On the one hand, red dwarfs are the longest lived stars in the Universe, the perfect place for life to hang out for trillions of years. On the other hand, they’re tempestuous little balls of plasma, hurling out catastrophic flares that could wipe away life. Are they good or bad places to live?
- Red dwarf (Wikipedia)
- Red Dwarfs: The Most Common and Longest-Lived Stars (Space.com)
- Red Dwarf (COSMOS)
- Red Dwarf Stars (Universe Today)
- Proxima Centauri (Wikipedia)
- Red Dwarf Stars Might Be Best Places to Discover Alien Life (Astrobiology Magazine)
- Every red dwarf star has at least one planet (Astronomy.com)
- Thermonuclear fusion (Wikipedia)
- Superflares From Young Red Dwarf Stars Imperil Planets (NASA)
- Nuclear fusion (Wikipedia)
- Life Among the Dwarfs (Discover)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast. Episode 557: Red Dwarfs: Friends or Foes? Welcome to Astronomy Cast, your weekly facts based journey through the cosmos where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today, with me – as always – Dr. Pamela Gay, senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela. How you doing?
Dr. Gay: I’m doing well. How are you doing, Fraser?
Fraser: I’m doing great. I’m really excited about this topic. We’ll talk about it in one second, but before we did, I just want to give a huge congratulations, again, to you and all the folks at the CosmoQuest community for all the work done with mapping out asteroid Bennu. OSIRIS-REx took more close-up pictures of Bennu from an even closer altitude. It’s all rocks!
Dr. Gay: Yeah.
Fraser: How did anybody get all that done?
Dr. Gay: Yeah, I think I’ve mentioned this before. We all have been traumatized by the rocks and I found out while travelling with a couple of the CosmoQuest crew members, that if you say “Bennu,” it’s like a call-and-response where someone responds, “Eff Bennu,” and someone else is like, “So many rocks!”
Fraser: Yeah, I see that in the chat right now. So, my point of this is, 1.) Congratulating everybody who’s involved in the project for doing such an enormous amount of incredible and useful science. You helped make this happen.
Dr. Gay: Yes.
Fraser: And, for those of you who are like, “Wait a minute. I can help make something like that happen?” How can people get involved in future science projects like this?
Dr. Gay: So, we have a whole lot of ways that you can get involved. One of the things that we’re doing right now is since we don’t have any really time serious citizen science, we’re doing a complete rebuild to make sure that we upgrade all of our privacy and informed consent check boxes, so that people know exactly what they’re consenting for us to do with their data. Your data will be published.
Fraser: “You will become sick of rocks.” Check. I agree.
Dr. Gay: Exactly.
Dr. Gay: So, if you want to help, join us on GitHub, CosmoQuestTeam. CSB7 is the repository. And, I’m hoping to start deploying, bit by bit, our new home in the coming months, starting with a: “Yes, I consent to have my real life name used in publications.” Moving through to generating new science with new worlds. So, join us.
Fraser: Yeah, the dream has always been that we can help build this platform that people can come who want to participate in science, without having to go and get the pesky planetary science degree, and can actually help out and get their name on a paper. And, it’s all coming together. So, I hope that everybody listening is as proud of you as I am for what you’ve accomplished with this incredible project and all the people who’ve worked on it. And, I encourage everybody to go to cosmoquest.org to sign up in one of the quiet times, when people can hang out and have contemplative conversations and you can look into the glassy-eyed stare of the people who’ve seen things, who have seen rocks –
Dr. Gay: Join us on Discord.
Fraser: – and prepare yourself for the future.
Dr. Gay: Yeah. Share the memes, share the dialogues, and let’s contemplate throwing rocks back at Bennu.
Fraser: Yeah, many hands make light work. On the one hand, red dwarfs are the longest-lived stars in the universe. The perfect place for life to hang out for trillions of years. And, on the other hand, they’re tempestuous little balls of plasma hurling out catastrophic flares that could wipe away life. Are they good or bad places to live? That was not a rhetorical question, Pamela. Tell me. Are they good or bad places to live?
Dr. Gay: It depends on exactly how old they are and –
Fraser: Okay –
Dr. Gay: – how much you want to live a nice, easy life. And, I think this is –
Fraser: Right. So, okay –
Dr. Gay: Yeah, we need to start with: What is it?
Fraser: Complicated answer? All right. Well, let’s dig into it.
Dr. Gay: Yeah.
Fraser: Okay. So, first, what is a red dwarf?
Dr. Gay: A red dwarf is a tiny star. We’re talking – these things are, on average, at least 40 percent the size of the sun, if not smaller. They do come a bit larger and, in fact, there’s a lot of argument over exactly where you draw the line at the top of what the size of a red dwarf is. At the bottom, these are the smallest objects capable of prolonged hydrogen burning via the proton-proton chain deep in their core. They are that thing just bigger than a brown dwarf.
And, what’s kind of amazing is the way these things process material. They’re effectively convecting just like a giant spherical lava lamp, and in the process, they’re mixing up their entire planetary – not planetary – they’re mixing up their entire stellar atmosphere all the time. So, all they ever do is burn hydrogen and they’re able to basically burn through all their hydrogen over trillions of years.
Fraser: Right. So, they are both slow and, at the rate that they consume the fuel in them – and they are also very efficient because they’re constantly mixing and they’re using every part of themselves, so that when – I guess – a red dwarf finally runs out of fuel, there’s effectively no hydrogen left. It used it all up.
Dr. Gay: And, they just sort of go, “Sigh.” And, instead of doing anything dramatic, instead of having a red giant phase or anything else that a bigger star might do, they just sort of collapse down to a tiny little white dwarf and they hang out unless they have a binary star that offers them the potential to do something dramatic. But, because they’re so long-lived, the only hope they have of doing something dramatic is to be captured into a binary late in life.
Dr. Gay: One growing up on its own – there’s no drama except when it’s a baby star.
Fraser: And, so, that efficient use of fuel, that slower use of fuel, these things live – as you say – for trillions of years. So, I think we can put that into the “good” category.
Dr. Gay: Yes.
Fraser: More time, more better. So, how are they bad?
Dr. Gay: Well, so, we have three things working against us with them. The least worrisome – I’m gonna go with – is they’re super cool. So, they don’t have that big of a habitable zone, and that habitable zone they have is snuggled up super close to the star, so you have to be in exactly the right place in order to have a nice, temperate climate. Now –
Fraser: Right. And, it’s a little worse than that because it is a habitable zone in that it is warm enough that you can have liquid water on your planet, but they’re bad photons.
Dr. Gay: Oh, yeah!
Fraser: Right? They’re far to the red end of the spectrum. So – I don’t know if you had read this – I saw a calculation of a woman saying that they have just a fraction of just the total useable – if there’s photosynthesis on a red dwarf world – they have a fraction of the amount of just available energy that plants have here on earth. Even though it’s still – thanks to infrared – it’s still warm enough that the water is liquid, but it’s this feeble, terrible photons.
Dr. Gay: So, the way to think of it is the light that you’re dealing with, is equivalent of being deep under water. And, so, just like some deep underwater plants have to adapt to deal with none of the happy, bright, whiter colored – or, I guess, bluer colored wavelengths. Even at the very surface of a world going around a red dwarf, you’re gonna be subjected to the very red colors. Now, the problem is, that’s not all you’re being subjected to. So, problem two with these [inaudible – crosstalk] [00:08:54] –
Fraser: That’s the least of your problems.
Dr. Gay: Yeah, we’re starting with the least of your problems and working our way worse and worse. So, if you are that close to your star, any lack of roundness in your planet shape is going to cause you to become tidally locked to your star. So, the same face of your planet is always facing your star. So, here I’m gonna do a turtle-turtle interaction because I have turtles. So, here we have large lava turtle pretending to be a star, so.
Fraser: For the podcast listeners, Pamela is holding a turtle made of lava.
Dr. Gay: And, then, here we have a small porcelain turtle that will be our planet. Now, clearly, planet turtle is not a circle. It is not a sphere. It is not symmetrical. And, this means that if it’s trying to rotate about the center of its shell, every time the excess mass that represents its head goes past, it’s gonna get pulled back. A torque is going to get exerted trying to slow its rotation as it goes past, and it accelerates its rotation as it gets toward. And, so, it’ll eventually settle in so that as it goes around our star, that head of the turtle – our gravitational extra bit – stays pointed at its star. Now, planets aren’t as asymmetric as turtles –
Fraser: Right, but still –
Dr. Gay: – but they’re asymmetric, which means –
Fraser: Right. And, we’re all familiar with this process, here in the solar system, with the moon.
Dr. Gay: Yeah.
Fraser: The moon only shows us one face. All of the major moons around Jupiter only show Jupiter one face. All the major moons around Saturn only show Saturn one face. So, this concept of tidal locking is inevitable for objects close to each other like this.
Dr. Gay: And –
Fraser: But, is that super bad?
Dr. Gay: So, this is where when you say “friend or foe,” frenemy is a thing.
Dr. Gay: And, we have a nice, friendly star. We’re able to maintain a day/night cycle, which really helps with the thermodynamics of things around here. Our daytime side of the planet does cool down at night and this does help drive weather patterns but, overall, it’s not that severe. We can all survive the jet stream and life is pretty good. Now, if you’re tidally locked, one side of your world is going to get dramatically heated up. The other side is not except through thermodynamic processes that carry heat from one side to the other side, by which I mean wind.
Fraser: Right, right.
Dr. Gay: And, so, these worlds are going to have extraordinarily powerful winds, and depending on the ratio of what they’re made of – so, a lot of these worlds, it turns out, are actually 10 percent water from what we’re detecting. So, you’re gonna have high humidity, moist worlds with massive water that’s going to have massive circulation in the water, massive circulation in the atmosphere, and models are showing that it should be possible to have a climate that’s survivable.
Fraser: Yeah, yeah.
Dr. Gay: But, you’re living in a hurricane.
Fraser: Yeah. I think, originally, the idea was one side is a parched, baked, death desert. The other side is completely frozen and there is this thin, little area right at the edges of the planet that are maybe livable, but there was a fascinating new series of climate research that came out of NASA. Did you see these simulations that they did of Proxima Centauri b? So, that one they ran –
Dr. Gay: That one I haven’t seen.
Fraser: Yeah. They ran planetary simulations of just what the environment would be like on Proxima Centauri, and what you ended up with was that the near side is a lot more like a jungle. You get a lot of evaporation. You get a lot of clouds. You definitely have winds that’s pulling that temperature around to the far side, but in fact, the whole side that faces the star is probably very habitable.
And, then, it’s on the backside – it’s something that’s very icy, but it’s Antarctica bad, not “never sees the light of the sun” bad. And, you get this transfer of energy that’s coming from the back to the front, but also, the cold side is helping to regulate the temperature on the front. And, so, it would be more like you’re living in a constant jungle on half of the planet and various variations as you get closer and closer to the sides.
Dr. Gay: But, with very limited surface. Ten percent water by mass?
Fraser: Well, it depends, yeah. Oh, yeah. That’s a water world.
Dr. Gay: Yeah.
Dr. Gay: And, they’re finding that a lot of these worlds appear to have densities consistent with 10 percent water by mass. So, yeah, water world with nasty churned ice bergs, and hot water at the hot spot, and it’s gnarly out there.
Fraser: Yeah. Like I said – these simulations – they took earth’s continents, they took water world versions, and they – you know those really beautiful simulations that show all the cool – almost looks like an abstract painting with all the little currents and –
Dr. Gay: Yes.
Fraser: They did that, but for Proxima Centauri. It’s a absolutely fascinating sort of simulation. It’s possible we have story about this on Universe Today.
Dr. Gay: And, we have forgotten to mention that that star closest to the planet earth, Proxima Centauri – as we’ve been implying without actually saying – is a red dwarf –
Dr. Gay: Red dwarfs are, by the numbers, the most common kind of star out there. So, figuring out if they can support life is figuring out if the most common kind of star out there is capable of supporting life.
Fraser: All right. So, just for people who are keeping track right now, the first one seems bad, but we have plants that can handle being underwater. The second one seemed bad in the beginning, but now maybe it’s not quite so bad. [Inaudible – crosstalk] [00:15:56] two things that are –
Dr. Gay: I’m gonna with it’s difficult.
Fraser: Difficult doesn’t mean impossible.
Dr. Gay: Yes.
Fraser: So, let’s go to the worst problem. This one could be a deal killer.
Dr. Gay: So, for the first billion years or so, during that period of time when planets are forming, when life is starting, when all the chemistry of building your atmosphere is taking place, during this long, important, early developmental phase in a solar system, red dwarfs just aren’t having it. And, they are undergoing massive magnetic field, rearranging events that are capable of removing entire atmospheres in one foul magnetic flare outburst.
Fraser: Yeah. If you take the worst possible flare that the sun can do, red dwarfs can do flares which are 100,000 times more powerful.
Dr. Gay: In the far infrared – sorry, in the far ultraviolet – they will undergo flares, where their ultraviolet light – this is ionizing light here, folks – is 193 times brighter than normal, and it only does this for half an hour –
Fraser: Yeah, and it can do these –
Dr. Gay: – but that’s one bad half an hour.
Fraser: Yeah, and it can do these multiple times a day. So, you’ve got flares potentially releasing many, many more times the amount of energy than the sun ever gives off, and it’s doing it all the time. And, each one of these events would easily scour away the ozone layer from planet earth – would take the atmosphere and take it off to space with it, and you’ve got these things happening all the time. And, this seems to be a really common occurrence for these red dwarf stars.
Dr. Gay: There’s a team at Arizona State University that have been doing a survey with the Hubble Space Telescope that is called the Habitable Zones and M dwarf Activity across Time survey, which is one of those forged together acronyms, because the way they abbreviate it – it’s the HAZMAT survey.
Dr. Gay: And, they’re just trying to figure out just how bad is it out there and they’re finding, like you said, it’s a 100 to a 1,000 times more powerful than anything that we have experienced here on earth. And, so, now you’re looking at a picture where during that first billion years, all of the nearby parts of these solar systems is getting irradiated, blasted, atmospheres are getting removed.
And, so, you have to figure out – after the stars calm down and settled into a more beneficial lifestyle – you have to figure out how to either migrate healthy planets inward, or you have to figure out how to repopulate these inner worlds with volatiles. We know know this happens ‘cause we’re seeing things, like I said, that are consistent with them being 10 percent water by mass.
Fraser: So, they get water. Yeah.
Dr. Gay: They get water, but the question becomes how then does life start? How does this happen?
Fraser: Yeah, the – I mean –
Dr. Gay: We don’t know.
Fraser: So, there was some recent research that showed, in fact, just how bad these flares are. They are pushing material out of the inner solar system like a snowplow, and you can actually see these flares and the coronal mass ejections, and the material that is flowing out of the red dwarf, and it is blobs of material just getting shoved out into deep space. And, so, as you said – right – you start with this nice, perfect environment – and the analogy that I like to use is you go to the store and you buy a dozen eggs, and you set it on your table, and you hammer it for an hour, and then you wonder how many chickens you’re gonna have. Right?
Dr. Gay: If you’re buying eggs capable of producing chickens, you have a different problem to deal with.
Fraser: So, it is just a terrible place in the beginning, but then we know that solar systems have a tendency to move things around. And, as you said, if they have all that water then it came back.
Dr. Gay: And, so, we just don’t know what is the composition, what is the viability, can you form life late in a solar system? If you can form life in a solar system, why don’t we still have new forms of life forming on earth? Well, probably because other things already ate those ecological niches.
Fraser: ‘Cause they were tasty!
Dr. Gay: But, it’s yet a new, ugly way to have to figure out how to form life, and we’re struggling to figure out how we got here in our nice, friendly solar system. So, it’s complicated out there. It’s really complicated.
Fraser: So, what do you think, then, is the best-case scenario here?
Dr. Gay: Wait, I lost –
Fraser: Did you catch that?
Dr. Gay: Yeah, yeah. I had a glitch for a minute. So, best-case scenario is after the star is done doing it’s “I shall irradiate all of you!” first billion years –
Fraser: Yeah. Yeah. You had your little tantrum, yeah.
Dr. Gay: – or longer, depending on its mass – how long it does this, depends – that somehow you end up with material infalling until it settles into new orbits within the habitable zone. Now, an object further out isn’t necessarily going to be tidally locked. The further out you are, the less likely you are to be tidally locked.
So, conceivably, you could have something spiraling in, getting angular momentum as it goes, grabbing it up from material it encounters, and starting out in that habitable zone with some rotation and a friendlier environment for life to get started. And, as that world slows down – just as our own earth is slowing down, but in a much more dramatic fashion – life takes hold and is able to continue evolving and changing to meet the special awfulness that is this kind of a situation.
Fraser: Yeah. If you dropped various forms of earth life into that environment – I’m sure if we just dumped cyanobacteria onto a world like that, that was warm, that had water, that was receiving some amount of sunlight, it would find a way. It would survive that kind of environment. So –
Dr. Gay: And, the best hope is life starting as we think could’ve happened here on earth. Around a subsea volcano of some sort and then evolving to meet the different and easier – in some ways – to survive environment with more and more sunlight towards the surface of the water.
Fraser: It’s kind of a fascinating concept to think about this idea that maybe the life did form around these volcanic vents and then you’ve got, say, 100 kilometers of water above you and it’s just an impossible gulf. And, maybe there could be some advanced civilization that rose up in this environment –
Dr. Gay: Of so much pressure.
Fraser: – and their idea of base exploration is to go higher and higher up through the water that they’re there – they’ve reached 10 kilometers above where they live and their astronauts are trying to make their way up to the surface. And, think about their concept. If they could reach the surface and look out into space and see the stars, and realize that they’re in a much wider universe than they had ever thought. It’s kind of a romantic notion. All right. Well, that’s your best-case scenario. So, flip it around. Hit us with your worst-case scenario.
Dr. Gay: So, worst-case is every time life starts to take hold on one of these migrated-in worlds, it gets blasted again with this radiation that the water that comes in from infalling objects is just the nastiest water out there, and it has the wrong ratios of chemicals to allow life. That everything is a special disaster of perchlorates. I don’t know if that’s a thing, but – well, I know perchlorates are a thing –
Dr. Gay: – I don’t know if [inaudible – crosstalk] [00:25:21] –
Fraser: Right, but you’ve got all this ultraviolet slamming into the top of the water –
Dr. Gay: Right.
Fraser: – poisoning it down below.
Dr. Gay: Yeah. And, we don’t know if our environmental models are correct. Now, imagine that as the world freezes, it ends up with some sort of a weird teardrop shape on the other side. That could create all sorts of weird eddies and patterns in the wind. There’s so much we don’t know.
We can’t even fully deal with our own weather here on the planet earth. How do we expect to be able to define the exact habitability of the environment of a planet that’s tidally locked, snuggled up to a star that has some sort of a weird chemical mixture in its atmosphere? And, the reason I say it probably has a weird chemical mixture, is after being blasted that much and not rotating, what kind of a magnetic field is it going to have? It’s gonna have to have an atmosphere of thick molecules. So, if you have life, it’s probably gonna have to be in that water because you’re not gonna have an atmosphere that’s necessarily breathable or thick.
Fraser: And, it’s times like this when I get sad that – probably not in our lifetime – but we see photographs of what these worlds would look like up close. We might have some hints of some ideas that – “Oh, Proxima Centauri? The best super-duper telescope told us that it’s probably got a surface that’s mostly water.”
Dr. Gay: I love the fact that you qualify that though and said “probably not –
Dr. Gay: – in our lifetimes.”
Dr. Gay: I am content to say we are not, in our lifetimes, going to see photos of the surfaces of –
Fraser: But, we all know that I’m gonna have multiple robot bodies, so.
Dr. Gay: That’s true, that’s true.
Fraser: Yeah. So, the jury’s out. Friend or enemy?
Dr. Gay: Frenemy.
Fraser: Frenemy it is.
Dr. Gay: It’s complicated.
Fraser: It’s complicated. Well, thanks Pamela. Do you have some names for us this week?
Dr. Gay: I do. I would like to thank – for making this possible through their patronage over on patreon.com/astronomycast – the following excellent human beings: Bruno Lets, Marco Rossi, Matt Rucker, Brian Gregory, Brian Kilby, Jessica Phelps, William Lower Jay, Alex Anderson, Brent Krynop, Omar Del Riviero, Tim Garrish, Dustin Ralph, Arthur Latts Hall, Joe Wilkinson Mark, Steven Raznack, Chad Collopy, Jeremy Kerwin, William Andrews, Nuderdude, Claudia Masteroni, Frederick Syorg, Paul Hayden, Joshua Pearson, and Jack.
Fraser: Right on. Thank you everyone for your generous support to help make Astronomy Cast even happen. Susie appreciates the salary that she gets and the server appreciates the electricity that it receives. All right, everyone. Pamela, we’ll see you next week.
Dr. Gay: Buh-bye.
Narrator: Thank you for listening to Astronomy Cast, a non-profit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at email@example.com, tweet us @astronomycast, like us on Facebook, and watch us on YouTube. We record our show live on YouTube every Friday at 3:00 p.m. Eastern, 12:00 p.m. Pacific, or 19:00 UTC. Our intro music was provided by David Joseph Wesley, the outro music is by Travis Surrell, and the show was edited by Susie Murph.
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Duration: 30 minutes