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Video Transcript:
I am in search of another planet in the universe where life exists.
I can't see this planet with my naked eyes or even with the most powerful telescopes we currently possess. But I know that it's there. And understanding contradictions that occur in nature will help us find it.
On our planet, where there's water, there's life. So we look for planets that orbit at just the right distance from their stars.
At this distance, shown in blue on this diagram for stars of different temperatures, planets could be warm enough for water to flow on their surfaces as lakes and oceans where life might reside.
Some astronomers focus their time and energy on finding planets at these distances from their stars. What I do picks up where their job ends. I model the possible climates of exoplanets.
And here's why that's important: there are many factors besides distance from its star that control whether a planet can support life.
Take the planet Venus. It's named after the Roman goddess of love and beauty, because of its benign, ethereal appearance in the sky. But spacecraft measurements revealed a different story. The surface temperature is close to 900 degrees Fahrenheit, 500 Celsius.
That's hot enough to melt lead. Its thick atmosphere, not its distance from the sun, is the reason. It causes a greenhouse effect on steroids, trapping heat from the sun and scorching the planet's surface.
The reality totally contradicted initial perceptions of this planet. From these lessons from our own solar system, we've learned that a planet's atmosphere is crucial to its climate and potential to host life.
We don't know what the atmospheres of these planets are like because the planets are so small and dim compared to their stars and so far away from us.
For example, one of the closest planets that could support surface water - it's called Gliese 667Cc - such a glamorous name, right, nice phone number for a name - it's 23 light years away.
So that's more than 100 trillion miles. Trying to measure the atmospheric composition of an exoplanet passing in front of its host star is hard. It's like trying to see a fruit fly passing in front of a car's headlight. OK, now imagine that car is 100 trillion miles away, and you want to know the precise color of that fly.
So I use computer models to calculate the kind of atmosphere a planet would need to have a suitable climate for water and life.
Here's an artist's concept of the planet Kepler-62f, with the Earth for reference. It's 1,200 light years away, and just 40 percent larger than Earth. Our NSF-funded work found that it could be warm enough for open water from many types of atmospheres and orientations of its orbit.
So I'd like future telescopes to follow up on this planet to look for signs of life.
Ice on a planet's surface is also important for climate. Ice absorbs longer, redder wavelengths of light, and reflects shorter, bluer light. That's why the iceberg in this photo looks so blue. The redder light from the sun is absorbed on its way through the ice.
Only the blue light makes it all the way to the bottom. Then it gets reflected back to up to our eyes and we see blue ice. My models show that planets orbiting cooler stars could actually be warmer than planets orbiting hotter stars.
There's another contradiction - that ice absorbs the longer wavelength light from cooler stars, and that light, that energy, heats the ice.
Using climate models to explore how these contradictions can affect planetary climate is vital to the search for life elsewhere.
And it's no surprise that this is my specialty. I'm an African-American female astronomer and a classically trained actor who loves to wear makeup and read fashion magazines, so I am uniquely positioned to appreciate contradictions in nature...
...and how they can inform our search for the next planet where life exists.
My organization, Rising Stargirls, teaches astronomy to middle-school girls of color, using theater, writing and visual art.
That's another contradiction - science and art don't often go together, but interweaving them can help these girls bring their whole selves to what they learn, and maybe one day join the ranks of astronomers who are full of contradictions, and use their backgrounds to discover, once and for all, that we are truly not alone in the universe.
Thank you.
According to the study, much of 62f's potential habitability revolves around the CO2 component of its atmosphere, if it indeed has an atmosphere.
As a greenhouse gas, CO2 can have a significant effect on the temperature of a planet, and hence, a significant effect on its habitability. Earth's atmosphere is only 0.04% carbon dioxide (and rising.)
Kepler-62f would likely need to have much more CO2 than that if it were to support life. It would also require other atmospheric characteristics.
The study modeled parameters for CO2 concentration, atmospheric density, and orbital characteristics.
They simulated:
An atmospheric thickness from the same as Earth's up to 12 times thicker.
Carbon dioxide concentrations ranging from the same as Earth's up to 2500 times Earth's level.
Multiple different orbital configurations.
It may look like the study casts its net pretty wide in order to declare a planet potentially habitable. But the simulations were pretty robust, and relied on more than a single, established modeling method to produce these results.
With that in mind, the team found that there are multiple scenarios that could make 62f habitable.
"We found there are multiple atmospheric compositions that allow it to be warm enough to have surface liquid water," said Shields, a University of California President's Postdoctoral Program Fellow.
"This makes it a strong candidate for a habitable planet."
Our dear, sweet Earth is the only planet
where life is confirmed (by us, the humans...)
Here it is, as seen on July 6, 2015
from a distance of one million miles
by a NASA scientific camera aboard
the Deep Space Climate Observatory spacecraft.
Credits: NASA
As mentioned earlier, CO2 concentration is a big part of it.
According to Shields, the planet would need an atmospheric entirely composed of CO2, and an atmosphere five times as dense as Earth's to be habitable through its entire year.
That means that there would be 2500 times more carbon dioxide than Earth has.
This would work because the planet's orbit may take it far enough away from the star for water to freeze, but an atmosphere this dense and this high in CO2 would keep the planet warm.
But there are other conditions that would make 62f habitable, and these include the planet's orbital characteristics.
"But if it doesn't have a mechanism to generate lots of carbon dioxide in its atmosphere to keep temperatures warm, and all it had was an Earth-like amount of carbon dioxide, certain orbital configurations could allow Kepler-62f's surface temperatures to temporarily get above freezing during a portion of its year," said Shields.
"And this might help melt ice sheets formed at other times in the planet's orbit."
Shields and her team used multiple modeling methods to produce these results.
The climate was modeled using the Community Climate System Model and the Laboratoire de Meteorologie Dynamique (LMD) generic model. The planet's orbital characteristics were modeled using HNBody.
This study represents the first time that these modeling methods were combined, and this combined method can be used on other planets.
Shields said,
"This will help us understand how likely certain planets are to be habitable over a wide range of factors, for which we don't yet have data from telescopes.
And it will allow us to generate a prioritized list of targets to follow up on more closely with the next generation of telescopes that can look for the atmospheric fingerprints of life on another world."
There are over 2300 confirmed exoplanets, and many more candidates yet to be confirmed.
Only a handful of them have been confirmed as being in the habitable zone around their host star. Of course, we don't know if life can exist on other planets, even if they do reproduce the same kind of habitability that Earth has.
We just have no way of knowing, yet.
That will change when instruments like the James Webb Space Telescope are able to peer into the atmospheres of exoplanets and tell us something about any bio-markers that might be present.
But until then, and until we actually visit another world with a probe of some design, we need to use modeling like the type employed in this study, to get us closer to answering the question of life on other worlds.