ESO instrument on the VLT may detect the first known exoearth.
It’s ‘nonsense’ to think that humanity is ever going to actually move to some nearby exoearth, says one of the world’s top planet hunters. Even so, Nuno Santos, a planetary astrophysicist at Portugal’s University of Porto, remains convinced that within the next decade or so we will be capable of detecting biosignatures of life from an extrasolar Earth.
But first, astronomers have to find a bona fide extrasolar Earth, Santos told me in his office at Portugal’s Institute of Astrophysics and Space Sciences.
Santos plans on using a powerful spectrograph at the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile to do just that.
ESPRESSO, the Echelle Spectrograph for Rocky ExoPlanet and Stable Spectroscopic Observations, can detect a planet’s periodic gravitational effect on its parent star down to 10-centimers per second. That is, a star’s movement towards or away from us along our line of sight, down to centimeters per second.
ESPRESSO saw first light in 2017 and after a year of commissioning, Santos, the Portuguese co-principal investigator for ESPRESSO, promises some “beautiful results soon.”
Originally, a doctoral student of the Nobel prize-winning exoplanet hunter Michel Mayor, Santos returned from Geneva Observatory to his native Porto and began setting up a cadre of researchers in exoplanetary science. It’s been a long two-decade long haul from the days when Mayor and colleagues were ecstatic to detect so-called hot Jupiters, gas giant planets on extremely short orbits around nearby stars. But today, the exoplanetary science community is impatiently waiting for a crack at a real exoearth analog.
ESPRESSO may solve that problem.
Santos says if there’s an earthlike planet around Proxima Centauri —- at 4.1 light years the nearest star to Earth —- then ESPRESSO will be able to detect it. ESPRESSO is now the most accurate spectrograph in the world for deriving radial velocities. That is, the velocity of a star or other body along the line of sight of an observer.
So, we could detect an earthlike planet orbiting a solar type star in the habitable zone, says Santos.
ESPRESSO covers the optical wavelength spectrum; the visible range and a bit more, says Santos. If you want to study planetary atmospheres then you need to know a planet’s mass to high precision, he says. The first step for ESPRESSO is to find planets and then characterize them using spectroscopy, he says.
Thus far, we haven’t found any exoearth candidates, says Santos.
In fact, of the more than 4000 planets known, Santos says most were detected by NASA’s Kepler space telescope and are too faint to study adequately.
Santos refuses to name his top exoplanetary candidates for life.
People tend to announce that they have found a planet that ‘can harbor life,’ says Santos. That’s indirectly telling people that maybe there’s life on that planet, he says, but we know nothing about it. As he points out what they’ve really found is a planet in the habitable zone, nothing more.
We haven’t detected any rocky planets in the habitable zone of a solar type star for which we know the mass and the radius of the planet, says Santos. And even if we had one, we could not say for sure there could be life there, he says.
In 2017, Santos and colleagues authored a paper in the journal Astronomy & Astrophysics that noted that recent studies suggest that the abundances of specific chemical species in a star’s photosphere (or surface) may give clues about the internal structure and composition of its planets. This is true both for giant planets and for their rocky counterparts, the authors note.
Nuno Santos (left) conferring with Jarle Brinchmann, Director of the CAUP (Center for Astrophysics ... [+]
“We established a correlation between the metal content of stars and the frequency of giant planets,” said Santos.
If you know the composition of the star it means in general you know the chemical composition of the planetary building blocks, says Santos. However, the future will test whether there is a real correlation or not. That is, when we start finding planets around stars with very different chemical compositions, says Santos. But to prove this correlation, we need more star-planet examples, he says.
To that end, the European Space Agency’s (ESA) forthcoming PLATO mission will look for rocky planets in the habitable zones of bright stars. Bright stars mean we have lots of photons to study the planetary atmospheres, says Santos.
“In the next decade or so, we will have a good catalog of potential habitable planets,” said Santos. Then we can start dreaming of finding biosignatures, he says.
