As scientists study the stars, we’re finding exoplanets closer and closer to home. Proxima Centauri b is just a few light years away, and now astronomers have tantalizing new details about the second closest exoplanet known as Ross 128 b. Through analysis of the host star, researchers say the exoplanet is small, rocky, and could potentially support life.
The red dwarf star Ross 128 is just 11 light years away, which is in our own backyard in interstellar terms. Most exoplanets are detected using the transit method, where instruments like the Kepler spacecraft watch for brief dips in light as planets pass in front of their host stars. However, that only works if the plane of a solar system is aligned with ours. That is not the case with Ross 128. Astronomers used a decade of radial velocity data from the European Southern Observatory’s HARPS spectrograph to show that a planet was tugging lightly on the star as it orbited.
Since Ross 128 b doesn’t transit the star, it’s difficult to study it directly. Therefore, a team from Brazil’s Observatório Nacional and the Carnegie Institution studied the star with the aim of extrapolating details about the planet. The chemistry of a star influences how planets form, and they likely share similar compositions.
Using the Sloan Digital Sky Survey’s APOGEE spectroscopic instrument, the team measured Ross 128’s near-infrared spectrum to measure the abundance of carbon, oxygen, magnesium, aluminum, potassium, calcium, titanium, and iron. They determined that Ross 128 has iron levels similar to our sun, but there’s more magnesium. That indicates Ross 128 b is probably slightly larger and more massive.
With an approximate mass from radial velocity measurements and the new star measurements, scientists were able to draw some conclusions about conditions on Ross 128 b. Exoplanets more than 1.7 times the radius of Earth are usually gas giants, but Ross 128 b is below that threshold. Based on the temperature of Ross 128 (which is both smaller and cooler than our sun), Ross 128 b should have a temperate climate that allows for liquid water on the surface. That assumes that it has an atmosphere, and there’s every reason to expect that it does based on the size and mass.
Ross 128 b is a tantalizing target for future study, but the lack of solar transit complicated matters. We may have to wait for instruments like the James Webb Space Telescope to come online before we can learn much more about this nearby world.
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