The Sun has been up to some pretty intense shenanigans lately, but a recent
eruption on the far side looks to be absolute science gold.
On the evening of September 5 GMT, an enormous coronal mass ejection (CME)
was recorded exploding on the far side of the Sun, sending a radiation storm
out across the Solar System. It was a type known as a halo CME, in which an
expanding halo of hot gas can be seen spewing out around the entire Sun.
Sometimes this means that the CME is headed straight for Earth. However,
this eruption was on the far side, so it's heading away, and we won't see
any of the usual effects of a solar storm here on our home planet.
But Venus was right in the path of the oncoming storm – and with it, Solar
Orbiter, a space probe jointly run by the European Space Agency and NASA
that is currently near Venus after a September 4 gravity assist on its
mission to take closeup observations of our home star.
This has given us the rare opportunity to observe and measure a gigantic,
farside CME, something that is usually rather difficult for us to do.
"This is no run-of-the-mill event. Many science papers will be studying this
for years to come," solar physicist George Ho of the Johns Hopkins Applied
Physics Laboratory
told Spaceweather.
"I can safely say the Sept. 5th event is one of the largest (if not THE
largest) Solar Energetic Particle (SEP) storms that we have seen so far
since Solar Orbiter launched in 2020."
It's unclear exactly where the Sun erupted from, but it seems likely that
the culprit is a sunspot region called AR 3088, which rotated away behind
the disk of the Sun at the end of August.
As it did so, it left a parting shot – a huge M2-class flare, directed away
from Earth.
Helioseismology – the study of internal oscillations of the Sun, based on
surface vibrations – can be used to detect sunspots on the far side of our
home star.
That's because accumulations of magnetic fields, such as sunspots, can
affect the speed of sound waves bouncing around inside the Sun.
Helioseismic measurements from NASA suggest that AR 3088 may have grown
after it departed our side of the Sun.
There are many spacecraft that might not survive such an intense buffeting
from the Sun. But Solar Orbiter, as the name suggests, was built to
withstand quite a solar pummeling.
And it's equipped with instrumentation to measure solar phenomena, including
the Sun's violent eruptions.
In fact, Solar Orbiter had been in the path of an
earlier CME
that erupted on August 30 GMT, just prior to the gravity assist maneuver.
Its instruments recorded, in both events, a significant uptick in solar
energetic particles. This is information that can help scientists categorize
these events, and better understand the behavior of the Sun, and its impact
on the space environment.
AR 3088 is still on the far side of the Sun, and, if it's going to
re-emerge, won't do so for some days. So it's entirely possible that, by the
time it gets back around to us, it will be smaller and quieter.
Currently, all is quiet in Earth-directed Sun-land, with no solar storms on
the horizon.
There are a few sunspot regions visible, but they all seem to be fairly
subdued for the time being, with only milder CMEs erupting on the solar near
side.
However, the Sun is getting into the peak of its 11-year activity cycle, so
we should see more powerful eruptions occurring in the not-too-distant
future.