
Nasa's Voyager 2 probe 'leaves the Solar System' - grahamel
https://www.bbc.co.uk/news/science-environment-46502820
======
japhyr
My all-time favorite graph is the plot of incident solar particles on Voyager
1 in 2012 [0][1]. That to me is the perfect image of scientific thinking. "We
anticipate that the probe will enter interstellar space and see a significant
drop in the number of incident solar particles." And then it happens, clear as
day.

I teach high school math and science, and I have shown this graph to students
every year. Many students get what this really means. They suddenly understand
how far Voyager is from us, and how small and isolated our solar system really
is in the universe.

Now it will be fun to show them the same graph from Voyager 2 [2][3]!

[0]
[https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/hire...](https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/hires/2012/jyguyg.jpg)

[1] [https://phys.org/news/2012-10-voyager-left-
solar.html](https://phys.org/news/2012-10-voyager-left-solar.html)

[2] [http://earth-chronicles.com/wp-
content/uploads/2018/11/voyaz...](http://earth-chronicles.com/wp-
content/uploads/2018/11/voyazh.png)

[3] [http://earth-chronicles.com/space/voyager-2-is-even-
closer-t...](http://earth-chronicles.com/space/voyager-2-is-even-closer-to-
the-border-of-the-solar-system.html)

~~~
simulate
Thanks for these graphs!

Your Voyager 1 graph [footnote 0, in the parent comment] shows two periods of
particles-per-second drops to around 10 particles per second followed by a
rebound and then a dramatic drop to 2 to 3 particles per second.

The Voyager 2 graph [footnote 2, in the parent comment] shows a single drop to
around 17 to 18 particles per second and what looks like the beginning of a
rebound. Wouldn't interstellar space be characterized by the drop to below 3
particles per second?

Is this the same issue we had with Voyager 1 where Voyager 2 is beginning the
process of entering interstellar space but has not yet actually entered it? If
not, why are the particle counts about an order-of-magnitude higher for
Voyager 2 then they were for Voyager 1 in interstellar space?

~~~
21
> _why are the particle counts about an order-of-magnitude higher for Voyager
> 2 then they were for Voyager 1 in interstellar space_

Better detector? Those are _detected_ particle counts

~~~
rohansingh
Voyager 2 was launched a couple weeks before Voyager 1. They are pretty much
the same.

------
jeffbax
If you haven't watched it yet, "The Farthest: Voyager in Space" is an
incredibly great documentary recently released by PBS

[https://www.netflix.com/title/80204377](https://www.netflix.com/title/80204377)

~~~
krylon
Cannot watch from Germany. :(

~~~
mrsteveman1
It's probably still available in your region as a $2 rental from one of the
other streaming services, and would be well worth it.

------
raquo
Voyager 2 has been "leaving the Solar System" regularly for quite a while now.
Example from 2007:
[https://www.nature.com/news/2007/071210/full/news.2007.365.h...](https://www.nature.com/news/2007/071210/full/news.2007.365.html)

I guess the actual thresholds crossed are different but at this point who
cares, unless you actually know those thresholds. It's out there and getting
farther out. Yay.

If you can't describe an achievement without sensationalizing the hell out of
it for the Nth time, maybe don't describe it.

~~~
m3at
Someone has been counting:
[https://m.xkcd.com/1189/](https://m.xkcd.com/1189/)

~~~
ohiovr
I was wondering if I had deja vue over the probe leaving the solar system.

------
listic
Have we been able to launch faster spacecraft since? I'm thinking whether
there could potentially be a newer interstellar probe that could overtake the
Voyagers 1 and 2 on the way out of the Solar system.

~~~
lodi
Not really, no. These probes don't really accelerate by burning fuel; instead
they pick up velocity by doing a bunch of gravity assists. The more of these
you do, the faster you go, but sometimes you have to coast around the sun for
years to align yourself with the next gravity assist, and this gets worse and
worse until you hit solar escape velocity. Using this method, your final
interstellar velocity will just depend on how many objects you can slingshot
around on your final 'kick' out of the solar system. (So, in other words, you
can get in the same ballpark as Voyager, but not orders of magnitude faster.)

Here's a video of what it takes "simply" to get out near Jupiter, nevermind
out of the solar system.
[https://www.youtube.com/watch?v=ktrtvCvZb28](https://www.youtube.com/watch?v=ktrtvCvZb28)

The Voyager spacecraft took advantage of a special planetary alignment that
won't happen again for over a hundred years.

\---

Having said that, if by 'spacecraft' you mean something weighing a few grams,
the Starshot program might be able to obliterate the Voyager records.
[https://en.wikipedia.org/wiki/Breakthrough_Starshot](https://en.wikipedia.org/wiki/Breakthrough_Starshot)

~~~
kartickv
What if you use an ion drive or other propulsion that uses less fuel, and run
it for years or decades? Yes, it generates little thrust, but won't it add up
over long timescales?

~~~
lodi
That'll certainly help a bit--you'll pick up several km/s of delta-v--but even
this will still be pretty irrelevant in terms of interstellar distances.

------
shshhdhs
> Voyager 1 departed Earth on 5 September 1977, a few days after its sister
> spacecraft, Voyager 2.

Well that’s unusual isn’t it? Perhaps there was a temporary issue/delay with
#1? I didn’t see the explanation in the article.

~~~
weberc2
IIRC Voyager 1 traveled faster than Voyager 2, so it quickly passed Voyager 2.
They named it Voyager 1 because it was going to arrive on target sooner.

~~~
jessriedel
> They named it Voyager 1 because it was going to arrive on target sooner.

Do you know this or are you speculating?

~~~
weberc2
I watched the documentary _The Farthest_ (really good, highly recommend
[https://www.imdb.com/title/tt6223974/](https://www.imdb.com/title/tt6223974/))
on Netflix a few weeks ago. I might be misremembering; feel free to fact check
me.

~~~
jessriedel
Thanks. This bit from Wikipedia doesn't explicitly confirm, but it makes your
answer very like:

> Two trajectories were selected. One was designated JST: its mission would
> take it to Jupiter, Saturn, and Titan, with the probe's trajectory designed
> to optimize the Titan flyby. The second was designated JSX: it would be
> launched on a trajectory that would preserve the option of a Grand Tour,
> while serving as backup for the first probe. It would arrive after JST, and
> if JST were successful, it could continue with the Grand Tour. If JST was
> unsuccessful, JSX could be diverted to perform the Titan flyby itself, which
> would eliminate the possibility of a Grand Tour.

> The two spacecraft that launched retained the same mission concept. Voyager
> 1's course was optimized for the Titan flyby and Voyager 2 for the Grand
> Tour. Voyager 2 would reach Saturn nine months after Voyager 1, giving
> plenty of time to decide if it should proceed with the Grand Tour.
> Additionally, by launching Voyager 2 first, Voyager 1's launch could be re-
> targeted to perform the Grand Tour if Voyager 2 were lost in a launch
> failure. An option to skip Voyager 1's Titan flyby and proceed from Saturn
> to Pluto was identified, though Titan was still considered the more
> interesting target, especially after images from Pioneer 11 indicated a very
> substantial atmosphere.

> With Voyager 1's mission complete, Voyager 2 was cleared for an extended
> mission to Uranus and Neptune, fulfilling the goal of a Grand Tour as
> proposed in 1964.

[https://en.wikipedia.org/wiki/Grand_Tour_program](https://en.wikipedia.org/wiki/Grand_Tour_program)

------
lordnacho
How do they manage to keep sending data back? Is there a really really
directional antenna that points at the Earth?

~~~
mlindner
Yes. Directional antenna with EXTREMELY low bitrates so that the bits have a
long time to accumulate any noise out of the signal. Specifically its at 160
bits per second at a transmit frequency of 8 GHz.

~~~
jfries
160 bits per second is actually pretty high. As comparison the German radio
time signal used by parts of Europe sends out 1 bit per second:
[https://en.wikipedia.org/wiki/DCF77](https://en.wikipedia.org/wiki/DCF77)

~~~
Sharlin
Yeah, at the time the probes were launched, 160bps would have been a fairly
respectable transmit rate between two computers connected by a cable, located
in the same city!

------
syntaxing
How much of a lag is there in the data transmission? I guess that should
correspond to how many light years it is away? How does the probe know which
direction to send the data? I have so many questions! I gotta watch that
documentary and listen to the podcast people are suggesting here!

~~~
rlanday
The current one way transmission times are 20 hours and 5 minutes to Voyager 1
and 16 hours and 38 minutes to Voyager 2:
[https://voyager.jpl.nasa.gov/mission/status/](https://voyager.jpl.nasa.gov/mission/status/)

The probes use a star tracker to determine their orientation (they apparently
look for the sun and one other star). I assume they keep track of their
expected position in the solar system, and this is fine-tuned with updates
from the ground station. If you have position and orientation, you can compute
where the Earth should be at the current time and point the antenna in that
direction.

~~~
jdmichal
Also, at their distance, they don't really have to be _that_ close in aiming.
Their beam is plenty wide by the time it reaches Earth.

------
swarnie_
Quote from the article:

"the US space agency says that Voyager 2 has a working instrument aboard that
will provide "first-of-its-kind observations of the nature of this gateway
into interstellar space"."

Does anyone know what Voyager 2 is carrying that Voyager 1 wasn't that might
give interesting data in this part of space?

~~~
tabtab
It's the "Plasma Science Experiment" I believe. Voyager 1 did have one, but it
broke along the way. This is based on
[https://www.jpl.nasa.gov/news/news.php?feature=7301](https://www.jpl.nasa.gov/news/news.php?feature=7301)

~~~
swarnie_
Thanks very much for the info!

------
kwoff
They should send these out every decade or so. Especially if they could get to
where they can relay data from probes further out. Technology advances so
quickly, after all.

~~~
alluro2
Yeah, as well as visit Titan and Europa more seriously...Why "we" don't do
such things that are silly inexpensive relatively, but burn millions on
reality shows is something I'll never learn to accept...

~~~
ryandrake
Be satisfied that hundreds of years from now, our descendants will look back
at how today’s society allocates and deploys its capital and shake their heads
asking “WTF were they thinking?”

~~~
hutzlibu
Or they scavange the ruins of it ...

------
pascalxus
just to be clear, it hasn't "left the solar system", it left the heliosphere.
They said it still needs to leave the OOrt cloud before it has officially
"left the solar system".

but, it's cool that it will continue transmitting until about 2027!

------
lholden
The big news is that Voyager 2 should be experiencing more interstellar medium
than atmosphere from our star at this point. It will still be a while before
it could be said to truly "leave the Solar System" if you consider
gravitational influence to be a factor. There are objects still orbiting our
star at more than a light year away for example (Oort cloud).

------
holoduke
Do we actually know where they end up? Is it possible to make a reliable
calculation on their trajectory in let's say 50.000 years? Do they get locked
in a next solar system or will they continuesly be catapulted between systems?
They are not solar powered right? So they won't be powered up again when
reaching a next star (assuming all electronics are still alive)

~~~
Sharlin
Neither probe is headed towards any particular star. In roughly 40,000 years
each will pass a small nearby star (Gliese 445 and Ross 248 for V1 and V2
respectively) at a distance of over 1ly, far too distant for the stars to have
much effect on the trajectory of the probes. Barring any chance encounters,
the spacecraft will be drifting in the interstellar space for a very, very
long time.

------
russellbeattie
What always amazes me is the vast difference between the visual and non-visual
effect of the sun. From that distance, the sun is just another glowing speck
in the distance, and yet its gravity and radiation is still felt. Like if you
had a speaker the size of a pinhead that you could hear from a mile away. (Or
probably a lot more).

~~~
Sharlin
Well, the probes definitely "feel" the visible radiation of the sun as well,
for some definition of "feel". At that distance the sun is still much brighter
than any other star, and it would be obvious in photos if they still had use
of their cameras.

~~~
dmurray
Even brighter than you might think. Based on the reasoning in this Quora
answer [0], which looks reasonable at first glance, it's 10-20 times brighter
than a full moon on Earth. If you were out there sitting on Voyager 2, you
could read a book by sunlight.

[0][https://www.quora.com/How-bright-is-the-sun-to-the-
Voyager-s...](https://www.quora.com/How-bright-is-the-sun-to-the-Voyager-
spacecraft-now)

------
kalimatas
> Voyager 1 will not approach another star for nearly 40,000 years That's a
> lonely ride...

------
jpmattia
Anyone happen to know if the Voyager's energy is such to exceed escape
velocity wrt sun?

~~~
DavidSJ
Yep, it and four other spacecraft.
[https://wikipedia.org/wiki/Interstellar_probe](https://wikipedia.org/wiki/Interstellar_probe)

------
saagarjha
Relevant xkcd: [https://xkcd.com/1189/](https://xkcd.com/1189/)

~~~
lmilcin
There actually isn't anything strange about it leaving solar system multiple
times when the heliopause recedes towards Sol and then expands forward again
enveloping the craft.

~~~
neaden
Well it's also that we have multiple ways of defining the border of the solar
system.

~~~
lmilcin
Sure, you can say that the Solar system ends where it stops being
gravitationally dominant.

But think about this, we say we left Earth for space when we actually leave
Earth's atmosphere. When you cross heliopause you are actually leaving
"atmosphere" of solar system. Within it it is dominated by the particles from
solar wind. And the change is very abrupt and well defined (but only in the
direction of the motion of the Solar system, ie. where Voyagers are) in
contrast to how Earth's atmosphere just gradually thins out and we have to get
into some sort of agreement when it actually ends.

------
a_rahmanshah
Again?

~~~
jmts
I had the same initial reaction. This time it's Voyager 2, not Voyager 1. And
the term 'leaves the solar system' is moderately misleading. See my initial
response:

[https://news.ycombinator.com/item?id=18650987](https://news.ycombinator.com/item?id=18650987)

------
garysahota93
Too soon to make a "one small step" joke?

------
stewbrew
This is great and everything but is there really a need to get this status
report every year. If so, shouldn't it rather read: still leaving the Solar
System?

~~~
davidcuddeback
You're thinking Voyager 1, which left the solar system in 2012. This is
reporting on Voyager 2.

~~~
stewbrew
Erm, well that's possible. Anyway I still think less would have been more:

[https://hn.algolia.com/?query=%22Voyager%202%22&sort=byDate&...](https://hn.algolia.com/?query=%22Voyager%202%22&sort=byDate&prefix&page=0&dateRange=all&type=story)

