In recent decades, astronomers have confirmed the existence of nearly 6,000 extrasolar worlds, and they have evidence of many thousands more. Most of them were discovered using the transit method, but there are other ways. Many stars are known to have more than one planet. The best known example is the TRAPPIST-1 system with seven Earth-like worlds, the orbits of three of which pass within its habitable zone.
But even in such systems, exoplanets can still be hidden that have escaped astronomers’ notice. This is possible if they are not transiting, or their signals are very weak, making them impossible to pick out from the data noise. How do we find such worlds?
A team of researchers from Australia and the US suggested the following approach. Rather than analyzing large data sets trying to catch traces of the presence of additional exoplanets, it is worth evaluating the overall orbital dynamics of the systems. This will make it possible to understand whether, in principle, the existence of additional worlds is possible in them.
The scientists explained their chosen approach as follows. Stellar systems are many millions or billions of years old, so the orbits of their exoplanets should be stable on these time scales. If the exoplanets in a system are “densely packed”, then adding more worlds will cause it to go all haywire. If the system is “loosely packed”, then it is possible to add hypothetical exoplanets between others, and the system will still be dynamically stable.
To show how this works, the study authors looked at seven systems in which the TESS satellite found two exoplanets. Since it’s actually quite unlikely that they only have two exoplanets, it’s reasonable to assume that there are other worlds hiding out there. The team then ran thousands of simulations of these systems with hypothetical exoplanets, calculating whether they could remain stable for millions of years.
The astronomers found that for the two systems, the presence of additional exoplanets (except for worlds much farther away than the known ones) can be ruled out for dynamical reasons. Additional bodies would almost certainly destabilize them. But the five systems can remain stable in the presence of additional exoplanets. That doesn’t mean they are there — only that they might be, and astronomers can try to find them.
The study shows that most exoplanet systems known to date are likely to have undiscovered worlds. This approach can also help scientists sort them to determine which ones deserve further study. This will save time and avoid being overwhelmed by large data sets.
Earlier we reported on how the Hubble and James Webb telescopes failed to find exoplanets near the famous star Vega.
Provided by Phys.org
