Scientists at MIT have discovered a “pi Earth”— an Earth-sized planet that orbits around its star every 3.14 days. The scientists found signals of the planet in data taken in 2017 by the NASA Kepler Space Telescope’s K2 mission. After installing the system earlier this year with SPECULOOS, the team confirmed that the signals were of a planet orbiting its star. Actually, the planet is still be circling its star today every 3.14 days.
“The planet moves like clockwork,” says Prajwal Niraula, the lead author of research of the Massachusetts Institute of technology.
Planet extraction
The new planet is designated as K2-315b, which is the 315th planetary system found in the K2 data — just one system that doesn’t have an even happier place on the list.
The scientists count up that K2-315b 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. The planet orbits its star every 3.14 days, at a blistering 81 kilometers per second, or about 181,000 miles per hour.
Its weight is not determined yet, scientists assume that K2-315b is terrestrial, like the Earth. But the pi planet is likely not habitable, as its tight orbit brings the planet close to its star to heat its surface up to 450 kelvins, or around 350 degrees Fahrenheit.
“This place would be too hot to be habitable in the general understanding of the phrase,” says Niraula. He adds that the excitement around this particular planet, aside from its associations with the mathematical constant pi, is that it may become a promising candidate for studying the characteristics of its atmosphere.
“Now, we know that we can mine and extract planets from archival data, and hopefully there will be no planets left behind, especially the really important ones that have a high impact,” says de Wit, a member of MIT’s Kavli Institute for Astrophysics and Space Research.
Dips in the data
The researchers are members of SPECULOOS, an acronym for The Search for habitable Planets EClipsing ULtra-cOOl Stars, which scan the sky across the southern hemisphere. Earlier, the network added a fifth telescope, which is the first to be located in the northern hemisphere, named Artemis.
The SPECULOOS telescopes are developed to search for Earth-like planets in the area, ultracool dwarfs — small stars that propose astronomers a better chance of spotting an orbiting planet and characterizing its atmosphere.
Especially, astronomers look at individual stars to observe signs of transits, or periodic dips in a star’s light, which signal a possible planet crossing in front of the star, and briefly blocking its light.
Earlier this year, Niraula came upon a cool dwarf, slightly warmer than the commonly accepted threshold for an ultracool dwarf, in data collected by the K2 campaign — the Kepler Space Telescope’s second observing mission, which monitored slivers of the sky as the spacecraft orbited around the sun.
Over several months in 2017, the Kepler telescope observed a part of the sky that included the cool dwarf, labeled in the K2 data as EPIC 249631677. Niraula look into this period and found around 20 dips in the light of this star, which seemed to repeat every 3.14 days.
The group analyzed the signals, testing different potential astrophysical options for their origin, and confirmed that the signals were probably of a transiting planet.
The researchers then planned to see it in a close-up at the star and its orbiting planet with SPECULOOS. But first, they had to determine a window of time when they would be sure to catch a transit.
“Determining the best night to observe from the ground is a bit hard to do,” says Rackham, who developed a forecasting algorithm to predict when a transit might next occur. “Even when you see this 3.14 day signal in the K2 data, there’s an uncertainty to that, which increases with every orbit”.
Thanks to Rackham’s forecasting algorithm, the team narrowed in on several nights in February 2020 during which they were most probably to see the planet crossing in front of its star. They then put SPECULOOS’ telescopes in the direction of the star and were able to see three clear transits: two with the network’s Southern Hemisphere telescopes, and the third from Artemis, in the Northern Hemisphere.
The researchers say 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.
“There will be more interesting planets in the future, just in time for JWST, a telescope developed for probing the atmosphere of these alien worlds,” says Niraula. “With better algorithms, possibly one day, we can search for smaller planets, even as small as Mars”.
