The discovery was led by Dr Alexander Venner, who carried out the research while completing his PhD at UniSQ, as part of an international collaboration. The candidate planet, designated HD 137010 b, was identified using data from NASA’s Kepler space telescope during its extended K2 mission, with observations dating back to 2017.
According to findings published in The Astrophysical Journal Letters, HD 137010 b is estimated to be just 6 per cent larger than Earth. Its surface temperature is believed to be closer to that of Mars, potentially dropping below minus 70 degrees.
The study suggests the planet sits near the outer edge of its star’s habitable zone – the region where conditions may allow liquid water to exist on a planet’s surface under the right circumstances.
HD 137010 b was detected after it passed in front of its host star during a three-month observation window, producing only a very faint signal. That subtle signature was first identified by a group of amateur astronomers taking part in a global “citizen science” project, which included Venner himself.
“I first got involved in this citizen science project, called Planet Hunters, when I was still in secondary school, and it played a major role in sparking my interest in research,” Venner said.
“It was incredibly rewarding to return to this work years later and uncover such a significant discovery.”
Venner estimates the planet’s orbital period is around 355 days, placing it with roughly a 50 per cent likelihood of orbiting within the habitable zone of its star.
“Most previously discovered Earth-sized planets in habitable zones orbit red dwarf stars, which are much smaller and dimmer than our sun,” he said.
“There are concerns these planets may lose their atmospheres due to intense radiation from their host stars, making them unlikely to support life as we know it.
“By comparison, the host star of HD 137010 b is much more similar to the sun, which increases the chances that the planet could retain an atmosphere, based on current models.”
If the planet has an atmosphere similar to Earth’s or Mars’, it would likely be colder than Antarctica. However, Venner said a thicker atmosphere could potentially trap enough heat to allow liquid water to exist on the surface – a key ingredient for life.
The researchers also noted that HD 137010 b is the first Earth-like planet candidate discovered transiting a sun-like star that is bright enough to allow detailed follow-up observations.
“While current instruments are unable to fully characterise this planet, it could become a prime target for future radial velocity studies aimed at detecting true Earth analogues,” Venner said.
“Planned space missions capable of directly imaging Earth-like planets, such as NASA’s proposed Habitable Worlds Observatory, may also be able to capture images of HD 137010 b.”
The study, titled “A cool Earth-sized planet candidate transiting a tenth magnitude K-dwarf From K2”, was co-authored by Venner, Dr Chelsea Huang, Shishir Dholakia and Professor Robert Wittenmyer from UniSQ, alongside researchers from Harvard University and the Smithsonian Institution, the University of Oxford, NASA’s Ames Research Center, Brorfelde Observatory in Denmark, and a global network of citizen scientists.