Starship Asterisk*

by **neufer** » Sat Dec 19, 2009 11:00 pm

Frenchy wrote:Do they know what caused the magnetic disconnection event in the ion tail?

Probably, a Coronal mass ejection;

or, perhaps, it was just clipped by "the Parker spiral:"

ttp://en.wikipedia.org/wiki/Interplanetary_Magnetic_Field wrote:
<<The Interplanetary Magnetic Field (IMF) is the term for the Sun’s magnetic field carried by the solar wind among the planets of the Solar System.

The heliospheric current sheet is a three-dimensional form of a Parker spiral that results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium. Since the solar wind is a plasma, it has the characteristics of a plasma, rather than a simple gas. For example, it is highly electrically conductive so that magnetic field lines from the Sun are carried along with the wind. The dynamic pressure of the wind dominates over the magnetic pressure through most of the solar system (or heliosphere), so that the magnetic field is pulled into an Archimedean spiral pattern (the Parker spiral) by the combination of the outward motion and the Sun's rotation.

Depending on the hemisphere and phase of the solar cycle, the magnetic field spirals inward or outward; the magnetic field follows the same shape of spiral in the northern and southern parts of the heliosphere, but with opposite field direction. These two magnetic domains are separated by a two current sheet (an electric current that is confined to a curved plane). This heliospheric current sheet has a similar shape to a twirled ballerina skirt, and changes in shape through the solar cycle as the Sun's magnetic field reverses about every 11 years.

The plasma in the interplanetary medium is also responsible for the strength of the Sun's magnetic field at the orbit of the Earth being over 100 times greater than originally anticipated. If space were a vacuum, then the Sun's 10-4 tesla magnetic dipole field would reduce with the cube of the distance to about 10-11 tesla. But satellite observations show that it is about 100 times greater at around 10-9 tesla. Magnetohydrodynamic (MHD) theory predicts that the motion of a conducting fluid (e.g. the interplanetary medium) in a magnetic field, induces electric currents which in turn generates magnetic fields, and in this respect it behaves like a MHD dynamo.>>

by **Frenchy** » Sat Dec 19, 2009 10:16 pm

Do they know what caused the magnetic disconnection event in the ion tail?

by **neufer** » Fri Dec 18, 2009 11:30 am

Frenchy wrote:If this is a comet, then where is the dust tail? All I see is an ion tail.

http://en.wikipedia.org/wiki/Comet_Hyakutake wrote:
After its close approach to the Earth, the comet faded to about 2nd magnitude. It reached perihelion on May 1, 1996, brightening again and exhibiting a dust tail in addition to the gas tail seen as it passed the Earth. By this time, however, it was close to the Sun and was not seen as easily. It was observed passing perihelion by the SOHO Sun-observing satellite, which also recorded a large coronal mass ejection being formed at the same time. Its distance from the Sun at perihelion was 0.23 AU, well inside the orbit of Mercury. After its perihelion passage, Hyakutake faded rapidly and was lost to naked-eye visibility by the end of May. Its orbital path carried it rapidly into the southern skies, but following perihelion it became much less monitored. The last known observation of the comet took place on November 2.

http://antwrp.gsfc.nasa.gov/apod/ap960313.html
http://antwrp.gsfc.nasa.gov/apod/ap960319.html
http://antwrp.gsfc.nasa.gov/apod/ap960322.html
http://antwrp.gsfc.nasa.gov/apod/ap960323.html
http://antwrp.gsfc.nasa.gov/apod/ap960325.html
http://antwrp.gsfc.nasa.gov/apod/ap960328.html
http://antwrp.gsfc.nasa.gov/apod/ap960502.html

by **Chris Peterson** » Fri Dec 18, 2009 6:58 am

Frenchy wrote:If this is a comet, then where is the dust tail? All I see is an ion tail.

It had both. Hyakutake was one of the most active comets ever studied. Despite a small core (only about 2km across) it had a very high rate of dust output. Radar also showed a cloud of pebble sized debris surrounding the nucleus.

There's no "if" about it being a comet. That is established with 100% certainty. What else would anybody imagine it to be?

by **Frenchy** » Fri Dec 18, 2009 3:44 am

If this is a comet, then where is the dust tail? All I see is an ion tail.

by **neufer** » Thu Dec 17, 2009 6:07 pm

DavidLeodis wrote:In 100,000 years humans may be so advanced in space travel than now that I wonder if objects seen then in 'Outer Space' will be such that a Comet Hyakutake will be considered of such minor significance that nobody will think anything of it! For now here's hoping a new bright comet will appear soon as I doubt I will be around to see Hyakutake's next appearance, which is a shame.

Remember that Comet Hyakutake was a bright "great comet" solely because of its close 1996 AD passage to earth.

I doubt that humans on Earth will be any more impressed with (magnitude 5.3 at 1 AU) Hyakutake
in 100,000 years than the Magdalenian culture was impressed 17,000 years ago.

It's not the comet but rather it's the random coincidence of passing close to earth.

http://en.wikipedia.org/wiki/Swastika wrote:
<<[In his book Comet, Carl Sagan] reproduces an ancient Chinese manuscript (the Book of Silk) that shows comet tail varieties: most are variations on simple comet tails, but the last shows the comet nucleus with four bent arms extending from it, recalling a swastika. Sagan suggests that in antiquity a comet could have approached so close to Earth that the jets of gas streaming from it, bent by the comet's rotation, became visible, leading to the adoption of the swastika as a symbol across the world.>>
A seal from the Indus Valley Civilization recovered at Dholavira in India.

http://antwrp.gsfc.nasa.gov/apod/ap970414.html wrote:

by **DavidLeodis** » Thu Dec 17, 2009 5:57 pm

In 100,000 years humans may be so advanced in space travel than now that I wonder if objects seen then in 'Outer Space' will be such that a Comet Hyakutake will be considered of such minor significance that nobody will think anything of it! For now here's hoping a new bright comet will appear soon as I doubt I will be around to see Hyakutake's next appearance, which is a shame.

by **Chris Peterson** » Thu Dec 17, 2009 4:46 pm

Czerno wrote:Can we say the 100,000 yrs figure is not the result of a deterministic trajectory calculation, rather being a statistical mean (mathematical expectation) considering probable perturbations plus inaccuracies in the measured astrometric elements ?

I believe the figure is derived from an accurate astrometric solution of the orbital elements. While in the inner Solar System, Hyakutake's orbit was very accurately determined, and that phase of its orbit was very stable. The resulting period was probably rounded to an even 100,000 years for two reasons: it's an easy number to quote and remember, and the actual value has a huge uncertainty attached to it because of the unpredictable effects of gravitational perturbations acting on it for most of its orbit. I doubt the rounding process involved anything as sophisticated as a rigorous error analysis.

by **Czerno** » Thu Dec 17, 2009 4:31 pm

Can we say the 100,000 yrs figure is not the result of a deterministic trajectory calculation, rather being a statistical mean (mathematical expectation) considering probable perturbations plus inaccuracies in the measured astrometric elements ?

by **bystander** » Thu Dec 17, 2009 3:16 pm

DavidLeodis wrote:Thanks for your reply bystander. I had read the "being gravitationally deflected" but my question was is such a large differnce in reappearance times usual or not, as 83,000 years difference does seem a lot. I apologise that my query may have been phrased badly.

Sorry, didn't mean to sound condescending. I got distracted. I had remembered an earlier post of Art's

neufer wrote:
(If it didn't affect later gravitationally deflections by the massive planets
_ a small nudge of just ~5 m/s during its passage of the Earth
could have ejected Comet Hyakutake from the solar system.)

I was going to add that along with the observation: Apparently minor disturbances in a comets trajectory can cause major changes in its orbit and period.

by **DavidLeodis** » Thu Dec 17, 2009 2:21 pm

Thanks neufer. Your post must have come in while I was still doing mine.

by **DavidLeodis** » Thu Dec 17, 2009 2:18 pm

bystander wrote:
DavidLeodis wrote:In the explanation it states Comet Hyakutake is not expected back for about 100,000 years. The explanation also states it may have been seen 17,000 years ago by the Magdalenian people and it was seen in 1996. Is it usual for the time between appearances of a comet to vary by such a long time.

APOD Robot wrote:Because of being gravitationally deflected by massive planets, Comet Hyakutake is not expected back for about 100,000 years.

Thanks for your reply bystander. I had read the "being gravitationally deflected" but my question was is such a large differnce in reappearance times usual or not, as 83,000 years difference does seem a lot. I apologise that my query may have been phrased badly.

by **neufer** » Thu Dec 17, 2009 2:11 pm

DavidLeodis wrote:In the explanation it states Comet Hyakutake is not expected back for about 100,000 years. The explanation also states it may have been seen 17,000 years ago by the Magdalenian people and it was seen in 1996. Is it usual for the time between appearances of a comet to vary by such a long time.

Unlike quasi-stable short period elliptical comets like Halley,
it takes very little nudging for a quasi-parabolic long period comet to become
a quasi-parabolic very long period comet (or even ejected from the solar system):

Hyakutake's previous aphelion was at about [2 x (17,000^2/3) AU] ~1320 AU.

Solar escape velocity at 1 AU is ~ 42.12 km/s
Solar escape velocity out at 1320 AU is [42.12 /sqrt(1320)] ~ 1.16 km/s

---------------------------------
Scenario #1) Hyakutake was nudged 11 m/s faster by its close encounter with Earth:

Hyakutake incoming velocity near Earth = sqrt(42.12²-1.16²) ~ 42.104 km/s
Hyakutake outgoing velocity near Earth = sqrt(42.12²-0.64²) ~ 42.115 km/s
---------------------------------
Scenario #2) Hyakutake was nudged 36 m/s faster by Jupiter:

Solar escape velocity near Jupiter is ~ 13.07 km/s

Hyakutake incoming velocity near Jupiter = sqrt(13.07²-1.16²) ~ 13.018 km/s
Hyakutake outgoing velocity near Jupiter = sqrt(13.07²-0.64²) ~ 13.054 km/s
---------------------------------

Or some combination of the above.

by **bystander** » Thu Dec 17, 2009 1:23 pm

DavidLeodis wrote:In the explanation it states Comet Hyakutake is not expected back for about 100,000 years. The explanation also states it may have been seen 17,000 years ago by the Magdalenian people and it was seen in 1996. Is it usual for the time between appearances of a comet to vary by such a long time.

APOD Robot wrote:Because of being gravitationally deflected by massive planets, Comet Hyakutake is not expected back for about 100,000 years.

by **DavidLeodis** » Thu Dec 17, 2009 12:37 pm

In the explanation it states Comet Hyakutake is not expected back for about 100,000 years. The explanation also states it may have been seen 17,000 years ago by the Magdalenian people and it was seen in 1996. Is it usual for the time between appearances of a comet to vary by such a long time.

by **neufer** » Thu Dec 17, 2009 12:51 am

Frenchy wrote:Could Hyakutake be a class B2 star shedding its heliosheath?

No.

by **Frenchy** » Thu Dec 17, 2009 12:11 am

Could Hyakutake be a class B2 star shedding its heliosheath?

by **neufer** » Wed Dec 16, 2009 5:09 pm

orin stepanek wrote:
Because of being gravitationally deflected by massive planets, Comet Hyakutake is not expected back for about 100,000 years.
And that's a long time. I would think such a long orbit would take it away from the suns influence completely; or it would have to be thrown into a more circular orbit and not come back at all.

Hyakutake should reach aphelion at about [2 x (100,000^^2/3) AU] ~4300 AU.

Solar escape velocity at 1 AU is ~ 42.12 km/s
Solar escape velocity out at 4300 AU is [42.12 /sqrt(4300)] ~ 0.64 km/s

(If it didn't affect later gravitationally deflections by the massive planets
_ a small nudge of just ~5 m/s during its passage of the Earth
could have ejected Comet Hyakutake from the solar system.)

by **orin stepanek** » Wed Dec 16, 2009 3:01 pm

Because of being gravitationally deflected by massive planets, Comet Hyakutake is not expected back for about 100,000 years.

And that's a long time.

I would think such a long orbit would take it away from the suns influence completely; or it would have to be thrown into a more circular orbit and not come back at all.

Anyway I think comets are among the coolest of solar objects when they come into the inner reaches of the solar system displaying the corona and tail.

by **APOD Robot** » Wed Dec 16, 2009 4:56 am

Comet Hyakutake Passes the Earth

Explanation: In 1996, an unexpectedly bright comet passed by planet Earth. Discovered less than two months before, Comet C/1996 B2 Hyakutake came within only 1/10th of the Earth-Sun distance from the Earth in late March. At that time, Comet Hyakutake, dubbed the Great Comet of 1996, became the brightest comet to grace the skies of Earth in 20 years. During its previous visit, Comet Hyakutake may well have been seen by the stone age Magdalenian culture, who 17,000 years ago were possibly among the first humans to live in tents as well as caves. Pictured above near closest approach as it appeared on 1996 March 26, the long ion and dust tails of Comet Hyakutake are visible flowing off to the left in front of a distant star field that includes both the Big and Little Dippers. On the far left, the blue ion tail appears to have recently undergone a magnetic disconnection event. On the far right, the comet's green-tinted coma obscures a dense nucleus of melting dirty ice estimated to be about 5 kilometers across. A few months later, Comet Hyakutake began its long trek back to the outer Solar System. Because of being gravitationally deflected by massive planets, Comet Hyakutake is not expected back for about 100,000 years.

>

Starship Asterisk*

Comet Hyakutake Passes the Earth (2009 Dec 16)

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