
A Moon of Saturn Has a Sea, Scientists Say - sheri
http://www.nytimes.com/2014/04/04/science/space/a-moon-of-saturn-has-a-sea-scientists-say.html?hp&_r=0
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netcan
The last paragraph is good writing.

 _The challenges are to make sure that the interesting particles would not
break apart, to take precautions that any alien life would not infect Earth,
and to fit it into the $500 million budget of one of NASA’s lower-cost
planetary missions._

It frames it all beautifully. Engineering feats solving problems you don't
quite understand. Sci fi potential. Budgetary drudgery.

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danieltillett
If there is an sea on Enceladus then there will already be microbial life
there [0]. Microbes can survive for ages in space [1] and there are plenty of
rocks moving from the earth and all of the other planets and moons of the
solar system [0,2].

One of the more interesting stories about microbes in space is that some
survived on the moon for almost three years inside a camera [3]. It is not
100% certain that the microbes cultured were not from later contamination, but
I know from working with them that microbes are really tough and I can believe
that they could have survived!

[0]
[http://users.tpg.com.au/horsts/transpermia.html](http://users.tpg.com.au/horsts/transpermia.html)

[1]
[http://www.ncbi.nlm.nih.gov/pubmed/19854226](http://www.ncbi.nlm.nih.gov/pubmed/19854226)

[2]
[http://en.wikipedia.org/wiki/Panspermia](http://en.wikipedia.org/wiki/Panspermia)

[3]
[http://en.wikipedia.org/wiki/Reports_of_Streptococcus_mitis_...](http://en.wikipedia.org/wiki/Reports_of_Streptococcus_mitis_on_the_Moon)

~~~
anigbrowl
Transpermia seems like a theory rather than a fact. While I think you're
_probably_ correct, it's better to be ultra-conservative on questions like
this.

~~~
danieltillett
Of course it is only a theory, but a very plausible one given the frequency of
rock transfer between planets and the toughness of microbes that allow them to
survive in space for long time periods (both empirical facts).

There is really no way of proving transpermia - even if we to travel to
Enceladus and found microbial life there how would we ever prove how it got
there.

~~~
conkrete
If we find DNA based microbial life it could certainly be amazing evidence in
favor of transpermia. We would at least compare to DNA on earth and analyze
similarities. Even plant and animal DNA are very similar (double helix shape)

~~~
danieltillett
Actually the easiest way to find life is to just look for DNA (or even better
RNA) in the environment of interest. This is basically the way life is found
in some of the amazing environments here on earth like the "lost city [0] or
far under the earth [1].

Because of the technical simplicity and sensitivity of looking for DNA, any
probe sent to any planet or moon would look for DNA first, basically assuming
transpermia is true.

[0]
[http://en.wikipedia.org/wiki/Lost_City_(hydrothermal_field)](http://en.wikipedia.org/wiki/Lost_City_\(hydrothermal_field\))

[1]
[http://aem.asm.org/content/74/1/143.full](http://aem.asm.org/content/74/1/143.full)

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hownottowrite
Cool shot of the ice jets from 2005:
[http://apod.nasa.gov/apod/ap091124.html](http://apod.nasa.gov/apod/ap091124.html)

Plus NASA's actual release about the sea: [http://science.nasa.gov/science-
news/science-at-nasa/2014/03...](http://science.nasa.gov/science-news/science-
at-nasa/2014/03apr_deepocean/)

------
jmpe
"Dr. Tsou devised a way to capture comet particles and bring them back to
Earth for NASA’s Stardust mission and has been suggesting a similar method for
a spacecraft that would fly through Enceladus’ plumes and then return to Earth
for scientists to examine.

The challenges are to make sure that the interesting particles would not break
apart, to take precautions that any alien life would not infect Earth, and to
fit it into the $500 million budget of one of NASA’s lower-cost planetary
missions."

Why bring it back to earth? Wouldn't it be safer & less expensive to return it
to ISS instead, (or is that what's implied) ?

Didn't know the carbon & nitrogen part of the story, read the article thinking
only 1 thing: "when are you going to mention Europa".

~~~
maaku
> Why bring it back to earth? Wouldn't it be safer & less expensive to return
> it to ISS instead, (or is that what's implied) ?

No, that would involve a very complicated and expensive breaking maneuver to
slow down the spacecraft, not to mention getting in exactly the right orbit to
rendezvous with the ISS. It's much, much easier to just the payload sturdy
enough to survive atmospheric entry and a crash landing.

~~~
mkingston
Expensive breaking is precisely what they're trying to avoid!

(Sorry, normally I wouldn't nitpick spelling when the meaning is clear, it was
just a funny error!)

~~~
maaku
Hah! I had to reread twice to spot the mistake. That's too awesome; I'm going
to leave it as-is.

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Mz
This is amusingly relevant to my life:

 _Dr. McKay, who was not involved with gravity measurements, noted that only
Enceladus was known to possess the four essential ingredients for life, at
least as it exists on Earth: liquid water, energy, carbon and nitrogen.

“I would say it’s our best bet,” he said.

Mars has a dearth of nitrogen, found in amino acids and proteins, and the
surface today is dry and cold. Europa, which also possesses an under-ice
ocean, may have all of the ingredients, but that has not been confirmed._

Amusingly, I have Europa as a colony in a comic I write. In mentioning this
elsewhere just now, a physicist has suggested this resource to me:
[http://en.wikipedia.org/wiki/Solar_System_in_fiction#Comics_...](http://en.wikipedia.org/wiki/Solar_System_in_fiction#Comics_and_animation)

I shall have to learn yet more about our solar system so I can make up dumb bs
for humor's sake.

(Not that I expect anyone here to really care. I am just cracking up over
this.)

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hellbanner
"They found that the moon’s gravity was weaker at the south pole. At first
glance, that is not so surprising; there is a depression at the pole, and
lower mass means less gravity. But the depression is so large that the gravity
should actually have been weaker."

They found the gravity was weaker.. but it should actually have been weaker.
So is it weaker or stronger?

~~~
wiredfool
I think that they mean that they gravity should have been even weaker than it
was.

    
    
      * There's a depression -> gravity weaker. 
      * Less of a difference than expected from the depression size -> something denser
      * Water is denser than ice, and in a known relation -> size/volume of lake.

~~~
mturmon
A bit more on this, from the abstract at
[http://www.sciencemag.org/content/344/6179/78](http://www.sciencemag.org/content/344/6179/78):

"We determined the quadrupole gravity field of Enceladus and its hemispherical
asymmetry using Doppler data from three spacecraft flybys. Our results
indicate the presence of a negative mass anomaly in the south-polar region,
largely compensated by a positive subsurface anomaly compatible with the
presence of a regional subsurface sea at depths of 30 to 40 kilometers and
extending up to south latitudes of about 50°.

And a little more on methodology, from the full article:

"The design of the Cassini spacecraft does not allow radio tracking from Earth
during remote-sensing observations. Therefore, only 3 of the 19 flybys of
Enceladus completed so far have been used for gravity measurements. In these
close encounters, the spacecraft was continuously tracked from ground antennas
while flying within 100 km of the moon’s surface, twice above the southern
hemisphere (in the flybys labeled E9 and E19) and once over the northern
hemisphere (E12). We determined Enceladus’ quadrupole gravity field and
degree-3 zonal harmonic coefficient J3 from measurements of spacecraft range-
rate.

And further detail on the effects modeled:

"Microwave links between the onboard transponder and ground stations of NASA’s
Deep Space Network enabled precise measurements of the spacecraft range-rate.
In addition to gravitational forces, our analysis accounts for the main
nongravitational accelerations, most notably neutral particle drag exerted by
the substantial gas plume formed by the jets of the south-polar region. Flying
by the moon at latitudes below –70°, the spacecraft interacts with the plume
at distances of up to 500 km from Enceladus’ surface..."

Amazing results. They're flying ~100 km from the moon's surface, while at a
distance of 1.3 billion km. And getting very accurate velocities due to the
mighty Doppler effect.

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kimonos
Interesting! Thanks for sharing!

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api_or_ipa
why did you not just say Enceladus? Surely HN doesn't need reductionist
titles.

~~~
gus_massa
It’s against the current guidelines that say that you should use the exact
title, but I don’t like this part of the guidelines. (But there are some
horror stories of heavy editorialized titles.)

On the other hand I didn’t know Enceladus until today. (I fist thought the
story was about Titan.)

My preferred title for the HN submission would be “Enceladus, A Moon of
Saturn, Has a Sea” or “A Moon of Saturn [Enceladus] Has a Sea”.

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twic
"All these worlds are yours, except Europa. Attempt no landings there. Oh, and
stay off Enceladus too."

Doesn't quite have the same ring to it.

