A research team at the UK Infrared Telescope (UKIRT) discovered celestial objects with masses similar to planets floating alone in space; they were later named "rogue planets". This discovery has prompted many questions about the accuracy of the current theories about planets and stars formation. According to current theories, the planet has to be bound to an orbit around a star due to gravitional forces, and cannot float freely in space. Over the past two decades, more rogue planets have been discovered; scientists have suggested four hypotheses to explain how they are formed:
- The planet is formed like stars, inside a nebula of cosmic dust and interstellar matter.
- The planet is already orbiting a star then a more massive planet approaches and pulls it out of its orbit, sending it alone into space.
- Two stars move closer, disturbing the orbits of planets around them and causing them to leave their orbits.
- When a star loses the balance between the inward and outward force of gravity, it explodes in an event known as a nova or a supernova, which may send the planet off course to float alone in space.
The Kepler Telescope—NASA's first planet-hunting telescope launched in 2009—estimated that the Milky Way galaxy contains at least as many planets as stars: approximately a trillion planets, all orbiting stars. Later, the James Webb Space Telescope observations revealed to scientists that rogue planets in our galaxy are twenty times more than planets orbiting stars. In 2023, it observed 80 planets as huge as Jupiter floating freely in space. A more striking discovery was 40 pairs of planets in the Orion Nebula, where each planet in the pair orbits the other, much like binary stars. This discovery has revealed another significant flaw in the current theories of planet and star formation, as they do not account for the existence of binary planets.
Scientists expect that the Nancy Grace Roman Space Telescope, set to launch in 2027, will uncover thousands of rogue planets thanks to its cutting-edge technology. It will be able to capture images that are 100 times larger than Hubble, with a vision that is 40 million times sharper than the naked human eye. Like the James Webb telescope, Grace Telescope's lense covers infrared wavelengths. However, while the former is designed to observe more distant objects, the latter will focus more on capturing a wider field of view. The Nancy Grace Roman Space Telescope will rely on direct imaging or gravitational microlensing, two common methods used to discover exoplanets. Gravitational lensing is a phenomenon caused by the gravity of massive objects that bends the spacetime. The stronger the gravitational pull of an object, the greater and more noticeable the curve of the spacetime. So far, 230 planets have been discovered using gravitational lensing.
References
A population of very young brown dwarfs and free-floating planets in Orion by P. W. Lucas & P. F. Roche in Monthly Notices of the Royal Astronomical Society.
earthsky.org
exoplanets.nasa.gov
spectrum.ieee.org
Cover Image: Artist’s impression of CFBDSIR2149, the rogue planet wandering through space roughly 100 light years from our solar system (Image: ESO/L. Calçada/P. Delorme/Nick Risinger (skysurvey.org)/R. Saito/VVV Consortium)