arXiv subjects

Ravi Kumar Kopparapu

Publications and source records attributed to Ravi Kumar Kopparapu.

23 records · Page 2Linked to original sources

arXiv2014

Geothermal heating enhances atmospheric asymmetries on synchronously rotating planets

Earth-like planets within the liquid water habitable zone of M type stars may evolve into synchronous rotators. On these planets, the sub-stellar hemisphere experiences perpetual daylight while the opposing anti-stellar hemisphere experiences perpetual darkness. Because the night-side hemisphere has no direct source of energy, the air over this side of the planet is prone to freeze out and deposit on the surface, which could result in atmospheric collapse. However, general circulation models (GCMs) have shown that atmospheric dynamics can counteract this problem and provide sufficient energy transport to the anti-stellar side. Here we use an idealized GCM to consider the impact of geothermal heating on the habitability of synchronously rotating planets. Geothermal heating may be expected due to tidal interactions with the host star, and the effects of geothermal heating provide additional habitable surface area and may help to induce melting of ice on the anti-stellar hemisphere. We also explore the persistence of atmospheric asymmetries between the northern and southern hemispheres, and we find that the direction of the meridional circulation (for rapidly rotating planets) or the direction of zonal wind (for slowly rotating planets) reverses on either side of the sub-stellar point. We show that the zonal circulation approaches a theoretical state similar to a Walker circulation only for slowly rotating planets, while rapidly rotating planets show a zonal circulation with the opposite direction. We find that a cross-polar circulation is present in all cases and provides an additional mechanism of mass and energy transport from the sub-stellar to anti-stellar point. Characterization of the atmospheres of synchronously rotating planets should include consideration of hemispheric differences in meridional circulation and examination of transport due to cross-polar flow.

astro-ph.EP↗

arXiv2014

On the Frequency of Potential Venus Analogs from Kepler Data

The field of exoplanetary science has seen a dramatic improvement in sensitivity to terrestrial planets over recent years. Such discoveries have been a key feature of results from the {\it Kepler} mission which utilizes the transit method to determine the size of the planet. These discoveries have resulted in a corresponding interest in the topic of the Habitable Zone (HZ) and the search for potential Earth analogs. Within the Solar System, there is a clear dichotomy between Venus and Earth in terms of atmospheric evolution, likely the result of the large difference ($\sim$ factor of two) in incident flux from the Sun. Since Venus is 95\% of the Earth's radius in size, it is impossible to distinguish between these two planets based only on size. In this paper we discuss planetary insolation in the context of atmospheric erosion and runaway greenhouse limits for planets similar to Venus. We define a ``Venus Zone'' (VZ) in which the planet is more likely to be a Venus analog rather than an Earth analog. We identify 43 potential Venus analogs with an occurrence rate ($η_{\venus}$) of $0.32^{+0.05}_{-0.07}$ and $0.45^{+0.06}_{-0.09}$ for M dwarfs and GK dwarfs respectively.

astro-ph.EP↗

arXiv2011

On the likelihood of non-terrestrial artifacts in the Solar System

Extraterrestrial technology may exist in the Solar System without our knowledge. This is because the vastness of space, combined with our limited searches to date, implies that any remote unpiloted exploratory probes of extraterrestrial origin would likely remain unnoticed. Here we develop a probabilistic approach to quantify our certainty (or uncertainty) of the existence of such technology in the Solar System. We discuss some possible strategies for improving this uncertainty that include analysis of moon- and Mars-orbiting satellite data as well as continued exploration of the Solar System.

physics.pop-ph↗

arXiv2008

Host Galaxies Catalog Used in LIGO Searches for Compact Binary Coalescence Events

An up-to-date catalog of nearby galaxies considered as hosts of binary compact objects is provided with complete information about sky position, distance, extinction-corrected blue luminosity and error estimates. With our current understanding of binary evolution, rates of formation and coalescence for binary compact objects scale with massive-star formation and hence the (extinction-corrected) blue luminosity of host galaxies. Coalescence events in binary compact objects are among the most promising gravitational-wave sources for ground-based gravitational-wave detectors such as LIGO. Our catalog and associated error estimates are important for the interpretation of analyses, carried out for LIGO, to constrain the rates of compact binary coalescence, given an astrophysical population model for the sources considered. We discuss how the notion of effective distance, created to account for the antenna pattern of a gravitational-wave detector, must be used in conjunction with our catalog. We note that the catalog provided can be used on other astronomical analysis of populations that scale with galaxy blue luminosity.

astro-ph↗

arXiv2006

Population Boundaries for Galactic White Dwarf Binaries in LISA's Amplitude-Frequency Domain

Detached, inspiraling and semi-detached, mass-transferring double white dwarf (DWD) binary systems are both expected to be important sources for the proposed space-based gravitational-wave detector, LISA. The mass-radius relationship of individual white dwarf stars in combination with the constraints imposed by Roche geometries permit us to identify population boundaries for DWD systems in LISA's ``absolute'' amplitude-frequency diagram. With five key population boundaries in place, we are able to identify four principal population sub-domains, including one sub-domain that identifies where progenitors of Type Ia supernovae will reside. Given one full year of uninterrupted operation, LISA should be able to measure the rate at which the gravitational-wave frequency $f$ and, hence, the orbital period is changing in the highest frequency subpopulation of our Galaxy's DWD systems. We provide a formula by which the distance to each DWD system in this subpopulation can be determined; in addition, we show how the masses of the individual white dwarf stars in mass-transferring systems may be calculated.

astro-ph↗