What would we look for in a distant exoplanet in search of Earth-like worlds, and perhaps life? A recent observation made by the Hubble Space Telescope found signatures of narratives of our home planet by looking at a trusted source under extraordinary circumstances: Earth’s Moon, during a total lunar eclipse.
The experiment was conducted by the Hubble Space Telescope, launched in 1990 and now in its 30th year of operation. Hubble orbits the Earth once every 96 minutes, and is generally focused on faint galaxies in the distance, not the brilliant moon nearby. Researchers from the University of Colorado (Boulder) and the Space Telescope Science Institute decided to do just that, during the full eclipse of the month in January 2019.
A total lunar eclipse occurs when the moon passes in the shadow of the earth. As eclipse fans know, the moon does not disappear completely when it enters the dark inner umbrella shade, but instead appears red in color. This is thanks to the light of thousands of sunbeams filtered through the earth’s atmosphere, thrown back on the moon. From the lunar surface back on Earth, you would see a total solar eclipse. Moreover, not every total lunar eclipse appears the same. During totality, a lunar eclipse can appear anywhere from a yellowish-bright orange, to a dark brick rat. The color to be seen depends on how deep the Moon appears in the shadow of the Earth, and how much dust and aerosols are suspended in the Earth’s atmosphere.
In ‘Exoplanet Eclipse’
Researchers realized that the light reflected from the moon would mimic something that researchers are currently on the hunt for: light streaming through the atmosphere of a distant exoplanet as it passes in front of its host star. The current exoplanet stands at 4,302 and is growing. What’s more, a new generation of space observers led by the James Webb Space Telescope (set to launch in October 2021) will soon be able to transition directly to exoplanets. Another future mission, the Large Ultra Violet Optical Infrared Surveyor (LUVOIR), can also image exoplanets directly into the ultraviolet, a major wavelength. This will usher in an exciting new era of exoplanet science, enabling astronomers to gain spectra. This, in turn, will tell us something about exactly what the atmospheres of these exotic worlds are made of. This could also give us hints of all the interesting chemical processes at work on these distant worlds.
Hubble discovered an important chemical in the eclipse: ozone. The combination of three oxygen atoms, ozone on Earth is the result of photosynthesis over geological periods.
“Finding ozone is important because it is a photochemical by-product of molecular oxygen, which is itself a by-product of life,” said Allison Youngblood (Laboratory of Atmospheric and Space Physics) in a recent press release. “In addition to ozone, you would need other spectral signatures to conclude that there was life on the planet, and these signatures cannot necessarily be seen in ultraviolet light.”
Although ozone is not only generated by life – ozone can also result from nitrogen and oxygen exposed to sunlight – a seasonal fluctuation in ozone levels would be a strong bio-signature. Likewise, large amounts of oxygen and methane – which are both reactive and need to be replenished in time to hang on long time scales – would be strong indications that something new is interesting in a distant world.
This also marked the first time that a space telescope made ultraviolet observations of the wavelength during a total lunar eclipse. The detection of terrestrial ozone, along with oxygen and methane seen in the Earth’s terrestrial spectra, was supported by observations based on the same eclipse of January 2019. However, ground-based observers need to correct for the passage of the atmosphere of ‘ the Earth, while space-based observatories do not suffer from this hindrance.
Another clue we may detect in the spectra of an exoplanet is what is known as the ‘red border’ a signature that is solely due to plants and photosynthesis. While this would be a remarkable discovery, it would also be appealing if especially a blip on a chart. What we would really as you can see that strange jungles …
“Photosynthesis is perhaps the most productive metabolism that can evolve on any planet, as it is powered by starlight energy and uses cosmically abundant elements such as water and carbon dioxide,” Giada Arney (NASA / GSFC) said in a recent press release. “These essential ingredients should just be on habitable planets.”
e has sent out our very own bio-signature across the galaxy to anyone who might be able to see the last 2.4 billion years now. That is since the beginning of the Proterozoic era, when oxygen first began to build up in the Earth’s atmosphere.
However, it’s great to see that there is real science that occurs during total lunch eclipses. The next chance you will be wondering about the crimson moon will be during the next total lunar eclipse on May 26thth, 2021. Perhaps science introduced by Hubble will soon usher in a new era of exoplanet science.
Read the full study here.
Lead Image Credit: A concept of the Hubble artist dying after Earth’s Moon during a total lunar eclipse. Credit: M. Kornmesser / ESA / NASA.
