Hi I’m Alex McColgan, and you’re watching Astrum.
Now today we are going to be looking at the beautiful yet hellish planet of Venus.
We’re going to be delving into what makes this planet so unique in our solar system,
so get ready to find out everything you could want to know about Venus.
Visually, it is a very beautiful and elegant planet.
Seemingly very calm and almost tranquil on the surface.
From an outsider’s perspective, it’s clear why it’s named after Venus, the Roman god
of Love.
Go beneath the cloud layer, and you’ll find quite the opposite.
Scorching temperatures, volcanism and a crushing atmosphere are what you'd actually find on the
surface.
But let’s step back a bit and see where this planet fits in our solar system.
Venus is the 2nd planet from the Sun and is our closest neighbour.
Its average orbital radius around the Sun is 0.72AU or roughly 108 million kms.
It doesn’t vary much at all from this mean orbital radius, as it’s the planet with
the least eccentric orbit, orbiting nearly in a perfect circle.
At Venus’ closest approach to us, it is the closest of any other planet, being only
41 million kms away.
Interestingly though, this is not when it’s brightest in our sky, as when its closest
to us, we only see the night side as it’s between us and the Sun.
It is still visible though as the sunlight refracts through the atmosphere.
It’s actually brightest when it’s a thinner crescent shape in the sky, and when this happens,
it is the brightest object in the night sky after the moon.
As such, Venus is a commonly misreported "unidentified flying object".
U.S. President Jimmy Carter reported having seen a UFO in 1969, which later analysis suggested
was probably Venus.
Countless other people have mistaken Venus for something more exotic due to its startling
brightness.
I recently had the pleasure of looking at Venus through a telescope and remarkably the
crescent shape of it was very visible.
With Venus orbiting between us and the Sun, it may make you wonder if Venus ever eclipses
the Sun from our viewpoint on Earth, and the answer is yes, but surprisingly, very rarely.
Transits happen in pairs, the pairs being 8 years apart, but every pair only happens
once every 100 or so years.
The last transit we had was in 2012, but if you didn’t see that I’m afraid the next
one won’t be until 2117.
The reason for this rarity is because the orbiting plane of Venus is not exactly the
same as Earth’s.
Also, Venus only catches up with Earth every 584 or so days.
These two things combined ensure that although a spectacular and predictable sight, it also
means we’ll probably only ever have the chance to see it twice in our lifetimes.
All the planets orbit anticlockwise around the Sun and with this, Venus is no different.
But unlike all the other planets it rotates clockwise, or in other words in a retrograde
rotation.
Not only that, but it has an extremely slow rotation, rotating once every 243 Earth days
– slower than any other planet.
This makes a sidereal day longer than a Venusian year, a Venusian year lasting 224 Earth days.
A sidereal day, if you remember from the Mercury episode, is one rotation of the planet.
Because of this retrograde rotation though, a solar day (which is sunrise to sunrise)
is considerably shorter, at 117 Earth days.
This means you’d only experience just less than 2 days on Venus in one year.
To give some perspective as to how slowly it rotates, at the equator the planet is only
rotating at 6.5km/h!
This slow rotation makes it the second most spherical object in the solar system, after
the Sun.
It is unclear why Venus rotates backwards compared to the rest of the planets, but it
could be due to a big impact with another object billions of years ago, or tidal locking
with the Sun, or tidal effects on the Venusian atmosphere.
Its mass and size are very similar to our Earth, hence why it’s often referred to
as our sister or twin planet.
Venus is one of the four inner terrestrial planets and it is a rocky planet.
Its diameter is slightly smaller than Earth’s at 12100km compared to 12740km and its density
is 5.243 g/cm3 compared to our 5.514 g/cm3.
This means the gravity on Venus is only a tenth weaker than on Earth, surface gravity
being 8.87 m/s2, or 0.9g.
But this is where the similarities end.
On the surface of Venus, the atmosphere’s pressure is 92 times greater than on Earth’s.
That’s an equivalent of 1km under Earth’s oceans.
The reason for this is because the density of Venus’ atmosphere is 93 times greater
than Earth’s.
And fit that amount of gas into a space slightly smaller than what we have here on Earth, and
you can understand why it’s so densely packed.
The atmosphere consists mainly of CO2 gas, and combined with sulphur dioxide clouds,
you’re left with the strongest greenhouse effect in the solar system, with temperatures
462c at the surface on average.
This makes the surface temperature greater than Mercury’s, even though Mercury is the
closest planet to the sun and Venus only gets 25% of the solar radiation Mercury does.
The difference is that Mercury doesn’t have an atmosphere to retain the heat, whereas
Venus certainly does.
This means at night time and even at the poles, the temperature remains fairly constant.
Venus really is cooking, it absorbs so much heat but like a thermal flask it retains it
and doesn’t let much escape.
With an axial tilt of only 3 degrees, it also means seasonal changes in temperature are
also very minimal.
Wind speeds aren’t very high on Venus’s surface, only being a couple of kilometres
an hour, but because of the thickness of the atmosphere it applies a very strong force
on obstructions, moving small rocks and dust across the surface.
On the other hand, wind speed at the cloud layer is much faster, reaching speeds of 300km/h.
These winds at the cloud tops circle the planet about every four to five Earth days which
makes the planet look like its rotating a lot faster than it actually is.
The cloud layer itself sits above the thick CO2 and consists mainly of sulphur dioxide
and sulphuric acid droplets.
Sulphuric acid, just as a side note, is highly corrosive and this acid rain just adds to
the hellish nature of Venus, although it does evaporate before it hits the surface.
The clouds on Venus are highly reflective, only allowing about 10% of the sunlight through,
and because they cover the entire planet, it obstructs a visual view of the surface
from space.
These clouds are also capable of producing lightning much like on Earth, although not
as common.
Recently it has been discovered that Venus has a large vortex at the South Pole much
like on Saturn.
Venus is the image on the left, and Saturn on the right.
They are shaped quite differently, and Venus only has the one storm, whereas incredibly
every single black dot in the Saturn image is a separate storm, with the main vortex
in the centre.
The vortex on Venus is at an altitude of 59km which is just above the cloud deck.
Which leads on to an interesting point about the atmosphere of Venus.
At about 50km up, the air pressure and temperature are tolerable for Earth standards.
Even the gravity would feel very much like Earth.
The only problem with a person being there is the air itself.
But if you were to have an airtight plane or something, conditions would be very Earth
like.
I want to head back down to the surface of Venus a little bit, as we actually have real
photos of the surface thanks to the pioneering efforts of the Russians back in the 60s to
80s.
The probe Venera 7 in 1970 was the first probe to ever land on another planet and send back
data, the previous attempts resulted in the probes signal terminating before touchdown.
Venera 7 probably fell over on impact though, and so the only reading it gave was the temperature
at the surface of 475 degrees.
Venera 8 confirmed that at the surface the visibility was quite clear, with about a km
range, as the cloud layers end at quite a high altitude meaning it was suitable for
cameras in future missions.
Venera 9 sent back the first ever image of the surface of Venus.
Venera 10, 13 and 14 over the course of 6 years sent back more imagery, this time in
colour, as well as a lot of data regarding the conditions of the planet.
Since then, there have been a number of probes that have mapped out the surface of Venus.
Using radar, they were able to see through the cloud cover and see the planet’s landscape
in very high definition.
The surface of Venus is dotted with a lot of big, but not necessarily active volcanos.
It has 167 volcanos which are over 100km in diameter.
The only complex this size on Earth is the big island of Hawaii.
This doesn’t mean Venus is more volcanically active than Earth, but this is due to the
fact that Venus has a much older crust than Earth.
Earth has plate tectonics releasing heat and renewing the surface fairly regularly, (regularly
being 100 million years) but Venus doesn't have any plate tectonics.
Instead its crust is estimated to be about 300-600 million years old, when a global resurfacing
event likely occurred.
The theory is that the mantel under the crust heated up so much that it forced its way through
the crust, covering most of the surface with lava.
An incredible 80% of Venus' surface is made up of cooled lava plains, and there are literally
hundreds of thousands of volcanos in one form or another.
There are 900 impact craters also to be found on Venus, although none less than 3 km in
diameter.
This is because anything smaller than 50m in diameter would fragment and burn up before
it even hit the surface.
And finally let’s have a look at the magnetosphere.
Venus doesn’t have its own magnetic field, which surprised everyone when it was first
discovered as Venus’ composition is similar to Earth’s.
But without more data, it’s hard to say why this might be.
As a result of this, solar and cosmic radiation interacts a lot with the upper atmosphere
of the planet, producing lightning and an induced magnetosphere.
Solar wind also strips off the low density molecules out of the upper atmosphere meaning
that Venus has a tail, similar to a comet.
Under certain conditions, this tail can tickle Earth when they in conjunction with each other.
Unfortunately this tail isn’t visible with the naked eye.
Sadly, we''ve come to the end of the video.
But I'd just like to say thank you so much for watching this far.
And if you enjoyed it, I have a lot of other videos about our other planets which may be of interest to you as well.
So be sure to check those out!
And if you find space generally interesting, please subscribe! As this channel is dedicate just to that.
Thanks again for watching and see you next time.