For us Earthlings, there are few things as constant as the Sun.
But the Sun is actually spinning… and weirdly, the layer of gas at its surface spins slower
than the gas beneath it.
We’ve known about this for a while.
Like, almost thirty years.
But scientists have never had a great explanation for it.
But now, a team of astronomers thinks they have finally cracked the case.
They think that outside layer could be moving more leisurely because the Sun is just so
The light acts as a brake!
This all started back in the 1980s, when scientists were studying the Sun with something called
It’s kind of like how seismologists monitor the waves moving through the Earth to learn
more about earthquakes.
With helioseismology, physicists can use vibrations to understand what’s going on in the Sun.
Using these techniques, they could see that the Sun’s equator rotates faster than the
poles — something astronomers had known for centuries.
They also saw that the solar surface rotates slower than the gas underneath it.
But here’s the thing: helioseismology is really only good at giving astronomers a really
big picture — what’s happening in chunks of the Sun like 3,000 kilometers across or
And the Sun’s surface is constantly moving and changing for loads of different reasons.
So, scientists knew about the different-layer, different-speed mystery, but didn’t have
a way to explain it.
Now, three decades later, astronomers have a new tool: NASA’s Solar Dynamics Observatory
This satellite lets them watch how the gases at the very edge of the Sun’s surface move,
with a resolution of 10 kilometers.
Using three and a half years of data, the team tracked changes in the Sun’s outer
And in a paper published in Physical Review Letters, they show that most of the slowdown
happens in just the outer 70 kilometers of the solar surface, not the entire thing.
This very outer edge is where light escapes into space, and the researchers realized that
that sunlight itself might be what’s slowing down the Sun’s spin.
That’s because photons of light have momentum, which they takes from whatever’s emitting
And if whatever’s emitting the light is moving sideways, like the Sun’s surface
does, light steals some of that sideways momentum, too.
Each photon of light steals an unimaginably small amount of momentum, but the Sun is really
bright, and it’s given off a lot of photons over its lifetime.
The researchers did the math, and found that sunlight slowly siphoning off momentum can
just about completely explain the difference in speeds between the Sun’s layers.
They still aren’t positive that this is the major cause of the slowdown, but it seems
And do not worry, the Sun won’t stop spinning any time soon.They checked, and a total slowdown
would take far longer than the five billion years our stellar neighbor has left.
Next, let’s talk about NWA.
No, not the hip-hop NWA.
Not the airline — that doesn’t exist anymore.
The rock version…
NWA stands, here, for Northwest Africa, because that’s where the rock was found.
But it’s no ordinary rock.
It’s from Mars.
And a group of scientists think this meteorite could be proof that at least one Martian volcano
has been continuously spewing magma for more than two billion years.
That is unheard of on the Earth’s surface.
Here, we have plate tectonics shifting everything around, so volcanoes would never really last
for more than a few million years.
NWA 7635 是科学家们在地球上发现的几百块陨石之一
NWA 7635 is one of about a hundred Mars rocks scientists have found on Earth, expelled from
the Martian surface by things crashing into it.
On their way here, those rocks get exposed to high-energy cosmic rays that change some
of their atoms into weird isotopes or elements that weren’t originally there.
And the longer they’re floating out in space, the more weird atoms are in the rocks.
So based on what they’re made of and how long they were in space, scientists can tell
roughly when they got kicked off Mars.
NWA 7635 is really similar to 10 other volcanic rocks called shergottites, which are Martian
meteorites made up of certain elements and minerals.
This specific group of shergottites got launched into space about a million years ago and formed
about three to six hundred million years ago.
But when these researchers actually checked NWA 7635’s age, they found that it’s not
a few hundred million years old… it’s nearly two and a half billion years old.
Because these rocks are all made of the same stuff, that means that there must have been
a volcano or volcanic system making new rocks in the same spot for more than 2 billion years.
In other words, it was erupting for over forty percent of Mars’s history!
And that is a persistent volcano.
Planetary scientists have argued for years about whether Mars has or ever had plate tectonics…
and they’ll probably keep arguing.
But NWA 7635 shows that even if the surface did shift around, it probably never worked
much like Earth, where the planet is significantly rearranged every couple hundred million years.
And it just goes to show that we don’t always need to jet all the way over to the Red Planet
to learn about its history.
The rocks just come to us!
Though we should totally go to the rocks, as soon as possible.
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