Cassini Probe Will Dive Through Enceladus's Water Jets (nasa.gov)

An anonymous reader writes: NASA's Cassini probe has a daring mission tomorrow: dive through the water jets spraying from the south pole of Saturn's moon Enceladus. The probe will be a mere 30 miles above the surface, traveling at a relative speed of 19,000 mph. Researchers hope to gain insight into the chemical composition of the jets. "[T]he plumes are more than just gas and water: samples show that they also contain many of the building blocks essential to Earth-like life. This lends itself to the exciting possibility that organisms similar to those that thrive in our own deep oceans near volcanic vents exuding carbon dioxide and hydrogen sulfide might exist on Eceladus." The molecules suspended among the water may tell us whether Enceladus's oceans are capable of harboring life. "The spacecraft's sensors will pick up gases in the plume searching for the presence of molecular hydrogen (H2). The amount of H2 found could reveal how much hydrothermal activity is occurring in the ocean."

Comments

Hmm

[BigSlowTarget]

Cool science but it sounds like "Hold my beer and watch this" on a planetary scale.

Re:Hmm

[Anonymous Coward]

It sort of is, but Cassini only has a year or so left in its mission before it is out of propellant needed for adjusting its orbit around Saturn. From here on, missions will get riskier, finishing with the Grand Finale, where it orbits between Saturn and the innermost ring a couple dozen times, before it plunges into the planet to keep from possibly contaminating Enceladus

Re:Hmm

[nospam007]

"It sort of is, but Cassini only has a year or so left in its mission before it is out of propellant "

That's why they drive it through the probe wash. Clean probes bring more money with aliens.

Re: Hmm

[Muad'Dave]

Being Plutonium-powered, the remnants of the probe (even if reduced to its atoms) will leave an indelible* mark on Saturn that someone with nuclear technology was here.

*The half-life of Pu-238 is 75k years and doesn't occur naturally. Its daughter product, U-234, is only 55ppm in naturally-occurring Uranium (at least here on Earth) and has a half-life of 246k years. U-234 decays to Th-230, and its half-life is another 75k years.

Rings

[Anonymous Coward]

This is great. They're incurring a degree of risk to investigate Enceladus.

My dream is that one day they'll risk Cassini to get a better look at this.

Re:kinetic energy

[Anonymous Coward]

At "pharmacist drop" of 20 drops per milliliter its mass is 50mg
19000mph is 8493.76m/s
The kinetic energy is 1803J.

Energy of a typical NATO rifle round, 5.56x45 mm is 1796J

Slashdot

[wonkey_monkey]

molecular hydrogen (H2)

Okay, so you think Unicode is too hard. But why can't we even have <sub> and <super>?

And yet we can have <code>...

Re:kinetic energy

[Rei]

But of course these aren't like Earth "water drops", they're more like frozen dust grains.

Still, potentially destructive.

There's interesting potential for future missions (almost assuredly ion-powered) to do Enceladus sample return by doing flybys with a carbon collector (better than the silicon aerogel used by Stardust). But for that you have other options than just doing a straight flyby - you could enter a highly elliptical orbit around Enceladus with the apogee - or the ascent - positioned over the geysers. The latter may be better because even if you had no relative velocity, the ice grains still have significant speed of their own, even at Enceladus escape. - so by ascending relative to Enceladus, you're further reducing (to a limited degree) the relative velocity at impact (some grains move slower than others, of course, you'll likely have some collisions in any circumstance at almost zero relative velocity). The craft could sit in orbit for a very long period of time, even years, until its collector is basically saturated, before sealing it, breaking orbit (little energy required if you're already in a highly elongated orbit), thrust-and-gravity-boost your way out of Saturn via flybys of other moons (giving additional science in the process), and return to Earth.

Regardless of the form, an Enceladus sample-collection mission wouldn't have to be limited to Enceladus. Other Saturnian moons have at times presented evidence of lesser cryovolcanism, and Saturns' many different rings themselves could prove to be potential collection targets if mission planners felt confident enough about the safety of the trajectory.

Electric Geysers

[trout007]

The EU guys have an interesting take on this. Will be cool to see how charged this geyser is.
https://m.youtube.com/watch?v=...

But contaminating Saturn is ok?

[Viol8]

Seems to me there's just as much chance of interesting chemistry possibly leading to some form of life happening deep down in a gas giant as there is on a small moon.

Re:But contaminating Saturn is ok?

[necro81]

Consider the end scenarios:

1) Cassini crashes into Enceladus. Because it has no atmosphere to speak of and a solid surface, the spacecraft will impact on the ice and make a real mess. Fragments of the spacecraft may survive, more or less in the condition that they left Earth (although much older), including the plutonium RTGs. Eventually, these may work their way through the ice and into the subsurface ocean, contaminating a fairly interesting environment (the ocean-ice interface and the ocean-crust interface).

2) Cassini crashes into Titan. Because there is a significant atmosphere, Cassini will burn up to some extent, but some of it, surely, will survive re-entry, distributed over a large area, and thump into the surface. Due to the thick atmosphere and low gravity, the terminal velocity is quite modest (slower than Earth's), so any bits of Cassini that survive re-entry will have a pretty soft landing. This, too, is contamination of a fairly interesting environment (the surface-atmosphere interface, or in the hydrocarbon lakes).

3) Cassini is intentionally de-orbited into Saturn. Saturn is basically all atmosphere and has no surface to speak of: it'll burn up pretty much all the way down, eventually floating in the deepest parts of the planet that are especially dense enough so that even metals are buoyant. These deep reaches are also really hot, which will at least kill anything still alive or viable on the spacecraft, and probably just melt everything in some extreme chemistry. Compared to permanently scattering the spacecraft across a moon, the amount of time Cassini passes through the various layers of Saturn before reaching its hot death is quite brief. Finally, Saturn is the 2nd most massive planet in the solar system, 10^3 -to- 10^6 times the size of its moons, so any contamination from Cassini will be much more diluted.

So, considering that getting Cassini out of the Saturn system is not possible, tossing it into Saturn itself seems the best option.

Re:But contaminating Saturn is ok?

[Viol8]

"tossing it into Saturn itself seems the best option."

I would have thought putting it in a parking orbit would have been the best option. That way it could still be used.

Re:This is just corporate welfare

[B33rNinj4]

Neither does building roads, or maintaining bridges and dams. Still, science is worth the minimal costs involved, because we should always be actively trying to learn.

They should probe...

[Anonymous Coward]

They should probe Uranus!