Are there planets that are better than Earth?

There are better worlds than the earth

More habitable than Earth: Astronomers have identified 24 exoplanets that could be even more life-friendly than our home planet. They are slightly older, warmer, and larger than Earth, and orbit slightly cooler and smaller stars than the Sun. This gives these planets better starting conditions and more time for life to develop, as the researchers explain. It is not known whether there is extraterrestrial life on these “super-habitable” worlds.

In order for life to develop on a planet, the prerequisites must be right - the planet must be habitable. This includes an atmosphere that retains water and breathing gases, a temperature that enables liquid water, and the presence of suitable chemical starting substances and habitats. In addition, there is the time factor: Venus and Mars were also life-friendly in their early days, but this habitable phase ended before life could develop - at least according to the current state of knowledge.

There could be better planets out there

But what does it look like beyond the solar system? After all, astronomers have now discovered hundreds of exoplanets that are Earth-like, water-rich and potentially life-friendly. Even our closest neighbor, Proxima Centauri, has a planet in the habitable zone. The search for extraterrestrial life could therefore be particularly worthwhile on such planets.

“But we have to be careful not to just look for a second earth, because there could be planets that are even more suitable for life,” explains Dirk Schulze-Makuch of Washington State University. He and his team have now investigated in more detail which characteristics such super-habitable exoplanets should have and whether they exist among the more than 4,500 planet candidates identified by the Kepler space telescope via transits.

Sun is not the optimal home star

What makes a super-habitable planet? The first factor is the home star: so that life has enough time to develop, a star that is as long-lived as possible with few bursts of rays is optimal. The sun, however, could make all life on earth impossible in just over a billion years - all in all, it will only offer life-friendly conditions for a good five billion years.

"Life on planets around sun-like G stars could simply run out of time," the researchers say. Smaller, lower-mass stars would therefore be cheaper, as they live longer. Red dwarfs, however, experience too many powerful bursts of radiation that can sterilize planets close to them. The astronomers identified a star of spectral class K as the most suitable as the home star - an orange, around 1,000 degrees cooler and 20 percent smaller star than the sun.

Bigger and warmer than the earth would be better

Even with the planetary factors, the earth is not the ultimate: A super-habitable planet would have around 1.5 earth masses - it would therefore be more of a super-earth. Because it can hold an atmosphere better, generates more heat inside through radioactive decay and, thanks to a larger surface, offers more choice for habitats, as the researchers report. A large moon, a more even distribution of land and water and active plate tectonics would also be beneficial.

A slightly higher temperature would also be ideal: “Based on our experience of the earth, most biomass and biodiversity are found in the tropics,” explain Schulze-Makuch and his team. Therefore, a planet without cold polar regions and with a warm and humid climate would probably be even more optimal - such conditions prevailed, for example, in the Carboniferous Age. According to the researchers' calculations, a planet that would be around five degrees warmer than today's earth would therefore be ideal for life.

24 potentially super-habitable worlds

Based on their list of characteristics for a super-habitable planet, Schulze-Makuch and his team have tracked down 24 exoplanets that could offer even more life-friendly conditions than Earth. Sixteen of them are between five and eight billion years old and nine of them orbit K stars. Many of these exoplanets are super-earths that are twice to a good four times the size of Earth.

However, none of the 24 candidates met all the criteria for a super-habitable world. Still, some come very close to the ideal, at least in some respects. Extraterrestrial life could find even better conditions on them than on Earth - if it exists there. However, this cannot be verified with the telescopes and sensors available today. Because all 24 planet candidates are well more than 100 light years away from us.

Greatest chance of extraterrestrial life

“Even if these exoplanets are therefore outside the range of the TESS space telescope, we consider it very possible that there are some super-habitable representatives among the exoplanets known today,” say the astronomers. "Should such a world be discovered in our immediate vicinity in the near future, it would in any case have a higher priority for the further search for extraterrestrial life than most earth-like planets." (Astrobiology, 2020; doi: 10.1089 / ast.2019.2161 )

Source: Washington State University

October 6, 2020

- Nadja Podbregar