Transcript vmc_mod2_eng

ANTARES ON MARS
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The Mars express spacecraft
•Left Earth in June 2003
•In August 2003, the two planets were at a minimum
distance, a condition that recurs every 26 month, even if not
always under similar conditions, because it not always
happens at perihelion for both planets. In that occasion the
two planets were distant “only” 55.758.713 kilometers,
practically the minimum distance possible;
•The spacecraft took 6 month to reach Mars, at an average
speed of 10800 km/h;
•Five days after it released the Beagle 2 lander on the
surface;
•Then the orbiter spacecraft reached a highly elliptical orbit
to perform observations.
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The journey from Earth to Mars
Released 13/08/2003 4:41 pm.
Copyright ESA 2003. Illustration by
Medialab.
While the two planets
were at the closest
approach of the last
60 000 years, the ESA’s
spacecraft passed the
middle point of its
journey to Mars.
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MarsExpress and Mars
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Antares and Mars in 2003
The Antares Association
organized a special evening
for the opposition of Mars in
2003 at the Municipal
Observatory, which was a
huge public success.
Here is the picture done by the
member Stefano Ceccucci
with the use of a 90mm
refractor, a 1300mm focal
length and a webcam. We can
easily see the south polar cap.
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The VMC camera
The visual monitoring camera is
placed on the Mars Express, the ESA
spacecraft, which is currently in orbit
around Mars.
At the beginning it needed only to
control the lander Beagle’s
separation with simple photographs.
Nowadays, however, it is used as a
“Mars Webcam”. It is not a scientific
tool but provides us beautiful Mars
photos, that cannot be obtainable
from Earth.
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'Mars Webcam'
Since 2007 the VMC has been used by the ESA team in
order to get pictures of Mars, simple photos but taken at a
few thousands kilometers to the surface of the planet.
It was so possible to observe the climate variation during
Martian Seasons or the main geological conformations.
The photos are available to everyone in flickr canal:
https://www.flickr.com/photos/esa_marswebcam
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Polo nord vision
• Mars seen
at 01:53:24
UTC on 16
May 2014.
Credit:
ESA
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Technical specifications
•Sensor CMOS (IMEC IRIS-1)
•Filters B/N and RGB
•Image size: 640x480 pixels
•Dynamics: 8 bits
•Field of view: 40 x 31 degrees
•Distance from the surface of Mars: : 300-10000 km
•Resolution calcolated to 10000 km: 11.5 km/pixel
•Resolution calcolated to 300 km: 0.347 km/pixel
•Mass: 430g
•Dimensions: 65 x 60 x 108 mm
•The VMC isn’t controlled by scientists as the other
board instruments, but by the team flight control of the
Mars express (Mars Express Flight control team)
located in Darmstadt, Germany.
•The MEFCT loads VMC images in a flickr account with
an automatic process that makes images freely
available to the general public shortly after being
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discharged by the spacecraft.
VMC
We can easily see on all images taken, two artifacts (which
may have been caused by space debris that have settled or
have scratched the lens); other artifacts appear randomly.
The MEFCT is always at work to define the best exposure
conditions, because the light and pointing conditions change at
each new orbit.
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During the conjuction with the Sun, when Mars is on the
opposite side of the Sun from the Earth, there’s a period of
five weeks in which comunications must be interrupted.
In 2005, during this period, the Mars Epress Team has
interrupted scientific works four days before, to realize a
special project.
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The VMC Schools Campaign
Make available to groups of astronomers or students
the VMC, for amateur projects.
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Campaign of observations
From the 25th to the 27th of may 2015 groups of students,
astronomers or scientific centers involving young people
worldwide have been able to propose goals for the filming of
the VMC.
This goals had to be compatible with the orbits of the Mars
Express.
They had to have a scientific or artistic value.
They have been selected 25 including ours!
The results will be published on the blog of ESA
(blogs.esa.int/VMC)
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Our purpose
The chosen region of Mars
(Cavi Angusti, a latin name
as almost all the geological
Mars structures) is located
in the south polar region of
the Red planet, and is
characterized by vast and
deep valleys where the thin
atmosphere of Mars can
produce fogs or mists with
daily development.
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Our project
In this month of May 2015 summer is ending in the
southern hemisphere of Mars ,and on Cavi Angusti
day and night are alternate as on Earth, waiting to
dive for several months in the continuous polar
night.
The low Sun will casts long shadows and the
change in temperature between night and day may
give rise to condensation and dissolution of low
clouds of water vapor or carbon dioxide.
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The expectation
During the days spent on the project, the Mars
Express spacecraft will pass several times on Cavi
Angusti at a distance of about 3000 km, at different
times of martian days, thus allowing to study the
area with a detail of a few kilometers, enough to
reveal any cloud formations.
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Mars atmosphere 1
The atmospheric pressure on Mars is an average of 600
Pascal (0087 psi), about 0.6% of the Earth's 101.3
kilopascals (14.69 psi).
It varies from a minimum of 30 pascal (0.0044 psi) on
Olympus Mounth to over 1,155 pascal (0.1675 psi) in the
depression of Hellas Planitia.
This pressure is well below the limit of Armstrong for the
protection of human body from solar radiation. The overall
mass of the atmosphere of Mars of 25 teratonnes compared
with that of the Earth of 5148 teratonnes with a height of
about 11 kilometers (6.8 mi) against 7 kilometers (4.3 mi) of
the Earth.
Mars atmosphere 2
It is composed of the following layers:
LOWER ATMOSPHERE: a warm zone affected by the heat
of ground and sand storms.
MIDDLE ATMOSPHERE: the area where fast jet streams
blow
UPPER ATMOSPHERE OR THERMOSPHERE: area with
very high temperatures, caused by solar heat. Atmospheric
gases start to separate each other at this altitude.
ESOSPHERE: It begins at 200 km and over, in this area the
last atmosphere’s tracks disappears into the void.
There is also an area of IONOSPHERE and a layer of
seasonal ozone over the South Pole.
Mars atmosphere 3
This graph shows the abundance of gas in
the Martian atmosphere, as measured by
the NASA rovers in 2012.
The graph uses a logarithmic scale to
display the values of very different
concentrations.
Carbon dioxide (carbon dioxide CO2) is
definetly the more abundant gas, in fact
reaches the 95.9% of the volume.
The other four most abundant gases, are in
order argon (Ar), nitrogen (N), Oxigen(O)
and carbon monoxide (CO). These data
are obtained from the rover CURIOSITY in
the Gale crater, and have never shown
environmental conditions prosperous to life.
Climate 1
Of all the planets of solar system, Mars is the one
with the climate more similar to the Earth one,
because of the inclination of its axis of rotation.
However seasons last about twice, since the
distance from the Sun leads it to have a revolution
in just under 2 years. Temperatures range from -140
° C of polar winters to +20 ° C summer. The
strong temperature difference is due to the fact that
Mars has a thin atmosphere (and therefore a low
atmospheric pressure) and a low capacity to keep
the ground heat.
Climate 2
Both polar caps are mainly composed of ice
covered with a layer of about one meter of solid
carbon dioxide (dry ice) to the North Pole, while the
same layer reaches eight meters in the south one;
the overlap of dry ice above that of water is due to
the fact that the first condensate at much lower
temperatures, and then after water during the
cooling season. Both poles have spiral designs
caused by the interaction between the unevenly
solar heat and sublimation and condensation of
ice. Their sizes change also depending on the
season.
Celestia
Celestia’s software (free)
allows you to see the
planets of our solar
system as if we were in a
spaceship in orbit around
the planet.
We used it to identify the exact times of transits of Mars
Express on Cavi Angusti.
ESA has provided a script for Celestia that allows to display
exactly the spacecraft orbit in the period of interest.
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Mars seen by the Hubble Space Telescope in the opposition of 2003. We
can easily see the South polar cap, during late spring.
In the right picture is clearly visible the Mount Olympus in the center of the
northern lowland.
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Detail of the HST photo of South polar cap.
Cavi Angusti is under the hood of the ice.
The scale is about 7 km / pixel, but the polar area is
seen very inclined, so the resolution is much worse.
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The study
The south cap of Mars, seen on two maps made with the data
of the Viking orbiter’s mission. Along with the software
Celestia they have been used to identify craters on the
surface of Mars.
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Guys of Antares
Students visiting the Observatory to observe Venus and
Jupiter at twilight.
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The images obtained
Photos of VMC were taken at intervals of one minute at
shutter speeds of 1s, 0.5s, 0.25s. All of this was in order to
show well areas that were saturated with longer exposures.
In our case, given the grazing light, also the poses of 1s were
slightly underexposed.
Of the three orbits dedicated to the project by the ESA team,
only one was suitable for us, because in the other two
passages of Cavi Angusti was night.
A total of 46 photos were taken, 16 of which are well exposed
(80/255 counts).
It wasn’t so possible to search the formation effects of haze at
different hours of the day, as the original project.
The minimum distance of the spacecraft from Cavi Angusti
was 1980 km.
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Plan B
So we developed our project in three parts:
1.Making a movie of overflying the south polar area, using
the best frames available.
2.Measure the diameter of the polar cap, the main crater of
Cavi Angusti and the near crater Schmidt.
3.Search of possible soil color variations because of the
different amounts of Martian atmosphere interposed between
the spacecraft and the ground during transit.
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Whatch the video (separately)
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Diameters
Measurement of diameters of some craters:
The measurement was made only on images of 1s to have a
better S / N ratio. The measurements were made with GIMP,
using the ruler tool, and zooming images x4 in order to minimize
the error in the mouse position.
The distance from Cavi Angusti’s spacecraft was obtained with
Celestia, using the script ESA to identify its location at the time
of each photo.
Taking the point of view of the VMC technical specifications, we
calculated the approximate flat angular scale per pixel, and from
this, the linear scale on surface.
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Cavi Angusti area at the center of the VMC image and the
correspondent card of Mars
In the vertical of Cavi
Angusti. Distance 2280
km, scale 2.48 km/pixel
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Cavi Angusti
Scale 2.5 km / pix, much better than the picture of the HST,
and we see it from above !!
South Pole at
the top.
Cavi Angusti in
the middle.
Schmidt crater
at the bottom.
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The theory
From the technical specifications the angular scale of VMC is 225 "/ pixel.
The apparent diameter d (in radians) of a crater of diameter D (km) at a
distance r (km) is d = tan (D / r);
If the angle is small (less than 2 degrees) tan (alpha) = alpha, and then d
= D / r.
Turning to arc seconds (arcsec) instead of radians from = D / r * 206265
(number of seconds of arc in a radiant).
To switch from the measure in arcseconds to that in pixel simply divide by
the nominale scale factor mentioned (225 "/ pix).
For a crater of 100 km we have that the diameter in pixels (dp)
dp = D / r * 917.
So the diameter in kilometers and 'D = dp * r / 917
We measured the diameters in pixels of three formations:
Cramped cables, Schmidt, Polar Cap snow.
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Trend expected
Measurements of diameters in the
various pictures at different
distances: the curves show the
values expected in pixels
according to the angular scale.
Our values are in good agreement
with those obtained by the Viking
map
Crater
Our Viking
Schmidt 200 178
Cavi Ang. 80 74
Calotta P. 460
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Atmospheric
absorption
We’ve tried to verify if the
presence of the Martian
atmosphere produces visible
effects in the VMC.
During the overflight, the height
of Mars Express above Cavi
Angusti’s horizon changed from
40 to 90 degrees, and
consequently the thickness of
atmosphere changed from 1:55
to 1.00.
The measured Blue/Red flux
changed from 1.13 to 1.64
The color difference of the
ground is visible in the two
images.
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Conclusions
This project has allowed to perform several operations with an
important educational content:
1.realize a team with the division of works.
2.use an astronomical software for the measurement of the
distance of the Mars Express spacecraft from the surface of
the planet .
3.Familiarize ourselves with the Martian geography and the
coordinate systems
4.Measure the dimentions of some structures with success.
5.Understand the informatic structure of color images
When we’re going to watch Mars through a telescope once
again we will see him with eyes much more aware.
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