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The Hubble Telescope uses the moon as a mirror to study the earth



On January 20 and 21, 2019, the planet earth came between the sun and the moon and draped the rocky body with its shadow in a total lunar eclipse.

The moon may have appeared dark to us here on earth, but it served as a giant moon mirror from space.

NASA’s Hubble Space Telescope used the moon to reflect sunlight to observe Earth’s atmosphere and fingerprint the planet’s ozone. By looking at the earth’s ozone, scientists will be able to determine the conditions under which life can take place on other worlds outside of our own.

Hubble’s observations were detailed in a study published in this week The Astronomical Journal.

This diagram shows the total lunar eclipse and shows the sunlight reflected from the moon.M. Kornmesser (ESA / Hubble), NASA and ESA

Hubble was launched in 1990 and the space telescope has been in orbit ever since.

In order to observe the earth’s atmosphere, the telescope did not look directly at the planet, but used the moon to reflect the sunlight that had passed through the earth’s atmosphere during the total lunar eclipse when the planet was wedged between the moon and the sun.

Astronomers have used this method before, but this is the first time a total lunar eclipse has been detected by a space telescope in ultraviolet wavelengths, somewhere between visible light and X-rays.

In this way, the space telescope was able to capture the spectral fingerprint of ozone. Ozone is a gas made up of three oxygen atoms in the earth’s upper atmosphere and serves as a protective shield against the sun’s ultraviolet radiation.

Ozone forms naturally when oxygen in the earth’s atmosphere is exposed to high levels of ultraviolet light and acts as a blanket around our planet.

“Photosynthesis is possibly the most productive metabolism a planet can develop because it is powered by energy from starlight and uses cosmically abundant elements like water and carbon dioxide,” said Giada Arney, scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland and co-author of the new study, said in a statement. “These necessary ingredients should be common on habitable planets.”

While scientists look for signs of life on other planets, ozone is a powerful indicator of habitability in other worlds.

“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, researcher at the Laboratory of Atmospheric and Space Physics in Boulder, Colorado and lead author of the new study. said in a statement.

However, finding oxygen alone is not an indication that life is in abundance on any other planet. There are many other factors that must be considered before astronomers can confirm an exoplanet’s habitability.

As exoplanets migrate in front of their host stars, telescopes detect the signatures of chemicals in the planets’ atmosphere as they filter out certain colors in the star’s light. However, smaller Earth-like planets have a thinner atmosphere, making this type of detection much more difficult.

Therefore, larger telescopes are needed to view smaller exoplanets.

The recent Hubble of Earth observations are part of ongoing experiments to perfect these types of observations, as our planet is the only small rocky world we know to be home to life. Earth serves as the perfect and only analog to find life on other planets.

Abstract: We observed the total lunar eclipse in January 2019 with the STIS spectrograph of the Hubble Space Telescope to get the first observation of Earth as a transit exoplanet in the near UV range (1700–3200 Å). The observatories and instruments that can perform transmission spectroscopy of exo-earths start planning, and characterizing the Earth’s transmission spectrum is critical to ensure that important spectral features (e.g., ozone or O) are present3) are adequately recorded in mission concept studies. Ö3 is produced photochemically from O.2, a product of the metabolism prevailing on earth today, and will be sought in future observations as critical evidence of life on exoplanets. Ground-based observations of lunar eclipses have provided the Earth’s transmission spectrum at optical and near IR wavelengths, but the strongest O.3 Signatures are in the near UV. We describe the observations and methods used to extract a transmission spectrum from Hubble lunar eclipse spectra and identify spectral features of O.3 and Rayleigh scattering in the range of 3000-5500 Å in the transmission spectrum of the earth by comparison with earth models which include refraction effects in the earth’s atmosphere during a lunar eclipse. Our near-UV spectra are without features, which is due to the fact that the narrow period of time was missed during the solar eclipse when the sunlight in the near-UV is not completely attenuated by the earth’s atmosphere due to the extremely strong O.3 Absorption and when sunlight is transmitted to the lunar surface at altitudes where it passes through the O3 Layer instead of above.


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