounded on physics-based models may fail to achieve required accuracy for collision avoidance and have led to satellite collisions already. This paper presents a methodology to predict RSOs’ trajectories with higher accuracy than that of the current methods. Inspired by the machine learning (ML) theory through which the models are learned based on large amounts of observed data and the prediction is conducted without explicitly modeling space objects and space environment, the proposed ML approach integrates physics-based orbit prediction algorithms with a learning-based process that focuses on reducing the prediction errors. Using a simulation-based space catalog environment as the test bed, the paper demonstrates three types of generalization capability for the proposed ML approach: 1) the ML model can be used to improve the same RSO’s orbit information that is not available during the learning process but shares the same time interval as the training data; 2) the ML model can be used to improve predictions of the same RSO at future epochs; and 3) the ML model based on a RSO can be applied to other RSOs that share some common features.

Read this paper on arXiv…

H. Peng and X. Bai
Tue, 16 Jan 18
35/79

Comments: 30 pages, 21 figures, 4 tables, Preprint submitted to Advances in Space Research, on December 14, 2017

SETI is Part of Astrobiology [IMA]

http://arxiv.org/abs/1801.04868


“Traditional SETI is not part of astrobiology” declares the NASA Astrobiology Strategy 2015 document. This is incorrect. In this white paper, I argue that SETI$-$seen as the search for technosignatures characteristic of the future of life in the universe$-$is a neglected complement to the search for biosignatures in NASA’s astrobiology portfolio, and may offer the more fruitful avenue to the discovery of life elsewhere in the universe, as recognized by the Astro2010 decadal survey. I rebut six erroneous perceptions that may contribute to the field’s absence from NASA’s astrobiology strategy, and argue that since SETI is, quite obviously, part of astrobiology, SETI practitioners should at the very least be expressly encouraged to compete on a level playing field with practitioners of other subfields for NASA astrobiology resources.

Read this paper on arXiv…

J. Wright
Tue, 16 Jan 18
65/79

Comments: 5 pages, submitted as a white paper to the National Academies of Sciences, Engineering, and Medicine ad hoc Committee on Astrobiology Science Strategy for Life in the Universe, 2018. this http URL

Distribution specificities of long-period comets' perihelia. Hypothesis of the large planetary body on the periphery of the Solar System [EPA]

http://arxiv.org/abs/1801.04451


The present paper reviews selected aspects of the Guliyev’s hypothesis about the massive celestial body at a distance of 250-400 AU from the Sun as well as the factor of comets transfer. It is shown, that the conjecture of the point around which cometary perihelia might be concentrated, is not consistent. On the issue of perihelia distribution, priority should be given to the assumption that there is a plane or planes around which the concentration takes place. A total of 24 comet groups were investigated. In almost all cases there are detected two types of planes or zones: the first one is very close to the ecliptic, another one is about perpendicular to it and has the parameters: ip = 86{\deg}, {\Omega}p = 271.7{\deg}. The existence of the first area appears to be related to the influence of giant planets. The Guliyev’s hypothesis says that there is a massive perturber in the second zone, at a distance of 250-400 AU. It shows that number of aphelia and distant nodes of cometary orbits in this interval significantly exceeds the expected background. Analysis of the angular parameters of the comets, calculated relative to the second plane (reference point is the ascending node of a large circle) displays clear patterns: shortage of comets near i’ = 180{\deg}, excess of them near B’= 0{\deg} (ecliptic latitude of perihelion) and shortage near B’=-90{\deg}. The analysis also shows irregularity of distant nodes, overpopulation of perihelion longitudes in the range 350{\deg}-20{\deg}. Plotted distributions of aphelia N(Q) and distant cometary nodes clearly indicate a perturbation of the natural course near 300 AU. On the basis of collected cometary data, we have estimated orbital elements of the hypothetical planetary body: a = 337 AU; e = 0.14; {\omega} = 57{\deg}; {\Omega} = 272.7{\deg}; i = 86{\deg}.

Read this paper on arXiv…

A. Guliyev and R. Guliyev
Tue, 16 Jan 18
70/79

Comments: N/A

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. VI. HD 238914 and TYC 3318-01333-1 – two more Li-rich giants with planets [SSA]

http://arxiv.org/abs/1801.04379


We present the latest results of our search for planets with HARPS-N at the 3.6 m Telescopio Nazionale Galileo under the Tracking Advanced Planetary Systems project: an in-depth study of the 15 most Li abundant giants from the PennState – Toru\’n Planet Search sample. Our goals are first, to obtain radial velocities of the most Li-rich giants we identified in our sample to search for possible low-mass substellar companions, and second, to perform an extended spectral analysis to define the evolutionary status of these stars. Methods. This work is based on high-resolution spectra obtained with the Hobby-Eberly Telescope and its High Resolution Spectro- graph, and with the HARPS-N spectrograph at the Telescopio Nazionale Galileo. Two stars, HD 181368 and HD 188214 , were also observed with UVES at the VLT to determine beryllium abundances. We report i) the discovery of two new planetary systems around the Li-rich giant stars: HD 238914 and TYC 3318-01333- 1 (a binary system); ii) reveal a binary Li-rich giant, HD 181368 ; iii) although our current phase coverage is not complete, we suggest the presence of planetary mass companions around TYC 3663-01966-1 and TYC 3105-00152-1 ; iv) we confirm the previous result for BD+48 740 and present updated orbital parameters, and v) we find a lack of a relation between the Li enhancement and the Be abundance for the stars HD 181368 and HD 188214 , for which we acquired blue spectra. We found seven stars with stellar or potential planetary companions among the 15 Li-rich giant stars. The binary star frequency of the Li-rich giants in our sample appears to be normal, but the planet frequency is twice that of the general sample, which suggests a possible connection between hosting a companion and enhanced Li abundance in giant stars. We also found most of the companions orbits to be highly eccentric.

Read this paper on arXiv…

M. Adamow, A. Niedzielski, K. Kowalik, et. al.
Tue, 16 Jan 18
73/79

Comments: A&A, accepted

A machine learns to predict the stability of circumbinary planets [EPA]

http://arxiv.org/abs/1801.03955


Long-period circumbinary planets appear to be as common as those orbiting single stars and have been found to frequently have orbital radii just beyond the critical distance for dynamical stability. Assessing the stability is typically done either through N-body simulations or using the classic Holman-Wiegert stability criterion: a secondorder polynomial calibrated to broadly match numerical simulations. However, the polynomial is unable to capture islands of instability introduced by mean motion resonances, causing the accuracy of the criterion to approach that of a random coin-toss when close to the boundary. We show how a deep neural network (DNN) trained on Nbody simulations generated with REBOUND is able to significantly improve stability predictions for circumbinary planets on initially coplanar, circular orbits. Specifically, we find that the accuracy of our DNN never drops below 86%, even when tightly surrounding the boundary of instability, and is fast enough to be practical for on-the-fly calls during likelihood evaluations typical of modern Bayesian inference. Our binary classifier DNN is made publicly available at https://github.com/CoolWorlds/orbitalstability.

Read this paper on arXiv…

C. Lam and D. Kipping
Mon, 15 Jan 18
13/59

Comments: Accepted by MNRAS. Deep neural network and implementation can be found at this https URL