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Episode 8: Neighbourhood Watch Pt2! - Life in our Solar System

  • Writer: Abigail James
    Abigail James
  • Mar 23, 2020
  • 18 min read

This blog post is a transcript of Series 1, Episode 8 of my science podcast, Don't touch my Radium! All sources, references and recommended material can be found here.


This is part two of our episode on the search for life within our Solar System. In part 1, we set up how to use the Hohmann transfer method and gravitational slingshots to travel through our solar system sending probes and landers out to investigate other planets and objects for signs of life. We talked a bit about our solar system in general and reminded ourselves of some important facts about our planet Earth and what makes it habitable. So let’s get straight back into it, continuing directly from where we left off last week.


We’re going to take a trip around our neighbourhood, searching for signs of habitability, the potential for life, so let’s start by ruling out the least likely locations, which is nearly all of them!


Venus

First up are the terrestrial planets and we’ll start with Venus, the second planet from the Sun and the planet that has the hottest surface in our solar system! There have been a number of missions to Venus with the Magellan spacecraft by NASA, the VIRTIS satellite launched by the ESA and Japan's Akatsuki mission all providing flyby and orbital information. The Venera group of missions launched by Russia, are the only spacecraft to have landed on the surface of Venus providing images of the planet. Venera 13 lasted for 2 hours under the heat and pressure on the surface of the planet.


Some facts about Venus:


  • It is a similar size and structure to Earth

  • It orbits at about 108 million km from the Sun, 0.7 AU and light will reach it in 6 minutes.

  • It orbits on its axis very slowly and one Venus day is about 243 Earth days.

  • One Venus year is about 225 Earth days. (a year is shorter than a day!)

  • It has no moons and no rings.

  • Venus has an extremely weak magnetic field in comparison to Earths.

  • Its surface is covered with plains of solid land and high volcanic mountains, tens of thousands of volcanoes!

  • Venus has an almost perfectly circular orbit and an axial tilt of about 2.7 degrees so like Mercury it doesn’t have any seasons.


Habitability:


Venus has a super slow rotation about its axis but the atmosphere is a lot more active, the winds travel at hurricane force so while it may take 243 days for one rotation of the planet, it only takes 5 days for the clouds to travel all the way round. Venus has a thick atmosphere in contrast to Mercurys’ thin one. But this atmosphere is full of carbon dioxide, and some sulfuric acid clouds, not very life friendly! This thick atmosphere traps the heat from the Sun so that the surface of the planet is about 470 degrees celsius, this is hot enough to melt lead! This means that the rocks are so viscous, that the lava from all the volcanoes can flow as easily as water. It may be possible that water itself once existed on the surface of the planet and it may be possible that life once existed there but the extreme temperatures nowadays make it virtually impossible for water to exist currently. It’s hard to imagine life surviving in these temperatures with the acidic clouds and super heavy atmosphere making you feel like you’re about 1.6km under water.


Mercury

Next for the terrestrial planets we have the closest planet to the Sun, Mercury. Mariner 10 did three flybys of Mercury between1974 and 1975 and was able to map half of the planet's surface, indicate the presence of a thin atmosphere and detect the presence of a weak magnetic field. Messenger was the first probe that was sent out to become a satellite around Mercury. Launched in 2004 it successfully reached Mercury and went into orbit in 2011. The reason it took seven years, was that the path it had to take required it to loop around Mercury 3 times before it could eventually use its thrusters to slow down and be captured by the gravity of the planet, pulling it into its orbital path. Amazingly, this action of using the thrusters used one third of the fuel that the probe was launched with. Messenger was equipped with seven instruments to study the planet's surface, measure topology and investigate the magnetic field.


Some facts about Mercury:


  • Smallest planet in our solar system, slightly larger than our moon.

  • Closest planet to the Sun, 58 million km (0.39 AU), but it doesn’t have the hottest surface, Venus does. Light from the Sun reaches the planet in 3.2 minutes.

  • One day is 59 Earth days, while a year is 88 Earth days.

  • It has no moons or rings.

  • Mercury has a magnetic field about 1% the strength of Earths.

  • The Sun would be three times larger in the sky if you were on Mercury’s surface.

  • Mercury has an almost zero tilt, 0.01, so it’s poles have regions that never see sunlight and the planet doesn’t experience seasons.


Habitability:


Aside from the assumptions we can make given its location! I don’t think factor 50 suncream is gonna help us on a planet that can be up to 430 degrees celsius in the daytime, and besides that we’d all likely freeze to death in the -180 degrees celsius nighttime temperatures. These extreme temperature changes could indicate why there is no evidence of liquid water on the surface but the poles seem to indicate ice caps. The atmosphere on Mercury is a thin exosphere that is composed of molecules of O2, Na, H2, He and K. Solar winds from the Sun hit the surface of the planet sending atoms into the atmosphere creating the exosphere layer. Unfortunately this thin layer doesn’t do much to protect the planet in a way that we would look for in order to indicate life signs. This doesn’t totally discount the idea that life could exist, but it’s highly unlikely that life as we know it could survive in these conditions.


Uranus and Neptune

I’m going to skip to the ice giants next, I know they orbit further out than the gas ones but bear with me! So hold onto your hats and your childish giggles, we’re going to talk about Uranus for a while, as well as Neptune. As we move farther out into our solar system the distances become so great that the probe missions become less. Neither Uranus or Neptune has ever had a dedicated mission, as of yet. Most of what we know about these worlds comes from ground based telescopes and the Hubble Space Telescope. The only probe to ever come close enough to send back information was the voyager 2 spacecraft which passed close to Uranus in 1986 and eventually passed by Neptune, three years later in 1989.


Some facts:


  • Uranus and Neptune are both around the same size, four times larger than Earth.

  • Both of the ice giants have magnetic fields that are stronger than Earths, but strangely, they both are knocked off the axis of rotation so they have huge variations as the planets rotate.

  • Both planets have a lot of moons! The current count is that Uranus has 27 while Neptune has 11. There aren’t any indications so far that they could harbour life.


Habitability:


As ice giants these planets are made up of a small rocky core that is surrounded by a hot dense fluid of materials that we refer to as ‘icy materials’, such as water, methane and ammonia. They have gassy atmospheres that are mostly made up of hydrogen and helium with some methane present, but there is no real surface where you could stand and winds can travel up to 900 km per hour on Uranus and up to 2,000 km per hour on Neptune. Neither planet has an environment that would support life as we know it.


Jupiter and Saturn

So here they are, the gas giants, Jupiter and Saturn. There have been nine missions to Jupiter, the very first being a flyby in 1973 by the Pioneer 10 spacecraft. This mission gathered data on the magnetic field, radiation belts and atmosphere of Jupiter that was vital information for the design of future spacecraft. Currently there is one active mission to investigate Jupiter, Juno was launched in 2011 and used one Earth flyby (gravitational slingshot) to reach Jupiter and enter into orbit in 2016. It’s mission relates to investigations of the atmosphere, magnetic field and gravitational field. There have been four missions to Saturn so far, three have been flybys, Pioneer 11 in 1979 and then the twins, Voyager 1 and Voyager 2 in 1980 and 1981. Then came Cassini, the only satellite to go into orbit around Saturn back in 2004 and stayed there for 13 years revealing information about weather and seasonal changes, the complexity of the planet’s ring system as well as the uniqueness of the moons in orbit.


Some facts:


  • Jupiter is big, like really big, the radius is over 5 times the radius of Earth. It’s actually described as being more than twice as massive as all the other planets combined. Saturn is then the second biggest planet in our solar system about 9 times the size of Earth.

  • Both planets have magnetic fields with strengths that far out do our planets one.

  • Both planets have ring systems, while Jupiter's is faint, Saturn is the glory of our solar system and has made Saturn a well loved planet. What’s funny, is that both planets have 53 confirmed moons each, there are a number of yet to be confirmed potentials but the count for each currently stands at 53.


Habitability:


So in terms of habitability; well they are both gas giants, so they don’t have solid surfaces, just swirling gases and liquids! Both planets have atmospheres that mostly consist of hydrogen and helium, with the pressures causing there to be a layer of liquid hydrogen. Jupiter actually has the largest ocean in our solar system, it's just not a water ocean! Any spacecraft that tried to enter the atmosphere of either planet would be crushed, melted and vaporized! So there isn’t any likely place for life to exist...on the planets themselves! But remember all those moons? Jupiter’s moon Europa and Saturn's moons Enceladus and Titan are some of the most likely places that we could find life in our solar system.


Well since I’ve brought up these moons...let’s move onto the objects in our solar system that could possibly contain life.


Europa

Starting with Jupiter's moon Europa. So far we have managed to gather up close data on this moon thanks to the Voyager twin spacecrafts, the Galileo spacecraft and most importantly, the Huygens probe that landed on the surface in 2005. Roughly the same size as our moon, Europa is tidally locked to Jupiter orbiting the planet every 3.5 Earth days. As Jupiter's axial tilt is only 3 degrees, this means that Europa does not experience much seasonal variation. It is believed that Europa has an iron core and rocky mantle like we do and the surface is mostly solid water in ice form. From the data gathered so far on Europa it appears that the moon may have a salty water ocean just below the icy surface making it the most promising place in the solar system to find life. Research suggests that the distortions to Jupiter's magnetic field around Europa means that the moon is inducing its own special magnetic field which is being caused by an electrically conductive fluid under the icy surface, salt water. But even with this any life would be living in conditions unlike our own, I hear you say! Well there are organisms on Earth, called extremophiles, that live in regions of subterranean volcanoes or deep-sea vents, extreme locations on our very own planet that we wouldn’t take to be habitable. So maybe there is the potential for life to exist in Europas waters. While it does have an oxygen atmosphere, it is very thin so we would not be able to breathe on the surface. What is interesting though, is that data from Hubble has indicated that the moon may be actively venting water, suggesting that it is geologically active, today!


But as with any of our investigations into life signs, we need more information. NASA has an orbital mission in development, the Europa Clipper, confirmed in 2019 with a proposed launch sometime around 2025 and a travel time of approximately six years. We are not joking when we say that this shit takes time! The satellite will go into orbit around Jupiter in order to observe the moon and from a suite of cameras, spectrometers, ice-penetrating radar, a magnetometer and thermal instruments will be able to investigate the surface, composition, structure, magnetic field, gravity and temperatures of this, the most potentially habitable place in our solar system! We talk about life having three main requirements, liquid water, the appropriate chemical elements and an energy source. Europa may have all these qualities, it’s not a guarantee of life, but its a start. Unfortunately we won’t know for at least another decade.


Titan

Next up is the largest moon to orbit Saturn, Titan! The same missions that were sent to Saturn gave us information about Titan, Pioneer 11, Voyager 1 and Voyager 2 on flybys and Cassini getting a good look during its 13 year orbit of the planet. Titan is larger than our moon, it’s actually bigger than the planet Mercury. Tidally locked to Saturn it orbits in 16 Earth days. Saturn has an axial tilt similar to Earths so Titan also has a similar tilt relative to the Sun giving the moon seasonal variations, however, given the distance from the Sun, about 9.5 AU, each season lasts for more than seven years! The Cassini-Huygens mission allowed data to be sent back to help us to understand a bit about the structure of Titan, in general it’s thought that there is a rock core and a layer of salty liquid water with an outer crust of water ice. Apparently, the surface of Titan is the closest to being Earth-like, just a bit colder where rock is ice, and volcanic lava is made up of liquid water. As well as this, there are rivers and lakes of liquid natural gases in the form of methane and ethane. The surface temperature is around -180 degrees Celsius. What is really interesting about Titan aside from this sci-fi rich surface, is that it has an atmosphere. In fact it’s the only moon with a thick atmosphere. The atmosphere is about 95% nitrogen and about 5% methane. On the surface the atmospheric pressure would be similar to if you were diving 15 meters in Earth's ocean and it’s the only place we’ve looked at where you could actually stand on the surface! You’d need an oxygen mask and protection from the insanely cold temperatures, but you wouldn’t need a spacesuit! In the higher layers of the atmosphere, UV light from the Sun breaks these molecules apart allowing for oxygen and other organic chemicals to form. But we don’t know yet where the methane comes from, it’s likely to be abiotic but there is always the potential that it comes from an actual biological process.


Although we have learned so much from the Huygens probe who held instruments to analyze the atmosphere, wind speeds, radiation levels, light intensity, chemical composition as well as return the first images of the surface of this moon. There are still many questions about the potential for life to exist. Thankfully, the Dragonfly mission has been confirmed as the next mission to Titan and it’s headed to the surface. But this ain’t no rover, Dragonfly will fly to different locations on the moon allowing for repeated and targeted access to surface materials for scientific experimentation. Due to launch in 2026, it will take 8 years to arrive at Titan by 2034 and search for evidence of past or current life. The oceans could hold life as we know it from extreme environments on Earth, but even more intriguing...the lakes and rivers on the surface could potentially hold life as we don’t know it.


Enceladus

The last moon on our trip is Enceladus, another one of Saturn's natural satellites. As with Titan, a lot of our information comes from the voyager missions as well as data from Cassini as it orbited Saturn. Enceladus is pretty small in comparison to what we’ve looked at so far, it’s actually seven times smaller than our Moon. Enceladus orbits within one of Saturn's rings circling the planet in 32.9 hours. As with most objects out at this distance from the Sun, it is cold! Covered with a smooth white ice, it is the most reflective object in our solar system leaving the surface temperature at -210 degrees Celsius. But as we’ve just learned with Europa and Titan, that doesn’t necessarily mean that it couldn’t host life. There is an ocean below this icy surface and Enceladus sprays mineral rich water out into space where the Cassini orbiter was able to collect particles for analysis showing that this cold place does actually hold the chemicals required for life as we know it. This can happen if Enceladus has hydrothermal vents beneath the surface causing ‘warm’ fractures in the crust where jets of particles can escape from, we have hydrothermal vents on our ocean floor where there is a host of oceanic life. These jets are referred to as ‘plumes’ and can contain water vapour, carbon dioxide and methane, along with some smaller quantities of a few other gases, but this is a higher than expected density of organic materials.


Unfortunately there are no planned missions to explore this moon in the coming years, with the most recently proposed Life Finder probe not making the cut in NASAs New Frontiers programme.

I’ve saved the best for last, or rather, the most obvious. The only planet that we haven’t talked about is our terrestrial neighbour, the most explored object in our whole solar system, we have been searching for evidence of life on the red planet since the 1970s with the Viking lander missions! Mars is the only other planet to orbit within the habitable zone of our star and the place we all have our sights set on for the future.


Mars

As of December 2019, we have six satellites in orbit around the planet from NASA and ESA along with India's first Martian satellite. When it comes to the surface of the planet, there have been around 16 missions since the first landers, the Viking pair, hit the surface back in 1976. Apparently 3 more are due for launch this year by NASA and the ESA. At this time, March 2020, there are two operational missions on the surface both by NASA, the Curiosity rover and the InSight lander. The Insight lander has been delving into Mars’s interior since it arrived on the planet nearly two years ago. But Curiosity, so so aptly named, landed on the surface back in 2012 with an initial mission time of 2 years, over 8 years later this guy is still roving about the martian land searching for indications of previous or even current life.


Some facts about Mars:


  • Mars is about half the size of Earth.

  • It orbits at around 228 million km from the Sun, 1.5 AU.

  • One day on Mars is pretty close to a day on Earth, it’s 24.6 hours.

  • One year though, is about 687 Earth days.

  • It takes 13 minutes for sunlight to reach Mars.

  • Mars has no rings, but it does have 2 moons, called Phobos and Deimos.

  • Mars doesn’t currently have a magnetic field, but evidence shows that one may have existed 4 billion years ago.

  • It’s surface is dusty, cold and resembles a desert. It also has the largest volcano in our solar system, Olympus Mons, three times the size of Everest.

  • Mars has an axial tilt of 25 degrees, pretty close to Earth's 23.4 so it has seasons. As its orbital time around the Sun is longer, just over two Earth years, the seasons last longer and vary in length because it’s orbit is more elliptical than Earths, less circular.


Habitability:


There is a lot of hope out there that we will find signs of life on Mars, no matter how small. Any indication that tiny microbes may still be there or remnants of a lost world. But even though Mars is in the habitable zone of our star, this is not a guarantee for life. We learned in the very first episode that it took a lot more than the distance from the Sun for life to thrive and evolve on our planet.


The imagery of the surface features gathered through all these missions indicate the possibility of ancient rivers and lake beds. And while water may not be flowing through them now, at the polar regions, there is water-ice just under the surface and salt water actually flows seasonally down some hillsides. Unfortunately the atmosphere is too thin to allow liquid water to exist for very long on the surface. This atmosphere is made up mostly of CO2, argon (Ar), nitrogen (N2) but there is also a small amount of oxygen and water vapour, which is cool. Not enough to support life, but it’s nice that it’s there. But Mars has also shown some indication of CH4, that would have to have arisen from either volcanic activity or biological activity and this happens seasonally, in Autumn. The CH4 disappears quicker than expected which could suggest that something is heating up or breaking down the CH4, but this is still being investigated as the current equipment can’t determine if it would be geological or biological.


One more thing, Mars is cold! It’s highest temperatures are 20 degrees celsius while the lows hit about -153 degrees celsius. The thin atmosphere means that the heat from the Sun escapes really easily and so much so, that even you standing there would feel a massive temperature difference from your feet to your head. So while Mars may not be currently hold life, it has all the potential to have held it in the past, back in the days when there was a magnetic field to protect the atmosphere and water on the surface with warmer climates. It makes you wonder what happened!?!? I guess that’s why it’s the most explored object in the solar system.


As we approach a time in the orbital paths of our solar system where Earth and Mars are closest to each other, this year is a big year for new launches to the planet.


  • The UAE are set to launch their first Mars probe in July this year, the Hope mission will focus on trying to understand what happened to the Martian atmosphere which could allow for better modeling of our own atmosphere.

  • NASA are set to send another Rover to the red planet which I think has been named Perseverance, also launching in July of this year. The aims are to learn about the environmental conditions on the planet in the past by a ‘Maritan sample return’, this is cool because the plan is to collect samples and then a future mission will return these Martian rocks and minerals to Earth for testing. I do not know how they plan to do this! The general idea is that the rover will store the samples in tubes and then drop them at a ‘depot’ site for future collection, I guess a time when technology allows us to send a return mission to the planet.

  • Articles that I’ve read state that Chinas’ Global Remote Sensing Orbiter, Lander and Small Rover is set for launch this year. I don’t know if there is a more compact name, but the mission plans what it says on the tin, it consists of an orbiter, a lander and a Rover that will be tasked with demonstrating the technology needed for a sample return mission which would then occur sometime in the 2030s. Now, I couldn’t find any specific details on this so I don’t know what the actual status of the mission is, all the resources are kept to online articles and when I had a look at the China National Space Administration site I couldn’t find any references to the mission but this may just be that the English version of the site doesn’t have as much info.

  • Also set for launch this year is Japan’s Mars Terahertz Microsatellite, this small sensor will head to the surface of the planet and measure the oxygen isotope ratios in the atmosphere to try to determine how the atmosphere is supplied with carbon dioxide.

  • The last mission I want to mention is the ESA-Roscosmos Rosalind Franklin lander which is designed to search for past and present life on the planet, this is actually one of two missions that make up the ExoMars programme. The first stage of this programme was launched in 2016 and is the Trace Gas Orbiter that was tasked with analysing traces of methane and atmospheric gases in the Martian atmosphere. The lander was due to launch this year in the 2020 July/August window but recent issues that require further testing has led to a delay to the 2022 launch window.


So far, you might feel a little bit disappointed. We have yet to find life signs. We are getting closer, but mission concepts take time to be developed and delays are normal, launch dates have to be set to minimise travel times and then the length of time it takes to reach the destination means that it will still be years before we have any sense of confirmation. And that’s if life actually is out there in our solar system and that our current technology can detect it. No matter what, life does not exist in our solar system to the level that it does on Earth, people and animals walking around the surface living and breathing, Venus has a too thick atmosphere, Mars a too thin one. Titan, Enceladus and Europa are all too cold. But as life began on Earth in the form of microbial organisms that lived in vastly different conditions than we do now, and life like this, including extremophiles, currently survive in extreme environments such as intense heat, places with high acidity, areas under extreme pressure or extreme cold. Then it’s not too far of a stretch to believe that it could be out there.

You might have lost interest by now, if it’s not little green men or intelligent aliens you might encounter in a sci-fi movie, but finding microbial life here is important to how we apply our knowledge to exoplanets out there, because if life is found elsewhere in our solar system then that shows that it’s more common than we expect, which means that life could be abundant in our galaxy. And we may be the only life like ours in our neighbourhood but there’s a lot of neighbourhoods out there, billions of them!.


Still to come this series, how Kepler found so many exoplanets, what is the future of space telescopes and are we even looking for the right signs?


Thanks for listening. Come back next week if you’d like to learn more. If you want to get in contact you can email dtmyrad@gmail.com or drop by our instagram @dtmyrad.


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Artists impression of the planets of our solar system.

 
 
 

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