Astronomers directly capture world described as 'Jupiter's younger sibling'

A Jupiter-like exoplanet

The newly-discovered planet, designated AF Lep b, is one of the first to be discovered using a method called astrometry.

The technique measures the very subtle movements of a host star over several years to help astronomers determine whether planets are tugging at it with their gravitational pull. A new paper, detailing the discovery was published in the Astrophysical Journal Letters.

Though planets have much smaller masses than their host stars, they cause stars to wobbly in a very subtle, but perceptible way in astronomical observations. Before the discovery of AF Lep b, 25 years' worth of observations from the Hipparcos and Gaia satellites suggested that the planet's host star would host a planet.

Another successful exoplanet photo shoot @keckobservatory using direct imaging + astrometry, this time of AF Lep b, a Jupiter-like planet orbiting a Sun-like star 👉 https://t.co/c3Lceu5bZt Congrats to Kyle Franson of @UTAustin & team! pic.twitter.com/BTTCNgyZof

— W. M. Keck Observatory (@keckobservatory) June 22, 2023

"When we processed the observations using the Keck II telescope in real time to carefully remove the glare of the star, the planet immediately popped out and became increasingly apparent the longer we observed," Kyle Franson, study lead, from the University of Texas at Austin, explained in the statement.

The images captured by Franson's team showed that AF Lep b is roughly three times the mass of Jupiter. The distant planet orbits AF Leporis, a relatively young Sun-like star approximately 87.5 light-years away from Earth. Its mass and orbit make it one of the most Jupiter-like planets observed to date.

"This is the first time this method has been used to find a giant planet orbiting a young analog of the Sun," explained Brendan Bowler, assistant professor of astronomy at UT Austin and senior author on the study. “This opens the door to using this approach as a new tool for exoplanet discovery."

Directly imaging a distant world

The researchers directly imaged the planet by using the Keck Observatory's adaptive optics system as well as the Keck II Telescope's Near-Infrared Camera 2 (NIRC2) Vector Vortex Coronagraph. The latter was used to suppress light from the host star to allow the astronomers to directly capture the planet.

The scientists behind the observation believe their method opens up a whole new avenue for discovering, and directly capturing, distant exoplanets. "Imaging planets is challenging," Franson said. "We only have about 15 examples, and we think this new 'dynamically informed' approach made possible by the Keck II telescope and NIRC2 adaptive optics imaging will be much more efficient compared to blind surveys which have been carried out for the past two decades."