A rogue planet it was discovered using gravitational microlensing in which the celestial body passed in front of a star, distorting its light and revealing its presence. Over 5,000 planets have been found orbiting other star systems. One of the satellites looking for them is TESS, the Transiting Exoplanet Survey Satellite.
The rogue planet
We all know the eight planets of our solar system and perhaps we are becoming familiar with the concept of exoplanets. But there is another category of planets, which is identified as the rogue planet.
These mysterious objects travel in space without being gravitationally bound to any star. Their origin has been the subject of much debate, but popular theory suggests that they were ejected from the host star system during formation, or perhaps later, due to gravitational interaction.
Simulations have suggested that these “floating planets” or rogue planets should be abundant in the galaxy, but so far not many have been detected. The popular theory of ejection from star systems may not be the full story, however.
It is now believed that different formation mechanisms will be responsible for different rogue planet masses. High-mass FFPs may form in isolation from gas collapse, while low-mass ones (comparable to Earth) have likely been subjected to gravitational ejection from the system. A paper published in 2023 even suggests that these FFPs will likely outcompete bound planets across the galaxy.
Detecting such errant objects among the stars is a more complex challenge than you might expect. Their limited emission (or reflection) of electromagnetic radiation makes them practically impossible to observe. Enter gravitational microlensing, a technique that relies on a rogue planet passing in front of a star, it's gravity then focusing light from the distant star resulting in a brief change in brightness as the planet moves across its line of sight . To date, only three FFPs have been detected from Earth using this technique.
A team of astronomers used TESS to search for such microlensing events. TESS was launched in April 2018 and while in orbit it scans large portions of the sky to monitor the brightness of tens of thousands of stars. Detecting changes in light can reveal the passage of a rogue planet as it moves silently in front of the star.
It's not an easy hunt, as asteroids in our solar system, star-bound exoplanets, and even stellar flares can give false indications, but luckily the team led by Michelle Kunimoto has algorithms that will help identify potential targets.
The team published i results on the arXiv preprint server and reported an FFP candidate event associated with the star TIC-107150013 which is 3.2 parsecs away.
The event lasted 0.074 days +/- 0.002 and revealed a light curve with the expected characteristics of an FFP. This marks the first rogue planet discovered by TESS, an exciting step along the path to begin unraveling the mysteries surrounding these strange, unknown worlds.
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