Sky & Telescope - September 2022 - 10

SUN: NASA / SDO; ASTEROIDS DELIVERING ORGANIC
MOLECULES: NASA GODDARD / CI LAB / DAN GALLAGHER
NEWS NOTES
SUN
The Solar Cycle Restarts
THE SUN IS WAKING UP: After years
of solar quiescence, recent months have
seen numerous X-class flares, large sunspot
groups, and coronal mass ejections.
The uptick isn't surprising: The Sun
goes through 11-year cycles of magnetically
instigated activity. But while such
action last peaked between 2011 and
2014, that meager maximum marked
the quietest cycle in 100 years (S&T:
Nov. 2013, p. 10). The more recent
revival, on the other hand, marks a
change in the Sun's behavior. Even
though it's still a weak cycle, Lisa Upton
(Space Systems Research Corporation),
co-chair of the Solar Cycle 25 Prediction
Panel, says that for the first time in
50 years, this solar cycle may be stronger
than the one before it.
In 2019, the prediction panel
reviewed available models and found
that physics-based scenarios resulted
METEORITES
DNA Building Blocks Found in Meteorites
A NEW METHOD has revealed the presence
of the full DNA and RNA " alphabet "
within meteorites. These prebiotic
molecules might have evolved even
before Earth existed.
Scientists have previously found evidence
of prebiotic molecules in meteorites,
including the nucleobases guanine,
adenine, and uracil that are among the
building blocks of DNA and RNA. These
discoveries established that organic
chemistry occurred on asteroids.
Now, Yasuhiro Oba (Hokkaido
University, Japan) and colleagues have
reported on April 26th in Nature Communications
the detection of the " missing "
pyrimidine nucleobases, cytosine
and thymine, which make up the rest of
our genetic code.
The team developed a milder and
more sensitive extraction method,
which involved mixing a small amount
of meteorite powder with water and
then sending intense ultrasound waves
through the medium. The resulting
pressure waves " sorted " molecules
within samples from three ancient
meteorites, revealing a small amount of
pyrimidine nucleobases.
To determine whether the newfound
molecules were truly extraterrestrial,
Oba's group compared soil at
the impact site of one of the meteorites
(dubbed " Murchison " for the location
of the strewn field in Australia) with
the meteorite itself. " Although some
nucleobases were identified in the soil
This conceptual image shows meteoroids
delivering nucleobases to ancient Earth.
10 SEPTEMBER 2022 * SKY & TELESCOPE
Now, with more than two years of
pThe Sun fired off a powerful solar flare (lower
left) on May 3, 2022.
in the most successful forecasts. Using
these models, the panel predicted that
the new solar cycle had started within
six months of December 2019, and
that activity would peak in 2025 with
a maximum sunspot number between
105 and 125. (The wiggle room in these
predictions reflects that even the various
physics-based models are not 100%
in agreement.)
the cycle under our collective belt, the
predictions are holding up well, albeit
with numbers veering toward the earlier
and higher end of the forecast. But
that doesn't mean there isn't room for
disagreement. Scott McIntosh (National
Center for Atmospheric Research), for
one, has gone against the consensus in
predicting that this cycle will be one of
the strongest on record. By 2023, if not
before, it should become clear which
prediction is correct.
The cycle's earlier and more active
start has some practical consequences:
An earlier minimum means an earlier
maximum, which brings the peak of
the solar cycle closer to the 2024 total
solar eclipse. When totality reveals the
Sun's corona, the white wisps could take
on different shapes depending on solar
activity. " We should have a very interesting
Sun to see during the 2024 Great
American Eclipse, " Upton says.
¢MONICA YOUNG
sample, " Oba says, " the concentration
and molecular distribution are clearly
different from those detected in the
Murchison meteorite. "
At 7 billion years old, the Murchison
meteorite formed while the Sun was
still a protostar. If the nucleobases are
original to the space rock, then they
support an extraterrestrial origin for
life on Earth.
However, Michael Callahan (now at
Boise State University), who performed
an earlier study of the meteorite, cautions
that the pyrimidines are found in
such low concentrations that they can't
explain the emergence of genetic material
on their own. These molecules must
have emerged on Earth, too.
Sample-return missions from the
asteroids Ryugu and Bennu will help
us better understand the evolution
of extraterrestrial organic molecules.
The methods pioneered by Oba's group
could help determine the true composition
of these pristine asteroids, as
well as the origin of complex organic
molecules in interstellar space.
¢ARWEN RIMMER
Sky & Telescope - September 2022

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