Zodiacal lights are a faint diffuse roughly triangular glow that is visible in the night
sky. It was believed that sunlight, scattered by interplanetary dust, causes this phenomenon.
But new startling evidence from the Juno probe may provide evidence that is actually caused
by dust emitted from Mars which seems to terminate at Earth.
The source of the dust is something that has been debated for a long time. Until recently,
it was thought that the dust originated from the tails of active comets and from collisions
between asteroids in the asteroid belt. Many of our meteor showers have no known active
comet paren bodies. The first fully dynamical model of the zodiacal cloud postulated that
only if the dust was released in orbits that approached Jupiter would it be stirred up
enough to explain the thickness of the zodiacal dust cloud. The problem with any model is
that it requires a continuous source of new particles to maintain it.
A team of scientists from the Juno mission argue that Mars may be the culprit. In a recently
published paper, they describe how an instrument aboard the Juno spacecraft was able to detect
dust particles slamming into the spacecraft during its journey from Earth to Jupiter.
Originally they were not looking for this at all. Onboard Juno there are 4 cameras that
are used as part of the magnetometer investigations. These snap photos of the sky every quarter
of a second to determine Juno’s orientation in space by recognised star patterns in its
images.
They were hoping that these cameras might also catch the sight of an undiscovered asteroid
and hence they were programmed to report any objects that appeared in multiple consecutive
images but were not in the catalogue of known celestial objects.
They had not expected to find much as most objects have already been accounted for. So
when the cameras started reporting thousands of images of unidentified objects with streaks
appeared and then mysteriously disappearing they were initially baffled.
They then started to consider the many plausible causes. One of these was the unnerving possibility
that the camera had caught a leaking field tank on Juno. The images looked as if someone
was shaking a dusty rag out of the window.
They then started to analyse the apparent size and velocity of the objects in the images.
Dusty grains had smashed into Juno at about 16,000 km per hour, chipping off submillimeter
pieces of the spacecraft. The spray of debris was coming from Juno’s expansive solar panels
- the biggest and most sensitive unintended dust detector ever built!
Each piece of debris they tracked records the impact of an interplanetary dust particle.
This allowed them to compile a distribution of dust along its flight path. Juno was launched
in 2011. By 2012 it performed a deep space manoeuvre in the asteroid belt to allow it
to return to the inner solar system for an Earth gravity assist in 2013. From there it
would fly directly towards Jupiter.
When they analysed the data they noticed that the majority of dust impacts were recorded
between Earth and the asteroid belt, with gaps in the distribution which are related
to the influence of Jupiter’s gravity.
This was of particular importance as up until this point scientists have not been able to
directly measure the distribution of these dust particles in interplanetary space. Most
dust detection systems had very limited collection areas. By comparison, Juno’s solar panels
have 1000 times more collection area than these.
By detailed analysis, they were able to determine that the dust cloud ends at Earth. They speculate
that Earth’s gravity sucks up all the dust that gets near it.
They believe that this dust ends just beyond Mars. This they speculate may be due to the
influence of Jupiter’s gravity acts like a barrier, preventing dust particles from
crossing from the inner solar system into deep space.
The fact that the dust particles are in a nearly circular orbit around the Sun and situated
no further than about 2 AU means the most likely culprit is Mars.
At this stage, the scientists who made this discovery do not have an explanation as to
how or why the dust is being released from Mars
Related to this, new research strongly suggests that part of the Martian surface is being
pulled apart and implies Mars is still seismically active.
The observations were made using a series of instruments on the Mars Reconnaissance
Orbiter. This satellite has been orbiting Mars since 2006. In an area called Elysium
Planitia which literally means plains of Heaven, they have identified an area which shows many
parallel cracks in the Martian crust.
These cracks are thought to form when the ground is pulled apart from pressure under
the surface. Something underneath is causing an expansion which causes the brittle crust
to crack very much like a fresh bread loaf rising in the hot oven.
A team of planetary scientists studied one of these cracks. It stretches over 34 kilometres
in length and is about 100 meters wide. There are also lobes of dark material extending
for many kilometres on either side of the fissure.
Using a different instrument onboard the MRO they identified that the material is rich
in a mineral commonly found in volcanic flows. They believe the deposits were from a pyroclastic
flow. These are incredibly hot gas and particle flows that can move at hundreds of kilometres
per hour across the surface. They do however note that it is also possible that the deposits
are not volcanic at all but simply dust and sane blown out of the fissure by the wind.
It is believed that Mars was volcanically active some 2-3 billion years ago but there
has been some evidence that activity continued into geologically recent times some dating
to around 2 million years ago. So when they started to determine the date of these cracks
they were in for a bit of a surprise. They used the number of craters and their size
to estimate its age. This gave a figure of only 50-200 thousand years old!. And the only
way this could happen they believe is if Mars is still volcanically active.
Now of course the idea of dating this by the craters is possibly flawed. The EU hold that
large parts of Mars were etched away in the not so recent past and therefore many of these crater marks are not craters at all
If we examine the crater near these fissures we see a very interesting alignment which
seems to show them running through the crater and out the other side. There are also some
other fissures that run parallel to this main one. Some of the fissures end in a more
rounded shape and others start in a very fine point. Some of them appear not like fissures
at all but seem to be carved from underneath leaving large sections above intact. As if
something had melted the channel. Looking further along this line we see this appearing
and disappearing ending finally in what appears as more a sputtering of pitting. Could these
have been carved by electrical discharges that in parts seem to travel along
the surface and in some parts below the surface? The crater itself may also be connected as
a larger discharge point, etching away the crater. Many of these fissures appear
to have very sharp edges with very little material in the middle and still seem to retain
more of a V shape rather than being filled in with infall material if the two edges had
indeed been pulled apart. It is more reminiscent of something etching out some of the material.
So I guess the question is wether this is actually still going on today.
Now we have also previously covered evidence of Mars having a stronger magnetic field in some areas than
previously thought and the idea that this might be caused by electrical current flowing
in the atmosphere of Mars. Could these carry particles up high enough into the atmosphere
to escape Mars altogether?