It's amazing how much you can learn about a distant planet by studying the light from its host star.
Using the APOGEE instrument from the Sloan Digital Sky Survey, an international team of astronomers conducted a detailed study of Ross 128 and confirmed that the exoplanet in its orbit, which was announced last fall, is indeed rocky, has moderate temperatures, and may contain seas and oceans on its surface. … The findings of the scientists are presented in The Astrophysical Journal Letters.
“Understanding what elements are present in a star and in what quantity helps to estimate the composition of exoplanets orbiting it, which gives clues about their similarity to Earth. Until recently, it was difficult to obtain detailed chemical readings for the Ross 128, but the APOGEE tool and new method helped us do this,”says Diogu Suto, lead author of the study at the National Observatory in Rio de Janeiro, Brazil.
The star Ross 128 is a red dwarf star 11 light-years distant from Earth. In November 2017, a team of researchers announced the discovery in its orbit of the exoplanet Ross 128 b, which is the second Earth-like planet after Proxima b in our proximity and the closest of those that orbit an inactive red dwarf star.
Unfortunately, because of the orbit of Ross 128 b, we cannot observe its transit, and therefore scientists have no way to determine its radius and study its atmosphere "directly", so researchers have to resort to indirect methods, one of which was to obtain the composition of its star …
In adolescence, stars are surrounded by a disk of rotating gas and dust from which rocky worlds grow. A star's chemistry can affect the contents of the disk, as well as mineralogy and the internal structure of the planets around it. For example, the amount of magnesium, iron and silicon will control the mass ratio of the inner core to the mantle of future planets.
“The high resolution of the APOGEE infrared spectrometer is the key to this research. It allowed us to address some of the fundamental questions about the "landlike" Ross 128 b ", - explained Joanna Teske, co-author of the study at the Carnegie Institution (USA).
The team determined that Ross 128 has iron levels similar to what we see in the Sun. And while the researchers were unable to measure the abundance of silicon, the star's iron to magnesium ratio indicates that the core of exoplanet Ross 128 b must be larger than that of Earth. Then, knowing the minimum mass of the planet from previous studies, they were able to estimate the radius of Ross 128 b and show that it is rocky. Finally, by measuring the temperature of its star and adding the resulting size of the planet to the equation, the team determined that our second closest Earth-like neighbor has a temperate climate.
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“It's amazing how much we can learn about a distant planet by studying the light from its host star, which tells us about the chemistry of the system. Although Ross 128 b is not Earth's twin and we still do not know much about its potential geological activity, we were able to confirm that this is a temperate planet, on the surface of which water in liquid water may be present,”concluded Diogu Souto.
Roman Zakharov