Lunar Eclipse: Tool for Studying Exoplanets

Lunar Eclipse: Tool for Studying Exoplanets

The Moon has fascinated every one of my kids. Sometimes they would look out the window with their favorite stuffed animal. Often they made sure everybody knew the Moon’s location if they found it in the sky. My oldest son witnessed his first lunar eclipse at the age of four. This intriguing cosmic body has not only captivated my children’s imagination, but also provides a tool to help researchers find more detailed signatures that could tell us whether or not life exists on the Earth-sized planets astronomers are beginning to soon detect.

For billions of years, life-forms have played a key role in maintaining Earth’s habitability. Specifically, life dramatically altered the gases surrounding primordial Earth to ensure that the biosphere thrived until the present. Today, biological organisms transfer carbon dioxide from the atmosphere to the ocean floor, they produce all the oxygen (including the ozone that shields Earth’s surface from the Sun’s ultraviolet radiation) that comprises one fifth of the atmosphere, and they provide the seeds necessary for rain to fall. While not conclusive, finding signatures of oxygen (specifically ozone) and other biologically produced gases in the atmospheres of exoplanets would provide a strong test of whether or not they support life. A  team of astronomers used a lunar eclipse to simulate the challenges of seeing these gases around an exoplanet.

During a lunar eclipse, Earth blocks much of the sunlight headed toward the Moon. However, the edge of the shadow that moves across the Moon’s surface (called the penumbra) contains a mix of direct light from the Sun and light that passes through Earth’s atmosphere—a situation similar to when a planet transits across the disk of its host star. By training the spectrograph (a detector that senses the amount of light at a given wavelength) on this light, the telltale signs of oxygen, ozone, and other important gases can be seen.1

This research demonstrates the feasibility of applying more definitive tests for the existence of extraterrestrial life. In the next decade, astronomers should find many planets similar in size to Earth and located in the habitable zone (i.e., the region around a star where liquid water can exist). However, finding a planet that meets these minimum requirements does not mean that the planet hosts any sort of life.

RTB’s cosmic creation model contends that Earth’s capacity to support life arises from a Creator’s care, not from strictly natural processes. Thus, we contend that the more scientists learn about the five-hundred-plusand-counting exoplanets, the more that evidence will point to supernatural creation.

  1. A. Vidal-Madjar et al., “The Earth as an Extrasolar Transiting Planet,” Astronomy and Astrophysics, preprint.