
Caltech Researchers Find Evidence of a Planet Beyond Pluto - cyanbane
http://www.caltech.edu/news/caltech-researchers-find-evidence-real-ninth-planet-49523
======
hackuser
The NY Times covers the story well:

[http://www.nytimes.com/2016/01/21/science/space/ninth-
planet...](http://www.nytimes.com/2016/01/21/science/space/ninth-planet-solar-
system-beyond-pluto.html)

EDIT: After reading the comments in this discussion, many of which are
addressed in the NYT article, I'd say the NYT article is almost certainly
worth reading.

~~~
purpled_haze
I just wished they hadn't indicated this new planet is the "ninth planet".
Dwarf planets are no less planets than little people are people.

~~~
karlshea
> Dwarf planets are no less planets than little people are people.

They certainly are, since they haven't cleared their orbit.

If you're not going to accept the term, then where's the cutoff? Should we
count every asteroid in the belt just because they are orbiting the sun?

~~~
kefka
The answer is that Pluto isn't some sort of classification issue.

The proper answer is that Pluto is a planet because of historical reasons (by
fiat). By definition, it is a planet, and the asteroids in the asteroid belt
are simply asteroids.

From then on, you can apply the rules of a "planet" later on to other bodies,
like this one.

~~~
karlshea
> The proper answer is that Pluto is a planet because of historical reasons
> (by fiat)

I disagree that Pluto should somehow have this distinction. Along with all of
the reasons it shouldn't be considered a planet under the current definition,
it was only discovered in 1930 so it's not like we've been seeing this dot in
the sky since humanity was in caves.

Even if I were to agree, then Ceres should also be considered a planet since
it was discovered earlier.

------
dexwiz
We have been looking for a "missing" objects for a while. The nemesis star
theory says the sun has a brown dwarf companion. This object would interact
with the Oort Cloud instead of the Kuiper belt. But this theory has been
pretty much refuted.

This theory definitely looks more promising. Finding eccentric Kuiper belt
objects, and aligning them with a missing object seems to be a good bet.
Giving the object an orbit should make the search easier, and we will probably
have a conclusion one way or another within a few years.

[https://en.wikipedia.org/wiki/Nemesis_(hypothetical_star)](https://en.wikipedia.org/wiki/Nemesis_\(hypothetical_star\))

------
xenophonf
No one's mentioned Tyche yet?

[https://en.wikipedia.org/wiki/Tyche_%28hypothetical_planet%2...](https://en.wikipedia.org/wiki/Tyche_%28hypothetical_planet%29)

In searching for Tyche, the WISE missions ruled out the possibility of
anything larger than Saturn (95x the mass of Earth) out to about 10000 AU and
anything larger than Jupiter (317x the mass of Earth) out to about 26000 AU.
WISE was able to detect objects the size of Neptune (17x the mass of Earth)
out to about 700 AU, so it should be possible to find the object proposed by
the Caltech astronomers here (10x the mass of Earth at around 600 AU). I don't
know if WISE's current condition would allow it to perform such a search, as
it's completely out of coolant.

~~~
mutagen
Their site at [http://www.findplanetnine.com/p/blog-
page.html](http://www.findplanetnine.com/p/blog-page.html) addresses the areas
the Tyche survey and other surveys cover.

My TLDR:

* The WISE survey might only find Planet X at it's nearest approach. Kevin Luhman has redone the survey using the most sensitive WISE bands that only cover a narrow area of the sky and hasn't found Planet X.

* They reviewed the Catalina Sky Survey and eliminated most of the areas they'd expect Planet X.

* The Pan STARRS site survey didn't find Planet X.

Conclusion: Planet X is at aphelion, difficult to find with the Milky Way as a
(stunning) backdrop.

I just found their paper:
[http://iopscience.iop.org/article/10.3847/0004-6256/151/2/22](http://iopscience.iop.org/article/10.3847/0004-6256/151/2/22)

I wonder how their conclusions match with David Nesvorny's paper predicting a
5th planet having been ejected from the Solar System:
[http://arxiv.org/pdf/1109.2949v1.pdf](http://arxiv.org/pdf/1109.2949v1.pdf)

~~~
rplnt
> Planet X is at aphelion, difficult to find with the Milky Way as a
> (stunning) backdrop.

I would have assumed that planets are easier to detect when they have a
backdrop? That the light can be blocked, partially blocked, bent, .. Isn't
that the case?

~~~
xenophonf
You're thinking about one of the ways extrasolar planets can be detected, when
they cross in front of their parent star (transit photometry) or when they're
imaged using light magnified or redirected by a massive foreground object
(gravitational microlensing). I don't think we have the capability to detect
something in this solar system eclipsing a background object (whether that's a
star or a galaxy or whatever else is out there).

~~~
versteegen
Correction, rogue planets are detected when their gravity causes micolensing
of distant objects (stars), not the other way around.

[https://en.wikipedia.org/wiki/Rogue_planet#Observation](https://en.wikipedia.org/wiki/Rogue_planet#Observation)

Not an astronomer, but my impression is that microlensing couldn't be used to
detect objects in our own solar system, but I don't see any reason why
eclipsing of distant stars couldn't be used... it would be far too rare to be
practical to find a planet, though.

~~~
xenophonf
Thanks for the correction!

------
gregwtmtno
Skepticism is warranted, but keep in mind that Mike "pluto killer" Brown, one
of the authors, has an impressive track record. He discovered Eris and Sedna.

------
nkoren
If it holds up, this is fantastic. Given how interesting the Pluto system has
turned out to be, I can only fantasise about a potential super-earth system
relatively nearby.

However, to be completely pedantic: would this actually be a _planet_? Or
still a _dwarf planet_ , despite its massive size? Keep in mind that the
definition of planethood is not only that it's large enough to be rounded by
its own gravity, but that it has also "cleared its orbit". I get the
impression that this would cut through broad swathes of the still-cluttered
Kuiper belt, and thus would only qualify as a "dwarf" despite its massive
size.

I checked the original papers for references to whether it had cleared its
orbit, and couldn't find any. Correct me if I'm wrong?

~~~
Symmetry
The criteria for clearing an orbit are apparently somewhat involved[1]. It
can't just be a matter of no other bodies having the same distance from the
sun or Pluto would disqualify Neptune and Jupiter would be disqualified by its
trojans. Because the planets in these cases mass so much more than other other
nearby bodies those other bodies dance to the planet's tune and aren't counted
against the planet in terms of clearing it's neighborhood. But if you look at
the large bodies in the asteroid belt or the TNOs then their influence is very
much mutual.

It's not entirely obvious if the new body would be a planet under the listed
criteria since I don't think we have a good handle on the total trans-
Neptunian population. In fact by Soter's µ criteria we might just need a
single Pluto-sized object to cross this planet's path to disqualify it.

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

~~~
Symmetry
I was misremembering Pluto's mass as being 1/10 of Earth's when it's really
1/500th. It would take a large number of TNOs to push this hypothetical object
from being a planet to being a dwarf planet.

------
logingone
I don't seem to have a grasp of our visibility of our solar system. We can see
a number of the planets with the naked eye, a number of the moons with
binoculars and a few hundred $/£/€/.. telescope. Yet even with these great big
radio telescopes, antenna arrays, Hubble, etc, we seem to be quite unaware of
what's in our neighbourhood. Anyone have figures of how much we've surveyed?

~~~
bzbarsky
It's all about distances. The planets we can see with the naked eye are at
most 11AU from us (Saturn is at 10AU at aphelion).

For comparison, Neptune is never closer than about 29AU to us. Brightness goes
down as the square of the distance. But it gets worse, because that's
brightness at given source brightness. Planets don't radiate intrinsically;
they reflect sunlight. And sunlight brightness drops off as the square of
distance from the sun. Which is to say that even if they were the same size
and albedo (they're not), Neptune would appear about 81 times dimmer than
Saturn to us. Oh, also (linear) angular size goes down linearly with distance.
So if you want to see the two planets as disks of the same size, you need to
have a field of view three times narrower, which means you need 9 times as
many of them to cover the sky. And if you want the same amount of light
gathered, you have to spend 81 times longer gathering it, per the above
brightness calculation.

All of which is to say that the time needed to do an "equivalent" sky survey N
times further away (within the solar system, where all the illumination is
coming from the sun) scales as N^6. And planets do move, so you might still
miss one if you survey a place where it's not yet, then take a while to get to
where it used to be, such that it has moved. This is why Neptune was found via
its gravitational interactions followed by a survey of a small part of the
sky, not brute-force observation.

Anyway, back to the topic at hand, the proposed Planet Nine orbits 20 times
farther out than Neptune. 20^6 is 64 million. So if we assume we've pretty
much surveyed everything out to the radius of Neptune's orbit at some
resolution, and then spent about 64000 times as much time surveying stuff out
to the distance Planet Nine is proposed to be at, at the same resolution (I
doubt we have), then we've probably surveyed about 0.1% of the stuff out
there.

I can't tell you what the actual number is, unfortunately, but I suspect the
answer is we haven't really done very good systematic surveys out at that
distance.

~~~
jessriedel
Shouldn't it be fourth power of distance (N^4) not sixth? For objects beyond
the diffraction limit (i.e., objects whose radius cant be resolved),
visibility is determined by total light reaching the observer. Angular size
isn't important. (And, if anything, diffusing a fixed amount of light over a
larger solid angle makes it _harder_ to see.)

~~~
bzbarsky
If you're just trying to see all the objects, then yes, N^4. But if you're
trying to figure out whether they're planets, you need to either resolve disks
or take multiple observations to observe motion. I don't have a good feel for
how the latter scales with N in practice...

------
ilyagr
There is an awesome summary by Emili Lakdawala at the Planetary Society (as is
often the case with such news).

[http://www.planetary.org/blogs/emily-
lakdawalla/2016/0120095...](http://www.planetary.org/blogs/emily-
lakdawalla/2016/01200955-theoretical-evidence-for-planet-9.html)

------
japaget
Link to paper by Batygin and Brown:
[http://iopscience.iop.org/article/10.3847/0004-6256/151/2/22...](http://iopscience.iop.org/article/10.3847/0004-6256/151/2/22/pdf)

------
rbanffy
The scales involved are astonishing. If the orbit is correct, less than one
year has passed on it since the invention of writing here on Earth.

~~~
blue1
What do you mean? 700 AU it's about 4 light days.

~~~
rbanffy
"Planet 9" takes about 11 thousand years to go around one orbit.

------
sandworm101
Giant, weird orbit, debate ... there can be only one name. This is Planet X.

Also because X would be 10th discovered planet, a reference that pluto, while
not a planet today, was indeed the ninth _discovered_ planet.

~~~
slg
If you are going by that logic, Pluto was at least the 10th planet discovered
and this is at least the 11th. Ceres was discovered before either Neptune or
Pluto and spent 50 years as a "planet". It eventually went through a similar
reclassification process as Pluto as other similar objects were discovered.
The only reason you don't see the same controversy around its classification
is because it was recategorized a century before any of us were born.

~~~
sandworm101
If naming was all about logic then 1/2 the places on earth would need to be
renamed. Naming is about emotion, style, history, and personal preference.
Even total mistakes (the Giant Squid) are grandfathered through. Galileo named
the moons of Jupiter after his sponsors. I just hope this thing doesn't become
"X, brought to you by iPhone8".

~~~
asavadatti
I think you are confusing naming and classification.

~~~
sandworm101
Something can be called "Planet X" without being classified as a planet. Take
"Planet Hollywood". Incorporating planet into the name should at least protect
against future reclassification.

------
tdaltonc
> Batygin and Brown inferred its presence from the peculiar clustering of six
> previously known objects that orbit beyond Neptune.

This raised a big red flag in my mind. This must produce a literally
astronomical multiple comparisons problem. Yes they reported sigma = 3.8, but
if they didn't do their multiple comparisons correction right (which I am in
no position to determine), they're basically reading tea leaves.

If you're not familiar with multiple comparisons, it's kind of like
[this]([https://www.goodreads.com/quotes/649893-you-know-the-most-
am...](https://www.goodreads.com/quotes/649893-you-know-the-most-amazing-
thing-happened-to-me-tonight)) or
[this]([https://xkcd.com/882/](https://xkcd.com/882/)). If you look at enough
extra-neptunian bodies, some of them are going to be in an odd looking
cluster.

~~~
logicallee
So I might not have a great enough understanding but isn't 3.8 sigma not high
for this kind of announcement (with the current title)? if someone wants to
report finding a planet in the solar system ten times the size of Earth
wouldn't they do so at more than @3.8 sigma. In particular, the prior is quite
low because it would affect a bunch of other astronomical calculations,
wouldn't it? So you would want the confidence that much higher....

[http://www.dummies.com/how-to/content/how-to-calculate-
six-s...](http://www.dummies.com/how-to/content/how-to-calculate-six-sigma-
quality.html)

What I mean is that in human terms, Google says the average man is 5'9" with
standard deviation 2.9 inches, then 3.8 sigma (the chances of this happening
by chance) are the same as the chances of finding someone 6'8". It doesn't
seem unbelievable -
[https://answers.yahoo.com/question/index?qid=20101208183308A...](https://answers.yahoo.com/question/index?qid=20101208183308AA4LYym)

If a woman is set up on a blind date and told the guy is 6'8" would she find
it like not credible?

My understnading of statistics then is that the idea that there just so
happens to be a planet ten times the size of Earth in our solar system is
pretty unbelievable. So I'd want the chances of it being an experimental fluke
to be lower than seeing a 6'8" guy, anywhere, at any time, in any context.
Because I would think that's what happens when you look at enough data.

\- Aren't the chances of this being completely spurious literally exactly the
same as a researcher saying "I saw a 6'8" guy somewhere", meaning anywhere, in
any context?

Wouldn't you want higher evidence before stating "evidence found for ninth
planet in our solar system, ten times the mass of Earth"?

~~~
umanwizard
I wish people wouldn't downvote you without explaining why you're wrong.

I have zero education in statistics and your comment makes intuitive sense to
me so I'd like to learn more.

~~~
logicallee
Before your comment, I edited it to be much more civil and less presumptuous,
my original phrasing had included "3.8 sigma is fuck-all", I was briefer, more
resolute, and had just included my first link. (You can see evidence of my
original phrasing if you remove the hedging I added.)

But the downvotes meant I'm probably wrong - rather than delete I edited it to
be much nicer so I could find out why I'm wrong.

~~~
daveguy
Upvoted for tempering the aggression and because I agree with you. As far as I
can tell your interpretations of the statistics are correct. I don't see how
an argument can include information stronger than the statistics of indirect
detection of the object (without direct detection).

------
onetwotree
This is pretty solid science, even if, as others have pointed out, there's a
bit of academic drama-rama and green jellybean stuff going on. In particular,
their model made a prediction that they didn't set out looking for, which
corresponded to existing observations. And of course, the whole hypothesis is
easily testable. While they don't know where the hypothetical planet might be
on it's orbit, it sounds like there's a good shot that small telescopes should
be able to spot it.

Exciting stuff.

------
dluan
More from the folks behind the paper:
[http://www.findplanetnine.com/](http://www.findplanetnine.com/)

~~~
Faint
Have to recommend this, especially Konstantin Batygins piece has great
narrative.

------
ChuckMcM
Ah Planet X which is now planet IX with Pluto's demotion :-). I am guessing
that you can confirm it by looking for star occulusions. Presumably the planet
would blank out stars as it passed between earth and those stars. So would it
be possible to find it using existing plates?

~~~
dzdt
It is pretty well impossible to discover a planet by occultations. For one
thing, in most parts of the sky the density of stars is pretty low. People do
study occultations by known distant objects -- that provides some of the best
available info on physical size and presence of atmosphere for KBO's. But in
most parts of the sky, it is years in between occultations, which last just
minutes. You have to be looking in the right place at the right time. And the
sky is full of variable stars, so just looking for changes is hard.

------
runewell
The biggest casualty of Science this decade has been elementary school
dioramas.

~~~
wnoise
*dioramas

------
beamatronic
Why wouldn't their calculations be able to suggest possible locations for the
planet?

~~~
antognini
They do, and at the end of the press release it says that Brown has begun an
observing campaign to find the planet. Unfortunately detecting these very
distant objects is very difficult. The light we see from them is reflected
light from the Sun, so their apparent brightness goes as 1/r^4, not 1/r^2 like
most objects. And because they are so close, there is a strong parallax from
the motion of the Earth. THe consequence from this is that the object will
actually drift across the image as you are taking it, smearing it out. In
order to detect it you either have to take very short images so that it
doesn't move too much (in which case you don't get very much light), or have
some idea as to the direction of the smear so that you can correct for it.
Either way it's a very hard observation to make! Fortunately if this planet is
as big as they claim it to be it should be relatively easy to detect compared
to Sedna and the other Kuiper Belt objects.

~~~
qb45
Are you sure it's _r^4_ , not _4r^2_?

~~~
antognini
Yes. The solid angle subtended by the planet (and hence the amount of
reflected light) goes as 1/r^2, and then the apparent brightness of the
reflected light to us goes as an additional 1/r^2. The total dependence is
then 1/r^2 * 1/r^2 = 1/r^4.

~~~
gohrt
This is a really good physics puzzler.

The key point is that Pluto does not _reflect_ light like a mirror, it
_scatters_ light relatively uniformly, causing more light loss to an observer
than, say, a mirror that points the reflection directly at an Earth observer.

------
givan
[https://en.wikipedia.org/wiki/Zecharia_Sitchin](https://en.wikipedia.org/wiki/Zecharia_Sitchin)

He believed this hypothetical planet of Nibiru to be in an elongated,
elliptical orbit in the Earth's own Solar System, asserting that Sumerian
mythology reflects this.

~~~
ceejayoz
A broken clock is right twice a day.

------
FreedomToCreate
If Planet Nine exists I wonder how the astrologers will tweak there models.

~~~
nkrisc
This is the most important question here.

------
mast
Very cool.

It reminds me about a book I read called "In Search of Planet Vulcan"
([http://www.amazon.com/In-Search-Planet-Vulcan-
Clockwork/dp/0...](http://www.amazon.com/In-Search-Planet-Vulcan-
Clockwork/dp/0738208892)). Before Einstein, astronomers tried to explain the
motion of Mercury by suggesting there might be another planet inside Mercury's
orbit.

------
theptip
Did anyone else notice that the rendering of the orbits in the article looks
strikingly similar to Kerbal Space Program's orbit UI?

~~~
SolarNet
Or is it perhaps the other way around. Did Kerbel use the same UI as a popular
rendering program used by astronomers.

~~~
ceejayoz
Or, third option, "there's only a few decent ways to represent orbits on a
graphic".

~~~
theptip
The colour schemes are very similar though. There are many colour schemes one
could choose.

------
richmarr
Reading the article I didn't see a mention of a previously hypothesised fifth
gas giant... so here's a link in case anyone's interested or knows something
more.

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

------
ck2
If true, voyager hasn't left the solar system yet.

------
axxl
At WWDC last year one of the lunchtime presentations was by Michael Brown, one
of the researchers involved here. He was one of the people who proved that
Pluto should not be considered a planet and went over the history of the
discovery/classification of planet bodies. He also mentioned that they had
_some_ evidence of a planet body beyond Pluto due to its gravitational affect
of some of the smaller bodies out there even then. Interesting to see this is
finally coming to something! He has the appropriate/amusing twitter handle of
[http://twitter.com/plutokiller](http://twitter.com/plutokiller)

------
danieldrehmer
I'm puzzled by how a planet this big could form in an orbit so distant.

The fact that the material in that region is so spread out and the orbital
period of such object is so long matters.

I would love to read some thoughts on that.

~~~
losteric
As mentioned in the article, this planet could have formed closer to the sun
before getting thrown out by Jupiter/Saturn.

------
photonwins
Does it mean Voyager hasn't really escaped Sun's influence yet?

~~~
skykooler
Voyager won't escape the Sun's influence for hundreds of years. The "boundary
of the solar system" is not the same as the Sun's influence (and, indeed, is
somewhat poorly defined, given how many times Voyager has crossed it.)

------
c3534l
I've been seeing news stories about Planet X for far too long to take any of
this seriously, no matter how seemingly trustworthy the news source is.

------
carlosgg
Thanks for the link. There's a course taught on Coursera by one of the CalTech
researchers, Mike Brown, if anyone is interested. It's archived but they have
kept it open.

[https://www.coursera.org/course/solarsystem](https://www.coursera.org/course/solarsystem)

------
pavpanchekha
They should call it Pluto.

------
jharohit
Now only if they name the ninth planet starting with a 'P', my childhood
mnemonic "My Very Educated Mother Just Served Us Nine Pizzas" would finally be
complete again! :D My suggestion is 'Prometheus' \- sounds tragic and bad ass
at the same time!

~~~
dr_zoidberg
Well that would be consistent with the roman/greek names for planets and large
moons. Now we have to find a stronger tie between the theory and the myth. In
some article regarding this news I've read that Planet 9 might have ended in
its orbit due to encounters with Jupiter/Saturn. Not exactly an eagle eating
its liver, but it can be paralled to "the punishment from Zeus(Jupiter)".

~~~
jharohit
:) well nicely connected with the punishment story! I would further go and say
that we can draw parallels with the Kuiper Belt objects to the eagles
"tormenting" Prometheus while he is chained to a "cold, lonely mountain rock"
like our new mysterious planet stuck in a dark lonely corner of the solar
system!

~~~
dr_zoidberg
Alright, time to write to IAU with a name proposal!

------
JamesUtah07
At first I thought this was another one of those planet x articles that talks
about some hypothetical planet way out but then I saw that Mike Brown was
involved and immediately got really excited. I hope they find something out
there and we can send a probe to it in my lifetime.

------
dmichulke
May it receive a name starting with P so that

 _My Very Educated Mother Just Showed Us Nine Planets_

works again

------
pavel_lishin
> * the putative ninth planet—at 5,000 times the mass of Pluto—is sufficiently
> large that there should be no debate about whether it is a true planet*

That's 10x the mass of the Earth, right, or about 3x the size of Neptune?

~~~
zeroonetwothree
This is the second sentence of the article: "The object, which the researchers
have nicknamed Planet Nine, has a mass about 10 times that of Earth"

------
johngossman
This is very cool. Along with a visible supernova and a super bright comet,
this is one of those things I dreamed about as an astronomy nerd kid.

Though part of me wants to say "Pictures or it didn't happen!"

------
based2
[https://news.ycombinator.com/item?id=9872387](https://news.ycombinator.com/item?id=9872387)

------
bpg_92
For a moment there, I thought of Nibiru :D

------
luckystarr
If this turns out true, that planet needs to be called "Tartarus". :D

~~~
david-given
Yuggoth, surely?

------
neur0tek
Niburu!

------
mgav
Maybe it's a Death Star?

------
mturmon
Provocative title for this Caltech press release.

Mike Brown, the co-author of the paper reported here, discovered Eris, a KBO
like Pluto, in 2005. This discovery prompted the IAU in 2006 to demote Pluto
out of the realm of "planet" into a "dwarf planet".

At the time, Alan Stern's New Horizons mission to Pluto had just been
launched, it finally arrived last year. Stern was incensed that NH started out
as a visitor to the 9th planet and was going to end up as a visitor to one of
many KBOs, and not even the largest one (Eris is more massive).

The quotes given at the time ([http://www.space.com/2791-pluto-demoted-longer-
planet-highly...](http://www.space.com/2791-pluto-demoted-longer-planet-
highly-controversial-definition.html)) are revealing:

"Pluto is dead." \-- Mike Brown

"This definition stinks, for technical reasons...It's a farce." \-- Alan Stern

For more: [http://www.space.com/12709-pluto-dwarf-planet-
decision-5-yea...](http://www.space.com/12709-pluto-dwarf-planet-
decision-5-years-anniversary-iau.html)

Stern is visiting Pasadena on a New Horizons victory lap next week. Should be
interesting.

~~~
lhorie
Small nitpick: "largest" refers to mean radius, "massive" refers to mass (aka
weight). Pluto is the second most massive, but it is the largest. (To be fair,
it is a very close call: its diameter is only ~25km larger than Eris)

I'm excited to see this story unfold, if nothing else because it's fun looking
up the mythological[1][2][3] origins of the names given to new celestial
bodies :)

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

[2]([https://en.wikipedia.org/wiki/90377_Sedna](https://en.wikipedia.org/wiki/90377_Sedna))

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

~~~
overcast
Mass isn't weight, it's the amount of matter. Weight is the measure of the
pull of gravity on mass.

~~~
lhorie
Sorry, you're right. I should've qualified that I meant the colloquial usage
of the word "weight".

------
mud_dauber
LV-426. Just sayin'.

------
empressplay
I just want to know if Planet X is covered by human-enslaving robots.

------
peter303
This how Qigong found the Clone Planet in Star Wars 2. Although the planet had
be erased from the galactic database, it left a gravitational signature on
nearby systems.

