Astronomy: Possibility of Life on Other Planets

IntroductionFor the longest time, scientists and laypeople have wondered, is there life on other planet?. What would these planets be like, and what kind of creatures would live on those planets? Many scientists have put forth theories, and considering the high amount of stars within our own galaxy (100 Billion!) it seems as if life on other planets is inevitable. However, in order for life to exist, the right conditions have to exist as well, and this is not so common to other star systems.

The Goldilocks ZoneOne of the unique conditions of Earth (or Terra as it is properly known) is that it has liquid water. As far as we know, liquid water is almost necessary to the development of life. This means that any planet capable of sustaining life must be far away enough from its sun so that the water on that planet is not vapor, but close enough to the sun so that the water is not ice. In other words, this is one condition necessary for a planet to have life. The term for planets that are ‘in the right spot’ is Goldilocks Zone planets. (This means that the planet is not to hot or cold, not to large or small, etc.) Temperature is not the only factor, as stars come in different types and shapes, and each star type might affect its planets in a particular way.

The examples to the left, are just a few of the many types of stars. For example, our star is classified as a White Star even though it is more of a Yellow Star. The importance of a star’s type is that it will emit heat and radiation at different levels. Each star will have its own gravity and will also affect the planets’ atmospheres, particularly if they are close to the star.

Another huge issue is that many of the star systems in our galaxy have multiple stars in them. There are quite a few binary and trinary systems. Indeed, the closest star system to our own is Alpha Centauri, which is a three-star system. In this case, the planets in those systems would have orbits that are affected by more than one star, this could create some very odd seasonal affects.

Consider this possibility, that a planet could orbit one main star, but be pulled very far away from it during its yearly cycle. Imagine a world

where it gets very close to its main sun during the summer, causing scorching hot weather, but is pulled extremely far away in the winter, causing the temperature to drop precipitously to the point where all water becomes ice. This would be a tough place to survive.

Red Dwarf

Orange Star

White Star

Blue Star

Red Giant

The Drake EquationThe Drake Equation is a theory for calculating the number of extraterrestrial civilizations in our galaxy. While this is an interesting theory, the issue is that many of the values in the formula are guesses or are unobservable.

Another issue with the Drake equation is that while it deals with many variables within Astronomy, it does not have any concrete evidence on how evolution would work on an environment dissimilar from Terra.ExoplanetsAn exoplanet is a world that exists outside of our solar system. Unfortunately, these planets are too far away from our own for us to see them. However, we have other means of detecting these objects. For example, our scientists have been able to discern the size and location of exoplanets using the movement of the stars that they orbit. Although the planets orbit stars, because the stars generally have the higher mass, the small mass of the objects orbiting the stars also affect their movement, even if only by a small amount. For example, if a person were to throw a rock, the rock would fly out of that person’s hand. However, the person would slightly be pulled forward by the light weight of the rock.

Additionally, using spectrums of light, we can detect gases and other data from possible planets. Unfortunately, because we use light to detect this, the information is often quite old. Even the closest star system to us, Alpha Centauri, is four light years away. Just to give an idea of how far away that is, light travels at approximately 12 million miles a minute.

Star Systems closest to our Solar SystemStar System # of Suns & Colors Distance from Sol

Alpha Centauri 3 (Red, Yellow & Orange) 4 light years

Barnard’s Star 1 (Red) 6 light years

Wolf 359 1 (Red) 8 light yearsLalande 21185 1 (Red) 8 light years

Sirius 2 (Blue-white, White) 8 light years

Luyten 726 2 (Red, Red) 9 light years

Ross 154 1 (Red) 9 light years

Ross 248 1 (Red) 10 light years

Eridani 1 (Red) 10 light years

Gliese 667CcSince the ability to detect exoplanets has been obtained, scientists have begun to put several of them in the Goldilocks Zone. One such planet is Gliese 667Cc. This particular planet was discovered using Doppler Spectroscopy, where the sun’s movement was determined to be affected by objects orbiting it. It is theorized that Gliese 667Cc is much larger than earth, but not as large as some gas giants. While this planet is in a zone where it could theoretically sustain life, it contains some variables that are not possessed by Terra.

For example, Gliese 667Cc is tidally locked. Therefore it does not rotate the way the Earth does, but has one face which always is directed towards the object it orbits (such as our

moon). It also possesses over three times the mass of Terra, indicating that it would have much higher gravity. It has also been determined that the surface facing the sun is much hotter than the Earth, rendering most of the planet unlivable. However, there is a chance for life to exist on fringes, where the planet is not exposed directly to the sun.

Gliese 667 Cc is a perfect example of the variables that need to be calculated when looking for life on other planets. Very few exoplanets are likely to be exactly the same size and shape of Terra. Very few will be orbiting a similarly sized star. One way to examine how other planets outside of our solar system might sustain life, is to look at the objects within our own solar system for comparison.

Artist’s impression of Gliese 667CcOur Planets (and some moons)Fortunately, our own system has a substantial amount of satellites orbiting the sun and each other. We have planets, dwarf planets, moons, comets and asteroids that we can observe through our telescopes and human-made devices that have been sent on missions to examine them. The amount of data we have accumulated on these celestial objects is helpful in estimating whether or not they could be life-sustaining.

Terra (Earth)

Luna (The Moon)

Venus Mercury Mars Ganymede Titan0123456789

1010

2.5

9.1

3.8

5.34.1 4

10

0.1

8.2

0.51.1

0.2 0.2

10

1.6

9.1

3.8 3.8

1.4 1.2

Known Satellites Compared to Earth

Size Mass Gravity

The above table illustrates the difference between Terra and other similarly-sized objects in our Solar System. Terra is given a value of 10 in all categories (Size, mass & gravity) and the other objects are all rated against that value. One of the most notable elements in the chart is the low mass in every object except Mercury. This in turn leads to low gravity for most of those satellites. The statistics seem to support Venus as the most likely candidate for extra-terrestrial life since it is very close to Earth in every category. However, there are other factors not addressed by the chart which severely affect each candidate’s ability to sustain life.

For example, looking at the planets within our system, each has their own issues which would make it difficult for them to sustain life. Mercury is too close to the Sun, and as a result, has no atmosphere. Venus is covered in gas creating a greenhouse effect which results in an average surface temperature in excess of 800 degrees Fahrenheit. Mars has the opposite issue. While it can become warm on Mars (80 degrees), the temperature can drop to below 200, which would make it hard for animals to survive the nearly 300 degree shift. The rest of the planets are all gas giants which come with their own issues.

Conclusion

There are many factors which would make it difficult for planets to support life. The chance of life on a planet developing a civilization are even less likely. However, this speculation is with the data that we know. Given the immense size of our galaxy and the possibility of factors and knowledge that we do not possess, any chance of accurately calculating the likelihood or unlikely-hood of life is quite limited.

Further Questions1. This chapter talks about factors that make alien civilized life improbable. What factors might make it more probable?

2. Imagine that there was life on Gliese 667 Cc. What do you imagine it would be like given the conditions of that planet?

3. Do some online research about other exoplanets and explain why some scientists are optimistic about the possibility of life on that particular planet.