Α groundbreaking discovery was announced on Wednesday, when it was confirmed that an ‘Earth-like’ planet is in orbit around the ‘red dwarf’ star Proxima Centauri, 4.37 light years from the Sun. This star has been known for more than a century, but this is the first time that it is proved to have a planet orbiting around it. Named Proxima Centaur b, the exoplanet is believed to be 1.3 times the mass of the Earth and lies within the so-called ‘habitable zone’, meaning that liquid water could potentially exist on it. The discovery, announced by the researchers of the European Southern Observatory (ESO), has spread excitement in the world of astronomers, who see this as a major step in the quest for life outside our solar system. One of the astronomers that took part in the research, Yiannis Tsapras, a Gliese Fellow at the Centre for Astronomy in Heidelberg, guides us through the discovery.
Living generations, for the first time in human history, are very likely to have an answer to the question of whether we are alone or not in the Universe.
How was Proxima Centauri b discovered?
The planet was discovered through a coordinated international effort involving 31 scientists from eight different countries. We used the HARPS spectrograph on ESO’s 3.6m telescope in Chile to measure how the star ‘wobbles’ as the planet goes around it. At the same time, we also used the Las Cumbres Observatory Global Telescope Network (LCOGT) and ASH2 telescopes to record how active the star is, so that we would not mistake stellar activity for a real planetary signal.
Are you excited about this discovery?
Absolutely! We already know of thousands of planets orbiting distant stars, but this is an almost Earth-mass planet in a temperate zone around Proxima Centauri, which is right next door, only ~4.2 light years away!
How did you become part of the project?
In 2013, when I was still a Fellow at Queen Mary University in London (at the School of Physics and Astronomy), a colleague had some observations from Proxima Centauri that raised suspicion of a planet being there. We have been discussing since how to organise a series of observations that would lead to the confirmation or rejection of this signal. I used the LCOGT network of telescopes to monitor Proxima’s stellar activity throughout the campaign and analysed the observations, which showed without question that the planetary signal was not due to the activity of the star.
How do we know that it is a terrestrial planet?
The planet’s minimum mass (1.3 Earth masses) comes straight from our measurements. We have no direct indication of the composition of the planet, but considering solar system planets and our theoretical models of planet formation and structure, it is very likely that this planet is rocky. The distance from its star implies that, if there is water on this planet’s surface, it could potentially be liquid, depending on the planet’s atmosphere. We do not currently know whether there is water there, or whether the planet has an atmosphere. The Doppler method tells us the orbital period and the size of the orbit. This combined with the star brightness tells us the approximate temperature on the surface of the planet. In this case, Proxima b without an atmosphere would be at -55 C (an Earth with no atmosphere would be at -30C). However, greenhouse gases keep the Earth warmer so the temperature on Proxima b could be comfortable too.
Could there be life there?
If it has an atmosphere and if there is water there, and these are big ‘ifs’, the local conditions might support life; but we do not really know. We need to study this system a lot more over the coming decades in order to be able to start answering such questions. However, it is a great place to start looking for it.
What are the prospects of establishing contact or going to the planet?
If there were a technologically advanced civilisation with radio technology on Proxima Centauri b, sending and receiving signals would take 4.2 years either way. However, the system has been studied extensively in the past and there are no indications of any signals coming from there. Knowing that there is such a planet, it might be worth searching a bit deeper. The good thing is that a two-way call has a lag of ‘only’ 8.4 years, so after sending a powerful radio message we do not need to wait that long for a possible answer. We are also not likely to visit anytime soon, at least with current technology.
How long would that take?
With current technology, assuming we got the spacecraft to travel at 56,000km/h (this was the velocity achieved by the Deep Space 1 mission), it would take at least 81,000 years to get to Proxima Centauri. If we also use the gravity of some of the Solar System planets to perform a so-called slingshot manoeuvre to achieve higher speeds, we could get there in about 15,000 years (but then we would need to somehow slow down once we get there). So, unless we discover some new physics that allows us to traverse such distances on much shorter timescales, enjoying a cool Pan Galactic Gurgle Blaster* at a Proxima Centauri pub will have to wait. On the other hand, the ambitious Starshot Project aims to send tiny robot voyeurs to the Centauri system in a voyage lasting a mere 20 years.
When will extraterrestrial life be discovered?
We already have evidence that Earth-mass planets are common in the universe. All this helps us to understand better how planetary systems form and evolve. Within five years we will have good estimates of their abundance from a combination of different planet-detection techniques. Once we have established their abundance and picked out the best candidates, the next step would be to launch high-tech space telescopes to look for indications of life on them, which would probably take one or two decades. This means that living generations, for the first time in human history, are very likely to have an answer to the question of whether we are alone or not in the Universe. But in most probability, this will be some kind of bacterial life, not hollywood aliens. But even this kind of discovery will be enough to shake biology to its core, because all we know about life comes from a single specimen – life on Earth, which is diverse, but has a common origin.
How has your work affected your outlook on life?
Anyone interested in Astronomy has a rather different perception of the ‘self’, in regards to what is ‘out there’. Carl Sagan summarised it like this: ”astronomy is a humbling and character-building experience”.
What is your personal aspiration?
I don’t have aspirations, only insatiable curiosity.
*(ed. note: a reference to a cocktail mentioned in Douglas Adams’ ‘The Hitch-Hiker’s Guide to the Galaxy’ series of books).