This video is sponsored by MagellanTV.
The European Space Agency released the first images from the Solar
Orbiter spacecraft. These are the closest images of the Sun ever taken
and reveal details that have never been seen before. But though these images
were only taken to test the spacecraft’s instruments, they are already hinting at
a possible answer to a mystery that has puzzled astronomers for over 150 years.
Welcome back to Launch Pad, I’m Christian Ready,
your friendly neighborhood astronomer.
ESA’s Solar Orbiter began its journey to the Sun when it lifted off from
Cape Canaveral on February 9, 2020 at 11:03 PM local time.
Its mission is to make the most comprehensive study of the Sun.
It does this with a battery of instruments to study the Sun’s
atmosphere, corona, solar wind, and magnetic fields. Its imaging system
has already provided the closest images ever taken of the Sun,
and will make the first ever direct images of the Sun’s poles.
All of this is critical for understanding how the Sun drives
space weather and how solar storms directly affect our home planet.
In fact, there’s a great documentary about Solar Superstorms available
on MagellanTV, who are very kindly sponsoring today’s video.
Solar Superstorms takes you to the Sun’s surface to witness the solar
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After separating from the Atlas V booster,
Solar Orbiter deployed its solar arrays,
antennae, and instrument booms. It then begin its commissioning period.
This is when the science instruments are turned on, checked out, and calibrated.
Normally this would be done with everyone working at ESA’s Operations
Center. However, the UK and most of the EU countries imposed strict
stay at home orders early on in the outbreak of the novel coronavirus.
So, Solar Orbiter became ESA's first
spacecraft to be commissioned largely from people’s homes.
As part of its commissioning, test images of the Sun were made
in May during Solar Orbiter’s first perihelion; that is,
it’s first close approach to the Sun. At the time, the spacecraft was 77 million
km away from the Sun, which is about half of Earth’s distance. Even though
these were just test images, they revealed details never seen before.
These images were taken with the Extreme Ultraviolet Imager.
It images the Sun’s outer atmosphere, called the corona.
Throughout the images are what appear to be tiny flares dubbed "campfires". These
flares appear just beneath the corona, near the Sun’s surface. They seem
like miniature versions of the large solar flares that we see form Earth.
From this distance, each pixel corresponds to about 400 km,
so these campfires are still large by Earth standards. But the fact they’re
showing up in these test images when the Sun is so quiet is quite surprising.
You see, the Sun undergoes an 11-year cycle of magnetic activity.
It starts out with a largely stable magnetic field.
But as the Sun rotates, its magnetic field gets tangled.
This leads to sunspots, flares, and even coronal mass ejections.
Right now, there’s very little magnetic activity so we are experiencing a
"quiet" Sun. But these images show that even a
"quiet" Sun is remarkably active. producing the same features we see
during active periods, but on a much smaller scale.
Like I said, these were just tests to
make sure the cameras are working. They’re not the science-quality
images that we’ll get when Solar Orbiter gets closer. But these
campfires hint at a possible answer to the mystery of the Sun’s corona.
Even though the corona is the Sun’s upper atmosphere, temperatures there
are about a million degrees hotter than at the surface! That makes no sense.
It’s like raising your hand away from a hot stove and suddenly getting burned.
This phenomenon was first noticed in 1869 and scientists have been
trying to figure out the reason for it ever since.
One long-held theory is that there could be small
"nano-flares” continuously erupting in the quiet corona.
In the nano flare hypothesis, local regions of the Sun’s
magnetic field become entangled due to convection in the Sun’s surface.
Electrically charged particles - or plasma - get trapped in the
magnetic field lines. As the magnetic field lines become further entangled,
they come together and snap apart like rubber bands,
unleashing a flare of energized plasma. This is called 'magnetic
reconnection' and is the mechanism at the heart of all explosions on the Sun.
Individually, these small-scale magnetic reconnections are not
significant events;
not a lot of energy is produced. But the cumulative effect of maybe trillions of
these things might account for the corona’s million degree temperature.
It sure looks like that’s what’s happening here,
but just because something looks like what you expect to see,
doesn’t mean it is. Even if the campfires really turn out to be
nano flares, it doesn’t mean they’re producing enough energy to account
for the corona’s temperature. It’s also possible that these aren’t nano flares
at all, but some other phenomenon that mimics their appearance.
Speaking of mimicking appearances, there’s also what appears to be a
giant tardigrade about 2/3 the size of Earth jumping around.
This is actually a defect in the EUI sensor. The reason
it’s jumping around is because the original images were a bit shaky.
The EUI team corrected this and stabilized the images. But now that
the images are rock solid, the original defects of the sensor become shaky.
Eventually, the EUI team will be able to further optimize their imaging
algorithms and remove the defects from future images. But for now,
we have a giant tardigrade and his buddies jumping around campfires.
In order to find out what these campfires really are, Solar Orbiter
needs to get a lot closer to the Sun, but getting there will take some time.
You see, getting to the Sun requires getting rid of a lot of orbital energy
inherited from Earth. To do that, Solar Orbiter will make
a series of flybys of Venus - and one flyby of Earth - to
dump orbital momentum and descend closer to the Sun.
Eventually, it will reach a closest approach of about 0.3 AU in October
2022. There, the spacecraft will make its highest resolution images as well
as direct in situ measurements of the solar wind particles as they pass by.
Additional Venus flybys will send Solar Orbiter to higher
and higher inclinations above the ecliptic plane.
That will allow the spacecraft to obtain the first direct images
of the Sun’s north and south polar regions. The only other spacecraft to
fly over the Sun’s poles was Ulysses, which was launched in 1990.
Ulysses used a gravity assist from Jupiter to change its
orbit and overfly the Sun. But it didn’t carry any cameras. Instead,
it made in situ measurements of the environment surrounding the spacecraft
as it flew overhead. After three orbits, Ulysses was retired in 2009.
Solar Orbiter won’t directly overly the Sun’s poles, because it won’t be able to
generate enough change in velocity with flybys of Venus. But it will be able
to image the poles and study how the Sun’s magnetic field converges there.
Solar Orbiter is equipped with 6 remote sensing instruments
and 4 in situ instruments.
The Extreme Ultraviolet Imager images
the Sun’s lower atmosphere at ultraviolet wavelengths.
This alone is the reason why we need a spacecraft in the first place.
The Daniel K. Inouye Solar Telescope is the largest solar telescope ever built.
When commissioned in 2019, it made the highest-resolution images of
the Sun to date, revealing details as small as 30km (18 miles) across.
However, DKIST is underneath Earth’s atmosphere, which blocks most of the
Sun’s ultraviolet radiation. In order to study the high-energy corona,
we need to go to space so we can see at UV wavelengths.
The METIS coronagraph images the corona by blocking out the
Sun. It makes two images simultaneously;
one in visible light, shown in green, and one in ultraviolet light,
shown in red. The ultraviolet light is caused from emission by neutral hydrogen
in the corona. The images show streamers emanating from the Sun’s equator,
which is pretty typical of the Sun during its quiet period.
However, METIS captured even higher resolution images
when it closed in to 0.52 AU on June 21st.
The Heliospheric Imager - or SoloHI - images the solar wind by capturing
the light scattered by electrons in the wind. This image is a mosaic from four
separate detectors in the imager. The partial ellipse visible on the right
is sunlight reflecting off the dust particles that are orbiting the Sun.
This is called Zodiacal light. The solar wind outflow is faint by comparison,
but the SoloHI team developed techniques to reveal it.
The Polarimetric and Helioseismic Imager (PHI)
measures the magnetic field near the Sun's surface. It also allows for the
investigation of the Sun's interior via the technique of helioseismology.
The PHI Full Disk Telescope shows the Sun pretty much as it would appear to
the naked eye, as long as it was wearing enough welding glasses.
The lack of sunspots really shows how magnetically quiet the Sun is right now.
PHI’s High Resolution Telescope reveals a magnetogram of the surface.
The small structures seen here are magnetic regions
with north and south polarities, some of which have sizes of a few 1000 km.
From this data, magnetic field lines can be extrapolated into
the upper solar atmosphere, which the EUI telescope images.
The same region imaged by the magnetogram is shown here in
visible light, which reveals the Sun’s photosphere. The granules
are the up and down convection cells of hot, electrically charged plasma.
That’s just four of the 10 instruments aboard Solar Orbiter. Four other
instruments are in situ instruments to measure the magnetic field, sample the
solar wind, charged particles, and radio and plasma waves. These instruments will
become very important when Solar Orbiter gets closer to the Sun.
However, Solar Orbiter won't come anywhere near as close
as the Parker Solar Probe. When Parker makes its closest approach, Parker
will come to within 0.05 AU. It will actually fly through the Sun’s corona!
So it's natural to wonder why they didn't just put a camera
on Parker to take even closer images? Well, it turns out that at 0.05 AU,
the radiation environment is so strong that there's no
feasible way to fit a camera capable of surviving those conditions.
However, its WISPR camera looks sideways to image the solar wind passing by.
So the two spacecraft compliment each other, each making different
measurements in different regions. A while back, I made a video about
Parker just before it launched. So, if you’d like to learn more about the
Parker mission, make sure to check out this video when we’re done here.
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