potatoes. Producing arguably
more calories per square metre
of growing space than any other
conventional crop, potatoes are
a logical choice. Trials have shown
that the nutritional value of spuds
means a person can survive eating
little else for up to two years.
However, Watney starts his
farming operation using tubers
from a shrink-wrapped packet.
Live, raw tubers are constantly
respiring and so wouldn’t survive
shrink wrapping. And you will
have zero chance of getting a
harvest by planting cooked spuds.
A small but catastrophic error.
In 2007’s Sunshine, a team
of astronauts journeys to the sun
on a ship filled with a payload of
nuclear weapons in the hope of
reigniting the dying star. The ship
has a fascinating “oxygen garden”,
which is designed to produce the
life-giving gas for our heroic crew
through photosynthesis.
Given the average adult uses
about 550 litres of oxygen per day,
the crew of eight would require
at least 4400 litres on a daily basis.
Plants produce oxygen as a
T
HROUGHOUT 2021, one
of my mentors has had
to remind me that this
year wasn’t a good time to judge
whether I like my job. After all,
in the middle of a pandemic,
no professor likes their job.
An overstatement, perhaps,
but probably not by much.
Despite all of this, my
experience with teaching this
fall reminded me of one thing
that first drew me to becoming an
academic: a life of learning. This
semester, I taught an introduction
to stellar astrophysics. In the
process, I learned not just about
teaching, but also some physics.
So, as we finish another orbit
around the sun and enter the
third year of the coronavirus
pandemic, let’s talk about a
different kind of corona that
I came to better understand this
year: the solar corona and the
problem it is giving scientists.
Our local star is extremely
average, and that is good news.
If you had a diagram of the
universe’s stars and their
properties, the sun wouldbe right in the middle. In other
words, our sun is a good sample
of the cosmic stellar population.
This is great for science because
the sun isn’t an experiment we
can tweak. All we can do is observe.
It is our good fortune that what
we can learn by watching the sun
is probably broadly applicable to
lots of other stars too.
To say that the sun is average
doesn’t mean it is boring or“ Let’s talk about a
different kind of
corona: the solar
corona, and the
problem it is giving us”simple. The fact that it is more
or less one gigantic nuclear
fusion reactor is perhaps its most
exciting feature. I have treasured
talking to my students this
year about how – through a
combination of incredible heat
and strange quantum effects –
our sun transmutes hydrogen
into helium, and in the process
creates the photons that
illuminate our planet.
In about 5 billion years, the
sun will expand, transforming
from the yellow star we know
into a red giant possibly 100 times
its current size, and burn some
of that helium into carbon.
For now, though, we have a
yellow star that has layers like
an onion. Among these is the
core, where the fusion happens.
Then there is a convective zone
where hot blobs of plasma move
up and cold blobs sink.
Most interesting of all is the
sun’s atmosphere, particularly
a part of it called the corona.
This is made of strands of
plasma millions of kilometres
long that look like flames dancing
in a circle around the sun.
And here’s the thing: you would
expect that the corona – being one
of the outermost layers of the sun
and so one of the furthest from
the nuclear fusion in the core –
would be relatively cool. Not so.
The corona is 500 to 1000 times
hotter than the sun’s surface.
We have no idea why this is the
case. This conundrum, called
the coronal heating problem,
is a major, unresolved puzzle.
As we head into 2022, I am
excited about the possibility that
one of my students will become
interested in solving this problem.
Even if not, I am hoping that by the
time I come to teach this course
again, I will be telling students
about a fantastic discovery that
has been made quite recently:
the solution to the coronal
heating problem. ❚Chanda Prescod-Weinstein is assistant
professor of physics and astronomy
at the University of New Hampshireby-product of photosynthesis,
and it has been calculated that for
every 22 litres of oxygen produced,
plants gain 150 grams in dry
weight. That’s 30 kilograms of
new plant matter a day to meet
the crew’s needs. Even with the
fastest-growing species on Earth,
say a tropical bamboo, that is a big
ask. The oxygen garden, however,
was populated by Tasmanian
tree ferns, which grow at barely a
couple of centimetres a year under
normal conditions. In practical
terms, this garden would need
to be hundreds of times bigger
than is depicted in the film and
include totally different species.
Finally, let’s look at the 2012
film Prometheus. It opens with
a panoramic shot of an alien
race of “engineers” giving life to
a supposedly barren Earth billions
of years ago by seeding DNA into
a waterfall. The same shot then
pans over rolling green, mossy
landscapes. But wait, wasn’t Earth
supposed to be barren? It is as
if plants don’t count as life. It is
enough to infuriate even the most
mild-mannered botanist. ❚18/25 December 2021 | New Scientist | 35