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Better than Earth? Are there any over-inhabited worlds in the Milky Way?



  Better than Earth? Are there habitable worlds in the Milky Way?
NASA preview of ocean currents. Credit: NASA / SVS

I have said many times in the past that Earth is the best planet in the universe. No matter where we go, we will never find a planet that is a better home for Earth life than Earth. Of course, this is because we and all other life on Earth evolved in this environment. Evolution is adapting us to this planet and it is unlikely we will ever find another planet that is good for us.


However, is this the best planet? Are there any places in the universe that could have conditions for more diversity in life?

The fact that we have life on Earth at all is pretty incredible. We are in the habitable zone of a star with a major sequence that does not produce too much sunshine.

We have a dense atmosphere full of oxygen and nitrogen that we can breathe. The planet is large enough that it is still melted in its core, with a rotating ball of iron that supports a planetary magnetic field. This, combined with a dense atmosphere, protects the planet's surface from cosmic rays, the worst of the sun's ultraviolet radiation and deadly solar storms.

We have plate tectonics that constantly recycle material on the planet's surface, carrying fresh chemicals from within.

We have a relatively large moon that probably keeps our planet more stable in its axial slope, with ebb and flow that helped the early lifestyle to move from the oceans to land. But not a very big moon.

We have vast oceans that help to regulate the planet's climate by moving warm waters to cooler regions, making them more diverse and habitable.

  Better than Earth? Are there any over-inhabited worlds in the Milky Way?
Planets similar to Earth. Credit: JPL

The list goes on and I'm sure there are factors we haven't even figured out yet.

And when it comes to Earth, life thrives, finding its way into every possible ecological niche, adapting through evolution to deal with bitter cold, intense heat, intense pressure at the bottom of the oceans, even cities that live next to humans.

But could the Earth be better? Can there be planets that are super habitable?

If there's anything that astronomy has taught us, it's that we're not special. We are not the center of the solar system. This is not a special place or time in the universe. This probably means that the Earth is not the best place to live. This is the best place for people, but not for life.

According to a 2013 document, state astrobiologist Pen Ravi Kumar Koparapu and others calculated where the edges of a star's habitable zone should really be based on current climatic data. They calculated that the habitable zone around a solar star should be between 0.99 and 1.7 times the distance from Earth to the sun.

  Better than Earth? Are there habitable worlds in the Milky Way?
An artist's illustration of a habitable zone around different types of stars. Credit: NASA

Which means that the Earth is actually right on the inner edge of the habitable zone of the Sun. Like, barely. If it were closer to the sun, we would experience a greenhouse effect like Venus.

You probably want to be closer to the middle of the habitable zone, where orbital variations will not push your planet to extremes.

Earth is relatively young. Given the fact that the planet has existed for only 4.5 billion years and has only been inventing multicellular life for the last several hundred million years.

The sun is heating up, and because we are so close, we are actually only a few hundred million years, at most a billion years, before temperatures rise and the oceans evaporate. But what if life could take billions more years of evolution to create new, more diverse forms of life?

You think a mud is unusual, imagine what you would get with another 2 billion years of evolution. Or 20 billion.

  Better than Earth? Are there any over-inhabited worlds in the Milky Way?
Planets have discovered G, K and M type stars around the orbit of the Kepler Space Telescope. Credit: NASA / JPL

In a 2016 document called Superhabitable Worlds, René Heller and John Armstrong go through conditions that could make the most habitable planet possible. This is a very readable paper with many cool ideas. If you're a science fiction writer looking for world-building ideas, definitely check it out.

They offer stars with less mass than the sun, classified as K stars, probably the best candidates for diversity, as they & # 39; again durable and relatively stable. The K-type star will have a life of 20-70 billion years without these annoying red dwarf megaflars.

You will want other planets in the star system capable of redirecting asteroids and comets with their gravity to deliver water and other chemicals necessary for life. Thanks for that, Jupiter.

And ideally you want several habitable planets in the same system capable of sending life back and forth. A process known as panspermia.

Make your habitable planet the moon of a gas giant to get powerful tidal forces that keep fresh volcanic material erupting on the surface.

  Better than Earth? Are there any over-inhabited worlds in the Milky Way?
The magnetic field and electric currents in and around the Earth generate complex forces that have an immeasurable impact on daily life. The field can be thought of as a huge balloon, protecting us from cosmic radiation and charged particles that bombard the Earth in solar winds. It is formed by a wind of particles that blow from the sun, called the solar wind, cause it to be flattened on the "sunny side" and be thrown into a long tail on the opposite side of the Earth. Credit: ESA / ATG medialab

Better yet, have a binary planet where two worlds orbit around you, supplying tidal forces and exchanging life forms back and forth.

And we're just getting started!

Make the planet bigger and you get more surface to circulate the water temperature (more than that per second) but also more surface for life forms to use different niches.

So we're talking about a bigger, more massive planet. Once you get about twice the mass of the Earth, plate tectonics starts to shut down, so try to stay below that amount.

You also want a world big enough and hot inside for the movement of iron alloys in its core to support the magnetosphere throughout the planet.

You may be worried about surface gravity, but a planet with a double mass on Earth should be only about 40 percent larger in order to have roughly the same surface gravity.

  Better than Earth? Are There Super Milky Way in the Milky Way?
Simulation of pre-industrial Earth. Credit: NASA / GISS

At a recent conference in Barcelona, ​​Dr. Stephanie Olson of the University of Chicago presented the work they had done in their search for environments that would best support exoplanet life.

They used a NASA tool called the ROCKE -3-D model for general circulation. This is a truly amazing tool that is freely available to the public. You can go to the website and then see what the conditions would be in different worlds, from ancient Venus to planets orbiting Centaur.

You can simulate their air temperatures, precipitation, soil concentrations and more.

Let me show you some examples. Here is a pre-industrial Earth with air temperatures of about 35 ° C near the equator to colder than -60 ° C at the poles.

But you can replace Earth with ancient Venus, as the planet looks like 2.9 billion years ago, when the sun was 20 percent darker than it is today. However, it rotates once every 243 days and there was probably a shallow ocean that reached a depth of 310 meters across its lowlands.

  Better than Earth? Are there any over-inhabited worlds in the Milky Way?
Simulation of ancient Venus. Credit: NASA / GISS

And here is a planet orbiting the red dwarf star Proxima Centaur, the closest star to the sun. Because it orbits so close to its star, the planet is probably well finished. This has a dramatic effect on air temperature, with one side facing the star and the other facing

which roughly matches the atmosphere of nitrogen and oxygen on Earth, then you find yourself a world that seems much more comfortable to live.

Olson and her team used this software to simulate the climate and ocean habitats of different species of exoplanets. Here on Earth, the diversity of life depends on the absorption of material from the deep into the oceans, its return to the surface where life can use it.

More excitement means more biological activity, more diversity.

In other words, to find the planets with the most diversity of life, you want to find worlds that have a high amount of ocean circulation.

  Better than Earth? Are there any over-inhabited worlds in the Milky Way?
Simulation of a planet rotated in orbit by Proxima Centaur. Credit: NASA / GISS

Is there anything better than Earth? According to Olson, if a planet rotates slower, has a higher atmospheric density, and has continents, then you can increase the amount of ocean circulation.

And this gives us an idea of ​​what astronomers will be looking for as they explore the extra-solar worlds. When NASA's LUVOIR or HabEx missions fly in the 2030s, they will be able to directly depict extrasolar planets. They will measure chemicals in their atmosphere, detect water and even determine what part of the planet is covered on the continents.

We really should not be surprised if we find super habitable worlds in the Milky Way, worlds that are obviously more habitable than Earth. Once again it turns out that we are not special. That's good, at least we'll have company.


Studies redefine the lower limit for the size of the planet
Reference :
Better than the earth? Are there any over-inhabited worlds in the Milky Way? (2019, September 25)
retrieved September 25, 2019
from https://phys.org/news/2019-09-earth-superhabitable-worlds-milky.html

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