Earth 2.0 – Are There Actually Habitable Planets Out There?
A dying Earth has long been the catalyst for stories about the search for a new home for humanity. These stories touch us deeply because our homes are so fundamental to who we are and how safe we feel. Take that a stage further, and the potential dangers facing the whole planet are deeply emotive subject matter for fiction as well as non-fiction.
Science rates the potential for habitability on a planet in several different ways. One is the planet’s location in the habitable zone – known as the “Goldilocks region” which is a geographical band around a star which is neither too hot, nor too cold, for liquid water to exist on the planet’s surface. Another measure is the Earth Similarity Index, which compares the planet’s radius, density, and surface temperature to that of Earth.
In 2010, Gliese 581g cooked up a considerable storm of excitement as THE Goldilocks Planet – maybe giving real media life to the term. It was the first planet scientists had found within the habitable zone around a star. Sadly, once the furore had died down, some scientists started to seriously doubt whether Gliese 581g actually existed at all, because the signal was so weak. And it looks as if they might have been right about that.
The planets in the Gliese 581 star system can't actually been seen – planetary candidates were detected by monitoring the star's light. As a planet orbits, its gravity tugs on the star and distorts the light coming off it, changing the wavelengths and thus the color of light that reaches telescopes here on Earth. The problem is that the star itself also moves, and as it does, its sunspots and other solar activity also distort the light coming off of it.
But it captured the public's imagination and it was well timed too: it is very interesting that the focus seems now, in popular media and even popular science, to be more on finding ourselves a new place to live than finding planets which are like Earth and therefore might conceivably contain alien life. A function of climate change concerns, perhaps? That the world as a whole is not convinced by world governments' lack of dynamism on the issue of the threats facing Earth in the future? So we keep looking.
So how feasible is it for us to up sticks and find somewhere else to live? Let's ignore the fact that we haven't yet perfected interstellar travel, whether it's via wormholes or through some warp-drive like that proposed by Alcubierre. Of course, it's entirely plausible that exoplanets (a planet that does not orbit Earth's Sun and instead orbits a different star, stellar remnant, or brown dwarf) are out there that are just as hospitable as Earth. Scientists think there could be 40 billion Earth-sized habitable worlds in the Milky Way alone. Several have already been detected.
A team of researchers from University of California at Berkeley released a study last year that looked at how common Earth-size planets are around stars that are more like our sun. Using data from Kepler, lead author Erik Petigura and his team analyzed 42,000 G- and K-type stars visible to the naked eye from Earth. The study found that for stars that more closely resemble our sun, about one in five have Earth-size planets within the habitable zone. The most exciting prospect of the study was the finding that the closest potential Earth-like planet is only 12 lightyears away.
“I think that in the big scheme of things, the idea that we’ll someday have to escape the solar system to continue surviving is irrefutable,” says Lee Billings in an interview for Popular Science. Billings recently wrote the very interesting Five Billion Years of Solitude: The Search for Life Among the Stars. “But that’s a long time in the future, and we probably shouldn’t be too eager to abandon our home planet without very good reasons.”
Maybe we won't have a choice. Perhaps we should be funnelling more resources into the future, rather than the present. Should we be looking at interstellar travel more seriously? Yes, and right now. Not because the planet might capitulate under our relentless disrespect for it, but because we need to know have a future beyond this tiny, over-crowded place. Should we fund theoretical physics in order to understand the way the universe actually works before we fly off into the unknown which our shiny new Alcubierre drives? What about getting ourselves some ultra-efficient, renewable energy sources (rather than paying lip-service to research into those which are 'environmentally friendly')?
Breakthroughs. NASA needs visionaries to get those breakthroughs. What about stasis capabilities to suspend the vital functions of the human body for periods of time to prolong life on what will be huge journeys? Think of the effects of interstellar travel on human anatomy and physiology? What about 'terraforming' technology to process the atmosphere and biology of a planet if we can't find one that completely suits us – is it possible? These are all science-fiction staples, but there is good sense to the reasoning behind them – they are necessary issues to be resolved, but are we spending enough on resolving them? If the science is not yet practicable, what are the alternatives? We are a society rooted in the present, not spending on our future. We buy on credit, ignoring the consequences. We smoke and drink, even though we know what it does to our lungs and livers. We need to think differently; spend more on research into these non-science-fiction areas.
There is a new technique for confirming exoplanets’ existence (rather than simply ruling them out), and this will, we hope, make it easier to locate more Earth-sized planets. “For very low-mass planets like Earth, their Doppler signals will be smaller than those created by stellar activity for nearly all stars,” says astronomer Paul Robertson from Penn State University, the lead author on a new study. “It is necessary to remove the stellar activity signals in order to find these very exciting planets.”
There are other problems when considering the criteria to measure habitable planets. Most of the potentially habitable exoplanets discovered so far have been seen orbiting dim stars called M-dwarfs. Since M-dwarfs radiate less heat than our Sun, planets around them must be closer to the star in order to have liquid water – too close to be habitable, because other factors play a part. Any planets in orbit in the habitable zone of an M-dwarf would be at risk of devastating solar flares and tidal locking (where one side of the planet continually faces the star, similar to Earth's moon, potentially resulting in a hot side and a freezing cold side). The search goes on, and in reality, it's not clear how much of it we can do solely from Earth.
“Most of the planets we’ve found so far are borderline cases,” says Billings. “We don’t know enough about them to know what their environments are like, and in some cases we don’t even know for sure that they exist.”
But there’s good news too: “The nearest candidate for that is being called Earth 2.0 (by the new film, Interstellar among others) is probably only a dozen light-years away or less,” Billings says. “I think we’re on the cusp of finding it, and there are lots out there, but we don’t have a bona fide, true-blue planet like Earth yet.”
Nor do we have a way to get there, even if we do find one. Nor do we really understand the physiological effects of interstellar travel, even if we did. How many generations of highly-trained astronauts (rather than ordinary people) would it take to get there? And what do we do when we do get there – will we have something more than the habitation facilities described by Andy Weir in The Martian?
NASA says we need visionaries. How many of them are currently engaged in high-profit banking, stock-market trading, law or a thousand other professions which pay hugely? How many of those visionaries fall in love with physics in school, rather than some other random diversion? Katy Perry or Stephen Hawking – who is the real hero to humanity; who has more face time? More twitter followers? Where are our priorities (although I love her music)...
Space is big, but we have a long way to go at home, let alone out there.