Scientists imagine what a Planet B would be like

Since the first exoplanets were discovered in the 1990s, many have wondered if we could find another Earth, a place called Planet B.

Natalie Batalha, professor of astronomy and astrophysics at the University of California, Santa Cruz, has seen the science of exoplanets grow and change since the first discoveries. Battle was a co-investigator and mission scientist on the Kepler mission, the first that can survey Earth-sized planets around other stars. The mission transformed the science of exoplanets.

“In the first decade of exoplanets, it was as if we were collecting postage stamps, discovering one planet at a time”, he compared. “But after the Kepler mission was launched we blazed a trail in terms of sensitivity. We were able to discover planets by the hundreds at once. (The James Webb Telescope) will give us a new lens in the study of exoplanet diversity. We are entering the third era of characterizing the atmosphere of exoplanets.”

So far, the study of exoplanets hasn’t revealed another Earth, and that’s unlikely, even with the launch of the James Webb Space Telescope in December. It will examine the atmosphere of exoplanets orbiting stars much smaller than our sun.

“One of the key aspects of Webb is understanding whether these exoplanets actually have at least some of the habitability properties, but they’re not going to be true Earth twins,” said Klaus Pontoppidan, Webb project scientist at the Space Telescope Science Institute in Baltimore.

But the planets that will be studied by the telescope may be linked to an intriguing idea: what if life happens differently outside Earth? It’s a topic that the successors of the Webb telescope will be able to investigate for decades to come.

“There really isn’t a Planet B for us,” said Jill Tarter, an astronomer and former director of the SETI Research Center, who currently holds the Chair Emeritus for SETI Research (an acronym that means “life beyond the earth”). “Unless we figure out a way to solve all of the global problems we face here and how to mitigate those challenges, wherever we go we’re going to create the same problems we’ve created here on this planet. There is no emergency exit”.

What is Planet B?

If there is a Planet B somewhere in space, is it more like Earth, or is it going to surprise us and be something completely unexpected?

“When we find a Planet B, it needs to be a true Earth twin, a planet orbiting a Sun-like star, in an Earth-like orbit, with a thin atmosphere, oceans and continents”, detailed Sara Seager, astrophysicist, planetary scientist and professor at the Massachusetts Institute of Technology (MIT).

As astronomers were keen to point out, each telescope brought many unexpected discoveries beyond what they were expected to observe. Planet B might be similar.

“I want us to find life in something that doesn’t look too much like Earth,” said Nikole Lewis, an astrophysicist and assistant professor of astronomy at Cornell University.

“It’s safe for us to say that if it looks like Earth and smells like Earth, then it’s probably Earth and therefore has life. But I don’t think that’s enough of the adventure, so I’d love to start looking at the atmospheric chemistry and temperature of planets that are perhaps a little larger than Earth,” he continued.

The search for Planet B is not simple: it is incredibly complicated to balance what we understand about the process of life on Earth with what we don’t know.

On Earth, even in the most extreme environments, life is based on carbon, liquid water plays its role as a solvent for biochemistry and DNA encodes genetic information, as explained by Batalha. It stands to reason that life elsewhere is likely carbon-based and water-dependent. Hydrogen, oxygen and carbon are very abundant elements in the universe.

“Planet B, from what we look at, is a planet with liquid water on the surface,” said Batalha. “In addition to looking for biosignatures, I think what the Webb telescope can do best is look for signs of a habitable environment.”

It is also possible that if conditions are not right elsewhere, life will find a way to “exist in niches and perhaps even find other biochemical pathways when pressed”.

Perhaps life on another planet could use methanol instead of water for biochemistry. Or that, in the future, we will develop different metrics and signatures to detect habitable planets and life.

The main thing the astronomers we spoke with agreed with was to keep an open mind in the search for life – and to always respect what is found.

“If there is a Planet B, it is not, by definition, our planet”, stated Batalha. “We talked about this idea of ​​looking for habitable worlds as if they were our own. And if a planet is exactly like Earth with the conditions of life, then by definition it is a living world, and not ours.”

Sign of life

The Webb telescope is unlikely to be the key tool in identifying signs of life on another planet. The task is for future telescopes, as described in the recently launched Astro2020 survey (a survey done every ten years), which will observe 25 potentially habitable exoplanets.

“We know how to find this planet, but the search has been delayed until 2045 or later,” Seager said.

According to the astronomer, life, as we understand it, needs energy, liquids and the right temperature. What happens when a potential sign of life is detected? Finding the signal is fantastic – but figuring out the next step is crucial, as Seager said.

Lewis of Cornell University says that if it is determined that there is no other way to create a potential sign of life, it will take collective work to advance the discovery. Engaging with chemists, biologists and people from different disciplines outside astronomy and planetary science can determine the way forward.

“My hope is that we’ll be careful and engage with all the relevant experts to try to understand if this is in fact a signature that could only mean there’s life on this hypothetical planet and then announce something to the public,” Lewis said.

It will probably not be a unique moment that will happen overnight.

“It will be a long process of studying the biochemistry of the world because, in any biosignature we can find, it is necessary to demonstrate that there is no other abiotic form (physical rather than biological) producing that signal. This will take a long time”, explained Batalha.

The quest for life is a journey that involves taking new paths, asking new questions and developing new hypotheses. Experiments will be devised to answer these questions.

Batalha hopes future telescopes can help scientists complete the planetary census, including how often Earth-like planets occur in the galaxy. “I think the most important thing is that we continue to move forward and move forward,” he said.

Understanding the significance of what scientific observations and results mean in the quest for life is a priority for NASA, as written in a recent report. Led by Jim Green, NASA’s chief scientist, the document encourages the establishment of a new scale to assess the evidence that answers the question of whether we are really alone.

“Having a scale like this will help us understand where we are in terms of the search for life in specific locations and the capabilities of missions and technologies that help us in the search,” Green wrote in a statement.

The seven levels of this scale reflect the rungs of a ladder on the way to proclaiming the encounter of life beyond Earth.

“So far, we’ve left everyone thinking that there are only two options: it’s life or it’s not life,” recalled Mary Voytek, head of NASA’s Astrobiology Program, in a statement. “We need a better way to share the excitement of our discoveries and demonstrate how each discovery paves the way for the next, so we’ll engage the public and other scientists along the way.”

the long search

Tarter of the SETI Research Center believes the answer to finding life may depend on technosignatures rather than biosignatures, because the evidence of past or present technology is “potentially much less ambiguous.”

Biosignatures can be gases or molecules that show signs of life. Technosignatures are signs that can be created by intelligent life.

They are “something we can look at to indicate that not only does life exist on a distant planet, but that it is logically competent and has built or created something that we can observe with our ever-increasing abilities to look at the universe,” she said.

Since the 1960s, scientists have been listening to radio signals or looking for wavelengths of optical light that indicate someone is transmitting something.

If an intelligent civilization “modified its environment, like building solar collectors to gather a lot of energy and use it on the planetary surface, it’s possible that we can detect the consequences of using this technology,” said Tarter.

Tarter is encouraged by investment in missions investigating the search for past and present life in our own solar system, such as the many missions exploring Mars, Dragonfly which will explore Saturn’s moon Titan, and Europa Clipper which will fly through the vapors of oceanic material on the moon of Jupiter.

In the future, she thinks missions will dig even deeper into planets than the Perseverance rover, which is collecting rock samples on Mars. Digging deeper than 10 meters can show evidence of ancient technology.

“I think that in just a century we will have done a good job of exploring life, but I really like to keep an open mind,” said Tarter.

If the samples collected by Perseverance, which will be returned to Earth on future missions in the 2030s, show evidence of ancient biological life on Mars, that raises another question.

“Are we Martians? At the beginning of the solar system, there was a lot of material exchange, collisions were abundant and pieces of rock that chipped Mars ended up landing on Earth”, says Tarter. “It’s possible that life started somewhere other than Earth.”

An even more exciting possibility is the example of a second genesis if the biology of Mars does not relate to us, and brings the hypothesis of an independent origin of life. For Tarter, “It would mean that life has happened twice and is ubiquitous everywhere. It would be amazing. I hope I live to see it.”

(Translated text. Click here to read the original in English)