We are answering more of our listeners’ questions in this episode. Jake wonders: how come all the planets in the solar system orbit almost on the same plane? And the answer has a culinary analogy!

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Chris
This episode’s question comes from @BlueMouseEeek on Twitter, who asks: “My four year old is space obsessed. He wants to know how far away the closest planet is that could support life. I’m not kidding, this boy knows about dwarf planets, exoplanets, gravity makes the solar system in Lego playdough Minecraft.

Alfredo
Well, that is a great question. And my sincere answer is I wish we knew. As far as we know, there’s only one plant that can support life: Earth. I’m not saying there are no other planets out there in the universe. We just haven’t found them. We’ve seen a lot of planets that are in the habitable zone, which we have explained in a few episodes, the region where life could potentially exists, or at least where we expect liquid water, ice and water vapor on a planet. But we don’t know if any of those planets have all the other aspect to all the other characteristics that could make a planet habitable.

Chris
A couple of years ago, there was a star system found and I can’t remember its name now. I don’t… It wasn’t Proxima… It was…

Alfredo
Proxima is a good example. Proxima has two planets, now confirmed. One is a gas giant and the close one is a Earth-sized rocky planet in the star habitable zone. Proxima Centauri is are red dwarf so much smaller than the Sun, the planet orbits in just a matter of days…

Chris
TRAPPIST!

Alfredo
TRAPPIST!!

Chris
TRAPPIST!!!

Alfredo
the TRAPPIST-1 system

Chris
When that was discovered, there was one of the planets there’s 1, 2, 3, 4, 5, 6… 7 planets in the TRAPPIST star system.

Alfredo
Yeah, TRAPPIST-1.

Chris
And one of those was touted for a possibility of well, being habitable or having life because of its conditions.

Alfredo
I think three of them are in the habitable zone.

Chris
What is sorry to go off on another tangent, but what are the first three things that astronomers would look for that might suggest life on a planet?

Alfredo
So at the moment we are not able to find those characteristic, but let’s assume that we are a few years down the line. There is the Extremely Large Telescope, which I know it’s a very unimaginative name, but is going to be a revolutionary instrument in studying the universe. There is the James Webb Space Telescope, you might think: “Oh, at least this is an original name”. Yes, named after a homophobe. misogynist, racist. Yeah. What can you do apart complaining?

Chris
That telescope never gonna come out anyway.

Alfredo
Yeah, it was supposed to be launched a decade ago and then as had a very, very long gestation. So those kind of instruments, the next generation of observatories should have the capabilities to study the atmospheres of these exoplanets. And this is how we are going to find the closest habitable planet to Earth. What do you need to look for? You need to look for an atmosphere, a planet that can support life. And again, we are assuming life as we know it; there might be life completely different from us out there. For life as we know it, you need a thick atmosphere. And this is why for those planets like TRAPPIST-1 or the one around Proxima, we’re a bit uncertain. We’re thinking they’re very unlikely that the might have atmospheres because red dwarfs a little smaller than our sun, they are a lot more active, they produce a lot more flares. And since the planets are a lot closer, those flares might be eroding away the atmosphere.

Chris
It could just be a star system of Mars’s.

Alfredo
Yeah. What you need to have to guarantee an atmosphere then is a magnetic field; the magnetic field will protect from the flaring of the star and also from cosmic rays etc. Giving more chance to the molecule of life to evolve. Let’s assume that we have this atmosphere what can astronomer look at in the atmosphere and they’re looking for signal that are categorically life. They call it the bio-signatures. By setting the atmosphere of this planets, they hope to just get a glimpse of what kind of chemicals, what kind of compounds are present in the atmosphere of the planets. So something that has strong link to life could be methane, could be carbon dioxide.. Oxygen clearly is important for us

Chris
A little bit.

Alfredo
Yeah, not about before the first photosynthetic organism evolved on earth, life on Earth didn’t use Oxygen. Oxygen is toxic. Then first photosynthetic organism appeared and 98% of all species went extinct because of these primordial algae. Technically, what we do with oxygen is a very, very slow combustion. In a way we are fire breathers.

Alfredo
It is like we are breathing something that just burns, and we use it to burn molecules but it’s the same reaction. If again, we’re assuming habitability and life is like us, we expect a planet that has oxygen but we cannot have like an atompshere of pure oxygen that is too reactive. So, you need a nice element that keeps it quite stable like nitrogen. So, again that you were looking things based on earth is the place that we know life exists life works and life thrives. So, habitability should be like us. And this on similar topic about defining the spectrum is why it is so difficult to go and explore other places in the solar system, because they are so incredibly inhospitable.

Chris
What’s the most inhospitable planet in our solar system?

Alfredo
That you could stand on?

Chris
Um, yeah..

Alfredo
Venus.

Chris
Not mercury.

Alfredo
Nope. Venus is hotter.

Chris
Oh, also there is acid rain…

Alfredo
And on the ground is I think 94/98 atmosphere.. in the 90s, o it’s like being

Chris
..crushed.

Alfredo
Yeah.

Chris
Wow. Wait, doesn’t it rain diamonds on Venus?

Alfredo
No.

Chris
Where does it rain diamonds?

Alfredo
Different planet. We think the atmosphere of the ice giants, so Neptune and Uranus, should be dense enough at the certain level to crush carbon into diamonds, which will then rain down towards the core of the planet.

Chris
Diamonds are carbon right?

Alfredo
Diamonds are carbon, yes.

Chris
I know a lot of sci-fi delves into the subject of an alien life that is not carbon based.

Alfredo
Very good, that was a very good segue from the diamond rain, well done.

Chris
Are there any planets in our solar system where silicon is abundant apart from Earth?

Alfredo
Damn it, because I was about to say you’re standing on it. Silicon is an extremely abundant element everywhere.

Chris
Do you think that’s why sci fi tropes tend to go for a silicon based life form that’s different from ours.

Alfredo
That’s not the reason. I think we need to go back to your GCSE in chemistry [Dun-Dun-Dun]

Chris
No, that’s not go there

Alfredo
Well, I’m afraid so. So let’s open another chapter of Chris’s

Chris
dark past of science education in Welsh.

Alfredo
How do you say silicon in Welsh?

Chris
Silicon.

Alfredo
Okay, how do you say bond in Welsh?

Chris
Bondio ionig is ionic bonding,

Alfredo
okay, can carbon form ionic button?

Chris
Yes.

Alfredo
No

Chris
Damn. One question.

Alfredo
So carbon is group four of the periodic table. And silicon is also group four.

Chris
Ah, so is that why? So? Is that why scientists sort of say it’s the same sort of chemical? Well, the building blocks.

Alfredo
Yes. So what is interesting about carbon? What do you remember? About covalent bonds?

Chris
I really, really, really don’t remember much. To be honest. I was not a fan of chemistry. It did not agree with me. I don’t know.

Alfredo
Okay. In a covalent bond, he atoms shared electrons. elements in group four can form four bonds because they have four electrons on their outer shell. So they can form bonds with four different atoms. They can form double bonds, they can form triple bonds,

Chris
which I’m guessing is is good in general because it means it can grow it can be bigger it can have more chemicals attached to it.

Alfredo
They’re very good at forming chains.

Chris
Yes. So proteins,

Alfredo
Like proteins, or DNA, etc. Carbon is very versatile. I would assume that at four they are gonna make him listen to this episode, but carbon is the slut of the periodic table. It’s there ready to party, want to make friends and like a good slut, those friendships lasts, those bonds can be strong. And has a big network of concrete a big network of sluts, sort of thinking. Oh, we can do the same with silicon, silicon is the same. But given that silicon is heavier, as a lot more protons and neutron in the nucleus of the atom, and more electrons, but again, only four on the outer shell, it form the same amount of bonds, etc. The chains are building not to be as strong. So, it is a fascinating idea. There are things like self-replicating silicon molecules, but not in the same way as DNA, for example. It is very, very cool thought experiment, but there’s not been any evidence to suggest that that you can have a silicon based life form. But as I say, never say never. It’s we haven’t found, I think, any strong evidence that the life is just like us. We just need to assume, given that we only know one example of life, that the way we work is a good model. So it’s the weird balancing of “we’re very special. We’re the only one!” and “we need to pretend there were not special because there is no reason why we should be special.”

Alfredo
This is why it is quite likely that the blueprints to make us “us” are shared across the universe.

Chris
That’s a fantastic note to end on.

Alfredo
Fantastic. I’m sorry that I cannot pinpoint a location in the galaxy where there is an habitable planets, but I’m hoping that maybe in a few years time, post 2025 and the ELT coming online, we might have a better idea of where to look at least.

Chris
Thank you very much.

Artistic Impression: The Surface of TRAPPIST-1f
Illustration Credit: NASAJPL-CaltechSpitzer Team, T. Pyle (IPAC)