Astrobiological papers from Arvix and everywhere

[Roger E. Moore]

How advances in exoplanetary science are affecting the way in which we search for extraterrestrial intelligence (SETI).


https://arxiv.org/abs/2007.12645

Habitability of M dwarfs is a problem for the traditional SETI

Milan M. Ćirković, Branislav Vukotić

We consider some implications of the much-discussed circumstellar habitable zones around M-dwarf stars for the conventionally understood radio SETI. We argue that the flaring nature of these stars would further adversely impact local development of radio communication and that, therefore, their circumstellar habitable zones should be preferentially studied by other methods. This is a clear example how diversity of astrobiological habitats is introducing contingency into the cultural evolution, thus undermining the universality of cultural convergence as one of the major premises of the traditional SETI. This is yet another example of how specifics of the physical environment strongly shape cultural evolution taken in the broadest, most inclusive sense.

[Roger E. Moore]

More on the "location, location, location" aspect of galactic habitability. NOTE: The closer to the Galactic Center, the less desirable the real estate.

================

https://arxiv.org/abs/2008.09988

The Impact of Tidal Disruption Events on Galactic Habitability

E. Pacetti, A. Balbi, M. Lingam, F. Tombesi, E. Perlman

Tidal Disruption Events (TDEs) are characterized by the emission of a short burst of high-energy radiation. We analyze the cumulative impact of TDEs on galactic habitability using the Milky Way as a proxy. We show that X-rays and extreme ultraviolet (XUV) radiation emitted during TDEs can cause hydrodynamic escape and instigate biological damage. By taking the appropriate variables into consideration, such as the efficiency of atmospheric escape and distance from the Galactic center, we demonstrate that the impact of TDEs on galactic habitability is comparable to that of Active Galactic Nuclei. In particular, we show that planets within distances of ∼0.1-1 kpc could lose Earth-like atmospheres over the age of the Earth, and that some of them might be subject to biological damage once every ≳ 10^4 yrs. We conclude by highlighting potential ramifications of TDEs and argue that they should be factored into future analyses of inner galactic habitability.

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https://arxiv.org/abs/2008.01419

The Habitability of the Galactic Bulge

Amedeo Balbi, Maryam Hami, Andjelka B. Kovačević

We present a new investigation of the habitability of the Milky Way bulge, that expands previous studies on the Galactic Habitable Zone. We discuss existing knowledge on the abundance of planets in the bulge, metallicity and the possible frequency of rocky planets, orbital stability and encounters, and the possibility of planets around the central supermassive black hole. We focus on two aspects that can present substantial differences with respect to the environment in the disk: (i) the ionizing radiation environment, due to the presence of the central black hole and to the highest rate of supernovae explosions and (ii) the efficiency of putative lithopanspermia mechanism for the diffusion of life between stellar systems. We use analytical models of the star density in the bulge to provide estimates of the rate of catastrophic events and of the diffusion timescales for life over interstellar distances.

[Roger E. Moore]

Might aliens communicate with each other by using FRBs (fast radio bursts)?


https://arxiv.org/abs/2006.08493

A Quantitative Assessment of Communicating Extra-Terrestrial Intelligent Civilizations in the Galaxy and the Case of FRB-like Signals

Bing Zhang (UNLV)

A formula is proposed to quantitatively estimate the signal emission rate of Communicating Extra-Terrestrial Intelligent civilizations (CETIs) in the Galaxy. I suggest that one possible type of CETI signal would be brief radio bursts similar to fast radio bursts (FRBs). A dedicated search for FRB-like artificial signals in the Galaxy for decades may pose a meaningful upper limit on the emission rate of these signals by CETIs. The Fermi-Hart paradox is answered in terms of not having enough observing times for this and other types of signals. Whether humans should send FRB-like signals in the far future is briefly discussed.

[publiusr]

I wonder if some of these radio bursts might answer several questions.

Putting things in orbit around magnetars and such could give power, but perhaps also produce heavier elements.

If asteroids are bombarded over deep time— might that allow for more gold to be generated than stellar collisions alone account for?

[Tom Mazanec]

Re: Lunar Opportunities for SETI
The great thing about farside is that it is always shielded from Earth and that you can find natural craters that would dwarf the lamented Arecibo.

[Roger E. Moore]

The first contact we get might be with a much older, more powerful civilization.


https://arxiv.org/abs/2010.12358

Contact Inequality -- First Contact Will Likely Be With An Older Civilization

David Kipping, Adam Frank, Caleb Scharf

First contact with another civilization, or simply another intelligence of some kind, will likely be quite different depending on whether that intelligence is more or less advanced than ourselves. If we assume that the lifetime distribution of intelligences follows an approximately exponential distribution, one might naively assume that the pile-up of short-lived entities dominates any detection or contact scenario. However, it is argued here that the probability of contact is proportional to the age of said intelligence (or possibly stronger), which introduces a selection effect. We demonstrate that detected intelligences will have a mean age twice that of the underlying (detected + undetected) population, using the exponential model. We find that our first contact will most likely be with an older intelligence, provided that the maximum allowed mean lifetime of the intelligence population, τmax, is > e times larger than our own. Older intelligences may be rare but they disproportionality contribute to first contacts, introducing what we call a 'contact inequality', analogous to wealth inequality. This reasoning formalizes intuitional arguments and highlights that first contact would likely be one-sided, with ramifications for how we approach SETI.

[Roger E. Moore]

QUOTE: As we near the end of the year, what were the biggest stories related to the search for life beyond Earth? It seems fitting that we start with a loss—of the Arecibo Telescope in Puerto Rico.

https://www.airspacemag.com/daily-pl...020-180976585/

[Roger E. Moore]

Robust stellar flares might not prevent life on exoplanets, could facilitate its detection.

QUOTE: If there is life on M and K dwarf exoplanets, previous work hypothesizes that stellar flares might make it easier to detect. For example, stellar flares can increase the abundance of life-indicating gasses (such as nitrogen dioxide, nitrous oxide and nitric acid) from imperceptible to detectable levels. "Space weather events are typically viewed as a detriment to habitability," Chen said. "But our study quantitatively shows that some space weather can actually help us detect signatures of important gases that might signify biological processes."

https://phys.org/news/2020-12-robust...xoplanets.html

https://scitechdaily.com/alien-life-...space-weather/

[Roger E. Moore]

Two planetary articles with peculiar intertwined headlines about the past of Earth and Venus--we were them and they were us.

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Venus was once more Earth-like, but climate change made it uninhabitable.

https://earthsky.org/space/venus-was...climate-change

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Early Earth Was No Inviting Blue Planet—It Was More Like Venus.

https://www.airspacemag.com/daily-pl...nus-180976534/

[Roger E. Moore]

Planets, planets, literally everywhere. Life everywhere, too? A planet called KOI-5Ab orbits in a triple-star system with a skewed configuration.

https://phys.org/news/2021-01-planet...ar-skewed.html

[Roger E. Moore]

Good news for photosynthesis under red-dwarf skies!

https://arxiv.org/abs/2101.04448

Super-Earths, M Dwarfs, and Photosynthetic Organisms: Habitability in the Lab

R. Claudi, E. Alei, M. Battistuzzi, L. Cocola, M. S. Erculiani, A. C. Pozzer, B. Salasnich, D. Simionato, V. Squicciarini, L. Poletto, N. La Rocca

In a few years, space telescopes will investigate our Galaxy to detect evidence of life, mainly by observing rocky planets. In the last decade, the observation of exoplanet atmospheres and the theoretical works on biosignature gasses have experienced a considerable acceleration. The~most attractive feature of the realm of exoplanets is that 40\% of M dwarfs host super-Earths with a minimum mass between 1 and 30 Earth masses, orbital periods shorter than 50 days, and radii between those of the Earth and Neptune (1--3.8 R⊕). Moreover, the recent finding of cyanobacteria able to use far-red (FR) light for oxygenic photosynthesis due to the synthesis of chlorophylls d and f, extending in vivo light absorption up to 750\ nm, suggests the possibility of exotic photosynthesis in planets around M dwarfs. Using innovative laboratory instrumentation, we exposed different cyanobacteria to an M dwarf star simulated irradiation, comparing their responses to those under solar and FR simulated lights.~As expected, in FR light, only the cyanobacteria able to synthesize chlorophyll d and f could grow. Surprisingly, all strains, both able or unable to use FR light, grew and photosynthesized under the M dwarf generated spectrum in a similar way to the solar light and much more efficiently than under the FR one. Our findings highlight the importance of simulating both the visible and FR light components of an M dwarf spectrum to correctly evaluate the photosynthetic performances of oxygenic organisms exposed under such an exotic light~condition.

[Roger E. Moore]

According to astronomers at Villanova University, the best stars for life are one step along the Hertzsprung-Russell chart of star types - that is, K-type stars, which are orange stars a little cooler than the Sun, and a little warmer than a red dwarf. "K-dwarf stars are in the 'sweet spot,' with properties intermediate between the rarer, more luminous, but shorter-lived solar-type stars (G stars) and the more numerous red dwarf stars (M stars)," explained Villanova astronomer and astrophysicist Edward Guinan. "The K stars, especially the warmer ones, have the best of all worlds. If you are looking for planets with habitability, the abundance of K stars pump up your chances of finding life."

https://www.sciencealert.com/astrono...ould-host-life

[Roger E. Moore]

Planets almost since the universe began. Chances of life in the universe look better, maybe?

Astronomers Find an Astonishing 'Super-Earth' That's Nearly as Old as The Universe. Around one of the galaxy's oldest stars, an orange dwarf named TOI-561 just 280 light-years away, astronomers have found three orbiting exoplanets - one of which is a rocky world 1.5 times the size of Earth, whipping around the star on a breakneck 10.5-hour orbit. Obviously an exoplanet so close to its star isn't likely to be habitable, even if it is rocky like Earth, Venus and Mars. It would have a temperature of 2,480 Kelvin, tidally locked with a magma ocean on the permanent day side. But the TOI-561 system, planets and all, is one of the oldest ever seen, at an estimated age of around 10 billion years. That's more than twice as old as the Solar System, nearly as old as the Universe itself, and evidence that rocky exoplanets can remain stable for a very long time. "TOI-561 b is one of the oldest rocky planets yet discovered," said astronomer Lauren Weiss of the University of Hawai'i. "Its existence shows that the universe has been forming rocky planets almost since its inception 14 billion years ago."

https://www.sciencealert.com/an-asto...s-the-universe