Cambridge: Scientists at the Massachusetts Institute of Technology (MIT), along with others, have discovered an earth-sized "Pi Planet" that revolves around its star every 3.14 days.
The orbit of the planet, which the scientists suspect is likely not hospitable as its tight orbit brings the planet close enough to its star to heat its probably terrestrial surface up to 450 Kelvins, or around 350 degrees Fahrenheit, is reminiscent of the universal mathematics constant.
The researchers discovered signals of the planet in data taken in 2017 by the National Aeronautics and Space Administration (NASA) Kepler Space Telescope's K2 mission. By zeroing in on the system earlier this year with SPECULOOS, a network of ground-based telescopes, the team confirmed that the signals were of a planet orbiting its star.
According to Prajwal Niraula, a graduate student in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS), "The planet moves like clockwork." Niraula, is the lead author of a paper published in the Astronomical Journal, titled: "p Earth: a 3.14-day Earth-sized Planet from K2's Kitchen Served Warm by the SPECULOOS Team" along with co-author Julien de Wit.
The co-authors of the paper include Benjamin Rackham and Artem Burdanov, along with a team of international collaborators. The new planet is labeled K2-315b; it is the 315th planetary system discovered within K2 data. According to the researcher's estimate, 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 circles its star every 3.14 days, at 81 kilometers per second, or about 181,000 miles per hour.
The scientists suspect that K2-315b is terrestrial, like the Earth, although its proximity to its star would make it too hot for life to exist. "This would be too hot to be habitable in the common understanding of the phrase," says Niraula.
"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 added.
The researchers are members of SPECULOOS (The Search for habitable Planets EClipsing ULtra-cOOl Stars), named for a network of four 1-meter telescopes in Chile's Atacama Desert, which can scan the sky in the Southern hemisphere.
The network had recently added a fifth telescope, the first in the Northern hemisphere, named Artemis. The SPECULOOS telescopes are designed to search for Earth-like planets around nearby, ultracool dwarfs -- small, dim stars that offer astronomers a better chance of spotting an orbiting planet and characterizing its atmosphere, as these stars lack the glare of larger, brighter stars.
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 combed through this period and found around 20 dips in the light of this star, that seemed to repeat every 3.14 days.
The team analyzed the signals, testing different potential astrophysical scenarios for their origin, and confirmed that the signals were likely of a transiting planet, and not a product of some other phenomena such as a binary system of two spiraling stars.
The researchers then planned to get a closer look at the star and its orbiting planet with SPECULOOS. But first, they had to identify a window of time when they would be sure to catch a transit.
"Nailing down the best night to follow up from the ground is a little bit tricky," 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 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 clear transits: two with the network's Southern Hemisphere telescopes, and the third from Artemis, in the Northern Hemisphere.
According to the researches, the new pi planet may be good candidate to follow up with the James Webb Space Telescope (JWST), to see details of the planet's atmosphere. The team is now looking through other datasets, such as from NASA's Tess mission.
"There will be more interesting planets in the future, just in time for JWST, a telescope designed to probe the atmosphere of these alien worlds," Niraula said. "With better algorithms, hopefully, one day, we can look for smaller planets, even as small as Mars," he added. This research was supported in part by the Heising-Simons Foundation, and the European Research Council.
