Rain outside the earth

Rain in the solar system

  In fact, rain is not the only phenomenon on the earth. It rains on many planets outside the earth, including planets, satellites and stars. So, what is the rain outside of the earth? Is this rain the same as the rain on the earth? What is so strange about them?
  According to previous research, scientists have found rain on a number of different planets. For example, Jupiter has a very violent weather phenomenon, because its climate system is an almost endless cycle, where storms will continue to develop and grow, and then form rainfall. The raindrops evaporate before reaching the core of Jupiter, and rise again in the form of vapor to give birth to a new round of storms, which repeats endlessly. Generally speaking, Jupiter’s rain is formed in areas with high temperature and pressure, where helium and neon combine to condense into raindrops and then fall toward the center of Jupiter.
  At the same time, it rained on Titan, Saturn’s moon. The “Cassini” interstellar probe provided evidence of rain on Titan. When it flew over the equatorial area of ​​Titan several times, it found that the surface there had changed in brightness. It seemed that a rain of methane wet the surface, and then the rain evaporated or was lost. According to various studies and surveys, it is very common to rain methane on Titan, and the amount of rain should be greater than that on Earth.
Rain on exoplanets

  Today, people have discovered many planets outside the solar system. As the technology for detecting exoplanets continues to advance, people have also discovered exoplanets with rainfall phenomena. For example, an exoplanet named K218b is considered a rainy planet. This planet was discovered in 2015, about 110 light-years from Earth. Astronomers used the Kepler Space Telescope to spot a red dwarf star around a dark star.
  The environment of K218b is very different from that of the earth, but it is located in the habitable zone. The right temperature makes this planet possess liquid water, and the existence of liquid water is very important for life. Data from space telescopes and computer simulations indicate that the atmosphere of K218b contains water vapor. Scientists believe that there are clouds in the atmosphere of this planet. They are formed in a specific place, where there may be the right pressure and temperature to allow liquid water to form and condense into rain. But these raindrops may never fall to the ground, they can only reach a certain point in the dense atmosphere, where the pressure and temperature are so high that the raindrops are evaporated before they reach the ground, so the water vapor again Rise to form a cloud.
  It is speculated that K218b may not have a solid surface, and the solid surface is where people know that life can evolve. The diameter of K218b is a little more than twice that of the earth, but its mass is 8 times that of the earth. Scientists believe that in the Milky Way, most exoplanets are similar in size to this planet, but it is now difficult to tell whether they are a rocky “super earth” or a gaseous “mini Neptune”, or a “water World”.
  In addition, people have also detected the possibility of metal rain falling on an exoplanet named Wasp-76b. This planet is very close to its host star. The side close to the star has a temperature of more than 2400°C during the day, which is enough to evaporate metal, while the side facing away from the star has a temperature that is 1000°C lower at night than during the day, which allows some metal particles to be able to Condensed and fell like raindrops.

There is rain in Jupiter’s atmosphere. This is the Jupiter vortex cloud photographed by the “Juneo” Jupiter probe.

The performance of raindrops is similar throughout the galaxy.
Rain on stars

  In addition to planets, people have also found that there is rainfall on some stars, which are called “brown dwarfs.” They are a bit special, the radiation is very weak, and the temperature is very low. Some of them seem to be more planetary, especially similar to those gas giants. For example, they will have an atmosphere full of carbon monoxide, hydrogen sulfide, methane, ammonia, and water. This layer of atmosphere is tumbling and surging, forming a strange and abnormal weather system. The internal heat causes the airflow to rise, which condenses into clouds. People have also noticed that the atmospheric activity on brown dwarfs is very intense, with powerful storms similar to Jupiter’s Great Red Spot, but the scale is far larger than Jupiter’s Great Red Spot.
  Some brown dwarfs have higher atmospheric temperatures, and there may be gaseous iron and silicates on such brown dwarfs. These iron and silicate will condense and turn into rain as the altitude rises and the temperature falls. Based on this, you can imagine iron rain pouring down in a swirling cloud layer composed of hot sand.
  Obviously, the rain in the universe is different. Astronomers have studied various types of rain under various specific conditions, including rain on Earth, methane rain on Titan, and rain that quickly evaporates in the atmosphere of exoplanets. These rains are composed of different substances and formed in various places. However, are there really no similarities between them?
Rain’s “Code of Conduct”

  In April 2021, planetary scientist Caitlin Loftus of Harvard University and colleague Robin Wordsworth published their latest research results. Their analysis shows that raindrops behave similarly throughout the galaxy. Whether it is the methane rain on Titan or the metal rain on the exoplanet Wasp-76b, they all obey the same rule, that is, no matter what material they are made of, the size of the liquid raindrops is always similar.
  In the universe, no matter how different the environment is, raindrops are still governed by some simple laws of physics. Therefore, any falling liquid raindrops tend to be spherical, and the rate at which they evaporate depends on their surface area. The laws they follow are basically fluid mechanics and thermodynamics.
  Caitlin Loftus and Robin Wordsworth considered a variety of different planetary environments, including Earth, Jupiter, Titan, and exoplanets. They believe that the different rainfalls in all these places behave similarly. At the same time, they also found that a world with stronger gravity tends to produce smaller raindrops, but the size of all raindrops will not exceed a narrow range, and their radius is mostly between 1/10 mm to a few millimeters. Bigger, not smaller. This is because huge raindrops will split as they fall to form smaller raindrops, while raindrops that are too small will evaporate before hitting the ground.
  Studying the phenomenon of rainfall in the universe is an important part of understanding the extraterrestrial atmosphere. At this point, the Earth cannot be completely centered. Astronomers believe that people should understand the different rainfalls in the universe, understand their universal laws, and establish a universal model of how the atmosphere and planets work.