The universe is a big, big place. According to astronomers, there are 100 billion to 200 billion galaxies in the universe. Each galaxy is filled with stars. Our galaxy, the Milky Way, contains up to 400 billion stars of various sizes and brightness. So, if you ask yourself how many stars are there in the Universe? The answer is mind-boggling. If you multiply the number of stars in our galaxy by the number of galaxies in the Universe you get a septillion stars, that’s a 1 followed by twenty-four zeros. But there could be even more stars than that.
NASA’ Kepler telescope has proven that many stars in our galaxy have planets. It is estimated that potentially habitable planets may be circling around 15 to 25% of stars in the galaxy.
Conservatively speaking, if 15% of stars have a planet between 1 and 1.6 times the size of Earth in the Habitable Zone, then you’d expect 15 percent of 90 percent of 100 billion stars to have such planets. That’s 14 billion potentially habitable worlds. Astrophysicist Natalie Batalha explained.
So from a mathematical perspective, it seems like life should exist somewhere else. But if life exists then where are all the aliens? Why haven’t we encountered any yet? Now, a new study could be the answer to the famous Fermi Paradox, which in its simplest form asks: Where is everybody?
Researchers from the Australian National University have proposed an explanation: life on other planets was probably brief, it has already come and gone.
The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens,
explained Aditya Chopra ~ lead author of the paper which is published in the journal Astrobiology.
Early life is fragile, so we believe it rarely evolves quickly enough to survive. Most early planetary environments are unstable. To produce a habitable planet, life forms need to regulate greenhouse gases such as water and carbon dioxide to keep surface temperatures stable.
About 4,000 million years ago, Earth, Venus and Mars might have hosted life when they were more similar. However, about one billion years after its formation, Venus became a boiling hothouse while Mars becoming a frigid desert, both fell victim to a runaway greenhouse effect.
Early microbial life on Venus and Mars, if there was any, failed to stabilize the rapidly changing environment,
said co-author Associate Professor Charley Lineweaver.
Life on Earth probably played a leading role in stabilizing the planet’s climate,
he said. Dr. Chopra said their theory solved a puzzle.
The mystery of why we haven’t yet found signs of aliens may have less to do with the likelihood of the origin of life or intelligence and have more to do with the rarity of the rapid emergence of biological regulation of feedback cycles on planetary surfaces,
If this theory is correct, wet and rocky planets, capable to host life seem to be everywhere, however, these planets haven’t environmental conditions conducive to life that Earth possesses. (this phenomenon is known as the “Gaian Bottleneck.”) So, maybe the universe is a microbial graveyard.
One intriguing prediction of the Gaian Bottleneck model is that the vast majority of fossils in the universe will be from extinct microbial life, not from multicellular species such as dinosaurs or humanoids that take billions of years to evolve,