This ESPRESSO machine doesn't make coffee but scans the skies for habitable planets

A new planet hunter has been fired up in Northern Chile — the ESPRESSO machine doesn't make coffee but is a massive spectrograph that is the most powerful planet-hunting tool ever to scan the cosmos. 

What does ESPRESSO stand for?

It stands for the Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations. It is a light detector that determines what wavelengths or colours are coming from the distant reaches of the galaxy. It's a device that is connected to European Southern Observatory's Very Large Telescope in Chile that doesn't have a lens exactly like a traditional telescope but instead detects electromagnetic frequencies, which includes light waves.

What is ESPRESSO looking for?

It is scanning the skies for habitable planets. We have heard a lot in the news about various planet hunting missions, Kepler for instance, and the James Webb Space Telescope to be launched in spring 2019. 

But this ESPRESSO spectrograph is bound to an Earth-based telescope. It's a little harder to see beyond the atmosphere of Earth, but it's also a lot easier to fix when things go wrong.

So far, dozens of rocky Earth-like planets have been found. The first step in finding planets like Earth is to just find other planets orbiting around other stars — there are literally an infinite amount of them. Then, those planets have to be narrowed down to those that are rocky, those that are also the right distance away from the star they orbit to not be too hot nor too cold, something called the Goldilocks zone. 

This Goldilocks zone is essential because it's when it is just right that liquid water could form on a rocky planet. And voilà … a second Earth. If only it were that easy.

How do you hunt for planets far off in space?

There are a few different strategies to do this. ESPRESSO uses something called radial velocity. We can tell approximately how fast a star is moving in space by detecting the light coming off of it, and we can look for differences in that light if a planet orbits. 

Francesco Pepe from the University of Geneva is the lead author on this project. He explains radial velocity this way: "You imagine that you have a star which is low in the universe, so it's travelling by its own. So it will travel with a constant speed. If there is a planet around this star, then by gravitational pull, the heavier the planet and the closer to the star, the easier it is that it will produce a larger gravitational pull, so the signal will be bigger."

In other words, an orbiting planet around a star will make the star wobble every now and then as it orbits, because it is being dragged around by the mass of the planet. That's what they are looking for. The problem is the planets that could be habitable are small rocky ones that aren't massive so the signals ESPRESSO is trying to detect are unimaginably small.

Has anything been found?

No, the instrument has taken what is called first light, which is a maiden voyage of sorts to see if everything works. There is an extended calibration phase to make sure any signals that are detected are real. But the ESPRESSO team are already looking at our stellar neighbourhood. 

To start the search, the telescope will be looking at the regions of our own galaxy, the Milky Way, about 10 light-years away. But results won't be truly available until the middle of next year as the researchers make sure that the spectroscopic detector is working with the precision needed.

What does the detector look like?

It's a beast. In order to detect such tiny shifts in the flight of the stars it must be big and full of expensive and incredible engineering and be incredibly precise.

"It's a huge vacuum tank of about five metre length, two metres in diameter with huge optical components, lenses and so on on it," Pepe said.

Everything closed into this vacuum vessel in order to work without air pressure variations because otherwise these would disturb our measurements, and everything is then kept to one mili-degree of temperature stability and this spectograph and this 10-tonne beast is enclosed in the cellar of the Paranal Observatory, just below the telescopes."

Pepe was in charge of overseeing the dismantling, crating and reassembly of the ESPRESSO detector on site in the mountains of Chile and crossed his fingers the whole time that everything would work. The initial calibration results are going extremely well. Soon, it will be online and analyzing all the stars that we can see on a dark night to determine, perhaps, if an Earth-like planet is out there within our view.