APOD: MyCn18: An Hourglass Planetary Nebula (2015 May 10)

[RocketRon]

Chris is extending the Solar System limits into the Oort Cloud.

The Oort cloud goes for half a light year (approx) out into space ?

Mentioning the Solar System and a light year even in the same sentence seems a somewhat mismatched size comparison...

[neufer]

Chris is extending the Solar System limits into the Oort Cloud.

The Oort cloud goes for half a light year (approx) out into space ?

<<The Oort cloud is thought to occupy a vast space from somewhere between
2,000 & 5,000 AU (0.03 & 0.08 ly) to as far as 50,000 AU (0.79 ly) from the Sun.>>

Mentioning the Solar System and a light year even in the same sentence seems a somewhat mismatched size comparison...

• Old fashion & parochial thinking!

[RocketRon]

Yes, they keep shifting the goalposts, without even consulting.
Alas, poor pluto the ex-planet.

Didn't they relatively recently announce that one of the Voyagers had left the Solar System.
That was nothing like that distance ?

Can even we see all these oorts that far out ?

[neufer]

Yes, they keep shifting the goalposts, without even consulting.
Alas, poor pluto the ex-planet.

Didn't they relatively recently announce that one of the Voyagers had left the Solar System.
That was nothing like that distance ?

Can even we see all these oorts that far out ?

• We can always see fallen oorts. But Voyager 1 will be defunct long before it reaches the cloud.

[b][color=#0000FF]Plot showing a dramatic decrease in the rate of solar wind particle detection by Voyager 1 (October 2011 through October 2012)[/color][/b]

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<<On September 12, 2013, NASA officially confirmed that Voyager 1 had reached the interstellar medium in August 2012 as previously observed, with a generally accepted date of August 25, 2012, the date durable changes in the density of energetic particles were first detected. By this point most space scientists had abandoned the belief that a change in magnetic field direction must accompany crossing of the heliopause; a new model of the heliopause predicted that no such change would be found. A key finding that persuaded many scientists that the heliopause had been crossed was an indirect measurement of an 80-fold increase in electron density, based on the frequency of plasma oscillations observed beginning on April 9, 2013, triggered by a solar outburst that had occurred in March 2012 (Electron density is expected to be two orders of magnitude higher outside the heliopause than within). Weaker sets of oscillations measured in October and November 2012 provided additional data. An indirect measurement was required because Voyager 1's plasma spectrometer had stopped working in 1980. In September 2013, NASA released audio renditions of these plasma waves. The recordings represent the first sounds to be captured in interstellar space.

While Voyager 1 is commonly spoken of as having left the Solar System simultaneously with having left the heliosphere, the two are not the same. The Solar System is usually defined as the vastly larger region of space populated by bodies that orbit the Sun. The craft is presently less than one seventh the distance to the aphelion of Sedna, and it has not yet entered the Oort cloud, the source region of long-period comets, regarded by astronomers as the outermost zone of the Solar System.

Voyager 1 will reach the Oort cloud in about 300 years and take about 30,000 years to pass through it. Though it is not heading towards any particular star, in about 40,000 years, it will pass within 1.6 light years of the star Gliese 445, which is at present in the constellation Camelopardalis. That star is generally moving towards the Solar System at about 119 km/s. NASA says that "The Voyagers are destined—perhaps eternally—to wander the Milky Way."

Provided Voyager 1 does not collide with anything and is not retrieved, the New Horizons space probe will never pass it, despite being launched from Earth at a faster speed than either Voyager spacecraft. New Horizons is traveling at about 15 km/s, 2 km/s slower than Voyager 1, and is still slowing down. When New Horizons reaches the same distance from the Sun as Voyager 1 is now, its speed will be about 13 km/s (vs. 17 km/s for Voyager 1).>>

[Chris Peterson]

Can even we see all these oorts that far out ?

We can't see the Oort cloud at all. Its very existence is based on theory. Of course, it's pretty solid theory, supported by the evidence of bodies in the inner system that are best explained as having originated in a distant halo. And in recent years, we've observed such structures around other stars.