The scientific exploration of potentially habitable locations within our solar system is one of the most intriguing and exciting undertakings in human history. Even though we haven’t discovered life anywhere else yet, there are a lot of people who wonder if there was ever life, or might even be life right now, on other worlds right here around our own star. What do you think? If there is some form of alien life here in our solar system, how would we go about finding it? We humans can learn a lot by interacting with the world and using our own senses to make discoveries, but it turns out to be pretty hard to send humans to other worlds to explore. So far, the furthest humans have ever traveled away from our planet is just beyond the Moon. But, for us to send humans to worlds like Mars and the moons of the outer solar system it’s going to take some time. So, in the meantime, we send out robotic spacecraft as explorers for us. Sometimes we send spacecraft that will fly by another world and collect information, sometimes they go into orbit around the planet or other object in order to study it, and sometimes we even send robots that can land on the surface in order to look at these other worlds close-up!

When we design our spacecraft, we have to consider the kinds of tools that we want to send along in order to study things. The instruments that we put on the spacecraft will depend on the type of spacecraft it is, on the goals of the mission, and on where it’s going. Flyby and orbiter missions will often have cameras that are meant for getting pictures of worlds from afar and instruments that are good at characterizing atmospheres or measuring radiation around the world. Landers and rovers will gather data about the geology and history of the surface of another world. They might even look for signs of life by measuring organic molecules in surface samples. Future technologies for our exploration might include things like ice drills, submarines, underground robots, and spacecraft that can survive in the atmospheres of gas giants.

Mars is a good example of a place where we’ve been looking for signs of past or present life. Mars is a cold, rocky planet with a thin atmosphere, but, long ago, Mars had rivers and lakes and maybe even an ocean of water at the surface. It had a denser atmosphere than it does today and lots of active volcanoes. Ancient Mars had the chemical ingredients for life, there was energy, and plenty of water. When we send our orbiters, landers, and rovers to Mars, we keep an eye out for potential signs of ancient life. Our orbiters around Mars, like the Mars Reconnaissance Orbiter ( MRO ), can help in the search for life by taking really good pictures that give us a broad view of the environments on the surface and by using spectroscopy to measure the composition of surface environments. Spectroscopy is a fundamental technique in science where we measure how light interacts with matter to learn more about the chemical nature of that matter. Spectroscopy onboard our orbiters around Mars can allow us to measure the general types of minerals that are present over large regions of the Martian surface. Putting together information from these orbital pictures and spectroscopy allows us to pick the best places to send our landers and rovers. The Curiosity rover, which is active on Mars right now, has cameras for looking at the structure of the rocks and minerals up close, it has instruments for looking at organic molecules in the Martian soil, and it also has an instrument for learning about the kinds of minerals that are present in samples or rock. Using these tools, Curiosity is looking for signs of past habitable environments on Mars, like places where the minerals show signs of having formed in a watery environment. Although Curiosity isn’t necessarily looking directly for things that are alive now, there may be some potential places on Mars where things are living today. Mars has lava tubes (caves formed by volcanoes), water ice in the ice caps identified by the Mars Reconnaissance Orbiter ( MRO ), and might have places in the subsurface where water is liquid and where live could be present. Orbiters, landers, and rovers will continue to reveal more information about Mars and whether it had, or maybe even has, life.

Another place we’re exploring using spacecraft and specialized instruments is Europa, a moon of Jupiter. We now know that this world has an icy shell on top of a deep liquid water ocean. Our first images of Europa up-close came from the spacecraft Pioneer 10 and 11 and Voyager 2\. With Voyager 2, we saw for the first time that the icy crust of Europa has dark streaked lines all over it. These lines (which we refer to as “lineae”) were the first indication that the icy surface could be cracked and might have an ocean below. The Galileo spacecraft, which spent 8 years studying Jupiter and its moons (from 1995 to 2003), had an instrument onboard for measuring magnetism in the space environment. If you’ve ever put one magnet close to another, you’ve seen the effects of magnetism. We have tools that allow us to measure the effects of magnetism and they’re called “magnetometers”. Just as we can use a compass to tell us which way is north on Earth, a magnetometer can tell us about the magnetism coming from a planet or a moon. Our Earth produces a magnetic field due to the liquid metal outer core, which spins around and produces the field. Jupiter has the biggest and strongest magnetosphere in the solar system, and we’re pretty sure it’s formed by the movement of an ocean of liquid metallic hydrogen that acts as Jupiter’s outer core. The magnetometer instrument that was on the Galileo spacecraft showed us that Jupiter’s magnetic field is being disrupted around Europa due to a small magnetic field coming from Europa itself. This told scientists that there must be a salty liquid water ocean down below its surface.

On Earth, hydrothermal vents are a source of heat and energy on the ocean floor and have developed ecosystems around them where sunlight isn’t needed for energy. Could there be hydrothermal vent ecosystems within the ocean of Europa? With future spacecraft, we’ll flyby and even orbit Europa, taking pictures and looking for potential organic materials at or near the surface. The Europa Clipper mission will tell us more about Europa’s ocean, study the chemistry and geology of the surface ice, and will help us to figure out where we might want to send a lander. A lander mission to Europa will likely dig into the ice, just beneath the surface, to look at the chemistry and geology of the ice and to potentially look for organic molecules and isotopes that indicate the activity of life. There’s also a lot of interest in possibly drilling down through the ice to look for life directly in the ocean. That will be a big undertaking, since the ice is very thick, but could be a really important step in looking for life in an ocean of icy moon like Europa.

There are other icy moons in the solar system that we’re considering for possible signs of life. These include moons like Enceladus, Titan, Triton, and Ganymede. There have also been some proposals that there could be signs of life to be found in the clouds of Venus or maybe even within the icy material at the surface of a comet. We’re only just beginning in our work to better explore our solar system and use our spacecraft and various instruments to look for possible signs of past or present life. With some skillful engineering and a little imagination, we’ll be able to design and build better and better tools for studying the solar system and may even one day send humans out to search for signs of extraterrestrial life in the solar system. Our exploration has only just begun.