Scientists have discovered a lonely orphaned planet wandering the Milky Way without a parent star to guide it – a “cheating” planet sunk in endless darkness without days, nights or gravitational siblings to keep it company.
It is possible that our galaxy is completely filled with them, but this is particularly unusual for a special reason: it is the smallest ever discovered – even smaller than Earth – with a mass similar to Mars.
Scientists have discovered more than 4,000 “extrasolar” planets, also known aswhich are planets orbiting a star other than the sun. Many exoplanets ̵
But just a few years ago, astronomers in Poland found evidence of free-floating planets not gravitationally attached to a star in the Milky Way galaxy. In a new study, the same astronomers have now discovered the smallest such planet to date.
Exoplanets are difficult to detect, usually found only by observing light from their receiving stars. Because free-floating planets have no parent star and emit almost no radiation, astronomers must take a different approach to finding them.
The deceptive planets are spotted using gravitational microlensing, the result of Albert Einstein’s theory of general relativity. In this case, the gravity of the planet (lens) acts as a kind of magnifying glass, able to bend the light of a bright star (source) behind it, so that the observer of the Earth can detect its presence.
“The observer will measure a brief illumination of the source star,” lead author Dr. Przemek Mroz, a PhD student at the California Institute of Technology, said in a news release Thursday. “The chances of observing a microlens are extremely slim, as three objects – a source, a lens and an observer – must be almost perfectly aligned. If we observe only one star source, we will have to wait almost a million years to see the source that is microlensed. ”
Researchers who observe these events observe hundreds of millions of stars in the center of the galaxy, which provides the highest chance of microlens.
The study with experimental optical gravitational objectification, led by astronomers from the University of Warsaw, is one of the largest and longest studies in the sky, operating for more than 28 years. Currently, with the help of a telescope at the Las Campanas Observatory in Chile, astronomers are looking at the center of the galaxy on clear nights in search of changes in the brightness of stars.
Because this technique relies only on the brightness of the source, not the lens, it allows astronomers to spot faint or dark objects – such as deceptive planets.
Measuring the duration of such an event, in addition to the shape of its light curve, can give an estimate of the mass of the object that astronomers are looking for. While most observed events caused by stars last several days, the small planets provide only a window of a few hours.
In this case, OGLE-2016-BLG-1928, the shortest microlensing event ever recorded, lasted only 42 minutes. Based on the event, astronomers calculated that the planet had a Mars-like mass and determined that it was a rogue.
“When we first noticed this event, it was clear that it must have been caused by an extremely tiny object,” said co-author Dr. Radoslaw Poleski of the Warsaw University Astronomical Observatory. “If the lens orbited a star, we would detect its presence in the light curve of the event. We can rule out that the planet has a star within about 8 astronomical units (the astronomical unit is the distance between the Earth and the Sun).”
It is not entirely clear why these deceptive planets do not have parent stars, but scientists do not believe that the planets had a say in the matter. Rather, they may have originally formed as “ordinary” planets – only to be ejected from their parent systems after gravitational interaction with other planets.
NASA is currently building the Roman Nancy Grace Space Telescope, which should start operating in the mid-2020s. Studying these free-floating planets can help astronomers better understand the volatile history of young planetary systems – including our own solar system.