This image from supercomputer simulations shows how some exoplanets form as 'flattened Smarties' rather than spheres. It shows the same planet from the top (left) and the side (right.) The images are from supercomputer simulations of planetary formation. Image Credit: Fenton and Stamatellos 2024.
One of contemporary astronomy’s most pressing questions concerns planet formation. We can see more deeply than ever into very young solar systems where planets are taking shape in the disks around young stars. But our view is still clouded by all the gas and dust in these young systems.
The picture of planet formation just got cloudier with the discovery that some young planets are shaped like flattened candies rather than spheres.
Researchers were able to directly image newly forming exoplanet AB Aurigae b over a 13-year span using Hubble’s Space Telescope Imaging Spectrograph (STIS) and its Near Infrared Camera and Multi-Object Spectrograph (NICMOS). In the top right, Hubble’s NICMOS image captured in 2007 shows AB Aurigae b in a due south position compared to its host star, which is covered by the instrument’s coronagraph. The image captured in 2021 by STIS shows the protoplanet has moved in a counterclockwise motion over time.
Credits: Science: NASA, ESA, Thayne Currie (Subaru Telescope, Eureka Scientific Inc.); Image Processing: Thayne Currie (Subaru Telescope, Eureka Scientific Inc.), Alyssa Pagan (STScI)
Hubble’s most remarkable feature might be its longevity. The Hubble has been operating for almost 32 years and has fed us a consistent diet of science—and eye candy—during that time. For 13 of its 32 years, it’s been checking in on a protoplanet forming in a young solar system about 530 light-years away.
Planet formation is always a messy process. But in this case, the planet’s formation is an “intense and violent process,” according to the authors of a new study.
Interior of Jupiter. Image Credit: NASA / R. J. Hall
It’s likely that Jupiter-like planets’ origins root back to either the rapid collapse of a dense cloud or small rocky cores that glom together until the body is massive enough to accrete a gaseous envelope.
Although these two competing theories are both viable, astronomers have, for the first time, seen the latter “core accretion” theory in action. By studying the exoplanet’s host star they’ve shed light on the composition of the planet’s rocky core.
“Our results show that the formation of giant planets, as well as terrestrial planets like our own Earth, leaves subtle signatures in stellar atmospheres”, said lead author and PhD student Marcelo Tucci Maia from University of São Paulo, Brazil, in a press release.
Maia and colleagues pointed the 3.5-meter Canada-France-Hawaii Telescope toward the constellation Cygnus, in order to take a closer look at two Sun-like stars in the distant 16 Cyg triple-star system. Both stars, having formed together from the same gaseous disk over 10 billion years ago and having reached the same mass, are nearly solar twins.
But only one star, 16 Cygni B, hosts a giant planet. By decomposing the light from the two stars into their wavelengths and looking at the difference between the two stars, the team was able to detect signatures left from the planet formation process on 16 Cygni B.
It’s the perfect laboratory to study the formation of giant planets.
Difference in chemical composition between the stars 16 Cyg A and 16 Cyg B, versus the condensation temperature of the elements in the proto-planetary nebula. Image Credit: M. Tucci Maia, J. Meléndez, I. Ramírez.
Maia and colleagues found that the star 16 Cygni A is enhanced in all chemical elements relative to 16 Cygni B. Hence, the metals removed from 16 Cygni B were most likely removed from the protoplanetary disk in order to form the planet.
On top of the overall deficiency in all elements, 16 Cygni B has an added deficiency in the refractory elements — those with high condensation temperatures that form dust grains more easily — such as iron, aluminum, nickel, magnesium, scandium, and silicon. This helps verify what astronomers have expected all along: rocky cores are rich in refractory elements.
The team was able to decipher that these missing elements likely created a rocky core with a mass of about 1.5 to 6 Earth masses, which is similar to the estimate of Jupiter’s core.
“16 Cyg is a remarkable system, but certainly not unique,” said coauthor Ivan Ramírez from the University of Texas. “It is special because it is nearby; however, there are many other binary stars with twin components on which this experiment could be performed. This could help us find planet-host stars in binaries in a much more straightforward manner compared to all other planet-finding techniques we have available today.”
The results were accepted for publication in The Astrophysical Journal Letters and are available online.
