Eleven light-years from Earth, orbiting a dim red star, there’s an exoplanet called Ross 128b that, as we recently reported, has some the best prospects for life of any known distant world. New results may help astronomers figure out what the planet is made of—and they offer more evidence that it might be inside its parent star’s habitable zone.
The international team of researchers analysed data from the high-resolution infrared-measuring instrument on a telescope in New Mexico. They calculated the star’s temperature, and its abundance of eight different elements. Studying the star helped the researchers make some inferences about the planet, such as that it seems to orbit at a distance that’s not too close or too far, placing it in the so-called habitable zone. But what can this really tell us about the planet itself?
“Nearby M dwarfs likely provide some of the best opportunities for detecting and characterising potentially ‘Earth-like’ exoplanets in the near future,” the authors write in their new paper published in The Astrophysical Journal Letters. “An approach to study the exoplanet composition, albeit an indirect one, is the analysis of the individual host star.”
You might remember using a spectrometer in chemistry class to determine which elements, when excited, produce which colours of light. That’s how much of astronomy works, and pretty much how APOGEE, an instrument on the Sloan Digital Sky Survey Telescope, works—though it uses infrared, rather than visible light. The scientists looked at APOGEE data on Ross 128 and calculated how much carbon, oxygen, magnesium, aluminium, potassium, calcium, titanium, and iron the star had. The star’s abundances of these elements can help determine its exoplanet’s temperature, and hint at what elements were initially available in the dust ring around the star when the planet first formed.
The planet probably has a larger core than the Earth, and a nice average temperature around 294 Kelvin, based on those results.
One researcher not involved with the new study had some reservations. “As far as I can tell, they measured elemental abundances on the star (that’s the new thing) and then do a lot of modelling and extrapolation,” Guillem Anglada Escude, astronomer at Queen Mary University of London, told Gizmodo. “I would not call this a breakthrough, and inferring the planet’s properties this way takes a big leap of faith.” He explained that there are still tonnes of unknowns, like how the star’s elemental abundances correspond to those of the planet, and where the planet formed in the early dust disk.
Emily Rice, associate professor in the Department of Physics and Astronomy at the CUNY College of Staten Island in the US, who was not involved with the study, told Gizmodo that it’s still useful to understand the composition of the parent star, “especially when talking about Earth-like or potentially habitable ones.”
New results about potentially habitable exoplanets are always tantalising. But there’s only so much information we can gather about them with present-day technology. Truly determining whether these exoplanets are actually Earth-like will take better technology, like the upcoming James Webb Space Telescope or another future flagship telescope, like LUVOIR or HabEx. [ApJ Letters]