Experiment Confirms Earth Is Habitable, but Not as Nice as It Was in the '90s

Good news: Earth is definitely habitable. Obviously, you knew that already since you breathe its air, drink its water and enjoy its climate. But scientists had a very good reason for confirming it: doing so allows them to test their ability to recognize other life-supporting planets when they see them.

That's why last fall, the spacecraft OSIRIS-REx turned its instruments back to Earth on its way out to an asteroid. It took photographs and measured characteristics like how bright the planet's surface is and what chemicals are found in its atmosphere.

Scientists studied that information as if it had come from a distant, alien world. The brief description of their findings, posted online in conjunction with their presentation at the 49th Lunar and Planetary Science Conference, makes for eerie reading.

Read more: We Could Discover Aliens Before 2100, Leading Scientist Predicts

The experiment was designed to mimic a similar set of observations taken in 1990, when a spacecraft en route to Jupiter took a moment to study its home. The new results highlight a concerning change visible even from a distance: rising concentrations of greenhouse gases.

Carbon dioxide and methane are more than 10 percent more common in the atmosphere than they were in 1990. That means the OSIRIS-REx team identified the fingerprint of climate change while pretending they knew nothing about Earth.

Given the spacecraft's point of view, scientists couldn't spot the ice caps at the poles. They noted that if they weren't studying their own home, they would have had no way of confirming there was ice on the planet at all. They also note that their perception of Earth was shaped by their timing; the images they took included hurricanes Maria and Jose, which allowed them to conclude that the planet's atmosphere supports forming large storms.

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OSIRIS-REx took this photo on September 22, 2018, as part of its quest to pretend Earth was an alien world. NASA's Goddard Space Flight Center/University of Arizona

While these conclusions sound obvious, this sort of analysis isn't something scientists have ever managed to accomplish beyond our solar system. Instead, these distant worlds are usually identified indirectly, by changes in characteristics like the brightness of the star they circle.