Unexpected Characteristics of a Distant ‘Super-Jupiter’ Planet Revealed
It was already known that this system harbored a planet. However, the properties of this ‘super-Jupiter’ planet significantly deviate from what researchers had expected.
Located just 3.6 parsecs away from Earth lies the star Epsilon Indi A. Although previous analyses had suggested that this star might host a giant planet, no direct observations had been made until now. In a new study, researchers directed the powerful James Webb Space Telescope at the star. Not only did they manage to clearly capture the giant planet, but they also found that it is a remarkably unusual planet.
Imaging the Planet
In previous studies, researchers had tried to determine the properties of the predicted giant planet around Epsilon Indi A by using radial velocity measurements. However, the challenge was that the planet has a large orbit. Observations spanning only a few years are insufficient to measure the orbit accurately. Investigating just a small part of the orbit often leads to incorrect conclusions. Therefore, a new research team opted for another approach: they aimed to capture the planet directly.
This is easier said than done. Epsilon Indi A is an extremely bright star, which overshadows other nearby objects easily. Therefore, researchers employed the Mid-Infrared Instrument (MIRI) of James Webb, which is equipped with a coronagraph. The coronagraph blocks the star’s bright light, making fainter objects nearby, such as planets, more visible.
Eps Ind Ab Revealed
Thanks to Webb, researchers succeeded in directly capturing the giant planet for the first time. “We were very excited when we discovered that we had imaged this new planet,” says researcher Elisabeth Matthews. The planet orbits the primary star of the nearby triple star system Epsilon Indi, specifically Epsilon Indi A, an orange dwarf star approximately 3.5 billion years old, slightly smaller and cooler than our Sun. The planet has been named Epsilon Indi Ab.
Unanticipated Findings
When the researchers examined the data more closely, they discovered something was not right. “To our surprise, the bright spot on our MIRI images did not match the expected position of the planet,” explains Matthews. “Earlier studies had identified a planet in this system but had misestimated the mass and distance of this super-Jupiter.” Thanks to the JWST, the team corrected these estimations.
Surprisingly Cold and Massive
The new data show that the planet is a so-called ‘super-Jupiter’ with a mass six times greater than that of Jupiter. This planet orbits in an elongated elliptical path around its star, at a distance 20 to 40 times that between Earth and the Sun. Remarkably, the planet takes about 200 years to complete a full orbit around its star. This means that the planet is not only much more massive but also much further from its parent star than researchers had previously thought. The team notes that the planet is unusually bright and cold, even considered the coldest exoplanet ever imaged.
Atmosphere Analysis
So far, only a few cold gas giants orbiting stars of similar age to the Sun have been known, mostly discovered through radial velocity measurements. By directly imaging planets and analyzing their spectra, astronomers can learn more about their atmospheres and how planetary systems evolve. This aids in understanding how planets form and develop. In this particular case, researchers aimed to learn more about the exoplanet’s atmosphere by observing it in three colors: two from JWST/MIRI and one from VLT/VISIR. Epsilon Indi Ab appears less bright at shorter wavelengths than expected. This could indicate that the planet contains many heavy elements, such as carbon, which often form molecules like methane, carbon dioxide, and carbon monoxide found in gas giants. It might also suggest a cloudy atmosphere. Further research is needed to determine this definitively.
This research marks just the first step in understanding Epsilon Indi Ab. The researchers’ next goal is to obtain spectra that will provide more insight into the planet’s climate and chemical composition. “In the long term, we also want to study other nearby planetary systems to search for cold gas giants that may not yet have been discovered,” says Matthews. “This would help us better understand how gas planets are formed and evolve.”
