When it comes to the universe, it’s all a matter of balance. Moons orbit planets,
planets orbit stars, stars orbit their galactic center, and galaxies play off of one another
as they make their steady way through the cosmos. Put it all together and you have
a mighty impressive lightshow! But, in amongst the infinite expanse of space,
there’s also infinite room for things to behave not as we’d necessarily expect,
and therefore potentially threaten that balance. And, in one star system far, far away,
that’s exactly what could be happening. This is Unveiled, and today we’re answering
the extraordinary question; did this new massive planet break the rules of the universe?
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While, in 2022, it’s been the newly launched James Webb Space Telescope stealing most of
the headlines, its predecessor still has a lot to offer to science. The Hubble Space Telescope
has been busily scanning the skies since it was launched way back in 1990. And it’s
thanks to Hubble’s incredible longevity that this latest discovery was possible. In the year 2007,
Hubble spotted (and photographed) a particular object in a particular part of the universe,
the proto-exoplanet now known as AB Aurigae b. Then, in the year 2021, the same planet was
photographed again, to monitor its progress, and details were released in 2022, with an in-depth,
multi-authored study also published in the journal “Nature Astronomy”. The images themselves appear
little more than an orange-red blur to anyone not attuned to exactly what they show, but astronomers
have gotten quite excited by them - mostly because they appear to show a planet that
must have formed in a quite unusual way. The AB Aurigae system is centered around a young
star, some 530 lightyears away from us. It’s not likely, then, to ever directly affect our
particular corner of space. And yet, we can learn just a little bit more about the solar system,
our galaxy, and the universe in general just by looking at it. The visuals produced by Hubble (in
conjunction with the Subaru Telescope, located in Hawaii and operated by the National Astronomical
Observatory of Japan) have provided insight into a little-known planetary behavior. The
planet AB Aurigae b is widely described as being Jupiter-like in terms of composition, but it’s
also around nine times the mass of Jupiter… and it orbits some ninety-three astronomical units
away from its star. Which is a seriously long way. It’s more than eight-and-a-half billion
miles. For comparison, the Jupiter that we know orbits just a little over five astronomical units
away from its star. Even Neptune, the furthest planet from the sun, is only a third of AB Aurigae
b’s distance, at around thirty AU. The reason why this is so strange
is because the leading model of planet formation doesn’t really allow for planets to form at such
an incredible distance. And yet, we know that AB Aurigae b is there… having been birthed
out of a protoplanetary disk of debris like all planets are. For a long while, the leading theory
on how Jupiter-like worlds like this form - huge, enigmatic gas giants - has been something known
as core accretion. This is when a planet’s core is gradually forced into being, as small
chunks of debris in the protoplanetary disk are brought together, via collisions and mergers.
Over time, a stable core is made, which attracts more and more material, until voila you have a
planet. But that can’t be what’s happening here, because AB Aurigae b is simply too far away.
Its orbit is too long and too wide, to the point that core accretion should just take far
too much time, even in cosmological terms… or it could, in fact, be impossible. So,
what’s actually happening? We have clear evidence that a planet exists… but, based on the most
prominent theory, we don’t immediately know how it exists. There is, however, another approach.
As well as core accretion, scientists also refer to the disk instability model.
And, while it’s not quite as popular an explanation as to how planets form in general,
it could be what happened to bring AB Aurigae b into life. Disk instability is in many ways the
reverse of core accretion. While core accretion relies on space debris drawing itself together
to form something bigger than its smaller parts… disk instability relies on would-be-core objects
breaking free of the protoplanetary disk. Those at Hubble describe it as a
“top-down model” where a massive disk cools, and gravity “causes the disk to rapidly break up
into one or more planet-mass fragments”. In particular, it’s a candidate for what could
be happening whenever a planet forms far away from its star. Under those conditions,
the protoplanetary disk is massive, cutting (as it does) a hugely long-distance path around its
gravitational anchor. And, if we were to somehow teleport ourselves to the AB Aurigae system
right now to view it from the outside, then a setup like this is what we’d find.
Perhaps some of the surprise around this planet, then, AB Aurigae b, is a little
unexpected. After all, it’s not as though it’s a world that has truly appeared out of nowhere.
Science is fairly certain of a way in which it could’ve come into being, it’s just that
it’s a totally different way compared to the gas giants in our own star system. But that,
of course, makes it extremely interesting. It may continue to be described as Jupiter-like
forever more… but, in terms of its origin, it story is quite unlike what Jupiter experienced.
But what else can be derived from this observation? In some ways, this is just the latest
on an ever-lengthening list of new planets found. But could it also have repercussions for us,
here, in the solar system? What if, for example, disk instability had happened in
our corner of space, too? Would that mean that a similarly distant (but unknown) planet could
be orbiting the sun right now, way beyond Neptune or even Pluto? There are, of course,
various theories pertaining to a “Planet Nine”, a proposed hidden world that’s said to cruise
through the very outer edges of the solar system… waiting for us to one day find it. And, really,
if there were a planet so far out from the sun that we still haven’t actually discovered it…
then perhaps it would have been formed via disk instability. However, as yet, there’s little
by way of solid evidence that Planet Nine does exist. There are many compelling possibilities
(many of which we’ve investigated in a previous video) but, so far, there’s been no great moment
of discovery or revelation. There’s been no great arrival of another solar system world.
As for the Hubble Telescope, what will become of it now that the James Webb is up and operational?
For so long it’s been an astronomical icon and a symbol of humanity’s technological drive,
but is it on its way out? Will it still be around in another fourteen years or so, for example,
to take another picture of AB Aurigae b and update us on its progress? Sadly,
the answer is “probably not”. While Hubble doesn’t have a specific date at which it will
end its service, predictions are that it will finish sometime in the late 2020s or 2030s.
When it does so, there are a couple of options, including allowing it to fall back to Earth… and,
if it does drop from the sky then it’ll truly be the end of an era. Arguably more so than any
other mission or machine, Hubble has opened up the universe to us. It’s helped solve
countless mysteries and has infinitely added to our collective knowledge. And, really,
the charting of AB Aurigae b, an alien world that’s hundreds of lightyears away from us, is
a prime example of exactly what Hubble does best. So, what’s your verdict on AB Aurigae b? Should
its existence mean that we start viewing all star systems with an entirely new perspective?
Has the hunt for exoplanets just been blown wide open? Might the disk instability model have
more influence on the universe than it’s currently given credit for?
In some ways this does rank as a particularly significant study, and AB Aurigae b can
be considered something of a maverick world alongside most of the rest of the other planets
we know about. But, also, science does at least have an answer as to how it came to be there.
Core accretion remains the prevailing method for planet formation we’ve theorized so far,
but disk instability offers another option. So, while it might not be exactly fair to say
that it’s broken the rules of the universe… that’s why this planet is at least a little
unconventional. When it comes to the universe, it’s still all a matter of balance… but AB
Aurigae b is proof that there’s more than one way to exist within it.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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