Newsgroup: it.scienza.astronomia
Titolo: Voyager 1 vicina ai confini dell'eliosfera

From about August 1, 2002 to February 5,
2003, scientists noticed unusual readings from
the two energetic particle instruments on
Voyager 1, indicating it had entered a region
of the solar system unlike any encountered
before. This led some to claim that Voyager
may have entered a transitory feature of the
termination shock. Just as small bumps and
"fingers" appear and disappear in the rough
edge of the water flow over a plate, Voyager
might have entered a temporary "finger" in the
edge of the termination shock.
The controversy would be resolved easily if
Voyager could still measure the speed of the
solar wind, because the solar wind slows
abruptly at the termination shock. However,
the instrument that measures solar wind speed
no longer functions on the venerable
spacecraft, so scientists must use data from
the instruments that are still working to infer
if Voyager pierced the termination shock.
Evidence for crossing the shock includes
Voyager's observation that high-velocity
electrically-charged particles (electrons and
ions) increased more than 100 times during the
August 1, 2002 to February 5, 2003 period.
This would be expected if Voyager passed the
termination shock, because the shock
naturally accelerates electrically charged
particles that bounce back and forth like ping
pong balls between the fast and slow winds
on the opposite sides of the shock.
Secondly, the particles were flowing
outward, past Voyager and away from the
Sun. This would be expected if Voyager
already crossed beyond the termination shock,
because the acceleration region in the
termination shock would now be behind the
spacecraft. Third, an indirect measure of the
solar wind speed indicated the solar wind was
slow during this period, as would be expected
if Voyager was beyond the shock.
"We have used an indirect technique to show that the solar wind slowed down from about
700,000 mph to much less than 100,000 mph. This same technique was used by us before,
when the instrument measuring the solar wind speed was still working, and the agreement
between the two measurements was better than 20% in most cases," said Krimigis.
Evidence against entry into the shock includes the observation that while there was a
dramatic increase in low-speed particles, they weren't seen at the somewhat higher speeds
scientists believe the termination shock generates.
However, the strongest evidence against entry is Voyager's observation that the magnetic
field did not increase during this period. According to theoretical models, this must happen
whenever the solar wind slows down. Imagine a highway with moderate traffic. If
something makes the drivers slow down, say a puddle of water, the cars pile up - their
density increases. In the same way, the density (intensity) of the magnetic field carried 
by the solar wind will increase if the solar wind slows down. 
"The analysis of the Voyager 1 magnetic field observations in late 2002 indicate that it did
not enter a new region of the distant heliosphere by having crossed the termination shock.
Rather, the magnetic field data had the characteristics to be expected based upon many years
of previous observations, although the intensity of energetic particles observed is unusually
high," said Burlaga.
The teams agree that Voyager 1 has seen a new phenomenon: a six-month period when
low-energy particles were very abundant and flowing away from the Sun. When the unusual
period ended, both agree that Voyager 1 was back in the solar wind, so if this was a
temporary passage beyond the termination shock, the shock will be seen again, probably in
the next couple years. Finally, the observations indicate that the termination shock is a lot
more complicated than anyone thought. 
For their original missions to Jupiter and Saturn, Voyager 1 and sister spacecraft Voyager 2
were destined to regions of space where solar panels would not be feasible, so each was
equipped with three radioisotope thermoelectric generators to produce electrical power for
the spacecraft systems and instruments. Still operating in remote, cold and dark conditions
26 years later, the Voyagers owe their longevity to these Department of Energy-provided
generators, which produce electricity from the heat generated by the natural decay of
plutonium dioxide.
The Voyagers were built by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.,
which continues to operate both spacecraft 26 years after their launch. The spacecraft are
controlled and their data returned through NASA's Deep Space Network (DSN), a global
spacecraft tracking system also operated by JPL. The Voyager Project Manager is Ed Massey
of JPL. The Voyager Project Scientist is Dr. Edward Stone of the California Institute of
Technology.
 

 VOYAGER SPACECRAFT APPROACHING SOLAR SYSTEM'S FINAL FRONTIER
Per me il voyager 1 e 2 hanno una nota "sentimentale" visto che sono stati
lanciati nell'anno della mia nascita!
Ale
www.spazio77.altervista.org


Anche per me in un certo senso. Il mio primo ricordo "spaziale" e' 
quello della missione Apollo-Soyuz, ma e' estremamente confuso. Ricordo 
invece perfettamente il fly-by di Saturno della Voyager-2 che e' stato 
anche quello che ha fatto scattare il mio interesse nell'astronautica...
lancio un sondaggio: qual'e' l'evento spaziale piu' vecchio che ricordate??

 lancio un sondaggio: qual'e' l'evento spaziale piu' vecchio che ricordate??
Le Gemini, con le prime "passeggiate spaziali" e i primi attracchi tra
veicoli (Gemini/Agena).
Poi ovviamente tutto il programma Apollo.
La notte tra 20 e 21 luglio 1969 è stata la mia prima "notte brava"...
Ciao.
 
-- 
Roberto Rosoni
<roberto...@tisLOCKcali.it> (Remove the lock in your replies)
 
"Ai bambini buoni la Dolce Euchessina" "E a quelli cattivi?" "Che spingano!" (M.Marchesi)
 

 lancio un sondaggio: qual'e' l'evento spaziale piu' vecchio che
ricordate??
Quello che ricordo piu' distintamente e' il flyby di Voyager 2 con Urano nel
1989.
Ho qualche ricordo confuso di un pericoloso rientro di un satellite: mi
aveva fatto molta impressione una storia su "topolino" ispirata proprio
all'evento :-)
Ciao!
-- 
 Paolo Sirtoli
 Homepage:    
http://www.vialattea.net/sirtoli
 Divulgazione scientifica:   
http://www.vialattea.net
 Societa' Astronomica Orobica:  
http://www.vialattea.net/sao

 1989.
Oooppsss volevo dire Nettuno ..

 
Potrebbe essere il Kosmos 954 nel 1979, se non ricordo male, quello 
caduto in canada col suo generatore nucleare...

 caduto in canada col suo generatore nucleare...
Ho scovato un sito con un database delle storie di Topolino
http://www.cce.unifi.it/~marcobar/DisneyIndex/indice.html
e la storia di cui parlavo e' "Zio Paperone e il satellite bomba" del
novembre 1981.
In effetti potrebbe essere stata ispirata dalla caduta del Kosmos 954. Un
altro kosmos cadde nel gennaio 1983 ma ... senza storie :)



l'impatto con la cometa Shoemaker-Levy su Giove
avrņ avuto sģ e no sei anni ...


Il lancio di Gagarin. Avevo poco piů di quattro anni ma lo ricordo ancora.
Altro evento che mi ricordo (forse anche di piů) fu il lancio nel 1963 del
Telstar, primo satellite per telecomunicazioni attivo (in precedenza erano
stati lanciati dei palloni che dovevano funzionare da riflettori ma non mi
ricordo il nome). Mi ricordo che la sera uscivo dall'albergo che allora
avevano i miei genitori per cercare fra le tante stelle una che si
muovesse!!!
Renzo
--------------------------------
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 ha scritto nel messaggio
news:81Z73Z113Z169Y1...@usenet.libero.it...
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 Inviato via 
http://arianna.libero.it/usenet/
Ciao,
-- 
      Ermanno Polli che tra qualche anno (Berlusconi permettendo) andra'
in pensione.  (INFN-LNF)
    user:      hostname:  subdomain:  domain:  country:
ermanno.polli    N/A        lnf         infn     it

 Da cui la famosa frase "il satellite sta per lasciarci".
Il problema, visto il livello qualitativo di tante trasmissioni, č che poi
ritorna :-(((
Renzo

 > Piu' in la' non si puo' andare...
 Come no,  4 ottobre 1957  l'annuncio alle ore 12,10 alla radio (Gazzettino
Padano) del lancio del missile balistico intercontinentale R7 con il primo
satellite artificiale della storia: lo Sputnik-1.
saluti


Appunto.
Ermanno parlava proprio di quello!
