The possibility that life may exist on other planets is something which has long fascinated the world and managed to bring together groups of individuals that would otherwise never even think of intermingling. From scientific researchers to crackpot conspiracy theorists there are so many theories out there that center on the possibility of life on Earth that many people devote their lives to proving or disproving the theory. There seems to be one common thread for all of these diverse groups of people; however, where some may believe that life on other planets consists of little green men and others believe that life on other planets consists of human like beings, the common thread for each of these groups is the presence of intelligent life forms on a planet other than Earth.
Is There Life On Other Planets?
Ask most people across the world and they will tell you that they believe in the possibility of life on another planet and they will generally clarify themselves so as not to appear as a “crackpot” that the life on other planets does not have to be “aliens.” There are others who will openly admit to a belief in alien life forms and they will even share with you stories of alien abduction. While everyone’s understanding of life outside Earth varies nine out of every ten people will admit to believing in some other life force outside of our planet. For many people this belief tends to stem from science fiction but for others this belief in alien life forms comes from a desperate hope that humans cannot possibly be the most intelligent life form in the universe. Pointing to the signs of destruction all over the planet and pointing out how quickly the human race is destroying the one and only planet they can survive on to date, people tend to panic. How can the most intelligent life force in the universe be destroying the one planet which is able to sustain it? For this reason many people believe that there must be a more intelligent life force across the universe somewhere.
Finding Proof of Extraterrestrial Life
Despite NASA missions in to space, landing on the moon and sending satellites and vehicles up to other planets scientists have yet to be able to offer any proof of life on other planets. The point of contention; however, comes when the basis of life on other planets is based around the basic human needs for life to be sustained. Who is to say that oxygen levels are what it takes to allow survival of alien life forms? Who is to say that alien life forms thrive in similar temperatures to Earth? Who is to say that what is inhospitable to us is also inhospitable to alien life forms. After all isn’t the very definition of something “alien”, something that is different from our own? Still scientists, astronomers, physicists and even geologists scan the planets looking for traces of life based on what we know as a race, based on our basic needs and our requirements for survival.
What Types of Conditions Would Extraterrestrial Life Require?
Assuming that alien life forms do require similar conditions to humans to exist and sustain life on a planet there is no chance that they would be able to live on any of the planets within the Milky Way Galaxy. Within the Milky Way Galaxy are the planets that most children learn while they are in school, although the actual planets seem to be expendable, at least in the case of Pluto. The planets within our solar system as most of the current generation learned them include: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto (now recognized not as a planet but as a dwarf planet.) Life forms that have the same requirements as the human race are unable to sustain themselves on any of the above listed planets with the exception of Earth.
We will begin with Earth as we know it to be the only planet that has the ability to sustain life. Located as the third planet from the sun – some 93 million miles or one Astronomical Unit away, the Earth is the fifth largest planet in the solar system and has just one moon. The mass of the planet Earth is 5.98 x 1024 kg and has an average density of 5520 kg/m3. As such the Earth is known to be the densest of all the planets contained within the Milky Way galaxy. While temperatures on the Earth’s surface vary considerably most of the face of the planet is hospitable to life with temperatures ranging between -127 degrees Fahrenheit and 136 degrees Fahrenheit. The atmosphere of the planet Earth is made up of a variety of gasses which are primarily made up of 78% nitrogen, 21% oxygen, .9% argon and .03% carbon dioxide. In combination with the availability of water and the abundance of oxygen these conditions make Earth a suitable planet for life.
Comparing Earth to Other Milky Way Planets
So if the conditions listed above make Earth so hospitable to life why are other planets within the solar system considered so inhospitable to life? It is the combination of the factors listed above that make Earth hospitable to life, the balance of the gasses and chemicals needed to sustain cell life and generation is optimal within the Earth’s atmosphere, the temperature is comfortable enough for the most part to be able to sustain life, water is readily available to maintain appropriate levels of hydration (we are composed of mostly water you know) and all of these elements come together to allow life to flourish. So what is it about the other planets that make them inhospitable to life that resembles the human and animal races that thrive on Earth?
Mercury is the planet closest to the sun in the Milky Way Galaxy meaning that the temperature makes the planet inhospitable by itself with blazing hot temperatures in the day and freezing cold temperatures at night. The lack of atmosphere around Mercury means that there is no ability for the planet to maintain heat and temperatures would move from one extreme to the other very quickly. Mercury lack of atmosphere also means that the essential elements needed to support life in any form are missing. Mercury is also a particularly small planet measuring in at around one third the size of the planet Earth meaning that even if it were able to support life it would likely never approach the populations that we see on the planet Earth. The gravity on Mercury is also considerably less than the gravity on Earth meaning that living conditions would be altered dramatically for any life forms that were able to sustain life in Mercury’s atmosphere. As for the moon that controls so much on the planet Earth? Well, Mercury has no moon.
Venus is the second planet from the sun in the Milky Way Galaxy and is known to be the single hottest planet within the solar system making it completely inhospitable to life. As far as life on other planets goes, Venus is one of the most inhospitable planets in the solar system. With an atmosphere that is mostly composed of carbon dioxide and huge clouds of sulfuric acid soaking up the heat from the blazing hot sun there is absolutely nothing about Venus that suggests that life in any form is possible. There is not even a remote possibility that life would be able to survive on Venus due to the thick toxic atmosphere as well as the immense heat. Unlike Mercury Venus is similar in size to the planet Earth measuring around 95% of the diameter of Earth and in addition to this the gravity on Venus is also similar to that of Earth coming in at some 91% of Earth’s gravity. Venus, similar to Mercury has no moons and it also has extremely high atmospheric pressure which further ensures that life on Venus is simply impossible.
Mars was once believed to have been capable of supporting life because it is the planet that most resembles the planet Earth. Mars is the fourth planet from the sun in our solar system and while it resembles the Earth in some ways it is only about half of the size. The surface of Mars is dusty but the ground is frozen. Mars features north and south poles much like Earth and each of these are characterized by ice caps made from water and carbon dioxide. It is the possibility of water on Mars that leads many people to believe that life on Mars is sustainable. Recent missions to Mars sent back photographs which suggest that at once time Mars had rivers and other large bodies of water which give hope that life would have been, at least at one time, sustainable on the planet. Most of this water now forms the permafrost which coats the planet’s surface. The crust on Mars is thin, much like the crust on the planet Earth; however, the mass of Mars in comparison to Earth is a mere 1/9th of the mass of the planet Earth. Mars is located further from the sun than the Earth and it also has an atmosphere which lacks oxygen (Mars’ atmosphere is comprised primarily of 95% carbon dioxide, 3% nitrogen and 1.6% argon) and is significantly lower pressure than the atmosphere found on Earth. These factors are some of the few which would greatly impact any life which attempted to survive on the planet Mars. Mars does have two moons but they are significantly smaller than the Earth’s moon.
Jupiter is the largest of all of the planets in the Milky Way Galaxy and is the fifth planet from the sun. The atmosphere on Jupiter is particularly thick and the planet itself is made of gas for the most part. One of the most inhospitable aspects about the planet Jupiter in terms of supporting life is that Jupiter absorbs heat from the sun but then outputs twice as much heat making it an extremely hot and uncomfortable planet. As far as size, Jupiter is somewhere around 11 times the size of the planet Earth and in comparison to the gravity pull on Earth the gravity pull on Jupiter is considerably less in comparison to the sheer mass of the planet itself. Jupiter does have moons, four large moons to be exact and some thirty five smaller ones all of which would wreck havoc on life forms living on the planet. As if the idea that Jupiter is made mostly of gasses wasn’t enough to discourage concepts of life on Jupiter it should be mentioned that the average temperature of the clouds on Jupiter comes in at around -244 degrees Fahrenheit.
Saturn comes in second after Jupiter in terms of the sheer size of planets, and it is located as the sixth planet from the sun in the Milky Way Galaxy. The rings that Saturn is most recognized for are made from large chunks of both rock and ice and the planet itself is made up mostly of helium and hydrogen gasses. In size Saturn is about nine and a half times the size of planet Earth and is around 95 times the mass of the planet Earth although the pull of gravity on Saturn is approximately the same as that on the planet Earth. One of the unique factors about Saturn is that it is the only planet to be less dense than water although there are trace amounts of water to be found on Saturn, the majority of the water that would be available to inhabitants is found in the ice chunks within the rings of Saturn. The average temperature on Saturn is around -290 degrees Fahrenheit, simply impossible for life to be sustained. Saturn does have a variety of moons, over thirty to be exact; however, in comparison to the requirements needed for human type life forms to sustain life, Saturn is simply inhabitable.
Uranus is the seventh planet from the sun and due to its rotation on its axis; the seasons on Uranus alone are so extreme that they are inhospitable to life. In terms of size Uranus is about four times the size of the planet Earth and is about 14 times the mass of planet Earth; however, the pull of gravity on Uranus is only 91% of the pull of gravity on Earth. Uranus is 19 times further from the sun than the planet Earth and the mean temperature of the planet is around -350 degrees Fahrenheit which makes Uranus even more inhospitable than Saturn in terms of temperature. Saturn is considered to be a frozen planet and the atmosphere is made up of some 83% hydrogen, 15% helium and 2% methane, which is equally as inhabitable as the extreme temperature. Saturn has five moons; however, this planet is simply not suited to sustaining life similar to that of humans as a result of all of the other factors listed above.
Neptune is the eighth planet from the sun in the Milky Way Galaxy and it is the first planet that was predicted mathematically. Neptune is around 3.9 times the size of the planet Earth and is around 17 times the mass of Earth with just 1.19 times the gravity found on Earth. Neptune is some thirty times further from the sun than the Earth and as such the temperature averages at around -373.27 degrees Fahrenheit. Such frigid temperatures alone make Neptune inhospitable to life forms similar to those of the human race. Additionally on the planet Neptune seasons last for some forty years at a time which means that the north and south poles are in complete darkness or complete sunlight for 40 years at a time meaning that in the average lifetime of one person living close to these poles they would see the sunrise only once. The atmosphere of Neptune is believed to be thick and hazy and consist of 74% hydrogen, 25% helium and 1% methane which also make it inhospitable to human life. It should also be noted that Neptune is a particularly stormy planet with the fastest winds known to be found on any planet in the solar system which would not only make human life impossible even if the atmosphere were hospitable, but it would also make plant life impossible to sustain as well.
Note: we realize that Pluto was recently "decommissioned" as a planet, but being fans of Pluto, we are treating it as one for the purposes of this discussion.
Lastly is Pluto, the pseudo-planet or “dwarf planet” as it is now known. When it was known as a planet Pluto was the smallest of the planets in the solar system and it is about 1/5 the size of the planet Earth. Pluto is believed to be around 1/500th of the mass of the planet Earth and gravity is only around 8% which means that a person weighing 100 pounds would weigh just 8 pounds on Pluto. Pluto is 39 times further from the sun than the planet Earth and as such temperatures tend to average at around -393 degrees Fahrenheit which means that it is absolutely impossible for any human like life form to survive on Pluto. Pluto has never been visited to date and so scientists are unsure as to the makeup of Pluto’s atmosphere but it is believed to be made up of mostly nitrogen with some carbon monoxide and methane meaning that it would be impossible for any human like life form to even breathe. Pluto has one large moon and two smaller moons.
Finding Life Far, Far Away...
While the concept of life resembling human life on other planets may be possible as far as other planets in the universe it is certainly not a possibility on the planets that we have recognized so far in our own solar system. From temperature extremes to inhospitable atmospheres the planets within our own solar system are simply not able to sustain life with the same demands as humans. Now, were these other life forms to be so drastically different from humans that they were created from some new element all together and not carbon based life forms then perhaps the question of life on other planets within our solar system can be raised again. However, until there is proof of life forms other than those based on carbon, the possibility of life on other planets will have to depend on planets outside of our own solar system.
Detecting Life in the Cosmos [VIDEO]
This video, courtesy of PBS, addresses how we might find life on Earth-like planets. Harvard astrophysicist Lisa Kaltenegger shows us that the planet's atmosphere provides the key to finding life on other planets. Learn more on the PBS NOVA website.