Every time astronomers peer through their telescopes, there’s the possibility of discovering
something new. Something that’s never been seen before, that either confirms a long-held theory…
or completely rewrites the future of science and space exploration. It’s invariably described as
a difficult job, perhaps a somewhat repetitive pastime, but an exciting one, as well, because you
just never know what you’re going to see next! This is Unveiled, and today we’re answering the
extraordinary question; did scientists just discover a giant planet that should not exist?
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The business of exoplanets is booming these days. Yes, at the time of writing, we’re still at less
than 5,000 of them officially confirmed, but scientists are certain that there are many, many
more out there. And it seems that new exoplanet candidates are being discovered on a daily basis.
Every so often, though, one comes along that just doesn’t fit with all that have gone before it.
And that’s what has happened with the discovery of b Centauri b.
Situated in the b Centauri two-star system, some 325 lightyears away from Earth, the planet b
Centauri b is surviving under seemingly impossible conditions… leading many to claim that it should
not exist. The two-star system has a mass at least six times greater than the Earth’s sun…
and just the main star (a B-type star) is said to be at least three times as hot as our sun is.
Up until now, scientists had debated whether planets could exist in a setup such as this,
and no planet had ever been discovered orbiting a star that’s more than three times the mass
of the sun. So, b Centauri b is already a record breaker. But the strangeness of this
particular alien world goes further. In terms of solar system planets,
it has been much more readily compared to Jupiter rather than Earth. It’s said to be
around eleven times more massive than Jupiter is, making the star-to-planet mass ratio about
the same in the b Centauri system as it is for Jupiter in the solar system. However, the
planet b Centauri b orbits much further out, at a distance more than 100 times what Jupiter does.
At this early stage, scientists believe that this may be what has allowed it to survive. Because, if
it were any closer to its two-star centre, then it would surely burn up, disintegrate, and perish.
Interestingly, though, the b Centauri b orbit (as far out as it is) is also reportedly
quite circular. This isn’t the case in the solar system, where planets carve an elliptical path
around the sun, instead. This part of the story is particularly tricky to square up,
but there is an early suggestion that it may have been influenced by b Centauri b at one time
arriving at its current location from somewhere else. Indeed, those behind its discovery have
commented that “the planet is unlikely to have formed in situ… but might have formed
elsewhere”. One possibility, then, could be that it was a rogue world, cutting through the galaxy
in ancient times, before it was captured by the two-star anchor that guides it today.
Its discovery is thanks to a team working at the European Southern Observatory’s Very Large
Telescope, in Chile’s Atacama Desert. The planet was found via direct imaging, using the facility’s
Spectro-Polarimetric High-Contrast Exoplanet Research instrument, otherwise known as SPHERE,
as part of a more than two-year survey ending in April 2021. The study’s lead author,
Markus Janson, has described the finding of b Centauri b as “very exciting”, explaining that
it “completely changes the picture about massive stars as planet hosts”. Before b Centauri b,
it might’ve seemed pointless to look at massive systems like b Centauri with the hope of finding
planets… but now we know that it isn’t. So, where do we go from here? In the case of
this particular planet, at ‘only’ 325 lightyears away from Earth it’s nowhere near as distant as
so many of the other stars and planets we’ve discovered to date. That’s not to say that
we’ll be visiting anytime soon, as we’re still far from the technology needed to get us there
in even a half-manageable timeframe… but we should be able to study it with clarity and confidence.
And we already know that b Centauri b has done its part to rewrite the rulebook on exoplanet hunting,
so it’s sure to influence countless more surveys and studies in the coming years.
It’s worth remembering, too, that this isn’t the first newly discovered planet
to be labelled as something that “should not exist”. Back in September 2019, for example,
another planet was granted the same dubious descriptor; the faraway gas giant, GJ 3512 b. This
was again considered a massive world, although it’s nowhere near as massive as b Centauri b,
it should be noted… coming in at roughly half the mass of Jupiter. It does have a wider
diameter than Jupiter though, so references to it being a giant are more than fair.
What truly sets GJ 3512 b apart, though, is again the nature of the star that it orbits. Only this
time the star is very small instead of very big. We’re talking here about the red dwarf known as
Gliese 3512, which is just thirty-one lightyears away from us, and has a mass that’s only around
one eighth that of our sun. Up until the 2019 discovery, scientists had suspected that only
smaller planets could orbit smaller stars. Earth-sized planets, or perhaps slightly bigger,
but nothing so big as a world that’s half a Jupiter. Since the 2019 discovery, however,
our eyes have been open to the possibility and, indeed, the reality that larger worlds
are out there. And now something similar is happening again, with b Centauri b.
We know that one of the most prominent drives in all of astronomy - from a mainstream news point
of view, at least - is the search for Earth-like worlds. For much of the 2010s, it was the Kepler
Space Telescope that was fuelling so many of the headlines, as super-Earths and second
Earths seemingly presented themselves all across the galaxy. But, as we move through the 2020s,
perhaps the emphasis is changing, and scientists are fully embracing the weirder planets in the
universe. We’re discovering worlds that don’t fit with our best predictions and models,
and that’s prompting everyone - astronomers, cosmologists, anyone with even a passing
interest in space - to adapt their understanding. Nowadays, too, while the search for Earth-like
worlds is still very much in full swing, we’re looking at other star systems and asking what’s
possible? It’s clearer than ever before that our solar system is just one way of doing things.
It’s a well-balanced setup that works particularly well for us, allowing as it does for life on our
planet, but in a universe of infinite variations… what else is out there? The likes of b Centauri b
and GJ 3512 b have caught us by surprise, and they have been widely labelled as places that “should
not exist”, but that idea is already outdated. We of course know that they do exist, and therefore
it’s perhaps a reasonable suggestion that there should be many more planets just like them.
And it truly is a case of watch this space. With major missions, including the James Webb Space
Telescope, set to generate endless streams of data over the coming years, we could well
find ourselves inundated with new exoplanets to study before long. What’s more, there are various
concept missions in the pipeline, too, including the Habitable Exoplanet Observatory (or HabEx)
mission. This is a proposed NASA project that - if the Agency goes ahead with it - will specifically
seek out habitable worlds, based on a wide number of variables. Someday in the future, then,
the HabEx (or something similar) could operate as our first port of call whenever we’re sizing up
another planet for human life that isn’t Earth. What’s clear is that discoveries such as that of
b Centauri b offer a vital contribution to our progress in space. This faraway,
Jupiter-like world, flagged up on a telescope in the Chilean desert in the twenty-first century,
has prompted astronomers all over the world to take note. Here, we have a new type of planet,
a world we’ve never seen before, and something that was once deemed impossible… made possible.
And that’s why scientists have discovered a giant planet that’s cause for celebration…
but it can’t be something that should not exist. Because we now know that it does.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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