NASA uses the Earth as a laboratory to study distant worlds

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The study of the exoplanets-planets that lie outside our solar system could help scientists answer big questions about our place in the universe, and if life exists beyond Earth. But these distant worlds are extremely weak and difficult to image directly. A new study uses the Earth as a substitute for an exoplanet, and shows that even with very little light – as little as a pixel – it is still possible to measure the key features of distant worlds.

The new study uses data from NASA's Earth Polychromatic Imaging Camera (EPIC) instrument, which is aboard the Deep Space Observatory of Ocean Administration. and atmospheric (DSCOVR). DSCOVR bypasses the Sun at point 1 of Lagrange, a specific orbit that provides the EPIC a constant view of the sunlit surface of our planet. The EPIC continuously observes the Earth since June 2015, producing nuanced maps of the planet's surface over multiple wavelengths and contributing to climate and weather studies

The EPIC instrument captures the reflected light from the Earth in 10 different wavelengths. So, whenever the EPIC "takes a picture" of the Earth, it actually captures 10 images. The new study averages each image into a single brightness value, or the equivalent of a "single pixel" image for each wavelength. A single snapshot of a pixel on the planet would provide very little information about the surface. But in the new study, the authors analyzed a set of data containing single-pixel images taken several times a day, in 10 wavelengths, over a prolonged period. Despite the fact that the entire planet was reduced to a single point of light, the authors were able to identify clouds of water in the atmosphere and measure the rate of rotation of the planet (the duration of his day). The authors say that the study, in the issue of June 27, 1945 Astrophysical Journal demonstrates that the same information could be derived from observations of single-pixel exoplanets

"The advantage of using the Earth as a proxy for an exoplanet, is that we can verify our findings derived from single pixel data with the wealth of data we actually have for Earth – we can not do it if we use data from a real and distant exoplanet "Jonathan Jiang, atmospheric and climate scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, and lead author of the new study

A Little Point of Light

When Jiang's daughter, Teresa, was in elementary school, he organized a star-watching event for her and her friends . Jiang pointed to the stars and told his daughter that the Sun was also a star, and that there were planets orbiting other stars, just like planets orbiting the Sun. She urged her father for more information, asking how scientists could possibly learn these distant worlds from such small dots of light in the sky. "The children are asking a lot of good questions," Jiang said. "And this question has remained in my mind – if I can see an exoplanet as a tiny dot of light, can I see clouds, oceans and land?"

Jiang started his career in astrophysics, but for his doctorate. At work, he decided to apply his computer skills and physical modeling to the Earth's climate. Now he uses climate data to help study exoplanets. Exoplanets are significantly weaker than stars and much more difficult to detect. The Earth, for example, is about 10 billion times weaker than the Sun. Only about 45 exoplanets were discovered by direct imaging, all larger than the Earth. The majority of known exoplanets (more than 3,700 have been confirmed) have been detected indirectly, using techniques such as the transit method, in which scientists observe the slight attenuation of a star caused by the passage of time. an exoplanet on the face of the star. ] NASA uses the Earth as a laboratory to study distant worlds “/>

The EPIC instrument captures reflected light from the sunny side of the Earth in 10 different wavelengths, or colors, because different materials reflect different wavelengths of light at different degrees – plants, for example, mainly reflect green light. And a reddish planet like Mars, for example, would have a very different color profile compared to an ice-covered planet.

The new study shows that by observing a planet with distinct characteristics in time – like oceans and continents – it is possible to measure the rate of rotation of the planet by observing a repeated pattern in the reflected light. This model would result from these planetary characteristics moving in view with a regular cadence. For example, every 24 hours, Australia and the Pacific Ocean fill the field of view of the EPIC and about 12 hours later, South America and the United States. Atlantic fill the frame, with Africa and the Indian Ocean passing between the two. This changing light pattern is repeated day after day. In the new article, the authors show that they can detect this repetition cycle and thus determine the rate of rotation, or the duration of the day of the planet. The rate of rotation of a planet can reveal information about how and when the planet has formed, and is a particularly difficult property to measure with current methods.

"People have been talking for a long time about using this approach to measure the turnover rate." Exoplanets, but there's no demonstration that it could work because we had not of real data, "said Renyu Hu, an exoplanet scientist at JPL and co-author of the new study." We have shown that in each wavelength, the 24-hour period appears, which means that this approach to measure the rotation of the planet is robust. "

The authors note however that the effectiveness of this method would depend on the unique characteristics of the planet.A daily cycle cycle may not be visible on a planet that Venus, for example, is covered with thick clouds and has no oceans on its surface, so it's a recurring pattern of one day. may not appear or be distinct enough to r be observed in an image of a pixel. Planets like Mercury and Mars would also be a challenge, but Jiang said planetary features like craters could also contribute to a model that could be used to measure the rotation period.

Exoplanets for Imaging

Previous studies have used the Earth as a proxy for exoplanets, to study what kinds of planetary properties could be obtained remotely, but no previous study has done so. Has examined as many bands of wavelengths. This is also the first study of its kind to take into account such an important data set, over a long period: it used more than 27 months of observations, with images taken by the company. EPIC about 13 times a day

have far less data than was used in the new study, but researchers report that to measure the turnover rate of an exoplanet with more than 90% confidence, it would only take two to three times per orbital period (that is to say on this particular exoplanet for about seven orbital periods

                    

The time required for astronomers to observe an exoplanet in order to identify its rate of rotation also depends on the amount of unwanted light included in the exoplanet data. EPIC data offers an exceptionally clear view of the Earth, largely free of light from other sources. But one of the main challenges in direct imaging of exoplanets is that they are much weaker than their parent stars. The light of the neighboring star can easily drown the light of an exoplanet, making the latter invisible. With the planet's signal competing with the star's light, it may take longer to discern a pattern that could reveal the planet's rate of rotation. NASA is studying potential designs for next-generation telescopes that may be able to directly image exoplanets the size of the Earth.

With the field of direct imaging by exoplanet, Jiang has not finished thinking about the question posed to him by his daughter. a decade ago. If scientists can learn about the surface features of distant planets, then could they answer an even bigger question posed by his daughter – does any of these planets harbor life?

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