This episode is supported by 23andMe.
It's been said that the Apollo missions achieved
all of the science goals that require live astronauts,
that we no longer need manned missions to do science
on the moon.
Whether or not that's true, what about the science
we can do from the moon?
I'm talking about building a telescope there.
Actually, China already has one.
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In December 2013, a Long March 3B Rocket blasted off
in southwestern Sichuan, carrying with it the Chang'E 3
Lander.
After five days of travel and another week of lunar orbit,
it descended onto the surface and became
the first soft landing on the moon since the Soviet Lunar 24
in 1976.
It's been doing science ever since.
That includes soil analysis, extreme ultraviolet
observations of Earth's magnetosphere,
exploration with an ill-fated Rover--
I'll come back to that, and of course, a telescope.
The lunar-based ultraviolet telescope, LUT,
isn't large at only around 15 centimeters diameter,
yet it has one of the clearest views in the universe.
See, the moon has essentially no atmosphere.
That means-- one, the potential for extreme image
sharpness with no turbulence to blow light from above.
Two, Earth's atmosphere blocks all but
a few narrow windows of the electromagnetic spectrum.
From the moon, the entire spectrum is accessible.
And three, on earth, sunlight is scattered to make our blue sky.
On the moon, the stars are visible day and night.
In addition, nights are especially great because they
last a month due to the moon being tightly locked
with the Earth.
The LUT takes advantage of all of these,
but its biggest advantage is that it
can see into near ultraviolet wavelengths
and in the visible range observable
within our atmosphere.
Here's a UV picture of the pinwheel galaxy taken by LUT.
OK, so it's not quite the Hubble Space Telescope.
But remember, LUT is only a 15 centimeter diameter scope.
Some of you probably have bigger telescopes at home.
I know I do.
And the diameter of a telescope's aperture
is everything.
Not only does it allow the scope to collect more light,
increasing sensitivity, but when you're in space or on the moon,
aperture size defines image sharpness.
We talked about this in our recent episode, telescopes
of tomorrow.
The diffraction limit defines the smallest resolution
a telescope can achieve and is inversely
proportional to diameter.
The LUT is a small scope, so its diffraction limit isn't great.
We can think of it as a proof of concept
for building a much larger telescope on the moon.
Normally, there's a pretty strict limit
on how big a mirror you can get into space.
It has to fit in a rocket.
Even clever solutions like the upcoming James Webb Space
Telescope's folding mirrors still have a limit.
In addition, mirrors are notoriously fragile things.
Subject them to the few G's of acceleration
during a rocket launch, and you risk seven billion years
of bad luck.
But on a platform as stable as the moon,
it may be possible to construct a telescope mirror right there.
In that case, there is no fundamental limit to its size.
And there are plans, big plans.
I'm going to come back to a couple of the most
promising in a moment.
But before I do, let's talk about why
we've never sent anything larger than the cute little LUT.
Two of the big challenges the Chang'E program pretty hard.
So Chang'E was named after the Chinese goddess of the moon.
Her mythological pet is Yutu, the jade rabbit.
Appropriately, Yutu is also the name of the Rover sent with
the Chang'E lander.
Poor little Yutu was ravaged by the moon's harsh environments.
It was gruesome.
Let me tell you all about it.
An extremely thin atmosphere confers several advantages,
but it also has its issues.
To start with, Earth's thick atmosphere
is a powerful buffer against rapid changes in temperature.
It warms up gradually during the day
and cools gradually during the night.
There is no such protection on the moon.
When exposed to the sun, temperatures
rise to around 125 Celsius, well,
above the boiling point of water.
But put up some shade, and temperatures drop
to minus 150 Celsius or lower.
During it's relatively short roll on the lunar surface,
Yutu was experiencing a massive temperature differential
between its sunny side and shaded side.
That fried and frozen robot stopped moving pretty quickly.
Even with no mobility, Yutu's science instruments
remained operational for a couple of years
before succumbing to a worse problem.
Tiny shards of electrically charged glass--
in other words, moondust.
See without an atmosphere there is no erosion
of the lunar regolith.
This is the upper surface of the moon that
has been pulverized by 4 and 1/2 billion years of meteor
impacts.
Hit by sunlight, tiny regolith particles
build up electric charge, and so repel
each other into dust fountains in the low lunar gravity.
They stick to electronics, impede solar panel function,
and grind away at moving parts, nasty stuff.
It eventually killed Yutu.
Fortunately, the Chang'E telescope is better shielded,
and so it's still operational.
However, the greatest obstacle to putting a telescope
on the moon is, of course, getting it there.
But in that challenge, this evil moondust
may actually be our friend.
Perhaps we can build mirrors out of the stuff.
Pete Ching, at NASA's Goddard Space Flight Center,
proposes shipping a relatively small amount of epoxy
and carbon nanotubes and combining it
with a whole lot of moon dust to make a sort of concrete.
Grind it into shape and coat it with aluminum,
and it may be possible to build a 50 meter mirror on the moon.
They've already built a 1 foot prototype
and are planning a much larger test telescope here on earth.
Just as ingenious is the idea of a liquid mirror telescope.
When a cylindrical container of liquid
is rotated into a gravitational field,
the liquid assumes a smooth parabolic shape,
exactly the shape needed to bring light to a perfect focus.
Liquid mirror telescopes already exist on earth.
The biggest is British Columbia's Large Zenith
Telescope.
It spins a six meter dish of mercury
at 8.5 revolutions per minute, creating the cheapest telescope
of that size ever constructed.
The caveat is that it only points straight up.
Tip it and the parabola is ruined.
Tip it too far, and you spill mercury
all over your grad student.
But what you can't do with hardware,
you fix with fast cameras and software
to reconstruct a still image.
Its also possible to correct with
a movable secondary mirror.
Pointing options are still limited,
but by taking advantage of Earth or the moon's rotation,
it's possible to scan a narrow arc across the sky.
But mercury is expensive, heavy, and likely
to evaporate in the moon's low pressure Atmosphere Pete
Worden, Director of NASA's Ames Research Center and Ermanno
Borra of the University of Quebec, are working on a plan
to instead use nonevaporating ionic liquids, basically molten
salts for the mirror base.
They'll coat it with 50 to 100 nanometers of silver,
which will solidify on the slowly flowing surface.
Lower gravity could facilitate the formation
of large liquid mirrors, maybe up to 100 meters across.
Such a telescope could gaze on the universe
from when it was just 500 million years old.
It's a cosmologists dream, especially
because cosmology tends not to require complex pointing.
The whole liquid mirror configuration
would weigh a few tons and could possibly
launch in an Aries 5 Mission in the 2020s.
Maybe I'm biased by the cool factor,
but this all sounds like a great reason
to get back to the moon, both robotically and in person.
Plans are underway.
More Chang'E missions will launch over the next couple
of years
The International Lunar Observatory Association
in combination with Moon Express formed
the first private enterprise to receive approval
for lunar landing.
They're hoping to set up an optical telescope
just 7 centimeters in diameter, which is small.
But momentum is building.
And Moon Express has a manned base in the planning,
useful if we really want a giant lunar telescope.
The moon with its thin atmosphere, stable surface,
and long nights is an astronomer's dream.
If we can meet its distant challenges
with creative solutions, perhaps the moon
will become the Earth's lookout tower,
granting the clearest views of all the rest of space time.
Thanks to 23andMe for sponsoring this episode.
The name 23andMe comes from the fact
that human DNA is organized into 23 pairs of chromosomes.
23andMe is a personal genetic analysis company
created to help people understand their DNA.
You'll be able to see which regions around the world
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your facial features, hair, sense of taste and smell,
even sleep quality.
Learning this information starts with just spitting in a tube.
And within a few short weeks, you'll see your results.
I'm sending in some of my DNA, and I'll share the results
with you on a future episode.
My background is Irish, and there's
just one story in which one of my ancestors married a mermaid.
I'm not sure whether they fully sequenced a mermaid genome yet,
but I'm really excited to see if there's anything
really weird in my DNA.
Go to 23andMe.com/Spacetime to support the show and learn more
about your personal DNA story.
As always, a huge thank you to all our Patreon supporters.
And an especially big thank you to Shane Robinson,
who just joined us at the Big Bang level.
Shane, thank you so much.
This is going to be an enormous help.
Last week on "Space Time," we talked
about time space, the way time and space, which rolls,
beneath the event horizon of a black hole.
You guys had a lot of good comments.
Feinstein 100 asks whether energy
could be extracted from the flowing space
time inside a black hole.
Well, not really from the flow of space time actually
inside the black hole.
You could transform the gravitational potential energy
of things falling towards the event horizon
into usable energy.
Quasars do this all the time to power
their insane luminosities.
Hydroelectric power plants on earth
do it with the flow of space time
that we experience as Earth's gravitational field.
Falling converts gravitational potential energy
into kinetic energy but that kinetic energy
is only positive relative to something
that's not also in freefall.
It's tricky to find a solid surface inside a black hole.
One possibility could be in a Reissner-Nordstrom black hole,
so one with electric charge, but no spin.
Here's a weird black hole fact.
The electric field in a charged black hole at the singularity
is expected to produce an antigravitational effect
through negative pressure, in a way that's mathematically
similar to dark energy.
So there should be a point inside such a black hole
where this anti-gravity perfectly
balances regular gravity, and it's possible to float.
You'd also expect that surface to contain
a vast amount of energetic particles converted
from infalling material.
So I mean you could try to use that energy for something,
like being instantly fried.
I see a whole episode here, so I'll leave it at that.
NuclearCraft Mod spotted a missing plus sign
in our full [INAUDIBLE] line element.
Well, I bet you were a real pain for your professors.
But you also give nice compliments,
so I'm sure they forgave you for calling out their wrongness
all the time.
By the way, speaking of those extra angular components
in the line element, AntiTwister over at the Space Time
subreddit had some interesting thoughts.
He points out correctly that it's only the radial component
that becomes timelike.
The sideways components, angular or orbital components
in spherical coordinates, stay space-like.
But they become degenerate close to the singularity.
That means that just before you reach the singularity, perhaps
your sideways extent should wrap around and merge with itself,
just before you merge with the singularity.
Sort of like a piece of tortellini,
except that you'd be spaghettified before that
happened.
So do you get infinitely spaghettified
before you are tortellinified?
Sounds like a challenge question.
Nazar Chadhi left this wonderful comment
for anyone reading deep in the comments section.
Hey, Nazar.
Thanks for your kind words.
My day is going great.
I hope yours is, too.