Nearly 80 exoplanet candidates identified in record time

Scientists at MIT and elsewhere have analyzed data from K2, NASA's Kepler space telescope tracking mission, and have discovered a mine of possible exoplanets among nearly 50,000 stars.

In an article that appears online in The astronomical journal, scientists report the discovery of nearly 80 new planetary candidates, including a special star: a likely planet orbiting the HD 73344 star, which would be the brightest planet host ever discovered by the K2 mission.

The planet looks orbital HD 73344 every 15 days, and depending on the amount of light that it blocks each time as it passes in front of its star, scientists estimate that the planet is about 2.5 times the size of the Earth and 10 times more massive. It is also incredibly hot, with a temperature in the range of 1200 to 1300 degrees Celsius, or about 2000 degrees Fahrenheit – about the temperature of the lava of an erupting volcano.

The planet is at a relatively close distance of 35 parsecs, about 114 light-years from Earth. Given its proximity and the fact that it orbits around a very bright star, scientists believe that the planet is an ideal candidate for follow-up studies to determine its atmospheric composition and the presence of the stars. other characteristics.

"We think it would probably look more like a smaller, warmer version of Uranus or Neptune," says Ian Crossfield, an assistant professor of physics at MIT, who co-directed the study with the 39, graduate student Liang Yu.

The new analysis is also remarkable for the speed with which it was carried out. The researchers were able to use the existing tools developed at MIT to quickly search through the light intensity graphs called "light curves" of each of the 50,000 stars that K2 has followed in his last two viewing campaigns. They quickly identified the planetary candidates and communicated the information to the astronomy community a few weeks after the K2 mission made available the raw data from the spacecraft. A typical analysis of this kind takes between months and a year.

According to Crossfield, such a quick search on the planet allows astronomers to track ground telescopes much earlier than they would otherwise, giving them a chance to spot planetary candidates before the Earth passes. by this sky zone. the sun.

Such speed will also be needed when scientists start receiving data from Transiting Exoplanet Survey's TESS satellite, which is designed to monitor nearby stars in 30-day windrows and ultimately cover almost the entire sky.

"When the TESS data falls, there will be a few months before all the stars that TESS has watched for that month" settle in "for the year," says Crossfield. "If we send the candidates quickly to the community, everyone can immediately begin to observe the systems discovered by TESS, and do many great planetary sciences. So that [analysis] was really a dress rehearsal for TESS. "

Speed ​​Dips

The team analyzed data from the 16th and 17th K2 observation campaigns, known as C16 and C17. During each campaign, K2 observes a parcel of the sky for 80 days. The telescope is in an orbit that drags the Earth as it moves around the sun. For most other campaigns, K2 has been oriented "backwards", in which the telescope observes the stars that are essentially in its rearview mirror.

Since the telescope travels behind the Earth, the stars observed are generally not observable by scientists until the planet revolves around the sun towards this part of the sky, nearly a year later. So, for backward-oriented campaigns, Crossfield says that there has been little motivation to analyze K2 data quickly.

On the other hand, the C16 and C17 campaigns were oriented towards the front; K2 observed the stars in front of the telescope and in the Earth's field of vision, at least for the next few months. Crossfield, Yu and their colleagues took the opportunity to speed up the usual analysis of K2 data, giving astronomers the chance to quickly observe planetary candidates before the Earth overtakes them.

During C16, K2 observed 20,647 stars over 80 days, between December 7, 2017 and February 25, 2018. On February 28, the mission released the data, in the form of pixel-level images, to the astronomical community. Yu and Crossfield immediately began to sift through the data, using algorithms developed at MIT to move the field from 20,000 stars to 1,000 stars of interest.

The team then worked 24 hours a day, looking through these 1,000 stars looking for signs of transits or periodic dives in the light of stars that could signal a passing planet. In the end, they discovered 30 of the planet's "highest quality" candidates, whose periodic signatures are particularly likely to be caused by planets in transit.

"Our experience with four years of K2 data leads us to believe that most of them are indeed real planets, ready to be confirmed or validated statistically," the researchers write in their article.

They also identified a similar number of candidates from the planet in the recent C17 analysis. In addition to these planetary candidates, the group also selected hundreds of periodic signals that could be signatures of astrophysical phenomena, such as pulsating or rotating stars, and at least one supernova in another galaxy.

Stars with shovel

Although the nature of a star does not usually change over the course of a year, Crossfield says that the sooner researchers can track a possible global transit, the better the chances of confirming that a planet exists Actually.

"You want to observe [candidates] again relatively quickly, so you do not lose the transit completely, "says Crossfield. "Maybe you could say," I know there's a planet around this star, but I'm not sure at all when the transits are coming. "It's another motivation to follow these things faster."

Since the team published its findings, astronomers have validated four of the candidates as defined exoplanets. Crossfield says that the brightness of this star, combined with the speed with which its planetary candidate has been identified, can help astronomers focus on even more specific features. of this system.

"We found one of the most exciting planets that K2 found in all of its mission, and we did it faster than any previous effort," says Crossfield. "This shows the way forward for the TESS mission to do the same thing with a shovel, all over the sky, for the next few years."

This research was supported, in part, by NASA and the National Science Foundation.