Hubble has just celebrated its 30th Anniversary of peering into the far reaches of the cosmos,
capturing spectacular images of galaxies and nebula many light years away.
But even though it wasn’t designed for it, did you know that Hubble has also looked at
objects much closer to home, objects found in our own solar system?
And because it did so, it allowed us to view planets and worlds without their own dedicated
missions, to see events that we would have otherwise missed.
I’m Alex McColgan, and you’re watching Astrum, and in this episode of the Hubble
Images series, we will again explore some of the spectacles that occurred in our own
Solar System that Hubble has witnessed.
Number 55, Hippocamp.
The outer ice giants, Neptune and Uranus have largely been forgotten by space agencies around
the world, only ever having one flyby in 1989 by NASA’s Voyager 2 probe.
This means that our knowledge about these massive worlds is still pretty limited, and
it would be more limited still were it not for Hubble observing them from time to time.
One of the major discoveries Hubble made about Neptune was the discovery of a new moon in
2013, which has now been named Hippocamp.
Now, Hubble has discovered many moons in its time, especially around Jupiter and Saturn,
but what makes Hippocamp special is that it could well be a fragment from the much larger
moon of Neptune, Proteus.
The 400km wide moon does indeed look like it has had a tumultuous past, with giant impact
craters 50-100km in diameter.
One of these collisions likely fragmented parts of Proteus, which then fell into orbit
around Neptune.
Hippocamp is probably the biggest fragment, as it’s an irregular, 35 km long object,
and it orbits fairly closely to the larger Proteus.
While we’re here, let’s move onto number 56, which is about Neptune itself.
As I mentioned before, Hubble was never really designed to monitor our solar system, however
in 2015 it was decided to dedicate more of Hubble’s time to the outer ice giants, having
roughly one observation per year.
This has meant we can better monitor seasonal changes in those planet’s atmospheres.
One of the most noticeable of these changes are the giant storms spanning thousands of
kilometres.
Voyager 2 saw one such storm as it passed Neptune back in 1989, which was later dubbed
the Great Dark Spot, comparable to Jupiter’s Great Red Spot.
However, unlike Jupiter’s storm, the one on Neptune has since disappeared altogether.
Other storms have come and gone, and the latest one was seen in 2015.
It has lasted a few years, but it too is disappearing.
While there is not enough data to speculate how these vortices develop, it could be that
Neptune is like Jupiter with bands in the atmosphere.
While they won’t be as defined or as many as there are on Jupiter, the bands on Neptune
would travel at different speeds.
This could cause vortices to appear where the bands meet.
Once the storm has got going, it can drift around the planet, even between bands, but
once it leaves its power source, it begins to slowly diminish, which is what we have
seen.
Interestingly, Hubble is the only program that can monitor these weather changes, as
in most light wavelengths, they are very hard to spot.
Hubble, though, can probe Neptune and Uranus in the ultraviolet.
Number 57, 2007 OR10.
You would be forgiven if you have never heard of this object before, even if it is the third
biggest dwarf planet in our solar system, third only to Pluto and Eris.
And like them, this dwarf planet is also found billions of kilometres away in the Kuiper
belt.
While this object was not discovered by Hubble, Hubble did find out that it had a moon.
It was not discovered by the original investigator as it was very faint in the images, however
recently a research team had a suspicion that 2007 OR10 could have a moon as it has a slow
rotation, about 45 hours.
Most other Kuiper belt objects rotate in under 24 hours.
It was hypothesised that a moon’s gravitational tug may have slowed it down, and after searching
some archival Hubble data, it proved to be so.
This discovery means that nearly all the dwarf planets in the Kuiper belt have now been found
to have their own moons.
This could be because out in the Kuiper belt, objects move pretty slowly.
This means that if there ever were collisions between objects, then fragments would have
stayed in orbit around the body, rather than escaping the object’s gravity.
This could be why asteroids in the asteroid belt don’t tend to have moons, collisions
there are a lot more energetic, meaning debris just shoots off into space.
Finding the moon around 2007 OR10 means that we can have better constraints on our solar
system formation models, so useful data indeed!
Number 58, Jupiter’s aurora.
Earth isn’t the only planet to experience auroras.
While you can see aurora with your naked eye occasionally on Earth, auroras are actually
brightest in the ultraviolet!
As I mentioned before, Hubble can detect ultraviolet light, meaning we can closely observe this
phenomenon on other planets too.
Jupiter’s is the easiest to spot, it’s the biggest and closest of our neighbouring
gas giants, and its powerful magnetic field and strong radiation produce a bright aurora.
In 2016, the Juno spacecraft was on its way to Jupiter, which provided scientists with
a unique opportunity to measure solar wind on its way to Jupiter with the Juno spacecraft,
and observe subsequent changes in the aurora with Hubble.
As a result, Hubble observed Jupiter almost every day for several months.
What Hubble found out was that these auroras are hundreds of times more powerful than on
Earth, with a radiant power of 100 terawatts, but also surprisingly, they never cease.
On Earth, aurora light up around the poles during a solar storm.
This implies that auroras on Jupiter are not just powered by the solar wind.
Since Juno has arrived at Jupiter, the data it has collected suggests that the auroras
are mainly powered by charged particles in Jupiter’s fierce radiation belt, which feed
into the planet’s atmosphere via its magnetic field lines.
The magnetic field also has been found to produce alternating currents rather than direct
currents.
This accounts for the radiant energy of the aurora, which would be impossible if energy
was transferred through the magnetic field via direct currents.
Number 59, Europa.
For those of you that don’t know, Europa is a large moon of Jupiter, and is one of
the most promising candidates for life in the solar system.
We aren’t expecting to find anything on the surface, but rather underneath in an ocean
of liquid water.
Europa is an icy world and being this close to Jupiter produces extreme tidal flexing.
The theory goes that the energy produced from the tidal flexing keeps the underground ocean
warm enough for it to remain liquid.
Various missions have since been looking for evidence of this ocean.
Surprisingly, Hubble has been very helpful in this endeavour.
Galileo and the Voyagers were able to produce much higher resolution images of Europa compared
to Hubble because they passed the moon by reasonably closely, however these missions
were not able to observe in the ultraviolet.
With this ability, Hubble has spotted possible plumes of water erupting on Europa’s surface.
Volcanic activity would imply that the interior mantle of Europa is liquid, and because it
must be water, this suggests the ocean theory is correct.
Since the first observation, lots more plumes have been detected.
Hubble’s vision was utilised again to detect salts on Europa’s surface.
Most missions use infrared to examine a planet’s surface, as most of the interesting emission
bands of substances are found in the infrared.
However, sodium chloride, or salts similar to those found in our oceans, are mainly visible
in the visible light spectrum, which means these salts on the surface of Europa were
undetected by Galileo.
Hubble, viewing in the visible light spectrum, confirmed that sodium chloride is found all
over the surface of Europa, likely having originated from the underground ocean, and
then carried up in the plumes to be deposited on the surface.
The exciting prospect about an ocean of sea salt is that it indicates the ocean floor
could be hydrothermally active.
These thermal vents on Earth can be a hive of life, so scientists are excited to investigate
this further, although sadly, we may still be a few decades from having a submarine mission
to check this out.
Number 60, Uranus.
Much like Jupiter and Neptune, Uranus has also had Hubble observe storms on its surface,
and even had aurora detected around its magnetic poles, which apparently do not line up with
the rotational axis at all.
Uranus’ rotational axis is already pretty weird, appearing to be on its side compared
to the rest of the planets in our solar system.
This means that at some points in Uranus’ year, it appears to roll along its orbit.
It also means that it hardly ever experiences a solar eclipse from its moons.
2006 was the first opportunity we have had to witness this event, as the last time the
moons were aligned correctly was in 1965, before telescope technology was good enough
to see a satellite transit on an object so far away.
Hubble not only saw Ariel’s shadow crossing over Uranus’ surface, but also saw a complete
view of Uranus’ bands.
Since this equinox view, through Hubble observations of Uranus over a section of its lengthy 84-year
orbit, we have also been able to see seasonal variations develop in the atmosphere.
As a pole becomes more exposed to the Sun, the atmosphere seems to get lighter in colour.
This is believed to be a large cloud cap that forms during that hemisphere’s summer and
it is expected to dissipate again as Uranus heads back towards its year’s equinox.
As Hubble is only 30 years old, it hasn’t even been able to see half a year on Uranus,
so there’s still a lot to learn about its seasons yet!
You can see from just this episode how important Hubble has been to humanity’s knowledge
about space and our solar system.
And it has done far more than just this over the course of the last 30 years.
Hubble may well be the most important space mission to date, expanding our horizons and
providing data that will be utilised for many years to come.
And the good news is that Hubble may well stick around for another 10-20 years.
I’m excited for what the James Webb Space Telescope will bring, but this is definitely
a good time to appreciate Hubble’s accomplishments and I look forward to what the future will
bring for it too!
If you want to see more of what Hubble has done, I recommend checking out my Hubble playlist
here!
Thanks for watching!
And thanks to all of you who make videos like these possible, from your views, likes and
shares.
A big thanks as well to those of you who are members and patrons, your support really goes
a long way.
If you find value in these videos, and would like to support to, check out the links in
the description.
All the best and see you next time!