Among the vast number of planets discovered outside our solar system, a majority exhibit surprisingly close orbits to their host stars.
Over 80 percent of confirmed exoplanets have orbits shorter than 50 days, positioning them at least twice as close to their stars as Mercury is to the Sun. However, planets with longer orbital periods remain less understood due to their difficulty to detect.
Two new planets with extended orbits have been added to this category. Scientists from MIT and the University of New Mexico have identified a rare system housing two such planets orbiting the star TOI-4600, situated 815 light years from Earth.
The system comprises an inner planet with an 82-day orbit, similar to Mercury’s, and an outer planet with a 482-day orbit, placing it between Earth’s and Mars’ orbits.
These discoveries were made possible using data from NASA’s Transiting Exoplanet Survey Satellite (TESS), an MIT-led mission monitoring nearby stars for exoplanets. Notably, the farther planet features the longest orbital period detected by TESS, and it’s one of the coldest at approximately -117 degrees Fahrenheit.
Both planets likely resemble gas giants such as Jupiter and Saturn, though the inner planet might have a gas-ice composition mix. These planets offer insight into the gap between “hot Jupiters” and the colder, longer-orbit gas giants in our solar system.
Katharine Hesse from MIT’s Kavli Institute for Astrophysics and Space Research notes the importance of such long-period systems, which aid in understanding the variety of planetary systems beyond our own. This discovery underscores the complexity of exoplanetary systems and the uniqueness of our solar system.
TESS, NASA’s Transiting Exoplanet Survey Satellite, plays a pivotal role in unveiling the secrets of these distant planets. It observes patches of the sky for 30 days at a time, continuously measuring the brightness of stars in those sectors. This method helps detect dips in brightness caused by planets passing in front of their host stars.
In 2020, TESS picked up a transit signal from a star labeled TOI-4600 in the northern sky near the Draco constellation. The star was further investigated by the TESS Single Transit Planet Candidate Working Group, comprising scientists from MIT and the University of New Mexico, dedicated to identifying longer-period planets from single-transit events.
Katharine Hesse explains that due to TESS’s 30-day observation window for each region of the sky, stacking up observations is necessary to find planets with orbits exceeding a month.
The team located three more transits from TOI-4600 and deduced that they originated from a planet, later named TOI-4600b, with an 82-day orbit. They also spotted a fifth transit, initially causing confusion. To ascertain if it resulted from another star momentarily eclipsing the first or a second orbiting planet, Ismael Mireles joined the team in 2021.
Mireles conducted further observations and discovered two more transits. These observations supported the existence of a long-orbiting planet, eventually identified as TOI-4600c. The team discerned that the two transits were produced by a single object orbiting the star either every 964 days or every 482 days, with the latter being more likely based on simulations.
To validate their findings, researchers employed ground-based telescopes, eliminating false-positive scenarios. The conclusion: TOI-4600 indeed hosts two long-period planets, TOI-4600b and TOI-4600c, bridging the gap between hot Jupiters and the colder gas giants.
The researchers are keen to explore the possibility of more planets in this system and note that TESS has the capability to identify both warm and cold Jupiters.
This groundbreaking research, supported by NASA, is a significant step toward unraveling the mysteries of distant planetary systems and deepening our understanding of the variety of planets beyond our solar system.
At the forefront of unraveling the enigmatic nature of distant planets stands TESS, NASA’s Transiting Exoplanet Survey Satellite. TESS assumes a pivotal role by meticulously observing designated patches of the sky for 30-day intervals, ceaselessly measuring the luminosity of stars within these sectors. This methodological approach proves invaluable in identifying luminosity dips attributable to the passage of planets across their parent stars.
In 2020, TESS garnered a transit signal emanating from a stellar entity known as TOI-4600, positioned in the northern firmament near the Draco constellation. The potential discovery prompted rigorous investigation led by the TESS Single Transit Planet Candidate Working Group. This collective of scientists from prestigious institutions such as MIT and the University of New Mexico is fervently dedicated to uncovering longer-period planets through the analysis of singular transit occurrences.
Katharine Hesse elaborates on the need for amassing observations due to TESS’s confined 30-day observational window for each specific celestial region. Such accumulation becomes imperative when in pursuit of planets with orbital periods surpassing a single month.
The team adeptly traced three additional transits originating from TOI-4600, ultimately ascertaining their provenance ascribable to a planet, later christened TOI-4600b, bearing an 82-day orbit. Among these detections, a fifth transit emerged, initially confounding researchers. To decipher whether it originated from a fleeting stellar eclipse or a secondary orbiting planet, Ismael Mireles joined the endeavor in 2021.
Mireles spearheaded further investigations, uncovering two additional transits. These findings substantiated the presence of a long-orbiting celestial body, ultimately identified as TOI-4600c. The team adroitly inferred that these two transits were the result of a singular object circumnavigating the star, each orbit occurring every 964 days or, more likely based on simulations, every 482 days.
With the aim of validating their deductions, the researchers harnessed the power of ground-based telescopes, adeptly dispelling false-positive scenarios. Their collective deductions solidified a resounding confirmation: TOI-4600 serves as the abode for two long-period planets, christened TOI-4600b and TOI-4600c. This discovery is instrumental in bridging the conceptual gap between the hot Jupiters and the frigid gas giants in the cosmic menagerie.
Eager to extend their inquiry, the researchers harbor intentions of delving into the prospect of additional planets within this stellar system. Notably, they highlight TESS’s exceptional capacity to pinpoint both warm and cold Jupiters in various orbits.
Supported by NASA, this groundbreaking research marks a profound stride in comprehending the enigmatic tapestry of distant planetary systems, further enriching our knowledge about the multitude of planets that reside beyond the boundaries of our solar system.
