Hello, and welcome to the Physics World Weekly
podcast.
I'm Hamish Johnston.
We are entering a second golden age of
space travel
with human missions to the moon and Mars
planned for the near future.
In this podcast, we explore 2 very different
challenges facing the next generation
of cosmic explorers.
Coming up, I'm in conversation with 2 physicists
about how we could implement
a universal
time standard for the moon
which would come in handy for navigating
lunar environments.
But first, Physics World's Tammy Freeman is in
conversation
with an expert on the biological
effects of radiation
on space travelers.
Radiation from space is all around us,
whether this is solar radiation from the sun
or the constant bombardment by galactic cosmic rays.
On Earth, we're protected from most of this
radiation
by our planet's geomagnetic field and thick atmosphere.
But for those who venture beyond the protection
of the Earth,
exposure to space radiation can have a significant
impact on the human body.
And with future missions planned to return astronauts
to the moon or beyond,
the radiation associated risks of such space travel
are a serious consideration.
A newly published ebook
entitled Space Radiation
takes an in-depth look at the astrophysical
origins of this radiation,
its biological effects, and the implications for space
travelers.
I'm speaking today with the book's author,
James Welsh,
from Loyola Medical School in Illinois, USA
to find out more. Welcome to the podcast,
James.
Thank you.
So you've written an extremely comprehensive book looking
at all aspects of space radiation.
What motivated you to write this?
Well, thank you very much, Tammy, for this
opportunity to speak with you today.
And that might be the toughest question
of all
because to this day, I still don't know
what truly
provided the motivation to embark on such a
monumental task. But
number of years back, I had the opportunity
to teach an astrobiology
honors course
at Northern Illinois University.
And astrobiology
got me very interested in this topic of
space radiation.
I then had the chance to give a
couple of lectures at Fermilab,
Fermilab National Accelerator Laboratory in Illinois,
on the Ask A Scientist program.
One of the
topics I chose to, talk about was called
radiation from outer space, gamma rays of death,
doom, and destruction.
And then I did a follow-up one on
the sky's the limit,
radiation hazards of space travel.
Preparing for and delivering those lectures really got
me fascinated in the subject, and so I
wanted to maybe tabulate all my ideas
in the form of a book.
But what started out as a a small
project
in which I was planning to collect and
edit a series of chapters from,
colleagues,
the whole concept deteriorated
during the COVID 19 pandemic,
and I could no longer get my colleagues
to contribute
chapters.
So I wound up writing the whole
book myself.
It developed into a very stressful
several year project in which the 800 pages,
were finally completed,
earlier this year. And so this product of
the pandemic is now completed and available.
That's the best answer I have for
got me going and this project.
Oh, that's a great answer. So, and who
are the targeted readers for the book?
So
perhaps
based on the idea that, this really got
started after teaching the honors undergraduate
course at Northern Illinois University,
I suppose that the book,
could be
geared for undergraduate level
physics majors,
biology majors,
astronomy majors. It is largely written at the
introductory level, so it could be for undergraduate
students in those subjects. But it could also
be useful for graduate students
and even active researchers
who might benefit from a refresher,
on some of the interdisciplinary
aspects of
this work. For instance,
a radio biology researcher might want some basics
on the relevant astrophysics
and the nature of the origins of the
radiation that they're studying.
Similarly,
astronomers might seek some basics on
radiation science, radiation chemistry,
and the biological
effects
of the radiation that stems from the astrophysical
phenomenon that they study, such as solar flares,
supernovas,
gamma ray bursts, and related events.
Okay. So so on that note, let's let's
move on to the key themes in the
book.
Can you briefly describe the main sources of
space radiation?
Sure. I don't know about briefly explaining them,
but,
basically,
some of the sources of radiation,
that
come from outer space and affect us here
on Earth include cosmic rays.
And, cosmic rays are charged particles. They're atomic
nuclei ranging from ranging from,
protons, which are hydrogen nuclei, all the way
up to uranium
nuclei.
These cosmic rays can be classified as
primary cosmic rays
that come from the sun and beyond our
solar system,
and secondary cosmic rays that stem from spallation,
which is the shattering
of atomic nuclei
in our atmosphere after they are struck by
the speeding primaries.
The secondary cosmic rays
spread out in our atmosphere far and wide,
kinda like a shotgun
as opposed to the,
the laser
like or rifle bullet nature of the original
incoming primary cosmic ray. So while primary cosmic
rays are atomic nuclei,
secondary cosmic rays are
smaller atomic nuclei, protons, neutrons,
pions,
muons, and other entities.
Here at the surface, most of the cosmic
radiation that we are exposed to is in
the form of muons, which can be thought
of as
the big brother of the electron,
since muons are about 200 times as massive
as electrons but are otherwise very similar.
They're both,
negatively charged leptons.
The muons can arise through the decay of
pions, which were formed even higher in the
atmosphere, but decay extremely rapidly
and can't reach our surface.
But thanks to the slightly longer half life
of the muons
and
the time dilatation
of special relativity,
some muons do make it here to the
surface.
Another way of classifying cosmic rays is through
their site of origin.
Cosmic, rays sent come some cosmic rays come
from the sun and
others come from beyond the solar system. Those
coming from beyond the solar system are collectively
called galactic cosmic rays.
But the the name galactic cosmic rays may
be a bit too restrictive
since some of the ultra high energy
cosmic rays,
which
get to phenomenal energies,
10 to the 18th
e v, for instance,
seem to, originate from beyond our Milky Way
galaxy altogether.
So the the solar charge particles come in
4 from 4 basic sources.
There's
a steady but low energy
solar wind,
then there are sporadic
explosions on the sun that release large amounts
of energy
in the form of solar prominences,
coronal mass ejections, and solar flares.
But our atmosphere is able to attenuate
most of this cosmic radiation,
and our geomagnetic
field
deflects a large fraction of the incoming cosmic
rays,
because they are charged particles, and they are
influenced by magnetic fields, including our geomagnetic
fields. So just as electrons, protons, and carbon
ions
that are used in medical radiation therapy and
produced,
by linear accelerators,
cyclotrons, and synchrotrons,
the earth's geomagnetic
field is able to deflect these
incoming charged particles
and,
protect us that way.
But this deflection
leads to another
source of radiation,
the Van Allen belts. The Van Allen belts
are 2 radiation belts
made of trapped charged particles.
They're arranged around the earth like giant donuts
or bagels
with the earth in the center.
The outer belt is where the most energetic
electrons reside,
and the inner belt is where the most
energetic protons live.
Some of the protons in this
inner Van Allen belt are produced through a
process called CRAN,
c r a n d, or cosmic ray
albedo neutron decay.
So like I said before, incoming primary cosmic
rays smash into atmospheric molecules
and atoms and shatter their nuclei through spallation.
When this happens,
free neutrons can be liberated.
Free neutrons are unstable.
They decay with a half life of around
10 minutes, and the decay products include
high energy protons.
The high energy protons get accelerated to even
higher energies, get trapped in the Van Allen
belt,
and contribute to the, that,
the source of protons there.
And on rare occasions, there could even be
a third,
Van Allen belt. This can happen after severe
space weather like coronal
mass ejections,
And the 3rd belt is transient, typically lasting
just a few weeks or so,
and there's probably a splitting of the outer
belt.
I just read recently that a third belt,
may have formed earlier this month.
And another
oddity about the Van Allen belts is the
presence of antimatter.
Among the, the truly exotic radiation species in
the Van Allen belts are,
antiprotons.
So we've learned a great deal about the
Earth's radiation belts through NASA's,
Van Allen probes, and we continue learning more
each and every year. That's a long winded
way of saying that the three main sources
of space radiation in our vicinity are solar
cosmic rays, galactic cosmic rays, and the Van
Allen Belts. But beyond our local environment
here in the solar system, there are numerous
other weird
exotic sources of radiation such as supernovas,
soft gamma repeaters, gamma ray bursts, x-ray pulsers,
the Fermi bubbles, and a host of other
oddities that are discussed in the text.
What are the main health issues associated
with the exposure to all this space radiation?
So that's an important question, and it is
a a main topic of the text.
Of course, whole body
radiation exposure to any form of penetrating ionizing
radiation
can be hazardous and could even lead to
acute radiation syndrome as the if the dose
is high enough.
And given the
high energy of cosmic rays, which can get
well into the, well above
the GEV and even TEV range and higher,
this form of radiation is very penetrating. And
since
atomic nuclei
are highly charged,
these cosmic rays are highly ionizing.
So acute radiation syndrome
is certainly possible,
and
acute radiation syndrome can be fatal. So awareness
of this space radiation is important.
But
the reality is that here on Earth's surface,
we're well protected
from this. Our atmosphere and our geomagnetic
field
absorb or deflect a lot of the radiation.
And at sea level, at most places,
depending on the latitude,
the higher the latitude, the more radiation we
get from space,
because of the
the channeling and funneling of these charged particles
by our magnetic poles. But depending on the
latitude,
space radiation contributes to about 0.3, maybe 0.4
millisieverts
per year or 30 to 40 millirem per
year to use the older units.
This is generally inconsequential
in terms of its health impact.
But
interestingly, there are times
when the dose here on the surface could
be significantly
higher. For example, when the north and south
poles,
reverse their polarity and the geomagnetic
field transiently collapses.
This happens on average now about every 200,
300000
years,
But the last time this happened was the
so called Brunus Macayama
reversal. That was about 780,000
years ago,
and so we're well past due now.
And by some estimates,
when this happens, the weakened magnetic field might
fall to only about 10% of its original
strength,
and this might last for about a century
or so.
But that's, here on Earth. Out in space,
astronauts
who,
are out there are exposed to a lot
more radiation than we'll ever be here on
the surface, regardless of
geomagnetic
field,
and,
and atmosphere.
In addition to the constant low level,
radiation from galactic cosmic ray exposure and the
solar winds, astronauts in space could be exposed
to and at the mercy of high dose
unpredictable solar
particle events that are caused by things like
coronal mass ejections
or solar flares.
If astronauts were out on a spacewalk
during a strong solar particle event,
they could get significant and potentially dangerous doses
of radiation.
But even in
outer space, depending on the dose and depending
on the dose rate,
I don't think that this radiation
is really as harmful as one might expect.
In fact, one of the
most fascinating topics that's being researched right now
is,
further
investigation and evaluation,
of the so called adaptive response.
In this model,
small doses of radiation
serve as a primer that prepares the body,
so to speak, for
larger, otherwise
hazardous doses of radiation. It's as if the
the small dose gears the body up for
a subsequent high dose challenge so that the
high dose
is no longer as dangerous as it would
have been otherwise.
This is sometimes called the, Yanazawa
effect,
and,
that's one of the fascinating,
subjects that I and others are studying. Another
thing that we're studying is,
based on some of the observations
coming from the so called NASA twin study,
in which,
Scott Kelly stayed on board the ISS for
about a year, International Space Station for about
a year, while his identical twin brother, Mark
Kelly, remained on Earth during that same period,
and some fascinating
biological changes were noticed
in areas such as Scott's microbiome
and, most curiously, in my opinion, in chromosomal
telomere lanes. Since telomeres
tend to progressively
shorten with age and serve as biological
clocks,
and since radiation is considered to accelerate the
aging process,
it was really surprising to see that Scott's
telomeres
seem to actually lengthen
relative to his brother, Marx, during this year
in space. This is the opposite of what,
might have been predicted. I like to call
it a twin paradox
of another sort. It's not the one that
we learn about in school when we're studying
special relativity.
But,
but confusingly,
his telomeres
shortened back to the normal anticipated length after
he returned to earth.
So the implications on health and longevity are
still unknown, but the initial results
seem reassuring.
And
importantly, I say that they assuaged the fears
that otherwise might be faced by,
astronauts Tooney Williams
and but Butch Wilmore, who are presently on
the ISS
and might have to wait on another another
8 months
to get the
a ride back with SpaceX in early 2025.
Yeah. I don't think that their health is
gonna be compromised by this long duration trip,
but, what was supposed to be an 8
day,
adventure
is turning into an 8 months,
episode in outer space. It's kinda a severe
form of a modern,
Gilligan's Island story.
I was gonna ask you about, you know,
that we've already got people living in space
on the ISS
and sort of how this space radiation
affects them.
Is there a time limit? You you said
that, the astronauts were out there for a
year. Is
do we have a time limit to how
long we let people live on the space
station?
Well, if we do,
it remains
unknown
how long that duration might be.
And one of the,
the things that I'm most curious about
is the adaptive response
and the body's
ability to repair
biological damage induced by space radiation.
Unlike
electronics,
which
if damaged by radiation cannot repair themselves for
the most part,
cells, tissues, organs, and organisms
are capable
of effecting,
repair
of damaged
DNA,
proteins,
membranes,
lipids,
enzymes,
or replace those damaged
entities if necessary.
That's
a key difference
between
biological entities and inanimate
objects. And that's why I'm not convinced at
this time that
the duration is gonna be very short. I
think that the, the limit, if there is
one,
might be quite,
quite lengthy
in healthy individuals who are capable of
repairing,
DNA in a normal fashion.
Are there ways that we can things that
we can do to help protect
the space travelers,
via perhaps shielding or even sort of radio
protector agents?
Sure.
Radiation protectors
are,
one of the things one of the topics
that are being investigated
intensely at this time.
And among the,
novel radiation
protectors
being investigated
is apigenin.
Apigenin
and other polyphenols,
like curcumin,
work through a variety of different mechanisms
and work through mechanisms that differ from some
of the classic
entities,
such as amiphosphine.
Amiphosphine
works as a salt hydrol
containing
radiation
free radical scavenger.
But,
these polyphenols
work through
different mechanisms,
including,
one of the mechanisms that we were surprised
to observe ourselves,
which is a modification
of the gut microbiome.
And
radiation
can alter
the gut microbiome
leading to what we call gut dysbiosis.
And it appears that
apigenin and probably other
polyphenols
and other agents
are able to effectively reverse this gut dysbiosis
and restore
gut microbiome
balance,
which
probably is helpful in recovery
of radiation damage from the organismal level. This
is a topic that hasn't really been actively
investigated up until this point.
So
in the past,
most of the the
radiation protecting agents have been examined on the
molecular and cellular level, but we now appreciate
a bit better that, you have to look
at the whole organism, and the whole organism
includes
gut microbiota
that may be affected by radiation. And if,
if dysbiosis
occurs,
balance may be reestablished
by,
agents such as apogenin.
Okay. And then looking at sort of the
idea of shielding,
I see that the NASA Artemis missions
include returning to the moon and even,
they have a proposal for a lunar space
station.
I would imagine living on the moon, perhaps
the risks from radiation will be greater.
How could they sort of create the shielding
required to protect people living there?
So,
yes, indeed. The,
the shielding
on the moon
and on Mars and in deep space would
have to be far different
from the shielding
even on the International Space Station
because
the International Space Station
is,
on average about 250
miles above the Earth's surface, and
that puts it well above
the the troposphere
and the stratosphere and even the mesosphere, but
technically,
it's still within the atmosphere
orbiting in the,
in the the, thermosphere.
And
while
there's no,
significant
atmospheric
friction at that level,
it's still
within
the atmosphere
and still
within the confines and the protection
of the, the geomagnetic
field. There's no significant amounts of air that
are attenuating the radiation above, but the geomagnetic
field does offer some deflective
protection.
That is all lost when you're beyond the
geomagnetic
field
and, in interplanetary
space or on the moon or on Mars,
which does not have a significant atmosphere or
magnetic field for shielding.
And therefore,
radiation protectors become more important biologically,
shielding becomes more important,
for astronauts
and
in the future
maybe
exploration
and
exploitation
of
geological phenomenon or structures such as lava tubes,
which could serve as shelters
if,
a radiation event is on its way. Then
maybe, these would become more important to avail,
ourselves of.
You mentioned briefly as well how radiation can
impact electronics.
Is this a problem for current space travel
or perhaps for future long duration
missions?
Both.
So,
like I said,
biological entities
such as cells,
and tissues are capable of of repair
of damaged DNA or disposal and,
replacement
of,
irreparably damaged enzymes.
Electronic equipment, for the most part, is
unable to
affect its own repair. And therefore,
many of the electronic
devices
have to be so called hardened
against radiation.
One of the things that's very interesting to
me is the fact that
electronic radiation hardening
is studied and investigated in-depth and and,
tested
at radiotherapy facilities because
after all, if much of the space radiation
is in the form of protons,
and we use protons,
for,
cancer radiotherapy,
those facilities
are a gold mine for
conducting tests on hardened,
electronics.
So,
the computer hardware,
electronic hardware
must be hardened against, space radiation,
and,
this could become a limiting factor. So I
do believe that,
now and in the future,
it's not going to be
the
the biological
consequences of space radiation
so much as the,
durability
of our electronics
and computers
in the long term. So if we were
to go on a long term deep space
mission where,
like in the science fiction
stories,
people are put into suspended animation
for years on end.
I don't think that it's gonna be the
radiation
effect on the biology
of the people so much as the radiation
effect on the electronics and computers
that proves to be the, the limiting factor.
In fact,
if you recall the, the great Arthur c
Clark
book and movie,
2001, a space odyssey,
I think the computer, Hal, goes nuts and,
becomes a homicidal
maniac and kills the astronauts.
Literary experts always tell me that, oh, you
know, this is a great allegory. Arthur c
Clark was talking about,
how the conflict in Hal's mind about him,
having to,
be subservient
to these intellectually
inferior humans or the fact that he wasn't
fully told about the real
underlying
cause of the mission.
The the main purpose of the mission led
to some psychic
conflict, and he broke down.
Nah. In my opinion, nobody was talking about
the fact that they were near Jupiter,
and Jupiter has intense radiation belts that put
our Van Allen belts to shame, and he
just suffered from radiation sickness
and went crazy for that reason.
But that's just my interpretation.
Excellent. That's really interesting. I mean, you've you
kind of answered my final question, which was,
you know, looking
beyond the moon to Mars or long distance
travel.
Will space radiation be the limiting factor in
how far we can explore?
I was asking that from the point of
view of, you know, the human body, but
perhaps, like you say, it will be the
electronics that's the limiting factor.
I think it could be at this point.
So,
in my opinion,
radiation biology
is a fascinating subject and is very different
from space electronics and computer hardware
electronics
in that
cells and biological molecules are capable of being
replaced or repaired,
and the current generation of electronics
is not,
self repairing.
But perhaps that could be something that
will be affected by,
by artificial intelligence as it detects damage to
itself
and directs its own repair.
So perhaps there could be interesting
horizons that, have never been considered before.
Thanks very much for joining us today in
discussing this fascinating subject.
If listeners want to find out more, I'd
recommend taking a look at James' ebook.
It can be found on the IOPscience
website,
and it's part of the IPEM IOP series
in Physics and Engineering in Medicine and Biology.
Thanks again, James, for speaking with us today.
Well, thank you very much, Tammy. It's been
a pleasure.
That was Tammy Freeman in conversation with James
Welsh,
the author of Space Radiation,
Astrophysical
Origins,
Radiobiological
Effects,
and the Implications
for Space Travelers.
Global navigation
satellite systems such as GPS
have revolutionized
how we get around on Earth.
As well as telling us exactly where we
are,
the atomic clock precision
of GPS time signals
have a wide range of applications,
including the coordination of telecoms
networks,
energy grids, and financial markets.
Humans look set to return to the moon
very shortly,
and the creation and operation of lunar bases
and other infrastructure
would benefit from a universal
time system
just like the one we have here on
Earth.
To find out more, I caught up with
Neil Ashby and Biju Patla
of the National Institute of Standards and Technology
in the US.
They've written a paper called a Relativistic
Framework
to estimate clock rates on the moon,
and they join me down the line from
Boulder, Colorado.
Hi Bijou and Neil. Welcome to the podcast.
Thank you for having us
on your podcast.
So my first question is
why would it be useful to create a
lunar standard time
as opposed to using a time signal from
Earth,
when you're on the moon?
Well,
we're,
at a stage where
people are envisioning,
a much larger presence
of humans on the moon and robots as
well.
So if there are many assets
on and near the moon,
then they would
saturate
the communications
channels,
between the moon and the earth. And so,
it's it's better to have an independent,
time
system for navigation
near the moon,
so that one does not have to worry
about
communications problems with the earth, and as well
as the time delay
between,
what happens on the moon and the,
news
that that has happened that arrives at the
Earth.
And and in your recent work, you also
talk about,
time dilation, which is a which is a
relativistic
effect.
The fact that,
a clock
on the moon would run
is it faster than a clock on Earth?
It would that affect how
timekeeping is done on the moon?
And, you you know, any sort of comparisons
to to clocks on Earth?
Yeah. Yeah.
The clocks on the moon
tend to run faster because they'll they're away
from the Earth.
And Earth is a heavier object, and so
heavier objects slows down time. And so moon
is away from the Earth, so the time
ticks, clocks tick faster there.
But
the main reason
why we need to know the difference, the
rate offset
between these two bodies is
that the command and control of all the
operations,
robotic operations on the moon,
is on earth.
So we would want to
local
transfer all the local
information on the moon to the earth,
using a broadband
and a communication
line. And so
the time stamping of information is essential in
the packets not being dropped.
So that's why we have to synchronize the
time
and then use a common time so that
the order of arrival and transmission back and
forth, you know, do not run into some
causal issues with time and pack and resulting
in packet losses and things like that.
And also
to,
the previous point that Neil made,
the why why we need a time,
for the moon of its own. So
imagine
there are so many,
you know, robots or,
electronic devices on the moon. Every electronic device
has a oscillator, a clock in it.
And so the local
clocks there
tend to be showing the natural time of
the of the moon lunar surface, and that
is different than the Earth.
And so
it is easier to have
robotic communication
and GPS like system on the moon to
use the lunar time because the assets will
be running on the moon time.
And then if we extend this time to
everywhere around the moon, then you have established
a common time.
And once you have the time and this
is the common time in the physics textbooks
when you,
learn about time and space. The time axis,
that is a coordinate time.
So, essentially, this is a time that we
want to have. And so that we can
solve the navigation equations and then
locate,
you know, different,
assets. And, you know, they then they can
just,
help with the PNT position navigation and timing
on these,
I know, these celestial bodies.
And and so
how how would we go about creating
a lunar standard? I mean, here on Earth,
we use atomic clocks,
both on the Earth and also in orbit
to create sort of a network
of of very accurate
timekeepers.
Would we do the same,
on on the moon? Would we replace
atomic clocks on the moon and and perhaps
also
at Earth Moon Lagrange points,
to to sort of afford
the communication of time between Earth and moon?
Yes. You would have assets on the moon's
surface
and also in orbit around the moon.
Because if you have an asset in orbit,
you can cover more of the moon's surface
than,
than if if you have a fixed asset,
on the moon's surface.
Lagrange points
might not be usable
in this way
because they're so far
from the Earth and the moon.
It's more likely you would want,
something in orbit around the moon. The Lagrange
points, like l4 and l5
are,
are so far that they're more likely to
be used as communication
links,
between the Earth and the moon.
There's one Lagrange point between the Earth and
the moon,
which,
which would be subject to,
interference,
with direct communication between the moon and the
Earth.
Summarizing, I think, it's it's that you want
assets on the moon
surface
and,
widely distributed if possible,
and assets,
in orbit around the moon.
And and today, there, you know, there are
lots of atomic clocks,
in orbit. You know, that's that's what makes
GPS work.
So would it be fairly straightforward
to,
to put atomic clocks
on the moon, seeing that we we've already
put them into space? Or or would you
have to or are there other considerations
that that you would have to deal with
before
you could build such a network?
Well, I think there are space qualified,
atomic clocks available. Some of them off the
shelf, like, rubidium
clocks
are generally available. They would probably have to
be modified,
because they would now be
so far from the earth rather than rather
than a few
1000 miles or kilometers. They would be
100 of 1000 of kilometers away from the
earth. So the antennas would have to be
probably redesigned,
and other modifications would probably have to be
made.
So one of the main roadblocks or constraints
is the power requirement
for, running this operation from the moon.
And
so
right now, it
the agencies like NASA have a staggered approach.
1 is to test a demonstration,
in the near term
with,
oscillator or crystal oscillator and similar,
you know, oscillators
and use them as clocks and then
just demo it from
send
the earth time there and,
downlink,
the moon time using a two way communication.
It's, it's it's, satellite
communication channels.
And that is a technology demonstration mission,
kind of,
type of thing. And next would be,
a combination of clocks as Neil suggested
with rubidium,
cesium,
and aggregate it, and then keep track of
the Earth and the moon time differences,
and then beam the moon time back into
cislunar space,
and then use that for,
recreating
GPS like
environment,
on the moon
around moon 2.
And also,
for the Lagrange points,
are necessary
there is you cannot use it just like
a point. You have to,
define orbit around it, and they can be
from fairly large orbits,
in cases.
Mostly, they,
some
satellites are parked there
as a relay.
So if you want to extend
the
Earth's infrastructure
out into the cislunar space,
you can imagine these as
space or a setting up communication towers or,
like, for the cell phone situation on earth
where there are big towers and then,
they relay and and sync with each other.
And so using Lagrange points, you can get
a full
view
the of,
the Earth,
moon, and everywhere else.
So that is, networking
and, relaying,
type of,
setup.
I see. And,
you you've already touched on how,
this lunar timekeeping
system could be used.
I mean,
I'm sort of thinking the 2
main applications would be,
sort of coordinating
communication systems, coordinating
robots, as you mentioned. But would also a
sort of a lunar GPS system
be possible where,
you could you could accurately,
locate,
robotic systems, for example, or even human
explorers on the surface of the moon?
Yes. It's entirely
feasible and and most likely would will happen
ultimately.
If you have, lots of assets
on the moon,
whether they'd be robotic,
or or human,
assets,
you want to avoid
collisions.
You want to be able to go back
to the same place. For example, if you're
exploring
for minerals or water,
or something else,
and you find something that's interesting,
you may not have all of the all
of the tools
or instruments you need to investigate. So you
want to be able to go back to
the base and get it and and return
to the same spot.
So you need accurate
navigation.
And for that, you need to you need
to be able to be in the line
of sight of a number of assets that
have clocks.
I see. And and, you know, the moon,
I suppose, is is on the near horizon.
NASA is very keen on on returning to
the moon very shortly. But what what about
Mars?
For Mars ex exploration, I would imagine it's
it's that much further away from Earth.
Communicating back and forth between Mars and Earth
is is going to be difficult. There's gonna
be a big time lag. I would imagine
that a a
a time a Martian,
time system would would also be important.
And that's true. This is seen
over the long term as a step toward,
a test step toward the,
establishment of the independent
time system
or Mars.
And one could envision, in fact,
with assets around
planets like Venus, I doubt if there's ever
gonna be any,
any, human presence
or even robots much
on Venus or other,
other planets.
You could have assets in orbit
around other planets and have the independent time
systems
or positioning
and navigation
around
around them.
And and what about,
using these clocks
for for science,
you you know, rather than communications
and navigation?
Could, I mean, could could these clocks be
used to, I don't know, make more accurate
measurements
of the motions of the moon and the
planets,
and,
you know, tell us tell us something about
that? Or or would that require some some
very, very accurate
clocks that maybe
it wouldn't be possible to send,
to the moon or Mars?
It's it's possible,
but I think that,
in in talking about using them for science,
you're talking more
more about,
using them for scientific
investigations on the moon
or on Mars rather than rather than
the intrinsic
science of timekeeping,
which is which is not interesting,
but,
probably of a less,
of less interest.
I see.
Okay. So so would you be talking about
there, you know, for example, measuring,
making a very accurate measurement of the gravitational
field of the moon or Mars
using very
precise clocks,
and and learning something about the interior, for
example,
from that.
I think it's quite possible that that could
occur, but you would need what you need
is,
in times is that gives you very precise
positioning
so that you can study things like motion
of the surface of the moon or motion
of the surface of Mars.
For example,
one of the early
applications of GPS was to study
the motion of crustal plates
on the earth, which are
many thousands of kilometers apart,
but you could still
measure the motion,
of the order of a few centimeters
per year
using these systems. So you can get very
accurate,
measurements
of motion
of other objects using a very good,
positioning and timing system.
The first point is
the even on earth,
the best atomic clocks using,
the best atomic clock,
the geodesy and aspects like that
are still in the very nascent stages.
I mean, there is a possibility of doing
better measurements with good clock. And these are
very good clocks,
with very high stability,
at the 10 raise to minus 18 level.
Otherwise, mostly,
gravimeters
are used for mapping surfaces and, things like
that.
But for the moon, that having a good
time standard or local time for the moon
is,
is, especially useful for astronomy,
for the using them and, you know, other
dark side of the moon.
It's a very quiet environment for astronomers,
And, a certain very large baseline,
kind of experiments
can be done simultaneously
using the Earth and the moon locations,
for,
observation no astronomy.
For clocks
itself,
if you have,
excellent clocks, which I think would be a
little,
too soon at this time,
We would we would be looking at 10
raised to minus 16
ish stability clocks
because you need,
the the technology is not ready to launch
and operate,
some of the best clocks on earth in
these environments.
So but the time standard for the moon
using lunar gravity
is useful for,
other applications,
for astronomy.
Also, the link the communication
link between Earth and moon
would help a little bit
with,
you know,
equivalence principle kind of test
and,
aspects like that. But we already have the
retroreflectors
there, and,
we are shooting lasers from Earth here to
the moon back.
So I would
it it would help,
not as much
to further this cost because we already have
very good,
setup,
for the earth moon. But we can learn
a lot,
going,
from this,
to extend it to Mars and other,
future,
inner solar system exploration
would be this moon would be a stepping
stone in that sense for,
establishing a coordinate time
and doing
measuring local experiments
using, this,
constellation
GPS like constellation around the moon.
And with what we learn, we can, you
know, we can
extend it to other. So this would be
the first time that humans would do anything
like this,
away from the earth. And so that in
itself is a very,
new,
enterprise.
Yeah. That is I mean, it is very
exciting, isn't it, the idea
of putting precision timekeepers
on the moon?
So yeah. Thanks, Biju and Neil. Thanks for
coming on the podcast
and, and talking about your research.
You're welcome.
Thank you very much for
having us. It was a delight to explain
these notions of, you know, the time itself
having a change and the rate. Is hard
to conceive, but,
this would be a good demonstration. This is
the opposite of usually, people know about time
in the sense of going to the black
hole, but time slows down. This is the
opposite case where the time actually
is running faster.
So that
it's a very strange situation because because of
the earth, our time is slightly slower. So
Mhmm. So thank you for having us.
Yeah. It was my pleasure. Thanks, guys.
That was NIST's Biju Patla and Neil Ashby.
Their paper is published
in the Astronomical
Journal, and it's called a relativistic
framework
to estimate clock rates on the moon.
And you can find it at IOPscience.
I'm afraid that's all the time we have
for this week's podcast.
Thanks to James Welsh,
Neil Ashby,
Biju Patla, and Tammy Freeman for joining me
today.
We'll be back again next week when I'm
in conversation
with a physicist
who has won a King Charles the third
Coronation
medal for her outreach work.
And I also chat about the future of
graphene
with the director of the sustainable
advanced
materials
research group at Turkey's
Sabanciu
University.