Earth is an Exoplanet to Aliens. This is What They’d See

Reconstruction of what Earth's light curve would look like. Credit: S. Fan et. al., arXiv (2019) arXiv:1908.04350

The study of exoplanets has matured considerably in the last ten years. During this time, the majority of the over 4000 exoplanets that are currently known to us were discovered. It was also during this time that the process has started to shift from the process of discovery to characterization. What’s more, next-generation instruments will allow for studies that will reveal a great deal about the surfaces and atmospheres of exoplanets.

This naturally raises the question: what would a sufficiently-advanced species see if they were studying our planet? Using multi-wavelength data of Earth, a team of Caltech scientists was able to construct a map of what Earth would look like to distant alien observers. Aside from addressing the itch of curiosity, this study could also help astronomers reconstruct the surface features of “Earth-like” exoplanets in the future.

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What is the Direct Imaging Method?

Direct image of exoplanets around the star HR8799 using a Vortex coronagraph on a 1.5m portion of the Hale telescope. Credit: NASA/JPL-Caltech/Palomar Observatory

Welcome back to the latest installment in our series on Exoplanet-hunting methods. Today we begin with the very difficult, but very promising method known as Direct Imaging.

In the past few decades, the number of planets discovered beyond our Solar System has grown by leaps and bounds. As of October 4th, 2018, a total of 3,869 exoplanets have been confirmed in 2,887 planetary systems, with 638 systems hosting multiple planets. Unfortunately, due to the limitations astronomers have been forced to contend with, the vast majority of these have been detected using indirect methods.

So far, only a handful of planets have been discovered by being imaged as they orbited their stars (aka. Direct Imaging). While challenging compared to indirect methods, this method is the most promising when it comes to characterizing the atmospheres of exoplanets. So far, 100 planets have been confirmed in 82 planetary systems using this method, and many more are expected to be found in the near future.

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