Welcome to NASA's Science Live,
an opportunity
for you to interact
with NASA experts
and have your questions
answered in real time.
I'm your host to Tahira Allen.
We are so happy
to have you here today
to dive
into the mysterious world
of planets in retrograde.
If you have questions
throughout the show,
you can send them in
using the hashtag.
Ask NASA on social media
or you can drop your question
directly
into the comment stream
wherever you're watching.
Now, some of us may groan
when we
hear about certain planets
being in retrograde,
but what on earth
actually is retrograde?
Well,
it is a fascinating phenomenon
in our solar system
that involves planets
and how they appear
to be moving in the night sky.
We have two
very special guests today
that are here to answer
all of your burning questions.
Dr.
Henry Throop
is a program scientist
at NASA headquarters.
Welcome, Henry.
Hello here.
Thank you so much.
And we have Dr.
Marina Brozovic,
who is a planetary scientist
at NASA's
Jet Propulsion Laboratory.
Pleasure to be here to hear.
Now, thank you
both so much for joining us
to talk about,
you know,
what it means to have
for a planet
to be in retrograde.
And Henry,
if you could just kick us off
with that exact question.
What does it actually mean
for a planet
to be in retrograde
so retrograde going backwards?
And there's a couple
of different places
that we use that
in the in the solar system
where we talk about things
being retrograde.
If you look at
the solar system,
all the planets and everything
going the same direction.
If you were to zoom out
above the solar system,
look down on it
like this animation
and all the planets
orbiting in the same direction
and they're orbiting
the same direction
around the sun,
and they're also
mostly rotating
in the same direction.
And if there's something
which is
moving in
the opposite direction,
you can call it retrograde.
Now, there's not
very many things
that actually orbit backwards
because, you know,
if you're orbiting backwards
and everything else is kind of
like driving down the highway
and in the
wrong direction, you know,
if you're going this way
and everything else is going
this way,
you're going to have
a collision
and it's going to be game over.
So there's not too
many of those things
which are orbiting
in in retrograde direction.
But there's a couple of planets
that are actually
spinning backwards.
And so rather than spinning
in this counterforce direction
and seem about
they're spinning
in the opposite direction
and Venus and Uranus are
the two of
those are spinning backwards.
And so that's what we mean
about something
spinning in retrograde.
And finally,
then there's the most common
usage of retrograde.
And that's where things
actually look
like they're moving backwards,
but they're not.
It's kind of the illusion
and what's going on there.
It's actually,
again, kind of like
the highway, You know,
if you're driving the fast lane
and there's this slow
truck over you next to you
and you want to overtake it,
you know,
you pull up to that truck and
and you look out your window
and that truck looks like it's
moving backwards
as you overtake it.
And that's kind of
what we're doing
in the solar system.
You know,
the earth is sort
of the fast lane
because we're close to the sun
and we're overtaking
these slower planets
like Mars and Jupiter
further out,
further to the sun.
So the movement lower.
And so as we
look out our window,
essentially
we see Jupiter and Mars
and other planets outward
and they look like
they're moving backward
in that period
where we're approaching them
and passing them.
And so that's when we say that
those clouds are
moving retrograde.
So in our solar
system,
it's kind of just
an optical illusion.
With that explanation,
you would say, yeah,
the planets are still moving
forward.
The orbits are being
just like in the animation.
The orbits are still going
from scene through about.
They're going counterclockwise
and those orbits are stable
and they've been doing that
for billions of years.
But as we overtake
these slower moving planets,
they look from our perspective,
looked like
they're moving backwards
in the sky.
So, Marina, can you actually
can you explain to us then,
why aren't any planets
in our solar system
in a true retrograde orbit?
Well, that has to do with
how our system, solar system
was forming
from a rotating
protoplanetary disk.
And it has to do
with the subsequent
orbital evolution
of the newly formed planets.
So basically the planets today,
they're orbiting
in the same direction
as that original
original
cloud of dust and gas
from which they formed.
So there are ways
their physical mechanisms
that can flip the orbits
so that planets start
going the other way.
But if such conditions
ever occurred,
those planets
where not long lived
because we obviously don't
see any planets
in our solar system
that are going backwards today,
interest rings.
So an orbit can tell you a lot
about the formation
of a solar system.
Yes. Orbits each orbit.
Tells a story.
I love that.
And, Henri,
how can
retrograde affect us
earthlings?
So, you know,
it used to
I mean,
people have been looking up
at the sky
for thousands of years. Right.
And so it it used to be,
you know, in every culture,
every culture
across earth, people have
had names and stories and
about
the stars and the planets
and the constellations.
And those stories
really connected
people to the sky
and the world around them.
And people used to think
that the planets controlled us
like where the stars were
when you were born
actually influenced you
and that's because back
thousands of years ago,
we didn't know
much about physics, biology
and human behavior
and those sorts of things
which actually do confer
our lives.
And so now that we understand
much better
how the solar system
works,
the laws of physics and biology
and so forth,
you know,
we're in a new era
where we understand
this stuff much better.
But you know what?
It's kind of interesting.
The more we know about physics,
the more people actually,
I think, like to go outside
and they like to see the planet
and the moons,
the comets
and the meteor showers and,
you know,
all these
other things in the sky.
We like to observe
those for themselves.
You don't need a telescope
or binoculars.
You can see the motion,
the planets just with your eyes
and just look up them
from one night
to the next
to the next to the next.
You'll see the motion
of the planets
and you can see the moon.
People love
having this connection
with the solar system
today, much like they did
thousands of years ago.
Even though our understanding
of the physics is
so different now.
And Marina, can you actually
talk to this
evolution of human humanity's
relationship
with the planets over time?
Well, you know,
humankind has been
we've been really fascinating.
But these bright
specks of light
moving against
stellar background
since the beginning of time.
And, you know, we.
So even the word planets
in old Greek,
it means wanderer.
So the wandering star
in the antiquity.
We only knew about
five planets.
We did not know about
Uranus or Neptune.
And we thought about planets
in highly abstract terms.
They were part of the heavens
with Earth
at the center of the universe.
And as Henry mentioned,
they were even thought to be
a representation of gods.
Now we know that
planets are not evolving about,
you know,
they're not revolving
around Earth,
they're revolving
around the sun.
We even developed
a branch of science
called Celestial Mechanics
that describes their orbits.
And I would say that today
we are
probably even more fascinated
with planets
because we can study them
from close up.
We have these
powerful telescopes
in space missions.
And so that really these
these little bright
specks of light
become worlds to us.
And they write that we are
we become even more
curious about them.
Thank you both so much
for this fantastic
introduction to planets
and planets
being in retrograde.
Now, we have lots of questions
coming in online
right now from our viewers.
And if you're just tuning
in with us, remember,
you can submit questions
for our experts
to answer live on air
by using the hashtag Ask
Nassau on social media
or by dropping them
directly into the comments
wherever you're watching.
But first,
a question for our viewers
before we start.
What is your favorite planet
to be in retrograde?
Think about it.
Drop your answer into the chat.
Wherever you're watching.
Now, let's take a minute
and get to some of these.
Ask NASA's.
Our first question is from
Kevin Waring's on Instagram
who asks,
Do all planets in our system
I guess go into retrograde?
So, Henry, why
don't you take this one?
Yes.
So
you can answer that
in a couple of different ways.
But. But.
So all the planet's
orbit
in what we call the program
the normal direction.
And that isn't going to change
even over the course
of billions of years
from when the planets
were formed.
But from an
observational standpoint,
from when we overtake
that planet
or past
that planet, that happens
with all of the other planets,
and that's going to happen
for the planets
which are
both further away than
than we are like Mars
and Jupiter
and Uranus and Neptune
and four planets inward
of us like Mercury and Venus.
You're going
to see the motions.
Those planets
sometimes move forward
and sometimes we move backwards
in the sky.
That's kind of like
kind of like this
perspective thing.
Kind of like passing cars
in the highway.
You're all moving
in the same direction.
But they have perspective.
They're going to look
like they're moving
forwards, apparently.
Yeah, I can.
I can add to that.
Yeah. Yeah, I can. I can.
I can add to that.
For example, you know,
so Mercury has this
you know, it's orbiting
very close to the sun.
It has orbital period
around the sun of 88 days.
So it kind of overtakes
the earth several times a year.
So Mercury is actually
apparently retrograde
and the sky
several times a year.
But if you look at Jupiter,
Jupiter is only once a year
and it has to do with Earth
overtaking its orbit.
So so it really depends.
You know,
it can happen for
inner planets,
you know, for mercury,
it happens
fairly often,
for the outer planets,
it happens
about once a year,
but it last much longer.
They apparently move
in the sky backwards
four months,
as opposed to,
you know, mercury
that only spends
a couple of weeks
moving backwards.
This is all
when I say moving backwards,
it has to do with
respect to stars.
So,
yeah, and in
an on this topic of Jupiter.
So we we have Ali
Ali dog
here on YouTube who asked
is there a mission
to learn about Jupiter's moons
Henry Marina.
Jupiter is probably
one of the best study
planets that we have
in the solar system.
It's a huge interest
to NASA
and the people
around the world.
We have we've sent
a large number of missions
up to Jupiter.
We have one up there right now,
which is called Juno,
and we have another
one on its way,
which is a collaboration
with NASA
or with ESA,
A European space agency
called JWST.
Juno is focusing
mostly on the planet itself,
not focusing on the moons,
but it's doing some
fantastic flybys
of some of the moons,
including IO.
Coming up shortly, IO is a
is a moon,
which is has volcanoes on
its surface
is one of the most dynamic
and active places
in the solar system.
Thank you.
I also had to.
Yeah, I would just like that.
I want to
walk over your phrase
that is national mission
that is going with exploring
the Moon Europa.
And I actually have
the privilege
of looking at the spacecraft
right now.
They're building it
just behind my building.
So that is
one of the privileges
working of JPL.
That's, you know,
I can take a peek
of how they're doing.
And this ginormous spacecraft
is growing
in the building next door,
and it's going to be launched
next year.
Thank you both.
And so, Marina,
I have actually
a great question for you.
It's definitely not
faith on Instagram.
sorry, I read that wrong.
Fantastic.
129 on YouTube
says that I am 14 years old
and have a question
and want to know
does the sun spin?
And if so, which way?
Absolutely.
So the
sun is spinning
and actually really fast.
Very rapidly.
It is spinning
in a prograde direction.
So because is this
as I mentioned,
it really has to do with the
with the way
the whole solar system formed,
some from
this rotating
disk of gas and dust.
And so everything spins
the same way,
sun spins the same way
and orbits
and the planets are revolving
around the sun in the same way.
And you know so well, sun is
a sun is obviously a star.
And and it's layers of sun
tend to spin in the
they need to
have actually different
different speeds
with which they spin.
But on top of my head
sun is I think its
period is spinning
is something at hours
but maybe Henry can correct me
if I'm wrong here.
But it is it is
it is spinning pretty rapidly.
I think the
solar rotation
period is on the order
of a month or so.
Solar rotation period.
The sun really? Okay.
Okay.
At 24 days is what it is.
I remain I remain correct.
It
can also because it's so big,
the diameter of sun is so huge.
So in kilometers
per second that it's moving,
it's probably moving faster
than anything else
in the solar system
just because actually
I was watching,
I was remembering
I think I was remembering
Jupiter.
Jupiter is a very
large Jupiter.
Yeah.
Jupiter is
it goes around in
about 10 hours.
It's super fast.
Yeah. Yeah.
It's very it's over 2 hours is
so I our next question is from
definitely not
based on Instagram.
Henry this good one for you?
Do other planets
go through seasons
just like Earth
and I'll tack on a second
part to that.
How do their orbits
affect that as well?
Yeah, so,
so we go through
things like seasons
and all the planets.
The seasons
on earth are influenced
by where the North Pole is
and what
the tilt of the earth is
relative to the tilt of
other things
in the solar system,
such as the orbit of the Earth
or the orbit
of the other planets.
And so all of the planets
go through
different seasons,
different amounts.
Uranus is one
which goes through seasons
essentially
more than anything else,
because it's tilted
essentially on its side.
And so you have half of Uranus
that for, you know,
dozens of years is
is seeing the sun full on.
And then on the other half
it's on the other half.
But seeing it,
seeing the sun fall on and so
it's it's
seasons of some
of the most extreme
of anything else
in the solar system.
Wow.
Well, for many reasons lucky.
Yes. We do not live there.
And so we have
our next question.
Who is Rebecca on Facebook?
Who asks,
should we associate retrograde
as a bad omen
or that bad things will happen?
Marina
Henry,
either of you
feel strongly about that one?
Yeah, it has.
It has really
nothing to do with us.
It's just the optical illusion.
As Henry mentioned
in the intro.
It is.
It it looks neat
on our on our night sky
to see a planet moving
opposite direction
that what we expect.
But what it really
in the grand scheme of things
it's it's just a pretty sight
it has really
no influence on essilor
and I want to go back to Uranus
Henry
I think now everybody is
really focused
on that planet, that topic
we have as a sunny year
out on YouTube,
who asks,
Why does Uranus show
the retrograde motion
and what are the reasons
behind its axis
97 degree tilt Basically, like,
why do we know why
it is that way?
Yeah.
So Uranus is
is that mysterious here?
Because we
unlike the other planets, it's
really tilted,
tilted on its side there.
We think that it might be due
to an impact in its past
that that tilted it
and we think that the
public formed in the same
in the same way
as the other planets
spinning in the same direction.
But then
a couple of possibilities
that it could
have been impacted
by something else
like another,
you know, small planet
like plants looking like that
and tilted around
or a gravitational interaction
with something else.
And I think Marina knows
a little bit more about her.
Yeah, well, it is.
It is.
It really is.
I mean, Henry
kind of pretty much summarized
it all, but,
you know, so basically,
if Uranus was just your regular
planets,
it would just be spinning
in the same direction
as it's revolving
around the sun,
but instead it's kind of tilted
98 degrees on the side.
And it's
we're kind of rolling
like a little barrel
around the sun.
And.
Yeah, and it's
this is really this
this big question of why
it is that way.
And what is also fascinating
not only is
the planets
tilted on their side,
it's the entire system of rings
and moons
is also tilted on this side,
which is kind of tricky
to explain with just the impact
theory, because, you know,
the impact
would be
just tilting the planets.
But now we are talking
about the system moves
also being tilted on the sides.
It is the
Uranus is a
future destination
for massive missions.
So hopefully
next decade or something.
And I really can't
wait for us
to have a kind of grand
spacecraft mission like Cassini
was around Saturn,
fingers crossed.
And so on.
This topic of planetary orbits,
what can they tell us
about solar system formations?
Marina
So, so yeah,
as I was mentioning before,
so you really kind of
have to
look at each
one of them individually.
For example.
So we establish
there are no retrograde planets
because everything
the initial protoplanetary disk
from which
the entire solar system formed
was spinning
in the same direction.
So for example,
I like to mention
my favorite topic and objects
that fascinate me
are the retrograde moons
of the outer planets.
So for example,
maybe I would like to start
with the planet Saturn.
So Saturn has this
because of really
this great system of rings.
And then it also has
a system of regular moons
and it has 24 regular moons.
And these regular moons,
which you see
their orbits
in nearly perfect circles
in equatorial
plane of the planets
and in the same direction
as the planet is spinning
and revolving around the sun.
But then when you pull away
from the planets,
you are entering
the realm of
so-called irregular satellites.
And the reason
why they are called
irregular is
because their orbits
are really all over the place.
They are
orbiting planets
at great distances.
So the ones
that are shown here in yellow,
those are still orbiting
in a prograde direction.
But the larger population,
these red ones,
they are orbiting
in the opposite direction.
And I always say, you know,
orbits tell a story.
Basically
what this tells you is
they were not original
to the system.
They didn't
form with the planet
itself, like the regular boots
they didn't plant,
they didn't form
from the same circum
planetary nebula.
These guys were captured
by Saturn.
And sometimes
in the early history
of the solar system.
And we still don't
fully understand
the physics
behind these capture,
and we really don't know
their source region.
But they're currently
we know 122 of these guys
and there's more to come.
And what is really neat
is that all outer planets,
so Jupiter, Saturn,
Uranus and Neptune,
they all have population
of these
irregular captured satellites.
And I have a great
follow up to that.
James PC Y on YouTube asks
What is the use of these
retrograde observations?
So, you know,
you mentioned that
we observe them,
they tell a story.
Henri,
could you share any specifics
about what
we're trying to learn
from observing
these irregulars,
irregular orbits?
You know,
what we learn by observing
is that everything is a clue
in kind of doing
the forensic analysis of
how did the solar system
come to be.
And so you look at the orbits
of the big planets,
you look at
what they're made of.
You look at the
orbits of the small stuff,
much of which
is kind of left around
from that
from when
the solar system form.
And you put that all together
and piece
by piece, it's
kind of like
looking at the puzzle piece
by piece.
You can assemble the picture
of how the solar system formed.
And and that's that's
kind of what we're going
after, is trying to understand
the formation
evolution of solar system
making, evolution
of earth information
like life on Earth,
where we come from.
It all gets back
to those origins and so on.
On the topic
of observations too, we have
sorry, one second.
We have James White on YouTube
who wants to know,
how do we know
that a planets, say,
for example,
Uranus is rotating on its side.
Marina
Well, this comes really
from observational data.
And you know,
we have big telescopes
that can resolve planets
really, really well.
And it's just
the feature tracking.
So, you know,
you're well,
first of all, we see
that entire system is tilted.
So we're kind of looking at it
like almost bullseye.
So instead of looking
at the system of rings,
kind of you're seeing them
parallel to your line of sight.
You're seeing
Uranus tilted on the side.
So you're kind of looking
really kind of
bull's eye system
and and
yeah, and we know
which way planet is rotating.
Just Yeah,
but we're looking
where these clouds in
the atmosphere are and Yeah.
So we that's pretty well
it's pretty,
pretty well established
and we actually have Voyager
two flew by
both Uranus and Neptune
and those are our best data
on that system.
And, and
hopefully we are
going to see it again soon.
So when you say
observational data,
is it
like these spacecraft
are taking videos
and you can actually see it's
spinning on its star structure,
okay, Hubble can resolve
it really well.
James Webb,
I saw some fantastic
images from from James
Webb close
just the just
a quick picture of the system.
And, you know,
I'm really interested
in these inner
satellites of Uranus.
There are 13 of them.
They're orbiting
really close to the planet
and they're interleaved
with the dust rings. And
they're not easy
to to they're not easy to see
because they are,
you know, faint
and they get lost in the bright
glare of the planets.
And James Webb with just like
even a very short exposure
can you can see them
clearly, all of them
popping out.
And it's a it's
a really fascinating system.
Thank you, Marina.
And our next question
is from Mama three on YouTube.
Who asks, Does
NASA have any plans
to study Venus?
Now, Henry,
I know
this was a
favorite planet of yours.
Why don't you take this one?
Yeah.
So, yeah,
you know, Venus is a
Venus is a planet which has
been of interest.
It's been studied in the past
and it's
a huge amount of interest
to master right now.
In fact,
we have a mission
in the pipeline
called Da Vinci,
which the deep atmosphere
mission is composed,
which goes down
to the surface of Venus
through its atmosphere.
Let me just tell you about
Venus here, because it's
you know, all of the
other planets are unique.
But Venus has something
really different with it
When when we talk about
spin, because,
you know, it's it's
I mean, Venus is it's
roughly the size of Earth.
It's about the same stuff,
rocks of the Earth.
But it has a super, super
thick atmosphere like in this,
like you're kind of peering
through in this video here.
And this atmosphere is
like 90 times thicker
than Earth's atmosphere.
And so it really controls
the system in a way
that it doesn't
control in a much bigger way
than it does on Earth.
And so
we actually think
that what's happening
with Venus,
the rotation of Venus,
is essentially
not rotating or rotating
backwards at a very slow rate.
It takes more than a year
to rotate more,
one of its years to rotate.
And we think the reason
why is because the atmosphere
is actually influencing
and kind of dragging down,
interacting with the surface
to to pull Venus around
in a different way than
than would happen in a
planet with a
smaller atmosphere.
And so that interaction
between the surface
of the atmosphere
and the dynamics
of how the atmosphere works
is one of the things
which is going to be studied
by The Da Vinci Mission
and then
by a number of other missions
in the in the pipeline.
Yeah.
Thank you, Henry.
And so I'm going to go back
to a question
that we already hit on
earlier in the show.
But for our viewers
that are just now tuning in,
definitely not.
Faith on Instagram asks,
do other planets
go through seasons
just like Earth?
So, Marina,
you want to take that one? Yes.
Well, so everything
that has any tilt goes
through seasons.
For example, Saturn.
So Earth is tilted 23 degrees
and that's why we have seasons.
So it
instead of Earth
is not spinning
perfectly perpendicular
to its orbit plane.
It's actually tilted
23 degrees.
For example,
Saturn, Saturn
is tilted 27 degrees.
And something very dramatic
is going to happen to Saturn.
Rings,
because exactly of this
tilt in 2025,
we are going to be seeing them
like air drawn
and for a little bit
because they're very,
very thin,
we are going to actually
not kind of almost
not see them for a little bit.
So that is actually one thing
that always fascinated me about
Saturn's rings.
They're incredibly
I mean, they're huge.
It's like 300,000 kilometers
wide.
But thickness
thickness is
less than a kilometer.
And actually most of it
is only a few hundred meters.
So it is actually incredible
that you can see it
from this huge
distance from Earth.
You're seeing something
that is so delicate.
And I'm
saying and
we get to see different views
of the Saturn's rings
because Saturn
is also going through seasons.
Wow.
And I mean,
that is really exciting.
So
while what we give them,
what we give our viewers
some more time
to drop in some questions,
I want to
focus on this idea of orbits
with planets
being in retrograde
and earlier,
again, we've been touching on
these weird, wacky,
unconventional orbits.
And I do want to ask
a fun question, Marina,
I know that you're all
about the irregulars,
the satellites,
things like that.
Are there any
satellites or
comets, asteroids,
things like that
that you find most fascinating
with maybe again, a
an unconventional orbit?
Yeah.
I mean, we know
we know that
there are a lot of comets
that actually have
retrograde orbits.
So we also
have a population of asteroids,
relatively small one
that are also
these retrograde orbits.
So obviously they are
some make
or some physical mechanisms.
So either
it was
gravitational interaction
with the planets
or some kind of
other mechanism
that ended up flipping them.
And so they are
actually revolving the sun
the opposite way.
And and,
you know, people were actually
inspired to even have claims
about captured
interstellar objects
because, you know,
it used to be that
stars are forming in clusters.
The material around one
star doesn't
necessarily go in the same way
as the material
of another star.
And if there are four,
if they're forming
close together,
sometimes one star ends up
stealing material
from another star,
maybe another object.
And that's how you end up
with this kind of object
going the other way
than anything else.
Now, these are usually not
very long lived and actually
be the conventional wisdom
these days
is that that really
we don't have
we don't have evidence
for any of the asteroids
really being interstellar
that there are these other
and more plausible
physical mechanisms
to flip their orbits.
But but, you know,
who knows in the
in the Oort cloud
from where the comets
are coming from,
you know,
there were these papers
that were showing that
maybe in the Oort
cloud, the material there.
So some of the objects
there that are in retrograde
orbits are truly originating
from different star system,
from the same little cluster
where our sun was forming.
Wow.
And I mean, it's
it's pretty crazy to think
that this is all
still a mystery.
Like every
every observation
just puts together
one more piece of the puzzle.
And I want to take a moment
right now
and remind our viewers
that you can submit a question
for our experts to answer
live on air
by using the hashtag ask Nassar
or by dropping your question
directly
into the comment stream
wherever you're watching.
Now, while we give our viewers
a second
to drop those questions,
I have a question
for both of you.
What do you find
most fascinating in this field?
Henry, we'll start with you
and then we're
you know, one of the things
that I think is
fascinating here
is that
is it
the laws of physics can
describe so well
and so easily
the motions, the solar system.
And, you know,
many people watching
are taken in
like a high school
puts this class
and you learn very early enough
in that
physics class
that the Newtonian
laws of mechanics,
you have them right.
And the law of gravity,
which involves the
G and then over R squared,
which the masses
and the distances.
And so you have the forces
and the gravity
and you balance those things.
And that pretty much
explains the motions of,
you know,
the bulk of motions
of the solar system.
And you can write
those equations
down on a
on a postage stamp and,
and that underneath
that explains the,
you know, that the large scale
motions of the solar system
and, and the universe.
Now there's a lot
of other things that come in
that that
changes to various degrees.
But,
but by and large
just the basic physics
which we've had
for hundreds of years,
does an excellent job
of explaining
even the the
you know, even the largest
large scale motions
throughout the
throughout the solar system.
Yeah.
I can add if I can add to that,
what is fascinating to me
is that we can
we actually know orbits
so well
that we can navigate
in deep space?
So, you know, here at JPL,
I'm sitting in
my I'm
part of mission design
and navigation section
and it really is kind of I'm
sitting among these navigators
that are guiding the spacecraft
from Earth onwards
to different planets.
And it is incredible
what goes into planning
and how precisely
everything is executed.
So You know,
you have to know the
the orbits of planets extremely
well because you
are moving so fast.
I mean, this
you know, we're talking about,
you know, tens of kilometers
a second.
There is no room for error.
You're going from one
moving platform to another
and there is no absolute
because you need to know
everything.
So, you know, it's,
you know, very few people
know that we
we know orbits,
for example, of Venus, Mars
Mercury exceptionally well.
We know that
we know where they are within
a kilometer from
maybe even
a few hundred meters.
You know,
we know extremely where
where Jupiter is.
So Jupiter
is this really kind of,
you know, 5.2 A.U., five times
more distant from the sun than
Earth is.
And, you know,
we know where Jupiter is
within a few kilometers.
We know where Saturn is
within a few kilometers.
So it is incredible
what we have achieved and what
and how we can do this
deep space navigation.
And so a few minutes ago,
we did establish,
you know, that
there are no planets
in our solar system
that are moving backwards.
And I want to hit on this fact
once more.
Are there asteroids or comets
which actually do
move backwards
or in the opposite direction
from everything else? Marina
Yeah, So
so yeah,
we mentioned
that we mentioned already
that there are comets
that do go in retrograde
direction from everything else.
And
we think that
they came to be in these orbits
because I said
there was some kind of
gravitational interaction
that ended up putting them
kind of
flipping them backwards.
And one thing
that also is interesting
to mention
is that maybe, you know,
so in planets
in our solar system
don't go
in retrograde direction,
but planet
exoplanets, some exoplanets
around other solar systems,
they do go
in a retrograde direction.
And that was kind of
one of the kind of
fascinating things is like
that, you know,
how do they get that way?
Because
you don't know whether when
the planetary
system is forming,
you know how
everything is spinning.
One way,
how you still end up
with a whole planet
going the opposite direction.
And so people
have very interesting
theories of
of how that flipping happens.
But yeah,
we do have
retrograde exoplanets,
not in our solar system,
but this is around other stars.
And this, you know,
this is a curious thing
and to follow that up, Henry,
is there a
you know, of a retrograde
orbiting exoplanet?
Yeah.
One of the well known ones
is it's called WASP 17.
B, WASP is the name of
of the telescope
and discovered it.
It was a wide angle survey
and this is one of these
one of these
telescopes, which is its job
is to look for
look for exoplanets out there
by looking at the blue
with the drop in the light.
That's from the star
as the planet
moves in front of it.
And B means
it's the second body
and so that the planet itself
is going around
the 17th stars of WASP, 17 B
and and
with this particular planet,
we can measure the
or we can measure the rotation
direction of the star itself.
We can observe that.
So we can tell
if the is moving this way
and the planet
is actually moving
the other way around it.
And as Marino was saying,
you know,
that's it's
hard to understand
how it's going to be
put that way because you can't
you know,
you can't really
if you have one
large cloud of gas,
which is how we believe
that most Stars platform,
you know,
you have a big cloud of gas
that's kind of like
the tea leaves in the
you know, in your coffee cup
or tea cup.
But they
they're all spin
in the same direction,
you know.
And so
we would think that with us
forming a planet, it's
going to form
the same direction.
Somehow
something happened to this one
and it's going in
the other direction
from the star itself.
And so this
this is the system
which has been studied
with Hubble.
It studied with the study and,
you know, I'm sure
we're going to
find other ones
which are,
which are some of the best
eventually put that,
put that picture together too.
What's causing it's
a, it's unique motion.
Do either of you know,
is that the only planet
in that system
that is
orbiting backwards
or is the whole system
going against its stars spin?
I don't know
how many planets.
Yeah. Yeah.
I'm not for that
particular system.
Yeah, I am.
I'm not completely sure.
I can only tell you
that kind of.
What are some theories of
of how this came to be.
It all has to do with the way
the planetary systems really
kind of stars
are not little islands
and planetary systems
don't form in
isolation
usually have a cluster
of stars.
If you remember Hubble
has that kind of famous
some famous pictures of
stellar nurseries in Orion,
when these little kind
of planetary systems
are emerging
from a ginormous
like cloud of dust,
gas and dust.
And so so anyway,
so it tends to be
they're so closely packed
that gather,
they tend to steal material
from each other.
And then that's
how you end up with that.
You know,
most of the system
is spinning one way,
but you do have a part,
sometimes even part of a disk.
So so
it's not even
planet formed yet,
but it's a disk,
part of the disk
that is spinning in
the opposite direction.
And so
some interaction has to happen.
Usually it is
the neighboring star
or sometimes it needs to happen
that this thing is spinning
one way.
The star, the central star,
ends up changing its end state
again.
Mechanism
pretty exotic move and this
weird magnetic
field of the star tilting
or something like that.
So so it's pretty interesting.
The physical processes
need to occur
in order for a star or disk.
That is so cool.
Thank you
both for that explanation.
And now before we check in
with some more questions
on social media,
I do want to share
with everybody watching
that you can actually see
some of the planets
and moons
that we've touched on
in today's show In the Sky
this month,
Saturn, Jupiter
and Venus are all visible Now.
If you want to know when
and where to look up,
you can visit, go dot, NASA.gov
or word slash. What's up?
Okay,
let's hop
back into some more of those.
Ask massive questions.
So we have a viewer on YouTube
who asks,
Do dwarf planets also go
through retrograde? Henry
Yes.
So dwarf planets are
going to be exactly
the same in their
in emotions as
as as other
things in the solar system.
And so, in fact,
the dwarf planets
are further out
than Jupiter and
Mars and Jupiter and so forth.
And look at look at the arrows
and so forth.
And so just like them,
they're, you know,
they're moving forward.
They're moving in this
in this
counterclockwise direction
as seen from the top.
But our orbit
is going to overtake them
because they're moving
super slowly out there.
So they take much longer
to pass through the sky.
So you don't see them moving
so quickly in the sky.
And so,
you know,
dwarf planets are
harder to observe.
You have to use a
telescope to observe,
and you can't see them
with your naked eye.
So it's not quite like,
you know, with Jupiter,
you can see the motion
and you can actually see
this little plot out
to prove of position
relative to the stars
night after night.
You can actually
see that yourself
to watch
anything further out like the
dwarf planets
you really need to a telescope
so you can see them,
but then you can
plot out their motion.
It makes a little loop
in the sky as it goes
backwards
and then forwards again.
well, you reminded me
something.
You reminded me of something.
Reminded me
of actual retrograde,
my favorite
true retrograde dwarf planets
and that is Triton.
So Triton is moon of Neptune,
but once upon a time,
it was probably just
your regular dwarf planet
like Pluto
that was orbiting the sun.
But somehow,
in the early history
of the solar system,
it ended up
being captured by Neptune.
And you can see it
orbiting Neptune in this weird,
you know,
it is something size of Pluto.
It's it's really it's a huge
and it is orbiting
in a different direction.
So it definitely did not form
with the planet itself.
And one thing that we think
is that it wrecked
that this capture of Triton
ended up
really racking the inner moons,
the original population
of moons that Neptune had.
So the so you see here is that
Neptune has seven inner moons.
We don't think this is
the original population.
They probably formed
after the capture of Triton
from the rings
because all these inner
moons ended up colliding
and and just making like
a basically big debris
ring around Neptune.
And they moons again coalesced
and then orbiting in
the same way as the
as the planet.
But you see
Triton moving
in this retrograde orbit.
You find them?
Yeah.
Cool.
Well, thank you both for that.
Our next question is Alisa
Slay on Facebook,
who asks, Do other planets
have North and South poles
like Earth and otherwise?
How do we know
with 100% certainty
that the planets are tilted in?
So we know
the planets are tilted
because we can take pictures
of them?
It's pretty simple.
So you can go out there
and you can actually see
with a
with a small telescope,
you can observe
Jupiter and you can see,
you know, Jupiter has
belts of gas going on.
It may look like wine
and even a small telescope
a couple of inches across.
You can see these.
There we go. There we go.
And so you can see those easily
and you can see that the
you can see the motion of them
and you can see
the orientation of them.
And you can
definitely distinguish whether
whether they're this way
or whether they're this way.
And you can
you can see where that
where the planet is tilted.
And that's
maybe easiest for Jupiter
because it appears very
big and really bright.
But you can see it with you can
you can see that
in the other planets as well.
Certainly
you can see that on Saturn
pretty easily,
because the alignment of the
of the plane
and the rotation of Saturn
is where the rings are.
And so you look at the at the
at the
where the rings of point is,
and that's where the weather
how the planet is rotating.
And so,
you know, rings are like here.
And then the
the North Pole
kind of goes out like that.
The North Pole
or the South Pole on any planet
is going to point
at a place in the sky.
But that's not going to be
the North Star.
It's not going to be
our North Star.
It's going to be
that planet's North star,
which is going to be
different than Polaris,
which is the
Earth's north star.
And so
if you go to
one of those planets,
the planet's rotating, it's
got a north north pole,
it's got a star,
probably somewhere around where
that north
three rotation axis it.
But it's going to
be a different star
than what we recognize here
on Earth.
Well, and so my next question
for both of you.
Well, it's for both of you.
And Delinda
on Facebook
wants to know what both got
you interested in the sky
and the solar system arena.
Why don't you pick us up?
Well, you know, I was kind of
a amateur astronomer
since the early age,
and, well,
you know,
I was fascinated
by the night sky,
and I taught myself
Constellation very early on.
And I had a little telescope,
and I joined other
amateur astronomers
and I started
observing meteors.
And, you know,
I studied physics.
And so a little by little,
but it really was something
that started in childhood
and just propagated
propagated forward.
So
I'm also I have to admit,
I am a sci fi nut,
so I do read a lot of sci fi
and that probably
also inspired you to
work for NASA.
So,
Henry, what about you?
So unlike Rina, I was not into
astronomy when I was a kid.
I was into dinosaurs
and I thought I would
be a paleontologist.
And so then I went to
I went to college and
and I didn't study
anything about astronomy,
but I spent a
I spent a summer
doing some astronomy
research out of the
observatory.
And I thought,
Wow, this is so cool.
And at the time
there was a group of people
who were looking
at building a spacecraft
to go up to Pluto.
And I'm like,
Man, that is so and so awesome.
So I kind of kind of
got attracted
by that area and got attracted
by studying about astronomy.
And then I ended up
going to graduate school
and getting a Ph.D.
in astronomy
because of this experience.
And the more I get to do this,
the more I appreciate
that we are so lucky
that we get to explore
the solar system around us
and figure out
what makes it work.
Yeah, and it's only
getting better.
I mean, it's like every month,
every day, every year
we learn something else.
And so I love to see too, that,
you know,
there are many
different pathways
into careers like this,
into being at NASA.
So thank you
both for sharing that.
Now we have our next question.
That is from
Z Art Gallery on Facebook,
who asks,
Why do the planets rotate
in different directions?
Marina,
do you want to take this one?
So we're already established.
So
most of the planets are
rotating in
exactly the same way
as they are
revolving around the sun.
This just has to do
with the initial conditions
of how the solar system formed.
We have two of them
that are different.
That is Uranus,
that is tilted on a side
98 degrees.
So it's kind of rolling.
And then there is Venus
that is really
spinning upside down
and there are
just physical processes
that can flip the planet
from being upright
to being sideways.
We already mentioned
potentially there,
they got hit,
they got just impacted
by a protoplanet
during the
early days of the solar system.
There are also some
other explanations of
that has to do
in the case of Venus,
it has to do
with the sun
also influence
on the very dense
atmosphere that Venus has
and this friction
that happens
between atmosphere and mantle
and the core that ends up
kind of
dissipating energy
and slowing the planet down.
I actually read
one more theory on Venus
that it was basically
it was just slowing down
because of the Sun
influence on Venus,
that it was slowing down
more and more and more.
And then until
it was kind of pretty
much tidally locked
and then it started
spinning the other way.
So it kind of it
never really
went from here to here.
It just kind of was spinning,
spinning, spinning, started
slower and slower
and then started
going the other way
with their very series,
these announced areas
that, you know,
you can cook in your computer.
Yeah. Thank you.
Thank you for that.
And so earlier,
you know, Henri,
you were talking about
being able to see some planets
in retrograde
and others
might be too far away.
Can you see any planet
that might look like
it's in retrograde
from Earth with the naked eye?
Yeah.
So you can observe.
People have been looking
at the planets
for thousands of years
and people,
you know, it's easy
to see Mercury and Venus
and Mars and Jupiter
and Saturn.
Those five
you can see easily
with your naked eye
like people have been doing
for thousands of years.
And the inner planets,
the ones like Mercury
and Venus,
those are the ones
which are overtaking us,
as Marina was mentioning.
And so
they spent part
of their part of their
time moving in that in
from our perspective,
moving forwards and prograde
and part of their time
moving retrograde
or backwards in the sky,
it's a little bit
different pattern
for the ones
which are outside of us, Mars
and Venus
and Mars
and Jupiter and Saturn.
Those are outside of us.
And so
we're moving faster than them
because it's the now,
the closer
you are to the to the sun,
the faster you go,
because the sun's like
the racetrack is out.
That's like the racetrack.
Exactly.
So we're kind of
on the fast lane
on this racetrack.
Since we're close to the sun,
we're overtaking
Mars and Venus.
And that's
just like looking out
the window of your car
as you're overtaking
someone on the highway
that you look.
You know,
you've got the slow truck
and the slow lane
that you're passing beyond.
You look out your window and
and they're going behind you.
It looks like they're
going backwards there.
You're actually
still moving forward.
But but from your perspective,
it looks like
they're moving backwards.
And that's what we mean
by retrograde
for the outer planets.
Well, thank you both.
We have
time for one more question.
And so I actually have one
for both of you.
Marina,
we can start with you
and then Henry
would love to hear
your thoughts,
but do you have any advice
for our viewers that are,
you know,
potentially
considering a career or a path
in astronomy?
Well, I could tell you that,
you know, here at JPL,
I've been working with
some people
that have been in the field,
the STEM
field, for 40, even 50 years.
So and I still
these are both scientists
and engineers,
and I can still see that
they had that
same spark in them
that they probably
had early in their careers.
So my advice
is that
study that back very hard
because knowing math can lead
to a very happy
and long career.
Henry
So I would say advice for,
you know, for anybody.
Find something
that you really love to do
because that's
what you're going to be
the best at,
you know,
And that might be in astronomy,
it might be in math
and physics,
in design or engineering
or writing
and building things
or art or whatever it is.
And people at NASA
do all these things. Now.
It is not just astronomy,
but math involves
all of these
wide variety
of other of other things.
So find the thing
that you love. Keep doing that.
Be great at it.
And there really
are possibilities for everyone.
Yeah.
And who knows, 40,
50 years down the line,
you've still got that
same spark.
And so thank you both for that.
Fantastic advice.
And and to just for
all of your help
breaking down planets
in their orbits
and what retrograde
actually means today.
Thank you.
Was pleasure to be our guest.
Thanks for having me.
Yeah.
And thank you to everyone
who joined us online as well.
It was so fun
answering you so many questions
about your favorite planets
and again,
what being in retrograde
actually means.
Now, we hope you'll keep up
with NASA's efforts
studying our solar system
and beyond.
And you can do so
by following NASA's
solar system
on Facebook and Instagram.
Now, if you're looking
to deepen
your personal connection
to the amazing places
that NASA's studies
you can visit, go NASA.gov.
Forward. Slash. What's up?
There is always something
to observe in the night sky.
And with NASA's monthly tips,
you can know when
and where exactly to look up.
Again,
thank you all for joining us