At first humans only thought there was only himself and planet Earth as the only place to live. After that, the existence of other planets and the Milky Way galaxy was revealed. Then found the planets outside the solar system called exoplanets (extrasolar planets). At the same time there are researchers who wonder whether there are other creatures that live beyond Earth. With the discovery of more than 4,000 exoplanets, researchers are increasingly convinced that humans are not alone on Earth. There is another possibility of life out there. In addition, there is also the possibility of other Earths in the solar system or habitable planets.
Do aliens really exist?
One of the aviation agencies whose mission is to find signs of life on other planets is NASA. That is a very interesting question and one that NASA has been trying to understand, explore, and solve for a long time. However, NASA hasn't found life on other planets anywhere. NASA also hasn't seen any scientifically backed up evidence for extraterrestrial life. Although no evidence of aliens or other life beyond Earth has been found, NASA continues to explore.
“The universe is a pretty big place. If it's just us, it seems like a terrible waste of space," said US astronomer Carl Sagan.
Meanwhile, Nobel Prize-winning physicist Enrico Fermi tries to answer the question of the existence of aliens.
"Fermi understands that any civilization with modest amounts of rocket technology and meager imperial incentives can rapidly colonize entire galaxies," a representative from the Search For Extraterrestrial Intelligence (SETI) Institute in Mountain View, California, wrote in the Fermi Paradox explainer.
It was also written that within a few tens of millions of years, any star system could be brought under the imperial wing. Tens of millions of years may sound like a long project, but it's actually quite short compared to the galaxy's age, which is roughly a thousand times more. Then Fermi died in 1954, so the exploration and explanation of ideas fell to others, such as Michael Hart who wrote an article entitled "An explanation for the absence of extraterrestrials on Earth". The article was written in the journal Quarterly of the Royal Astronomical Society (RAS) in 1975.
"We observe that no intelligent extraterrestrial beings are currently present on Earth," Hart wrote in the abstract of the paper.
He also wrote stating that this fact is best explained by the hypothesis that there are no other advanced civilizations in this galaxy. Hart argues that intelligent aliens may have visited Earth at some point in the planet's history, unless they started their journey less than two million years ago. He thought the lack of such visits was most likely due to a lack of intelligent aliens. But he also outlines four other potential explanations:
1. Aliens never come here because of physical difficulties "which make space travel impossible", which may be related to astronomy, biology, or engineering.
2. Aliens choose never to visit us.
3. Advanced civilizations beyond Earth appeared too recently for aliens to reach us.
4. Aliens have visited Earth in the past, but we have not observed them.
Is the neighboring planet Earth habitable?
According to Mary Voytek, senior scientist for astrobiology at NASA Headquarters in Washington, DC, although some planets appear habitable or habitable, so far there are only humans on Earth.
"There is nothing else in the solar system with a lot of life on it. Otherwise, we might detect it," said Mary Voytek
Here are some planets that are called Earth-like but uninhabitable:
1. Venus
Venus is often called Earth's "sister planet". With a size and structure similar to Earth, Venus has a big difference. The differences include a surface hot enough to melt lead, a very heavy atmosphere, and a very volcanic geology. Venus was born like Earth, perhaps even with an ocean that spanned the entire planet. But the runaway greenhouse effect may have boiled Venus' oceans and turned the planet into eternal hell and the hottest world in the solar system.
"The planet's divergent path includes habitability loss, surface water loss, sulfuric acid clouds, and a dense carbon dioxide atmosphere," said Vikki Meadows, astrobiologist who heads the Virtual Planetary Laboratory at NASA's Nexus for Exoplanetary Systems Science.
2. Mars
Investigations by orbiters, and rovers on the surface, confirm that the Red Planet was once wet with rivers, lakes, possibly even oceans like Earth and was potentially habitable.
"The most interesting thing about Mars is that, at one time, 3.5 billion years ago, it was clear that the climate on Mars was more similar to that of Earth and had liquid water on its surface," Voytek said.
Then the solar wind and radiation strip away most of the atmosphere. Its minimally active core ceases to generate a protective magnetic field. Its surface becomes extremely cold and dry even when bombarded with radiation. Mars' shortcomings according to Voytek are the lack of available water and the absence of plate tectonics (the processes on Earth that move the continents over thousands of years and recycle buried nutrients back to the surface).
"Even if surface conditions don't match, we may find evidence of past life, or perhaps surviving life," said Morgan Cable of the Astrobiology and Ocean Worlds Group at NASA's Jet Propulsion Laboratory.
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