- Education and Science»
- Astronomy & Space Exploration
Are there Aliens in our Galaxy?
Where is everybody?
Sometimes when dealing with large numbers, such as billions, it is useful to use statistics. The human mind is rather lackluster with statistics. Most of us have awful intuition in this field. If we find evidence of life, or evidence of absence of life, statistics will help us answer how common life is in our galaxy. Here's a quick quiz to prove that statistics don't make sense (if you want to skip it, I won't be offended):
How good is your statistics intuition?view quiz statistics
These statistical questions are relevant when we are trying to determine the likeliness of different kinds of life in the galaxy. Around 1950ish a physicist named Enrico Fermi (kind of a cool name, and he was very essential to the Manhattan project) famously mused "Where is everybody?". Here's the basic argument, from wikipedia, and I added a few bits:
- The Sun is a young star. There are 200-400 billion stars in the galaxy, and billions are older than the Sun (the Sun is brighter than about 85% of them)
- The current estimate is that 20% of these stars have rocky planets in or near the "habitable zone"
- Even with our current technology we could develop propulsion mechanisms that can colonize the galaxy within tens of millions of years.
- Depending on the definition of a galaxy, the Milky Way is anywhere from 8 to 13 billion years old
If there are billions of chances for intelligent life to develop, and intelligent life can colonize the 100,000 light year wide galaxy over about 10 million years, why haven't we seen any sign of aliens?
Ultimately, however, we need a bigger sample size to start using statistics. We need to find another planet with life! Or start proving life isn't anywhere else!
As an aside, there is a stellar Drake equation calculator here, where you can estimate the chances of life in the galaxy using your own statistical parameters:
Life in the Solar System
Finding weird life in the most extreme places on Earth gave scientists reason to believe extraterrestrial life on other planets was likely. Is it likely enough to be on other planets or moons in our Solar System? Is our Solar System extremely special, one of the only ones with life?
Reasons why microbial life is still possible in the Solar System:
- Bacteria deep in our ocean live in almost complete darkness...darker than many places in the Solar System
- Bacteria can survive space voyages across the Solar System
- Asteroids and volcanoes can eject debris into space, opening up the possibility of planetary cross-fertilization
- Recently we found organisms that had adapted to survive in window cleaner
- There are organisms that survive high acidity or high basicity
- Some organisms survive boiling temperatures
- Life is found in permafrost
- Life can be found in the driest desert in the world (the Atacama)
- Some organisms survive without oxygen
- Fossils on Earth date back to 3.5 billion years ago. In that time period, the Earth barely had any oxygen at all. It was receiving only about 75% of the sunlight it does now. It was being bombarded with asteroids still colliding with it from the formation of the Solar System. Mars could've been much more hospitable, and Venus probably had hydrogen and water (unlike it does today). If life was here on Earth during that time, it isn't a giant leap to say it was present somewhere else.
Where would we find life?
Unfortunately life was much more likely 4 billion years ago. I just included it because it's a popular sci fi habitat for life.
Things we know that life absolutely needs:
Things on Europa:
- A warm ocean, heated by the same mechanisms our mantle is heated by (also remember the Earth was covered in ice 600 million years ago...and life may have been what heated it back up)
- Plenty of oxygen.
In fact, many scientists agree that it is possible that complex life could be found there. More articles come out about Europa everyday. Do we NEED another reason to send a probe to Europa?
Titan looks like Earth used to look like (when we had life). It has lakes and seas and rivers and all that stuff (okay, but they're all methane and ethane).
- We've shown that DNA and RNA can form in Titan's atmosphere
- It's possible there are warm subsurface oceans (of ammonia, but still)
- We came up with possible biochemistry for Titan's atmosphere. It involves hydrogen and acetylene and methane.
- When we took a close look at the atmosphere, the chemical signatures were completely different than this biochemistry would suggest. Just kidding, it's exactly what was predicted. However most scientists are looking for other explanations
The biggest problem is that Titan's surface is really cold. Like I said before, life needs energy.
Enceladus is the lesser-known version of Europa. It orbits Saturn, and is one of the only outer moons known to be active geologically. What else is fun about it? It probably has a liquid ocean beneath its surface, too. Surface temperatures are only 200 degrees below celsius, but we know from eruption data that liquid pockets underneath the ocean have to be at least 27 degrees fahrenheit (temperatures at which some Earth organisms of course could survive).
Okay, Venus probably doesn't have life. I brought it up because I thought that it would be easy to organically terraform with all that carbon dioxide and stuff. I'm not the first person to propose this; Carl Sagan did the same in one of his books. Turns out I'm wrong.
Unfortunately the surface of Venus completely recycles itself every 600 million years or so, and standing on the surface would be like a constant game of "the floor is lava". I was never good at that game in pre-school, and I don't want to take my chances now.
More unfortunately, lack of a magnetosphere has allowed solar radiation to ionize water particles in the atmosphere and subsequently escape into space. Basically, all the water is gone.
In order to terraform it we'd have to somehow barrage it with incredible amounts of hydrogen. We'd have enough here on Earth, but I feel like we don't want to use that. It's a lot of work (if not impossible) to extract hydrogen from a source like Jupiter, so I don't see that happening any time soon.
I read a quote from a scientist that said we cannot exclude a carbon-dioxide-cycle-based organism existing in the atmosphere of Venus...but if I was a betting man...
Also, interesting fact, Venus probably had enough water for oceans when it first formed. In fact, we're pretty sure it looked very similar to Earth. Watch out for greenhouse gases!
Are those the only options in our Solar System?
Europa, Enceladus, and Titan are seemingly far and away our most likely candidates for life.
Maybe we are thinking too narrowly.
Some have suggested that life might exist in the atmosphere of Jupiter or Saturn. This has been deemed unlikely, because vertical jet streams would carry these building blocks of life as we know it into temperatures that would break them down.
Perhaps there are "stable" spots in the upper atmosphere of these planets that allow life to develop. There is a storm on the south pole of Saturn that has probably been around for billions of years; that's a few billion years chance for a self replicating chemical process to occur.
This is speculation, even more so than other talk of extraterrestrial life.
Life in the Galaxy
We are just now discovering extrasolar planets. It is starting to seem like almost every star has a planet that is a potential habitat for life. Our narrow thinking human minds have only come up with about 4 broad explanations for the Fermi Paradox and SETI results (no radio signals in our very immediate galactic neighborhood) that I'm aware of:
- It is extremely hard for microbial life to develop. This seems unlikely since it developed Earth's history, but there isn't any evidence to really determine the likelihood.
- It is extremely hard for complex life to develop. Archaea, for example, is a term for single celled organisms that evolved differently than bacteria. They are probably the closest things to aliens on Earth in that they are completely separate from most life. It may be possible that single celled organisms are common in the galaxy, but complex multicellular organisms are not.
- Evolution of complex life is unlikely to produce tool-using, human-like intelligence. Although many Earth animals have been documented to use tools, and we are closely related to most of them, we are (obviously) different in that we started inventing complex tools. This took 4.54 billion years to occur on Earth, and that may not happen in other places.
- Intelligent life is common throughout the galaxy. Perhaps we have been visited, but the aliens deemed our planet to not have intelligent life.
Common Myths of Life in the Galaxy:
Aliens will have two eyes, two arms, and be incredibly humanoid
This is by far the worst misconception. It probably comes from shows like Star Trek where half the aliens look almost exactly like humans.
There are certain evolutionary attributes that we consider more likely to be universal, and some that we consider unique to life on Earth. The Cambrian explosion, which produced most of the recognizable life that's on Earth today, seemed like a completely random massive version of the hunger games. Evolution could have taken many different courses.
Some attributes that have been deemed "more likely" universal attributes for complex life (again, let's acknowledge speculation):
- Some form of skeleton
- Mouths of some form
- Photosynthesis (although possibly not with chlorophyll)
Some more likely Earth-specific attributes:
- Eyesight in the visible range (Aliens might have echolocation, or infrared sight)
- Skin (many ancient fish had thick armor and scales, or aliens might have more jellyfish-like membranes)
- Two eyes...the eye itself is a very interesting and specific evolutionary development
- Vocal communications (or any form of communication, it's hard to say)
- A similar life cycle. If there's an immortal jellyfish on Earth, there's probably an immortal organism somewhere else in the galaxy.
We will be able to communicate with other intelligent life
Reasons this is unlikely:
We cannot even communicate with chimpanzees, and they share 98.5% of our DNA. It is always possible that other intelligent life will have technologies that are currently unfathomable to us, which will allow them to communicate with us. Maybe they have been rapidly traveling the galaxy for a billion years and know how to handle new encounters.
Intelligence only comes in one variety
Reasons this is unlikely:
If you're an alien that is not exactly like us, why would you need a radio station? Why not just survive until your star burns out? If aliens are resistant to cosmic events, and can last for billions of years, is that intelligence? There is an argument I make in my most interesting animals hub that octopi are more intelligent than us in certain ways. Heck, there might be aliens out there that just constantly pump drugs into their system to be ridiculously high without any side effects. Why would they care about anything else?
We will have similar intelligence capabilities as the aliens if we encounter them
Reasons this is unlikely:
If there is a variety of intelligent beings in the galaxy, then it is very, very unlikely that we are the most intelligent ones. Unless intelligent life (the way we think of it) only occurs in one out of a billion billion planets, there are aliens capable of thinking more complex thoughts than ourselves somewhere in the Universe.
Also, we are only 1.5% genetically different than chimps and we've been to the moon. Imagine if we move another 1.5% in that same direction. Would our babies solve string theory equations? (This is a Neil DeGrasse Tyson argument)
Aliens will be similar in size to us
Reasons this is unlikely:
Oxygen, water, and every other chemical level will vary depending on the planet's mass, magnetic field, host star, and history. Minor tweaks in any of these chemical levels would dramatically change evolutionary history on Earth. High oxygen levels, for example, could produce much much larger alien creatures (like the large dinosaurs that used to be here).
What do you think the chances are of complex life elsewhere in the Milky Way?
What do you think are the chances of microbial life within 15 lightyears of our Solar System? (There are 2 stars with confirmed planets, probably more...almost reasonably reachable with today's tech)
Moral of the Story
If you've read this far, you're probably interested in space exploration.
19% of the United States' expenditures go to military applications. Less than 0.5% goes to NASA. Think about what we could accomplish if NASA's budget was increased to 3-5%.
The question in the title of this article might be answered 6-10x faster in that case.