Solar activity reached new levels this year, with solar wind declining at lowest values in five decades, since the first measurements began. The observations, made by Ulysses spacecraft, suggest that this phenomenon is likely to affect the solar system, as well as our missions in space.

Solar winds are streams of particles ejected from the Sun, and are extremely important for our planet, as they shape the Earth’s magnetosphere and are a constant energy supply. The particles, a mix of protons, with 5% helium, but also oxygen and other elements, flow at average speeds of 400 km/sec, at distances 30 times longer than the Sun-Earth distance.

“The Sun’s million mile-per-hour solar wind inflates a protective bubble, or heliosphere, around the solar system,” explained Dave McComas, Ulysses’ solar wind instrument principal investigator, and senior executive director at the Southwest Research Institute in San Antonio. “Ulysses data indicate that the solar wind’s global pressure is the lowest we have seen since the beginning of the space age.”

According to NASA, this bubble produced by the solar wind contains material emanated from the Sun, although there are also some electrically neutral atoms from interstellar space, which are able to penetrate it. While the solar wind is known to travel at 1,000,000 mph in Earth’s vicinity, as it meets gases in the interstellar medium, somewhere way beyond Pluto, the solar wind begins to slow down, a point also known as heliopause.

The heliopause is basically the point where the power of the solar wind is not great enough to push back the winds from other stars. The heliopause region also acts as a barrier against cosmic rays outside the galaxy, protecting our solar system.

The implications of a diminishing solar wind are of extreme importance for us: “galactic cosmic rays carry with them radiation from other parts of our galaxy,” Ed Smith, NASA’s Ulysses project scientists at the Jet Propulsion Laboratory in Pasadena, Calif., explained. “With the solar wind at an all-time low, there is an excellent chance that 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.”

As Smith noted, we are currently at a period of minimal activity for the Sun, however this phase appears to have stretched longer than anticipated. On the other hand, it is normal for the Sun to have periods of great and lesser activity.

Based on total solar output observations made by Ulysses in previous years, the strength of solar wind pressure and the magnetic field embedded in the solar wind were found to have decreased by 20 percent compared to the previous solar cycle. Furthermore, the field strength near the spacecraft has decreased by 36 percent, NASA revealed.

The changes that we acknowledge at this point might have a significant impact on the space missions beyond low-Earth limit, for both manned and unmanned attempts. As solar winds decrease, galactic rays begin to penetrate the bubble and reach the inner part of our Solar System, which poses a great risk of exposure for space missions.

It still remains unclear what will happen, although scientists do know for a fact that the Sun has had such week activity prior to the space age. We may not expect to see changes that pose a direct threat to Earth anytime soon, however, from the space exploration point of view, things get tougher and tougher.

The Ulysses spacecraft began its mission on October 6, 1990, when shuttle Discovery propelled it toward Jupiter; here, gravity forces redirected Ulysses’ flight path, placing it on an orbit around the Sun, following its north and south poles. The spacecraft carried its mission four times longer than expected, lasting for more than 18 years.