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Assorted Personal Notations, Essays, and Other Jottings

Posts Tagged ‘extraterrestrial life

[LINK] Two links from The Dragon’s Gaze about dying Venus and Mars

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The Dragon’s Gaze recently-ish had two interesting links examining Venus and Mars, two worlds in our solar system’s youth which could have been rather more Earth-like than at present. The first link was to the paper “Exploring the Inner Edge of the Habitable Zone with Fully Coupled Oceans”.

Rotation in planetary atmospheres plays an important role in regulating atmospheric and oceanic heat flow, cloud formation and precipitation. Using the Goddard Institute for Space Studies (GISS) three dimension General Circulation Model (3D-GCM) we investigate how the effects of varying rotation rate and increasing the incident stellar flux on a planet set bounds on a planet’s habitable zone with its parent star. From ensemble climate simulations we identify which factors are the primary controllers of uncertainty in setting these bounds. This is shown in particular for fully coupled ocean (FCO) runs — some of the first that have been utilized in this context. Results with a Slab Ocean (SO) of 100m mixed layer depth are compared with a similar study by Yang et al. 2014, which demonstrates consistency across models. However, there are clear differences for rotations rates of 1-16x present Earth sidereal day lengths between the 100m SO and FCO models, which points to the necessity of using FCOs whenever possible. The latter was recently demonstrated quite clearly by Hu & Yang 2014 in their aquaworld study with a FCO when compared with similar mixed layer ocean studies and by Cullum et al. 2014.

We also show how these results have implications for Venus in the early history of our Solar System since even at this time Venus received more solar flux than Earth does today while it may still have had a slow retrograde rotation. The Venus runs utilize a 2.9Gya solar spectrum generated with the code of Claire et al. 2012, a modern Venus topography with an ocean filling the lowlands (giving an equivalent depth of 310 meters if spread across the entire surface), atmosphere of 1 bar N2, CO2=0.4mb, CH4=0.001mb and present day orbital parameters, radius, & gravity. We demonstrate that ancient Venus could have had quite moderate surface temperatures given these assumptions.

The second link was to “The early geodynamic evolution of Mars-type planets”.

It is not clear whether Mars once possessed active tectonics, yet the question is critical for understanding the thermal evolution of Mars, and the origin and longevity of its early dynamo. To address these issues, we have coupled mantle flow simulations, together with parameterized core evolution models, to simulate the early evolution of Mars-like planets, and constrain the influence of early mobile-lid tectonics on core evolution. We have explored a wide parameter suite, encapsulating a range of uncertainties in initial conditions, rheological parameters, and surface strength. We present successful models that experience early mobile-lid behaviour, with a later transition into a stagnant-lid mode, which reproduce core dynamo histories similar to the magnetic history of early Mars.

Written by Randy McDonald

February 10, 2016 at 7:30 pm

[LINK] “Earth from afar would look only 82% right for life”

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Universe Today’s Evan Gough writes about an amusing analysis of Earth’s suitability for life.

You might think, because, well, here we are, that the Earth would look 100% habitable from a distant location. But that’s not the case. According to a paper from Rory Barnes and his colleagues at the University of Washington-based Virtual Planetary Laboratory, from a distant point in the galaxy, the probability of Earth being habitable might be only 82%.

Barnes and his team came up with the 82% number when they worked to create a “habitability index for transiting planets,” that seeks to rank the habitability of planets based on factors like the distance from its star, the size of the planet, the nature of the star, and the behaviour of other planets in the system.

The search for habitable exo-planets is dominated by the idea of the circumstellar habitable zone—or Goldilocks Zone—a region of space where an orbiting planet is not too close to its star to boil away all the water, and not so far away that the water is all frozen. This isn’t a fixed distance; it depends on the type and size of the star. With an enormous, hot star, the Goldilocks Zone would be much further away than Earth is from the Sun, and vice-versa for a smaller, cooler star. “That was a great first step, but it doesn’t make any distinctions within the habitable zone,” says Barnes.

To rank candidates for further study, Barnes focused on not just the distance between the planet and the host star, but on the overall energy equilibrium. That takes into account not just the energy received by the planet, but the planet’s albedo—how much energy it reflects back into space. In terms of being warm enough for life, a high-albedo planet can tolerate being closer to its star, whereas a low-albedo planet can tolerate a greater distance. This equilibrium is affected in turn by the eccentricity of the planet’s orbit.

The habitability index created by Barnes—and his colleagues Victoria Meadows and Nicole Evans—is a way to enter data, including a planet’s albedo and its distance from its host star, and get a number representing the planet’s probability of being habitable. “Basically, we’ve devised a way to take all the observational data that are available and develop a prioritization scheme,” said Barnes, “so that as we move into a time when there are hundreds of targets available, we might be able to say, ‘OK, that’s the one we want to start with.’”

So where does the Earth fit into all this? If alien astronomers are creating their own probability index, at 82%, Earth is a good candidate. Maybe they’re already studying us more closely.

The University of Washington press release is here, and the paper is at arXiv, “Comparative Habitability of Transiting Exoplanets”.

Written by Randy McDonald

February 8, 2016 at 8:37 pm

[BLOG] Some Wednesday links

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  • BCer in Toronto Jeff Jedras foodblogs from different Ottawa junkets.
  • The Broadside Blog’s Caitlin Kelly lists 20 ways to enjoy winter. (If it comes.)
  • Centauri Dreams shares the latest Pluto imagery and examines the ancient impact that created the Moon.
  • Crooked Timber notes that volunteers who help refugees arriving in Greece might be criminalized.
  • The Dragon’s Gaze notes that some Earth-like worlds at different points in their history might be difficult to identify, and notes a SETI search looking for flashes from KIC 8462852 has turned up nothing.
  • Geocurrents maps development in the Philippines.
  • Marginal Revolution shares Alex Tabarrok’s opinion that home ownership is overrated.
  • The Planetary Society Blog’s Marc Rayman notes how important light is for Dawn“s imaging of Ceres.
  • pollotenchegg notes the historical patterns of ethnic change in southeast Ukraine, the Donbas standing out as especially Russian in population in language.
  • The Russian Demographics Blog notes demographic changes in Chechnya.
  • Transit Toronto notes that Toronto has gotten its 14th and 15th streetcars from Bombardier.
  • Window on Eurasia examines possible outcomes from Tatarstan’s confrontation with the Russian federal government, notes the influence of Central Asian migrants on Russian Islam, suggests Russia is over-centralized, and notes one proposal to abolish Russia’s ethnic units.

[BLOG] Some Wednesday links

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  • blogTO notes underground constructions, from subways to roads, which never took off.
  • Centauri Dreams suggests that an analysis of KIC 8462852 which claimed the star had dimmed sharply over the previous century is incorrect.
  • The Dragon’s Gaze looks at the greenhouse effect of water vapour in exoplanets and wonders if carbon monoxide detection precludes life.
  • Lawyers, Guns and Money notes the economic radicalism of early Marvel.
  • Marginal Revolution argues China’s financial system should remain disconnected from the wider world’s so as to avoid capital flight.
  • The Numerati reacts to the recent snowstorm.
  • Personal Reflections examines Australia Day.
  • The Planetary Society Blog depicts an astronomer tracking a comet.
  • The Russian Demographics Blog notes that Ukraine now hosts one million refugees.
  • Towleroad notes that gay refugees are now getting separate housing in Germany.
  • Window on Eurasia talks about the worrying popularity of Chechnya’s Kadyrov and suggests that when the money runs out Russia’s regions will go their separate ways.

[LINK] On the possible rarity of sustainable extraterrestrial life as an answer to the Fermi paradox

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This is not an implausible outcome, although I would note we need much more information about the cosmos. From Centauri Dreams:

[A]long come Aditya Chopra and Charles Lineweaver (Australian National University), with a new paper suggesting a different kind of filter. The authors call it the Gaian Bottleneck, and it’s a filter that life on Earth has already passed through. The scenario is that life is fragile enough that it rarely develops into intelligence.

The reason: Young planetary environments are unstable. The life that does emerge needs to find ways to regulate greenhouse gases like water and carbon to keep surface temperatures in the habitable range. Normally we think of the decrease in the incoming bombardment of Solar System debris going back 4.5 billion years and extending to about 3.8 Gya as being a key to making the Earth more suitable for life, but the Gaian Bottleneck sees early life as being under strong selection pressure to modify and regulate its own environment. From the paper:

… bombardment rates inevitably decrease in the circumstellar habitable zones (CHZs) of stars, but the timescales for the evolution of Gaian regulation are probably unpredictable and would not inevitably evolve rapidly (or at all). Thus, if there is anything special about what happened on Earth to allow life to persist here, it might have less to do with the decreasing bombardment rate in the Hadean, or special chemical ingredients, or sources of free energy, or even a rare recipe for the emergence of life. The existence of life on Earth today might have more to do with the unusually rapid biological evolution of effective niche construction and Gaian regulation in the first billion years. Habitability and habitable zones would then not only be a passive abiotic property of stellar and planetary physics and chemistry (such as stellar luminosity, initial water content, and decreasing bombardment rate) but would also be a result of early life’s ability to influence initially abiotic geochemical cycles and turn them into the life-mediated biogeochemical cycles that we are familiar with on the current Earth…

In this view, we have gotten through the filter already, finding ourselves in a position not shared by planets around us. Conceivably, both Mars and Venus were once habitable, but a billion years after formation, Venus turns into the hell it is today and Mars goes into a deep freeze. Chopra and Lineweaver argue that if there was early microbial life on either world, it was unable to stabilize its environment, whereas on Earth, life played an active role in doing just that[.]

Universe Today has more.

Written by Randy McDonald

January 26, 2016 at 12:05 pm

[BLOG] Some Wednesday links

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  • blogTO identify five neighbourhoods in downtownish Toronto with cheap rent.
  • The Dragon’s Gaze notes one paper suggesting Earth-like worlds may need both ocean and rocky surfaces to be habitable.
  • The Dragon’s Tales reports that Pluto’s Sputnik Planum is apparently less than ten million years old.
  • Geocurrents begins an interesting regional schema of California.
  • Language Log notes a Hong Kong ad that blends Chinese and Japanese remarkably.
  • Lawyers, Guns and Money notes that societies with low inequality report higher levels of happiness than others.
  • The Map Room points to the lovely Pocket Atlas of Remote Islands.
  • Marginal Revolution wonders why Amazon book reviews are so dominated by American reviewers.
  • Savage Minds considers, after Björk, the ecopoetics of physical geology data.
  • Window on Eurasia “>commemorates the 25th anniversary of the Vilnius massacre.
  • The Financial Times‘ The World blog looks at Leo, the dog of the Cypriot president.

[LINK] “The most likely spots for life in the Milky Way”

Science‘s Ramin Skibba writes about a new study looking at galactic habitable zones.

To support life as we know it, planets must have liquid water and orbit in the right place in their solar systems, not too close and not too far from their star. Similarly, life will not emerge or survive for long near the centers of galaxies. Here, the high density of stars means that at any given time several could be exploding, frying off a planet’s ozone layer and exposing any surface life to deadly ultraviolet rays.

So in the new study, researchers led by physicist Duncan Forgan of the University of St. Andrews in Fife, U.K., focused on the regions far from a galaxy’s center. They used computer simulations to model an entire Milky Way–like galaxy and its neighbors, the Andromeda and Triangulum galaxies. They then simulated the distribution of gas, stars, and planetary systems within those whorls of stars. Finally, they allowed these galaxies to evolve over billions of years, while mapping out their evolving habitable zones. “We’re the first to look at how the history of galaxies affects their habitability,” Forgan says.

For every type of star in the simulation, Forgan and his colleagues estimated the probability that terrestrial planets would form, some of which might be Earth–like or might be as inhospitable as Mercury. They also estimated the chance that a giant planet as large as Neptune would form near the star, as it would disrupt potential earths that could have assembled there. Then they analyzed the likelihood of short-lived life-friendly worlds that happened to be in stellar systems too close to dying, exploding stars.

The team’s simulations show, perhaps not surprisingly, that potentially habitable planets are more likely to remain so if they form in areas far from dense conglomerations of stars, where more supernova explosions occur. The results indicate that for the Milky Way and other spiral galaxies, the most dangerous regions are in the galactic centers, whereas the more diffuse spiral arms pose fewer hazards and are therefore more hospitable to life. Earth lies near the inner edge of this habitable zone.

Written by Randy McDonald

December 16, 2015 at 4:10 pm


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