Dwarf planetary systems will transform the hunt for alien life
It would be disappointing and surprising if Earth were the only template for habitability in the Universe.
Written speculation about life beyond the confines of Earth dates back thousands of years, to the time of the Greek philosophers Epicurus and Democritus. Unrecorded curiosity about this question undoubtedly goes back much further still. Remarkably, today’s generation seems about to get an answer from the study of exoplanets – planets orbiting other stars than the Sun. The early results are upending many assumptions from that long history.
Two months ago, our research team at the University of Cambridge and the University of Liège in Belgium reported that a nearby star, called TRAPPIST-1A, is orbited by seven planets similar in size and mass to Earth. All seven planets are temperate, meaning that under the right atmospheric and geologic conditions, they could sustain liquid water. Three of the planets show particular potential for habitability, receiving about as much energy from their star as the Earth receives from the Sun.
Our discovery received ecstatic and gratifying news coverage around the world. In many ways, though, the TRAPPIST-1 system is an odd place to look for life. The central star is just 1/12th the mass of the Sun and scarcely bigger than the planet Jupiter. It gives off just 0.05 per cent as much light as the Sun. TRAPPIST-1A belongs to a class that we call ultra-cool dwarfs, the very smallest stars that exist.
Searching for habitable planets around ultra-cool dwarfs has long been considered a waste of time. Even as astronomers found that exoplanetary systems are generally different from the solar system, old attitudes lingered. The Earth and Sun appear so normal and hospitable to our eyes that we get blinded by their attributes. Major programmes are therefore directed at finding an Earth twin: a planet the mass and size of our own, orbiting a star just like the Sun, at the same Earth-Sun distance. The detection of such a world remains decades away.
In the effort to answer the question ‘Is there life elsewhere?’ the focus on Earth twins is perceived as a safe path, since we can expect that similar conditions will lead to similar results (at least part of the time). However, we argue that this is far too conservative a goal, considering the huge number and diversity of available planets. That is part of the message of TRAPPIST-1. Research should be about finding what we don’t already know. Identifying a life-bearing Earth twin would be a resounding scientific success, but it would teach little about the overall emergence of biology in the Universe.
Our ambition is wider. Instead, we seek an answer to ‘How frequently is life found elsewhere?’ This simple change of words means that we should also be investigating planetary systems unlike the solar system. It would be disappointing and surprising if Earth were the only template for habitability in the Universe. Sun-like stars represent just 15 per cent of all stars in the Milky Way. More than half of those, in turn, exist in binary star systems that have also been disregarded as being too different from the conditions present in the solar system. The search for Earth twins therefore covers a nearly insignificant fraction of all the outcomes in nature.
Once we reset the goal to measuring the total frequency of biology, ultra-cool dwarfs become an obvious target. Half the stars in the Milky Way have masses less than one-quarter of the Sun’s. Our preliminary results suggest that rocky worlds are common orbiting low-mass stars, including ultra-cool dwarf system, possibly more so than in orbit around Sun-like stars. Ultra-cool dwarfs also open a much easier route to detecting and studying temperate, Earth-like planets.
The scientific advantages of ultra-cool dwarfs come from their stellar properties, from how we identify exoplanets, and from how we expect to investigate their atmospheres. The TRAPPIST-1 planets were found as they passed in front of their star, events known as transits. When the planet transits, it casts a shadow whose depth tells us how much of the stellar surface is being hidden by the planet; the bigger the planet, the deeper the shadow. Because ultra-cool dwarfs are so small, the transit of an Earth-sized planet in front of TRAPPIST-1A is approximately 80 times as prominent as an equivalent transit against a much larger, Sun-like star.
During a transit, any gases in the planet’s atmosphere change the appearance of starlight streaming through. Around ultra-cool dwarfs, the atmospheric signature is boosted by about a factor of 80. The atmospheric composition of the TRAPPIST-1 planets will be detectable using current and upcoming facilities, such as the James Webb Space Telescope launching in 2018, unlike the decades of technological development needed to study an Earth twin. Extracting a reliable atmospheric signal requires observing dozens of transits. Here, too, systems such as TRAPPIST-1 have huge advantages. Around tiny ultra-cool dwarfs, transits of temperate planets happen once every few days to every couple of weeks, instead of once a year for a planet exactly like Earth.
Astronomers, including ourselves, have already begun investigating the compositions of giant planets around other stars, detecting molecules such as water, carbon monoxide, methane, and hydrogen cyanide. With the discovery of the TRAPPIST-1 system, we can extend those explorations to Earth-sized planets. Our first efforts will be to characterise the greenhouse gas content of atmosphere, and assess whether the surface conditions are conducive for liquid water. Then we will seek out signs of biologically produced gases, analogous to ways that living organisms have transformed the composition of Earth’s atmosphere.
Claiming a discovery of life will be hard. We cannot rely on the detection of a single gas but instead will need to detect several, and will need to measure their relative abundances. In addition, we will have to be extremely wary of false positives. For instance, repeated stellar flares could build up oxygen in an atmosphere without the presence of life. The richness of the TRAPPIST-1 system is an important asset, because we can compare its planets to one another. All seven planets originated from the same nebular chemistry; they share a similar history of receiving flares and meteoritic impacts. Weeding out false positives will be much easier here than in planetary systems containing only one or two temperate, potentially Earth-like worlds.
More important, TRAPPIST-1 is not a one-off discovery. Ultra-cool dwarf stars are so common that there could be numerous other similar systems close to us in the galaxy. The TRAPPIST (Transiting Planets and Planetesimals Small Telescopes) facility we used to find the TRAPPIST-1 planets was just the prototype of a more ambitious planet survey called SPECULOOS (Search for habitable Planets Eclipsing Ultra-Cool Stars), which has already begun operations. We expect to find many more Earth-sized, rocky planets around dwarf stars within the next five years. With this sample in hand, we will explore the many climates of such worlds. The solar system contains two: Venus and Earth. How many different types of environments will we discover?
Using SPECULOOS, we will also begin to address the many objections scientists have raised about the habitability of planets around ultra-cool dwarfs. One argument is that such planets will be tidally locked, meaning that they have permanent day and night sides. Planets orbiting in close proximity around small stars could excite each other’s orbits, leading to major instabilities. Ultra-cool dwarf stars frequently flare up, emitting ultraviolet and X-rays that might vaporise a planet’s oceans into space.
Far from holding us back, those arguments motivated us. Now we can assess the actual conditions, and explore counter-arguments that Earth-sized planets around stars such as TRAPPIST-1A might in fact be hospitable to life. Oceans and thick atmospheres could mitigate the temperature contrast between day and night sides. Tidal interaction between close-orbiting planets might provide energy for biology. Some models suggest that planets forming around ultra-cool dwarfs start out with much more water than Earth has. Ultraviolet radiation could help to produce biologically relevant compounds… We are optimistic.
No matter what we find by studying planets orbiting ultra-cool dwarfs, we cannot lose. We can only learn. If we manage to identify the presence of life on a planet similar to those in the TRAPPIST-1 system, then we can start measuring how frequently biology emerges in the universe. We could have the first clues of extraterrestrial biology in a decade! If we find that none of those worlds is habitable, or that they are habitable but barren, we would learn that life is rare and precious. It will vindicate the Earth-twin approach without delaying it.
In either case, we will define the context of our existence: as one among many, or as an isolated outlier. Both possibilities are humbling. Both are thrilling.
Amaury Triaud & Michaël Gillon
This article was originally published at Aeon and has been republished under Creative Commons.
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Political division is nothing new. Throughout American history there have been numerous flare ups in which the political arena was more than just tense but incideniary. In a letter addressed to William Hamilton in 1800, Thomas Jefferson once lamented about how an emotional fervor had swept over the populace in regards to a certain political issue at the time. It disturbed him greatly to see how these political issues seemed to seep into every area of life and even affect people's interpersonal relationships. At one point in the letter he states:
"I never considered a difference of opinion in politics, in religion, in philosophy, as cause for withdrawing from a friend."
Today, we Americans find ourselves in a similar situation, with our political environment even more splintered due to a number of factors. The advent of mass digital media, siloed identity-driven political groups, and a societal lack of understanding of basic discursive fundamentals all contribute to the problem.
Civil discourse has fallen to an all time low.
The question that the American populace needs to ask itself now is: how do we fix it?
Discursive fundamentals need to be taught to preserve free expression
In a 2017 Free Speech and Tolerance Survey by Cato, it was found that 71% of Americans believe that political correctness had silenced important discussions necessary to our society. Many have pointed to draconian university policies regarding political correctness as a contributing factor to this phenomenon.
It's a great irony that, colleges, once true bastions of free-speech, counterculture and progressiveness, have now devolved into reactionary tribal politics.
Many years ago, one could count on the fact that universities would be the first places where you could espouse and debate any controversial idea without consequence. The decline of staple subjects that deal with the wisdom of the ancients, historical reference points, and civic discourse could be to blame for this exaggerated partisanship boiling on campuses.
Young people seeking an education are given a disservice when fed biased ideology, even if such ideology is presented with the best of intentions. Politics are but one small sliver for society and the human condition at large. Universities would do well to instead teach the principles of healthy discourse and engagement across the ideological spectrum.
The fundamentals of logic, debate and the rich artistic heritage of western civilization need to be the central focus of an education. They help to create a well-rounded citizen that can deal with controversial political issues.
It has been found that in the abstract, college students generally support and endorse the first amendment, but there's a catch when it comes to actually practicing it. This was explored in a Gallup survey titled: Free Expression on Campus: What college students think about First amendment issues.
In their findings the authors state:
"The vast majority say free speech is important to democracy and favor an open learning environment that promotes the airing of a wide variety of ideas. However, the actions of some students in recent years — from milder actions such as claiming to be threatened by messages written in chalk promoting Trump's candidacy to the most extreme acts of engaging in violence
to stop attempted speeches — raise issues of just how committed college students are to
upholding First Amendment ideals.
Most college students do not condone more aggressive actions to squelch speech, like
violence and shouting down speakers, although there are some who do. However, students
do support many policies or actions that place limits on speech, including free speech zones,
speech codes and campus prohibitions on hate speech, suggesting that their commitment
to free speech has limits. As one example, barely a majority think handing out literature on
controversial issues is "always acceptable."
With this in mind, the problems seen on college campuses are also being seen on a whole through other pockets of society and regular everyday civic discourse. Look no further than the dreaded and cliche prospect of political discussion at Thanksgiving dinner.
Talking politics at Thanksgiving dinner
As a result of this increased tribalization of views, it's becoming increasingly more difficult to engage in polite conversation with people possessing opposing viewpoints. The authors of a recent Hidden Tribes study broke down the political "tribes" in which many find themselves in:
- Progressive Activists: younger, highly engaged, secular, cosmopolitan, angry.
- Traditional Liberals: older, retired, open to compromise, rational, cautious.
- Passive Liberals: unhappy, insecure, distrustful, disillusioned.
- Politically Disengaged: young, low income, distrustful, detached, patriotic, conspiratorial
- Moderates: engaged, civic-minded, middle-of-the-road, pessimistic, Protestant.
- Traditional Conservatives: religious, middle class, patriotic, moralistic.
- Devoted Conservatives: white, retired, highly engaged, uncompromising,
Understanding these different viewpoints and the hidden tribes we may belong to will be essential in having conversations with those we disagree with. This might just come to a head when it's Thanksgiving and you have a mix of many different personalities, ages, and viewpoints.
It's interesting to note the authors found that:
"Tribe membership shows strong reliability in predicting views across different political topics."
You'll find that depending on what group you identify with, that nearly 100 percent of the time you'll believe in the same way the rest of your group constituents do.
Here are some statistics on differing viewpoints according to political party:
- 51% of staunch liberals say it's "morally acceptable" to punch Nazis.
- 53% of Republicans favor stripping U.S. citizenship from people who burn the American flag.
- 51% of Democrats support a law that requires Americans use transgender people's preferred gender pronouns.
- 65% of Republicans say NFL players should be fired if they refuse to stand for the anthem.
- 58% of Democrats say employers should punish employees for offensive Facebook posts.
- 47% of Republicans favor bans on building new mosques.
Understanding the fact that tribal membership indicates what you believe, can help you return to the fundamentals for proper political engagement
Here are some guidelines for civic discourse that might come in handy:
- Avoid logical fallacies. Essentially at the core, a logical fallacy is anything that detracts from the debate and seeks to attack the person rather than the idea and stray from the topic at hand.
- Practice inclusion and listen to who you're speaking to.
- Have the idea that there is nothing out of bounds for inquiry or conversation once you get down to an even stronger or new perspective of whatever you were discussing.
- Keep in mind the maxim of : Do not listen with the intent to reply. But with the intent to understand.
- We're not trying to proselytize nor shout others down with our rhetoric, but come to understand one another again.
- If we're tied too closely to some in-group we no longer become an individual but a clone of someone else's ideology.
Civic discourse in the divisive age
Debate and civic discourse is inherently messy. Add into the mix an ignorance of history, rabid politicization and debased political discourse, you can see that it will be very difficult in mending this discursive staple of a functional civilization.
There is still hope that this great divide can be mended, because it has to be. The Hidden Tribes authors at one point state:
"In the era of social media and partisan news outlets, America's differences have become
dangerously tribal, fueled by a culture of outrage and taking offense. For the combatants,
the other side can no longer be tolerated, and no price is too high to defeat them.
These tensions are poisoning personal relationships, consuming our politics and
putting our democracy in peril.
Once a country has become tribalized, debates about contested issues from
immigration and trade to economic management, climate change and national security,
become shaped by larger tribal identities. Policy debate gives way to tribal conflicts.
Polarization and tribalism are self-reinforcing and will likely continue to accelerate.
The work of rebuilding our fragmented society needs to start now. It extends from
re-connecting people across the lines of division in local communities all the way to
building a renewed sense of national identity: a bigger story of us."
We need to start teaching people how to approach subjects from less of an emotional or baseless educational bias or identity, especially in the event that the subject matter could be construed to be controversial or uncomfortable.
This will be the beginning of a new era of understanding, inclusion and the defeat of regressive philosophies that threaten the core of our nation and civilization.
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