Thanks to Babbel for sponsoring today’s video. On Earth, we are used to our years lasting way
longer than our days, and because of this, it doesn’t come naturally for us to imagine how
in other parts of the universe, years and days can be very, very different from what we are used to.
I want to have a look at the extremes of what a year can look like in this video,
a look at some of the longest and shortest years that we know of.
Let’s start off close to home. Mercury has a pretty short year,
only 88 Earth days, which is the shortest orbit that we know of in our solar system. And very
interestingly, due to the way Mercury rotates, one Mercurian day is twice as long as its year.
Yes, there’s exactly two years in its solar day, so, should anyone ever live on Mercury, you would
have to switch around your way of thinking when it comes to describing a shorter reference of time.
But its kind of cheating to say a year on Mercury takes half a day,
when it still takes 88 Earth days. So, let’s keep to Earth time scales as the point of reference.
Outside of the solar system, most exoplanets that we know of have really short years, and
that’s because of the way we detect the majority of exoplanets. There are observatories that look
closely at thousands of stars at the same time, looking to see if an orbiting exoplanet passes
in front of its parent star, causing the star to dim ever so slightly from our perspective.
In order for us to confirm that the dip in brightness is caused by an exoplanet,
we need to see a pattern of dips in regular intervals.
So, if an exoplanet does transit a star, but its year takes 2 Earth years before it transits again,
then we’d need to be constantly monitoring the star for many years before we can confirm that
the dips in the star’s brightness are caused by an exoplanet. On the other hand, exoplanets
with really short years, like a few days or weeks long, can be confirmed as exoplanets very quickly.
This means that most exoplanets that we know of take only a few days to orbit.
The famous Trappist system exoplanets all orbit their parent star within one month,
the closest planet to the star takes only 1.5 days. So, out of all these thousands of exoplanets
that we have discovered so far, which one has the shortest year? Incredibly, there is a pulsar out
there which has a planet, although it could also potentially be the core of another collapsed star,
which orbits around the pulsar in only 48 mins 58.5 secs. How can this happen?
Well, not only is the orbiting object extremely close to the pulsar, but it is moving very fast.
A neutron star is also very small, at most only around 30km across, yet it is incredibly massive,
so much so that its gravity even bends light around it. So, a fast-moving close object can
stay in orbit because the neutron star’s gravity is strong enough to keep it there. Although,
you may say this is cheating again. A pulsar isn’t really a star. More like a star remnant.
So, what about a main sequence star? In this case, the shortest year that we know of goes to K2-137b,
a planet that’s year lasts only 4.31 hours. Because it is orbiting a main sequence star, the
Earth sized exoplanet is surely orbiting within the star’s atmosphere and will eventually either
be ripped apart by tidal forces or fall into the star completely as atmospheric drag slows it down.
On the other end of the scale, the longest year that we know of belonging to a planetary
mass object is this beautifully named planet. This Jupiter type object’s year lasts roughly
1,000,000 years. Although, there’s another type of year that lasts even longer than that,
and that is what we call a galactic year, or in other words,
the time it takes to orbit the galaxy. For us, that is roughly a mind boggling 250 million years.
So, assuming the Earth is 4.5 billion years old, that makes Earth a galactic teenager,
only 18 galactic years old. And the fascinating thing is that there will be galaxies out there
that take even longer to complete one rotation, our galactic year would be comparatively short.
So there we have it, the longest and the shortest years out there.
Isn’t space a marvellous place? Our lifespans are barely a blink of an
eye relative to some years out there, yet relative to others, we would be millions of years old.
Today's video is sponsored by Babbel, the number one language learning app in the world.
As some of you may know, I live in Switzerland currently as my wife is Swiss, but despite this,
my German ist nicht so gut. So, I was excited when Babbel approached me as I thought this would be an
excellent tool to help me brush up on my German. The app started out by finding out my level,
and then gave me a lesson based on what it felt I needed to work on.
I really like it so far, I can do it on my PC or my phone, and the courses integrate vocabulary
and grammar with real life situations, so I can know why I should use certain words in different
situations in a way that’s relevant, which is something I have really needed help with.
If you have a language you want to learn from scratch, or a language you want to brush up on,
I highly recommend Babbel. In fact, studies have shown that 15 hours of Babbel is the equivalent of
a semester of learning a language at college. If you use the link in the description, you can get a
6-month subscription at 50% off, so definitely at least check it out for more information!
Thanks for watching. If you want more Astrum Answers, check out the playlist here. Also,
if you want to help pick the next question and support the channel,
become a patron or a member today! All the best, and see you next time.