Pi in the sky

'Clockwork' planet reveals a uniquely mathematical orbit

On K2-315b, every day is Pi Day.

NASA Ames/JPL-Caltech/T. Pyle, Christine Daniloff, MIT

Space telescopes scour the cosmos for exoplanets, finding thousands of strange and exotic worlds. Every now and then, one of those planets surprises us with their unique features.

In yet another cosmic twist, a team of astronomers discovered a planet roughly the same size as Earth that speeds its way around its host star in a period of just 3.14 days — the same number as the mathematical constant Pi.

The discovery is detailed in a study published Monday in The Astronomical Journal.

Astronomy meets mathematics in this latest discovery of an Earth-sized planet that zips by its star in just 3.14 days.NASA Ames/JPL-Caltech/T. Pyle, Christine Daniloff, MIT

While looking through old data recorded in 2017 by NASA's Kepler Space Telescope's K2 mission, astronomers found signals of a potential planet orbiting around a cool, small star. The scientists zoomed in on the potential planet using a network of ground-based telescopes in Chile's Atacama Desert called The Search for habitable Planets EClipsing ULtra-cOOl Stars, or SPECULOOS. The observations confirmed that the signals were in fact traces of an Earth-sized planet orbiting an ultra-cool dwarf star.

The planet, dubbed K2-315b, has a radius of 0.95 that of Earth’s, and orbits a low-mass star that's about one-fifth the size of the Sun.

K2-315b flies through its orbit, completing one full round about its star in just 3.14 days, at a speed of about 181,000 miles per hour.

“The planet moves like clockwork,” Prajwal Niraula, a graduate student at the Massachusetts Institute of Technology’s (MIT) Department of Earth, Atmospheric and Planetary Sciences (EAPS), and lead author of the paper, said in a statement.

The astronomers could not help but make the correlation between the planet's orbital period and Pi, the ratio of a circle's circumference to its diameter which appears in many formulas in physics and mathematics. Of course, Pi is better approximated at 3.14159, but there's no need to get too specific.

“Everyone needs a bit of fun these days,” Julien de Wit, assistant professor at EAPS and a member of MIT’s Kavli Institute for Astrophysics and Space Research, and co-author of the new study, said in a statement.

Unfortunately, there will likely be no Pi planet aliens. The astronomers suspect that K2-315b is not habitable since it orbits so closely to its host star. Temperatures on the Earth-sized planet likely reach 350 degrees Fahrenheit, which, coincidentally, is a perfect temperature to bake pie, according to the researchers.

“This would be too hot to be habitable in the common understanding of the phrase,” Niraula said.

But what the Pi planet lacks in habitability, it makes up for in being a testing ground for studying atmospheric conditions.

The astronomers believe that the planet has a rocky core, similar to that of Earth's. That makes it a good candidate to study the atmospheres of other planets. Such information is useful when astronomers are searching for conditions of habitability on other worlds.

“We now know we can mine and extract planets from archival data, and hopefully there will be no planets left behind, especially these really important ones that have a high impact,” de Wit said.

Abstract: We report on the discovery of a transiting Earth-sized (0.95R) planet around an M3.5 dwarf star at 57 pc, EPIC 249631677. The planet has a period of ~3.14 days, i.e., ~π, with an installation of 7.45 S. The detection was made using publicly available data from K2's Campaign 15. We observed three additional transits with SPECULOOS Southern and Northern Observatories, and a stellar spectrum from Keck/HIRES, which allowed us to validate the planetary nature of the signal. The confirmed planet is well suited for comparative terrestrial exoplanetology. While exoplanets transiting ultracool dwarfs present the best opportunity for atmospheric studies of terrestrial exoplanets with the James Webb Space Telescope, those orbiting mid-M dwarfs within 100 pc such as EPIC 249631677b will become increasingly accessible with the next generation of observatories.
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