StarChild Question of the Month for January 1999

Question:

Is Pluto or Neptune farthest from the Sun?

Shuttle

Answer:

Pluto is usually farthest from the Sun. However, its orbit "crosses" inside of Neptune's orbit for 20 years out of every 248 years. Pluto last crossed inside Neptune's orbit on February 7, 1979, and temporarily became the 8th planet from the Sun. Pluto will cross back over Neptune's orbit again on February 11, 1999 to resume its place as the 9th planet from the Sun for the next 228 years.

Diagram of Pluto's and Neptune's orbit, on a distance scale in AUs.

So will Pluto and Neptune ever collide? No! You can see this in the image below, which shows a view as seen from the side as the planets orbit around the Sun. Most planets only make small excursions in the vertical and radial directions, but Pluto is an exception. Pluto at times will move closer to the Sun than Neptune, but it is always well above the orbit of Neptune when this happens. The orbits never actually cross the same point in space.

Side view of the orbits of the ninie planets in a graph labeled distance from the sun in AUs on the horizontial axis and distance out of the  ecliptic plane in AUs on the vertical axis.

You can read more about the orbital patterns of Pluto at:

http://nineplanets.org/overview.html

http://windows.engin.umich.edu/pluto/pluto_orbit.html

Regards,

StarChild

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