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NASA/JPL-Caltech/Space Science Institute
NASA/JPL-Caltech/Space Science Institute

How Many Rings Does Saturn Have?

NASA/JPL-Caltech/Space Science Institute
NASA/JPL-Caltech/Space Science Institute

Of all the planets surrounded by rings, Saturn is the most famous. These planetary rings are massive enough that Galileo was able to see them using a simple telescope way back in 1610, though it wasn't until half a century later that another scientist was able to figure out what the "arms" Galileo saw actually were. NASA has since called them "the most recognized characteristic of any world in our solar system."

So how many rings does Saturn have, anyway? If you can see them from your backyard, there must be a lot, right?

Scientists don't know for sure exactly how many rings Saturn has. There are eight main, named ring groups that stretch across 175,000 miles, but there are far more than eight rings. These systems are named with letters of the alphabet, in order of their discovery. (Astronomers have known about ring groups A, B, and C since the 17th century, while others are newer discoveries. (The most recent was just discovered in 2009.)

The rings we can see in images of the planet—even high-resolution images—aren't single rings, per se, but are in fact comprised of thousands of smaller ringlets and can differ a lot in appearance, showing irregular ripples, kinks, and spokes. The chunky particles of ice that make up Saturn's rings vary in size from as small as a speck of dust to as large as a mountain.

While the gaps between Saturn's rings are small, the 26-mile-wide Keeler Gap is large enough to contain multiple moons, albeit very small ones. The largest ring system—the one discovered in 2009—starts 3.7 million miles away from Saturn itself and its material extends another 7.4 million miles out, though it's nearly invisible without the help of an infrared camera.

Researchers are still discovering new rings as well as new insights into the features of Saturn's already-known ring systems. In the early 1980s, NASA's Voyager missions took the first high-resolution images of Saturn and its rings, revealing previously unknown kinks in one of the narrower rings, known as the F ring. In 1997, NASA sent the Cassini orbiter to continue the space agency's study of the ringed planet, leading to the discovery of new rings, so faint that they remained unknown until Cassini's arrival in 2006. Before Cassini is sent to burn up in Saturn's atmosphere in September 2017, it's taking 22 dives through the space between the planet and its rings, bringing back new, up-close revelations about the ring system before the spacecraft dives to its death.

Though it's certainly possible to see Saturn's rings without any fancy equipment, using a low-end telescope at your house, that doesn't mean you always can. It depends on the way the planet is tilted; if you're looking at the rings edge-on, they may look like a flat line or, depending on the magnification, you might not be able to see them at all. However, 2017 happens to be a good year to see the sixth planet, so you're in luck.

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Big Questions
How Are Speed Limits Set?
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When driving down a road where speed limits are oppressively low, or high enough to let drivers get away with reckless behavior, it's easy to blame the government for getting it wrong. But you and your fellow drivers play a bigger a role in determining speed limits than you might think.

Before cities can come up with speed limit figures, they first need to look at how fast motorists drive down certain roads when there are no limitations. According to The Sacramento Bee, officials conduct speed surveys on two types of roads: arterial roads (typically four-lane highways) and collector streets (two-lane roads connecting residential areas to arterials). Once the data has been collected, they toss out the fastest 15 percent of drivers. The thinking is that this group is probably going faster than what's safe and isn't representative of the average driver. The sweet spot, according to the state, is the 85th percentile: Drivers in this group are thought to occupy the Goldilocks zone of safety and efficiency.

Officials use whatever speed falls in the 85th percentile to set limits for that street, but they do have some wiggle room. If the average speed is 33 mph, for example, they’d normally round up to 35 or down to 30 to reach the nearest 5-mph increment. Whether they decide to make the number higher or lower depends on other information they know about that area. If there’s a risky turn, they might decide to round down and keep drivers on the slow side.

A road’s crash rate also comes into play: If the number of collisions per million miles traveled for that stretch of road is higher than average, officials might lower the speed limit regardless of the 85th percentile rule. Roads that have a history of accidents might also warrant a special signal or sign to reinforce the new speed limit.

For other types of roads, setting speed limits is more of a cut-and-dry process. Streets that run through school zones, business districts, and residential areas are all assigned standard speed limits that are much lower than what drivers might hit if given free rein.

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Do Bacteria Have Bacteria?
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Drew Smith:

Do bacteria have bacteria? Yes.

We know that bacteria range in size from 0.2 micrometers to nearly one millimeter. That’s more than a thousand-fold difference, easily enough to accommodate a small bacterium inside a larger one.

Nothing forbids bacteria from invading other bacteria, and in biology, that which is not forbidden is inevitable.

We have at least one example: Like many mealybugs, Planococcus citri has a bacterial endosymbiont, in this case the β-proteobacterium Tremblaya princeps. And this endosymbiont in turn has the γ-proteobacterium Moranella endobia living inside it. See for yourself:

Fluorescent In-Situ Hybridization confirming that intrabacterial symbionts reside inside Tremblaya cells in (A) M. hirsutus and (B) P. marginatus mealybugs. Tremblaya cells are in green, and γ-proteobacterial symbionts are in red. (Scale bar: 10 μm.)
Fluorescent In-Situ Hybridization confirming that intrabacterial symbionts reside inside Tremblaya cells in (A) M. hirsutus and (B) P. marginatus mealybugs. Tremblaya cells are in green, and γ-proteobacterial symbionts are in red. (Scale bar: 10 μm.)

I don’t know of examples of free-living bacteria hosting other bacteria within them, but that reflects either my ignorance or the likelihood that we haven’t looked hard enough for them. I’m sure they are out there.

Most (not all) scientists studying the origin of eukaryotic cells believe that they are descended from Archaea.

All scientists accept that the mitochondria which live inside eukaryotic cells are descendants of invasive alpha-proteobacteria. What’s not clear is whether archeal cells became eukaryotic in nature—that is, acquired internal membranes and transport systems—before or after acquiring mitochondria. The two scenarios can be sketched out like this:


The two hypotheses on the origin of eukaryotes:

(A) Archaezoan hypothesis.

(B) Symbiotic hypothesis.

The shapes within the eukaryotic cell denote the nucleus, the endomembrane system, and the cytoskeleton. The irregular gray shape denotes a putative wall-less archaeon that could have been the host of the alpha-proteobacterial endosymbiont, whereas the oblong red shape denotes a typical archaeon with a cell wall. A: archaea; B: bacteria; E: eukaryote; LUCA: last universal common ancestor of cellular life forms; LECA: last eukaryotic common ancestor; E-arch: putative archaezoan (primitive amitochondrial eukaryote); E-mit: primitive mitochondrial eukaryote; alpha:alpha-proteobacterium, ancestor of the mitochondrion.

The Archaezoan hypothesis has been given a bit of a boost by the discovery of Lokiarcheota. This complex Archaean has genes for phagocytosis, intracellular membrane formation and intracellular transport and signaling—hallmark activities of eukaryotic cells. The Lokiarcheotan genes are clearly related to eukaryotic genes, indicating a common origin.

Bacteria-within-bacteria is not only not a crazy idea, it probably accounts for the origin of Eucarya, and thus our own species.

We don’t know how common this arrangement is—we mostly study bacteria these days by sequencing their DNA. This is great for detecting uncultivatable species (which are 99 percent of them), but doesn’t tell us whether they are free-living or are some kind of symbiont. For that, someone would have to spend a lot of time prepping environmental samples for close examination by microscopic methods, a tedious project indeed. But one well worth doing, as it may shed more light on the history of life—which is often a history of conflict turned to cooperation. That’s a story which never gets old or stale.

This post originally appeared on Quora. Click here to view.

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