Life beyond Earth—no plate tectonics, no problem

Life beyond Earth—no plate tectonics, no problem
An artist’s impression of Ross 128 b, a temperate, rocky planet about 11 light-years from Earth that could have the necessary conditions for maintaining liquid surface water. Credit: European Southern Observatory/M. Kornmesser

Scientists looking for life on distant planets are making plans to search non-Earth-like planets based on discoveries within our solar system that are challenging long-standing ideas about habitable zones, plate tectonics and more.

In a new paper published online this week, Rice University geophysicist Adrian Lenardic and more than a dozen co-authors outline a path for both finding potential life signs around other stars and determining how likely it is that those signs are caused by alien life. The paper, "Exoplanet Biosignatures: Future Directions," is available online and due to be published in Astrobiology.

Lenardic, who specializes in studying planetary dynamics, also authored an associated paper, "Volcanic-Tectonic Modes and Planetary Life Potential," that will be published as a chapter in the upcoming "Handbook of Exoplanets" from Springer Publishing.

"It used to be the thought that life could only exist in a narrow zone near a planet's star because you need to be there to maintain liquid water," said Lenardic, professor of Earth, environmental and planetary sciences. "Then, we send Voyager out to a moon of Jupiter and, lo and behold, it shows strong indications of a subsurface ocean. That's because there is another energy source that did not get its proper due—tidal forces from the intense gravitational pull of Jupiter.

"This has opened up the range over our own solar system in which life can exist, and I think a lot of the gist of the forthcoming papers is that much of what we're seeing is expanding the zone and expanding our thinking about the conditions needed for life. So, as we look for life around other stars, we should also expand our or we might miss something."

Astronomers have cataloged more than 3,700 planets around . The 21-foot diameter mirror on the James Webb Space Telescope, which is set to launch in 2019, will be able to examine the atmospheres of rocky planets around distant stars, and astronomers are already designing future missions and instruments that will look for specific atmospheric signatures of life.

"A goal was to frame the problem," Lenardic said of the new biosignature paper, which sprang from an exoplanet workshop that brought together a range of scientists. "The workshop team wanted to come up with a means of assigning a likelihood of life based on a given set of observations of a distant planet."

He said the search for exolife is a team sport that involves biologists, astronomers, planetary scientists and others who collaborate through groups such as NASA's Nexus for Exoplanet System Science (NExSS) project and the European Space Agency's International Summer School in Astrobiology.

Lenardic's contribution is to examine how the internal energy of planets, and associated volcanic-tectonic activity, influence their climate and ability to sustain life.

"When I teach planetary science, one question I actually give students is, 'What is life? Give me a definition.' And it's not easy," Lenardic said. He noted that students and working scientists have put forward a range of answers.

"But if we can agree on one thing, it's that life needs energy," he said. "We've thought about the sun as an energy source for a long time, and we've come to appreciate a planet's internal energy, which comes from decay of radioactive elements within its rocky interior. Jupiter's moons have taught us to also appreciate tidal forcing, and we're starting to find exoplanets that have orbits that allow for significant tidal forcing."

Lenardic said , much like the narrow habitable zone, is another long-held criterion for planetary habitability that is being challenged by recent findings.

Plate tectonics is the large-scale process that governs the movements of Earth's crust.

"It is a particular surface manifestation of a planet's internal energy, but it is not the only possible mode of volcanic and tectonic activity on a planet," Lenardic said.

On Earth, plate tectonics plays a role in modulating climate, but the idea that plate tectonics is crucial for life is challenged by increasingly sophisticated models of planetary climates. For example, in a January study in the Journal of Geophysical Research, Lenardic and colleagues showed how water could be maintained on worlds without plate tectonics. The chapter in the upcoming "Handbook of Exoplanets" further explores this idea by considering planetary life potential under a range of tectonic modes that differ from Earth's.

"I'm an optimist," Lenardic said. "We're at the first point in our history as humans where we might actually have some observations from other that we can use to test any of these ideas about life beyond our own. It can be easy to be Earth-centric and assume that life requires a planet like our own. But what we are seeing within our solar system is causing us to question this. One of the things I have learned from the history of exploring our own solar system is to be prepared for surprise. As we move beyond our solar system, in our search for , that lesson is driving us to adapt our search strategies."

Explore further

Lush Venus? Searing Earth? It could have happened

More information: Exoplanet Biosignatures: Future Directions.

Volcanic-Tectonic Modes and Planetary Life Potential. … etary_Life_Potential

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Mar 28, 2018
IMHO, if the math checks out, this could be a game-changer as Plate Tectonics was thought essential for an advanced biome,,,

Mar 28, 2018
The thing about plate techtonics is that it resurfaces and recycles the surface of the earth it is not there for life. It allows the planet to renew itself regardless of what life is on it.

Mar 28, 2018
So many assumptions being leaped upon? You'd think you were at an Anuran orgy!

It is possible, even likely, that tidal energies upon the Jovan Moons have resulted in oceans of some undetermined type of liquid water.

My opinion that those bodies of liquid water will prove to be sterile? Is just as valid as your opinion there is indigenous life to be found.

One trivial bit of evidence against these speculations about tidal forces and the chances of Living Worlds? Luna, our own moon. Right next door, in the Goldilocks Zone. Deader'n doorknob!

Fantastical speculations about possible alternatives to the intricate cohesion of our Earth's structure and having the only biosphere confirmed to date? Are fun to imagine. But in the end, it will be verifiable evidence that establishes the actual reality for the existence of Living Alien Worlds.

Or not...

Mar 28, 2018
You are a what? There is no orgie with only 3 comments. Unless you are the one who starts it. My comment has nothing to do with life. I am saying it is a good thing to renew the planet even if there is not any life on it. I do not prose fairytails or fanciful opinions but the simple truth. I leave the speculation of other things to everyone else.

Mar 28, 2018
If life is found in some of the exotic environments in this solar system, then it can be assumed that life in general is ubiquitous throughout the universe. If not.... who knows, most likely life will be a rare occurrence.

Mar 28, 2018
Biologists claim to have successfully placed all life on earth on a single common tree. The SETI people have been searching for signs of intelligence since at least the 1960's. We have visited or sent robots to every significant body in the solar system. The Fermi Paradox suggests that if there were (intelligent) life, they would be here by now. So far as we know life only started in one place and at one time. Why this frantic, almost religious, zeal to demonstrate otherwise?

Mar 28, 2018

My opinion that those bodies of liquid water will prove to be sterile? Is just as valid as your opinion there is indigenous life to be found.

Everyone halt all research and pondering of life beyond earth! It's @rrwillsj opinion that it is not so. His opinion based on the fact that the moon is uninhabited and that is just as valid as anyone else's opinion. This is the nail in the coffin for the age old question "are we alone in the universe". Oh what a day.

Mar 28, 2018
Sb2001, your hostility to conflicting opinions is rather childish. I admit, my opinion is unconfirmed and unverified. I could be proven wrong. I am sanguine at the prospect of having to acknowledge an error. I do not fear being proven wrong, with empirical evidence.

Do you have the strength of character to acknowledge your errors of speculative opinions? When there is any verified evidence against your fantasist claims?

Or will you join in those repetitious cults of crankery and hoaxes that infest these commentaries?

"Desire is only the first step on the path to accomplishment."

Mar 29, 2018
You are a what?
Willis is a self-absorbed clown who enjoys fabricating facts
There is no orgie with only 3 comments. Unless you are the one who starts it
Willis enjoys using words like orgie because he gets little thrills from them.
Sb2001, your hostility to conflicting opinions is rather childish. I admit, my opinion is unconfirmed and unverified. I could be proven wrong. I am sanguine at the prospect of having to acknowledge an error. I do not fear being proven wrong, with empirical evidence
I... I... I... I... I... I... proves my case. Probably wears a bathrobe with flowers all over it all day long.
repetitious cults of crankery and hoaxes that infest these commentaries
What a fruit...

Mar 29, 2018
otto, As long as you are daydreaming about dressing me as your mother and what perversions you want to perform with fruit?

I am a pitaya blanca.
Which makes you a kumquat.

Mar 29, 2018

Oh I'm sorry @rrwillsj, you miss understood the direction of my jovial sarcasm. It wasn't toward the fact that you have an opinion, it was toward your unproductive, asinine attitude toward other people conducting valuable research.

If you have a hypothesis and wish to prove its validity to yourself or others please do the research (as well as the observation and experimentation required). If you do enough valid research you could convince people. If you can convince enough people you can gather resources to launch probes to other worlds and prove or disprove your hypothesis. If you prove yourself right then yay! If you prove yourself wrong yay! Get it?

Mar 30, 2018
Sb2001, thank you for clearly enunciating my opinions. I appreciate your assistance at clarifying my comments.

Mar 31, 2018
nice info .. for the opinion

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