Exomoons are a hot topic in the scientific community because none have been confirmed and astronomers have found new and creative ways to identify them. But while astronomers have looked for exomoons orbiting exoplanets around single stars like our sun, could exomoons exist around exoplanets orbiting binary stars?

This is what a recent study submitted to The Astrophysics Journal hopes to answer as a team of Tufts University researchers studied the statistical probability of exomoons orbiting two-star exoplanets, also known as circumbinary planets (CBP). This study, available on the arXiv preprint server, has the potential to help researchers better understand the methods needed to identify exomoons in a variety of exoplanetary systems.

Here, Universe Today discusses this incredible research with Benjamin R. Gordon, a Master of Science student in astrophysics at Tufts University and lead author of the study, regarding the motivation behind the study, the significant results, studies of tracking potential, the importance of finding exomoons orbiting CBPs, and which known systems are most promising for identifying exomoons? So what was the motivation behind this study?

Gordon explains to Universe Today: “We were initially motivated by a few ideas, but my biggest inspiration was the idea that circumbinary planets would have a greater minimum distance than single-star planets, which means that There would be more circumbinary planets. likely to be located in the “habitable area“.

So any moon of these circumbinary planets could have the potential to form life, as it could be a similar size to Earth if the planet is very large. It’s not a trivial question to wonder if the moons of these chaotic systems of 2 stars and a planet would be stable, so we were eager to find an answer!”

For the study, the researchers used computer models to simulate how exomoons might orbit CBPs under various exoplanet system conditions, particularly what is known as a planet’s hill radius, which is the threshold for exomoons to revolve around them.

The researchers conducted the simulations on two populations of CBP and exomoons: population 1, which had an unlimited planetary radius to have exomoons; and Population 2, which had a planetary radius between 3 times Earth and the size of the corresponding exoplanet, which were identified as all gas giants orbiting Earth. binary stars.

The researchers then performed 390 computer simulations of the Population 1 planets and 484 computer simulations of the Population 2 planets. So what were the most significant results of the study?

“One of the key findings is that there is a section of the initial conditions parameter space of our system that always results in stable exomoons of circumbinary planets,” Gordon told Universe Today. “We also found that 30-40% of stable moons are in the habitable zone, which is a very large fraction. We also show that the disk-driven migration scenario for a circumbinary planet-moon system is a pathway of possible formation in the long term -the circumbinary planets of the period as well as the planetary mass objects which float freely in space.

The goal of exoplanet hunting is to find an Earth-like world whose size, distance from its star and atmospheric composition could provide the ideal conditions to support life as we know it. Unfortunately, of the 5,806 confirmed exoplanets, only 210 are rocky worlds like ours, and more than half of these confirmed exoplanets are gas giants.

Therefore, identifying exomoons orbiting CBPs in their star’s habitable zone could hold promise for potentially identifying Earth-sized exomoons orbiting gas giants larger than Jupiter. So what follow-up studies are currently underway and what are Gordon’s thoughts on the importance of potentially finding exomoons orbiting CBPs?

“It would be interesting to study the stability of these moons, including the effects of tilt and multi-planetary systems,” Gordon tells Universe Today. “I also hope to apply for telescope time with future missions such as the Nancy Grace Roman Telescope to track circumbinary systems similar to those we see in our simulations with stable exomoons.

“Currently, there have been no confirmed exomoons, so finding one in general would be remarkable! If we find one specifically orbiting a circumbinary planet, it could be a great candidate for follow-up searches of life via JWST.”

As noted, the existence of no exomoon has been confirmed, but there are currently nearly two dozen exomoon candidates, two of which were recently debunked due to exoplanet transit data, but these discoveries were later refuted only a few months later as probable candidates (Kepler 1625b and Kepler). 1708b), as well as two potentially volcanically active exomoons, each orbiting a “hot Jupiter” (WASP-49b and HD 189733b).

Of these four, HD 189733b resides in a binary star system, with the primary star thought to be an orange dwarf star – which HD 189733b orbits – and the secondary star thought to be a red dwarf star.

With that, the question then becomes: what about habitable ex-moons, since several moons in our solar system show evidence that they contain the building blocks of life as we know it, particularly Europa, Titan and Enceladus, and all of which orbit gas giants, although well outside the habitable zone of our sun.

If worlds like these exist in our own solar system, then similar exomoons could also orbit gas giants in other solar systems. The question then arises: could we find exomoons orbiting in the respective habitable zone of their star? For example, could a gas giant that orbits in its star’s habitable zone have ex-moons similar to Earth? Therefore, according to Gordon, which known systems are most promising for identifying exomoons?

“In my opinion, I think single-star systems would be the easiest to confirm an exomoon,” Gordon told Universe Today. “This is because the data used for the different proposed detection methods are much more complex for binary systems than for single stars, because an additional star provides another source of dynamic interactions. For example, there already exist a problem finding circumbinary planets using the transit methodbecause transits do not shift out of phase due to variations in transit time due to interactions with the binary.

Gordon goes on to tell Universe Today: “Trying to find a moon on a circumbinary planet light curve would make a difficult problem even more difficult, whereas a single-star exoplanet light curve would provide a clearer starting point where each of the candidates so far have been spotted (Kepler-1625b and Kepler-1708b). For circumbinary exomoons, our research shows that it would be best to search in systems with wide binary separation, as was the case for stable moons. capable of orbiting up to 10% of their planet’s hill radius (for context, our moon orbits at about 26% of Earth’s hill radius).”

As astronomers continue to search the skies for definitive evidence of an exomoon potentially orbiting an exoplanet or CBP, the technology and techniques used to search for exomoons will only improve in the future, particularly with the aforementioned Nancy Grace Roman Telescope (commonly known as Roman). , scheduled to launch between fall 2026 and May 2027.

In addition to searching for exoplanets using the gravitational microlensing method, Roman will also study cosmic structures, dark energy, general relativity and the curvature of space-time, while stationed in orbit around the Sun -Earth L2, located on the opposite side. of the Earth’s orbit relative to the Sun.