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In this post: the large versions of the Life Science and Physical Science channel photos, comments from readers, and the best posts of the week.

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Physical Science. Neon lights in an Arizona movie theater. From Flickr, by cobalt123

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Life Science. From Flickr, by law_keven

Reader comments of the week:

In Sputnik Challenges Our Current Definition of Life, GrrlScientist discusses a surprising new discover—a miniscule virus which actually infects other viruses. The new “virophage,” as it’s been named, is the first such species known. It calls into question the legitimacy of viruses as living beings, which depends on many fleeting and intangible definitions of life itself.

Reader Kevin thinks we have far to go before the question will be resolved:

I am not a biologist, but I have followed the discoveries of various extremophiles with interest. I have listened when respected scientists speculate on the realistic possibilities for life on Titan, on Europa, in the upper atmosphere of Venus, and of course Mars. It seems clear that our definition of life and its boundaries is woefully inadequate and that we will see it undergo significant revisions as science continues to push the boundaries of exploration.

In More Sailing, Matt Springer of Built on Facts responds to a reader’s question from his first solar sail post:

I have a question that’s been bugging me about solar sails for ages: what about the fact that light pressure falls off over distance? Every time I see the idea discussed, this is never mentioned…

Matt’s answer—which I’m not even going to attempt to explain here—prompted another question from reader Zifnab:

What is the suitable size for a space sail? I mean, you’re in space. You can basically build the damn thing as big as you want, can’t you?

And reader Nentuaby had a quick—and ethical—answer:

I’d say the actual ability of human space industry to fabricate and launch a sail ought to be taken into account, Zifnab. We probably won’t have the ability to truly build in space anytime soon, so at most we could launch about a 71 tonne vehicle (that’s the estimated capacity of an Ares V to the moon; I don’t know what it could truly escape with, but we’re working on orders of magnitude.)

The current lightest sail material we can actually make is a carbon fibre fabric at about 3 grams a square metre. (I’m sourcing all this from That Famous Wiki, btw, so pinch of NaCl and all that).

So… Ignoring structure… We get about 23,666,666 square meters of fabric up… Or about 4.8 km on a side. No significant digits were harmed in this egregiously back-of-the-napkin calculation.

Some other Life Science posts we thought were cool this week were:

If you think you know life, then please tell me what we have here…

What a pleasant surprise!

Domestication—it’s a matter of time (always is for me, that’s my ‘hammer’ for all nails)

PIG MONKEY!!!

The point of sleep, or, Do fruit flies dream of six-legged sheep?

And from the Physical Science channel:

The Speed of Light Rock

New Remote Operated Vehicle Smell

The search for August

Popular Media Should Do Science

Dewy Propionate (Funny functional group names)

Look for highlights from other channels coming up!