Unveiling New Habitability Prospects: Earth-Sized Exoplanet Candidate and Rogue Planet Moons

Astronomers have identified HD 137010 b, an Earth-sized planet candidate located approximately 146-150 light-years away, which orbits a Sun-like star and is positioned near its habitable zone. Simultaneously, a separate study has presented research suggesting that moons orbiting rogue planets, which drift through interstellar space without a host star, may be capable of supporting liquid water for billions of years under specific atmospheric and geological conditions. Both discoveries contribute to the ongoing understanding of planetary habitability beyond Earth.

Exoplanet Candidate HD 137010 b Identified

An international team of astronomers has identified HD 137010 b, an exoplanet candidate that is estimated to be approximately 6% larger than Earth, with some descriptions indicating it is slightly larger. The candidate orbits its host star with a period of approximately 355 days, comparable to Earth's orbital period.

Discovery and Characteristics

The discovery was led by Dr. Alexander Venner, with contributions from researchers at institutions including the University of Southern Queensland, Harvard University, the University of Oxford, and the Max Planck Institute for Astronomy. The planet's existence was initially detected using the transit method, analyzing data from NASA's Kepler space mission (K2 mission data captured in 2017). This method observes brief dips in a star's brightness as a planet passes in front of it. Citizen scientists, through the Planet Hunters project, played a role in flagging the faint signal.

HD 137010 b orbits HD 137010, a K dwarf star that is about 70% the size and mass of the Sun, making it cooler and dimmer but also potentially having a longer lifespan. Its brightness is considered sufficient for future follow-up observations. While some estimates suggest the planet could be approximately 1.2 times as massive as Earth, its exact mass has not yet been determined.

Potential Habitability

The planet candidate is located near the outer boundary of its star's habitable zone, defined as the region where conditions could allow for the existence of liquid water on a planetary surface.

Researchers estimate a 40-51% chance of the planet residing within this zone.

Despite its location, models suggest that HD 137010 b receives less than a third of the energy Earth receives from the Sun, potentially resulting in surface temperatures between -68 and -85 degrees Celsius, possibly colder than Mars. However, the presence of a moderately carbon dioxide-rich atmosphere could retain heat, allowing for the potential existence of liquid surface water. Conversely, a carbon dioxide abundance similar to Earth's could lead to a "snowball" climate, with temperatures potentially falling to around -100 degrees Celsius, resulting in a fully glaciated planet.

Confirmation and Future Research

The status of HD 137010 b remains a "candidate" because its detection is based on a single observed transit. Standard planetary confirmation typically requires three transits, which, given its year-long orbit, presents challenges for future observations. Measuring the star's radial velocity to confirm the planet's gravitational influence is also difficult with current technology if the planet's mass is similar to Earth's.

HD 137010 b is considered a significant target for future astronomical research due to its Earth-like size, long orbital period, and the brightness of its host star. It is an objective for instruments designed to detect Earth analogues and for upcoming missions like the NASA Habitable Worlds Observatory and ESA’s PLATO mission, which aim to directly image Earth-like planets. The research findings regarding HD 137010 b were published in The Astrophysical Journal Letters.

HD 137010 b is considered a significant target for future astronomical research due to its Earth-like size, long orbital period, and the brightness of its host star.

Study Proposes Rogue Planet Moons Could Sustain Life

In a separate development, a new study led by astrophysicist David Dahlbüdding of the Max Planck Institute for Extraterrestrial Physics suggests that moons orbiting rogue planets—planets that have been ejected from their star systems and now drift through interstellar space—could potentially sustain life.

"Moons orbiting rogue planets could potentially sustain life, even without a host star."

Mechanisms for Habitability

The research indicates that a combination of a dense hydrogen atmosphere and internal heating from tidal forces could enable these "exomoons" to maintain liquid water conditions for up to 4.3 billion years. This duration is comparable to Earth's current age, allowing ample time for the emergence and evolution of complex life.

While rogue planets themselves are generally considered too cold to host liquid water, their exomoons could be internally warmed. An elliptical orbit around a rogue planet would generate varying gravitational stresses, leading to internal heating.

Atmospheric Role

Previous models for exomoon habitability proposed thick carbon dioxide atmospheres to trap heat. However, carbon dioxide condenses in extremely cold environments, limiting the duration of habitability to approximately 1.6 billion years.

Dahlbüdding's team explored a hydrogen atmosphere as an alternative. Hydrogen remains gaseous even at extremely low temperatures and can effectively trap heat. Under high pressure, hydrogen molecules collide to form complexes that absorb thermal radiation. Models incorporating a hydrogen atmosphere showed stable liquid water conditions could persist for up to 4.3 billion years.

Models incorporating a hydrogen atmosphere showed stable liquid water conditions could persist for up to 4.3 billion years.

Implications and Future Work

Scientists estimate that trillions of rogue planets exist, with some, particularly larger ones, potentially retaining or forming their own moon systems. This research suggests that the presence of a star is not an absolute prerequisite for conditions supporting life.

Future work aims to investigate other atmospheric compositions and increase model complexity to further assess the habitability of these unseen worlds. The findings of this study were published in the Monthly Notices of the Royal Astronomical Society.

This research suggests that the presence of a star is not an absolute prerequisite for conditions supporting life.