10 | New Scientist | 9 November 2019
Space NeuroscienceJonathan O’Callaghan Jason Arunn MurugesuASTRONOMERS say they have
detected a telltale trace of water on
comet 2I/Borisov, the first known
interstellar comet. If confirmed,
it will be the first time water from
another planetary system has been
spotted inside our solar system.
Since comet Borisov was
discovered in late August,
astronomers have been racing to
observe it in detail before it hurtles
away following its closest approach
to the sun in early December.
Adam McKay at NASA’s Goddard
Space Flight Center in Maryland
and his colleagues used an
instrument at the Apache Point
Observatory in New Mexico to
study the light reflected by comet
Borisov. They found large amounts
of oxygen around it, possiblya result of water ice turning,
or sublimating, from solid to gas
as it is heated by the sun (arxiv.org/
abs/1910.12785).
“If a water molecule sublimates
off the surface, it gets released as
water vapour,” says McKay. From
there, ultraviolet light from the
sun will break the molecule apart
into hydrogen and oxygen, which
is what the team detected.
The findings suggest that the
comet is currently producing up to
19 kilograms of water per second.
Alan Fitzsimmons at Queen’s
University Belfast, UK, says the
observation is a clear detection
of oxygen atoms that points to
the comet containing water.
Although we have detected
water outside the solar system
before – such as in the atmospheres
of exoplanets or in star-forming
nebulae – we have never seen
water from another planetary
system this close. ❚We may have
spotted alien water
on comet BorisovA NEW kind of navigational
neuron has been discovered
in the mammalian brain,
and it fundamentally changes
our understanding of how we
relate to objects in our vicinity.
We already knew how
we locate ourselves within
an environment, thanks to the
Nobel prize-winning discovery
of the so-called place cells and
grid cells that form the brain’s
inner GPS system.
Now a third type of cell,
recently discovered in rats, adds
another layer of complexity to
this system. Known as vector
trace cells, these relate more to
the objects in an environment
than to the environment itself.
They become active when a
rat sees an object, helping the
animal judge how far away that
object is and its relative distance
to other objects within sight.
These cells are active even
when the object they have been
tracking is no longer visible or
has been removed, and they can
remain in this active state for
hours. In other words, vector
trace cells – assuming they are
present in the human brain –
may help us remember wherewe last saw an object.
Steven Poulter at Durham
University, UK, and his
colleagues found the new
neurons accidentally. The team
was working on an experiment
that involved putting obstacles –
wine bottles, in this case – in the
path of rats, while monitoring
activity in the rodents’ brains,
particularly in a region of the
hippocampus, a brain area
involved in memory and
interpreting space.
“One particular evening,
I took away a couple of the
bottles and I looked at the
neuronal response – but it
stayed the same,” says Poulter.
He initially assumed there was
an error in the software, but
soon realised that some cells
were consistently firing as if
the wine bottles were still there.
The team then confirmed,
through four years of further
experiments, that the cells that
continued to fire were a never-
before-seen type of neuron.
Team member Colin Lever,also at Durham University, says
the cells can’t identify objects.
Instead, they act as distance-
checkers. The information that
they generate and store is the
same regardless of whether
the object in question is a sofa
or a table.
The cells also don’t seem to
differentiate between objects
and obstacles. A brick that a rat
can simply crawl over activates
the neurons in the same way asa wine bottle that the animals
must travel around. Even a line
painted on the floor makes the
neurons fire in a similar way
(bioRxiv, doi.org/ddhx).
Lever suspects that vector
trace cells will be found in the
human brain, noting that there
is already indirect evidence for
their presence in people. He
suggests they are vital to how
we visualise a room or space.
In rats, vector trace cells
are located in the subiculum,
a region of the hipppocampus
that is one of the first areas
of the brain to degenerate in
people with Alzheimer’s. Lever
suggests that this could explain
why forgetting where you left
an object is often one of the first
symptoms of the disease.
Alastair Smith at the
University of Plymouth, UK,
says the findings seem to “move
us away from a system that tells
you where you are in space and
actually tells you where other
things are in that space”.
Neil Burgess at University
College London says the
discovery of the cells verifies
long-held theories about
spatial memory. ❚Brain cells could help
recall missing objects
GETTY IMAGESNews
Sometimes it can be
hard to keep track of
where things are19
Kilograms of water per second
seemingly coming off comet Borisov“ The cells become
active when we see an
object, and stay active
when it is moved”