![\"A](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2026\/03\/A-New-Spin-on-Planet-Formation-1.jpg\")
<\/p>\n <\/p>\n
\n A New Window into Planet Formation \u2014 Keck Observatory <\/p>\n
Astronomers using the W. M. Keck Observatory on Maunakea, Hawai\u02bbi Island, have confirmed a long-predicted relationship between planetary mass and rotation.<\/p>\n
By measuring the rotation rates of a large sample of directly imaged extrasolar planets and more massive brown dwarf companions, researchers discovered that gas giant planets spin faster than more massive counterparts when accounting for their mass, size and age.<\/p>\n
The result confirms a long-standing theoretical prediction and represents the largest survey of spin measurements for directly imaged companions to date.<\/p>\n
\u201cSpin is a fossil record of how a planet formed,\u201d said Dino Chih-Chun Hsu, lead author and researcher at Northwestern University. \u201cBy measuring how quickly these worlds rotate, we can start to piece together the physical processes that shaped them tens to hundreds of millions of years ago.\u201d<\/p>\n
The study, led by Northwestern University, is published in The Astronomical Journal.<\/p>\n
The team used the Keck Planet Imager and Characterizer instrument (KPIC) to isolate light from faint planets orbiting far from their host stars to measure fine details in their atmospheres.<\/p>\n
As these distant worlds rotate, features in their spectra broaden. By analyzing those broadened features, scientists can determine how quickly a planet is spinning.<\/p>\n
\u201cWith KPIC, we can detect these tiny signals that reveal a planet\u2019s rotation around other nearby stars,\u201d said Hsu.<\/p>\n
A New Window into Planet Formation<\/p>\n
Many of the planets studied orbit far from their stars, tens to hundreds of times farther than Earth is from the Sun. Astronomers are still debating how such distant worlds form. Some may grow gradually within a disk of gas and dust surrounding a young star, while others may form more like miniature stars through gravitational collapse.<\/p>\n<\/p>\n
Artist\u2019s animation comparing the rotation of a gas giant exoplanet (left) and a more massive brown dwarf companion (right). Astronomers measured the spin rates of distant worlds by analyzing subtle broadening in their spectra caused by rotation. The study reveals that, when accounting for their mass, size, and age, gas giant planets spin faster than heavier brown dwarf companions. Credit: W. M. Keck Observatory \/ Adam Makarenko<\/p>\n
The newly identified spin trend provides an important clue.<\/p>\n
\u201cOur results suggest that both the planet\u2019s mass and the ratio between the planet\u2019s mass and its star\u2019s mass influence how fast the planet ultimately spins,\u201d said Hsu. \u201cThat helps us narrow down the physics of how these systems form.\u201d<\/p>\n
One planet and one brown dwarf in the study illustrate this complexity: One of the infamous planets in HR 8799, roughly 7 times the mass of Jupiter, spins unusually fast for its mass, compared to a brown dwarf companion of 24 times the mass of Jupiter. This implies that the brown dwarf ended up spinning 6 times slower than the planet.<\/p>\n
This can be understood as the planet underwent braking by its magnetic field interaction with the disk around the planet during its infancy. The spin of a more massive companion was slowed down significantly more due to a stronger magnetic field.<\/p>\n
What It Means for Our Solar System<\/p>\n
Understanding how giant planets spin also helps scientists understand the history of our own solar system.<\/p>\n
Jupiter and Saturn both rotate rapidly each completing a rotation in roughly ten hours. Because Jupiter is so massive, it stores a large fraction of the solar system\u2019s rotational energy.<\/p>\n
\u201cThe way that angular momentum is distributed among planets influences the overall architecture of a planetary system,\u201d said Hsu. \u201cEven Earth\u2019s rotation and magnetic field ultimately connect to how that spin budget was divided when the solar system formed.\u201d<\/p>\n
A Legacy of KPIC and a Bright Future of HISPEC<\/p>\n
Most of the spin measurements in the study were obtained using KPIC, which was specifically designed to pair Keck\u2019s adaptive optics system with high-resolution spectroscopy. The instrument was designed and built by a team led by Dimitri Mawet, a professor of astronomy at Caltech and senior research scientist at JPL, and a team of students, postdocs, and engineers from Caltech Optical Observatories.<\/p>\n
The instrument recently completed its final observations in January, marking the end of a highly productive run.<\/p>\n
\u201cKPIC is the first instrument of its kind, opening an entirely new way to study exoplanets,\u201d said Hsu. \u201cIt allowed us to measure properties like spin that were previously almost impossible to detect.\u201d<\/p>\n
The research team plans to expand their studies by examining the spins of free-floating planetary-mass objects\u2014worlds that drift through space without a host star\u2014as well as investigating the chemical composition of planetary atmospheres across the population.<\/p>\n
\u201cWe\u2019re just beginning to explore what planetary spin can tell us,\u201d said Hsu. \u201cWith future instruments and larger telescopes, we\u2019ll be able to measure spins for even more worlds and connect rotation, chemistry, and formation history across entire planetary systems.\u201d<\/p>\n
Advanced future instrumentation, including Keck Observatory\u2019s upcoming HISPEC (High resolution Infrared Spectrograph for Exoplanet Characterization), also led by Mawet, is coming online in 2027. It will extend these measurements to even smaller and more distant worlds.<\/p>\n
\u201cWe took the lessons learned from KPIC, and put them into HISPEC, which will have better sensitivity, higher spectral resolution, and wider wavelength coverage\u201d, said Jason Wang, Assistant Professor at Northwestern and co-author of the study. \u201cWith HISPEC we will be able to drastically increase the number of planets that we can measure spins of, and in particular, we can study planets closer to our own Jupiter in nature to see if our own Jupiter is typical.\u201d<\/p>\n
Support for KPIC is generously provided by the Heising-Simons Foundation, Simons Foundation, Caltech, and NASA Jet Propulsion Laboratory. This project is conducted in collaboration with W. M. Keck Observatory, UC Santa Cruz, UCLA, and the University of Hawai\u02bbi Institute for Astronomy.<\/p>\n
These observations were conducted from Maunakea, a place of deep cultural significance to the Native Hawaiian community. The W. M. Keck Observatory is grateful for the opportunity to conduct observations from this sacred mountain and remains committed to respectful stewardship of the mauna and engagement with the Hawai\u02bbi Island community.<\/p>\n