Astronomers have confirmed thousands of exoplanets, yet direct imaging remains rare due to their stars' overwhelming brightness. A University of Hawaiʻi graduate student has achieved a breakthrough by isolating a planet sufficiently distant from its host star for direct observation—located just 35 light-years from Earth.
Exoplanet detection primarily relies on two proven techniques. The transit method identifies periodic dips in a star's brightness caused by a planet passing in front of it from our viewpoint. The radial velocity method detects subtle shifts in the star's light spectrum, resulting from its gravitational wobble induced by an orbiting planet.
These approaches excel at finding massive planets orbiting close to their stars, where signals are strongest. However, such proximity renders them invisible against their host's glare.
Breakthroughs occur with planets orbiting at vast distances, allowing direct visibility. This latest discovery, detailed in The Astrophysical Journal Letters, exemplifies that.
During the COol Companions ON Ultrawide orbits (COCONUTS) survey—targeting distant, Earth-proximate companions—University of Hawaiʻi student Zhoujian Zhang identified a world six times Jupiter's mass, orbiting over 6,400 astronomical units (AU) from its star.
At such separation, its orbital period spans roughly 1.1 million years, potentially the longest known for any exoplanet.
Dubbed COCONUTS-2b, it was first spotted in 2011 by NASA's Wide-field Infrared Survey Explorer (WISE) and initially classified as a free-floating object.
Zhang's thesis work revealed its gravitational bond to a low-mass star—about one-third the Sun's mass and ten times younger. The entire system lies approximately 35 light-years from Earth.
Aged around 800 million years, COCONUTS-2b ranks as the second-coldest directly imaged exoplanet, with a temperature of just 161°C. This image captures its self-emitted light, stemming from formation-trapped heat.
