Proxima B!

Physicist: Good news!  There’s an Earth-sized planet in the habitable zone of Proxima Centauri, a star so named because it’s the closest star to Earth and it’s in the constellation Centarus.  This isn’t a question anyone asked, but I thought it was worth mentioning: the closest star that could possibly host life is the closest star.

The new planet is called “Proxima B” because the naming convention says that’s what you should call the fist planet discovered around a star called “Proxima” (if/when another planet is discovered, it would be called “Proxima C”, then D, etc.).  This is hopefully a place holder until someone comes up with a better name, like Krypton or Xena.  Strictly because it’s a little cumbersome to refer to both the star, Proxima, and the planet, Proxima B, for the purposes of this post I do hereby declare that the newly discovered planet will be called “Bacchus”, after the god Bacchus.  (Bacchus: when you’re too drunk for organized religion, welcome to the Bacchanalia.)

The bright stars are . Proxima is the nearly invisible star below them (click to enlarge and see anything).

The bright stars are Alpha Centauri A and B, which are both about the same size as our Sun.  Proxima Centauri (sometimes called Alpha Centauri C) is the nearly invisible red star that’s circled below them.  A and B orbit each other every 80 years (so they switch places about every 40) and Proxima may orbit the pair every half-million years.  This picture is very zoomed in, so to the naked eye these appear to be a single star.

Just for a rough sense of scale, the Earth is 1 AU from the Sun (this is how the “Astronomical Unit” is defined), Proxima is a little over a quarter million AU away from us and less than a tenth that distance from Alpha Centauri (a pair of stars it may-be/probably-is orbiting).  Bacchus orbits Proxima every 11 days in an orbit that’s a twentieth the size of ours (0.05AU).

Bacchus was discovered using the radial velocity technique.  As Bacchus orbits, its host star, Proxima, wobbles and we can detect its tiny back-and-forth movement using the Doppler Effect (things moving toward us appear slightly bluer and things moving away appear slightly redder).  This wobble method reveals how long the orbit is (11 days) and gives a rough idea of the mass of the planet (around 1.3 Earths, give or take), but unfortunately it tells us very little more.  If we were lucky enough that Bacchus’ orbit brought it between its star and us, then we’d be able to (possibly) get a look at its atmosphere and determine its size.  Unfortunately, like the vast majority of exoplanets, Bacchus’ orbital plane is pointing off in some random direction, so it never eclipses Proxima from our perspective.

Venus and a bird transiting in front of the Sun. We can use alignments like this to study the atmospheres of other planets by looking at how sunlight/starlight filters through them.

A bird and a planet (Venus) transiting in front of the Sun. We can use alignments like this to study the atmospheres of other planets by looking at how sunlight/starlight filters through them.  Presumably we could study birds the same way, but it seems unlikely that anyone’s bothered to make the attempt.

So, beyond how much it weighs and where it is, we have no direct data on Bacchus.  But take heart!  We also have access to well-reasoned speculation!  Gas giants tend to be gigantic, so with only 1.3 (give or take) Earth masses to work with, Bacchus is almost certainly a rocky planet.  You’d expect that since Bacchus orbits so close to Proxima it would be hot, but Proxima is very dim (~1/10 the mass and ~1/10 the light of our Sun), so Bacchus should have more or less the temperature necessary for liquid water (the way Earth does).

Tight orbits also tend to lead to tidal locking.  Like our Moon’s relationship with Earth, Bacchus may have one side always pointed at Proxima.  It may literally have a dark side and a light side and if that’s the case, then there’s probably only a thin habitable region near the ring of twilight between the two.

We do know a lot about Proxima from telescopes.  In particular, it’s a flare star which means that its magnetic field plays a central role in its behavior; energy stored in its twisted up magnetic field is occasionally released as bursts of x-rays and solar flares.  That may mean that Bacchus’ atmosphere is already long gone.  This is something stars do to their planets (see Mercury and Mars, for example), it’s just that flares and x-rays are especially good at it and Bacchus is especially close.  That said, an already thick atmosphere and a healthy magnetic field go a long way toward preserving what air a planet has.  Fingers crossed.

There is some good news: Proxima is extremely stable.  Both our Sun and Proxima are about five billion years old, ours brightens over time and is due to burn out in another five billion years, but Proxima will still be doing what it does for the next few trillion (with a “t“) years.  When Proxima runs out of fuel the universe will be several hundred times older than it is now, so even if there’s no life on Bacchus (or any other planets around Proxima), there’s still an incomprehensible amount of time to get it right.  Things have a way of changing over a few trillion years (one would assume).

The bird/Venus/Sun picture is from here.

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13 Responses to Proxima B!

  1. stanley wallen says:

    It is too short a distance to be useful. The more useful is a Parsec.the distance at which the Earths orbit = one second of arc. This is 3.26 light years. Magaparsecs
    are used for long distances.

  2. If Proxima B has a strong field protecting its atmosphere maybe there are strong ‘norther lights’. The light from this would be at the discreet frequencies of the elements in the atmosphere and so perhaps quite distinct from light the Proxima.

    The background would still be huge! Do you think there’s any chance we could pull that out of the spectrum if we recorded it long enough?

  3. Max Graham says:

    Good News????? Let us get this ‘good news’ in perspective.
    It is 250,000 AU away from us. Voyager 2 (about the fastest space craft to date) has been traveling at 30,000mph for nearly 40 years and in 2012 was 98.3AU away from us or 9,114,000,000miles. The outer edge of our solar system is the Oort Cloud which is 63,240AU away and it will take Voyager 30,000 years to get to the edge of the Solar system. For it to get to Proxima B it will take it 88,000 years. Home Sapiens has been around for about 10,000 years. Maybe if we go the Science Fiction Star wars route instead of hard scientific facts and imagine warp speed etc. then maybe it is ‘good news’. For me it is interesting but somewhat irrelevant when looking at the real issues facing humanity here and now on this planet.

  4. The Physicist The Physicist says:

    @Max Graham
    Fair enough. I figured that “Good news!” read a little smoother than “Best possible news given the crushing realities of the situation!”.

  5. Nkosinathi M Zamisa says:

    Wow it’s seems as our night sky is getting more interesting

  6. Francisco L says:

    @The Physicist
    “Good News! There’s an Earth-sized planet in the habitable zone of Proxima Centauri” sounds a little bit like :” Fasten your sit belts ! The space ship is about to leave !!”

  7. The Physicist The Physicist says:

    @Traruh Synred
    Auroras are notoriously dim, but if we watched for a really, really long time, I don’t see why not.

  8. The Physicist The Physicist says:

    @Francisco L
    I would be willing to sell tickets.

  9. THE PLANET MAY BE HABITABLE OR MAY NOT BE. IF HABITABLE THEN HUMAN MAY TRY TO COLONISE THE PLANET.
    IT MAY BE POSULATED THAT AFTER 500 YEARS TECHNOLOGY WILL REACH TO A LEVEL WHEN HUMAN WILL BE ABLE TO FLY AT ABOUT A SPEED OF ABOUT HALF OF THAT OF LIGHT. LIFE EXPECTANCY OF HUMAN WILL BECOME 200 YEARS. FURTHER IT MAY BE POSSIBLE THAT HUMAN WILL BE ABLE TO CHANG THE POSITION OF PLANETS.

  10. Arthur says:

    Good to know.

  11. Siddharth gour says:

    if there are any intelligent life forms on the planet they will think of us an alien invasion

  12. THERE IS NO INTELLIGENT LIFE ANY WHERE OTHER THAN ON THE EARTH.
    HOWEVER IN FUTURE HUMAN CAN GO TO THE HABITABLE PLANETS AND COLONISE THE LIFE FRIENDLY PLANETS.
    IF HUMAN CAN LIVE THERE OTHER ANIMALS AND PLANTS WILL ALSO BE GROWN THERE BY HUMAN.

  13. ENGLISH BOB says:

    OH, THE ARROGANCE OF MANKIND.

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