Scientists Discover Hidden Earth-Like Planet in Old Data

A world with 100-foot tall waves and filled to the skies with water. A world you can walk around in 10 seconds. A world with raging volcanoes and ashy skies. Our universe is filled with trillions and trillions of planets, each with its own unique characteristics. Finding a planet with specific parameters among such diversity would be akin to finding a needle in multiple haystacks. However, this is exactly what scientists are currently doing: searching for a planet with Earth-like conditions that can sustain life and be humanity’s next home. As you can imagine, this is an extremely difficult task given the sheer volume of planets in our galaxy.

However, a new Earth-like planet was discovered by scientists while searching through old, hidden data on April 15, 2020. This unique planet is called Kepler-1649c, and it has reinvigorated planet exploration.

Introducing Kepler-1649c

Kepler-1649c is an exoplanet located 300 light-years away from Earth. For reference, that is equivalent to about 1.764 x 10^15 miles (the diameter of the Earth is around 8,000 miles). Though this may sound far, it is relatively close, cosmically speaking.

Like Earth, Kepler-1649c is located within its solar system’s circumstellar habitable zone. A circumstellar habitable zone is defined as the orbital region in which the conditions for liquid water to be present are met and temperature and atmospheric pressure are at levels that can sustain life. Liquid water is a required condition for life as we know it to exist. If a planet or other cosmic body orbits too close to a star, water will evaporate and form an atmosphere made of steam. The environment would be too hot for humans or any form of life to survive. On the other hand, a position too far away from a star would lead any water present on the planet to freeze, along with its inhabitants. These two situations are dichotomous, leading scientists to nickname the habitable zone the “Goldilocks Zone.”

Aside from its similar cosmic positioning, Kepler-1649c also shares multiple physical characteristics with Earth. It receives about 75 percent of the amount of sunlight Earth receives, leading scientists to wonder if its atmosphere might have similar temperatures and thus host a similar environment. Remarkably, its mass is only 1.06 times that of Earth’s. With these conditions in mind, if humans were to move to Kepler-1649c tomorrow, life would not be much different.

However, Kepler-1649c orbits a red dwarf star. In contrast, our Sun is a yellow dwarf. Red dwarves are much smaller and have lower masses, lower temperatures, and lower pressures. For life to be possible in these conditions, a planet would have to orbit extremely close to the red dwarf. Kepler-1649c conforms to this requirement. However, with such a close orbit to its star, it is susceptible to being tidally locked (a phenomenon where the proximity of the planet to the star keeps the planet from rotating, resulting in only one side of the planet receiving sunlight). In addition, red dwarves are also known to emit spontaneous solar flares, which may make life near them impossible. However, the occurrence of these two phenomena has yet to be observed.

A Needle in a Haystack

The Kepler telescope was active from its launch in March 2009 to November 2018, when it finally ran out of fuel and was decommissioned (taken out of service) after nine faithful years of duty. NASA’s mission for it was to search for new planets in the night sky that may one day become humanity’s next home. Kepler’s database contained novel discoveries of an astounding 2,682 planets. The discoveries made by Kepler have been of tremendous value to scientists. By exposing part of the vast number of planets out in space, Kepler’s findings spark hope that a planet with habitable conditions will be found; even uninhabitable planets provide valuable insight on astronomy and geology that will aid researchers’ future efforts to learn more about our own planet.

Kepler uncovered thousands of unique and remarkable planets—Kepler-1649c being one of them.

Transit Method

Kepler was able to discover and locate planets like Kepler-1649c by using the transit method. First, it was launched and oriented toward a fixed spot in the constellation Cygnus. This positioning would allow it to constantly monitor 100,000 main sequence stars, or stars similar to that of our Sun. Kepler would monitor a star’s luminosity (brightness) level through its equipped photometer. Dips in a star’s luminosity would indicate that a planet/cosmic body had come in between the star and the Kepler telescope. This event is called a transit—hence why it is called the transit method. Kepler recorded these dips in luminosity as planets.

Why was it Missed? (Robovetter…)

However, the transit method is extremely susceptible to occurrences of false positives. Other large cosmic bodies besides planets such as asteroids or meteoroids can perform a transit between the star and Kepler, causing a dip in the luminosity reading. The Kepler telescope would record this occurrence as it would with an actual planet discovery. As you might imagine, this would lead to quite a great number of false positives. For this reason, scientists wrote an algorithm called Robovetter that would filter out these false positives.

“Robovetter's job was to distinguish the 12 percent of dips that were real planets from the rest,” the California Institute of Technology said. Robovetter would assign every detection of a cosmic body from Kepler a value between 0.0 and 1.0. The closer a value was to 1.0, the more confident Robovetter would be that it was a planet. The closer the value was to 0.0, the more likely it was to be a false positive. However, its task was extremely complex, so it had quite a significant margin of error.

Being aware of this, scientists would manually double-check the false positives that Robovetter labeled in order to ensure that actual planets had not been filtered out. It was during this that scientists found Kepler-1649c, which was officially reported on April 15, 2018. "If we hadn't looked over the algorithm's work by hand, we would have missed it,” said Andrew Vanderburg, a researcher who had helped with proof-checking Robovetter.

Much is still unknown about Kepler-1649c. Its atmosphere might be acidic, rendering it completely uninhabitable, or it could be an entirely barren world. Kepler-1649c is still quite a few steps away from being named humanity’s next home. However, the real value lies in giving hope that the perfect planet is out there somewhere in the universe. Thomas Zurbuchen, the associate administrator of NASA's Science Mission Directorate in Washington, said, “This intriguing, distant world gives us even greater hope that a second Earth lies among the stars, waiting to be found.”