Click to enlarge
Like the wind adjusting course in the middle of a storm, scientists have discovered that the particles streaming into the solar system from interstellar space have most likely changed direction over the last 40 years. Such information can help us map out our place within the galaxy surrounding us, and help us understand our place in space.
The results, based on data spanning four decades from 11 different spacecraft, were published in Science on Sept. 5, 2013.
Vestiges of the interstellar wind flowing into what’s called the heliosphere — the vast bubble filled by the sun’s own constant flow of particles, the solar wind – is one of the ways scientists can observe what lies just outside of our own home, in the galactic cloud through which the solar system travels. The heliosphere is situated near the inside edge of an interstellar cloud and the two move past each other at a velocity of 50,000 miles per hour. This motion creates a wind of neutral interstellar atoms blowing past Earth, of which helium is the easiest to measure.
“Because the sun is moving though this cloud, interstellar atoms penetrate into the solar system,” said Priscilla Frisch, an astrophysicist at the University of Chicago, Ill. and the lead author on the paper. “The charged particles in the interstellar wind don’t do a good job of reaching the inner solar system, but many of the atoms in the wind are neutral. These can penetrate close to Earth and can be measured…”
The earliest historical data on the interstellar wind comes from the 1970s from the U.S. Department of Defense’s Space Test Program 72-1 and SOLRAD 11B, NASA’s Mariner, and the Soviet Prognoz 6. While instruments have improved since the 1970s, comparing information from several sets of observations helped the researchers gain confidence in results from that early data. The team went on to look at another seven data sets including the Ulysses information from 1990 to 2001, and more recent data from IBEX, as well as four other NASA missions: the Solar Terrestrial Relations Observatory, or STEREO, the Advanced Composition Explorer, or ACE, the Extreme Ultraviolet Explorer, and the MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission, or MESSENGER, currently in orbit around Mercury. The eleventh set of observations came from the Japanese Aerospace Exploration Agency’s Nuzomi.
“The direction of the wind obtained from the most recent data does not agree with the direction obtained from the earlier measurements, suggesting that the wind itself has changed over time,” said Eric Christian, the IBEX mission scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “It’s an intriguing result, which relied on looking at a suite of data measured in a bunch of different ways…”
From Earth’s perspective, the interstellar wind flows in from a point just above the constellation Scorpius. Results from 11 spacecraft over 40 years show that the exact direction has changed some 4 to 9 degrees since the 1970s…
“Previously we thought the local interstellar medium was very constant, but these results show that it is highly dynamic, as is the heliosphere’s interaction with it,” said David McComas, IBEX principal investigator at Southwest Research Institute in San Antonio, Texas.
Now, of course, scientists being the curious critters they are – time to set forth to find out how and why this happened, why it’s happening?