A New Planet Hunter is Coming!

We can not really see exo-planets directly, at least apart from a few exceptions. Instead, we use overlay observation, when a planet crosses over a star and we see the star getting less bright. But for that, we need a bit of luck. We need to planet and star to be aligned in a way that it crosses in front of the star from our point of view and that is not the most common thing.

A Taste of ESPRESSO - Source: Wikimedia Commons

But there is another, more effective way to do it. We can measure how much a star moves around the center of gravity of the whole solar system. Yes, even though the vast majority of mass in a solar system is concentrated in the star the gravity of the planets still moves the star a bit. That is detectable because the light spectrum of the star is then changed according to the Doppler effect. And the larger the planet the more it moves the star. Currently, we are using the High Accuracy Radial velocity Planet Searcher (HARPS) that belongs to the European Space Agency to do this. HARPS is made from 4 telescopes each with an 8.2 m mirror. These tools allow it detect movement of a star up to 1 m/s fast. It has been searching for exo-planets since 2003 and it has detected over 130 exoplanets so far.

But all the planets detected by HARPS have been gas giants. Because you need a gas giant’s gravity to move the star by that much. Now, if we want to detect rocky planets the same way, planets that are similar to Earth, that could allow for liquid water and thus the existence of life similar to ours we need a better tool. That will be ESPRESSO or Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations. ESPRESSO will take the detection ability to just a few cm/s.

Sources:

• http://www.eso.org/public/czechrepublic/teles-instr/paranal-observatory/vlt/vlt-instr/espresso/?lang
• https://en.wikipedia.org/wiki/High_Accuracy_Radial_Velocity_Planet_SearcherESPRESSO
• https://en.wikipedia.org/wiki/High_Accuracy_Radial_Velocity_Planet_Searcher