Title: Detection of an Earth-sized exoplanet orbiting the nearby ultracool dwarf star SPECULOOS-3
Authors: Michaël Gillon, Peter P. Pedersen, Benjamin V. Rackham, et al.
First Author’s Institution: Université de Liège, Liège, 4000, Belgium
Status: Published in AAS Nature [closed access]
The SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) project team has been paving the way in the search for rocky planets around cool stars. Their first remarkable feat was the discovery of the TRAPPIST-1 system, the first system of rocky planets found orbiting closely around an ultra cool dwarf host star. Now, the SPECULOOS team shines again with their latest detection of an Earth-sized exoplanet orbiting another ultra cool dwarf host star.
The Discovery
Using the TRAPPIST telescope, the authors of today’s paper detected a transiting Earth-sized planet around the star SPECULOOS-3, an ultracool dwarf star (T = 4,760° F, less than half the temperature of our Sun!). This star is among some of the smallest and coolest stars, known as M-type stars (also referred to as M dwarfs or red dwarfs) in the spectral classification scheme, but they are the most common type of star in our Milky Way galaxy. Because of their ubiquity, the SPECULOOS team set out to detect planets around M-type stars using the transit method. With this method, we can detect exoplanets by measuring a periodic dimming of a star’s light as a planet passes in front of it (see Figure 1). However, this is no easy task – due to their small sizes and cool temperatures, these stars are also extremely dim. Therefore, we are most sensitive to detecting planets very close to their star, as was the case for the planet SPECULOOS-3 b. SPECULOOS-3 b was discovered in a 17-hour orbit around SPECULOOS-3 – meaning one year on this planet is less than one day on our own! But that is not where the differences between SPECULOOS-3 b and Earth end. Despite the two planets having about the same radius (R = 0.977 ± 0.022 Earth radii), SPECULOOS-3 b’s proximity has caused it to become tidally locked. This means half of the planet experiences a permanent dayside where it gets blasted by high levels of stellar radiation, while the other half experiences an eternally dark nightside.
JWST Implications
Despite the planet’s high irradiation (16 times that of Earth), it is possible that it could be holding onto a volatile-rich atmosphere. To check for this, one popular way to study a planet’s atmosphere is through emission spectroscopy. In emission spectroscopy, astronomers probe a planet’s dayside right before and after a secondary eclipse, when the dayside of the tidally-locked planet is facing our telescopes. Typically, astronomers have only been able to study the atmospheres of large exoplanets since they are the brightest., The high level of irradiation on the dayside of this planet could make it bright enough to obtain detailed emission spectroscopy. Furthermore, SPECULOOS-3’s spectrum peaks in the infrared, making this system a perfect target to measure its emission spectrum with the Mid-InfraRed Low-Resolution Spectrometer (MIRI/LRS) on JWST (see Figure 2). The potential for JWST follow-up is very exciting, as this could be the smallest rocky exoplanet that we can get detailed information about its atmosphere. The discovery of SPECULOOS-3 b is paving the way for rocky exoplanet atmospheric studies, which will aid our understanding of life and habitability!
Astrobite edited by Archana Aravindan
Featured image credit: NASA/JPL-Caltech
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