As a newborn planet, Jupiter shone brightly in the sky and eclipsed today’s sun from the perspective of the gas giant’s largest moons. This early glow and upcoming visits by several spacecraft could help solve a 40-year-old mystery about the composition of these moons.

For decades, scientists have been trying to understand the strange differences in density of Jupiter’s four Galilean moons, which, in order from closest to the planet to farthest, are Io, Europa, Ganymede, and Callisto. Although these natural satellites must have formed from the same source material and therefore have a similar composition, density measurements show that Callisto and Ganymede are much icier than Europa, and Io has no ice at all. disclosed At a conference last month, Carver Birson, a planetary scientist at Arizona State University, can shed some light on the subject.

Giant planets are formed by the merger and compression of huge volumes of gas and dust. This process releases a lot of excess energy and gives the newborn giants a literal youthful glow that can last for millions of years. This is more than a theory: astronomers regularly use this glow to image young giant exoplanets that would otherwise be lost in the glow of nearby stars. But the less glaring question of how such a glow could shape accompanying moons has been largely unexplored. In the case of Jupiter, computer simulations by Birson and colleagues suggest that the planet’s early glow illuminated its newborn moons and evaporated most of their water over a period of several million years.

“It gave people the opportunity to think about a completely new process,” says Francis Nimmo, who studies icy moons at the University of California, Santa Cruz and was not involved in the study.

Four satellites, one source

The differential compositions of the four Galilean moons have puzzled researchers for decades, ever since the first high-quality satellite density measurements were made. Locked inside Jupiter’s radiation belt and heated from within by the planet’s powerful tidal forces that knead the Moon’s interior like dough, Io is a completely ice-free world of hyperactive volcanoes. A little more distant Europe is also in the grip of the radiation and tides of Jupiter. But more modest levels of internal heating have given the Moon a subsurface ocean and icy crust, rather than lava-spewing calderas. Ganymede and Callisto are relatively inert, rich in ice, and much farther from Jupiter than Io and Europa.

Although the differences in Jupiter’s gravitational hold clearly explain some of the differences between the moons, planetary scientists were still trying to understand how these objects could have a common origin, yet be so different from each other. Just as planets form from spinning protoplanetary disks of gas and dust around nascent protostars, large moons can form from smaller mini-disks around gathering gas giant worlds. Current thinking calls for Jupiter to gain most of its mass very quickly, during the first 10 million years of the solar system’s life, before the light and stellar winds from the ever-brightening sun swept all the gas from the protoplanetary disk.

This relatively compressed timeline means that Jupiter would have had to greedily, quickly gulp gas to reach its current size, which would have caused it to heat up and glow, reaching a temperature estimated at 1,160 degrees Fahrenheit (627 degrees Celsius). For the Galilean moons, which supposedly formed around the same time as Jupiter itself, the planet would have shone like a star in the sky and overwhelmed the light coming from the more distant sun. By carefully modeling the effects of Jupiter’s increased luminosity on the Galilean moons, Birson and his colleagues found that this beam of light could clearly solve the riddle of today’s diverse satellite composition.

Fragrant fresh baked moons

Torn apart by Jupiter’s gravity, Io today is a hellish landscape of volcanic eruptions and is the most active body in the solar system. But the team found that Jupiter’s youthful glow may have originally given Io Earth’s temperatures and perhaps even the ocean. “I think it’s likely that either during Io’s formation or just after Io’s completion, there is some water on the surface,” Birson says.

That would change quickly, Birson said, as Io received about 30 times more energy from Jupiter than it receives from the Sun today. If Io had as much water as its cousin Ganymede currently holds, all that moisture would be quickly removed, and any remaining ocean would evaporate in the first million years of the moon’s existence.

Europa, further away than Io, would have had slightly cooler surface conditions – although they might still have been hot enough for this moon to lose a significant amount of its water. Farther away, on Ganymede, Jupiter would appear barely brighter than today’s Sun, a level of isolation without significant impact on lunar ice. The distant Callisto, sent to the outskirts of the Jupiter system, would not have been impressed by the radiant youth of Jupiter. (All of this assumes the moons were in their current positions. They probably formed closer before migrating to their current locations, however, this means the results of the study are probably only a lower limit on how much each moon was baked by Jupiter. .)

“The advantage of this hypothesis is that there are several tests that you can apply,” says Nimmo.

SOK-y offer

If Europa had lost most of its ice in its lifetime, rather than formed from less ice than its siblings, the remaining hydrogen and oxygen would have a different isotopic fingerprint than the ice on Ganymede and Callisto. Thus, an isotopic comparison of Europa with one or both of the most distant moons could finally reveal the truth about how these moons diverged from their common origin. “The more comparisons you can make [among the chemistries of the moons]the more you will understand how things will develop at this very early time,” says Birson.

This is quite an attractive proposition, given the recent launch of the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) mission. Between 2031 and 2034, JUICE will make 35 flybys of Europa, Callisto and Ganymede before entering orbit around Ganymede. An extended tour can go a long way in determining whether all Galilean moons were born with the same amount of ice. JUICE has a mass spectrometer, which Nimmo says can make important measurements of hydrogen and water vapor that can come into space from moons, specifically Ganymede.

“The question is whether Ganymede provides enough material for the heights that JUICE can sample,” says Nimmo. He remains confident that this will be the case.

Even if JUICE research fails to crack the case, it won’t be the only moon-exploring spacecraft hovering in the Jupiter system. NASA’s Juno mission is already in orbit around the gas giant, and the space agency’s Europa Clipper mission is set to launch next year to travel to the mission’s moon of the same name. The Clipper data should provide a clear comparison of JUICE’s views of Europa’s ice that will be enough to extrapolate and distinguish from what a European spacecraft sees on Ganymede and possibly Callisto.

“Comparisons between moons will be extremely important,” Birson says. “It’s so exciting that JUICE and Europa Clipper will appear almost at the same time and maybe overlap a bit.”

As shown in the animation below, this was indeed a snow boom year in the western United States. This is especially true in water-stressed California and the mega-drought-hit Colorado River Basin, whose dwindling water is supporting a $1.4 trillion economy.

Incredible snow cover in California’s Sierra Nevada continues to make headlines, especially as heat builds up. threatens to meltraising the already high risk of flooding. As of April 26, snowpack levels across the Sierra Nevada were over 200 percent of the average for that date. In the southern part of the Sierra, this figure exceeded 300 percent of the average.

These numbers are not uncommon. right now in the western US, as shown on this map:

All these blues and greens show where the snow cover is above average.

The abundance of snow in the mountains of the Colorado River Basin is a relief to the 40 million people in the seven states, Mexico and the numerous Indian tribes that depend on its waters. Two large reservoirs, Lake Powell and Lake Mead, which were needed to meet their water needs, have dropped to record lows. The water level in other reservoirs of the basin dropped sharply.

Postponement

But now the snow cover gives hope that a further decline can be avoided – at least in the upcoming warm season. Based current forecaststhe reservoir for the basin as a whole will be filled to approximately 44 percent capacity on 30 September, at the end water year 2023. This is more than 33 percent at the beginning of the water year in October. January 1, 2022. Some good news for a change, but almost certainly not in the long run.

“This winter’s snow cover is promising and gives us an opportunity to help replenish Lakes Mead and Powell in the near term, but the reality is that drought conditions in the Colorado River Basin have been in place for more than two decades,” the US Bureau said. Land Reclamation Commissioner Camilla Kalimlim Tuton, in statements.

Recent Research shows that the region has suffered from the worst drought in the region for at least 1200 years. In the study, just over 40 percent of its severity was attributed to human-caused climate change, mostly due to rising temperatures that caused increased aridity.

As Touton points out, “despite welcome snow this year, the Colorado River system remains under threat from the ongoing effects of the climate crisis.”

Assuming that this year’s abundance of snow results in expected runoff into streams and rivers – which isn’t really a given – it would give politicians a little more time to make some very difficult decisions about how to deal with the inevitable fact that much more water is being used. for agriculture, industry and municipal needs than flows in the Colorado River. That is why Lake Mead and Powell have shrunk to record lows. And thanks to the climate crisis, the flow deficit is unlikely to be eliminated in the long term.

This long-term perspective is associated with rising temperatures due to the rising concentrations of carbon dioxide and other greenhouse gases in the atmosphere, which continue to their historically high growth rates in 2022, according to NOAA scientists.

“The bottom line is that to see any reduction in CO2 growth rates, emissions reductions need to be sustained and significant,” says Arlene Andrews, head of NOAA’s greenhouse gas emissions team.

Right now, we’re nowhere near seeing a reduction in emissions. Vice versa. In 2022, global energy-related CO2 emissions rose by 0.9 percent, according to the International Energy Agencyreaching a record level of almost 37 billion tons.