In this episode, we investigate the Goldilocks Zone, the area around a star where planets might have the right conditions for habitability, and we travel through the solar system to look for life outside Earth.

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Welcome to The Astroholic Explains and I’m your host, Chris

And I’m Alfredo, the Astroholic.

This is a podcast where I throw some cosmic conundrums your way,

and I try my best to answer them. Let’s get started!

Today’s question is a little bit of a two-parter, because I’ve tried to be a little bit smart and come up with something quite fun. But if my terminology is completely wrong, then it may screw up the entire question. In which case I’ve got a backup.

Can I take the Mickey out of you if it’s completely wrong?

I don’t think I get a choice in that.

Of course not. So go ahead.

Right. Okay. So up there in the sky at night,

So far, so good.

That’s great,

Although “up”…

..You’re not going to look down at the stars unless you’re upside down. Anyway, let me ask my question. In the sky up above us, we see Ursa Major, we see Ursa Minor, all of the bears in space. But today I want to talk to you about the Goldilocks zone.


It’s a nice little segue into that. I’m quite pleased with that. If it’s what I think it means anyway, so what I’m interested in is habitable zone in space, this Goldilocks zone.

Yeah, that is correct.

Not too hot. Not too cold. It’s just right. In terms of conditions for life. Tell us about that.

All right. Very good intro with the Ursa Major and Ursa minor since they are the bears. We need the third bear…

I couldn’t think of one.

Now, I will have to think about it. So the Goldilocks zone is this nickname for the habitable zone. Again, like all other classifications in science. It is limited by its own design and the design is “Humans”. So we think that the best places for life around the star is where water can be found in all its three states. So you have ice, you have liquid water, and you have water vapor in the atmosphere.

That’s really cool. I didn’t know it was to do with all three states. I mean, obviously there was a lot of talk on, you know, if there’s water, there could be life, but I didn’t know that other conditions were the three states.

Well, why is it important to the three states? And I’m asking you.

I’m not the Astroholic. This is the Astroholic Explains, not Chris explains!

All right. Well, the importance of the three states is that they’re crucial to the water cycle. So water… you are making a weird confused face… you should know the water cycle probably from primary school or GSCE.

Let’s not go there…

Okay, water moves around the planet and evaporates and forms clouds, which are also up in the sky.

And then the clouds that float over the pointy mountains are ripped open [he doesn’t really believe that.. anymore] and then there’s rain…

Rain and snow and form ice and glaciers, although, I don’t know, maybe by the time you listen to this podcast, there are no more glaciers… who knows nowadays. Then the water goes from the mountains to the sea, in rivers, etc. And that is important because you’re not just moving water, you’re also moving minerals and nutrients and life itself.

I never thought of it that way.

Yep. Other things that might be extremely helpful for life is volcanism and volcanic activity because something like geothermal vents have a lot of complex chemistry. So if you have hot springs you have complex chemistry!

I know that a lot of people think that anywhere where there are hydrothermal vents like underwater smoking volcanoes, or underwater smoking chimneys as they call them, they are teeming with life on Earth.

If you don’t know, Chris is a little bit of a nerd when it comes to the deep ocean. He hates getting into the shallow oceans but…

I would never go in it but it fascinates me!

So there are these phenomenal videos of hydrothermal vents at the bottom of the ocean, and you can see that they are like surrounded by so many life forms. And there are some bacteria that can survive inside at temperature of perhaps a few hundred degrees. I can’t remember exactly. These are called extremophiles. So there are bacteria that can survive these borderline impossible conditions, but life, uh, finds a way.

They’re not dinosaurs.

No, they’re better! Anyway back onto the habitable zone. So we assume that since for us, the best thing is the water cycle that’s what we need on exoplanets. So when we look at exoplanets, we have a range of the possible distances where the light of the star is enough to produce a temperature on the planet which would allow water to be in all three states.

Okay, so mostly what we’re interested in is the liquid water part; because it is further out, you will definitely have ice. There is a thing around the star system and even in our solar system called the snowline. And if it’s too close, you could have gaseous water vapor atmosphere. You want to be right in the middle, hence Goldilock.

So is that a perfect approach? No, there is a lot that we don’t know and understand about life. And it’s a very arbitrary life zone, but also as a limitation when it comes to planets because we’re seeing so many different exoplanets…

All within the Milky Way? Have we ever seen a planet outside the Milky Way?

I think that was possible detection around a pulsar in Andromeda. But now I don’t remember.

That’s amazing!

But I don’t remember so let’s assume that no, we haven’t seen them.


But we have a lot of planets within the habitable zone of their host stars.

Like the Trappist-1?

The Trappist-1 system has three planets there. So that is a red dwarf so much smaller and much dimmer than the sun, and it’s got seven planets, all of them are roughly the size of the Earth and three of them are in the habitable zone. But it doesn’t mean that they can support life. Habitable zone is a good place to start. But there is so much more that you need for a habitable planet. You need atmosphere, likely you need a magnetic field, especially Trappist-1. Something that’s making researchers question the possibility of life is although the star is smaller and dimmer than the Sun, the planets are much closer and its surface is a lot more active.

More radiation?

Yeah, like x-rays, solar flares, well star-flares. Yeah. So, magnetic storm and everything. If the planets don’t have a strong magnetic field like Earth does, they would end up losing their atmospheres, just like Mars did.

Coming back to the solar system briefly, sorry, is there anywhere else in our solar system that could support life theoretically?

Possibly. Let’s first set with the Goldilocks zone in the solar system. It’s roughly from Venus to Mars. But Earth is the only habitable planet. In the solar system, there are three possible places where life could be Well, these are the frontrunners… There’s Mars; we have some circumstantial evidence that there might be life underground.

Actual Martians!

Actual Martians! Though instead of little green people, they are probably bacteria or very simple life forms.

This is actually something else I was going to ask you as well is, what do you think other life in the universe could look like or may even be likely to look like? Are there infinite possibilities?

Not infinite possibility, but a lot of possibilities. Let me finish on the solar system first, though. The other two places are the moon of Jupiter, Europa and the moon of Saturn Enceladus. Both of them are icy moons with deep oceans underneath the ice crust and there is hydrothermal activity on both of them. Missions are being sent there to investigate. A mission to Europa is now in the works.

Wow, when is it expected to go?

I think late 2020s…

That soon? That’s just like 10 years. I mean that’s still really soon.

I didn’t know.. I want it like yesterday so… 

But the outer solar system is further away so missions are a lot more complicated and sending something to Mars that can arrive in seven months. Although we still have missions that failed because it’s very, very difficult to send something and make them land on a different planet. And I don’t think that the Europa mission would be landing. I think the plan is just to try and work out potential life signature using the emission from its geysers; from the materials that are released by the moon and so capturing those particles and try to work out what’s in it.

Oooooh, okay! Yeah, my idea for that would have been they just send something over there and like smash it through the crust into the the waters beneth the ice, but I don’t know… Is that not a good idea? You’re making a face and that tells me it’s a terrible terrible idea!

Why is it not a good idea?

Well, I would guess that sending something all the way over there just to smash it into the surface could result in destroying itself and being wasted mission anyway.

That is very good from a technical point of view…

If there was something living under this smashing through might scare it away and you wouldn’t see it… Or contamination!

Contamination is the right answer: Prime Directive

Prime directive… I suppose. What if rather than smashing it like that though, if they landed something on the surface and drill through and then put a tiny little probe would that be the same?

Until we work out how to make things really, really sterile (and we’re still not there) we shouldn’t be doing those kinds of mission, okay? But there is a discussion on how it is likely that contaminations from Mars and Earth might have reached the outer solar system moons already.

Contamination from Mars?

And Earth. Like we know that there are Mars asteroids and there’s been a long discussion if we saw ancient bacteria in these asteroids are not.. they look a bit like bacteria but they’re not the right size are much smaller than Earth’s bacteria… Are they bacteria or are they something else or are they just weird rock formations? We don’t know. 

Give it time, I’m sure you will see headlines of microplastics found in alien life…

Well, we are already contaminating and polluting the solar system. So when major impacts happen, material is thrown into orbit and calculations have shown that some of these rocks can reach the outer solar system moons. So is Earth biologically isolated? It’s a complicated question. So if we get to Europa and Enceladus and we detect bacteria that have similar approaches to how they work as Earth’s bacteria, that would be very interesting. And I think it would be as equally interesting if we get there and we found life and does something completely different from how it works on Earth. Both have very, very important implications.

So that allows me to answer your interrupty question which was “what is in life going to be like?” and sincerely, who knows? Anyone who tells you, it’s always going to be like this, doesn’t know. We don’t know. It’s complicated.

Carbon life forms?

There are ideas like could you have a silicon-based life form? Silicon doesn’t form long chains like carbon does So, carbon-base is probably still very likely. But maybe there’s something that we haven’t quite discovered yet. Carbon is also a lot more abundant. So, carbon makes sense. Structures like DNA makes sense. But they’ve recently shown that you can have eight bases DNA, they’ve created this artificial DNA. That just works fine. Instead of having the standard four, GACT bases, you can have eight bases and it still works fine. So, maybe something DNA-like but not DNA as we know it. It’s complex and complicated. And we cannot say “oh, this is what it will look like.” And they might be humanoid or they might not be humanoid,

Likely to be tiny little cells?

Likely to be tiny little cells,

Or equally as likely to be some giant monstrous alien that’s going to eat everyone?

We tend to be the giant monstrous aliens that tend to eat everyone. I don’t know. It’s just… everything is complicated. But yes, if we consider that the most prolific life forms on a planet, they are very simple organisms, then the most likely thing that we’re going to encounter in space anytime soon is another microorganism rather than some gigantic, monstrous overlord.

Well, that’s probably for the best, at least I’d hope anyway. So thank you very much for answering my alien based question today. I hope you had fun!

I always have fun and you’re very welcome!

Do you have any burning questions for the Astroholic? If so send them into me out @illucifer on Twitter, and I will spring it on him in an upcoming episode. See you next time!

Image Credit NASA