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Neptune
Note 22
So how do you find a new planet?
A. You can use a telescope and randomly
hope to find one or...
B. Observe another planet for an anomaly
that suggests something (like an
undiscovered planet) might be affecting its
orbit.
This is what happened with Neptune. In
1845, 2 mathematicians predicted Neptune
based on perturbations in Uranus' orbit
- Neptune was discovered in 1846 by a
German astronomer using the 1845
predicted position
- later that year, another
astronomer discovered
Neptune's
largest moon: Triton
More on moons:
- Neptune has 8 moons, most of which were
discovered by Voyager 2 in 1989. They are:
Naiad, Thalassa, Depoina, Galatea, Larissa,
Proteus, Triton, Nereid (all named for water gods)
- Triton is an unusual moon because it exhibits
retrograde orbit (which means it orbits
_______?)
- it's cold (-393°F) & has Nitrogen geysers,
volcanically acitve & probably was captured
Meanwhile, back to the planet....
* 3 billion miles from sun
* Smallest of Jovian planets –
diameter = 30,775 miles
Still would hold 60 Earths
* Orbital period = 165 years
(hasn’t even finished a single orbit around sun
since it was discovered!) 5 more years!
* Rotation Period = 16 hours
* Orbit is not a perfect ellipse (because of _____)
Storm Systems here?
- Yes, just like Jupiter, Neptune has several
monster storm systems that have been
swirling around for years
The top storm is
the “Great Dark
Spot”, middle one
is “Scooter” and
the bottom one is
“Great Dark Spot
2” (guess they
ran out of names)
What about rings?
- Neptune has 4 faint, thin rings discovered
in 1985 from earth and verified in 1989 by
Voyager 2
Voyager
and rings
of Neptune
And the last planet on our tour of the
solar system....
Pluto!
?
Basic Info:
* Smallest planet (9th planet, but sometimes
8th)
* Orbital period is 249 years and for 20 or
those years (last happened 1979 – 1999) it
crosses into Neptune's orbit. This won't
happen again until Sep. 2226 :(
* Discovered in 1930 while looking for
something that seemed to affect Neptune’s
orbit
At times, people debate whether it is a
planet, however it does satisfy the criteria
to be a planet:
A. it orbits sun
B. has strong enough gravity to maintain
spherical shape
C. has a history of atmosphere
Does Pluto have any satellites?
Yes, it has one (Charon – approximately the
same size as Pluto)
Charon
Pluto
Wait a second, I though moons were
supposed to be much smaller than their
parent planet.
This is yet another reason that Pluto gives
astronomers problems in classification. Not
only are they about they same size but, they
have the same rotational period (6.4 days)
Although it is common for a satellite to travel in
a synchronous orbit with its planet, Pluto is the
only planet to rotate synchronously with the
orbit of its satellite. So they always show the
same side to each other.
Comparison of sizes between Pluto,
Charon and the USA