Astronomers have discovered thousands of exoplanets (planets beyond our solar system), but few have been images directly, as they are extremely difficult to see with existing telescopes. A graduate student at the Institute of Astronomy (IfA) at the University of Hawaii has exceeded the odds and discovered a direct image exoplanet, and is the closest to Earth ever found, just 35 light-years away.
Using the survey COol Companions ON Ultrawide orbiTS (COCONUTS), a graduate student Zhoujian Zhang and a team of astronomers, Michael Liu and Zach Claytor (IfA), William Best (University of Texas at Austin), Trent Dupuy (University of Edinburgh) and Robert Siverd (Gemini Observatory / National Optical-Infrared Astronomy Research Laboratory) identified a planet about six times the mass of Jupiter. The team’s research, published in The Astrophysical Journal Letters, led to the discovery of the low-temperature gas giant planet orbiting a low-mass red dwarf star, about 6,000 times farther away than Earth orbiting the Sun. They named the new planetary system COCONUTS-2 and the new planet COCONUTS-2b.
“With a massive planet in a super-wide orbit and a very cool central star, COCONUTS-2 represents a planetary system very different from our own solar system,” Zhang explained. The COCONUTS survey has been the focus of his recent doctoral dissertation, with the aim of finding long-distance companions around stars of all types close to Earth.
Trapped heat helps detect the planet
COCONUTS-2b is the second coldest imaging exoplanet found so far, with a temperature of only 320 degrees Fahrenheit, which is a little cooler than most baking ovens do. The planet can be imagined directly thanks to the emitted light produced by the residual heat trapped since the formation of the planet. However, the planet’s energy production is more than a million times weaker than that of the Sun, so the planet can only be detected by lower-energy infrared light.
“Detecting and studying directly the light of gas giant planets around other stars is usually very difficult, as the planets we find usually have small orbits and are therefore buried in the light of the light from the stars. his guest stars, “said Liu, Zhang’s thesis advisor. “With its huge orbital separation, COCONUTS-2b will be a great laboratory for studying the atmosphere and composition of a young gas giant planet.”
The planet was first detected in 2011 by the Wide-field Infrared Survey Explorer satellite, but was believed to be a free floating object, not orbiting a star. Zhang and his collaborators discovered that it is in fact gravitationally bound to a low-mass star, COCONUTS-2A, which is about a third of the Sun’s mass and about ten times younger.
Because of their large orbit and their fresh host star, the COCONUTS-2b skies would look dramatically different from the observer compared to the Earth’s skies. Night and day would look basically the same, with the host star appearing like a bright red star in the dark sky.
Zhang’s discovery has fueled his desire to continue exploring exoplanets, brown dwarfs, and stars. The aspiring astronomer graduated from IfA this summer and will begin his postdoctoral research in the fall of 2021, with Brendan Bowler, an IFA alumnus, professor of astronomy at the University of Texas at Austin.
Reference: “The Second Discovery from the COCONUTS Program: A Cold Wide-orbit Exoplanet around a Young Field M Dwarf at 10.9 pc” by Zhoujian Zhang, Michael C. Liu, Zachary R. Claytor, William MJ Best, Trent J. Dupuy and Robert J. Siverd, July 28, 2021, The Astrophysical Journal Letters.
DOI: 10.3847 / 2041-8213 / ac1123