Scoperto il "motore" del vento solare. Forse può aiutarci ad avere energia da fusione.

Questa è bellissima. Una sonda NASA, Wind, lanciata nel lontano 1994 e dotata di una strumentazione i cui dati vengono registrati su nastro per essere ogni volta riprodotti e trasmessi a terra, contiene forse i dati che spiegano perché il vento solare soffi tanto veloce e tanto caldo. Un perché che i ricercatori della fusione nucleare sono molto interessati a capire, perché da questa spiegazione possono a loro volta ricavare un metodo che renderà più efficienti i futuri reattori a fusione.

Il sole è un po' come una pentola che bolle, rilasciando in tutte le direzione un "vapore" costituito da un gas magnetico ricco di particelle. Al contrario della pentola, però, questo vapore non diventa più freddo e lento man mano che si allontana dal sole. Al contrario: il vento solare accelera fortemente e si riscalda attraversando l'atmosfera solare, la corona. Secondo gli scienziati alle origini del fenomeno ci sarebbero le onde di ciclotrone ionico (ione cyclotrone waves), un effetto di risonanza che coinvolge gli ioni pesanti del plasma solare e li accelera come una fionda, conservandone l'energia e quindi il calore. Forse sfruttando questo stesso meccanismo, si potrebbero intercettare e eliminare gli ioni pesanti che staccandosi dalle pareti delle camere di reazione di fusione emettono calore togliendolo alla reazione stessa, e causandone l'interruzione.

Solar Wind Energy Source Discovered

March 8, 2013: Using data from an aging NASA spacecraft, researchers have found signs of an energy source in the solar wind that has caught the attention of fusion researchers. NASA will be able to test the theory later this decade when it sends a new probe into the sun for a closer look.

The discovery was made by a group of astronomers trying to solve a decades-old mystery: What heats and accelerates the solar wind?

The solar wind is a hot and fast flow of magnetized gas that streams away from the sun's upper atmosphere.  It is made of hydrogen and helium ions with a sprinkling of heavier elements.  Researchers liken it to the steam from a pot of water boiling on a stove; the sun is literally boiling itself away.

“But,” says Adam Szabo of the NASA Goddard Space Flight Center, “solar wind does something that steam in your kitchen never does.  As steam rises from a pot, it slows and cools.  As solar wind leaves the sun, it accelerates, tripling in speed as it passes through the corona. Furthermore, something inside the solar wind continues to add heat even as it blows into the cold of space."

Finding that "something" has been a goal of researchers for decades.  In the 1970s and 80s, observations by two German/US Helios spacecraft set the stage for early theories, which usually included some mixture of plasma instabilities, magnetohydrodynamic waves, and turbulent heating.  Narrowing down the possibilities was a challenge. The answer, it turns out, has been hiding in a dataset from one of NASA's oldest active spacecraft, a solar probe named Wind.

Launched in 1994, Wind is so old that it uses magnetic tapes similar to old-fashioned 8-track tapes to record and play back its data.  Equipped with heavy shielding and double-redundant systems to safeguard against failure, the spacecraft was built to last; at least one researcher at NASA calls it the "Battlestar Gallactica" of the heliophysics fleet. Wind has survived almost two complete solar cycles and innumerable solar flares.

"After all these years, Wind is still sending us excellent data," says Szabo, the mission’s project scientist, “and it still has 60 years' worth of fuel left in its tanks.”

Using Wind to unravel the mystery was, to Justin Kasper of the Harvard-Smithsonian Center for Astrophysics, a "no brainer." He and his team processed the spacecraft's entire 19-year record of solar wind temperatures, magnetic field and energy readings and ...

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Le forme del vento (solare) e altri Camps (In)visibles

Da un autorevole blog scientifico Renato Bruni segnala un post relativo a uno strano lavoro di videoart basato sull'elaborazione audiovisuale dei dati raccolti dalla rete di magnetometri canadese CARISMA della Università dell'Alberta. L'opera è stata realizzata da una coppia di artisti, Ruth Jarman e Joe Gerhardt meglio conosciuti come Semiconductorfilms. Il loro lavoro si chiama "20 Hz" ed è stato ottenuto rielaborando i file che CARISMA archivia da anni sul sito del Canadian Space Science Data Portal per mostrare, letteralmente, gli effetti del vento solare durante una tempesta magnetica, un insieme di suoni e forme geometriche che ricordano un caleidoscopio e ci appaiono misteriose e inquietanti.

Un esoterico laboratorio di ricerca che effettua le sue osservazioni nello spettro delle radiofrequenze ULF diventa così uno dei protagonisti di Camps Invisibles, una esposizione che si concluderà il prossimo 4 marzo e attualmente in corso presso la galleria di arte moderna Arts Santamonica di Barcellona (se vi sentite più a vostro agio con l'inglese piuttosto che con il catalano, ecco il link a Invisible Fields). La mostra vuole esplorare in chiave artistica le conseguenze dei nostri studi sulle radioonde nella comprensione del mondo e dell'universo.

Voyager 1: il vento (solare) non soffia più

Si trova a oltre 17 miliardi di chilometri di distanza da noi ma continua a stupirci con le sue misurazioni. Voyager 1, lanciata nel 1977, sta per raggiungere lo spazio interstellare ma continua a rilevare con la strumentazione LECP (low energy charged particles) le particelle del vento solare. Solo che questo vento ha ormai raggiunto una velocità pari a zero, dopo una decelerazione iniziata tre anni fa, quando la "brezza" soffiava a circa 200 mila chilometri all'ora. La sonda è entrata da allora nella Eliopausa, il guscio più esterno del volume di influenza del nostro astro. Ora quel guscio sta per finire, ma Voyager incredibilmente trasmette ancora, come la sua compagna Voyager 2, un po' più lenta e dunque leggermente più vicina a noi. La telemetria di Voyager 1 si riceve su 8,415 GHz, nel gennaio scorso ha fatto scalpore il caso dell'astrofisico spagnolo che era riuscito a riceverla con una parabola radioastronomica da 40 metri e un setup costituito da un ricevitore SDR Perseus (la sottile linea sghemba della foto). I dati strumentali viaggiano a un rate compreso tra 10 bit al secondo e i 115,2 ma il valore efficace è di soli 3,2 kbps. Potete ascoltare la voce del Voyager sul sito Sounds of Space, di Matthias Bopp DD1US.

NASA Probe Sees Solar Wind Decline En Route To Interstellar Space

PASADENA, Calif. -- The 33-year odyssey of NASA's Voyager 1 spacecraft has reached a distant point at the edge of our solar system where there is no outward motion of solar wind.

Now hurtling toward interstellar space some 10.8 billion miles from the sun, Voyager 1 has crossed into an area where the velocity of the hot ionized gas, or plasma, emanating directly outward from the sun has slowed to zero. Scientists suspect the solar wind has been turned sideways by the pressure from the interstellar wind in the region between stars.

The event is a major milestone in Voyager 1's passage through the heliosheath, the turbulent outer shell of the sun's sphere of influence, and the spacecraft's upcoming departure from our solar system.

"The solar wind has turned the corner," said Ed Stone, Voyager project scientist based at the California Institute of Technology in Pasadena, Calif. "Voyager 1 is getting close to interstellar space."

Our sun gives off a stream of charged particles that form a bubble known as the heliosphere around our solar system. The solar wind travels at supersonic speed until it crosses a shockwave called the termination shock. At this point, the solar wind dramatically slows down and heats up in the heliosheath.

Launched on Sept. 5, 1977, Voyager 1 crossed the termination shock in December 2004 into the heliosheath. Scientists have used data from Voyager 1's Low-Energy Charged Particle Instrument to deduce the solar wind's velocity.

When the speed of the charged particles hitting the outward face of Voyager 1 matched the spacecraft's speed, researchers knew that the net outward speed of the solar wind was zero. This occurred in June, when Voyager 1 was about 10.6 billion miles from the sun.

Because the velocities can fluctuate, scientists watched four more monthly readings before they were convinced the solar wind's outward speed actually had slowed to zero. Analysis of the data shows the velocity of the solar wind has steadily slowed at a rate of about 45,000 mph each year since August 2007, when the solar wind was speeding outward at about 130,000 mph. The outward speed has remained at zero since June.

The results were presented at the American Geophysical Union meeting in San Francisco. "When I realized that we were getting solid zeroes, I was amazed," said Rob Decker, a Voyager Low-Energy Charged Particle Instrument co-investigator and senior staff scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "Here was Voyager, a spacecraft that has been a workhorse for 33 years, showing us something completely new again."

Scientists believe Voyager 1 has not crossed the heliosheath into interstellar space. Crossing into interstellar space would mean a sudden drop in the density of hot particles and an increase in the density of cold particles. Scientists are putting the data into their models of the heliosphere's structure and should be able to better estimate when Voyager 1 will reach interstellar space. Researchers currently estimate

Voyager 1 will cross that frontier in about four years.

"In science, there is nothing like a reality check to shake things up, and Voyager 1 provided that with hard facts," said Tom Krimigis, principal investigator on the Low-Energy Charged Particle Instrument, who is based at the Applied Physics Laboratory and the Academy of Athens, Greece. "Once again, we face the predicament of redoing our models."

A sister spacecraft, Voyager 2, was launched in Aug. 20, 1977 and has reached a position 8.8 billion miles from the sun. Both spacecraft have been traveling along different trajectories and at different speeds. Voyager 1 is traveling faster, at a speed of about 38,000 mph, compared to Voyager 2's velocity of 35,000 mph. In the next few years, scientists expect Voyager 2 to encounter the same kind of phenomenon as Voyager 1.

Una strana smagliatura nella magnetosfera terrestre

Lo scorso anno le sonde della missione THEMIS con le loro misure hanno fatto una scoperta eccezionale proprio mentre stavano attraversando la linea di confine dove il vento solare interagisce con la magnetosfera terrestre. La missione THEMIS è stata concepita dalla NASA proprio per studiare questo tipo di interazioni, mettendo in evidenza i meccanismi che finiscono per generare fenomeni come la aurore boreali.
La scoperta consiste in una estesa smagliatura nel campo magnetico che avvolge la terra, un evento che ha stupito gli scienziati non tanto per il fatto in sé (queste smagliature sono all'ordine del giorno), ma per le modalità di comparsa. Finora si credeva che la magnetosfera si "allentasse" quando si trovava a interagire, nell'emisfero settentrionale, con un vento solare il cui campo puntasse verso sud. Questa regola, finora, era stata ferrea, ma le sonde THEMIS hanno misurato la smagliatura in una situzione del tutto opposta: con il campo sul fronte del vento solare che puntava a nord (la teoria voleva che un campo così orientato avrebbe dovuto rinforzare, non indebolire, il campo terrestre).
Quali conseguenze potrebbe avere questa scoperta? Quando nella magnetosfera si aprono questi squarci, il vento solare la carica come una pila. Una pila pronta a scatenare gli eventi aurorali quando il vento solare subisce le sue improvvise accelerazioni o in presenza di eventi coronali eiettivi. E' come se un forte colpo di frusta rompesse il vaso riempito di vento solare. Ora i fisici cominciano ad associare questa nuova osservazione con un'altra circostanza: durante i cicli solari di numero pari, come questo ciclo 24, il fronte del vento solare è orientato comunemente verso nord. Se un vento di questo tipo può "sfondare" facilmente la magnetosfera, dicono gli scienziati, ci si può aspettare eventi molto intensi nel corso delle tempeste che caratterizzeranno questo ciclo.

A Giant Breach in Earth's Magnetic Field

12.16.2008

Dec. 16, 2008: NASA's five THEMIS spacecraft have discovered a breach in Earth's magnetic field ten times larger than anything previously thought to exist. Solar wind can flow in through the opening to "load up" the magnetosphere for powerful geomagnetic storms. But the breach itself is not the biggest surprise. Researchers are even more amazed at the strange and unexpected way it forms, overturning long-held ideas of space physics.
"At first I didn't believe it," says THEMIS project scientist David Sibeck of the Goddard Space Flight Center. "This finding fundamentally alters our understanding of the solar wind-magnetosphere interaction."
The magnetosphere is a bubble of magnetism that surrounds Earth and protects us from solar wind. Exploring the bubble is a key goal of the THEMIS mission, launched in February 2007. The big discovery came on June 3, 2007, when the five probes serendipitously flew through the breach just as it was opening. Onboard sensors recorded a torrent of solar wind particles streaming into the magnetosphere, signaling an event of unexpected size and importance.
"The opening was huge—four times wider than Earth itself," says Wenhui Li, a space physicist at the University of New Hampshire who has been analyzing the data. Li's colleague Jimmy Raeder, also of New Hampshire, says "1027 particles per second were flowing into the magnetosphere—that's a 1 followed by 27 zeros. This kind of influx is an order of magnitude greater than what we thought was possible."
The event began with little warning when a gentle gust of solar wind delivered a bundle of magnetic fields from the Sun to Earth. Like an octopus wrapping its tentacles around a big clam, solar magnetic fields draped themselves around the magnetosphere and cracked it open. The cracking was accomplished by means of a process called "magnetic reconnection." High above Earth's poles, solar and terrestrial magnetic fields linked up (reconnected) to form conduits for solar wind. Conduits over the Arctic and Antarctic quickly expanded; within minutes they overlapped over Earth's equator to create the biggest magnetic breach ever recorded by Earth-orbiting spacecraft.

(a sinistra) A computer model of solar wind flowing around Earth's magnetic field on June 3, 2007; white arrows trace the extent of the breach. The model is based on actual measurements made by the THEMIS probes. Background colors represent solar wind density; red is high density, blue is low. Note the layer of relatively dense material beneath the tips of the white arrows; that is solar wind entering Earth's magnetic field through the breach.

The size of the breach took researchers by surprise. "We've seen things like this before," says Raeder, "but never on such a large scale. The entire day-side of the magnetosphere was open to the solar wind."
The circumstances were even more surprising. Space physicists have long believed that holes in Earth's magnetosphere open only in response to solar magnetic fields that point south. The great breach of June 2007, however, opened in response to a solar magnetic field that pointed north.
"To the lay person, this may sound like a quibble, but to a space physicist, it is almost seismic," says Sibeck. "When I tell my colleagues, most react with skepticism, as if I'm trying to convince them that the sun rises in the west."
Here is why they can't believe their ears: The solar wind presses against Earth's magnetosphere almost directly above the equator where our planet's magnetic field points north. Suppose a bundle of solar magnetism comes along, and it points north, too. The two fields should reinforce one another, strengthening Earth's magnetic defenses and slamming the door shut on the solar wind. In the language of space physics, a north-pointing solar magnetic field is called a "northern IMF" and it is synonymous with shields up!
"So, you can imagine our surprise when a northern IMF came along and shields went down instead," says Sibeck. "This completely overturns our understanding of things."
Northern IMF events don't actually trigger geomagnetic storms, notes Raeder, but they do set the stage for storms by loading the magnetosphere with plasma. A loaded magnetosphere is primed for auroras, power outages, and other disturbances that can result when, say, a CME (coronal mass ejection) hits.
The years ahead could be especially lively. Raeder explains: "We're entering Solar Cycle 24. For reasons not fully understood, CMEs in even-numbered solar cycles (like 24) tend to hit Earth with a leading edge that is magnetized north. Such a CME should open a breach and load the magnetosphere with plasma just before the storm gets underway. It's the perfect sequence for a really big event."
Sibeck agrees. "This could result in stronger geomagnetic storms than we have seen in many years."

Il vento solare ai minimi storici, lo rivela Ulysses

Il vento solare generato dalle emissioni di plasma dal sole avrebbe raggiunto un minimo storico registrato nel mezzo secolo di misurazioni di cui disponiamo da quando esiste una strumentazione adeguata. Lo ha annunciato oggi la NASA dopo aver esaminato i primi risultati delle misure effettuate dalla sonda Ulysses, una missione congiunta della NASA e dell'ESA. Il vento solare genera intorno al nostro sistema planetario una sorta di involucro protettivo, l'eliosfera, definito da una pellicola, l'eliopausa, che rappresenta il punto in cui cessa la sfera di influenza del sole e comincia quella degli altri astri. L'eliopausa ha una funzione importante nel tenere a bada i livelli di raggi cosmici galattici. Un plasma solare meno impetuoso porta con ogni probabilità una contrazione dell'eliosfera e quindi a una minore capacità di schermatura dei raggi cosmici, che potranno penetrare più a fondo nel sistema solare. Vi prego, non correte a indossare lo scafandro, gli effetti di questa maggiore penetrazione non sono tali da indurre il panico generalizzato nella popolazione. E se non altro sarà difficile attribuire questo calo del plasma alle attività dell'uomo.
Gli ingegneri della NASA si preoccupano soprattutto delle contromisure che dovranno adottare per le missioni nello spazio esterno, per esempio nelle passeggiate spaziali degli astronauti. Meno vento solare potrebbe anche voler dire meno tempeste magnetiche.

ULYSSES REVEALS GLOBAL SOLAR WIND PLASMA OUTPUT AT 50-YEAR LOW

WASHINGTON -- Data from the Ulysses spacecraft, a joint NASA-European Space Agency mission, show the sun has reduced its output of solar wind to the lowest levels since accurate readings became available.
The sun's current state could reduce the natural shielding that envelops our solar system.
"The sun's million mile-per-hour solar wind inflates a protective bubble, or heliosphere, around the solar system. It influences how things work here on Earth and even out at the boundary of our solar system where it meets the galaxy," said Dave McComas, Ulysses' solar wind instrument principal investigator and senior executive director at the Southwest Research Institute in San Antonio. "Ulysses data indicate the solar wind's global pressure is the lowest we have seen since the beginning of the space age." The sun's solar wind plasma is a stream of charged particles ejected from the sun's upper atmosphere. The solar wind interacts with every planet in our solar system. It also defines the border between our solar system and interstellar space.
This border, called the heliopause, surrounds our solar system where the solar wind's strength is no longer great enough to push back the wind of other stars. The region around the heliopause also acts as a shield for our solar system, warding off a significant portion of the cosmic rays outside the galaxy.
"Galactic cosmic rays carry with them radiation from other parts of our galaxy," said Ed Smith, NASA's Ulysses project scientist at the Jet Propulsion Laboratory in Pasadena, Calif. "With the solar wind at an all-time low, there is an excellent chance the heliosphere will diminish in size and strength. If that occurs, more galactic cosmic rays will make it into the inner part of our solar system." Galactic cosmic rays are of great interest to NASA. Cosmic rays are linked to engineering decisions for unmanned interplanetary spacecraft and exposure limits for astronauts traveling beyond low-Earth orbit.
In 2007, Ulysses made its third rapid scan of the solar wind and magnetic field from the sun's south to north pole. When the results were compared with observations from the previous solar cycle, the strength of the solar wind pressure and the magnetic field embedded in the solar wind were found to have decreased by 20 percent. The field strength near the spacecraft has decreased by 36 percent.
"The sun cycles between periods of great activity and lesser activity," Smith said. "Right now, we are in a period of minimal activity that has stretched on longer than anyone anticipated." Ulysses was the first mission to survey the space environment over the sun's poles. Data Ulysses has returned have forever changed the way scientists view our star and its effects. The venerable spacecraft has lasted more than 18 years, or almost four times its expected mission lifetime. The Ulysses solar wind findings were published in a recent edition of Geophysical Research Letters.
The Ulysses spacecraft was carried into Earth orbit aboard space shuttle Discovery on Oct. 6, 1990. From Earth orbit it was propelled toward Jupiter, passing the planet on Feb. 8, 1992. Jupiter's immense gravity bent the spacecraft's flight path downward and away from the plane of the planets' orbits. This placed Ulysses into a final orbit around the sun that would take it over its north and south poles.
The Ulysses spacecraft was provided by ESA, having been built by Astrium GmbH (formerly Dornier Systems) of Friedrichshafen, Germany.
NASA provided the launch vehicle and the upper stage boosters. The U.S. Department of Energy supplied a radioisotope thermoelectric generator to power the spacecraft. Science instruments were provided by U.S. and European investigators. The spacecraft is operated from JPL by a joint NASA-ESA team.
More information about the Ulysses mission is available on the Web at:
http://ulysses.jpl.nasa.gov

La NASA alle origini del vento solare

Un volo di 8 minuti per cercare di carpire il segreto del vento solare. Il prossimo mese di aprile la NASA caricherà a bordo di un vettore Black Brant in partenza dalla base del Nuovo Messico uno speciale telescopio. Denominato Solar Ultraviolet Magnetograph Investigation, lo strumento servirà a osservare nell'ultravioletto la cosiddetta regione di transizione nell'atmosfera solare a 5mila metri dalla superficie dell'astro. E' in questa regione, dove il campo magnetico del sole esercita la sua azione di contenimento dei vorticosi gas al suo interno, che si verificano fenomeni come i brillamenti. E dove il vento solare viene inspiegabilmente accelerato fino alla velocità di quasi due milioni di chilometri all'ora. La regione di transizione è il punto di origine dello space weather, della meteorologia spaziale, studiata per cercare di prevedere l'andament o della propagazione radio qui sulla terra. Purtroppo, è anche una regione dove non è facile effettuare misurazioni magnetiche. Sulla superficie del sole le macchie vengono analizzate sfruttando un fenomeno definito per la prima volta dal fisico olandese Pieter Zeeman, che aveva scoperto che immergendo in un campo magnetico una bottiglia riempita di gas, le linee spettrali emesse da questo gas subiscono uno split, una fessura centrale: si spaccano in due longitudinalmente. Più forte è il campo, più ampia e profonda la spaccatura. Grazie allo split di Zeeman gli spettrogrammi delle macchie solari rivelano l'intensità magnetica del fenomeno e possono persino servire per determinane la direzione.
Tutto questo nella regione di transizione non è possibile farlo perché i gas in quella zona non producono linee spettrali nel visibile. Lo fanno nell'ultravioletto, ma qui a terra l'ultravioletto non è ben osservabile. Da cui la necessità di spedire un telescopio UV a una quota sufficientemente elevata: 300 chilometri. Sarà un volo morto corto, ma si spera indicativo. Servirà soprattutto a capire che cosa fare "dopo", quali strumenti utilizzare su quali tipi di sonde.

NASA to Explore "Secret Layer" of the Sun

Sept. 5, 2008: Next April, for a grand total of 8 minutes, NASA astronomers are going to glimpse a secret layer of the sun.

Researchers call it "the transition region." It is a place in the sun's atmosphere, about 5000 km above the stellar surface, where magnetic fields overwhelm the pressure of matter and seize control of the sun's gases. It's where solar flares explode, where coronal mass ejections begin their journey to Earth, where the solar wind is mysteriously accelerated to a million mph. It is, in short, the birthplace of space weather. Researchers hope it is about to yield its secrets.
"Early next year, we're going to launch an experimental telescope that can measure vector magnetic fields in the transition region," explains Jonathan Cirtain of the Marshall Space Flight Center (MSFC). Previous studies have measured these fields above and below the transition region—but never inside it. "We hope to be the first."
The name of the telescope is SUMI, short for Solar Ultraviolet Magnetograph Investigation. It was developed by astronomers and engineers at the MSFC and is currently scheduled for launch from White Sands, New Mexico, in April 2009.
SUMI works by means of "Zeeman splitting." Dutch physicist Pieter Zeeman discovered the effect in the 19th century. When a glass tube filled with incandescent gas is dipped into a magnetic field, spectral lines emitted by the gas get split into two slightly different colors—the stronger the field, the bigger the splitting. The same thing happens on the sun. Here, for instance, are some spectral lines from gaseous iron being split by the magnetic field of a sunspot:


Zeeman splitting of spectral lines from a strongly-magnetized sunspot








By measuring the gap, astronomers estimate the strength of the sunspot's magnetic field. Furthermore, by measuring the polarization of the split line, astronomers can figure out the direction of the magnetic field. Strength + direction = everything you ever wanted to know about a magnetic field!
This trick has been applied to thousands of sunspots on the solar surface, but never to the transition region just a short distance above.
Why not?
"Just bad luck, really," says Cirtain. "Gas in the transition region doesn't produce many strong spectral lines that we can see at visible wavelengths." It does, however, produce lines at UV wavelengths invisible from Earth's surface.
SUMI will blast off inside the nose cone of a Black Brant rocket on a sub-orbital flight that takes it to an altitude of 300 km. "We'll be above more than 99.99% of Earth's atmosphere," says Cirtain. About 68 seconds into the flight, payload doors will open, affording SUMI a crystal-clear view of the UV sun. "From that moment, we've only got 8 minutes to work with. We'll target an active region and start taking data."
SUMI's "vector magnetograph" is tuned to study a pair of spectral lines: one from triply-ionized carbon (CIV) at 155 nanometers and a second from singly-ionized magnesium (MgII) at 280 nanometers. "There's nothing special about those ions," notes Cirtain. "They just happen to produce the best and brightest lines at temperatures and densities typical of the transition region."
Cirtain anticipates how it will feel to have his precious instrument hurtling 300 km above Earth at 5,000 mph: "Eight minutes of terror." He'll start breathing again when the payload doors close and SUMI begins its descent back to Earth. Cirtain ticks off the stages: "Reentry into the atmosphere. Open parachutes. Landing back at White Sands. Recovery."
The short flight probably won't lead to immediate breakthroughs. "But it will demonstrate the SUMI concept and show us if it's going to work." A successful flight would lead to more flights and eventually to a SUMI-style magnetograph permanently installed on a space telescope.
"That's the dream," he says. Transition region, prepare to yield...

Sonda Ulysses, 17 anni nella eliosfera

Per una missione STEREO che comincia a dare i primi risultati, è tempo di pensionamento per la sonda Ulysses, lanciata 17 anni fa da ESA e NASA proprio per studiare il sole e la sua eliosfera. C'è uno splendido articolo sul sito dell'ESA da cui ricavo i principali risultati ottenuti dalla missione dichiarata ufficialmente chiusa il primo di luglio. Altro materiale, qui.

Ulysses has shown that the heliospheric magnetic field is more complicated than had been thought: its field lines follow a chaotic pattern rather than a more regular Archimedean spiral and are also more spread out in latitude than was expected. The behaviour of the Sun's magnetic dipole was by contrast found to be more simple than expected: it simply rotates through 180° from sunspot minimum through sunspot maximum and back to sunspot minimum again in order to achieve the polarity reversal that has been observed.

Ulysses observed the solar wind in 4-dimensions and demonstrated the bimodal nature of the wind: it discovered that a steady fast wind (~750 km/s) is present throughout most of the solar cycle and only vanishes at solar maximum when the polar coronal holes disappear. The slow wind (~350 km/s) emerges from the Sun's equatorial zone. The transition from fast to slow is relatively abrupt.

Prior to Ulysses energetic particles had been studied in great detail near the equator, but not at higher latitudes. Ulysses has shown that such particles are present at all phases of the solar cycle. They can be found at all latitudes at solar maximum and are shown to be confined to the inner heliosphere in 'reservoirs' from which they slowly escape. During solar minimum energetic particles can reach into the polar caps - contrary to what was expected.

The distribution of galactic cosmic rays was shown by Ulysses to be essentially spherically symmetric with the flux being the same at the equator and in the polar regions.

Ulysses measured the abundances of many radioactive cosmic-ray isotopes, and showed that these cosmic rays spend much of their lifetime (typically ~20 million years) in the galactic halo before reaching us.

Ulysses directly measured the properties of interstellar gas (neutral helium) for the first time. It also showed that the interstellar wind is fast enough to create a bow shock upstream of the heliosphere.

Dust particles of interstellar origin were detected by Ulysses proving that they can enter the heliosphere. Large dust grains, with an average mass 30 times greater than expected, were also detected. These contribute ~2% to the total mass of the interstellar medium.

Measurements by Ulysses of interstellar helium isotope abundances at the current epoch are consistent with Big Bang theory of light element formation and with a matter density supporting an 'open' Universe.

Il vento del polo (solare) soffia su Ulysses

La missione Ulysses è arrivata alla terza orbita sovrastante i poli del sole. La sonda NASA/ESA offre l'eccezionale possibilità di studiare il vento solare emesso in corrispondenza delle regioni polari proprioall'inizio di un nuovo ciclo. Oltre a questo breve articolo della NASA, consiglio la lettura di un approfondimento proposto da ESA.

Ulysses Flyby of the Sun's North Pole
1.14.2008

Jan. 14, 2008: Consider it a case of exquisite timing. Just last week, solar physicists announced the beginning of a new solar cycle and now, Jan. 14th, the Ulysses spacecraft is flying over a key region of solar activity--the sun's North Pole.
"This is a wonderful opportunity to examine the sun's North Pole at the onset of a new solar cycle," says Arik Posner, NASA Ulysses program scientist. "We've never done this before."
Launched in Oct. 1990 from the space shuttle Discovery, Ulysses is a joint mission of the European Space Agency and NASA. Unlike other spacecraft, Ulysses is able to fly over the sun's poles, looking down on regions that are difficult to see from Earth:
"Just as Earth's poles are crucial to studies of terrestrial climate change, the sun’s poles may be crucial to studies of the solar cycle," explains Ed Smith, Ulysses project scientist at NASA's Jet Propulsion Laboratory.
Many researchers believe the sun's poles are central to the ebb and flow of the solar cycle. Consider the following: When sunspots break up, their decaying magnetic fields are carried toward the poles by vast currents of plasma. This makes the poles a sort of "graveyard for sunspots." Old magnetic fields sink beneath the polar surface two hundred thousand kilometers deep, all the way down to the sun's inner magnetic dynamo. There, dynamo action amplifies the fields for use in future solar cycles.
This week, "Ulysses will measure the sun's magnetic field above the North Pole to see what it's like during the change of solar cycles," says Posner.
Ulysses has flown over the sun's poles three times before in 1994-95, 2000-01 and 2007. Each flyby revealed something interesting and mysterious.
One big puzzle is the temperature of the sun's poles. In the previous solar cycle, the magnetic north pole was about 80,000 degrees or 8% cooler than the south. Why should there be a difference? No one knows.
The current flyby may help solve the puzzle because it comes less than a year after a similar South Pole flyby in Feb. 2007. Mission scientists will be able to compare temperature measurements, north vs. south, with hardly any gap between them.
Ulysses also discovered the sun's high-speed polar wind. "At the sun's poles, the magnetic field opens up and allows solar atmosphere to stream out at a million miles per hour," says Smith.
By flying around the sun, covering all latitudes in a way that no other spacecraft can, Ulysses has been able to monitor this polar wind throughout the solar cycle--and it is acting a bit odd.
Posner explains: "Eleven years ago, during a similar 'sea change' between solar cycles, the polar wind spilled down almost all the way to the sun's equator. But this time it is not. The polar wind is bottled up, confined to latitudes above 45 degrees: data."
Is this a detail of little importance or a major anomaly, signaling new things to come? Again, no one knows, and that's why now is a good time to visit the sun's North Pole.

Le aurore, battito cardiaco della magnetosfera

Un nuovo importante studio, effettuato da Applied Physics Lab della Johns Hopkins University e da Aeronautica Militare USA su una mole di dati raccolti da satelliti NASA e da altre agenzie, conferma che fenomeni come l'aurora boreale e altre turbolenze magnetiche non sono, come si credeva, correlati ai forti campi elettrici del vento solare e quindi ai brillamenti nell'atmosfera del sole. La correlazione più certa sembra essere quella, magnetica, ai confini tra i campi magnetici solare e terrestre. E' ciò che i ricercatori chiamano "battito cardiaco della magnetosfera": il tasso di "connessione" tra le linee di campo magnetico del sole e della terra (Radiopassioni aveva trattato questo stesso argomento qualche tempo fa parlando di uno studio molto simile).

Il testo del comunicato stampa rilasciato per l'occasione è interessante, ma ancora più dettagliato è il materiale diffuso per la presentazione della ricerca davanti alla American Geophysical Union a San Francisco, lo scorso 11 dicembre. Gli autori dello studio sottolineano di aver ricavato una singola formula che sulla base delle osservazioni magnetiche a circa 40 mila chilometri di quota (all'interfaccia tra i due campi magnetici) fornisce accurate previsioni sull'intensità delle aurore e altri dieci parametri significativi.

New findings indicate that the aurora and other near-Earth space weather are driven by the rate at which the Earth’s and Sun’s magnetic fields connect, or merge, and not by the solar wind’s electric field as was previously assumed. The merging occurs at a spot between the Earth and Sun, roughly 40,000 miles above the planet’s surface, and appears fundamental to the circulation of particles and magnetic fields throughout near-Earth space.
Researchers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and the Air Force Research Laboratory at Hanscom Air Force Base (Massachusetts) will announce the results of their study at the Fall American Geophysical Union Meeting in San Francisco on Dec. 11. The researchers, led by Patrick Newell of APL, have developed a formula that describes the merging rate of the magnetic field lines and predicts 10 different types of near-Earth space weather activity, such as the aurora and magnetic disturbances.
“Having this formula is a big step forward for understanding how the Sun and Earth interact,” says Newell. And that understanding could help predict the space weather that affects communications, navigation, and the health of humans in space.
The space between the Earth and Sun is not empty, but filled with energetic particles, most of which are generated in the solar atmosphere. Temperatures of a few million degrees accelerate a stream of these particles, called the solar wind, to roughly one million miles per hour. Space weather scientists had long assumed that near-Earth space weather phenomena could best be predicted by the behavior of the solar wind electric field. However, Newell and his colleagues were the first to put this theory to a rigorous test with many data sets from a number of years.

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