Cuando se cumplen 35 años de su lanzamiento, la sonda Voyager 1 está llegando a los confines del sistema solar pero puede que no esté tan cerca de la frontera como se pensaba hasta ahora. Así lo revela un estudio que investigadores de la Universidad Johns Hopkins (EEUU) publican esta semana en la revista Nature.
http://www.nasa.gov/multimedia/videogallery/index.html?media_id=150791351
Un estudio de la Universidad Johns Hopkins de Maryland (EEUU) concluye que la sonda espacial Voyager 1, lanzada el 5 de septiembre de 1977, no está tan cerca de la heliopausa (el límite donde desaparece el viento solar y comienza el medio interestelar) como consideraban los científicos.
La Voyager 1 está ahora en la heliofunda –la región anterior a la heliopausa– donde el viento solar disminuye y se empiezan a manifestar los efectos del medio interestelar. En esta zona de transición es en la que se supone que el plasma solar se desvía de su trayectoria radial a otra meridional.
Pero desde 2011, la sonda Voyager 1 se fue reorientando periódicamente para medir este flujo norte-sur, y los resultados muestran que no existe viento meridional significativo. Los nuevos datos indican que, al contrario de lo que se pensaba, la sonda no está a punto de cruzar la frontera del sistema solar.
La investigación, dirigida por Robert Decker, sugiere que nuestro conocimiento de los límites del sistema solar debería ser reconsiderado, y apunta también que quizá sea necesaria una nueva formulación teórica de la interacción del viento solar con el medio interestelar.
35 años de historia
La Voyager 1 se encuentra actualmente a casi 120 Unidades Astronómicas del Sol (una Unidad Astronómica equivale a la distancia entre la Tierra y el Sol, unos 150 millones de kilómetros). La nave fue lanzada como parte de la misión interestelar Voyager, junto con la sonda Voyager 2, hace justo ahora 35 años.
Inicialmente, la misión de estas dos sondas era la exploración de Júpiter y Saturno, y después de diversos descubrimientos en estos planetas, el proyecto se prorrogó. La sonda Voyager 2 exploró además Urano y Neptuno, y posteriormente las dos continuaron su viaje para conocer mejor las fronteras del sistema solar.
Referencia bibliográfica:
Robert B. Decker, Stamatios M. Krimigis, Edmond C. Roelof, Matthew E. Hill. “No meridional plasma flow in the heliosheath transition region”. Nature 489: 124-127, 6 de septiembre de 2012. Doi: 10.1038/nature11441.
Lanzadas en 1977 para realizar un largo viaje por los planetas exteriores, la buena suerte hizo que las sondas gemelas Voyager tomaran la dirección del movimiento del Sol relativo a las estrellas cercanas. Treinta y cinco años más tarde , la Voyager 1 parece a punto llegar a la frontera entre la heliosfera solar y el espacio interestelar.
La heliosfera es el reino del Sol definido por la influencia del viento solar y del campo magnético solar. ¿Cómo se puede saber, sin embargo, cuando una sonda cruza la frontera hacia el espacio interestelar? Una pista podría ser un aumento repentino en la detección de rayos cósmicos. Las partículas de alta energía atraviesan el espacio interestelar aceleradas por supernovas distantes de nuestra galaxia, pero normalmente son desviadas o ralentizadas por la heliosfera. Este gráfico cubre un período de 12 meses (septiembre de 2011 a septiembre de 2012) y muestra el espectacular aumento de la tasa de detección de partículas de rayos cósmicos por la sonda Voyager 1 en los últimos meses. Actualmente, la Voyager 1 se encuentra a 18 millones de kilómetros (17 horas luz, 122 unidades astronómicas) del Sol. Pronto será la primera sonda procedente de la Tierra que penetre en el reino de las estrellas.
THE MISSION
Mission Objective
The mission objective of the Voyager Interstellar Mission (VIM) is to extend the NASA exploration of the solar system beyond the neighborhood of the outer planets to the outer limits of the Sun’s sphere of influence, and possibly beyond. This extended mission is continuing to characterize the outer solar system environment and search for the heliopause boundary, the outer limits of the Sun’s magnetic field and outward flow of the solar wind. Penetration of the heliopause boundary between the solar wind and the interstellar medium will allow measurements to be made of the interstellar fields, particles and waves unaffected by the solar wind.
Mission Characteristic
The VIM is an extension of the Voyager primary mission that was completed in 1989 with the close flyby of Neptune by the Voyager 2 spacecraft. Neptune was the final outer planet visited by a Voyager spacecraft. Voyager 1 completed its planned close flybys of the Jupiter and Saturn planetary systems while Voyager 2, in addition to its own close flybys of Jupiter and Saturn, completed close flybys of the remaining two gas giants, Uranus and Neptune.
At the start of the VIM, the two Voyager spacecraft had been in flight for over 12 years having been launched in August (Voyager 2) and September (Voyager 1), 1977. Voyager 1 was at a distance of approximately 40 AU (Astronomical Unit – mean distance of Earth from the Sun, 150 million kilometers) from the Sun, and Voyager 2 was at a distance of approximately 31 AU.
It is appropriate to consider the VIM as three distinct phases: the termination shock, heliosheath exploration, and interstellar exploration phases. The two Voyager spacecraft began the VIM operating, and are still operating, in an environment controlled by the Sun’s magnetic field with the plasma particles being dominated by those contained in the expanding supersonic solar wind. This is the characteristic environment of the termination shock phase. At some distance from the Sun, the supersonic solar wind will be held back from further expansion by the interstellar wind. The first feature encountered by a spacecraft as a result of this interstellar wind/solar wind interaction was be the termination shock where the solar wind slows from supersonic to subsonic speed and large changes in plasma flow direction and magnetic field orientation occur.
As of March 2012, Voyager 1 was at a distance of 17.9 Billion Kilometers (119.9 AU) from the sun and Voyager 2 at a distance of 14.7 Billion kilometers (98.3 AU).
Voyager 1 is escaping the solar system at a speed of about 3.6 AU per year, 35 degrees out of the ecliptic plane to the north, in the general direction of the Solar Apex (the direction of the Sun’s motion relative to nearby stars). Voyager 2 is also escaping the solar system at a speed of about 3.3 AU per year, 48 degrees out of the ecliptic plane to the south.
Passage through the termination shock ended the termination shock phase and began the heliosheath exploration phase. Voyager 1 crossed the termination shock at 94 AU in December 2004 and Voyager 2 crossed at 84 AU in August 2007. Since passage through the termination shock, the spacecraft has been operating in the heliosheath environment which is still dominated by the Sun’s magnetic field and particles contained in the solar wind. The heliosheath exploration phase ends with passage through the heliopause which is the outer extent of the Sun’s magnetic field and solar wind. The thickness of the heliosheath is uncertain and could be tens of AU thick taking several years to traverse. Passage through the heliopause begins the interstellar exploration phase with the spacecraft operating in an interstellar wind dominated environment. This interstellar exploration is the ultimate goal of the Voyager Interstellar Mission.
Both Voyagers are headed towards the outer boundary of the solar system in search of the heliopause, the region where the Sun’s influence wanes and the beginning of interstellar space can be sensed. The heliopause has never been reached by any spacecraft; the Voyagers may be the first to pass through this region, which is thought to exist somewhere from 8 to 14 billion miles from the Sun. This is where the million-mile-per-hour solar winds slows to about 250,000 miles per hour—the first indication that the wind is nearing the heliopause. The Voyagers should cross the heliopause 10 to 20 years after reaching the termination shock. The Voyagers have enough electrical power and thruster fuel to operate at least until 2020. By that time, Voyager 1 will be 12.4 billion miles (19.9 billion KM) from the Sun and Voyager 2 will be 10.5 billion miles (16.9 billion KM) away. Eventually, the Voyagers will pass other stars. In about 40,000 years, Voyager 1 will drift within 1.6 light years (9.3 trillion miles) of AC+79 3888, a star in the constellation of Camelopardalis. In some 296,000 years, Voyager 2 will pass 4.3 light years (25 trillion miles) from Sirius, the brightest star in the sky . The Voyagers are destined—perhaps eternally—to wander the Milky Way.
The twin Voyager 1 and 2 spacecraft continue exploring where nothing from Earth has flown before. In the 34th year after their 1977 launches, they each are much farther away from Earth and the Sun than Pluto. Voyager 1 and 2 are now in the «Heliosheath» – the outermost layer of the heliosphere where the solar wind is slowed by the pressure of interstellar gas. Both spacecraft are still sending scientific information about their surroundings through the Deep Space Network (DSN).
The primary mission was the exploration of Jupiter and Saturn. After making a string of discoveries there — such as active volcanoes on Jupiter’s moon Io and intricacies of Saturn’s rings — the mission was extended. Voyager 2 went on to explore Uranus and Neptune, and is still the only spacecraft to have visited those outer planets. The adventurers’ current mission, the Voyager Interstellar Mission (VIM), will explore the outermost edge of the Sun’s domain. And beyond.
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