What is the purpose of the vast solar system, and all the stars and planets beyond? If the Jews are supposed to teach the world about G-d, does it extend to other planets? Why are we the only people with the Torah — maybe there really are more with access to it on other planets; shouldn't we know if there are? And where in the seven days of creation are the other planets mentioned -— it appears to center around the earth, sun and moon?
Radak (Rabbi David Kimchi) writes that the stars exert influence on earthly events, even upon the growing grass. This fits with the Talmudic teaching that "every single blade of grass below has a constellation above that strikes it and says ‘grow.' " This means that the heavenly bodies affect the earth — either by spiritual channels, or by the exertion of natural forces such as gravitation or radiation, or by some combination thereof.
The Prophet Yeshaya (Isaiah) tells us another reason for the vast universe: It's there for us to look at. Simply looking into the night sky can bring a person to long for connection to godliness.
"Raise your eyes aloft!" says Yeshaya, "And realize who created these!" By staring into the vast heavens, a universe so immense that it defies imagination, a person can achieve Awe of G-d.
It can bring humility, too, as King David describes his feelings: "When I see Your Heavens, Your handiwork, the moon and stars which You have established...What is a human that you should remember him? A Man, that your should be mindful of him?"
You ask, "Is there life in outer space?"
Relatively little regarding other worlds is mentioned in classical Jewish thought. Rabbi Chasdai Crescas (14th century) writes that nothing in the Torah outlook precludes the existence of life on other worlds. The verse "Your Kingdom is one which encompasses all worlds..." (Psalms 145:13) implies the existence of more than one world. According to the Talmud there are at least 18,000. The existence of these other worlds and the fact that they rely on Divine Providence make it reasonable to think that life might exist there.
The Sefer Habrit states that extraterrestrial creatures exist but that they have no free will. He adds that we shouldn't expect creatures from another world to resemble earthly life, any more than sea creatures resemble land animals.
Now you might ask what possible purpose could there be for the existence of "Martians" who possess no free will. This problem prompted Rabbi Yosef Albo (author of Sefer Ikkarim) to view such existences as illogical.
However, a possible purpose for their existence can be found in the work Tikunei Zohar, which states that in the future each tzaddik (righteous person) will rule over a star and have an entire world to himself. This world, with its entire population, would serve to enhance the tzaddik's spiritual growth.
That said, I must admit my own amusement at much of today's interest in the question "Is there life in outer space?" Am I just a provincial terrestrio-snob, or is the better question not "who cares?"
You see, there's a lot of interest — and hope — in finding the existence of other life forms; and I wonder if a lot of this doesn't stem from a desire to eliminate human responsibility: The smaller the fraction that we are of the universe, the less important our actions seem in the overall picture. What's murder, for example, if earth-life is just one of dozens, or jillions, of life-forms?
Your last question is "Why are the planets not mentioned in the Biblical account of creation?" The answer is that they are mentioned. The Hebrew word "cochav" means planet as well as star; so the planets are mentioned in the verse which says that G-d made the "cochavim." (Bereishet 1:16) Furthermore, all heavenly and earthly creations are summed up with the verse "The Heavens and the Earth and all their array (meaning everything within them) were finished." (Ibid. 2:1)
Rambam; Yesodei Hatorah 2:2
Yitav Panim 1: 167
The Aryeh Kaplan Reader