Scientists Use Moon as Mirror to Detect Extraterrestrial Life

Article by Claire Bugos                             August 10, 2020                            (smithsonianmag.com)

• In January 2019, there was a total lunar eclipse. During a two-day period, light from the Sun passed through the Earth’s atmosphere and hit the Moon, and was reflected back toward the Earth. The Hubble Space Telescope was able to intercept and gather data from this ultraviolet light. Though similar ground-based studies have been done before, this is the first time that scientists have used a space telescope to capture ultraviolet wavelengths. From this data, scientists from NASA and the European Space Agency are able to analyze the Earth’s own atmospheric spectrum. They reported their findings in an article published August 6 in The Astronomical Journal. (see 3-minute NASA video below)

• The main focus was on the Earth’s protective ozone layer. Ozone absorbs ultraviolet radiation. During the eclipse, Hubble detected lower amounts of UV radiation from the light reflected off the Moon than is present from unfiltered sunlight. Therefore, the Earth’s atmosphere absorbed some of it. If they can simulate this with a distant exoplanet, they can determine whether that planet’s atmosphere contains ozone. And along with oxygen, the detection of an ozone layer is considered an indication of possible life on that planet.

• Using this unique method, scientists can simulate observations of exoplanets. When an exoplanet crosses in front of its star, the star light is filtered through the planet’s atmosphere, creating a “halo” effect. Chemicals in the atmosphere filter out certain colors of starlight. Therefore, scientists can determine that planet’s atmospheric composition.

• “But how would we know a habitable or an uninhabited planet if we saw one?” queries Allison Youngblood of the Laboratory for Atmospheric and Space Physics, and lead researcher of Hubble’s observations. By developing a model of the Earth’s chemical spectrum, scientists can use this as a template for categorizing the atmospheres of exoplanets in other solar systems.

• The age of the planet is also be taken into account when determining its ability to host life. Earth had low concentrations of oxygen for more than a billion years, while organisms used photosynthesis to build the ozone layer. So it may be challenging to detect ozone in younger planets. Still, ultraviolet may be “the best wavelength to detect photosynthetic life on low-oxygen exoplanets,” says Giada Arney of NASA’s Goddard Space Flight Center and a co-author of the study.

• The Hubble telescope was launched in 1990, even before astronomers first discovered exoplanets. While its ability to observe extraterrestrial atmospheres is “remarkable,” NASA says future observations of Earth-sized planets will require much larger telescopes and longer observational periods, which the James Webb Space telescope, scheduled to launch in 2021, will provide.

In the quest to discover life beyond Earth, scientists are harnessing a very large and proximate tool—the moon.

During a total lunar eclipse in January 2019, the moon acted like a giant mirror, reflecting sunlight that had passed

through our atmosphere back toward Earth, reports Chelsea Gohd for Space.com. The Hubble Space Telescope, which was positioned between the Earth and moon, intercepted the reflected ultraviolet light for scientists to analyze.

Scientists from NASA and the European Space Agency studied the reflected light from a lunar eclipse during a two-day window. They reported their findings in an article published August 6 in The Astronomical Journal.

For the first time, scientists used a space telescope to capture ultraviolet wavelengths. Though similar ground-based studies have been done before, using a space telescope for this observation allows scientists to simulate future observations of exoplanets, Space.com reports.

The goal was for the telescope to detect the Earth’s ozone layer. The ozone molecule that makes up the Earth’s protective layer absorbs ultraviolet radiation. During the eclipse, Hubble detected lower amounts of UV radiation from the light reflected off the moon than is present from unfiltered sunlight, meaning the Earth’s atmosphere must have absorbed some of it, according to a NASA press release.

If scientists are able to detect an ozone layer or oxygen on a neighboring exoplanet, there’s a possibility that the planet may harbor life. On Earth, oxygen is often produced by life forms, especially those that photosynthesize. If scientists detect an oxygen-rich atmosphere on an exoplanet, especially if the amount of oxygen varies seasonally, there is a chance that it also hosts life. But scientists would need to further analyze the atmosphere using other tools before determining if it’s life-hosting, Allison Youngblood of the Laboratory for Atmospheric and Space Physics, and lead researcher of Hubble’s observations, says in the press release.

3-minute video “Hubble Views Moon to Study Earth” (‘NASA Goddard’ YouTube)

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