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On SciShow News this week, Hank explains how it can rain on the sun and dives in to findings from the NASA twin study!

Hosted by: Hank Green

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[♪ INTRO].

A study published this month in Astrophysical Journal Letters brings us one step closer to understanding one of the most intriguing phenomena in the sun's ever-shifting atmosphere: rain! Yes, it rains on the sun.

Though, it's not very similar to the rain that you get. Here on Earth, rain happens when water vapor cools and condenses into droplets. The surface of the Sun is thousands of degrees, so there's no cooling and condensing of water.

Instead, we're talking about it raining super hot electrified gas called plasma. You see, plasma at the sun's surface can become superheated to about 1 million degrees Celsius. And like any hot gas, hot plasma tends to rise.

But since it's electrically charged, it doesn't just rise anywhere—it leaps in fiery arcs along magnetic fields into the Sun's outer atmosphere, called the corona. Unlike the Earth, which has a pretty simple magnetic field with a north and a south pole, the Sun's magnetic field is very complicated, and it's constantly shifting and changing. This creates magnetic field lines that loop and arc through the corona, often carrying these plasma trails along the way.

As the plasma rises and cools, it can condense into globs of denser gas that descend back to the surface. And since that part is basically the same as what happens to water in our atmosphere, scientists call these falling globs coronal rain. Astronomers have known for some time that this rain happens, and they think understanding how and where can give them clues to solving an even bigger mystery: why the corona gets so much hotter than the Sun's surface.

It can be 300 times as hot in that outer atmospheric layer than on the surface, and scientists still aren't sure why. But, since coronal rain is a direct side effect of these temperature differences, understanding where the rain occurs might help scientists figure out exactly what's going on. So study leader Emily Mason pored over years of data collected by NASA's Solar Dynamics Observatory.

She expected to spot rain in the largest of the Sun's magnetic loops, called helmet streamers, which can extend over a million and a half kilometers from the Sun's surface. That's because the bigger the loop, the greater the temperature difference should be between the top and the bottom—so there's more opportunity for condensing. Instead, she found it on much smaller magnetic loops called null-point topologies, which only reach tens of thousands of kilometers high.

Those rain all the time, apparently, for tens of hours at a time. That suggests that these dramatic temperature changes can happen on a smaller scale than the researchers expected. But there are still questions to be answered here.

Now that astronomers have a better idea of where the corona gets heated, they still need to figure out how. And simulations say there should be coronal rain from those larger loops, so it's not clear why Mason and her colleagues didn't see it. They suspect that since the temperature change is more gradual, the rain globs that form might be smaller and harder to detect—like, a fine mist rather than a rainstorm—but that would still need to be confirmed.

Another mystery is why some plasma condenses into rain, while some of it becomes part of the constant flow of material ejected from the Sun called the solar wind. The researchers are hoping the Parker Solar Probe, which was launched in 2018, will shed more light on all this, as it has already gotten closer to the Sun than any other spacecraft and will continue to get closer. And in the future, we'll explore other objects in our solar system just as closely—if not more so—by sending humans out there to study them.

But before we can send people into space for such long missions, we need to understand how long-term space trips affect human bodies. Which brings me to the next bit of space news: The NASA Twins Study has released its major findings in the journal Science. In 2015, astronaut Scott Kelly joined a one-year mission on the International Space Station.

It was a golden opportunity for scientists to learn more about how being in space affects the body, in part because it was such a long mission, but also because Scott has an identical twin brother who stayed on Earth and acted as a control. For more than two years, including several months before and after the flight, scientists on 10 different research teams monitored Scott and Mark Kelly. And the gist of what they found was that spaceflight causes a lot of changes to the body, but nearly all of them are temporary, and none seem to be severe.

For example, they found that spending time in space caused changes to gut bacteria, alterations to cognitive functioning, and an increase in immune system activity. The exact causes for each change are probably very complicated and will take more research to sort out. For example, changes to gut bacteria might have just as much to do with the food they serve on the space station as with the low gravity and increased radiation.

But, none of these changes seemed to cause any major problems for the astronaut, and they went back to normal after the flight. Notably, though, the walls of Scott's arteries became thicker in space—probably because his cardiovascular system was trying to figure out how to deal with microgravity. And they stayed thick when he returned, which may mean very little, or may have health consequences down the line.

Of course, that's all stuff the scientists could have seen without a twin. What researchers really wanted to understand was how spaceflight affects the genome—and that is where Mark comes in. Since twins have identical genomes, the researchers were able to compare epigenetic changes to their DNA over time.

These are changes to the way genes function that aren't due to changes in sequence. And they happen all the time, so without a control, it's really hard to understand if they're from getting a year or two older or from being in space. Indeed, both men experienced thousands of small epigenetic tweaks over the time period, but there were notable differences in the changes to genes associated with immune responses while Scott was in space.

Yet, like the other changes, almost all of these were gone 6 months after he returned to Earth. The researchers also found that spending time in space caused the temporary lengthening of telomeres, the protective genetic caps that sit at the end of chromosomes. But when Scott came back to Earth, his telomeres rapidly shrank, and they ended up shorter than before the flight.

Since shorter telomeres are often correlated with increased risk of developing age-related diseases, doctors are particularly interested in seeing if this indicates a long-term health risk for astronauts. But they won't know that for some time. You see, there's a lot more work to be done to sort out exactly what all these changes mean and why they happen.

It's clear that extended spaceflight impacts the body in a lot of ways. Those alterations might be really important to understand or even counteract somehow if we want people to go on extended space missions. But it also seems like most of them go back to normal in six months or less once you get back at the bottom of the gravity well here.

Though, the researchers were quick to caution that this is a small study - about as small as you can get - one pair of subjects on one mission can only tell us so much. Fortunately, NASA is planning more long missions in the future, which will provide more subjects for similar studies. Which will hopefully help us be better prepared to start sending humans on space flights to explore distant objects like Mars or large asteroids!

But ... we'll probably still leave the remote-controlled probes for exploring the Sun. Thanks for watching this episode of SciShow! And thank you especially to all of our channel members, whose continued support helps us further our mission to provide free educational science videos.

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