Strange exoplanet discovered, only as big as Neptune but denser than steel

An exoplanet the size of Neptune and denser than steel has been discovered by an international team of astronomers. They believe its composition could be the result of a giant planetary collision.

Astronomers were stunned when they peered 545 light years out and discovered a very special exoplanet.

It's called TOI-1853b , an exoplanet with a radius 3.46 times that of Earth. The exoplanet orbits its host star, an orange dwarf about 80% the size of the Sun, every 1.24 Earth days. While its radius isn't huge, its mass is truly staggering: 73.2 times that of Earth.  Neptune is only 17.15 times the mass of Earth.

With that size and mass, the team of scientists calculated that TOI-1853b has a density of 9.7 grams per ^cubic centimeter. Meanwhile, Neptune has an average density of 1.64 grams per cubic centimeter and our Earth is just 5.15 grams per cubic centimeter. Iron has a density of 7.87 grams per cubic centimeter and steel is similar.

It's an exoplanet the size of Neptune - but puzzlingly, it has a mass of 73.2 times that of Earth. For comparison, Neptune has a mass of 17.15 times that of Earth, making it "denser than steel", its mass "almost twice that of any known Neptune-sized planet to date". (Image: Scitechdaily).

The density of TOI-1853b tells us that its composition must be more dense material and not have much atmosphere.

To classify exoplanets, or planets orbiting stars other than the Sun, astronomers rely on descriptions of the Solar System. After noticing an interesting object, roughly the size of Neptune and near a dwarf star, they sought more details about it from a variety of telescopes on the ground and in space. After confirming that what they saw was indeed a planet and not a star, they were left with the puzzle of what caused such a special planet to form.

The best explanation for its strange properties is a cataclysmic collision . The new research was published in the journal  Nature .

In a study published on August 31 in the journal Nature, scientists led by Luca Naponiello of the University of Rome Tor Vergata suggest that this is the result of a collision between planets. These large impacts would have stripped away some of the lighter atmosphere and water, leaving behind a plethora of rocks. (Photo: Inverse).

To date, more than 5,500 exoplanets have been discovered, and astronomers have learned that exoplanets come in a wide variety of sizes and compositions.

According to study co-author Phil Carter, a planetary computational scientist at the University of Bristol's School of Physics, exoplanets often have 'no analogues' in our Solar System.

The team ran simulations of impact scenarios to figure out why the exoplanet (called TOI-1853b) is so strange. The researchers concluded that TOI-1853b was likely originally a water-rich gas giant.

Associate Professor and co-author Dr Zoë Leinhardt concluded: 'We have not investigated such large impacts before because they are not what we expected. There is a lot of work to be done to improve the material models that underpin our simulations and to expand the range of large impacts that are modelled.'

Carter explained in a university announcement that in order to lose its atmosphere and lighter ices and become the extremely dense world it is today, another massive object like a planet would have to crash into TOI-1853b at a speed of 75 kilometers per second.

The planet provides new evidence of the prevalence of large impacts in planet formation across the galaxy. The discovery helps bridge theories of planet formation based on the Solar System with the formation of exoplanets. The discovery of this extreme planet provides new insights into the formation and evolution of planetary systems. (Image: ZME).

'This planet gives us a lot of surprises,' Jingyao Dou, study co-author and PhD student at the University of Bristol, shared in the announcement.

The team plans to conduct follow-up observations to search for traces of the atmosphere around TOI-1853b and analyze its composition to determine whether the predicted collision scenario actually occurred.

The new work is also a testament to what modern telescopes can achieve. It was made possible by data from NASA's Transiting Exoplanet Survey Satellite (TESS) in space, as well as the Keck II telescope in Hawaii, the Gemini North telescope in Hawaii, the Southern Astrophysical Research Telescope in Chile, and the Telescope Nazionale Galileo in the Canary Islands.