Solar Orbiter, nel 2017 mai così vicino al sole

Il Solar Terrestrial Center of Excellence belga, una delle mie fonti informative sull'attività solare misurata da osservatori europei, ha portato a termine un restyling della sua periodica newsletter a periodicità circa settimanale. Oggi la pubblicazione si presenta come una piccola rivista con articoli e fotografie. La neswletter è accessibile dal sito dove è possibile anche consultare l'archivio e si può visualizzare nel browser o in formato PDF. Uno dei primi articoli riguarda la missione Solar Orbiter, scelta recentemente dall'ESA insieme a Euclid (la missione che studierà la materia oscura) per caratterizzare i piani esplorativi dell'Ente spaziale europeo nel decennio 2015-2025. Il Solar Orbiter dovrebbe essere lanciato da un vettore Atlas della NASA nel 2017 con l'obiettivo di inserire in una orbita solare mai tanto ravvicinata (0,22 UA al perielio) una sonda in grado di visualizzare i poli del nostro astro e soprattutto di studiarne l'atmosfera e le emissioni di vento solare. Un piano molto ambizioso che utilizzerà strumenti di assoluta avanguardia come l'Extreme Ultraviolet Imager, una suite di tre telescopi EUV trasportati a bordo della sonda, insieme a tanti altri laboratori di misura. Sempre a proposito di dati solari, un'altra risorsa europea è il portale continentale di meteorologia spaziale.

Un posto (software) a due passi dal sole

Un incredibile strumento software (open source, multipiattaforma e disponibile anche in versione Web based) per accedere ai dati di imaging e astrofici sul nostro sole è stato rilasciato oggi dall'ESA. JHelioviewer è una spettacolare finestra aperta sul disco nel nostro astro, sia in tempo reale sia per quanto concerne i dati di un archivio alimentato da due missioni spaziali: l'ESA/NASA Solar and Heliospheric Observatory (SOHO) e il Solar Dynamics Observatory (SDO). Per molti si tratterà di immagini e informazioni assolutamente inedite, inserite in una interfaccia divulgativa che aiuterà a far luce sui misteri della meteorologia spaziale e di tanti fenomeni della fisica planetaria e della propagazione delle onde radio.

Il software (Windows, Mac e LInux/Java) può essere prelevato dal sito www.jhelioviewer.org o consultato nella versione Web all'indirizzo www.helioviewer.org

ESA offers a new way of looking at the Sun

14 Dec 2010

ESA has released interactive, open-source software that gives both scientists and the public an unprecedented insight into the ever-changing face of the Sun. JHelioviewer allows easy access to over 14 years worth of data from the ESA/NASA Solar and Heliospheric Observatory (SOHO) along with the latest information beaming back from NASA's Solar Dynamics Observatory (SDO).

The Sun has been under almost constant human surveillance from space since the SOHO mission was launched in December 1995. Since then, the space telescope has delivered a daily stream of 250MB of solar data back to researchers on Earth. With 12 instruments on board, probing every area of our star - from its interior out to the corona and the solar wind - SOHO has compiled a vast library of solar data. This solar opus is beginning to be complemented by SDO, which is returning 1.5TB of data per day. At 6000 times the data rate of SOHO, and containing a constant stream of high-resolution images of the Sun over 10 spectral channels, the volume of data from SDO has made it necessary to develop new ways of visualizing the data. This will be key in achieving SDO's goal of helping scientists understand how the Sun's magnetic field is generated and structured and how this stored magnetic energy is converted and released into the heliosphere.

The challenge is that with this vast and ever-growing forest of data it is hard to see the wood from the trees. "If you wanted to study a phenomenon in a specific region on the Sun on a certain day then you needed to download a large volume of data and calibrate it with the appropriate software. As part of a lengthy process you'd turn it into an animated sequence, that may or may not turn out to be useful," Daniel Müller, SOHO Deputy Project Scientist, explained. "JHelioviewer is a novel way of visually browsing the archive; you can quickly identify interesting stuff and then go and get the scientific data. It greatly speeds up the process," he added.

Developed as part of the ESA/NASA Helioviewer Project, JHelioviewer is an interactive, simple to use index of the data gleaned from fifteen years of watching the Sun from space. However, the true power of the tool lies in its ability to allow cross-referencing of different aspects of the large data sets; many events observed on the Sun are interconnected and occur over vastly different temporal and spatial scales. For the first time, JHelioviewer allows users to overlay series of images from the Sun, from different instruments, and compile an animated sequence, which they can then manipulate as they watch, in order to follow a solar event from start to finish.

"All solar scales are coupled: you have small scale phenomena tying into large scale events. We now have a unique tool to tackle this hierarchy of scales," said Müller. He went on to say: "Before, you could either see the large-scale corona, or small patches on the solar surface. But you've never had the option to overlay the two and zoom in and out as you watch the Sun's activity evolve."

In this marriage of scales lies fresh potential for scientists to tackle some of the most pressing issues in modern solar physics. With more than 14 years worth of SOHO data now easy to access, users can follow the Sun's changing activity over an entire 11-year solar cycle. Alternatively, the differential rotation of the Sun can be compensated for, allowing sunspots - indicators of solar activity cycles - to be tracked as they rotate across the solar surface. Researchers can also juxtapose images of the Sun's corona, from SOHO's LASCO coronagraph, with concurrent ultraviolet data of the lower corona, provided by the EIT instrument, and MDI measurements of the magnetic field on the solar surface. This can be done with the minimum of fuss, allowing more time for the links between coronal mass ejections (CMEs) and activity on the solar surface to be explored.

This leads on to the phenomenon of 'space weather': a term brought into everyday language through the pioneering work of SOHO over the last decade and a half. "JHelioviewer will help the search for the triggers or proxies that then translate into geomagnetic phenomena such as storms in Earth's magnetosphere," Müller suggested. Knowledge of such trigger mechanisms could allow Sun-watching scientists to give prior warning of such events, which have the potential to damage satellites and power grids.

And as well as opening up the Sun to solar researchers, JHelioviewer has already caught the eye of the wider scientific community. "We've already had discussions with the Mars Reconnaissance Orbiter team, as well as with the medical world, about how they might use the open-source software to analyse massive data sets in their own respective fields," Müller revealed.

However, the potential impact of JHelioviewer reaches out beyond the scientific community; the software has been specifically designed to be used by the non-expert as well. Interested members of the public have access to just the same data as the scientists and can use it to explore the Sun for themselves. "It puts millions of SOHO images at your fingertips. Anyone with a computer and internet access can use it to make a movie of how the Sun evolved over the last decade," pointed out Müller. "You could even see how the Sun looked on your birthday or Christmas; you can pick and choose whatever you like," he added.

JHelioviewer has been developed as part of the ESA/NASA Helioviewer Project (Principal Investigators: Daniel Müller (ESA), Jack Ireland (ADNET Systems, Inc. / NASA Goddard Space Flight Center)) by an interdisciplinary team of solar physicists and software developers. It is based on the JPEG 2000 image compression standard and written in Java and OpenGL. The server hosting the software and related JPEG 2000 files is located at the Solar Data Analysis Center (SDAC) at NASA's Goddard Space Flight Center.

The JHelioviewer software is available to download for several operating systems. It is complemented by the website Helioviewer.org, a web-based image browser.

Ai confini del vento solare

La missione STEREO, la coppia di satelliti lanciata per creare immagini stereoscopiche della superficie solare e misurare il flusso di ioni associato alle esplosioni del nostro astro, è riuscita a "fotografare" la zona non visibile con osservazioni tradizionali costituita dal punto in cui il vento solare, caldo e a velocità ultrasoniche, impatta con la materia interstellare. E' la cosiddetta elioguaina (heliosheath) la zona intermedia tra la bolla del cosiddetto termination shock, la soglia raggiunta la quale il vento cominia a decelerare, e l'eliopausa, il guscio più esterno della eliosfera (una turbolenta bolla dai confini molto variabili), dove il vento solare si placa definitivamente.
Le "osservazioni" della coppia di satelliti STEREO sono avvenute con strumenti che misurano il flusso di atomi resi ormai neutri dalla cessione di energia dovuta alle interazioni con la materia interstellare. Questi atomi rimbalzano allontanandosi dalla eliopausa e ritornano verso le strumentazioni STEREO. Sembra che la nuova "immagine" ottenuta sia servita a chiarire il perché le misurazioni effettuate nella elioguaina dalle sonde Voyager presentavano importanti discrepanze a livello di bilancio energetico.

STEREO CREATES FIRST IMAGES OF THE SOLAR SYSTEM'S INVISIBLE FRONTIER

GREENBELT, Md. -- NASA's sun-focused Solar Terrestrial Relations Observatory, or STEREO, twin spacecraft unexpectedly detected particles from the edge of the solar system last year. This helped scientists map the energized particles where the hot solar wind slams into the cold interstellar medium.
The two STEREO spacecraft were launched in 2006 into Earth's orbit around the sun to obtain stereo pictures of the sun's surface and measure magnetic fields and ion fluxes associated with solar explosions. From June to October 2007, sensors aboard both STEREO spacecraft detected energetic neutral atoms originating from the same spot in the sky, where the sun plunges through the interstellar medium.
Mapping the region by means of neutral, or uncharged, atoms instead of light "heralds a new kind of astronomy using neutral atoms," said Dr. Robert Lin, professor of physics at the University of California, Berkeley and lead for the suprathermal electron sensor aboard the STEREO spacecraft. "You can't get a global picture of this region, one of the last unexplored regions of the heliosphere, through normal telescopes," Lin said. The heliosphere is a bubble in space produced by the solar wind. It stretches from the sun to beyond the orbit of Pluto. The solar wind streams off the Sun in all directions at great speeds. Once beyond the orbit of Pluto, this supersonic wind must slow down to meet the gases in the interstellar medium. As the solar wind slows, it changes direction to form a comet-like tail behind the sun. This subsonic flow region is called the heliosheath.
The results, reported in the July 3 issue of the journal Nature, clear up a discrepancy in the amount of energy dumped into space by the decelerating solar wind. The solar wind was detected when Voyager 2 entered the heliosheath.
Researchers determined that the newly discovered population of ions in
the heliosheath contains about 70 percent of the dissipated energy from the solar wind, exactly the amount unaccounted for by Voyager 2's instruments. The Voyager 2 results also are reported in the July 3 issue of Nature. The Berkeley team concluded that these energetic neutral atoms were originally ions heated up in the termination shock area that lost their charge to cold atoms in the interstellar medium and, no longer hindered by magnetic fields, flowed back toward the sun and into the sensors aboard STEREO. "This is the first mapping of energetic neutral particles from the edge of the heliosphere," Lin said. According to Lin, the neutral atoms are probably hydrogen, which comprise most of the particles in the local interstellar medium.
The charge exchange between hot ions and neutral atoms to generate energetic neutral atoms is well known around the sun and planets, including Earth and Jupiter. Spacecraft have used this as a means of remotely measuring the energy in ion plasmas since neutral atoms travel much farther than ions. NASA plans to launch the Interstellar Boundary Explorer, or IBEX, later this year to more thoroughly map the boundary of the solar system.

For more information about NASA's STEREO mission, visit:

http://www.nasa.gov/stereo