Astronomers discovered a ‘pi-Earth’ that has a period of 3.14 days

The rocky world, with its baking-hot surface, is likely not habitable.


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Scientists at MIT and elsewhere recently detected an Earth-sized planet that has a period of 3.14 days. The planet zips around its star in an orbit reminiscent of the universal mathematics constant at a blistering 81 kilometers per second, or about 181,000 miles per hour.

Scientists labeled this planet as K2-315b. The 315th planetary system was discovered within K2 data—just one system shy of an even more serendipitous place on the list.

The planet has a radius of 0.95 that of Earth’s, making it just about Earth-sized. It orbits a cool, low-mass star that is about one-fifth the size of the sun.

Scientists discovered a planet’s signals in data taken in 2017 by the NASA Kepler Space Telescope’s K2 mission. By focusing on the system earlier this year with SPECULOOS, a network of ground-based telescopes, the team affirmed that the signals were of a planet orbiting its star.

Prajwal Niraula, a graduate student in MIT‘s Department of Earth, Atmospheric and Planetary Sciences (EAPS), said, “The planet moves like clockwork.”

Co-author Julien de Wit said, “Everyone needs a bit of fun these days.”

However, scientists have not yet determined the planet’s mass, but they suspect that the K2-315b is terrestrial, like the Earth. But the pi planet is likely, not habitable, as its tight orbit brings the planet close enough to its star to heat its surface up to 450 kelvins, or around 350 degrees Fahrenheit—perfect, it turns out, for actual baking pie.

Niraula said, “This would be too hot to be habitable in the common understanding of the phrase. The excitement around this particular planet, aside from its associations with the mathematical constant pi, is that it may prove a promising candidate for studying the characteristics of its atmosphere.”

de Wit, who is an assistant professor in EAPS, said, “We now know we can mine and extract planets from archival data, and hopefully there will be no planets left behind, especially these significant ones that have a high impact.”

The team analyzed the signals, testing different potential astrophysical scenarios for their origin, and confirmed that the signals were likely of a transiting planet.

Scientists then decided to take a closer look at the star and its orbiting planet with SPECULOOS. Before this, they had to identify a window of time when they would be sure to catch a transit.

Benjamin Rackham, a co-author of the study, said, “Nailing down the best night to follow up from the ground is a little bit tricky. Even when you see this 3.14 day signal in the K2 data, there’s an uncertainty to that, which adds up with every orbit.”

With Rackham’s forecasting algorithm, the group narrowed in on several nights in February 2020, during which they were likely to see the planet crossing in front of its star. They then pointed SPECULOOS’ telescopes in the direction of the star and were able to see three exact transits: two with the network’s Southern Hemisphere telescopes, and the third from Artemis, in the Northern Hemisphere.

Scientists noted, “the new pi planet may be a promising candidate to follow up with the James Webb Space Telescope (JWST) to see details of the planet’s atmosphere.”

Journal References:
  1. Prajwal Niraula et al., π Earth: A 3.14-day Earth-sized Planet from K2’s Kitchen Served Warm by the SPECULOOS Team, The Astronomical Journal (2020). DOI: 10.3847/1538-3881/aba95f


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