Ice-Cold Earth: New Planet Candidate Found in Kepler Data

Astronomers sifting through data from NASA’s retired Kepler Space Telescope have identified a potential Earth-sized exoplanet, HD 137010 b, orbiting a star 146 light-years away. While the signal requires confirmation, initial analysis suggests a rocky world with an orbital period close to Earth’s, though significantly colder – potentially an “ice-cold Earth,” as described by NASA.

The discovery stems from re-examining data collected during Kepler’s K2 mission. The candidate planet was identified through a single transit event – a slight dimming of the host star, HD 137010, as a potential planet passed in front of it. This dip in brightness, measured at roughly 225 parts per million, was subtle enough to have been easily overlooked in a cursory scan, but stood out during a careful reprocessing of the K2 data from 2017.

Understanding HD 137010 b

Based on the transit depth, researchers estimate HD 137010 b has a radius approximately 1.06 times that of Earth. The duration of the transit, combined with the star’s known mass and radius, suggests an orbital period of around 355 days – remarkably similar to Earth’s year. However, the similarities largely end there.

HD 137010 is a K-type dwarf star, which is smaller and cooler than our Sun. HD 137010 b receives significantly less energy from its star – approximately 0.29 times the amount of starlight Earth receives. This drastically reduces the planet’s potential temperature.

Initial temperature estimates, assuming the absence of a substantial atmosphere, place the planet’s equilibrium temperature around -90 degrees Fahrenheit (-68 Celsius). This frigid temperature is the basis for NASA’s description of the object as an “ice-cold Earth.” It’s crucial to understand that this is an equilibrium temperature – a theoretical value based on energy received and emitted. It doesn’t account for potential atmospheric effects.

The presence and composition of an atmosphere remain unknown. A thick atmosphere could trap heat, potentially raising the surface temperature and even allowing for liquid water. However, the low energy budget makes the existence of liquid water on the surface less likely. The planet’s position within the star’s habitable zone is near the outer edge, making atmospheric warming a critical factor.

The Challenge of Confirmation

The identification of HD 137010 b is currently considered a candidate planet, not a confirmed discovery. Single transit events can be caused by phenomena other than planets, such as eclipsing binary stars (where two stars orbit each other and periodically block each other’s light) or instrumental artifacts. The research team has performed checks to rule out common false-positive scenarios, but the most definitive way to confirm the planet’s existence is to observe another transit.

This presents a significant challenge. Given the estimated orbital period of nearly a year, the next transit opportunity is distant. Uncertainties in the orbital period calculation spread the predicted transit time over a wider window, making it difficult to schedule telescope observations. Telescopes have limited observing time and cannot continuously monitor a single star.

Follow-up observations, potentially using space-based telescopes, are being considered. The brightness of HD 137010 is advantageous, as it allows for more precise measurements of subtle dips in brightness. If a second transit is detected, the orbital period can be determined with greater accuracy, solidifying the planet’s status as a confirmed exoplanet and opening the door for more detailed study.

The discovery of HD 137010 b highlights the continued value of data from missions like Kepler, even after they have ceased operations. Kepler’s archive remains a rich source of information and careful re-analysis of existing data can yield new insights. It serves as a reminder that valuable discoveries can be found not only through new observations, but also through revisiting and re-interpreting existing ones.

For now, HD 137010 b represents a compelling hint – a potentially rocky, Earth-sized world in a nearby star system. While its icy conditions may preclude habitability as we know it, its characteristics make it a valuable target for further investigation, particularly as astronomers continue to refine their understanding of exoplanet formation and the conditions necessary for life beyond Earth.