The search for a habitable planet like Earth just hit a new challenge, from planets that could well be BETTER than Earth at fostering life. How could this be? We all know Earth is the template on which we base our assumptions about the chances for life elsewhere. We are searching Mars and other places in our own solar system, including Venus.

It turns out that the best habitable planet could have conditions much MORE suitable for life than Earth. A habitable planet, such as Kepler 62F, shown here, which orbits a K-type star, could have several variables that influence life. This world, and others like it, could be orbiting stars that are more slowly changing and longer life expectancies than the Sun. Astronomers have actually identified a couple of dozen contenders for the “Better than Earth” sweepstakes. They are called “super-habitable planets” and if they can be found, they’d all a little larger, warmer, and likely wetter than Earth. Those conditions make it easier for life to develop and thrive.

All of this comes from a study made by a scientist at Washington State University. Dr. Dirk Schulze-Makuch published an article in the journal Astrobiology that details the types of planets and stars that could be in the super-Goldilocks state. That is, more welcoming of life than our home planet. His contenders are more than 100 light-years away from us, so we’re going to need some superpower telescopes to observe them. That would include the upcoming James Webb Space Telescope, as well as the proposed LUVOIR space observatory and European Space Agency’s PLATO space telescope.

Searching for a Habitable Planet that’s “Super”

For now, Schulze-Makuch, a geobiologist with expertise in planetary habitability, is working with astronomers Rene Heller of the Max Planck Institute for Solar System Research and Edward Guinan of Villanova University to answer questions about superhabitability. They needed to identify the criteria that would make a world “superhabitable” and then look through the characteristics of the more than 4500 known exoplanets to see if they fit. Those worlds may not be inhabited, but they could have the conditions to host life.

What Makes a Habitable Planet “Super”

The first thing was to look at systems with worlds that could be terrestrial, and orbit within the stars Goldilocks zone. That’s the region where liquid water could flow on the surface of a supposedly habitable planet. But, there are other factors to consider, such as the age of a planet’s star. The Sun, for example, will live about 10 billion years.

That sounds like a long time, but think about this: life started here some 3.8 billion years ago, when the Earth was pretty young. However, but it took quite a long time before the more complex life forms appeared. So, it might make sense to look for worlds where the stars live longer to search out the possibility of complex life arising on them. Shorter-lived stars wouldn’t be around long enough for complex life (and indeed, intelligent life) to form. Or, they’d start to age before then, making conditions for life worse than before.

So, longer-lived G stars would be good candidates forhosting superhabitable worlds. And, it’s possible that K-type stars could be useful here. They’re cooler, less massive, and luminous than the Sun. Their big advantage is that they live a lot longer than the Sun — somewhere between 20 to 70 billion years. That lifespan would allow orbiting planets to be older as well.

All that extra time gives life a lot longer to develop and create more complex forms. The downside here is that much older planets could have exhausted their interior heat, which would affect their ability to create a magnetic field. Given these constraints, the sweet spot for life on any world is probably between 5 to 8 billion years. At 4.5 billion years, Earth is a precocious producer of life. It might be an outlier.

More Measures of Habitability

Age is only one factor to think about when we consider whether a habitable planet could be superhabitable. Their sizes and masses are also important. A planet that is 10% larger than the Earth should have more habitable land distributed among its oceans and continents. That gives more places for life to life and thrive. If we find a planet that is about one and a half times Earth’s mass, it’s very like to retain its interior heating. That usually happens through the decay of radioactive elements in the core. Finally, such a more-massive world would have a stronger gravity. That helps it retain an atmosphere much longer than smaller, less-massive worlds.

The atmosphere is a big player in the habitability of a planet. Water is a huge factor — in fact, it’s necessary for life. A little more water in the form of moisture, clouds, and humidity is always useful when fostering life. A slightly overall warmer temperature, a mean surface temperature of about 5 degrees Celsius (or about 8 degrees Fahrenheit) greater than Earth, together with the additional moisture, would be also better for life. Of course, we can see this playing out here on Earth. Places with higher warmth and moisture have a greater diversity of life (such as in tropical rain forests) than the areas with colder, drier conditions.

Are There Superhabitable Planets “Out There”?

The scientists looked at 24 planet candidates they thought might meet all the criteria for being “better than Earth” in terms of superhabitability. Only one meets four of the criteria, but none meet all of them. So, no superhabitables out there among the 24. But, the galaxy is huge and we’ve only just started the search for exoplanets in the past 25 years. Earth is still the only place we know FOR sure has life, and it does a good job at hosting life across a huge range of conditions. Still, the ideas in the current research pave the way for future searches around stars that may even provide better conditions for life than we have here.

The story of the early universe is one that astronomers are filling in with each new observation. To look back across billions of years of time, across the light-years, takes some pretty complex instruments and long observations. The story, as we know it from those studies is really intriguing.

First, we have the origin of the universe, which we actually cannot directly detect. That occurred nearly 14 billion years ago, and fairly soon after this “Big Bang” happened, there was a period of darkness called “The Dark Ages”. That was a time that the newly born universe was cooling. Eventually, conditions allowed light to pass through the masses of hydrogen and helium that existed at the time.

The period after the Dark Ages is the Epoch of Reionization, and it’s when the first stars could shine out. At that point, the first galaxies were starting to form. They were cuddled into various shapes by the gravitational influence of dark matter.

That’s sort of the executive summary of the first epochs of the universe. It would look strange to our eyes: first, just masses of gas, and, of course, darkness. Then, the formation of hugely massive monster stars, and clumps of material that would later become galaxies. It was a baby universe busily evolving and growing up using what it had at hand. There were black holes, too. But, no planets and no life.

Shaping Galaxies

Galaxy formation and evolution is another area where astronomers are still busy telling a story. The general tale is that galaxies form by cannibalizing and merging with each other. It started with little shreds of galaxies that existed more than 13 billion years ago. They collided, accreted, and got bigger. Galactic mergers and acquisitions still happen. And, somehow, black holes are involved. That part of the story is still very much under development.

Astronomers used the Very Large Telescope in Chile to look at a very curious grouping of galaxies around a black hole. This image shows an artist’s concept of what it might look like if you could be close by. There are six galaxies, all arrayed around a supermassive black hole in a cosmic “spider web” that is about three hundred times the size of the Milky Way Galaxy. The whole assemblage lies about 13.1 billion light-years away, in the direction of the constellation Sextans.

The fact that they saw such a supermassive black hole so early in the universe is a tantalizing clue to the development of these odd monsters of the cosmos. To get black holes, you need massive stars. In the early universe, the first ones would have died fairly quickly and formed black holes. To get a supermassive one takes a lot of stellar-mass black holes and then, somehow, they need to get crammed together to make a black hole of a billion solar mases. That takes time, too.

So, one of the big questions is “how do you get enough fuel to make these supermassive black holes so early and so fast in the history of the universe?”

Early Universe Mix: Galaxies, a Black Hole and Dark Matter

The answer could be right in front of us now. The six galaxies arrayed around the black hole are likely providing the fuel to turn a massive black hole into a supermassive one. There’s also another key ingredient needed: dark matter. It’s likely shaping the whole collective with its gravitational influence.

The observations of this six-galaxy collection and its black hole are another important clue to conditions in the early universe. They show that giant haloes of this unknown “stuff” are also part of creating the web-like structure around the six galaxies and their companion black hole. Understanding that, and finding more examples of such activity in the infant cosmos help explain more details of conditions “way back when”. Stay tuned!