I had thought that the prediction
of an energetic bow wave as at the least chancy simply because such a shock
wave would emit and be observed here. Where
such shock waves are observed, it is because of these emissions. It turns out that we have a bow wave and
relative velocities are much lower than expected.
This suggests that we are still
close to the apogee of our orbit through the Sirius cluster. We have reversed course and are how
travelling against the direction of the galactic rotation albeit slowly as yet.
This does suggest an alternative
cause of the global heating observed in the Antarctic Ice Cores every 200,000
years or so. The shock wave front is
turned on as speed increases and it begins emitting in the infrared and this
has the effect of warming the Earth a degree or so for a couple of thousand
years. It is in fact a much better
explanation that a swift passage of a hot star that would only last a year or
so.
The shock wave would become
visible around 2000 years out or for only one percent of the total orbit.
Bow-shock no-show shocks astronomers
May 11, 2012
The Sun moves much more slowly relative to nearby interstellar space
than was previously thought, according to scientists working on NASA's
Interstellar Boundary Explorer (IBEX) mission. Their study casts doubt on the
existence of an abrupt "bow shock" where the edge of the solar system
meets the interstellar medium – instead suggesting that the boundary between
the two regions is much gentler than previously thought. The discovery could
lead to a better understanding of how some cosmic rays can enter the solar system,
where they pose a threat to space travellers.
The bow shock refers to the region where the heliosphere – the huge
bubble of charged particles that surrounds the Sun and planets – is believed to
plunge into the interstellar medium. The commonly accepted idea is that the
solar system moves faster (relative to the speed of the interstellar medium)
than sound itself, rather like the shock wave that forms ahead of a supersonic
aircraft. Charged particles moving supersonically in the heliosphere therefore
pile up at the front of the shock, with the density of charged particles
dropping off rapidly where the heliosphere meets the interstellar medium.
Astronomers have always had good reason to believe the bow shock exists
because similar structures can be seen surrounding nearby stars. But the new
analysis of IBEX data – which has been carried out by David McComas of the
Southwest Research Institute in Austin ,
Texas
Fast-moving atoms
Launched in 2008, IBEX orbits the Earth and is designed to study
fast-moving neutral atoms. What McComas and colleagues did was to use IBEX to
characterize neutral atoms from the interstellar medium that cross into the
heliosphere. Because these atoms are not electrically charged, they are not
affected by magnetic fields – and so their speed should correspond to the
relative velocity of the interstellar medium.
The study suggests that the relative speed is about 84,000 km/h,
which is about 11,000 km/h less than previously thought. In addition, data
from IBEX and earlier Voyager missions suggest that the magnetic pressure found
in the interstellar medium is higher than expected. When these parameters were
fed into two independent computer models of the heliosphere, both suggested
that a bow shock does not exist, but rather a gentler "bow wave"
occurs at the interface.
Gliding through space
"A wave is a more accurate depiction of what is happening ahead of
our heliosphere – much like the wave made by the bow of a boat as it glides
through the water," explains McComas.
According to McComas, decades of research based on the presumption of a
bow shock must now be redone using this latest information. "It's too
early to say exactly what these new data mean for our heliosphere," he
says. Given that the heliosphere shields the solar system from some cosmic
rays, McComas says "there are likely [to be] implications for how galactic
cosmic rays propagate around and enter the solar system, which is relevant for
human space travel".
The work is described in Science.
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