The European Southern Observatory found a new, exciting exoplanets while we were on a break.

Called Proxima b, the planet tightly orbits Proxima Centauri, the closest star to us: “just” 4.3 light years away. It was just 25 years ago that we found planets outside our solar system at all. And look at us now, finding one in basically our cosmic backyard!

If you haven’t read the news, ESO put together a nice video with the main facts. There is also a short recap here (by yours truly) and a longer one (by Phil Plait).

There’s a couple of things I found particularly interesting, but not represented enough in the media: the über-cool technique used to find the planet, and a little reflection on habitability.

Something red, something blue, something old, something new

Most of the exoplanets were found using the Kepler space telescope, which measures how bright stars are. When a planet passes in front of the star, it blocks a tiny portion of the light. Kepler can perceive the microscopic change, and so detect planets. However, as the ESO team explained in a Reddit AMA, the Kepler way would not have worked, because the planet passes too rarely in front of the star.

They had to get clever. And get clever they did: they used the doppler effect.

The classic example is a siren passing by: its pitch seems to shift, becoming higher as the ambulance nears, lower as it goes away. Light does the same: the light from an object (say, a star) coming becomes ever so slightly bluer if the object moves towards you, and redder as it moves away.

Now comes the cool part: when a planet orbits a star, it tugs with its gravity, so the star ends up following it and moving on a little circle. Basically, it wobbles around a bit.

The scientists searched signs of this wobble in the minuscule changes in the color of the light coming from Proxima Centauri. Lo and behold, the star inches towards and away from us periodically, more or less at human walking pace (5 km/h).

Once sure that the star’s activity was not the source, they knew they had a planet.

Not just that: from the time it takes for Proxima Centauri to do a round and the speed at which it goes, they were able to tease out how long the planet takes to complete an orbit, how far it is from the star and (more or less) how massive it is.

Location, location, location?

As it turns out from these calculations, Proxima b’s orbit is quite tight: it stays about 20 times closer to its star than the Earth to the Sun. That’s very close. But, because Proxima Centauri is small and dim red dwarf, Proxima b is in the habitable zone.

So, does it have life? It’s early to say.

Being in the habitable zone is not enough to have water or life, a lot depends on a planet’s atmosphere. Venus and Mars, for example, are both in the Sun’s habitable zone. Venus has too thick an atmosphere and ends up looking a lot like our idea of hell, molten metal lakes and all. The Martian atmosphere is so thin that, except for that poisonous death mud found in 2025, it’s a frozen desert.

Plus, Proxima b probably has a permament day and a permanent night side. Unless it has the right type of climate, that could mean one is scorching hot, and the other is frozen: hardly the ideal conditions for water or life.

Actually, even if there turned out to be water, life could have a hard time there. Proxima Centauri is very prone to flares—sudden bursts of extreme heat and radiation. So, unless the planet has a protective magnetic field like Earth, any life could be burnt to a radioactive crisp any day.

Unfortunately, there is no way for us to send a probe there and figure this stuff out: it Proxima Centauri is the closest star to us, but still it would take thousands of year to reach it with current technology. Should Project Starshot actually take off, Proxima b would be its first destination.


Cover picture: M.Kornmesser/ESO

2 thoughts on “Two cool things about Proxima b

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