APOD: Voyager's Neptune (2014 May 15)

[Nitpicker]

Geckzilla, I guess I misinterpreted this:

the interplanetary perspective looks back toward the Sun

....to mean that the brightish star in the photo was the sun.

Yeah, it would be less confusing to say that the perspective is looking back toward the inner solar system. We are looking up at Neptune from below, though, so the sun and planets aren't in the frame at all. If the sun were in the frame Neptune would appear nearly totally black with only the thinnest sliver of crescent visible. If Neptune were occulting the sun, the rings would be brilliantly illuminated and details never before seen would be revealed. We'd need to send a new probe out to do that, though. I bet it would be an astonishing view, much like the two backlit Saturn portraits we have from Cassini.

The phrase "looks back toward the Sun" is only really accurate in a one-dimensional sense, in terms of a line from the Sun to the camera. In this context, if the planet has a crescent phase, we must be looking more toward the Sun, than away (assuming the Sun is further away than the planet). Maybe "the perspective looks back towards a backlit Neptune", might have been more straightforward straightbackward??? ... I give up!

[Charles Bull]

Wow. APOD is almost always good, but today you have outdone yourself.

Absolutely stunning!

[Nitpicker]

I'm having trouble with the perspective here. Either Triton is inside the rings, which I didn't think possible, or else it's at least 30 degrees off the equatorial plane, which also seems impossible.

Triton has an unusual orbit. It is inclined about -23° (or +157°) to Neptune's equator and ring system, indicating that it orbits in the opposite direction to Neptune's axial rotation. Triton's orbit is more than five times further out than the outer-most Adams ring.

I was going to second prh's comment/question, but you answered it well Nitpicker. Your point about Triton's unusual orbit reminded me of something from an old astronomy textbook about a theory that way back in wilder, younger day's of our solar system a close encounter with another planet sized body may have flipped Triton's orbit. The idea also suggested that the same near miss may have also torn former Neptunian moons loose, forming today's Plutonian system. Are these ideas still viable as possibilities?

I don't know if they are still viable as possibilities. I've read that the "current thinking" is, because of Triton's strange orbit and similar composition to Pluto, that Triton might have been captured, after escaping from the Kuiper Belt.

[BDanielMayfield]

Triton has an unusual orbit. It is inclined about -23° (or +157°) to Neptune's equator and ring system, indicating that it orbits in the opposite direction to Neptune's axial rotation. Triton's orbit is more than five times further out than the outer-most Adams ring.

Your point about Triton's unusual orbit reminded me of something from an old astronomy textbook about a theory that way back in wilder, younger day's of our solar system a close encounter with another planet sized body may have flipped Triton's orbit. The idea also suggested that the same near miss may have also torn former Neptunian moons loose, forming today's Plutonian system. Are these ideas still viable as possibilities?

I don't know if they are still viable as possibilities. I've read that the "current thinking" is, because of Triton's strange orbit and similar composition to Pluto, that Triton might have been captured, after escaping from the Kuiper Belt.

Yes, since posting my question I've searched a little too and have come up with nothing but the captured from the Kuiper Belt origin for both Triton and Pluto. The Kuiper belt itself might even have been unknown at the time of the book's writing.

[vmorand]

This image looks wrong to me. Judging by the angle of the terminator, a line to the sun must be perpendicular to the equator and rings of Neptune. In other words, Neptune appears to be tipped over on its side, with its pole pointing to the Sun. Uranus does this, but Neptune has an axial tilt similar to the Earth, with its poles pointing at a high angle to the ecliptic plane.

[neufer]

This image looks wrong to me. Judging by the angle of the terminator, a line to the sun must be perpendicular to the equator and rings of Neptune. In other words, Neptune appears to be tipped over on its side, with its pole pointing to the Sun. Uranus does this, but Neptune has an axial tilt similar to the Earth, with its poles pointing at a high angle to the ecliptic plane.

• Now that it's gone too far to call for a halt,
  I'll blame it on the moon
  'Cause it's not my fault;
  I didn't think that this would happen so soon
  So I'll blame it on the moon.

[url=http://physicsworld.com/cws/article/news/2011/dec/05/voyager-sets-sights-on-milky-way]Voyager sets sights on Milky Way[/url]

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<<Voyager 2's closest approach to Neptune occurred on August 25, 1989. Since this was the last planet of our Solar System that Voyager 2 could visit, the Chief Project Scientist, his staff members, and the flight controllers decided to also perform a close fly-by of Triton, the larger of Neptune's two originally known moons, so as to gather as much information on Neptune and Triton as possible, regardless of Voyager 2's departure angle from the planet. This was just like the case of Voyager 1's encounters with Saturn and its massive moon Titan.

Since the plane of the orbit of Triton is tilted significantly with respect to the plane of the ecliptic, through mid-course corrections, Voyager 2 was directed into a path several thousand miles over the north pole of Neptune. At that time, Triton was behind and below (south of) Neptune (at an angle of about 25 degrees below the ecliptic), close to the apoapsis of its elliptical orbit. The gravitational pull of Neptune bent the trajectory of Voyager 2 down in the direction of Triton. In less than 24 hours, Voyager 2 traversed the distance between Neptune and Triton, and then observed Triton's northern hemisphere as it passed over its north pole. The net and final effect on the trajectory of Voyager 2 was to bend its trajectory south below the plane of the ecliptic by about 30 degrees. Voyager 2 is on this path permanently, and hence, it is exploring space south of the plane of the ecliptic, measuring magnetic fields, charged particles, etc., there, and sending the measurements back to the Earth via telemetry.

While in the neighborhood of Neptune, Voyager 2 discovered the "Great Dark Spot", which has since disappeared, according to observations by the Hubble Space Telescope. Originally thought to be a large cloud itself, the "Great Dark Spot" was later hypothesized to be a hole in the visible cloud deck of Neptune.>>