Shine On, Cassini

“Each flyby gives us a little more knowledge of Titan and its striking similarities to our world. Even with its cold surface temperatures of minus 290 degrees Fahrenheit (94 kelvins), Titan is like early Earth in a deep freeze.”

(Hill)

It’s a cosmic diamond jubilee, of sorts. The clock is running, with Cassini set to undertake it’s T-99 flyby of Titan tomorrow (March 6, 2014; 0725 PST). An additional flyby undertaken after the original schedule was settled makes this officially the spacecraft’s one-hundredth survey of Saturn’s largest moon.

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Enceladus Unveiled

Inertia.

Never mind.

Let us start, then, with something a little more recent, since there is much to see.

Enceladus, perhaps our favorite celestial body in the solar system.

And, ah, Cassini!

The intensity of the jets of water ice and organic particles that shoot out from Saturn’s moon Enceladus depends on the moon’s proximity to the ringed planet, according to data obtained by NASA’s Cassini spacecraft.

The finding adds to evidence that a liquid water reservoir or ocean lurks under the icy surface of the moon. This is the first clear observation the bright plume emanating from Enceladus’ south pole varies predictably. The findings are detailed in a scientific paper in this week’s edition of Nature.

“The jets of Enceladus apparently work like adjustable garden hose nozzles,” said Matt Hedman, the paper’s lead author and a Cassini team scientist based at Cornell University in Ithaca, N.Y. “The nozzles are almost closed when Enceladus is closer to Saturn and are most open when the moon is farthest away. We think this has to do with how Saturn squeezes and releases the moon with its gravity.”

Cassini, which has been orbiting Saturn since 2004, discovered the jets that form the plume in 2005. The water ice and organic particles spray out from several narrow fissures nicknamed “tiger stripes.”

“The way the jets react so responsively to changing stresses on Enceladus suggests they have their origins in a large body of liquid water,” said Christophe Sotin, a co-author and Cassini team member at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Liquid water was key to the development of life on Earth, so these discoveries whet the appetite to know whether life exists everywhere water is present.”

Just a reminder: NASA is an example of a government agency doing its job; that’s why congresses and presidents alike prefer to cut its budget^†.
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^† No, really, click that link; it’s important.

But Does It Work On Ducks?

“So, a fake force is a force that is not an interaction between two objects. Rather it is like duck tape (I refuse to call it duct tape because it isn’t good for ducts) on your accelerating frame.”

—Rhett Allain

What? I mean, it’s an obvious question, right?

Er … never mind^*. But the consideration of physics in a game show context, from 2011, is still worth a read. Today’s discussion of gravity in a space movie is just as rewarding.
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^* I know … I know, I know. I just needed a title. Or, okay, to be honest, it was the first one that occurred to me.

A Brief Physics Lesson: Bicycle Edition

Math? Physics? Those who enjoy brief exercises in applied speculation will certainly learn a thing or two from Rhett Allain, who took some time to consider bicycles and hills. At first blush, it seems an easy enough question: What’s the steepest gradient you could possibly ride on a road bike?

Of course, there is a difference between the simplicity of straightforward mathematics and the complexity of accounting for all the factors required.

I think there are three reasons why a slope would be too steep. For all of these cases, I am going to assume that it is a prolonged slope. This means that you can’t just build up a large speed and zoom up the slope. If this was the case, you could go straight up a wall (which you can for a short time).

Those three reasons are the limitations of human power, center of mass, and friction. If one wishes to point out, “What if you used these tires instead of those?” or, “What if you had a different gear set?” it’s all well and fine to do so, but therein lies the point about the complexity of accounting for all the factors required.

Really, the friction problem might be worse than this. The bike only uses the back wheel for moving forward, so it is the friction on the back wheel that matters. If the biker is leaning forward, the weight distribution might not be even on the two wheels. I will leave this estimation (combining the previous two limits) as an exercise for the reader.

And, of course, one is welcome to pursue such endeavors. (In truth, that might be part of the point.)