Starts With A Bang Podcast #45: Beyond Earth 2.0
With all the planets out there in the galaxy and Universe, it’s only a matter of time and data until we find another one with life on it. (Probably.) But while most of the searches have focused on finding the next Earth, sometimes called Earth 2.0, that’s very likely an overly restrictive way to look for life. Biosignatures, or more conservatively, bio-hints, might not only be plentiful on worlds very different from our own, but around Solar Systems other than our own. Earth-like worlds, in fact, might not even be the most ubiquitous places for life to arise in the Universe.
I’m happy to welcome scientist Adrian Lenardic onto the Starts With A Bang podcast, and explore what just might be out there if we look for life beyond our idea of Earth 2.0!
(Image credit: JPL-Caltech/NASA.)
Is Alien Life Hiding Beyond Earth 2.0?
“It may be the case that life is rare in the Universe, in which case it will require us to look at a lot of candidate planets — possibly with very high precision — in order to reveal a successful detection. But if we search exclusively for planets that have similar properties to Earth, and we restrict ourselves to looking at parent stars and solar systems that are similar to our own, we are doomed to get a biased representation of what’s out there.
You might think, in the search for extraterrestrial life, that more is more, and that the best way to find life beyond Earth is to look at greater numbers of candidate planets that might be the Earth 2.0 we’ve been dreaming of for so long. But non-Earth-like planets could be home to life that we’ve never considered, and we won’t know unless we look. More is more, but “different” is also more. We must be careful, as scientists, not to bias our findings before we’ve even truly started looking.”
If we want to find life elsewhere in the Universe, it only makes sense to look at our own world, where we know it was successful, and to try and find other worlds similar to our own. But that absolutely cannot be the only thing we do, or the only inhabited worlds we’ll even have a chance at finding are the ones similar to our own.
We have many good reasons to favor or disfavor the probability of finding life on a variety of planets and moons out there in our galaxy, but the real truth of the matter is we don’t know how common or rare life is. We don’t know how common or rare a huge variety of processes are, or even whether life is more likely to arise under conditions very different from those we find on our own planet.
It’s possible that Earth-like worlds are the best bet for life in the Universe, but don’t count out the non-Earth-like worlds without looking. Here’s what everyone hopeful for discovering alien life should keep in mind as we search the galaxy.
Ask Ethan: Can We Find Exoplanets With Exomoons Like Ours?
“But, by far, the best possibility we have today is through direct measurement of a transiting exomoon. If the planet that’s orbiting the star can make a viable transiting signal, then all it will take is the same serendipitous alignment to have its moon transit the star, and sufficiently good data to tease that signal out of the noise.
This is not a pipe dream, but something that has already occurred once. Based on data taken by NASA’s Kepler mission, the stellar system Kepler-1625 is of particular interest, with a transiting light curve that not only displayed the definitive evidence of a massive planet orbiting it, but of a planet that wasn’t transiting with the exact same frequency you’d expect orbit after orbit.”
If you want to find an exoplanet, the most successful methods are to look for the effect it has on the light from it’s parent star. But what about if you wanted to find an exomoon? There are some subtle effects at play, but if we think hard about what they might be, we can come up with a series of methods that could reveal an exomoon’s presence indirectly, and pinpoint exactly where and when we could look to try and detect one directly. Thought to be a great technique for the upcoming James Webb Space Telescope to take advantage of TESS data, we’ve actually succeeded once already, using the Hubble/Kepler combo!
You may have missed it, but we think we’ve found the first exomoon as of late last year. What does the future hold for exomoons? Find out on this week’s Ask Ethan!
Ask Ethan: What Will Our First Direct Image Of An Earth-Like Exoplanet Look Like?
“[W]hat kind of resolution can we expect? [A] few pixels only or some features visible?”
I’ve got good news and bad news. With the next generation of space-based and ground-based telescopes on the way, we’ll finally be able to image Earth-sized and super-Earth-sized planets around the nearest stars to us directly. Unfortunately, even the largest of these telescopes won’t be able to resolve these planets beyond being a single pixel (with light leaking into the adjacent pixels) in angular size. But even with that limitation, we should be able to recover signatures of continents, oceans, icecaps, clouds, atmospheric contents, water, and potentially even life.
Come find out what we will (and won’t) be able to do with our first direct images of Earth-sized exoplanets, coming to you in just a few years!
Incredible First Discoveries From NASA’s New Exoplanet-Hunting Spacecraft: TESS
“The ultimate goal of TESS is to find possible Earth-like worlds, and star systems which may house rocky, potentially habitable worlds. Because TESS is optimized to scour the stars nearest to us, it’s greatest finds will be among the first targets for future, more powerful observatories that can not only detect these worlds, but measure their atmospheric contents. If we get lucky, some of those worlds might house molecules like water, methane, carbon dioxide, or even oxygen in their atmospheres.
It won’t be a slam-dunk that these worlds are inhabited, but TESS takes us one step closer towards finding the nearest worlds that might be humanity’s greatest hope for finding life outside of our own Solar System. The worlds we’ve found so far are absolutely fascinating, and just a few months into its primary mission, TESS is easily meeting even the loftiest expectations for it. By time the James Webb Space Telescope launches, TESS should provide us with many worlds that just might be the best place to look to take our next great leap towards our ultimate goal: finding an inhabited world.”
NASA’s exoplanet-hunting satellite, TESS, was launched in April of 2018, began taking data in July, and released their first data to the world last month. That data contains around 300 candidate exoplanets, and the first eight of them have already been confirmed. From worlds so hot that they might have liquid rock on their surface to a solar system so strange we’ve never found anything like it, these are the first highlights.
Someday, TESS might lead us to our first world with signs of life on it. Here’s where we are so far.
Aliens? Or Alien Impostors? Finding Oxygen Might Not Mean Life, After All
“This doesn’t mean that finding an Earth-like world with an oxygen-rich atmosphere won’t be incredibly interesting; it absolutely will be. It doesn’t mean that finding organic molecules coincident with the oxygen won’t be compelling; it will be a finding worth getting excited over. It doesn’t even mean that it won’t be indicative of life; a world with oxygen and organic molecules may well be overflowing with living organisms. But it does mean that we have to be careful.
Historically, when we’ve looked to the skies for evidence of life beyond Earth, we’ve been biased by hope and what we know on Earth. Theories of dinosaurs on Venus or canals on Mars still linger in our memories, and we must be careful that extraterrestial oxygen signatures don’t lead us to falsely optimistic conclusions. We now know that both abiotic processes and life-dependent ones can create an oxygen-rich atmosphere.
The hard problem, then, will be disentangling the potential causes when we actually find our first oxygen-rich, Earth-like exoplanet. Our reward, if we’re successful, will be the knowledge of whether or not we’ve actually found life around another star.”
If you were looking for life around a planet orbiting another star, how would you do it? Your first inclination might be to look for something just like Earth: an Earth-mass planet with Earth’s size and Earth’s orbital parameters around a Sun-like star. You might then go a step further and try to examine its atmospheric contents. If you found a large amount of oxygen and organic molecules in the same atmosphere, you might conclude that you’d found it: a world beyond our Solar System that was inhabited. But that’s not necessarily the case!
Out of Dr. Sarah Hörst’s lab comes a new finding: oxygen and organics can arise through abiotic processes on exoplanets. Oxygen may not mean life, after all.
Why Haven’t Scientists Found ‘Earth 2.0’ Yet?
“Over the past 30 years, astronomers have gone from zero known extra-solar planets to thousands. Periodic changes in a star’s motion or regular brightness dips give them away. Thanks to these techniques, we’ve revealed the masses and radii of worlds nearby and thousands of light years away. Over 200 are Earth-sized, with many residing in the so-called habitable zone around their stars. Yet with everything we’ve found, there are no potentially habitable Earth-like worlds around Sun-like stars.”
One of the greatest success stories over the past 30 years is the giant leap forward we’ve taken in understanding what worlds lie beyond our Solar System. We’ve gone, in that time, from exactly zero known planets beyond our Solar System to thousands. We’ve found worlds far larger than Jupiter, some of which revolve at distances interior to even Mercury’s orbit. We’ve found planets around blue supergiants and red dwarfs. And we’ve discovered small worlds, some of which are even smaller than Earth. Some of them even occur in the so-called habitable zone of their stars.
Yet, despite all of this, we have yet to discover a single Earth-sized world at an Earth-like distance orbiting a Sun-like star. Here’s why we haven’t gotten there yet.
We Know Almost Nothing About Proxima b, The Closest Exoplanet To Earth
“In reality, we do not even know whether this planet is Earth-like or Neptune-like. The typical border between an Earth-like world, where you have a rocky surface with a thin atmosphere, and a Neptune-like world, where you have a large gas envelope surrounding your world, is about 2 Earth masses. Proxima b has a minimum mass of about 1.3 Earths, but that’s if the alignment is perfectly edge-on. Since there’s no transit, we know the alignment cannot be exactly perfect, but how imperfect is it? That’s gloriously unknown.
If the alignment is inclined at more than about 25° from our line-of-sight, it’s likely to be a gaseous world, not a rocky, Earth-like one. But at this point, without further information, we cannot know.”
Two years ago, some amazing news came in from the astronomical world: the closest star beyond our Sun, Proxima Centauri, has a planet orbiting it. Named Proxima b, it has an orbital period of 11.2 days around a star just 0.17% as luminous as our Sun. This places it into what we call the habitable zone, as it receives approximately 65% of the energy that Earth receives from the Sun. It also has a mass that’s touted as 1.3 times the mass of Earth, but that figure is very suspect. We can claim that as the minimum mass, but can do no better than that. As far as life, water, oceans, or even an atmosphere goes, we have no idea. It could be a completely airless, barren world, or could have a thick gas envelope like Neptune.
Without more and better data, we simply cannot know. We know very little about Proxima b. Here’s how you can separate scientific fact from mere speculation.
Ask Ethan: Would Life On Earth Be Possible If We Were Anyplace Else In The Galaxy?
“[W]hat would happen if our solar system had formed a little farther up the arm of the galaxy? What would happen if we were at the tip of the arm? What if, theoretically, instead of the humongous black hole in the center of our galaxy, our solar system was there? Would there be major climate difference[s]? Would we be able to survive?”
We can all agree that what’s happened here on Earth is something that’s extremely special in the Universe. Our planet has developed and sustained life on it for over four billion years, and that life continues to thrive even at present. Our planet has been fortunate enough to have stable enough conditions and mass extinction events that have never eliminated 100% of the life that exists on our world. But how ‘special’ does that make Earth, that this is our story? Do we need a large Moon? A solar system like ours? A star like our Sun? And do we need to be located at our present location in the galaxy, or would many places be just as good?
It’s a tough question to answer with certainty given the paltry evidence we have, but we can certainly examine these questions in-depth. Let’s do exactly that for this edition of Ask Ethan!
New Podcast: Humanity’s 3 Hopes For Alien Life
There are three very different ways humanity is searching for alien life beyond Earth. We can directly search the various planets and moons in our Solar System for past or present biological signatures simply by sending decontaminated probes, and looking for the evidence in situ. We can indirectly look at distant worlds around other stars, searching for the characteristic changes to the atmosphere and surface that life would bring. And, most optimistically, we can search for intelligent signatures created, perhaps willfully, by a technologically advanced alien species. These are our three hopes for finding alien life, and we’re actively pursuing all three.
Here’s how the different searches work, along with some speculation about what we’re likely to find, and what motivates us to look!