ESPRESSO: The Decisive Spectrograph to Find Planets Like Earth


The transit method has proved to be very successful
at discovering new exoplanets. More than 3,000 transiting exoplanets have
been discovered, compared to the 800 exoplanets found with the radial velocity method. However, the majority of the most potentially
habitable exoplanets were discovered by measuring the radial velocity of the stars. In addition, a small fraction of exoplanets
have orbital planes with an inclination similar to the one of the Earth. Only 0.5 % of the Earth-like planets in the
Milky Way could be detectable by using transit photometry. The radial velocity method is, therefore,
the most effective method for detecting potentially habitable exoplanets. All of them could be detected with the suitable
spectrograph, except those exoplanets with orbital planes totally perpendicular to the
one the Earth. The main disadvantage of the radial velocity
method is that it doesn’t give information about the radius of the exoplanet and only
the minimum mass can be provided. Nonetheless, the true mass can be calculated
with other methods and the relationship between mass and radius appears to have a common functional
form. In other words, for an Earth-like planet with
a mass 3 times higher than Earth, the estimated radius would be 40% higher. This is the case of Tau Ceti e, which was
discovered with the HARPS spectrograph. HARPS can detect radial velocities up to 30
cm/s, whereas ESPRESSO can detect velocities of less than 10 cm/s, which are produced by
Earth-like planets. ESPRESSO is the most sensitive spectrograph
in the world, and it was installed in the Very Large Telescope, which is composed of
4 telescopes. The spectrograph is available for the scientific
community since 2018, but only for one of the telescopes. It is expected to become available for all
the telescopes in April 2020, so we might have soon the first discoveries of exoplanets
and, perhaps, the closest Earth-like planet. Thank you very much for watching and please
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