On the abundance of extraterrestrial life after the Kepler mission

Amri Wandel
The data recently accumulated by the Kepler mission have demonstrated that small planets are quite common and that a significant fraction of all stars may have an Earth-like planet within their Habitable Zone.
These results are combined with a Drake-equation formalism to derive the space density of biotic planets as a function of the relatively modest uncertainty in the astronomical data and of the (yet unknown) probability for the evolution of biotic life…
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Read also: How Data From The Kepler Space Telescope Is Changing The Drake Equation

Astrophysicists Identify The “Habitable” Regions Of The Entire Universe

It’s not just stars and galaxies that have habitable zones. Some regions of universe are more life-friendly than others

Gamma ray bursts are among the most powerful events in the universe. And although the SGR 1806 -20 flare was relatively mild, it was an unwelcome reminder that life on this planet is constantly threatened by events of unimaginable power.

But here’s the thing: gamma ray bursts are much more common in some parts of the universe than others. That raises the curious prospect that some parts of the universe ae much more inhospitable to life than others. So where are these death zones and what kind of constraints do they place on the origin of life?

Today, Tsvi Piran at The Hebrew University in Jerusalem, Israel and Raul Jimenez at Harvard University in Cambridge say they’ve worked out where in the universe gamma ray bursts are most deadly. As a result, they are able to work out for the first time the universe’s habitable zones.

Gamma ray bursts are a significant mystery—nobody is quite sure how or where the most powerful ones occur. But astronomers know that a burst could do significant damage to the Earth if it happened nearby. The gamma rays would rapidly strip the planet of its ozone layer, leaving the creatures on the surface vulnerable to ultraviolet light and other kinds of high-energy radiation. Indeed, several studies have examined the very real possibility that gamma ray bursts may have brought life on Earth to the edge of extinction on several occasions in the past.

Exactly how often a given planet would be hit by gamma ray bursts obviously depends on its neighbourhood. So the starting point for the work of Prian and Jimenez is to determine how common these powerful events are. Continue reading Astrophysicists Identify The “Habitable” Regions Of The Entire Universe

Astrosociology: Interwiews about an infinite universe

visible universe

click to enlarge

Erik Høg

If the universe is infinite now it has always been infinite. This is the opinion of many astronomers today as can be concluded from the following series of interviews, but the opinions differ much more than I had expected.
Many astronomers do not have a clear opinion on this matter. Others have a clear opinion, but very different from the majority. Detailed arguments by two experts on general relativity are also included.
Observations show that the universe is flat, i.e. the curvature is zero within the small uncertainty of measurements.
This implies an infinite universe, though most probably we will never know that for certain. For comparison with the recent interviews, opinions during the past 2300 years since Aristotle about the universe being finite or infinite have been collected from literature, and it appears that the scientists often had quite definite opinions…

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The Ĝ Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies

I.  Background and Justification

J. T. Wright, B. Mullan, S. Sigurðsson, M. S. Povich

We motivate the Ĝ infrared search for extraterrestrial civilizations with large energy supplies.
We discuss some philosophical difficulties of SETI, and how communication SETI circumvents them.
We review “Dysonian SETI”, the search for artifacts of alien civilizations, and find that it is highly complementary to traditional communication SETI; the two together might succeed where either one, alone, has not.
We discuss the argument of Hart (1975) that spacefaring life in the Milky Way should be either galaxy-spanning or non-existent, and examine a portion of his argument that we dub the “monocultural fallacy”.
We discuss some rebuttals to Hart that invoke sustainability and predict long Galaxy colonization timescales.
We find that the maximum Galaxy colonization timescale is actually much shorter than previous work has found (109 yr), and that many “sustainability” counter-arguments to Hart’s thesis suffer from the monocultural fallacy.
We extend Hart’s argument to alien energy supplies, and argue that detectably large energy supplies can plausibly be expected to exist because life has potential for exponential growth until checked by resource or other limitations, and intelligence implies the ability to overcome such limitations.
As such, if Hart’s thesis is correct then searches for large alien civilizations in other galaxies may be fruitful; if it is incorrect, then searches for civilizations within the Milky Way are more likely to succeed than Hart argued. We review some past Dysonian SETI efforts, and discuss the promise of new mid-infrared surveys, such as that of WISE…
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IRIS: Observing a Gigantic Solar Eruption

A coronal mass ejection burst off the side of the sun on May 9, 2014. The giant sheet of solar material erupting was the first CME seen by NASA’s Interface Region Imaging Spectrograph, or IRIS. The field of view seen here is about five Earth’s wide and about seven and a half Earth’s tall.

IRIS must commit to pointing at certain areas of the sun at least a day in advance, so catching a CME in the act involves some educated guesses and a little bit of luck.