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How We Found Jupiter’s 79 (At Least) Moons

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a tiny moon in front of jupiter

The moon Io is tiny compared to mighty Jupiter, but still among the easiest of Jupiter’s many moons to spot. (Credit: Cassini Imaging Team/SSI/JPL/ESA/NASA)

Jupiter is king of the planets. It’s huge, it’s bright in our night skies, and even four of its comparatively tiny moons are bright enough to see with the most basic of telescopes. We’ve sent nine probes either into orbit or on a close flyby of the planet. And yet, as recently as this past year, we discovered not one, but twelve new moons around Jupiter, bringing the total to 79. How haven’t we exhausted this particular moon mine yet?

The Easy Targets First

The answer is that most of Jupiter’s moons aren’t the grand companion that our own moon is to Earth, at nearly a quarter as wide as its host planet. The four moons first spotted by Galileo in 1610 — Io, Europa, Ganymede and Callisto — are big enough compared to our moon, but absolutely puny when compared to Jupiter, the planet they circle. And those are the easy targets. It makes discovering new moons against its bulk difficult.

It took the advent of photography before astronomers discovered any more moons around Jupiter, and the work over the next century or so was painstaking. By the time Voyager cruised by in 1979, the giant was up to 13 moons. Voyager added three to the count: Metis, Adrastea, and Thebe.

All three of these plus Amalthea (discovered in 1892 by famed astronomer E.E. Barnard) and the original Galilean moons comprise Jupiter’s regular moon group. This means they’re more or less spherical, orbit in the same direction that Jupiter spins and do so on well-behaved, near-circular orbits that don’t tip much out of the plane of Jupiter’s equator. In other words, what you probably imagine a moon to be.

The rest are the irregular moons, and these make up the vast majority of Jupiter’s satellites. These tend more toward potato shapes, and their orbits are often eccentric, tilted, or even retrograde, meaning they fly backwards to Jupiter’s spin. Most are probably captured asteroids or the results of long-ago collisions of larger bodies — perhaps past moons of Jupiter. They’re tiny and tend to orbit farther out from Jupiter than the regular moons. This makes them much harder to spot.

Astronomers found a few of these irregular moons. But after Voyager, the discoveries stopped for about two decades.

A Population Explosion

diagram showing prograde moons in blue, retrograde moons in red

One of Jupiter’s newest moons orbits prograde (normally), but since it’s among the retrograde (backwards) moon group, it’s probably marked for a deadly collision before too long. (Credit: Roberto Molar-Candanosa/Carnegie Institution for Science)

And then Scott Sheppard appeared on the scene. The Carnegie Institution for Science astronomer’s teams are responsible for 60 of the 79 known jovian moons — all irregular, but still an impressive feat. Sheppard’s team has been discovering moons around Jupiter since 2000. Just this past year, they added a round dozen to the list. The new moons add to our understanding of Jupiter’s neighborhood and help astronomers understand how the planet formed and its surroundings evolved over time.

It is true, though, that some of Jupiter’s moons have been “discovered” more than once. These glorified space boulders are sometimes spotted in images but their orbits are poorly understood. So when astronomers look for them again in a few months or years, sometimes they turn up missing and have to be found again.

These irregular moons are quite tiny — only a few miles to tens of miles across. They bear little resemblance to the complex worlds of Europa and Ganymede, or even our own moon. Instead, they are mostly misshapen hunks of rock, orbiting far out from Jupiter’s bulk. So the telescopes that find them have to be sensitive, and either look at a large swath of space or get very, very lucky.

Spotting Tiny Specks

The probes we sent to Jupiter, while far closer than Earth-bound telescopes, are mostly busy looking at the planet. They, too, would have to get quite lucky to catch one of these tiny irregular moons by accident while trying to image the planet. And frankly? The possibility of finding one more tiny space rock doesn’t tempt scientists who want to understand the deep mysteries of Jupiter’s storms or interior. They’re not wasting precious mission time looking very hard.

Sheppard’s most recent successes actually came while he was looking much farther out, trying to find a possible Planet Nine far past the giant planet’s orbit. But since Jupiter happened to be in the same region of the sky, Sheppard and his team checked to see if they could find any photo-bombing moons in their images. They got lucky, though hard work went into the find as well.

Astronomers have gotten much better at wide-field surveys where they scan large chunks of the sky at once. Our telescopes, of course, have also gotten better. But mostly, you have to be willing to spend a long time looking for very dim objects to discover any new satellites around Jupiter.

Most individual irregular moons aren’t considered groundbreaking discoveries on their own (though a few weird exceptions exist). But taken as a whole? Jupiter’s rowdy brood of moons, regular and irregular, tell a long and interesting story about what life is like around the solar system’s largest planet.

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Ecology

Globe Climate: Canada’s resource reckoning is coming

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Good afternoon, and welcome to Globe Climate, a newsletter about climate change, environment and resources in Canada.

This afternoon, the Alberta government announced that it is restoring a coal mining policy it revoked last spring. At the time, the move provoked a widespread public backlash detailed by The Globe. The original decision, which opened up more than 1.4 million hectares to exploration, was made without public consultation. Premier Jason Kenney previously defended the changes.

Lots more on coal and Canada’s resources industry in this week’s newsletter edition.

Now, let’s catch you up on other news.

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Ecology

‘Incredibly destructive’: Canada’s Prairies to see devastating impact of climate change

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As the climate continues to warm at an alarming rate, experts warn if dramatic steps to mitigate global warming are not taken, the effects in Canada’s Prairie region will be devastating to the country’s agriculture sector.

According to Environment and Climate Change Canada, the country is warming, on average, about double the global rate.

Scientists with the National Oceanic and Atmospheric Administration in the U.S. recently found 2020 was earth’s second-hottest year on record, with the average land and ocean surface temperature across the globe at 0.98 of a degree C above the 20th-century average.

However, the agency found the northern hemisphere saw its hottest year on record, at 1.28 degrees C above the average.

“(In Canada) we are looking at about 6.4C degrees of warming this century, which isn’t much less than one degree per decade, which is just a terrifying rate of warming,” Darrin Qualman, the director of climate crisis policy and action at the National Farmer’s Union said.

Qualman said there is “massive change coming” to Canada’s Prairies, which will be “incredibly destructive.”

“It’s not going too far to say that if we made that happen, parts of the Prairies wouldn’t be farmable anymore,” he said.

According to the federal government, in 2018 Canada’s agriculture and agri-food system generated $143 billion, accounting for 7.4 per cent of the country’s GDP.

The sector employed 2.3 million people in 2018. The majority of the 64.2 million hectares of farmland in Canada is concentrated in the Prairies and in southern Ontario.

The effects of climate change are already being felt on the ground in the Prairies, Qualman said, adding that the NFU has already heard from farmers complaining of “challenging weather.”

“People are sharing pictures of flattened crops and buildings, et cetera, that have been damaged,” he said. “And we’re still at the beginning of this.”

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Ecology

Insect-based dog food aims to cut your pet’s carbon pawprint

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Meat has an enormous carbon footprint, with livestock liable for about 15 per cent of worldwide emissions, as we have beforehand mentioned on this e-newsletter. That is prompted specialists to suggest consuming much less meat for sustainability (and well being) causes.

However what about your pet? One research discovered that the methane and nitrous oxide emissions generated by canine and cat meals within the U.S. alone had been equal to about 64 million tonnes of CO2, or roughly the quantity produced by 13.6 million automobiles. And it might be getting worse, with a development towards feeding pets “human-grade” meat.

That is prompted some pet meals makers to look to lower-carbon protein sources — together with bugs.

Research present that producing insect-based meals requires far much less feed, land and water and generates far fewer greenhouse fuel emissions per kilogram than meats comparable to beef, pork or rooster.

That is one of many causes increasingly more pet meals containing insect protein are hitting the market. Purina, a model owned by multinational Nestlé, launched a line of canine and cat meals containing black soldier fly larvae in Switzerland in November.

In Canada, Montreal-based Wilder Harrier began promoting canine treats made with cricket protein in 2015 and pet food made with black soldier fly larvae in 2019. It plans to broaden to launch a line of insect-based cat treats later this yr and cat meals in 2022 due to “a ton of demand,” mentioned firm co-founder Philippe Poirier.

Wilder Harrier initially labored with animal nutritionists on insect-based merchandise to unravel a unique downside — specifically, the founders’ canines had allergy symptoms to frequent meats utilized in canine meals. Poirier mentioned now about half its prospects hunt down the product due to their pets’ allergy symptoms and about half for environmental causes.

Dr. Cailin Heinze, a U.S.-based veterinary nutritionist licensed by the American School of Veterinary Vitamin, has written concerning the environmental influence of pet meals. She mentioned we’re typically “not as involved as we probably ought to [be]” concerning the environmental footprint of pets.

Alternatively, she famous that the longer-term influence of newer diets, comparable to vegan meals and people containing bugs, hasn’t been nicely examined in comparison with conventional pet meals.

Maria Cattai de Godoy, an assistant professor of animal sciences on the College of Illinois who research novel proteins for pet meals (together with bugs, yeast and plant-based substances), mentioned such substances are rigorously examined to find out their security and diet earlier than being added to pet meals. 

“This can be a very extremely regulated trade,” she mentioned, however admitted it is also evolving.

Relating to bugs, she mentioned constructive information “reveals promise in direction of utilizing them increasingly more in pet meals.” Insect-based proteins have additionally earned the endorsement of the British Veterinary Affiliation, which says some insect-based meals could also be higher for pets than prime steak.

However Godoy famous that there isn’t any one-size-fits-all resolution, and pet homeowners ought to take into consideration the wants of their very own particular person pet and analysis whether or not a specific weight loss plan can be appropriate.

She mentioned that other than the kind of protein, issues like packaging and manufacturing strategies may also make a distinction. For instance, utilizing meat byproducts that may in any other case turn into waste would not drive elevated meat manufacturing the identical approach as utilizing human-grade meat.

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