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NASA Mulling Life-Hunting Mission To Saturn Moon Enceladus
Published September 01, 2015  Space.com

A decade from now, NASA probes could be on their way to explore two
potentially life-supporting alien worlds.

The agency already plans to launch a spacecraft toward the Jupiter moon
Europa in the early to mid-2020s, and it's mulling a mission to the Saturn
satellite Enceladus that would lift off by the end of 2021. Many
astrobiologists regard Europa and Enceladus, which are both thought to
harbor oceans of liquid water beneath their icy shells, as the solar
system's two best bets to host alien life.

The possible Encelacus project, known as the Enceladus Life Finder (ELF), is
one of two dozen or so concepts submitted earlier this year for
consideration by NASA's Discovery Program, which launches highly focused,
relatively low-cost missions to various solar system destinations. [Inside
Enceladus, Icy Moon of Saturn (Infographic)]

NASA is expected to cull the original Discovery applicant pool to a handful
of finalists next month, then select the overall winner around September
2016. The people behind ELF - which, as its name suggests, would search for
signs of biological activity on Enceladus - believe they've put forward a
strong contender.

"We think we have the highest chance of success of getting an indicator of
[alien] life for really any mission at this point," ELF concept principal
investigator Jonathan Lunine, of Cornell University, told Space.com.

Going to Enceladus?

In 2005, NASA's Saturn-orbiting Cassini spacecraft spotted geysers of water
ice, salts, carbon-containing organics and other molecules erupting from the
south polar region of the 310-mile-wide (500 kilometers) Enceladus.

These jets, which are powered by Saturn's intense gravitational pull, merge
to form a plume that reaches far out into space. Indeed, Enceladus supplies
the bulk of the material making up Saturn's wide E-ring.

Scientists think the icy jets are in contact with Enceladus' underground
ocean, which offers a rare and tantalizing opportunity - gathering samples
from a potentially habitable alien environment without even touching down.
(Furthermore, the oceans of Europa and Enceladus lie beneath miles of ice,
which could make sampling by a landed mission tough.)

That's just what ELF intends to do.

"It's free samples," Lunine said of the plume. "We don't need to land,
drill, melt or do anything like that." [Enceladus' Surprising Geysers

Cassini has flown through the plume multiple times, but that spacecraft
isn't equipped to search for life. ELF, on the other hand, would probe the
habitability of Enceladus' ocean and hunt for evidence of biological

ELF would carry two mass spectrometers; one would be optimized to study
gaseous plume molecules, whereas the other would focus on solid grains,
Lunine said. These instruments would study amino acids (the building blocks
of proteins), fatty acids, methane and other molecules, allowing mission
scientists to perform three separate tests for life.

"Positive results for all three would strongly argue for life within
Enceladus," the ELF team wrote in a paper presented at the 46th Lunar and
Planetary Science Conference, which was held in March in The Woodlands,

"ELF brings the most compelling question in all of space science within
reach of NASA's Discovery Program, providing an extraordinary opportunity to
discover life elsewhere in the solar system in a low-cost program," they
added. (Whichever mission is selected for this Discovery round will have a
cost cap of $450 million, excluding post-lauch operations.)

A fourth life test should also be possible, Lunine said. Current ELF plans
call for including a technology-demonstration instrument designed to
determine the chirality, or "handedness," of amino acids. All Earth life
uses left-handed amino acids rather than right-handed ones; a similar
preference found in an extraterrestrial sample would be a strong indication
of alien life, astrobiologists say.

Solar-powered probe

If NASA chooses ELF, the mission will by ready by 2020 and could launch that
year or in 2021, Lunine said. The baseline concept calls for ELF to launch
aboard a United Launch Alliance Atlas V rocket and endure a 9.5-year-long
journey to Saturn (though the trip would be much shorter if NASA's Space
Launch System megarocket, which is currently in development, were used).

ELF would enter orbit around Saturn, then fly through Enceladus' plume eight
to 10 times over the course of three years. These sampling sojourns would
bring the robotic probe within about 31 miles of Enceladus' surface, Lunine

ELF is a logical follow-on from Cassini and leverages much of the older
mission's heritage, he added. But the two are far from carbon copies. The
school-bus-size Cassini, for example, cost $3.2 billion and features 12
onboard instruments.

Cassini is also powered by three radioisotope thermoelectric generators
(RTGs), which convert the heat of plutonium-238's radioactive decay into
electricity. But ELF would be solar-powered, because NASA, concerned about
its dwindling stockpile of plutonium-238, prohibited the use of nuclear fuel
for this Discovery mission.

No solar-powered spacecraft has ever operated as far away as Saturn, where
sunlight is considerably weaker than it is here on Earth. NASA's Juno probe,
in fact, will make history as the first solar-powered Jupiter spacecraft
when it reaches the solar system's largest planet next July.

But Lunine is confident that solar energy will do the job for ELF.

"We found that this was a very feasible way to conduct the mission," he
said, declining to provide technical details because the Discovery
competition is ongoing.

Demonstrating the utility of solar power at Saturn is an important goal in
itself, Lunine added, because nuclear fuel will always be in relatively
short supply and therefore reserved for future missions that cannot do
without it. Examples of plutonium-dependent missions include efforts to
explore the surface or atmosphere of Saturn's huge, haze-shrouded moon Titan
or probes that journey to extremely faraway destinations such as Neptune.

"We want to push the boundaries for solar power so that, for missions in
orbit around Saturn, we don't need to use that valuable inventory of
radioisotopic fuel that's going to be needed for these other missions,"
Lunine said.

NASA's upcoming Europa mission, which does not have an official name at the
moment, will also make use of solar power. The roughly $2 billion mission
will be based in orbit around Jupiter but will make 45 flybys of the
1,900-mile-wide Europa over the course of two and a half years or so.

The Europa probe will carry cameras, a heat detector, ice-penetrating radar
and a variety of other instruments to gauge the habitability of the Jovian
moon. But it's not designed to search for signs of life; NASA officials have
expressed hope that the Europa flyby mission could help pave the way for a
future landed effort that would get beneath the moon's ice shell. [Europa:
Jupiter's Icy Moon and Its Underground Ocean (Video)]

Other Enceladus efforts

Lunine and his group aren't the only scientists interested in exploring

For example, another team has been working on a idea called Journey to
Enceladus and Titan (JET), which would assess the life-supporting potential
of both moons. And another research group is developing a mission concept
called Life Investigation for Enceladus (LIFE), which would return samples
from the icy satellite's plume back to Earth for analysis.

Neither JET nor LIFE was proposed as part of the most recent Discovery call.
The LIFE team dropped out of the running primarily because it viewed nuclear
power as more or less a necessity for a Saturn mission, leader Peter Tsou
told Space.com.

But Tsou and his colleagues continue to work on LIFE and hope to submit the
concept during a future NASA call for proposals.

Enceladus is more than worthy of the attention it's currently getting, said
Tsou, who's based at Sample Exploration Systems in La Canada, California. A
life-hunting mission to the geyser-spewing moon would deliver impressive
"bang for the buck" astrobiologically, allowing humanity to take a solid
crack at perhaps the biggest mystery facing humanity, he said.

"This 'are we alone' question - potentially we can shed tremendous light on
it in a single mission," Tsou said.

Closing Thoughts:

Let me tell you the secret that has led to my goal: My strength lies solely
in my tenacity." -- Louis Pasteur, chemist and microbiologist

That's it for today,


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