A mystery lurks in the far reaches of our solar system. For a long time, astronomers believed that the eight planets revolve in near-perfect circular orbits because they once formed in a swirling disk of dust and gas surrounding the young sun. But in 2003, scientists discovered something strange: the dwarf planet Sedna has a strange orbit, changing position from two distances to Pluto to more than twenty distances from the Sun. And she's not alone. Over the years since then, astronomers have discovered nearly two dozen distant icy objects whose orbits are oblong and oddly tilted compared to the plane of the solar system.
To explain such oddities, scientists have suggested that perhaps these worlds are the scars of a violent past. Perhaps, once in the youth of the solar system, a star passed nearby and knocked these worlds off course. Or the distant ninth planet by its gravity has disturbed the order in our system.
The latter hypothesis has gained weight over the past few years, causing the former to sniff dust, says Suzanne Pfalzner, an astronomer at the Institute for Radio Astronomy. Max Planck in Germany. Anomalies in the orbits of several small objects in the outer solar system have accumulated evidence that the "ninth planet" is about 10 times the mass of Earth. Meanwhile, a star invader was considered too unlikely - until now. Pfalzner and her colleagues recently published a paper on the arXiv preprint server, which was accepted by The Astrophysical Journal, in which they showed that stars can fly close to our solar system much more often than they thought. These results not only lend weight to the stellar flyby theory, but may also explain how the "ninth planet" ended up in its strange orbit at all.
Sedna's strange orbit
Astronomers know that the sun hasn't always been this lonely. It was born in a cluster of hundreds or tens of thousands of stars that scattered across the galaxy just 10 million years later. Therefore, while our Sun was inside this cluster, the stars scurried to and fro in a dizzying dance that could easily lead to a flight into our nascent solar system. But after the cluster was torn apart, the likelihood of such an invasion dropped to almost zero. In any case, they believed so. But Pfalzner and her colleagues now argue that the chances of an invasion remained relatively high after the cluster began to crumble. After many lengthy computer simulations, they found that a star with the mass of our Sun with a probability of 20-30% could fly in 50-150 AU. from Pluto (1 AU is the distance from the Earth to the Sun,approximately 150 million kilometers). Surely such a close approach would shake up our young solar system.
Although the large planets would remain intact (the sun, for example, has almost no sense of the weak gravity of the eight planets), the invasion could push small objects apart, placing them in strange orbits around the solar system. What's more, simulations have also recreated a second trend that astronomers have observed in the solar system - the tendency for external objects to cluster. They move together in close groups. In simple terms, the invader star fits perfectly into observational models.
"But whether they will last 4.5 billion years," that is, as long as the solar system exists, "is a million dollar question," says Scott Kenyon, an astronomer at the Harvard-Smithsonian Center for Astrophysics who was not involved in the study. And Pfalzner agrees with him. She would like to simulate long-term behavior to see if the changes caused by the stellar invasion will persist throughout the life of our system.
Promotional video:
Scientists are eagerly seeking new data through a number of different observational campaigns. Several teams, for example, are already combing large chunks of the sky looking for oddities in the outer solar system. Scott Sheppard, an astronomer at the Carnegie Institute of Science who was not involved in the study, cannot contain his excitement ahead of the launch of the Large Synoptic Telescope, an 8.4-meter dish that will open hundreds of new solar systems.
Kenyon, meanwhile, hopes that the Gaia spacecraft, which is in the process of refining the position of a billion stars with unprecedented precision, will help find our star's siblings. This will allow scientists to better understand the star cluster in which our young solar system formed, as well as the likelihood of another star coming too close. Gaia is our new savior,”he says. A recent study by Gaia has allowed us to trace the paths of nearby stars in the past and project them into the future, only to discover that 25 stars could come dangerously close to our home over 10 million years. And, of course, everyone wants to find the "ninth planet".
But Pfalzner argues that the discovery of another major member of the solar system does not exclude a stellar flyby. “It's not a script or / or,” she says. "If the ninth planet exists, it does not rule out the flyby model, rather speaks in its favor." The projected orbit of the ninth planet, eccentric and tilted (relative to the plane of the solar system), could also have formed under the influence of a stellar flyby. The discovery of the ninth planet will dot the i's.
Ilya Khel
