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Discovering Insights While Flying Through the Plumes of Enceladus

In the next decade, space agencies will expand the search for extraterrestrial life beyond Mars, where all of our astrobiology efforts are currently focused. This includes the ESA’s JUpiter ICy moon’s Explorer (JUICE) and NASA’s Europa Clipper, which will fly past Europa and Ganymede repeatedly to study their surfaces and interiors. There’s also NASA’s proposed Dragonfly mission that will fly to Titan and study its atmosphere, methane lakes, and the rich organic chemistry happening on its surface. But perhaps the most compelling destination is Enceladus and the lovely plumes emanating from its southern polar region.

Since the Cassini mission got a close-up look at these plumes, scientists have been aching to send a robotic mission there to sample them – which appear to have all the ingredients for life in them. This is not as easy as it sounds, and there’s no indication flying through plumes will yield intact samples. In a recent paper, researchers from the University of Kent examined how the velocity of a passing spacecraft (and the resulting shock of impact) could significantly affect its ability to sample water and ice within the plumes.

The research was conducted by Prof. Mark Burchell and Dr. Penny Wozniakiewicz (an Emeritus Professor and a Senior Lecturer in Space Science) from the Centre for Astrophysics and Planetary Science (CAPS), part of the School of Physics and Astronomy at the University of Kent, UK. Their work could have significant implications for missions to Icy Ocean Worlds (IOW), bodies in the outer Solar System composed predominantly of frozen water and volatiles with oceans in their interior. These bodies have become of increasing interest to scientists since it is possible some could support life.

The term “Ocean Worlds” has become common in recent years as the number of potential candidates for exploration has increased. Since the Voyager probes passed through the system in 1979, scientists have speculated about the possibility of an interior ocean within Europa based on its surface features. This included patches of “young terrain” sitting next to older, cratered terrain – indicative of regular exchanges between the surface and interior. The Voyager probes noticed similarly youthful terrain on Enceladus when they few past Saturn in 1980 and 81 (respectively).

However, it was the Cassini-Huygens mission that discovered water vapor and organic molecules venting from the Enceladus’ southern polar region in 2004. Over the next thirteen years, the Cassini orbiter conducted several more flybys of the moon, yielding additional evidence of an interior ocean and an energy source at the core-mantle boundary. These findings placed Enceladus among the “Ocean Worlds” that scientists want to examine more closely with future missions. But unlike other IOWs, Enceladus is particularly attractive because of the nature of the plumes around its south pole.

Whereas Europa also experiences plume activity, these are more sporadic and difficult to detect. Due to Europa’s higher gravity (~13% vs. 1% of Earth’s), water vapor and vented material don’t reach nearly as far into space. As Burchell told Universe Today via email, collecting samples from these plumes seems relatively simple, at least in theory. “Like all IOWs, it has an internal ocean with lots of water. What is in that water is the subject of much speculation and interest,” he said. “And Enceladus ejects plumes of water into space, making any space mission that wants to sample the water much easier – you can just fly through the plume.”

However, in the realm of practice (as always), things get a little more complicated. Depending on how fast a mission is traveling, the impact it will inflict upon plume material will vary considerably. As Burchell explains, this could jeopardize the very samples a mission was trying to obtain:

“The problem with collecting samples at speed is that a lot of testing has been done with metal and mineral projectile, but less is known about the response of organics to the high-speed impacts. The bonds in the organics will break, but at what speed? And which bonds first? So what you end up with for analysis may not be what came out of Enceladus. But with what biases? What degree of alteration? Understanding this is essential to any successful collection of samples.”

Artist rendering showing an interior cross-section of the crust of Enceladus, which shows how hydrothermal activity may be causing the plumes of water at the moon’s surface. Credits: NASA-GSFC/SVS, NASA/JPL-Caltech/SwRI

According to Burchell, modeling how a spacecraft’s velocity would affect its ability to collect samples can be accomplished in one of two ways. On the one hand, there’s the computer modeling approach, where teams rely on advanced software to simulate impacts and measure the results. The other is the “kinetic” approach, which consists of firing small grains at targets at the right speeds and then measuring the force of impact. Burchell and his team prefer to do the latter. “In our lab, we like firing things at targets,” he said.

Their results clearly showed that the collection speed is critical to sample collection. However, they also found that the results vary from one body to the next. Said Burchell:

“In an orbit at a small body like Enceladus, it is fairly low. But for the larger IOWs, it is greater. And it just gets into the regime where the shock of the impact process in the collection causes increasingly severe alteration to the samples. If you do a flypast of the IOW without orbiting it, you are faster again, and the samples experience a greater shock. It suggests a low-speed orbital collection is best for un-shocked, minimally processed samples. But that needs more spacecraft design and restricts the other science you could do. It is always a tradeoff.”

Without the Solar System, there are several bodies where water and other volatiles are vented from the interior – a phenomenon known as cryovolcanism. These bodies vary considerably in terms of their size and gravitational pull, ranging from the microgravity (less or slightly more than 1%) of Mimas and Enceladus to the roughly 13-15% of Europa, Titan, and Ganymede. As a result, these findings could help inform the design of many sample-collection missions destined for IOWs.

Further Reading: Meteoritics & Planetary Science

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Forest Lawn Drive now free of RV encampment and parking

Nancy Sexton was thrilled when city crews cleared out more than 50 RVs in December that had been parked near her business for months, blocking parking spots and leaving behind trash and waste on Forest Lawn Drive.

Then she realized the long stretch of road near Barham Boulevard in the Hollywood Hills was suddenly off limits for not just parked RVs, but all parked vehicles. Much of the curb was painted red. No parking signs lined the sidewalk.

“It’s a dumb decision,” said Sexton, who owns the Muse Rooms, which offers leased office spaces. “It’s frustrating.”

The more than 50 RVs, which had been stationed along the winding road for months as a semi-permanent living encampment, were removed in December as part of the city’s operation known as Inside Safe. One goal of the program, which is part of Mayor Karen Bass’ initiative to bring people living on the streets indoors, is to end the cycle of homeless encampments being cleared by the city only to return a few weeks later.

But days after the RVs were removed, Sexton said, the curb was painted red and parking was limited. The new red zone is about a quarter mile long, running between Warner Bros. Studios’ Gate 9 entrance and North Coyote Canyon Drive.

The areas that do allow parking, meanwhile, have two-hour limits.

City officials also said the decision to restrict parking was done out of fire safety concerns, not to keep the RVs from resettling along the road. Sexton has her doubts.

The lack of parking along the street suddenly imposed a new, unexpected expense on her clients, prompting some to look elsewhere. The red curb has also become an irritation for some students and workers at the New York Film Academy and businesses nearby.

A road with RVs lining its right side.

RVs are parked on Forest Lawn Drive on June 27, 2023, in Burbank.

(David McNew/Getty Images)

Since the no-parking signs went up, Sexton said, she’s lost two regular members and two potential clients. All of them had aired concern about the lack of street parking and the added expense of paying $12 a day at the parking structure on site.

The parking fee, Sexton said, doubled the monthly costs for some members.

“I didn’t know how much of a problem it was going to be until there were people saying, ‘I can’t pay $12 a day,’ ” she said. “I’m really feeling it now.”

The situation highlights some of the unintended results as city officials look to address homelessness and the concerns of businesses and homeowners affected by makeshift encampments, whether they involve tents, vehicles, or both.

RV encampments have sprung up across the city amid a housing crisis that has left many people priced out of permanent homes. Local officials have looked for ways to address the issue, including new regulations that have targeted overnight RV parking.

According to the mayor’s office, the Inside Safe program has addressed 39 encampments so far, moving more than 2,400 people into interim housing and an additional 440 into permanent housing since December 2022.

Bass spokesperson Zach Seidl said the RVs that were removed from Forest Lawn Drive were themselves causing parking issues in the area, as well as raising other significant safety and public health concerns.

Members of the surrounding community have said removing the RVs “has helped on all three fronts,” Seidl said in a statement. “This operation has saved lives.

Stella Stahl, spokesperson for Councilmember Nithya Raman, said the city has helped many of the RV residents along Forest Lawn Drive to find housing indoors.

In a statement, Stahl credited the decision to limit parking to a request by the Los Angeles Fire Department, which called the area a “high fire severity zone.” A 2019 brush fire in the area burned more than 30 acres and threatened homes and businesses.

In a Sept. 19, 2023, letter, LAFD Assistant Chief Dean Zipperman asked the city Department of Transportation to install “Tow Away No Stopping Any Time” restrictions on the road due to the stopped and parked vehicles there.

To avoid the hassle of looking for parking, cinematography students Sanchin Vinay, Yifan Xiang, and Davide Picci carpool to their classes at the New York Film Academy, which shares a building with the Muse Rooms. Eliminating the RVs has opened some spots to them, although Picci said they’d been able to find spaces on the street before — “really far down.”

A couch on a sidewalk near an RV.

The curb along Forest Lawn Drive, where someone has left a couch.

(Robert Gauthier/Los Angeles Times)

Sometimes they pay the $12 for the daily parking to avoid being late for class. Carpooling helps cushion the cost.

Leslie Bates, a film production instructor, said she heard of students and faculty members having “volatile” interactions with the RV residents.

Now that the RVs have

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