Astronomers have discovered another orphan planet the size of Earth. They believe that there may be many times more such free-flying worlds in our Galaxy than there are stars and planets orbiting around them.
Not all planets spend their lives in the "cradle" orbiting their parent star. A random play of gravity or a powerful collision may well knock it off its usual trajectory and send it on a free solo journey across the galaxy. It is assumed that once and the solar system lost one of its young planets. And the new work of American and Japanese astronomers showed that such orphan planets can be even more "ordinary". Scientists write about this in a pair of articles, preparing for publication in the next issue of The Astronomical Journal. They are summarized in a press release from NASA's Goddard Space Flight Center.
David Bennett (David Bennett) and his colleagues used data from the MOA survey, which was conducted by the New Zealand University Observatory Mount John. Ground-based telescopes tracked changes in the luminosity of distant stars associated with microlensing - a distortion of the ray path caused when a massive body passes between the source and the observer.
Such events make it possible to detect objects virtually indistinguishable by other methods, including orphan planets. Indeed, in MOA observations, astronomers have detected evidence of a single planet close to Earth in size. They write about it in their first paper. It is noted that this is only the second such finding in the history of science (we reported on the previous one in 2020). However, it allowed scientists to revise previous estimates of the number of orphan planets in our Galaxy.
New calculations Bennett and his co-authors cite in the second article to be published in The Astronomical Journal. According to them, orphan planets in the Milky Way may be much more than thought - about six times more than the "normal" planets, gravitationally bound to their stars, and 20 times more than the stars themselves. In this case, among the orphans should be dominated by small planets of terrestrial type, and not at all gas giants, which are much more difficult to "knock" from their orbits.
Scientists expect mass discoveries of orphan planets to begin with the launch of the future Nancy Grace Roman telescope, which will continue NASA's string of "great space observatories" started by Hubble and James Webb. Its sensitivity should be sufficient to record single small planets, and its wide field of view will provide the necessary coverage. Bennett and his colleagues estimate that Nancy Grace Roman will be able to detect about 400 orphan planets, not 50 as has been thought so far. Work on the telescope is still ongoing, with observations scheduled to begin in 2027.
Now, before the scientific paper itself is released, NASA's press release raises more questions than it answers. For there to be such a large number of orphan planets in the Galaxy, the average planetary system must give birth to up to three dozen planets and subsequently lose most of them. In terms of existing models of planet formation, this is a rather extreme and atypical scenario. Therefore, we can expect that after the publication of the new paper we will hear a lot of criticism of the new calculations of Bennett and his co-authors.