10 Things You Should Know About the Search For Life on Other Planets

Everyone at one time or another has looked up at the stars on a clear night with wonder. People wonder about what is out there in a universe that is so big. They wonder if humanity is alone. They wonder if someone else on some distant planet is looking at the stars and wondering the same thing. Whether extraterrestrial lifeforms are science fact or science fiction is currently unknown. There is a branch of science that aims to find out what is necessary for life to exist on other planets. They also study whether any nearby planets meet those conditions. They ask themselves questions like: what might show that a planet has life on it? What caused Earth to develop life? What counts as life? How should they study the life they may find? The scientists working on this ambitious mission are called astrobiologists. This list is a mix of frequently asked questions and informative statements. It will help people understand the search for life on other worlds.

1. NASA’s Definition of Life

NASA defines life as "a self-sustaining chemical system capable of Darwinian evolution." This definition is, according to many astrobiologists, oversimplified. It is acceptable as a broad definition, though, because it allows for many different kinds of life. In layman’s terms, the NASA definition of life is chemicals that make up a stable unit that can adapt to change. The problem with the NASA definition of life is that it allows units that are not alive to read as a false positive. One example of this is crystals. Crystals are stable and they can adapt to change, but they are not alive. NASA's definition also makes it difficult to test for life with some degree of accuracy. Some astrobiologists suggest using a test that looks for a specific carbon compound. The compound can come from living things (LINK 1). There are two problems with this test. One: the carbon compound they have suggested can also come from things that are not alive. Two: the specific search for carbon compounds excludes the possibility of non-carbon-based lifeforms.

2. Current Theories on Earth’s Development of Life

The exact way life emerged on Earth is unknown, but there are many theories about the way life may have begun. Life on Earth began shortly after the surface of the planet cooled. At that time, the number of asteroids hitting the Earth decreased. The oldest confirmed fossil on record is 3.5 billion years old. Some chemical evidence suggests that life may have begun 3.8 billion years ago, though (LINK 2). Whether the chemicals were alive is still the subject of debate. Panspermia (LINK 4) is a theory which says that the chemical building blocks of life came to Earth as “cosmic hitchhikers.” The chemicals came on the asteroids and comets that often hit the young Earth. Another theory suggests that “primordial soup” created life. The “primordial soup” theory, is also known as abiogenesis (LINK 3). It suggests that the chemical building blocks of life were already present on the planet. They floated around in warm pools of water. Eventually, the chemicals came together at random to make the first early lifeforms.

3. What Conditions are Necessary for Life to Form?

For a planet to have life like us on it, it needs to have liquid water on its surface. A lot of the time, a planet has liquid water because it is in what science calls the “habitable zone” of its parent star. The habitable zone of a star system is the zone where a planet would be warm enough to have liquid water on its surface. Some studies disagree. They suggest that moons outside of our solar system's habitable zone could have liquid water. Underneath ice sheets that are several miles thick, there could be water. These moons are Titan, Europa, and Enceladus. The reason these moons could have liquid water is because of gravity or plate tectonics (LINK 5). The gravity of the planet they orbit causes tides. The tides keep the water underneath the ice moving so it cannot freeze. The plate tectonics allow for volcanic activity on these moons. Titan, for example, seems to have volcanoes that erupt liquid water instead of lava (LINK 6). Along with liquid water, a planet with life needs an atmosphere of some kind. Life like us needs certain levels of different gasses in the atmosphere. Our air is mostly nitrogen and oxygen.

4. Where in the Universe are People Looking for Life?

A lot of the places where astrobiologists are looking for signs of life are very far away. They look by examining which atmospheric chemicals reflect which color of light. This process is not perfect. Many chemicals can reflect the same colors of light as organic chemicals. Using this method, astrobiologists can study a planet thousands of light years away. Exoplanets like the three rocky planets of the TRAPPIST-1 system (LINK 9) are on the radar because they are close by. They are 40 light years away. These planets are close to the size of Earth and they are in their star’s habitable zone. Closer to home, a lot of astrobiologists are very interested in the moons of the gas giants. The focus is on Saturn's moons Titan and Enceladus (LINK 6) (LINK 8) and Jupiter's moon Europa (LINK 7). They are on the radar because they likely have liquid water under their ice.

5. How Long Would it Take to Reach the Nearest Possible Life-bearing Planet with Our Current Technology?

The nearest exoplanet that could have life on it is Proxima b (LINK 10) (LINK 11), which orbits Proxima Centauri. Proxima Centauri is the nearest star to our solar system (LINK 13) and it is part of the Alpha Centauri star system. It is only a little over four light years away. A light year is about six trillion miles (nine trillion km) (LINK 12). Proxima Centauri would be over twenty-four trillion miles (thirty-six trillion km) away. The Voyager 1 spacecraft might reach Proxima Centauri in seventy-three thousand years. For this reason, astrobiologists are interested in searching for life closer to home. It took Voyager 1 two years to reach Jupiter and it took three years and two months to reach Saturn (LINK 14). Other spacecrafts, like Voyager 2 and Cassini, have taken longer than Voyager 1 did. As of right now with Earth's technology, the best bet to find extraterrestrial life is to send probes to the moons of Jupiter and Saturn.

6. Ways of Studying Life on Other Planets

Once a probe reaches a planet or moon that may have life, what is the best way to study it? There are a couple of ways. One: the probe could land and release a rover. The rover would take images and samples for study. This is the technique that NASA used on Mars. Or two: the probe could remain in orbit and collect data. It would do this by taking images and samples without interfering with the surface. That is the technique used by the developers of the Cassini probe. Cassini (LINK 15) collected samples of water from the geysers that erupt on Enceladus. It found evidence of organic compounds. The compounds could or show either the presence of or potential for life. Because the gravity on Enceladus is different from the gravity on Earth, the geysers' jets are big. The geysers' jets are a combination of water vapor, ice crystals, and organic compounds. The jets shoot up so high that they reach space (LINK 16). This means that Cassini did not have to land to collect samples.

7. What do You Need to do to Become an Astrobiologist?

Astrobiology is a very interdisciplinary field. The first step to becoming an astrobiologist is to research to see which discipline you want to focus on. Then do some more in-depth research on that field. After that, it is a good idea to start building connections with scientists in your chosen field. You should also begin building relationships with astrobiologists. You can do this by attending summer classes and seminars. Next, get a bachelor’s degree in astronomy, physics, biology, chemistry, or geology. Continue building relationships with people in the field of astrobiology. You can do this by doing graduate work, going to more advanced seminars, and going to summer school. After that, earn a master’s degree in your chosen discipline. Continue to build relationships with other astrobiologists. Then earn a doctorate in your chosen discipline. Unfortunately, there are currently no doctoral degrees in astrobiology specifically. After that, visit the job board at NASA. Keep looking for other scientists who want to research the same subjects that you do (LINK 17). Congratulations! You have successfully become an astrobiologist!

8. If I Don’t Want to Become an Astrobiologist, are There Other Ways I Can Help with the Search?

If you do not want to become an astrobiologist, that's okay. If you still want to help find extraterrestrial life, there are plenty of ways to help with the search. One way to do this is to join the Planetary Society, which is run by Bill Nye (LINK 18). The Planetary Society funds its research projects using money from its members. These projects aim to advance space exploration. The Planetary Fund in particular is dedicated to the search for life on other planets (LINK 19). Another way would be to donate to SETI (Search for Extraterrestrial Intelligence) (LINK 20). If you are short on cash, there are still plenty of ways to help in the search. Sites like Zooniverse (LINK 21) focus on people-powered research. They have space projects. Some of those projects have to do with the search for extraterrestrial life. The space projects allow people from all over the world to analyse data. That helps scientists find things like stars and exoplanets faster.

9. How Many Planets in our Galaxy are Estimated to Have Intelligent Life?

For that question, it is best to look at the Drake Equation. The Drake Equation (LINK 22), which was created in 1961 by an astronomer named Frank Drake, goes as follows:

N=R* fp ne fl fi ft L

N is the number of planets in the galaxy that have intelligent life. This life would have to be intelligent enough to communicate with other planets. To do that, they would have to send signals into space just like the people of Earth are sending signals into space.

R* is the number of stars that are born in our galaxy every year.

fp is the number of stars that have planets. It is a fraction.

ne is the number of planets in each solar system that have the conditions necessary for life.

fl is the number of planets that actually do have life. It is a fraction.

fi is the number of planets that have intelligent life. This number is a fraction.

ft is the number of planets with intelligent life that has the technology to send signals. This number is a fraction.

L is the average lifespan for a society with technology that is capable of transmitting a signal.

Drake said that the “N” in the Drake Equation could be anywhere between 1 and 10 000. Carl Sagan said “N” could be a million or more.

10. Why Haven’t we Found any Concrete Evidence of Life on Other Planets?

So, if there are between 1 and 1 000 000 planets with life that is capable of transmitting signals, where are they? That is the question asked in the Fermi Paradox (LINK 23). There are many possible answers to the question. Perhaps the spacecrafts of alien races move too slow for them to reach us. Perhaps we are alone in the universe. Many papers were published. They present countless answers to the question: where is everybody? Some suggest that the extraterrestrials are choosing to be quiet. The theory says there is a big threat in the galaxy that the extraterrestrials need to hide from. Others say that the aliens are more focused on advancing their own technology and harnessing energy. The theory says they are not interested in exploring. Maybe the extraterrestrials are out there, but they are too far away. That means they will not receive our signals for millions of years. Maybe they died out (LINK 24). Or it could be that they have been sending signals and we have not found the right way to pick them up yet. We won’t know for sure until we make contact with people from other planets.

Links:

Link 1: https://www.sfu.ca/colloquium/PDC_Top/OoL/whatislife/Vikingmission.html

Link 2: https://cneos.jpl.nasa.gov/about/life_on_earth.html

Link 3: https://www.astrobio.net/meteoritescomets-and-asteroids/meteorites-a-rich-source-for-primordial-soup/

Link 4: https://helix.northwestern.edu/article/origin-life-panspermia-theory

Link 5: https://www.nasa.gov/feature/jpl/our-living-planet-shapes-the-search-for-life-beyond-earth

Link 6: https://solarsystem.nasa.gov/moons/saturn-moons/titan/in-depth/

Link 7: https://solarsystem.nasa.gov/moons/jupiter-moons/europa/overview/

Link 8: https://solarsystem.nasa.gov/moons/saturn-moons/enceladus/in-depth/

Link 9: https://exoplanets.nasa.gov/news/1419/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around-single-star/

Link 10: https://phys.org/news/2018-09-closest-planet-solar-habitable-dayside.html

Link 11: https://exoplanets.nasa.gov/news/1383/eso-discovers-earth-size-planet-in-habitable-zone-of-nearest-star/

Link 12: https://www.grc.nasa.gov/WWW/k-12/Numbers/Math/Mathematical_Thinking/how_long_is_a_light_year.htm

Link 13: https://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_info.html

Link 14: https://voyager.jpl.nasa.gov/mission/timeline/#event-voyager-1-encounters-jupiter

Link 15: https://www.esa.int/Science_Exploration/Space_Science/Cassini-Huygens/Cassini-Huygens_Frequently_Asked_Questions_FAQs

Link 16: https://www.esa.int/Science_Exploration/Space_Science/Cassini-Huygens/Complex_organics_bubble_from_the_depths_of_ocean-world_Enceladus

Link 17: https://astrobiology.nasa.gov/career-path-suggestions/

Link 18: https://secure.planetary.org/site/SPageNavigator/memberships.html

Link 19: https://secure.planetary.org/site/SPageNavigator/supportprojects.html

Link 20: https://seti.org/donate

Link 21: https://www.zooniverse.org/projects?discipline=astronomy&page=1&status=live

Link 22: https://www.seti.org/faq#seti3

Link 23: https://www.seti.org/seti-institute/project/fermi-paradox

Link 24: https://www.seti.org/if-extraterrestrials-are-out-there-why-havent-we-found-them

Photo Credit: Hubble Space Telescope, https://www.spacetelescope.org/images/archive/top100/