World – NEARLY Earth

HIGHLIGHTS

A planet that looks nearly
like Earth, but not quite.

Archipelago Planet
is larger than Earth, has
higher gravity, stronger
winds, and flat
terrain.

Super-Earth could be
superhabitable.

This is what we’ve been searching for the whole time: a planet just like ours! Well, … nearly. A few things may be different – like the colour of the sky, or the gravity, or the shape of the landscape, for example. Is a “Nearly Earth” really out there? Well, quite a few promising candidates have been identified, and some may even be more hospitable to life than our own planet.

What makes a planet Earth-like? It would have to be a rocky world, covered by oceans, but with a few continents that offer dry terrain. The planet would have an atmosphere that traps enough heat to keep the water liquid, and a magnetosphere that holds its host star’s damaging solar rays at bay. Most importantly, it would be located in the “habitable zone,” which means that the planet would orbit its sun at a distance close enough for water not to freeze solid, but far enough for water not to boil away. The zone where water stays liquid on a planet’s surface is also called the Goldilocks zone – it’s just right.

Have we found any Nearly Earths? Actually, we have, and some of them are turbo-charged versions of our home planet. Called Archipelago Planets, they are in the class of Super Earths, which are terrestrial planets about twice the size of Earth and up to 10 times its mass. Because of its larger mass, an Archipelago Planet’s gravity would be higher than on Earth, and it would have a thicker atmosphere and stronger winds. This would cause strong erosion, so there wouldn’t be any high mountains on this type of planet and the landscape would look very flat. In fact, this Super Earth would be covered by a shallow ocean dotted with island chains. The warm tidal pools of an Archipelago Planet would be an ideal environment for life to develop, making it “superhabitable.”

Other intriguing Earth-like candidates have been discovered which are very similar to our own planet but vary in one aspect or another. The Trappist 1 system, for example, hosts seven rocky worlds that orbit a star that is very similar to our own. Imagine living on a planet with nearby sister Earths that appear so large in the sky that you could easily see continents and other major features. Two planets in the Trappist 1 system orbit in the habitable zone and may host life. 

Another promising “Nearly Earth” example is Kepler 186f. It is about 10% larger than Earth and is located in the habitable zone, but it orbits a red dwarf star. As a result, daylight on this planet would be much dimmer, and any life relying on photosynthesis would likely be very dark, maybe even black, to absorb as much energy from its sun as possible.

Kepler 186f: The first Earth-sized exoplanet ever found

Astronomers have discovered the first Earth-size planet orbiting a star in the “habitable zone” – the range of distance from a star where liquid water might pool on the surface of an orbiting planet. The discovery of Kepler-186f confirms that planets the size of Earth exist in the habitable zone of stars other than our sun.
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Kepler 452b: A larger cousin of our Earth

This rocky world is about 1.5 times larger than Earth, but it orbits a star very similar to our Sun, and at the same distance, placing it in the “Habitable Zone.” How is this world similar to ours? How is it different?
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What we found when we went looking for another Earth

Exoplanet hunter Sara Seager talks with Adam Cole about how we started looking for planets outside our solar system and what we have discovered so far. Learn about the habitable zone, the Kepler mission, the Trappist 1 system, and sci-fi planets that actually exist.
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HABITABILITY

In the case of an Archipelago Planet, habitability would be excellent. This world’s many warm ponds and tidal pools would act like a series of experiments, each running an iteration of the origin of life. Different versions of life may develop, adapt to their “laboratories,” and then compete with the lifeforms around them. The entire planet would be a giant petri-dish.

If the Earth-like planet were orbiting a star that is cooler than ours, life would have a lot more time to develop there. Dimmer, redder stars live a lot longer than our Sun. A planet orbiting such a star may receive less heat and light, but surface conditions would be more stable, so life could potentially exist there for eons.

STORY IDEAS

What would it be like to arrive at a planet that resembles ours –  but something is slightly off? Maybe the gravity is slightly higher or lower, maybe the planet has a different kind of atmosphere, or the proportion of oceans and continents is reversed. How would you have to adapt?

We’re not just looking for a second “Earth,” we’re also looking for Earth as it is now. Earth used to look very different a few million years ago. Before life emerged, our planet had no oxygen atmosphere. There used to be periods when the entire Earth was covered in ice and snow. The continents used to be in different positions. What would happen if you identified an Earth-like planet but it changed by the time you got there? What would it be like to go back in time on our own world – or travel into the future?