We've explored a lot in our solar system over the past few decades.
Jupiter's moons, Mars, Neptune, even a comet!
But one place we haven't gone is into the Sun.
For kind of obvious reasons, but that is about to change.
In 2018, NASA plans to send a car-sized probe known as Solar Proble Plus
into the corona, or outer atmosphere, of the Sun.
That's the crown of light you see surrounding the body of the sun during a solar eclipse.
A few previous missions like Helios 2 in the 1970s
orbited the sun at a distance of 43 million kilometers to give us a closer look.
But Solar Proble Plus will get much, much closer. Only 6.2 million kilometers away.
Scientists hope that this mission will solve the mystery that has plagued solar science for decades:
Why is the corona hotter than the surface of the Sun?
Since the 1940s, scientists have known that the corona generates shorter wavelengths of light
which corresponds to higher temperatures compared to the visible surface of the sun
also known as the photosphere.
The differance in wavelengths is so great that astronomers actually think the corona
is 200 times hotter than the Sun's surface.
Which is confusing because normally fall when you move away from a heat source.
Which is actually true in the Sun's interior.
At the core it is 16 million degrees Celsius. But further out into the photosphere
it's a balmy 6 000 degrees Celsius.
But then temperatures rise a few million degrees when you enter the corona
about 500 kilometers above the photosphere.
The corona, which is made out of highly ionized elements like iron, helium and calcium,
is so hot that the Sun's gravity can't hold onto it.
As those atoms get all agitated by the extreme heat, ribbons of plasma called solar winds
peel off from the corona and begin accelerating away from the Sun at speeds of up to 900 kilometers per second.
These solar winds contain high levels of radiation that can harm satellites as well as astronauts in deep space.
So NASA wants Solar Probe Plus to help us understand what's heating
the corona and accelerating those solar winds.
The craft will use Venus' gravitation to sling it around the Sun 24 times over seven years,
getting closer to the corona with each orbit.
On it's closest approach the craft will skirt the outer edge of the corona
where temperatures only reach 1 300 degrees Celcius.
Which is still super hot!
Similar temperatures were generated when the space shuttles reentered Earth's atmosphere.
That's why the solar probe will have a thermal protection system.
Including a heat shield shaped like an enormous dinner plate, eleven centimeters thick and 2.5 meters in diameter.
It'll be made out of carbon composite and silica foam, which is the same stuff we used on the space shuttle.
The probe's electrical systems meanwhile will be powered by two sets of solar arrays,
Because... There's a lot of sunlight when you're going into the sun.
The first set of arrays will be bigger and will be used on the initial leg of it's journey.
Once the probe enters the corona however, those panels will retract and two tinier
liquid-cooled arrays will do the rest of the work.
As the probe flies through the corona at 189 kilometers per second, it will begin counting, collecting,
and analyzing particles including electrons, protons and ions.
Meanwhile, a telescope will create intricate 3D images of the corona and solar winds and send all that data back to Earth.
The craft will spend a total of 30 hours within the corona before NASA turns
off it's transmitter and leaves it to it's fate. And it's a fiery one.
Scientists hope that all the data gleaned from this mission will help us understand
the corona's dynamics so we can get better at forecasting solar wind events and
planning future missions into deep space.
So thanks in advance, Solar Probe Plus, for everything you're going to teach us!
And thank you for watching this episode of Sci Show Space.
If you'd like to learn how you can help us keep exploring the universe together,
go to Subbable.com/scishow and get some awesome stuff, like a SciShow DVD of
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