We continue our discussion of our picks for the annual countdown of the ten most exciting, important, and fun stories from the world of science in 2020 during this Pulsar podcast brought to you by #MOSatHome. We ask questions submitted by listeners, so if you have a question you'd like us to ask an expert, send it to us at sciencequestions@mos.org.

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ANNOUNCER: T minus 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, main engine ignition.

ERIC: We are back with Part Two of our countdown that answers the question, what were the Top 10 Science Stories of 2020? Last episode, we started off with an honorable mention story and got as far as number nine.

Today, we'll discuss the next few entries on our list of the most important, exciting, and cool stories from the world of science last year.

I'm your host, Eric, and here's the second part of my conversation about our countdown with Sarah from our current science and technology team.

All right, so our number eight story is our closest neighbor in space, and that is Venus that usually doesn't get a lot of love. We hear lots about Mars. We have spacecraft in the last couple of years exploring Saturn and Jupiter.

Venus, not so much. It's got that really thick atmosphere. It traps in so much heat from the sun that it's the hottest planet, 900 degrees on the surface. And we've sent spacecraft there. We've studied it. We've got maps of the surface. And then, there hasn't been that much news recently.

But in September, big news came out, which was some gases in the upper atmosphere of Venus, where the conditions are actually a lot more like the Earth, that are potential biosignatures that might have come from some kind of life process, which is insane to think about that could happen, of all places in the solar system, on Venus.

SARAH: Yeah, it's hard to overstate how brutal the conditions of Venus are. I mean, it rains acid there. The planet rotates backwards and very slowly, so the day on Venus is longer than the year.

All kinds of really strange things happen on Venus, but in the upper atmosphere where the pressure is much less and where the temperatures are much, we think, more similar to sort of Earth temperatures, people have asked for a long time, could life exist in the atmosphere of Venus?

And then, we discovered phosphine.

ERIC: Yeah, the big announcement was the detection of phosphine gas at this high level of the atmosphere. And that's exciting because it should be easily destroyed by sunlight.

So if we see the signal, then something is replenishing this phosphine, and there's no process that we're aware of that would do that on Venus. And since this gas is associated with the processes of life on Earth, well, maybe there could be life on Venus, too, high in the cloud tops.

SARAH: The presence of phosphine on Venus, especially in its upper atmosphere, got everyone crazy excited. I mean, every space agency on Earth was like, point everything at Venus.

Should we get a mission to go to Venus? What are we going to learn about Venus? And especially people were excited about the idea that learning about this could be learning from the surface. Because as Eric mentions, we have sent some landers to Venus, and they lasted for about an hour before they basically melted.

So I mean, the idea of having to land something on the surface of Venus, you have to have something that can stand up to this crushing pressure, intense heat, acid rain, all kinds of things.

But if we could just send a glider, a drone, a balloon to just go sail around the atmosphere of Venus, that would be way easier and potentially, now we're seeing, could be way more fruitful.

Then, you have to start looking more closely at where your signal came from. Because the thing is, a lot of what we understand about life, that's not even true. Literally everything we know about life comes from Earth.

And so, you'll often hear scientists saying things like, oh, we saw a big spike of methane on Mars. And here on Earth, methane is really largely caused by biological processes. So we get really excited when we see that.

But we can't rule out that there is not some weird geological process happening on Mars that releases methane, or indeed, that there's something happening in the atmosphere of Venus, which we haven't really sent that many spacecraft into.

Because then we went back to look for the phosphine, and it looked like it had been sort of a surge of phosphine, like a spike in the atmosphere, because we couldn't find it later.

And again, when I say find it, we're looking for sort of signals in the light that tell us, based on how our light changes, what chemicals are present. So we're not actually in there taking scoops of Venus clouds.

But I don't know, Eric. As a space nerd who spends your time reading and getting excited about space stories and then explaining them to visitors, can you sort of explain what it feels like when a big story like this happens? And we're excited, but also cautious.

ERIC: It's that super reserved excited, where you read the headline and you're like, there's no way it could possibly be aliens. And we've had a couple of these false alarms, even in the last couple of years, where it's just something that we can't explain.

And extraterrestrial life is in the list of possible explanations that we haven't ruled out yet. It's not maybe the best one. It's not maybe even a likely one. But it is possible that there are some kind of tiny microbes floating in the atmosphere of Venus producing this gas, and we picked it up.

Could it have come from chemical reactions high in the atmosphere that we haven't understood yet fully? Sure. And could it be that we picked up more in our instruments than is actually there by a factor of 10 or 100? Sure, that's possible, too.

But it's exciting because we need to look for more evidence. We need to have lots of scientists working on it, thinking of other ways this gas could have got there. We have to maybe send a mission there to investigate the conditions more closely so we can understand it better.

So these kind of stories, even if they don't pan out to actually be aliens, are just always super exciting.

SARAH: Yeah, we're just like you, everybody. When we hear something that sounds like it could be aliens, we also want it to be aliens. But so far, it hasn't been aliens yet. Scientific discovery is often like, what is this? How could this happen?

And sometimes, the most exciting possible explanation is true, but often, it's something else that just gets us closer to an understanding of how common life is in the universe and things like that.

ERIC: So our next story, number seven, takes us back in time. And it was a story that another one of our colleagues was just super excited about. We kind of knew it would be in our top 10 the whole year because it was the biggest dinosaur story.

So spinosaurus, this amazingly huge predator, turns out to be mostly aquatic, based on new studies and new fossils.

SARAH: This is wild because spinosaurus, which is a very-- listen, objectively-- just a sweet-looking dinosaur. It's a huge predator. It has sort of a long, almost crocodilian face. It had this sail along its back. And it was 30 feet long. It was this -

ERIC: Yeah, T-rex sized.

SARAH: Yeah, and based on the way, having this sail on its back, early people who discovered this were like, is this a fish? Is this a weird, big fish? Is this a weird, swimming creature? But it was so large, and it's a dinosaur. And that's significant.

Like, a plesiosaur or an ichthyosaur are a couple of animals that people bring up as an example of swimming dinosaurs. But they aren't actually dinosaurs. They're reptiles.

ERIC: Lived at the same time.

SARAH: Yeah.

ERIC: But completely different type of life.

SARAH: Yeah, and not part of the lineage that we see as modern dinosaurs, which is the sort of avian line. There are non-avian dinosaurs, but there also were non-dinosaur reptiles, which is really confusing. And ichthyosaur and plesiosaur are two famous examples of that.

We didn't really have evidence that there were swimming dinosaurs. This year, with a recreation of the tail of the spinosaurus, it turns out that thing's shaped like a rudder. Flat and wide and had a spade tip that flattened out - that's used to swim.

ERIC: There's no way that this dinosaur spent all of its time on the land, based on what we've been able to learn this year.

SARAH: And then, this also tells us more because big dinosaurs are great and super duper exciting. And also, because of the process of fossilization, the bigger the bones, the less likely they are to be kind of crushed in the process of all that rock smashing down and making fossils.

Finding a big dinosaur that swims like this doesn't tell us, wow, spinosaurus was so weird and probably was the only dinosaur that ever swam. It tells us more.

Wow, we don't have a complete picture of what dinosaurs were like. And there's probably a whole lineage of some aquatic dinosaurs that we don't know about that spent their time in water that spinosaurus hunted. Maybe spinosaurus was also eating fish and reptiles. But there were probably dinosaurs, too, who lived in this same environment.

So I mean, just awesome and just a really cool-looking dinosaur and a fascinating story into how we have to find the fossil evidence. We have to find the evidence of really what this creature looked like before we can start to get an idea of how it acted.

And finding these tail fossils was the perfect proof that, wow, this is an animal that lived a life that was unlike what we thought dinosaurs lived. So, just awesome. So cool.

ERIC: Another story where we're taking technology and learning more than what's just in front of us.

SARAH: Right.

ERIC: Instead of just taking the tail fossil and mounting it and then arguing about how it was used, the scientists 3D-printed the structure of the tail based on the fossil. They tested it in a tank, and they saw that, yes, it was a good tail for swimming.

So they actually have evidence that the dinosaur used its tail for this, instead of, well, maybe it did, and maybe it didn't. All we can do is look at it. So using technology to kind of actively learn about something that was so long ago still blows my mind.

SARAH: Yeah, the biomechanics in general of how these enormous creatures lived in a time when our planet had a different atmosphere, when our planet had different temperatures and different climates, is so cool. I'm never going to be over it. These beautiful animals were real. And they moved and lived in a way that we're learning more about. It's amazing.

ERIC: Our last story for today is number six, and this one is one that we've kind of covered this category in other years. It's our Nobel Prize in Chemistry that went to two scientists for the development of CRISPR for editing DNA.

SARAH: We've talked about CRISPR a lot at the Museum of Science because it is one of the most well-known and best proven tools for editing DNA.

So CRISPR is based on bacterial immune system. I know that's a weird thing to say, but it turns out that because bacteria are single-celled organisms, they don't have white blood cells, obviously. They don't have anything else to fight off viruses or anything that might try to infect them.

And so, instead, what they have is this sort of little immune system that's just sort of these proteins that are able to kind of proofread their genetic code and cut out things that are not supposed to be there, like viral DNA or something like that.

And so, CRISPR, in the last 10 years or so, has been used almost like a pair of molecular scissors to go in and find parts of non-bacterial genomes, like human DNA, and make changes to it. This is a big topic. CRISPR gets a lot of people sort of concerned.

ERIC: Yeah, there's a lot of ethical issues having to do with it, too.

SARAH: In many ways, what's important about CRISPR is that - I mean, it is one of the most effective tools we have for doing this sort of science, but more effectively, we're moving towards a world where this is a branch of medicine, where genetic treatments of diseases, especially things like sickle cell anemia, muscular dystrophy, these are genetic lifelong chronic illnesses that we are now finding ways to potentially be able to cure.

However, it's a long, long road. And the Nobel Prize this year was for two scientists who basically found a more effective and cleaner way to make those little cuts in DNA that you have to make in order to make any changes, whether you're trying to turn off a gene you don't want, turn on a gene you do want, get rid of a gene that's misbehaving, or put in a gene that wasn't there.

Those are basically the four basic uses of CRISPR. And these two scientists found a much more precise and effective way to make those cuts so that you won't affect any part of the DNA that you don't want to affect. But there's also one more really special thing about these two scientists.

ERIC: Yeah, and that is that they're both women. And looking at the history of Nobel Prize winners across all categories, there has been very few women, especially going back more than about 15 years - hardly any at all. And so, it was really exciting.

This was the first time that two women shared the Nobel Prize in chemistry. It's just really exciting, not that women are finally doing the science, it's that women are finally getting the recognition for it.

There have been plenty of examples of women in chemistry and physics and all the different fields that could have been considered, maybe should have been awarded the Nobel Prize.

But to see it actually happen this year and for something that's been such an amazing breakthrough that we've been talking about in current science and technology for years now, that's really why we wanted to include it on our list as a celebration of that.

SARAH: Yeah, for sure. This story is really, really meaningful, especially because I mean, the structure of DNA was largely discovered by a scientist named Rosalind Franklin, whose work was co-opted by Watson and Crick.

It is quite beautiful that these two scientists, Emmanuel Charpentier and Jennifer Doudna, were able to use this robust understanding of the structure of DNA, which we got from Rosalind Franklin, to begin to make huge strides toward being able to cure or eradicate some of the genetic diseases that have been sort of wreaking havoc on the human race for centuries.

ERIC: All right, well, Sarah, thanks so much for talking about the first half of our top 10. And we'll see you in a couple of weeks as we count down all the way to number one.

SARAH: Thanks for having me. Can't wait to get to number one.

ERIC: We'll be back at the end of January with the final entries on our countdown. Until next time, keep asking questions.

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