Cosmic voyager. Moving at some 23 kilometers per second, the solar system journeys through a cluster of thin gas clouds.
As Earth and the other planets orbit the sun, the solar system itself travels through space. Its slow journey is taking it though a wispy expanse of gas called the Local Interstellar Cloud. Now, astronomers have discovered signs of potential turbulence in the cloud, indicated by a shift in direction of helium atoms that flow into the solar system. If the shift is real and continues for hundreds to thousands of years—a dicey extrapolation—it could be a harbinger of more dramatic changes in our solar system, notes study co-author David McComas of the Southwest Research Institute in San Antonio.
The finding, which McComas, Priscilla Frisch of the University of Chicago, and their colleagues report in the 6 September issue of Science, could foreshadow a change in the heliosphere, the vast bubble that shields the solar system from harmful cosmic rays. The heliosphere consists of charged particles blown out by the sun in the so-called solar wind. The size and shape of the heliosphere depends on the balance between the outward push of the solar wind and the inward pressure from gas in the Local Interstellar Cloud—the interstellar wind.
To detect the wind shift, researchers drew on measurements by 11 spacecraft and satellites that have recorded directly or indirectly the flow of helium atoms into the solar system. Many kinds of atoms infiltrate the heliosphere, but helium is a particularly good tracer for all of them because it is abundant and typically survives in its uncharged, atomic state all the way to Earth’s orbit, Frisch says.
So far, the apparent change in direction is small, about 4° to 9° over the past 40 years. But if it continues to shift direction and flips to the other side of the solar system, the heliosphere could be substantially distorted, notes astronomer William Reach of the Universities Space Research Association at NASA’s Ames Research Center in Moffett Field, California, who is not a member of the study. A smaller heliosphere would let in a greater a number of galactic cosmic rays, which are harmful to life on Earth.
Jeff Linsky of the University of Boulder, Colorado, who is not a member of the team, says that the new result, if confirmed, indicates that the heliosphere is emerging from the Local Interstellar Cloud into another region, with a different wind direction. Frisch disagrees and thinks that it's small-scale turbulence. Either way, the finding will provide "interesting new twists" to modeling of the solar wind's interactions with the cloud, comments Gary Zank of the University of Alabama, Huntsville. In addition, simply having the ability to record such changes in the solar system’s environment “is a really big deal,” McComas says.
DURHAM, N.H. – Scientists, including University of New Hampshire astrophysicists involved in NASA’s Interstellar Boundary Explorer (IBEX) mission, have discovered that the particles streaming into the solar system from interstellar space have likely changed direction over the last 40 years.
The finding helps scientists map our location within the Milky Way galaxy and is crucial for understanding our place in the cosmos through the vast sweep of time—where we've come from, where we're currently located, and where we're going in our journey through the galaxy.
Additionally, scientists now gain deeper insight into the dynamic nature of the interstellar winds, which has major implications on the size, structure, and nature of our sun's heliosphere—the gigantic bubble that surrounds our solar system and helps shield us from dangerous incoming galactic radiation.
The results, based on data spanning four decades from 11 different spacecraft, including IBEX, were published in the journal Science September 5, 2013.
“It was very surprising to find that changes in the interstellar flow show up on such short time scales because interstellar clouds are astronomically large,” says Eberhard Möbius, UNH principal scientist for the IBEX mission and co-author on the Science paper. Adds Möbius, “However, this finding may teach us about the dynamics at the edges of these clouds—while clouds in the sky may drift along slowly, the edges often are quite fuzzy and dynamic. What we see could be the expression of such behavior.”
The data from the IBEX spacecraft show that neutral interstellar atoms are flowing into the solar system from a different direction than previously observed. Interstellar atoms flow past the Earth as the interstellar cloud surrounding the solar system passes the sun at 23 kilometers per second (50,000 miles per hour).
The latest IBEX measurements of the interstellar wind direction differed from those made by the Ulysses spacecraft in the 1990s. That difference led the IBEX team to compare the IBEX measurements to data gathered by 11 spacecraft between 1972 and 2011. The scientists wanted to gather as much evidence from as many sources as possible to determine whether the newer instruments simply provided more accurate results, or whether the wind direction itself changed over the years.
The various sets of observations relied on three different methods to measure the incoming interstellar wind. IBEX and Ulysses directly measured neutral helium atoms as they coursed through the inner solar system. IBEX's measurements are close to Earth, while Ulysses' measurements were taken between 1.3 and 2 times further from the sun.
In the final analysis, the direction of the wind obtained most recently by IBEX data differs from the direction obtained from the earlier measurements, which strongly suggests the wind itself has changed over time.
“Prior to this study, we were struggling to understand why our current measurements from IBEX differed from those of the past,” says co-author Nathan Schwadron, lead scientist for the IBEX Science Operations Center at UNH. “We are finally able to resolve why these fundamental measurements have been changing with time: we are moving through a changing interstellar medium.”
The paper, “Decades-long Changes of the Interstellar Wind Through our Solar System,” includes IBEX team members from the University of Chicago, the Space Research Centre of the Polish Academy of Sciences, the Southwest Research Institute, the University of Texas in San Antonio, UNH, Dartmouth College, Central Arizona College, the University of California at Berkeley, and NASA’s Jet Propulsion Laboratory.
IBEX is part of NASA’s series of low-cost, rapidly developed Small Explorer space missions. Southwest Research Institute in San Antonio leads the IBEX mission with teams of national and international partners. NASA’s Goddard Space Flight Center in Greenbelt, Md., manages the Explorers Program for NASA’s Science Mission Directorate in Washington.
The University of New Hampshire, founded in 1866, is a world-class public research university with the feel of a New England liberal arts college. A land, sea, and space-grant university, UNH is the state's flagship public institution, enrolling 12,200 undergraduate and 2,300 graduate students.
Quelle: University of New Hampshire