A comment on a facebook post I put up a few days ago got me thinking about habitability. Moreover, I got to thinking about the parameters of habitability.
We think that life here on earth is fragile, holding on to a thin silicate crust within a fairly narrow range of temperatures and conditions. For the most part it is. Life needs a fairly stable environment in order to keep on keeping on. However, there are plenty of examples of oddballs: extremophiles, that seem to do quite well in some pretty horrible places. The recent discovery of Antarctic microbes that derive energy from air itselfexpands the catalogue of organisms that could have analogues on other worlds.
Now, extremophiles do well in extreme environments. No brainer there, and there is no shortage of extreme environments in our solar system alone.
Venus is an example, and a good one. Analogous to Earth in size, density, gravity and composition, it differs markedly in others. No magnetic field, no water (at 0.002% of the atmosphere not worth mentioning), surface temperatures that melt lead, and atmospheric pressure ninety two times what we’re used to here. It’s horrible.
No plate tectonics. On earth we slowly sail about the globe on slabs of continental crust, which happen to be more buoyant than the thicker, denser oceanic crust. Driven by convection of magma in the mantle, crust is slowly pushed hither and thither by tectonic processes such as seafloor spreading.
To understand what this is, imagine a pot of something thick like soup or porridge on a stove top. As the contents of the pot heat up they begin to stir. Have you ever noticed when this begins to happen that as the surface begins bubbling the top layer is forced aside as new material wells up from below? This is seafloor spreading in a nutshell. Magma from within the earth wells up, heated by a radioactive core, and pushes the seafloor aside as it breaks through, forming new crust. The continental plates, perched atop this moving crust, slowly journey across the planet.
Why is this so important to life on Earth? Because our planets interior is so hot, plate tectonics (along with volcanism) is the primary means by which excess heat is released over time. If this didn’t happen, well, you wouldn’t be here reading this and there would be two Venuses in our solar system instead of one.
For reasons unknown, Venus shut down. It’s core stopped spinning, it’s magnetic field dwindled to nothing and radiation from the sun began a process of stripping the planet of water. Water is a true miracle ingredient. Not only is it a solvent for biological processes, it’s also a lubricant for plate tectonics. Venus seized up and overheated: exactly like a car without oil will do.
A stagnant lid world is one which has no plate tectonics. Climate is seriously affected by such a situation. With no means of escape, heat builds up within, and eventually it becomes an exo-Venus: scorching hot.
Researchers looking at the issue of habitability on exoplanets have looked at the implications of a stagnant lid regime for the possibility of life. Whilst it would obviously be different to life on earth, other factors can lend habitability to a planet.
These other possibilities are exciting indeed. I’ve been exploring astrobiology through images, producing a bunch of pictures. They will be appearing over the next few posts, so I hope you enjoy them. They’re doing well on Instagram!
Thank you for reading the ramblings of a space nerd. The universe is just too intetesting to ignore.
It’s been estimated that a good percentage of planets beyond our solar system may be water worlds.
We here on mother Earth like to think of our blue green marble as a water world. Indeed it is watery, and water is pretty much the reason anything lives here at all. That’s why astrobiologists naturally seek signs of water on exoplanets. “Follow the Water” is a central tenet in the search for extraterrestrial life.
But compared to some worlds, earth really isn’t that waterlogged at all. It’s 0.002 percent water by mass. Only a tiny fraction of that water is available to terrestrial life. That water which isn’t directly involved in biological processes is linked to them, linking life to the planet via seasons and climate.
Some exoplanets are believed to be up to fifty percent water! These are true ocean worlds. To date, up to thirty five percent of exoplanets larger than may be covered by vast layers of water that may or may not harbour life. The jury is well out on that, but the idea is intriguing (and tempting) as the traditional definition of habitable zones is being stretched and reinterpreted.
For now, we have only our imaginations with which to explore these worlds…
The universe is turning out to be a more interesting place with each passing day for me. It’s not all about reading research articles and trawling the internet for interesting news in the vast field that is astrobiology.
I’ve been working on images related to various themes in astrobiology. This field really is a playground for the imagination, and it has something for everyone….
Something really special here: possible traces of limestones found in the fragments of objects orbiting a nearby white dwarf star…
Differing definitions of the Habitable Zone further push the limits of life in the universe..
Svante Arhenius, a swedish chemist and early pioneer of the theory of panspermia..
Ruminations on the code (codes?) that make life possible. How many languages does life have in the Universe?
Does the chemical rich, pitch black seabed of Europa host life? Does that of Enceladus?
The first image I created. I hope you’ve like these. There will be more! By the way, the background for this image comes from an online simulator called Goldilocks, by Jan Willem Tulp. His work can be found here. It’s really cool.
It’s a story that began 20000 years ago, and has been waiting for you. Like something out of a “Star Trek” episode. The vista before you hangs in the black like a portal into the fiery underbelly of all that’s good in the Universe.
“Star Trek” You remember it now. The Battle of Wolf-359. It was a classic episode, in which a tattered human military force took on a vastly superior foe: the Borg. These creatures were bloodless and implacable. Truly unsettling bad guys.
This monster is just as unsettling. Wolf-Rayet-124 is real. It’s huge. You’ve come a long way to encounter it. A small fleet of drone-sats has been dispatched to get up close and personal with this Wolf-Rayet star, to see how extreme extreme sports can get.
As soon as humans got comfortable in space and started calling all kinds of dark corners and odd rocks home they were up to their usual mischief. As soon as all the laws were decreed and the soapboxes were all put away, humans got back to the serious business of finding new and bizarre ways to enjoy themselves.
Space tourism didn’t become big business. It became exponentially big business. Extreme sports fans weren’t interested in scuba diving with great white sharks anymore, or parachuting.
Ha! You recall the stories. The One-G-ers were those quaint old extreme sportsters who couldn’t let go of old mother earth. Most of them were toothless and half nuts decades ago, but they still harped on about climbing Mount Everest or wrestling crocodiles.
You look upon Wolf-124, blazing with a luminosity several million times greater than Earths sun back home. Wolf-124 is huge. How huge? These kinds of stars are rare. Of the millions of stars known to humanity only around 500 Wolf-Rayet stars are known to exist in this galaxy.
Wolf-Rayet stars are thought to be the powerhouses driving many planetary nebula or stellar nurseries. How does this work?
Your little drone sats are tasting the cloud of ionised gas and interstellar gunk that swirls around the star. This cloud is nearly 6 light years across; a dusty miasma flung outwards by the intense solar winds radiating from the star within. From your vantage point out here, looking down into this slow maelstrom you see chunks of the star heading outward. Earth sized pieces of WR-124 soar through the cloud like the volcanic rage of a demon tearing itself apart.
You write that last line down. The tourists will love it.
Sometime around 20000 years ago, when human beings were first discovering Europe WR-124 began tearing itself apart. Scientists never really ascertained why, but it’s made for some great observations over the years. Tourists will love this. You got here first, to set up the first fleet of solar sailing yachts. The winds from the star crack along at 1600 km per second, fast enough to twist the most iron stomachs.
These stars have unusual emission spectra. Many of the space tourists won’t care what this is, but there’s always someone in every group who just has to understand what they’re leaping into. Fair enough. What it means is that like any other star a Wolf-Rayet star burns up fuel. Our star, a relatively youthful star somewhere near middle age, is still burning hydrogen via the process of stellar fusion. As a star ages it’s supply of hydrogen becomes depleted, and it must burn heavier elements in order to survive.Wolf-Rayet stars are often seen to have high levels of quite heavy elements or “metals” such as carbon or nitrogen in their upper atmosphere. This is due to nearly complete depletion of hydrogen fuel so as a result heavier elements are being used up.
What does this have to do with spectra? Well, as elements transition from higher to lower energy states, ie when they’re being burned up inside a star, photons of particular wavelenghts are given off. It’s possible to tell just by analysing the wavelengths of light radiating from a star (it’s emmision spectra) what’s going on in and immediately around the star. This is why scientists know WR stars are old, and what they’re burning off in place of hydrogen. It’s also the reason they can infer the presence of extreme solar winds. The luminosity and heat given off by a WR star is extreme. At it’s surface a WR star can reach temperatures of between 30000 and 200000 Kelvin; hotter by far than most other stars. Such radiative pressure literally manifests as a “wind”, with the abilty to exert pressure on objects, such as solar sails!
Most of the drone sats are keeping a safe distance from WR-124. This might just be an imaginary blog post, but you have imaginary operating costs, you know?
So you’ve staked your claim here. Now, all that’s left to do is wait for the money to fly in!
Still, you’re thinking of your next venture. There’s an exoplanet out there somewhere: HD 189733B where it rains glass! Now that sounds like fun…..
While you’re here, join me on the AstroBiological YouTube channel. I’m hard at work sprucing it up. What do you think of this intro sequence?
One last thing!
Hop onto WeCreateEdu: an online community for educational you tubers. There is a galaxy of stuff to learn and explore here. Very much worth a look:
Hi all. It’s been a while I’m ashamed to admit. I’ve been working on a new Facebook group to raise the profile of my channel. It’s been fun. Here is the link (hint: join the group!)
Here is my newest video. A basic breakdown of what exactly the Goldilocks (or circumstellar habitable) zone is, and it’s importance to life on Earth. If you like the channel please subscribe!
I’ve also provided the script/transcript for my upcoming episode of “Astro-Biological:”, which introduces us to the concept of the Goldilocks Zone….
G’day! Welcome to Astro-biological:!
Ben what the heck are you talking about? What’s the connection?
Let’s go check out THE GOLDILOCKS ZONE!!!!
Life, as I like to remind you, is really special. Here on earth, life exists only because certain conditions are met. Today, we’ll consider water. Everything needs it, but it only exists as a liquid at the surface here on Earth.
So? Big deal right?
Well it is actually!
Check out the sun. Giver of life! Driver of climate! Pumping out some pretty respectable energy. How much?
1 yottawatt equals 10 with 26 zeroes after it!
Brutal! And the sun is a pretty average star! Nothing special about it!So there’s plenty of sunlight for everyone!
Could other planets benefit from the sun’s golden goodness the way we do? Let’s take a look at the inner planets. They’re the only ones that really matter in all this…
Let’s see…Mercury, Venus, Earth and Mars. The rocky planets. The so called “Terrestrial Planets”.
Mercury is 58 million kilometres from the sun. That’s really close. This close proximity has turned Mercury’s surface into an oven, where liquid water couldn’t possibly last.
Let’s visit the next in line: Venus. Venus is similar to Earth in composition, gravity and size. Long ago Venus might have had oceans just like Earth, but again the planets closeness to the sun and other factors saw all that water disappear into space. Venus is now the hottest place in the solar system. Definitely no liquid water there anymore!
Wanna know more about what happened to Earth’s twin? This guy I know made a video!
Earth! Beautiful Earth. Our home. Every thing’s home actually. Eighty per cent of earth’s surface is covered by liquid water. There’s so much spare water here that our bodies are mostly made up of it! It’s absolutely everywhere, even locked up deep in the earth’s crust! Enough of earth. We’ve all been there.
Next planet out:
Mars. The cool planet. Every one wants to go here. Pity it’s so cold! Liquid water may exist here in tiny amounts, but most of the red planet’s water is locked up as ice or permafrost just below it’s surface. Plenty there for future colonists to use, but nothing readily available for biological processes. Pity. It’s a beautiful planet. Just ask Matt Damon!
So what is the Goldilocks Zone then?
Here’s the inner solar system. Mercury, Venus, Earth and Mars. Let’s visit a special guest who can explain the Goldilocks Zone for us…
ChefBenbit. (Watch the video when it’s up!)
Nice work Chef! So, if Earth was a bowl of porridge it would be the one Goldilocks ate: the one that was just right! it’s that simple! Earth is lucky enough to be at the perfect distance from the sun, where water likes to slosh around in liquid form. Things would be a lot different here if that wasn’t the case.
So that’s it for now! A simple but important piece of information. The Goldilocks Zone!
How am I going so far?
If you thought I was alright, then subscribe for more. If you thought this video was useful to you, then give it a like! Likes help this channel get noticed. That little notifications bell is just the thing if you want to see more. Go on. You know you want to.
Thanks for watching astrobiological. Giving you the universe in plain human. Ciao!
There’s an old theory known as Panspermia, which hypothesises that life got its initial leg up on Earth (around 4-3.5 billion years ago) after a long journey across space. According to this theory, (which at the very least is quite reasonable) the ingredients and precursor molecules for life hitched a ride on comets and asteroids and reached earth early in its history, when these objects impacted our planet. As for where these molecules and ingredients came from…well, that is a real chicken and the egg type question, and one I will be exploring in more detail in future posts as well as videos.
Not all astrobiologists agree with this of course. Each to their own. Science and seeking the truth is all about disagreement. I’ll leave the debate alone and for the purpose of this post assume that Panspermia is a pretty valid idea.
This post (and the YouTube video it will eventually give birth too) is essentially a piece of speculation. Looking into the future of space exploration, what is waiting for us out there?
Europa has been the hearts desire of many an astrobiologist for decades now. Ever since the Pioneer 10 probe rushed past back in 1973 and sent back the first pictures it’s been a bit of a rock star. Why? Because it ticks a whole lot of boxes on the “Things could live here because…” checklist.
Things could live here because….
Let’s look at some of those boxes. And why they’re important. First of all:
1: Europa is now widely believed to harbour a substantial subsurface ocean: of actual honest to gosh water. How have we come to this conclusion?
Take a look at the surface of Europa.
It sure is striking. Huge channels and streaks criss cross the moons frozen exterior.
And that’s about it.
No craters? Callisto is part of the Jovian family as well, and is the most heavily cratered object in the solar system. Compared to Europa Callisto is a teenager with weapons grade acne.
Europas surface is geologically new, having been resurfaced recently (in geological terms). Something is wiping the slate clean on Europa, and this is our first clue that Europa is special. Something under that icy shell is acting upon the surface and rearranging it.
Astrobiologists think it’s water. A lot of it. Europas surface is basically a shell of ice, rafting and fracturing like pack ice on Earth. Essentially vast swathes of pack ice remodel the Europan landscape and are thought to be it’s version of our plate tectonics.
2: Some time ago, none other than the venerable Charles Darwin postulated that life began in a “warm little pond”, whereby the right combination of mineral salts and energy resulted in the first biomolecules. Ever since this first speculation, forwarded in a private letter from Darwin to his friend Joseph Hooker in 1871, science has placed an emphasis on water as the likeliest birthplace of life on Earth. Darwin believed in a warm little pool, many other theories have thought bigger, fingering the ocean as the culprit. Whatever the case may be, and whatever supporting evidence gives testament to it, water (for now) is the one thing no life can exist without.
And Europa has a lot of it. The deepest point on our planet lies at the bottom of the Marianas Trench, some 12 kilometres below sea level. That is deep to be sure, but the abyssal plains of the world’s oceans are on average about 4 kilometres beneath the waves. Europas subsurface ocean averages a cold dark 62 kilometres deep!
Where do the minerals fit into this? Patience, grasshopper!
Jupiter pumps out extremely high levels of electromagnetic radiation. This is, of course, a constant engineering hurdle for the various missions that have paid the gas giant a visit. It’s extensive family of moons: some 67 in total are constantly immersed in this field, which interacts with various bodies in various ways. Europas magnetic field is no different, and is an induced magnetic field. This is a special kind of magnetic field produced when an electromagnetic field is passed through some kind of conductive material. In the case of Europa this material is believed to be an ocean, brimming with conductive mineral salts. Such an ocean would be a vast salty brew, fulfilling Darwin’s vision somewhat.
What of Darwin’s energy source? To understand this a little more, and to see what it means for Europa, we need to understand that all life requires an energy source. On Earth, the vast majority of life is solar powered. What does this mean? You can’t just go outside and photosynthesise! You need to go to the fridge and get a snack. Food keeps you going, right?
Absolutely. But where did that food come from? Whether you’re a vegetarian or a carnivore, ultimately every single thing in that fridge of yours exists because of the sun. Either it grew from the ground, something came along and ate it, or something bigger came along and ate that something. The sun is at the base of this very simplified food web, and it’s been doing it forever of course.
No solar power is not some fandangled idea. Renewable energy has been around, well, since before life began. The sun provides energy not only for Earth’s climate and hydrological cycle, it also fuels all photosynthesis on Earth. Plant life not only provides food and oxygen for animal and fungal life, it also contributes to climatic processes. Yes, the Sun is really important.
Ah, you think, how does any of this relate to Europa? The frozen moon is a bit further out from the sun than warm little earth, at about 485 million kilometres. Not much use for solar power out there! Well it turns out that not all life on Earth is completely dependent on the Sun after all.
These are exciting and mysterious places, home to a bewildering and diverse array of lifeforms. They are found where life seemingly has no business existing, and yet there they are: on the vast abyssal plains of the ocean floor. Miles away from any sunlight, subjected to pressures and extremes that would kill us instantly life thrives in a hostile alien world.
These ecosystems are based not on photosynthesis, whereby sunlight is converted into a food source for plants, but chemosynthesis. Down here life has found a way, to steal a phrase from “Jurassic Park”. Literally, bacteria have evolved to survive at the hellish temperatures and pressures around these hydrothermal vents, where the water can reach temperatures of over 350 degrees Celsius. With nothing but a rich mineral brew spewing from these vents out onto the ocean floor, these bacteria have learnt to make use of this brew. These bacteria then form the basis for some of the most intriguing ecosystems on the planet. These vents are an oasis of life, all alone in the abyssal night.
Does Europa have the capacity for such vents, far beneath the ice? On Earth, the vents are geothermally heated. Earth posesses a core of molten iron, heated by slow radioactive decay of elements from the formation of the planet 4.6 billion years ago. This internal heat eventually reaches the upper mantle of the planet, seeping through in more threadbare regions of the Earth’s crust, Europa is heated by Jupiter itself. As the moon orbits the gas giant, tidal forces act upon it, squeezing and massaging. Resulting frictional forces are believed to sustain a heated core, which, just like earth, could provide energy to keep systems of hydrothermal vents running on the abyssal plains of Europa.
So. Europa may tick some really important boxes, for the existence of life. Water: definitely check. Minerals and organic compounds: check. A source of heat, to power possible life: check.
Now the only thing for it is to visit; to get through the icy shell to the ocean beneath….
To be continued….
Next post takes a ride beneath the ice.
17th November 2017:
And here is the video for which this post formed the script: