This Is How Earth Would Look to Alien Astronomers


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It has been less than 30 years since the discovery of the first exoplanets, and we’re still in the dark when it comes to the possibility of life on any of them. Our techniques for finding other planets isn’t particularly sensitive, and we’re not even certain what signals we need to prioritize. A new study could shed light on that question by using the only habitable planet known to exist: Earth. 

The study comes from the California Institute of Technology’s Division of Geological and Planetary Sciences (GPS) and the NASA Jet Propulsion Laboratory, led by graduate student Siteng Fan. The goal was to start with a planet we know supports life (Earth), and work backward to extrapolate what an alien looking in our direction might see. In that way, Fan and the team hope to nail down the “look” of a life-supporting exoplanet. To do that, they used 9,740 images of Earth taken by NASA’s Deep Space Climate Observatory. They include data on light reflected from Earth in multiple wavelengths. 

At our current level of technology, we can’t directly observe exoplanets. They’re too small and dim compared with stars, but we can infer their presence via gravity or the way they obscure light from their parent stars. Often, the most we can say about an exoplanet’s habitability is whether it has a chance of harboring liquid water based on proximity to the star. 

The team discovered that the second principal component of Earth’s reflected light curve correlates to the fraction of land in the illuminated hemisphere. Using the original images, they were able to pick out the values matching land and cloud cover and applied them to a contour map (see top). The green highlighted areas are landmasses, and the blue is water — Africa is in the center, and Asia is to the right. North America is peeking in at the left edge. 

If we apply these same light curve values to a distant exoplanet, it could help us determine if there’s cloud cover and liquid water on the surface. Confirming that a planet has a water cycle could be a big step toward proving habitability. Will we actually be able to gather such data? It’s possible! Upcoming instruments like the James Webb Space Telescope and Thirty Meter Telescope could have enough resolution to pick up some reflected light from small, rocky exoplanets. We could be on the verge of finding more Earth-like worlds.

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Astronomer: Earth’s Atmosphere Could Become the Lens of a Massive Telescope


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The conventional wisdom is that if you want to look at more distant objects in the universe, you need a bigger telescope. What if you didn’t have to build one, though? A new analysis claims it may be possible to use the Earth’s atmosphere as a giant lens to observe far-away stars and galaxies on the cheap. The process may even work in reverse to send signals to distant locales. 

Earth’s atmosphere has traditionally been seen as an impediment to astronomy. The thick envelope of gas that keeps us alive also obscures space. That’s why the most powerful telescopes are the ones we launch into orbit like Hubble and the upcoming James Webb Space Telescope. And then there are massive ground-based telescopes like the 25-meter Giant Magellan Telescope under construction in Chile. 

These projects are expensive and deviously complex. The Giant Magellan Telescope will cost around $1 billion, and the Webb Telescope is closing in on $10 billion after years of delays. The “terrascope” proposed by Columbia University astronomer David Kipping could be vastly easier. Using the Earth’s atmosphere as a lens to focus light has been proposed in the past, but Kipping’s new calculations demonstrate how powerful such a setup could be. 

As light from distant objects passes through Earth’s atmosphere, some of it passes through the upper atmosphere and refracts into a cone-like shape. If you were to place a small satellite in orbit around the moon, it could use a small mirror to collect that light, essentially magnifying distant objects. According to Kipping, a 1-meter terrascope could potentially amplify light by 22,500 times. That’s far, far beyond the capabilities of any telescope we could manufacture with current technology. 

Kipping also points out you could equip a terrascope with a radio transmitter rather than a mirror. By bouncing signals off the Earth’s atmosphere, you could potentially improve communication with other planets in the solar system. Some of them have atmospheres, so you could bounce the signal onward creating an “Internet across the solar system.”

That all sounds great, but there are a few potential pitfalls. For one, you can’t point the terrascope anyplace you like. Your lens is the Earth itself, so you can only spy on things that are behind the planet. That’s just a tiny fraction of the sky. Kipping’s calculations also use simplified atmospheric models that don’t take into account conditions like high-altitude clouds. Light contamination from Earth could also make terrascope signals too noisy to be useful. Kipping agrees there’s a lot of work to be done, but it’s a fascinating idea.

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