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Tuesday, September 30, 2014 | Last updated: 8:52am

New rotational phase mapping method aids in search for habitable planets

“A long time ago in a galaxy far, far away…” Fans of “Star Wars” get goosebumps just hearing those words. Many may consider the phrase to be nothing more than a pop culture sound bite, but scientists at the UA are seeking the reality of those words as they search for distant celestial bodies that could support life.

Unfortunately, the distance between these extraterrestrial objects and the Earth makes it difficult for researchers to learn more about them. That’s why Daniel Apai, an assistant professor of astronomy and planetary sciences, is exploring a new way to map and understand remote planets and planetary-mass objects.

Apai’s team is attempting to circumvent the distance using a new method called rotational phase mapping, and it may be the next big thing in extraterrestrial atmospheric research and the search for habitable planets.

The ultimate goal, in his research and in the search for other Earth-like planets, is to discover how rare life is in the universe.
Though the study of planets outside of our solar system only began recently, our knowledge in the field is rapidly expanding.

Tucson city lights give the night sky a special kind of glow while revealing the Milky Way in Kearny, Arizona.

“In 1995, we didn’t know if there were other planets [like Earth] or not,” Apai said. “In the last few years we discovered that [Earth-like] planets aren’t very rare or uncommon.”

However common they may be, these extra-solar planets ­­— deemed exoplanets — are much too far from Earth and much too close to stars for a contemporary telescope to return much atmospheric information.

“What we do is precisely measure the brightness,” Apai said. This process, known as rotational phase mapping, looks at changes in the light emitted from a planet as it rotates to yield a rough map of the surface of the planet.

“We will see not only variations in the brightness, but also in the color,” Apai said, “and we can even take spectra, so [we see] changes in the wavelength.”

Information about the changes in the light emitted and color of an extraterrestrial object can offer much-needed data on the composition of the object and its atmosphere.

In the future, the technology used by Apai to map gaseous planets will also be used to gather information about terrestrial planets, such as what kind of cloud cover they have. On Earth, our clouds are simple and water-based, but among the vast possibilities of the universe we can expect to find more complex cloud structures. This is important because clouds can have a drastic effect on planetary temperature.

“When clouds form, they basically change the composition of the atmosphere,” Apai explains. “They vary from gas phase to a solid phase, and if you trigger cloud cover, that stops the radiation from easily merging and escaping, so it’s actually like putting a blanket on the atmosphere … it will heat up.”

This result, called the greenhouse effect, is what warms the Earth to a temperature suitable for life. For a planet to be habitable, it would likely need cloud cover. But in something of a Goldilocks effect, the clouds need to keep the planet in an ideal temperature range — too hot, and the planet will likely not be able to support life. For example, it is the greenhouse effect that causes Venus to be more than twice as hot as Mercury, even though Mercury is closer to the Sun. Finding a planet with clouds similar to Earth’s, would mean finding a place with the potential to support life.

With these new tools at researchers’ disposal, the concept of habitable planets will soon make its way from the silver screen to reality as we learn more about the composition of far off celestial bodies.


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