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Jupiter’s Huge Moons Prevent It From Developing Beautiful Rings Like Saturn

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Jupiter’s Huge Moons Prevent It From Developing Beautiful Rings Like Saturn

It’s made of gas, yet more than twice as massive as every other planet in our solar system combined. It’s surrounded by 79 separate moon companions, one of which is the leading candidate in the quest to find extraterrestrial life. It’s even named after the king of the ancient Roman gods. Jupiter seems to have it all — except cool rings, that is. 

For some odd reason, this alpha planet has rings that are to Saturn’s spectacular hoops what chopsticks are to tree trunks. Flimsy. Insignificant. “Unlike Saturn’s icy rings full of large icy and rock chunks, they are composed of small dust particles,” according to NASA. Jupiter’s discs are so frail that we didn’t even notice them until 1979, thanks to the agency’s Voyager 1 spacecraft and a bit of lucky, perfectly placed sunlight. 

But on Thursday, researchers who set out to understand why Jupiter has this loopy deficiency said they might’ve finally found an answer. Details of their conclusions can be found on arXiv, and are soon to be published in the Planetary Science Journal, per a press release.

“We found that the Galilean moons of Jupiter, one of which is the largest moon in our solar system, would very quickly destroy any large rings that might form,” Stephen Kane, an astrophysicist from the University of California, Riverside, who led the research, said in a statement. “As a result, it is unlikely that Jupiter had large rings at any point in its past.”

A brightly lit Saturn and its rings against the dark of space

Saturn’s rings, photographed by the Hubble Space Telescope, are mesmerizing against a dark sky.


NASA, ESA, A. Simon (Goddard Space Flight Center), M.H. Wong (University of California, Berkeley), and the OPAL Team

In other words, Kane and colleagues believe the gravitational pull and sheer force of Jupiter’s orbiting moons — especially the four largest Galilean ones — would’ve obliterated any and all matter attempting to produce Saturn-like rings around the gas giant. 

“Massive planets form massive moons, which prevents them from having substantial rings,” Kane said. Potentially, this might also explain why Neptune’s rings are so lightweight as well – though the azure orb’s halos are still slightly more substantial than Jupiter’s, from the vantage point of Earth.

A glowing image of Jupiter and several of its moon.

Jupiter and some of its moons are seen through the NIRCam 3.23 micron filter of the James Webb Space Telescope. If you look closely, you can see the planet’s flimsy rings, too.


NASA, ESA, CSA, and B. Holler and J. Stansberry (STScI)

To reach their conclusions, the team basically ran dynamic computer simulations of Jupiter’s Galilean moons in orbit, as well as of Jupiter itself orbiting the sun. Then they waited and watched to see how long it’d take for some Saturn-like rings to form, if they did truly form, and observe what happened as they began to take shape. “The results largely demonstrate the truncation of stable orbits imposed by the Galilean satellites,” the study states, “and dynamical desiccation of dense ring material” within a specific region.

In a way, it’s unfortunate that Jupiter’s moons have been gatekeeping awesome rings from the peach-stripe, windy world — for both scientists and amateur space fans. 

First off, if Jupiter did have rings, they’d appear brighter to us than even Saturn’s, Kane said, because it’s so much closer. Saturn is nearly twice as far away from Earth. And second, rocky or icy rings can carry quite a bit of information for scientists looking to understand a particular planet’s past. 

“For us astronomers, they are the blood spatter on the walls of a crime scene. When we look at the rings of giant planets, it’s evidence something catastrophic happened to put that material there,” Kane said. Prior to conducting the simulations, in fact, Kane had hoped Jupiter held some stronger rings long ago, but perhaps lost them over time. It’s possible for such rings to be temporary, the researcher reasoned.

Jupiter's four Galilean moons. Ganymede on the top left is gray and streaked with some white splotches. Callisto on the top right is forest green, spotted with beige and orange. Io on the bottom left is bright orange and yellow. Europa on the bottom right is pale blue, almost white, with darker orange marking along its middle.

The Galilean moons of Jupiter. Europa is the one thought to possibly hold evidence of alien life.


NASA

“It’s long bothered me why Jupiter doesn’t have even more amazing rings that would put Saturn’s to shame,” Kane said, also mentioning the next step for the team’s research. It’s also poised to be about planetary ring mysteries, this time of Uranus, another gas planet. 

In essence, the study researchers think it’s possible Uranus appears tipped over on its side because of a collision with another celestial body long, long ago. Drawing on Kane’s blood spatter crime scene analogy, they believe its rings hold secrets that’ll decode whether their suspicion is correct.

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Google Pixel 7 and 7 Pro are getting a built-in VPN at no extra cost

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Google Pixel 7 and 7 Pro are getting a built-in VPN at no extra cost
Google Pixel 7 Pro hands on front Snow



(Image credit: Future / Lance Ulanoff)

Users of the Google Pixel 7 and 7 Pro devices will be able to secure their data without the need to pay for an additional Android VPN after the company said it would be including its Google One VPN service at no extra cost. 

The move will make the Pixel 7 and 7 Pro the first smartphones to include a free VPN connection. 

The offer is restricted to just some countries, though – and what’s more, some data won’t be secured inside the VPN tunnel.  

Peace of mind when you connect online ✨Later this year, #Pixel7 and 7 Pro will be the only phones with a VPN by Google One—at no extra cost.¹#MadeByGoogle¹See image for more info pic.twitter.com/P7lzyoMdekOctober 6, 2022

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Google Pixel 7 VPN

Despite the aforementioned limits, the big tech giant assures that the VPN software won’t associate users’ app and browsing data with users’ accounts. 

Google One VPN typically costs around $10 per month as part of the company’s Premium One plan, which also comes with a 2TB of cloud storage on top. 

This decision is the latest move to bring Google’s mobile data security to the next level. Not too long ago, the company made Google One VPN available also for iOS devices, and also introduced the option of having an always-on VPN across its latest smartphones. 

Google promises that its secure VPN software will shield your phone against hackers on unsecure networks, like public Wi-Fi. It will also hide your IP address so that third parties won’t be able to track your location.

Shorter for virtual private network, a VPN is exactly the tool you want to shield your sensitive data as it masks your real location and encrypts all your data in transit. Beside privacy, it can allow you to bypass geo-restrictions and other online blocks. 

Chiara is a multimedia journalist, with a special eye for latest trends and issues in cybersecurity. She is a Staff Writer at Future with a focus on VPNs. She mainly writes news and features about data privacy, online censorship and digital rights for TechRadar, Tom’s Guide and T3. With a passion for digital storytelling in all its forms, she also loves photography, video making and podcasting. Originally from Milan in Italy, she is now based in Bristol, UK, since 2018.

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The Steam Deck dock is finally here and will ship faster than you think

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The Steam Deck dock is finally here and will ship faster than you think
a steam deck placed in a steam deck dock



(Image credit: Valve)

After months of waiting and delays, Valve has finally announced that the Steam Deck dock is available for purchase on its official site.

Not only that but, according to Valve, the dock will ship out in an incredibly fast one to two weeks, which pairs with the fact that the Steam Deck itself is now shipping with no wait time (not to mention that it’s incredibly easy to set up). The port selection is pretty solid as well, with the dock featuring three USB-A 3.1 gen 1 ports, one Ethernet port, a DisplayPort 1.4, and an HDMI 2.0 port. And for its power supply, it uses a USB-C passthrough delivery.

A Steam Deck dock will run you $90 (around £81 / AU$140), which is a bit steeper than most third-party options on the market right now. But for those waiting it out for an official product until now, price most likely will not be an issue.

Is it worth buying? 

Considering that even Steam Decks themselves are shipping without a queue and that the dock has such a quick turnaround to delivery, it seems that the supply chain issues that had been gripping Valve are loosening considerably.

However, the deck itself is far from perfect. Because of the fact that it uses USB-C for the display port, a third-party USB-C dock that uses its own power supply and video out will output the display of the official dock. 

And as mentioned before, the price of the official Steam Deck dock is steeper than many third-party options on the market, meaning that those who are on a budget might pass this product up in favor of a lower-priced one.

There are also some bugs that Valve is working on fixing at this time, including one involving compatibility with LG displays. According to the FAQ, if the “Docking Station is connected via HDMI, sleep/wake can result in visual noise.”

It might be worth waiting for Valve to work out the kinks of its dock before investing in one. And while you’re waiting, research other options that might better suit your needs.

Allisa has been freelancing at TechRadar for nine months before joining as a Computing Staff Writer. She mainly covers breaking news and rumors in the computing industry, and does reviews and featured articles for the site. In her spare time you can find her chatting it up on her two podcasts, Megaten Marathon and Combo Chain, as well as playing any JRPGs she can get her hands on.

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Why doesn’t Bash’s `set -e` do what I expected?

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Why doesn’t set -e (or set -o errexit, or trap ERR) do what I expected?

set -e was an attempt to add “automatic error detection” to the shell. Its goal was to cause the shell to abort any time an error occurred, so you don’t have to put || exit 1 after each important command. This does not work well in practice.

The goal of automatic error detection is a noble one, but it requires the ability to tell when an error actually occurred. In modern high-level languages, most tasks are performed by using the language’s builtin commands or features. The language knows whether (for example) you tried to divide by zero, or open a file that you can’t open, and so on. It can take action based on this knowledge.

But in the shell, most of the tasks you actually care about are done by external programs. The shell can’t tell whether an external program encountered something that it considers an error — and even if it could, it wouldn’t know whether the error is an important one, worthy of aborting the entire program, or whether it should carry on.

The only information conveyed to the shell by the external program is an exit status — by convention, 0 for success, and non-zero for “some kind of error”. The developers of the original Bourne shell decided that they would create a feature that would allow the shell to check the exit status of every command that it runs, and abort if one of them returns non-zero. Thus, set -e was born.

But many commands return non-zero even when there wasn’t an error. For example,

if [ -d /foo ]; then ...; else ...; fi

If the directory doesn’t exist, the [ command returns non-zero. Clearly we don’t want to abort when that happens — our script wants to handle that in the else part. So the shell implementors made a bunch of special rules, like “commands that are part of an if test are immune”, and “commands in a pipeline, other than the last one, are immune”.

These rules are extremely convoluted, and they still fail to catch even some remarkably simple cases. Even worse, the rules change from one Bash version to another, as Bash attempts to track the extremely slippery POSIX definition of this “feature”. When a SubShell is involved, it gets worse still — the behavior changes depending on whether Bash is invoked in POSIX mode. Another wiki has a page that covers this in more detail. Be sure to check the caveats.

A reference comparing behavior across various historical shells also exists.

Story time

Consider this allegory, originally posted to bug-bash:

Once upon a time, a man with a dirty lab coat and long, uncombed hair
showed up at the town police station, demanding to see the chief of
police.  "I've done it!" he exclaimed.  "I've built the perfect
criminal-catching robot!"

The police chief was skeptical, but decided that it might be worth
the time to see what the man had invented.  Also, he secretly thought,
it might be a somewhat unwise move to completely alienate the mad
scientist and his army of hunter robots.

So, the man explained to the police chief how his invention could tell
the difference between a criminal and law-abiding citizen using a
series of heuristics.  "It's especially good at spotting recently
escaped prisoners!" he said.  "Guaranteed non-lethal restraints!"

Frowning and increasingly skeptical, the police chief nevertheless
allowed the man to demonstrate one robot for a week.  They decided that
the robot should patrol around the jail.  Sure enough, there was a
jailbreak a few days later, and an inmate digging up through the
ground outside of the prison facility was grabbed by the robot and
carried back inside the prison.

The surprised police chief allowed the robot to patrol a wider area.
The next day, the chief received an angry call from the zookeeper.
It seems the robot had cut through the bars of one of the animal cages,
grabbed the animal, and delivered it to the prison.

The chief confronted the robot's inventor, who asked what animal it
was.  "A zebra," replied the police chief.  The man slapped his head and
exclaimed, "Curses!  It was fooled by the black and white stripes!
I shall have to recalibrate!"  And so the man set about rewriting the
robot's code.  Black and white stripes would indicate an escaped
inmate UNLESS the inmate had more than two legs.  Then it should be
left alone.

The robot was redeployed with the updated code, and seemed to be
operating well enough for a few days.  Then on Saturday, a mob of
children in soccer clothing, followed by their parents, descended
on the police station.  After the chaos subsided, the chief was told
that the robot had absconded with the referee right in the middle of
a soccer game.

Scowling, the chief reported this to the scientist, who performed a
second calibration.  Black and white stripes would indicate an escaped
inmate UNLESS the inmate had more than two legs OR had a whistle on
a necklace.

Despite the second calibration, the police chief declared that the robot
would no longer be allowed to operate in his town.  However, the news
of the robot had spread, and requests from many larger cities were
pouring in.  The inventor made dozens more robots, and shipped them off
to eager police stations around the nation.  Every time a robot grabbed
something that wasn't an escaped inmate, the scientist was consulted,
and the robot was recalibrated.

Unfortunately, the inventor was just one man, and he didn't have the
time or the resources to recalibrate EVERY robot whenever one of them
went awry.  The robot in Shangri-La was recalibrated not to grab a
grave-digger working on a cold winter night while wearing a ski mask,
and the robot in Xanadu was recalibrated not to capture a black and
white television set that showed a movie about a prison break, and so
on.  But the robot in Xanadu would still grab grave-diggers with ski
masks (which it turns out was not common due to Xanadu's warmer climate),
and the robot in Shangri-La was still a menace to old televisions (of
which there were very few, the people of Shangri-La being on the average
more wealthy than those of Xanadu).

So, after a few years, there were different revisions of the
criminal-catching robot in most of the major cities.  In some places,
a clever criminal could avoid capture by wearing a whistle on a string
around the neck.  In others, one would be well-advised not to wear orange
clothing in certain rural areas, no matter how close to the Harvest
Festival it was, unless one also wore the traditional black triangular
eye-paint of the Pumpkin King.

Many people thought, "This is lunacy!"  But others thought the robots
did more good than harm, all things considered, and so in some places
the robots are used, while in other places they are shunned.

The end.

Exercises

Or, “so you think set -e is OK, huh?”

Exercise 1: why doesn’t this example print anything?

   1 
   2 set -e
   3 i=0
   4 let i++
   5 echo "i is $i"

Exercise 2: why does this one sometimes appear to work? In which versions of bash does it work, and in which versions does it fail?

   1 
   2 set -e
   3 i=0
   4 ((i++))
   5 echo "i is $i"

Exercise 3: why aren’t these two scripts identical?

   1 
   2 set -e
   3 test -d nosuchdir && echo no dir
   4 echo survived
   1 
   2 set -e
   3 f() { test -d nosuchdir && echo no dir; }
   4 f
   5 echo survived

Exercise 4: why aren’t these two scripts identical?

   1 set -e
   2 f() { test -d nosuchdir && echo no dir; }
   3 f
   4 echo survived
   1 set -e
   2 f() { if test -d nosuchdir; then echo no dir; fi; }
   3 f
   4 echo survived

Exercise 5: under what conditions will this fail?

   1 set -e
   2 read -r foo < configfile

(Answers)

But wait, there’s more!

Even if you use expr(1) (which we do not recommend — use arithmetic expressions instead), you still run into the same problem:

   1 set -e
   2 foo=$(expr 1 - 1)
   3 
   4 echo survived

Subshells from command substitution unset set -e, however (unless inherit_errexit is set with Bash 4.4):

   1 set -e
   2 foo=$(expr 1 - 1; true)
   3 
   4 echo survived

Note that set -e is not unset for commands that are run asynchronously, for example with process substitution:

   1 set -e
   2 mapfile foo < <(true; echo foo)
   3 echo ${foo[-1]} 
   4 mapfile foo < <(false; echo foo)
   5 echo ${foo[-1]} 

Another pitfall associated with set -e occurs when you use commands that look like assignments but aren’t, such as export, declare, typeset or local.

   1 set -e
   2 f() { local var=$(somecommand that fails); }
   3 f    
   4 
   5 g() { local var; var=$(somecommand that fails); }
   6 g    

In function f, the exit status of somecommand is discarded. It won’t trigger the set -e because the exit status of local masks it (the assignment to the variable succeeds, so local returns status 0). In function g, the set -e is triggered because it uses a real assignment which returns the exit status of somecommand.

A particularly dangerous pitfall with set -e is combining functions with conditionals. The following snippets will not behave the same way:

   1 set -e
   2 f() { false; echo "This won't run, right?"; }
   3 f
   4 echo survived
   1 set -e
   2 f() { false; echo "This won't run, right?"; }
   3 if f; then  
   4     echo survived
   5 fi

As soon as a function is used as a conditional (in a list or with a conditional test or loop) set -e stops being applied within the function. This may not only cause code to unexpectedly start executing in the function but also change its return status!

Using Process substitution, the exit code is also discarded as it is not visible from the main script:

   1 set -e
   2 cat <(somecommand that fails)
   3 echo survived

Using a pipe makes no difference, as only the rightmost process is considered:

   1 set -e
   2 somecommand that fails | cat -
   3 echo survived

set -o pipefail is a workaround by returning the exit code of the first failed process:

   1 set -e -o pipefail
   2 failcmd1 | failcmd2 | cat -
   3 
   4 echo survived

though with pipefail in effect, code like this will sometimes cause an error, depending on whether the output of somecmd exceeds the size of the pipe buffer or not:

   1 set -e -o pipefail
   2 somecmd | head -n1
   3 
   4 echo survived

So-called strict mode

In the mid 2010s, some people decided that the combination of set -e, set -u and set -o pipefail should be used by default in all new shell scripts. They call this unofficial bash strict mode, and they claim that it “makes many classes of subtle bugs impossible” and that if you follow this policy, you will “spend much less time debugging, and also avoid having unexpected complications in production”.

As we’ve already seen in the exercises above, these claims are dubious at best. The behavior of set -e is quite unpredictable. If you choose to use it, you will have to be hyper-aware of all the false positives that can cause it to trigger, and work around them by “marking” every line that’s allowed to fail with something like ||true.

Conclusions

GreyCat‘s personal recommendation is simple: don’t use set -e. Add your own error checking instead.

rking’s personal recommendation is to go ahead and use set -e, but beware of possible gotchas. It has useful semantics, so to exclude it from the toolbox is to give into FUD.

geirha’s personal recommendation is to handle errors properly and not rely on the unreliable set -e.

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