Water knows the answer - looking for liquid water is looking for possible alien life

On September 28, 2015, the media widely reported: NASA claimed that there is liquid water on the surface of Mars.

Some conspiracy theorists immediately said that this was a promotion in conjunction with the science fiction blockbuster "The Martian" which was released on October 2.

In fact, NASA’s original words are this: Using high-resolution imaging equipment and the Compact Mars Reconnaissance Imaging Spectrometer, spectral evidence of the presence of brine (perchlorate salt water) on Mars was discovered.

After reading NASA's detailed statement, someone joked: Before the release of the "Three-Body" movie, we can also publish a press release - "Shocked!" Centaur discovers Trisolarial soaking pool! 》

In fact, NASA has always been a clickbait.

On October 22 last year, NASA stated that it would release a "big news" "related to the moon." For a time, astronomy enthusiasts and related institutions around the world became excited again, and various speculations and deductions emerged one after another - is it life? Is it an organic molecule? Or at the very least, water?

Sure enough, in the early morning of October 27, the magazine "Nature Astronomy" published an article: "The Sophia Observatory discovered molecular water in the illuminated area of ??the moon."

To put it bluntly, there is no life on the moon, no organic molecules, and no bright puddles like ordinary people imagine. Scientists have only discovered through spectroscopy that there are water molecules in the lunar soil with a content of one percent of the Sahara Desert. Moreover, these water molecules are trapped in a structure called "impact glass". You can think of this structure as amber - the water molecules are the ancient bugs sealed in the resin.

When everything returns to reason, carnival is always hard to come.

The reason why this news does not excite those in the know is that water is not a rare thing in our universe. Water molecules are made up of two hydrogen atoms and one oxygen atom, and these two elements are the first and third most abundant in the universe respectively. At the same time, they are both highly chemically active elements and have countless opportunities to combine freely to form water molecules.

The universe is not short of water, and the same is true in the solar system.

If all the water on the earth became liquid, it could form an ocean several kilometers deep on the surface. But what many people don’t know is that the Earth has even less water than Pluto.

Even Europa, one of Jupiter's moons, contains much more water than Earth.

But in the solar system, Europa is still far from being the planet with the most water. Ganymede, which orbits farther away, has thirty times as much water as the Earth.

Is this the end? No, far from it. According to speculation, the total amount of water ice on Uranus is more than 40,000 times the amount of water on Earth!

Therefore, the discovery of a small number of water molecules in the illuminated area of ??the moon is really not something to cheer about. What's more, earlier, humans had directly detected the existence of water ice at the poles of the moon.

People who eagerly think of extraterrestrial life after hearing the preview of "big news" may be disappointed again.

But in the search for extraterrestrial life, water is indeed one of the indispensable conditions. The basis of life is various complex biochemical reactions, and liquid water is an excellent solvent that allows these reactions to proceed smoothly. It is not too much to say that finding liquid water is close to finding the possible birthplace of life.

So water is not important, what is important is liquid water.

In 2018, NASA once again claimed that a liquid water lake was discovered 1.5 kilometers under the Mars Antarctic ice cap. However, this water has only been detected so far, and is still far from being actually exploited. So in "The Martian", poor Matt Damon had to use hydrazine to create hydrogen to synthesize liquid water in order to water the potatoes, and he blew himself up.

Liquid water resources were quite abundant on ancient Mars, which has been confirmed by many evidences. Unfortunately, as the magnetic field of Mars disappeared, the atmosphere was stripped away by the solar wind, and the water bodies also decomposed and dispersed under the strong radiation. Currently, most of the water on Mars exists in the form of polar cap ice caps and underground ice layers. If they are all melted and spread on Mars, the depth of the water will not exceed five meters.

Earth and Mars are not the only places where liquid water exists. In fact, there are some 200 kilometers high water vapor fountains on Europa. Scientists believe that beneath the 10 to 30 kilometers of Europa's icy crust there is an ocean as deep as 100 kilometers, which is often imagined to be the cradle of life on Europa.

Another planet where water vapor jet plumes have been observed is Enceladus, so like Europa, it can directly prove the existence of an underground ocean.

But in addition to the two of them, humans have also speculated through some indirect data that in the high-pressure and high-salt environments beneath Ganymede, Callisto, Titan, and even Pluto and Uranus, there are also There are huge amounts of liquid water.

So the question comes again: With liquid water, is it possible for life to be born?

Scientists continue to add conditions: it depends on where liquid water was discovered. If stable liquid water is found on the surface of a star, it basically means that the star is in the habitable zone.

The opposite understanding is also true - when we say that a planet is located in the habitable zone, it means that liquid water may exist stably - this is the core feature of the habitable zone. Astrobiologist James Castine estimated in 1993 that the width of the solar system's "continued habitable zone" ranges from 0.95 to 1.15 astronomical units (astronomical units = the average distance between the sun and the earth). The Earth is right in the middle of the habitable zone, while Venus on the inside and Mars on the outside are close to the two boundaries respectively.

Knowing the proportion of the width of the habitable zone of the solar system, you will understand how incredible the position of the earth is - if the sun is the screen in the theater and the Oort Nebula is the last row of seats, then the solar system The habitable zone is only as wide as two hairs.

So, it seems that things have become: as long as a planet is found in the habitable zone of a certain star, it can be assumed that liquid water is stably present.

——They did the same thing.

In recent years, news about the discovery of habitable planets in the universe has emerged one after another. As of 2019, humans have discovered more than 200 exoplanets in the habitable zone. From "Super Earth" to "Super Earth 2.0", from "Kepler-22b" to "Proxima Centauri b", from Cygnus, which is 600 light-years away from the solar system, to Centauri, which is only 4.2 light-years away. It seems that every new discovery is suggesting that this planet is "closer to us", "more similar to the Earth", "looks more suitable for immigrants", and even - "liquid water may exist."

< p> Please note, it's just "possible"!

The British "Daily Mail" reported that after analyzing space data collected by the Kepler space telescope, scientists pointed out that for every red dwarf star in the Milky Way, there will be a star the size of the Earth. Similar planets suitable for human habitation; but a new study by scientists from the University of Chicago and Northwestern University shows that the number of habitable planets corresponding to each red dwarf star may be two, which means that the number of habitable planets in the Milky Way is There may be as many as 60 billion inhabited planets.

Therefore, although this direction cannot be said to be bankrupt when searching for so-called "habitable planets" based on the habitable zone idea, it actually does not have much reference significance.

So, what is a truly habitable planet?

It was still Professor James Castine who gave this answer: An Earth-like planet around a star has an atmosphere containing nitrogen, water and carbon dioxide, and the climate formed can maintain it for a long time. Life based on water.

So in the future, we don’t need to be excited about newly discovered “habitable planets”—unless they provide conclusive evidence that liquid water really exists on the surface of that planet.

After all, of all the life forms known to man, water may know the best answer.

Text/Liu Yanzeng