An international team of astronomers has discovered a planet the size of Neptune, denser than steel, and they believe it may be the result of a collision between giant planets. TOI-1853b’s mass is nearly twice that of any other known planet of similar size, and its density is incredibly high; this means that it consists of a larger piece of rock than would normally be expected at this scale.

In a study published Aug. NatureScientists led by Luca Naponiello of the University of Rome Tor Vergata and the University of Bristol suggest that it is the result of planetary collisions. These massive collisions may have removed some of the light atmosphere and water, leaving many rocks behind.

Bristol School of Physics senior scientist and co-author Dr. Phil Carter explained: “We have strong evidence for high-energy collisions between planetary bodies in our solar system, for example the existence of the Earth’s Moon and a small number of exoplanets.

“We know that there are a wide variety of planets in extraplanetary systems; many have no analogues in our solar system, but often have different masses and compositions than the rocky planets and Neptune/Uranus (ice giants).

“Our contribution to the work was modeling extreme giant collisions that could potentially remove the lighter atmosphere and water/ice on the primordial larger planet to create the measured extreme density.

“We found that to form TOI-1853b as observed, the original planetary body would likely have to be rich in water and undergo an extremely giant collision at speeds greater than 75 km/h.”

This planet provides new evidence for the prevalence of giant multipliers in planet formation throughout the galaxy. This discovery helps link solar system-based theories of planet formation to the formation of exoplanets. The discovery of this extreme planet provides new insights into the formation and evolution of planetary systems.

Graduate student and co-author Jingyao Dou said: “This planet is so amazing! We would normally expect planets with this much rock to turn into gas giants with densities similar to water, like Jupiter.

“TOI-1853b is the size of Neptune but has a higher density than steel. Our work shows that this can happen if a planet undergoes highly energetic interplanetary collisions during its formation.

“These collisions removed some of the lighter atmosphere and water, leaving behind a rock-rich, high-density planet.”

The team is currently planning detailed follow-up observations of TOI-1853b to detect any residual atmosphere and study its composition.

Associate professor and co-author Dr. Zoe Leinhardt concludes: ‘We haven’t studied such extraordinarily colossal effects before because we didn’t expect them. There is still a lot of work to be done to develop the material models that form the basis of our simulations and to expand the simulated supergiant shock range.”