The Kepler mission has proven to be invaluable to science today thanks to its formidable discoveries of exoplanets in our galaxy. It’s rather remarkable how scientists can tell so much from so little, like the size, mass, orbit and sometimes even composition of a distant planet all by analyzing light. On other hand, it’s frustrating at times not being able to tell how a potentially life harboring planet might look like.
This might change in the future. Using novel techniques, like the one developed by planetary scientist Nicolas Cowan, that can feedback the proportion of land, ocean and clouds of a planet by analyzing the reflect light, scientists might be able to map distant worlds and actually visualize how it looks like, albeit far from accurately.
The technique presented this month at a meeting of the American Astronomical Society in Long Beach, Calif works by analyzing specific signals that tell features apart similar to how some military satellites today analyze images and work out whether a feature is a natural surface, like a wooden area, or an unnatural one, like a bunker.
Mapping distant worlds
Cowan’s technique – called “rotational unmixing” – analyzes the changing color of starlight reflecting off a distant, spinning exoplanet to calculate the mix of planetary features – such as land or ocean – that might combine to create a specific hue.
The technique is similar to being in an otherwise dark room with a muted television and analyzing the light reflected on the opposite wall to figure what is playing on the TV.
Cowan’s technique, called “rotational unmixing” picks up startlight reflected off a distant world and analyzes the variation in color. So by analyzing the reflect light of a spinning exoplanet throughout its full rotation, the technique can output calculate the mix of planetary features – such as land or ocean. As an exercise of imagination, Cowan explains the technique works somewhat like when you’re in a dark room with a muted television set facing opposite from it and being able to tell what’s on TV simply but looking at the distorted and blurry reflections on the wall.
“You’re not seeing the picture, but you’re seeing the reflection of the picture and learning something about what’s going on there,” said Eric Ford, an astronomer at the University of Florida in Gainesville, who was not involved in the study.
A new tool for hunting Earth-like planets
Now, there are a number of challenges that make this technique difficult to implement. For one, in order to distinguish to color of reflect light bouncing off very distant worlds you’d need a really powerful optical telescope, the kind which doesn’t exist yet and won’t for quite a while from now on.
If this is the case how do we know the technique works in the first place? Well, Cowan thought of this and used images that capture planet Earth from some of the most distant vantage point photographs have ever been made, like those from NASA’s Deep Impact spacecraft as part of the EPOXI mission.
When the software was used to analyze the EPOXI images, it was able to extract reflectance signatures corresponding to three major surface types – land, ocean and clouds. Sounds familiar right?
The technique is far from being perfect however. Lisa Kaltenegger, an exoplanet researcher at the Max-Planck Institute for Astronomy in Heidelberg, Germany says the targeted he exoplanet must have highly contrasting surfaces, such as ocean and land, or ocean and clouds, for this technique to work well. Distinguishing between clouds and ice is yet another challenge which the technique fails to address.
“Being able to tell whether a planet is simply undergoing significant cloud cover, or is in the midst of a global glaciation is important from the standpoint of habitability,” said o Aomawa Shields, an astrobiologist at the University of Washington in Seattle.
Still, if the right planet is targeted, then the technique could allow for a very rough estimate of how much water to land to clouds the said planet presents. Then again, while the technique is unsuitable to be used for strange planets – the kind we couldn’t even imagine – it does sounds like it’s perfectly tailored for hunting other planets that look very similar to our own. And what better bet of finding extraterrestrial life on a distant planet is there than that on an Earth-like planet?
The resulting picture would not be a map in the traditional sense. “It’s not like a map that you can use to land a spacecraft on a planet … but it’s better than nothing,” Cowan said. It sure is, since Kepler reports 1 in 6 stars hosts at least an Earth-sized planet in a close orbit, raising the number of such planets in our own galaxy alone to 17 billion.
Tibi is a science journalist and co-founder of ZME Science. He writes mainly about emerging tech, physics, climate, and space. In his spare time, Tibi likes to make weird music on his computer and groom felines.