A World in the Habitable Zone

As Etta James once sang in the old standard, “At Last!”  And, now planet-searchers are singing the same tune. Kepler mission scientists have just announced the detection of one of the Holy Grails of exoplanet searches: the first Earth-sized planet in the habitable zone of its star. This is a momentous discovery in a long string of amazing exoplanet detections for the Kepler team and the teams of followup observers at the W.M. Keck and Gemini Observatories in Hawai’i. It means, among other things, that worlds similar in many ways to our Earth exist out there.

Earth orbits in the Sun’s habitable zone, which means that it is in a “safe zone” where liquid water can exist on our planet’s surface. Finding a world in the habitable zone of Kepler-186, which is an M-class red dwarf star about 490 light-years away from us, means that this planet could also support liquid water on its surface. And, where there’s water, there’s likely to be life. That doesn’t mean that there IS life on this planet. It’s too early to tell for that. But, it’s an exciting discovery because it means there’s another world out there that could (in some ways) be very like Earth.

The planet’s name (for now) is Kepler-186f. It’s the outermost of five planets orbiting the star and joins a group of 20 planets known to exist in their stars’ habitable zones.

What might it look like? There’s no way to know for sure, since Kepler doesn’t make images of its targets. The images here are artist’s concepts, and the planet’s landscape is based on assumptions that there could be water on its surface.  It will be up to additional teams of followup observers from the ground to look at this object, which is difficult since the planet is quite dim. Determining the existence of water (and possibly life) may have to wait until our technology improves to help us look at these dim distant objects from a distance.

Kepler  only provides light curves—meaning that it measures the light blocked by the planet as it crosses in front of its star. Those light curves have identified thousands of planet candidates, all of which are observed using follow-up ground-based techniques. This is where Gemini and Keck Observatories come in. They can use specialized techniques to stare at the star in visible and infrared wavelengths of light, which give a fuller and more nuanced view of these possible worlds.

If the star and its companions were a bit brighter (or closer) followup observations could focus on that light as it passes through the star’s atmosphere. The fingerprints of the chemical compounds in its atmosphere would show up in the spectrum of the starlight, and that would give us a clue about how much water the planet has, and if there’s any life on the planet. Yes, the fingerprints of life could be found in the atmosphere—oxygen, for example, or methane (if the life gives off such emissions), or if it’s life that has built a civilization, then there might be the fingerprints of whatever fuels are used to power that culture.

What if It IS a Water World?

This Kepler/Keck/Gemini discovery comes after some interesting news from NASA’s Jet Propulsion Laboratory about how Earth’s life took root on our planet nearly some 4 billion years ago. By all accounts, infant Earth was a nasty place to live in (particularly by human standards). It was wetter, more volcanic, bathed in UV from the Sun, not exactly a place where you’d want to take a vacation. Well, I HAVE vacationed briefly in places similar to that—hiking on volcanoes, for example. But, as a  long-term abode for life as we know it today, early Earth was not a great place.

Yet, life got its start in this hellhole. The first cells evolved to become multicellular beings, and from there the evolutionary rush took off. All of life today—from the slime molds to the frogs, elephants, humans (and our biomes of interior bacteria)—owe our existence to those first life forms eking out an existence on early Earth.

A new study from researchers at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and the Icy Worlds team at the Astrobiology Institute (at NASA Ames) talks about how electrical energy naturally produced at the sea floor might have given rise to life.  This makes sense from the standpoint of the three requirements for life: water, warmth (energy), and organic material (food). Electrical fields provide energy (think about the electricity powering the computer you’re using). This theory, called “submarine alkaline hydrothermal emergence of life, brings together decades of field, laboratory and theoretical research into a grand, unified picture of the origins of life on our planet.

This theory, which some have dubbed the “water world” theory, life could have gotten its start inside warm, gentle springs on the sea floor, when oceans churned across the entire planet. This idea of hydrothermal vents as possible places for life’s origins was first proposed in 1980 by other researchers, who found them on the sea floor near Cabo San Lucas, Mexico. Called black smokers, those vents bubble with scalding hot, acidic fluids. In contrast, the vents in the new study are kinder, gentler regions that percolate with alkaline fluids. Undersea explores found a towering complex of these alkaline vents in the North Atlantic Ocean in 2000. It quickly became known as the Lost City.

The trick to understanding how life could have thrived in these warm and gentle areas to look at what they did in the past. Earth’s early oceans were acidic and not very hospitable to forming life. These gentle, less-acidic (alkaline) regions were like little paradises for life to form in reasonable temperatures and fairly alkaline conditions.  There are many fascinating biological and chemical details in this scenario, which I encourage you to read in more detail here.

Suffice to say that if this theory comes close to explaining the biochemical reactions and events that led to the origin of life on our planet, then it poses an interesting challenge as astronomers discover more worlds similar to Earth, water-bearing and possibly hospitable to life. If conditions are right on another water world, the same reactions and events that occurred on Earth can happen there. And, that means life could originate and flourish on worlds such as Kepler-186f. That makes it all the more important to figure out IF that world has water, and if its atmosphere contains the chemical signatures that indicate that life has flourished there.

So, stay tuned. The world-discovery business just got a whole lot more interesting than it already was! I can’t wait to see what they find next!