A Moon of Saturn Has a Sea, Scientists Say | Hacker News Reader

A Moon of Saturn Has a Sea, Scientists Say

nytimes.com

178 pointssheri47 comments

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.

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

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

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

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

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.

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.

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)

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)

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

> given the frequency of rock transfer between planets

What is this frequency, exactly? My impression was that all planets are constantly bombarded with rocks from space (not from other planets), but that it would be extremely surprising for a rock to e.g. leave Earth and end up on Mercury.

Link 0 suggests that 150 kg of rock ends up on Mars every year from Earth. It is not too hard to find rocks from Mars here on Earth.

The point of this story is to demonstrate facts that make transpermia less of a theory and more of a reality. We're not there yet - so don't throw the baby out with the bathwater here. We're absolutely going to go there to find life.

And make sure to check the bathwater closely before you toss that.

Cool shot of the ice jets from 2005: 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...

"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.

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".

> 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.

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!)

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

What about crashing it into the moon? Higher cost, but much less chance of earth contamination. We could then check it out with cheap robots.

An object coming in from a rendezvous with Saturn would be traveling at a ludicrous speed. You would probably vaporize on lunar impact. The Earth's atmosphere can help slow it down to a reasonable velocity--otherwise you have to carry a lot more fuel to burn in a slow-down maneuver.

Similar to how a swing-by is used to accelerate a space-vehicle, I wonder if a swing-by could be used to decelerate as well.

According to Wikipedia, the MESSENGER mission to Mercury used a complicated series of fly-bys of Earth, Venus and Mercury to slow down.

It can. The boost is proportional to the cos(final exit trajectory in relation to the planet, velocity of planet) -- so if the probe leaves the planet opposite to the direction it goes around the sun, it slows down.

(that is, the probe as whole can still orbit the sun in the same direction as the planet, it just needs to do it slower.

Ludicrous speed?! I bet they have hyperjets on that thing!

(ducks)

Send two missions, one with the capture device, the other with a functioning remote-controlled robot laboratory. Leave them close to the region, set them up to explore for 50 years or so.

I know, I know, budgets. It'll 'never' happen.

But what if we just send a nano-factory with its own assembly/disassembly abilities? Feasible, 5 - 10 years on from now?

Well anyway, the point is: why bring it back, really? Just send more machines to do better jobs in space.

I doubt in orbit rendezvous with ISS would be safer and cheaper. It might be safer from planetary contamination standpoint, but complexity of such maneuver would handily offset that. On top of that there is a host of other issues due to the cramped space on ISS. For example: not enough space for proper isolation of sample, not enough equipment to properly study sample, and the fact that limited manpower would be available for examination.

Regarding planetary contamination, with the amount of meteorites hitting ocean I do not think we have anything to worry about.

That makes sense.

But regarding your last sentence: I'm not very fond of that risk analysis. Potentially introducing an alien aquatic micro-organism (that's what we hope to bring back, remember) into earth's system... No competition, paradise compared to its hostile home. No meteorite has ever been shown to carry life, but into this case we intend to deliberately introduce it, either controlled or uncontrolled.

NASA can bill me for the extra cost for taking it to ISS instead of earth's surface.

No competition?

A life form which evolved in a (relatively) low-energy environment (low temperature, low light level, lower pressure) is more in hell than in a paradise. Earth organism evolved to make the best of available resources on Earth, be it energy or materials; the organism would be teared apart in no-time.

That is, unless it is a highly intelligent and evolved life form with big environment alteration capacities, but then it might already be a problem, just one we aren't aware of.

Eh, I've played KSP, an orbital rendezvous in LEO on your return isn't that hard. If you have enough precision and fuel leftover to start a safe decent, you have enough precision and fuel to dock with the ISS.

I'm surprised that we aren't equally worried about contaminating Enceladus with terran microbes.

psst, kerbal is not a substitute for actual physics.

However, it turns out we can introduce actual physics into kerbal. http://forum.kerbalspaceprogram.com/threads/68502-WIP-Princi... + real solar system + realism overhaul.

You don't need any fuel to start a safe descent, except for a tiny amount for course corrections. The atmosphere does all the work.

KSP is intentionally a lot easier than actual Earth-based rocketry. Orbital velocities in KSP are much lower than in reality, and because the rocket equation is exponential that makes everything in KSP expenentially easier to do.

If you are coming in fast from interplanetary space, you'll either need to aerobrake or burn a good deal of fuel to get yourself into LKO. While aerobraking from interplanetary space to put yourself into a nice orbit is easy enough in KSP, in real life things are much more difficult (just for starters, in KSP your station is probably at 0 degrees inclination unless you went out of your way to put it somewhere else...).

Get FAR, RSS, Deadly Rentry, put your space station somewhere around 50 degrees inclination, then try it with suitably small probe. The Stardust spacecraft was 300kg; the sample return capsule was 46kg and reentered at nearly 13km/s.

Just one full small kerbal RCS tank puts you at 250kg, so you'll need to nearly empty that just for starters...

We're very worried about contaminating other worlds. But in this case, the plan (as I understand it) is to collect samples from the plumes of water that Enceladus shoots out into space, without ever landing on the surface.

> Regarding planetary contamination, with the amount of meteorites hitting ocean I do not think we have anything to worry about.

The amount of oxygen in the atmosphere helps a lot. The onset of photosynthesis caused a mass extinction ~two billion years ago.

https://en.wikipedia.org/wiki/Great_Oxygenation_Event

I love that name. It sounds like some kind of a party.

In regards to the contamination,

I don't think that would be a real risk. Earth life has spent billions of years both adapting and adapting to the environment to make it the best growing medium and even then it exists in exclusive bands. For example, put a polar bear in the desert or a fresh water fish in salt water. It is more likely that we would have to take extreme care not to kill any lifeforms we brought back than to worry about them killing us.

You're seriously underestimating this issue.

- rabbits/cane toads in Australia [0][1]

- Japanese knotweed [2]

- Tumbleweed (yep, not as native as Hollywood suggests) [3]

- Algae [4]

... and the list goes on and on, here's a top-100:

http://en.wikipedia.org/wiki/List_of_the_world%27s_100_worst...

[0] http://www.youtube.com/watch?v=pgPhn4tYxJQ

[1] http://en.wikipedia.org/wiki/Cane_toads_in_Australia

[2] http://www.environment-agency.gov.uk/homeandleisure/wildlife...

[3] http://en.wikipedia.org/wiki/Kali_tragus

[4] http://plants.ifas.ufl.edu/node/89

I don't think anyone is worried about space bears or space fish; but bacteria / viruses / other basic replicator forms have much bigger resistance to harsh environments.

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_...

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.)

"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?

it should have been weaker than it was

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.

A bit more on this, from the abstract at 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.

Weakerer is not yet a word.

Similar idea:

In the board game Evo, your odds of success in combat are determined by comparing the number of horns your species has to the number the other species has.

Specifically, the following circumstances are considered:

- Each species has the same number of horns as the other

- One species has one more horn than the other

- One species has two or more more horns than the other

It's always fun to explain that part.

In the current context, "weakerer" isn't a word, but it would be quite normal to say "even weaker".

Interesting! Thanks for sharing!

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

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”.

"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.

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