Extraterrestrial Life And Where To Find Them

We surely will, within this millennium.

Once upon a time, there was a lonely rock drifting in space around an ordinary star. Someone decided to seed it with a self-replicating molecule and take a vacation for a while and return to this uninteresting lacklustre place later. They never returned though but I wonder how they would react to be greeted by more than 8,500,000 different types of self-sustaining entities, each having something special and unique to itself.

By once upon a time, I mean about 4.6 billion years ago. As much as I would love to believe that this story is true and that ‘they’ will someday come back, the truth is probably different.

If someone asked me, “What are the two most extraordinary and mind-boggling things to you?”, my answer without a doubt would be, the vastness of this universe and the diversity of life on Earth. Countless nights staring at the sky and countless days observing nature, no conclusive answers yet.

What are we? Where did it all begin?

From our current understanding, our universe is about 13.8 billion years old. It is a very ancient ecosystem filled with historic moments, but above all, in the entirety of its existence, there is one remarkable event that stands out and marvels scientists to this date, the origin of life.

It’s almost as if the universe created life to define itself.

Today, I want to ask an inevitable question,

“Are we truly alone?”

I am not just going to ask but give a definitive answer by the end of this article.

To solve this, we must first understand how life came into being and what made it thrive as we know it today. If we know the ‘what’ part, we will know where to look for it.

We are actually a step ahead in our search. We have an Earth, an entire planet full of living things demonstrating to us the conditions needed for life to flourish. One impressive fact about our planet is that life is everywhere we look at. The deepest reaches of the oceans where even sunlight cannot penetrate, boiling natural geysers and areas around active volcanoes, freezing polar regions: life is everywhere.

The idea is simple, “If it happened once, it is all the more likely that it will happen again. After all, the universe likes periodicity.”

Let us now go on an interstellar treasure hunt to find a place elsewhere we could call home someday. We may eventually find life in the form of microbes, but finding intelligent life is a real deal. Let us limit our search for a place where we can survive the way we do here. Such a place would most likely have the kind of life that we know for sure to exist, the carbon-based life forms. We are also limiting our search to the Milky Way galaxy.

Upon pondering for a while, here is a list of prerequisite filters I came up with to narrow down our search.

✔ Filter 1: A Star and a Rocky Planet

A burning star (Image Source: Tenor)

The Sun is the primary source of energy for most life on Earth, directly or indirectly. Some life forms can sustain independent of the existence of a star, but on a larger and more complex scale, we definitely need a star’s energy. Until recently, scientists weren’t very sure if our solar system was “The One” or the one among many out there. With the recently concluded Kepler mission, these doubts have been put to rest. We can now confidently state that almost every other star out there has a planetary system around it, meaning there are more planets than stars in our galaxy. Let us just limit our search to the planets orbiting Sun-like stars because we know for sure that such a star can provide conditions suitable for life to exist.

Here is a simple intuition. If there existed a star elsewhere almost of similar size and age as the Sun, would it also have a similar planetary system around it? What is the probability that such a system will also have an Earth-like planet and that life would have evolved there the same way it did here?

The basic features of such a potential solar twin are as follows:

  • It should be a G type main sequence star, i.e., a star (essentially like a sun) that is similar in size as the Sun and is fusing hydrogen to helium, and will continue to do so for about 10 billion years until it runs out of fuel and then expand into a red giant only to ultimately shed its outer layers to become a white dwarf.
  • Its surface temperature should be about 5700 K and age should be about 4.6 billion years giving enough time for intelligent life (as we know it) to evolve.
  • It should have a metallicity similar to that of the Sun. This is a measure of various elements within a star that are heavier than hydrogen or helium. What makes this an interesting property is that it can indirectly indicate if and what kind of exoplanets the star system may have. Stars with higher metallicity may have gas giants and rocky planets revolving around them. We can have an estimation that a star with metallicity similar to that of the Sun can have similar kind of planets around it.

Filtering out from the current data of observed stars, we have many good candidates that are near solar twins. We will get back to them soon, but now let’s see other criteria considered.

✔ Filter 2: Liquid Water

Liquid water droplets (Image Source: Reddit)

One fine day, two hydrogen atoms bonded to an oxygen atom, and so the elixir of life was created. Water is quintessential for the survival of our kind. An average human will not last more than a week without it.

The distance from a star at which the temperature is perfect for liquid water to exist is often termed as the Goldilocks Zone. Ideally, the surface temperature must be between -15 to about 70 degree Celsius. Our focus is on the planets found in this zone of their parent star. Based on the Kepler data, astronomers estimated that there can be as many as 11 billion Earth-sized planets orbiting their parent stars within the Goldilocks Zone!

✔ Filter 3: Atmospheric Composition

Northern lights are formed when charged particles interact with our atmosphere.

We need oxygen for metabolism and an ozone layer to protect life from the harmful rays of the Sun. The pressure and composition must be just right to help us survive and thrive. We also need the greenhouse effect without which the Earth would have been much cooler. While several forms of life can exist in harsher conditions, let’s restrict ourselves in this search.

If you are wondering how we can comprehend the atmosphere of an exoplanet that is several light years away, we have a simple yet effective method to do it. By observing the spectrum of light from a star that also traverses through the exoplanet’s atmosphere, we can pinpoint the elements present in it. Atoms and molecules, in general, absorb certain wavelengths of light (this is specific to an element, hence is more like the fingerprint of that element). In our spectral observations, these wavelengths of light will be absent indicating their presence in the exoplanet’s atmosphere.

✔ Filter 4: A Magnetic Field

Earth’s magnetic field protecting us from the solar wind (Image source: NASA)

The presence of a magnetic field has a strong correlation to a lot of things. For example, consider our potential second home, Mars. Its atmosphere is far thinner (about a 100 times) than Earth’s. Although it is within the Goldilocks Zone, there is hardly any liquid water on the surface. Not surprisingly, there is no trace of life either. Earth, on the other hand, is thriving with life. One distinct difference here is the absence of a strong magnetic field on Mars.

From our current understanding, the magnetic field of a planet not only helps it in retaining its atmosphere to some extent but also protects us from solar winds and other high-energy charged particles by deflecting them away.

✔ Filter 5: Distance From The Galactic Center

If you thought being in the Goldilocks Zone of a star should be enough, you are wrong. The star system must also be present in what is known as the ‘Galactic Habitable Zone’. These are the areas of a galaxy where life has the greatest chance of sustenance. Ideally, it is at a comfortable distance from the galactic centre and not near any supernova or other violent stellar events that can pose the threat of extinction. Earth is in one such place with a relatively peaceful cosmic neighbourhood.

This is the galactic habitable zone of the Milky Way, as predicted by Lineweaver et al (2004).

✔ Filter 6: Other Miscellaneous Factors

There are several other factors that can have some effect on the evolution of life. Earth is the only known planet to host life, but that’s not it. Earth is also the only one to have plate tectonics (there have been some observations indicating similar activity on Jupiter’s moon, Europa). They help in maintaining a stable temperature on the planet. This hints that plate tectonics may be essential for life to exist but scientists argue that it may not be an absolute necessity.

Another consideration is the presence of so-called ‘Good Jupiters’ in the system. Gas giants like Jupiter which orbit farther away from their parent star may actually play a role in deflecting massive asteroids from a collision course towards the inner rocky planets. This could help in preventing mass extinctions giving enough time for intelligent life to evolve.

While the origin of life on Earth seems to be a result of a series of orchestrated events too good to be a mere coincidence, what makes me think that it is not unique is the sheer unfathomable size of this universe. Star systems and planets satisfying all the above criteria have a very good chance of having evolved extraterrestrial life. Considering huge numbers like 11 billion Earth-like planets, it feels plausible that some of them must have intelligent life, but something is strangely amiss.

There are just too many possibilities for us to not be alone. A small head start elsewhere by a few million years should have spawned a technologically advanced civilization that could have explored our galaxy already. and yet wherever we look into space, there are hardly any bio or techno-signatures, just a deep silence, a void of darkness. Any claims otherwise are almost always dismissed as false alarms. This is essentially the Fermi paradox. Just where is everyone?

Before we move on, let us first have an estimate of how common life should be, statistically speaking. This can be found out using the famous Drake Equation:

Source: Wikipedia

We do not have any accurate values for these parameters but two contrasting estimations tell us that, we are either all alone or there are over 15,600,000 civilizations within our galaxy. It’s either everywhere or nowhere scenario. There are no in-betweens.

Closer to the truth than ever before, it is time to explore the universe in using the data we have (at the time of writing this article).

Coming back to the discussion about the Sun-like stars, we have so far identified sixteen candidates that are near twins, out of which five of them have confirmed exoplanets orbiting them. But don’t get your hopes high. The universe always has something up its sleeve to shatter our expectations.

One of those stars, HD 164595 has a planet (named HD 164595b) at least 16 times more massive than Earth orbiting it every 40 days. It is assumed to be Neptune-like and probably cannot sustain life, but interestingly in May 2015, astronomers detected a peculiar radio signal coming from that direction. Some were excited that it could be of alien origin but lack of any further evidence and observations dismissed such a claim.

Another star named HD 98649 was found to have a planet orbiting it in a bizarrely eccentric orbit. It may be an unlikely home for life, but there is better hope at around 2700 light-years away. Here lies YBP 1194, one of the best solar twins found so far. However, this star is a part of a larger cluster of stars, unlike the Sun, yet there is an exoplanet orbiting it indicating that they can be common even among star clusters. This particular one is estimated to be 100 times larger than the Earth and orbits surprisingly close to its star. This puts a question mark on the habitability of this system even if there existed other undiscovered planets in the star’s Goldilocks Zone.

The planetary system of yet another solar twin HIP 11915 is far more exciting. We have confirmed that a Jupiter-sized gas giant is orbiting this star, and more interestingly, almost at the same distance as Jupiter is to our Sun. This hints at the presence of inner rocky planets within the system, one of which could be Earth-like. Scientists predict that this could very well be Solar System 2.0. More observations need to be made to confirm the same.

Saving the best for the last, we have the star Kepler-452 located at about 1402 light years from us. It has a confirmed exoplanet orbiting with a period of 384.843 days, quite close to a number we are very familiar with. This planet also happened to be within the Goldilocks Zone of its star and its surface temperature is estimated to be similar to that of Earth’s!

Just when you thought that the pieces of the puzzle are fitting in smoothly, we have a problem with its parent star. It is much older than the Sun (almost by about 1.5 billion years), hence this system is more like a future version of ours. Either way, if life did evolve there as it did on Earth, their civilization would be millions of years ahead of us, and so will be the conditions there. We don’t have clear evidence for this but it’s a strong bet to make. Scientists from the SETI Institute (Search for Extraterrestrial Intelligence) have already started scanning this area for potential alien signals. It may only be a matter of time before we find something.

Image Source: NASA

The Kepler mission has done an astounding job in discovering Kepler-452b and now the TESS mission is currently in operation with the sole objective of identifying more exoplanets. We have hardly even explored the tip of the tip of the iceberg. More and more data will be incoming in the years to come with new missions planned and we are on the right track in our search. Even after narrowing down several factors and imposing multiple strict restrictions, we still have so many places left to explore and look for life.

All these observations are made within the Milky Way galaxy, and just in the last 50 years, we have made some promising discoveries. Our universe is estimated to have far more than 200 billion galaxies. Even if we consider that life exists at just one planet in every spiral galaxy, the number of extraterrestrial civilizations should be humongous.

Instead of looking for ideal places where life can exist, a simpler approach would be to look for signals from deep space. The theory being, any intelligent life would most likely send transmissions into space just like we do. Detecting a radio signal depicting intentional or encoded transmission is a piece of guaranteed evidence for intelligent life. We have been listening for such signals for a very long time.

In the past, there have been several programs like Project Ozma, Projects Sentinel, META, BETA, and Project Phoenix, all of them with the primary objective to detect extraterrestrial signals. As you might have guessed, none of them succeeded so far.

This is not a random search, and there are several hints to look for. One of them is the waterhole radio frequency where scientists generally look for signs of communication. This special frequency corresponds to the spectral line of hydroxyl ions and hydrogen, two of the most abundant compounds in the universe. This makes it a ‘quiet channel’, i.e devoid of any noise (which is absorbed by them) making it ideal for extraterrestrial communication.

Scientists have also been looking for various alien megastructures that have been theorised, like a Dyson Sphere, Swarm or Ring, Space Mirror, Hypertelescope, Shkadov Thruster, etc. These are some crazy sci-fi structures but they are theoretically plausible and could be constructed by an advanced civilization. (Type 2 on the Kardashev Scale, the common measure used to grade the technological advancement of a civilization)

What signals have we found so far?

The Wow! signal represented as “6EQUJ5”. The original printout with Ehman’s handwritten exclamation is preserved by Ohio History Connection

Most of the time, space is eerily silent and even those few moments when something is detected, it is probably a false alarm. Even so, we have found some truly mysterious ones like the Wow! Signal which some scientists now think was just from a passing comet.

The SHGb02+14a radio source discovered in 2003 appears to be more unnatural. It’s within the waterhole region, and it was observed several times with a similar frequency drift. What makes it peculiar is that the direction from which it comes has no stars in the region! To this date, there is no clear explanation of its origin.

There are several programs in operation right now and we will continue finding more interesting signals. There is also a protocol formulated called the ‘Post Detection Policy’ laying out universal guidelines for what to do after a potential discovery.

The general intuition to consider an unknown signal to be of alien origin is as follows:

  • It should not look natural. There should be some obvious signs like narrow bandwidth, modulation, encoding, multiple frequencies, etc.
  • It should not be a one-time anomaly (which generally indicates that it is just some interference or false alarm). We should be able to observe it again and again from the same position in the sky.
  • It should be originating from a specific point and only from that point. If such a signal is received from all directions, it is more likely to be of natural origin although we may not have known what could have caused it. (for example, Fast Radio Bursts (FRBs))

If you are an amateur astronomer and find something satisfying these criteria, you could be on to something alien. Breakthrough Listen is a recent initiative started in an effort to listen to our neighbouring stars. The astronomical data collected during this program is made available to the public. You can access it and conduct your own research!

Lack of evidence may tempt us to draw early conclusions, but we have just started our search and I believe that our cosmic neighbourhood is full of secrets waiting to be discovered.

Know this, the next time you look up at the night sky. It is more likely that near a twinkling dot somewhere out there is a place someone calls home, and maybe, just maybe, that someone is staring right back at us pondering over the same question we have, “Are we all truly alone?”

My guess would be, within the next 1000 years or so, we will find or be found by our cosmic companions. And that moment shall be the most significant in all of humanity’s existence. Here’s a little message I want to leave to the aliens reading this article in the future (well, pretty ambitious I am):

“Hey there! Not sure if you can understand this but thank you for all the inspiration. Long before we knew about you, you inspired generations of curious minds and explorers like myself to dream of an existence beyond the skies…”

And here’s my answer to that question. No, we are not alone, we have never been and will never be. In the worst case scenario, even if my thoughts turn out to be wrong, we will still find them.

Somewhere down the line, we would have become the aliens we’ve been searching for all along.

The image above shows an artist’s rendition of a flow of events in a 13-billion year history of the Universe from the Big Bang at upper right counter-clockwise to the formation of life on Earth at lower right. (Image Credits: Indiana University Bloomington)

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