Date: Tue Jan 31 1989 13:44:46
From: Anson Kennedy
Subj: The final moments of Phobos 2
* Forwarded from "ParaNet Skeptics Conference"
* Originally by Anson Kennedy
* Originally to All
* Originally dated 31 Jan 1989, 13:43
The Jan/Feb 1993 issue of the Planetary Society's _The Planetary Report_
contains a brief note written by A.S. Selivanov and U.M. Gektin of the
Institute of Space Device Engineering, Moscow, on the mysterious end of Phobos
2. In the Question/Answer section on page 20, it says (all typos are my own,
copied without permission):
[Accompanying the article are two figures.
Figure 1 caption reads, "This chart illustrates how the positions of the
spacecraft, the moon Phobos and the planet Mars lined up to create the 'Phobos
Figure 2a caption reads, "Figure 2a is a thermal, or far-infrared, image of the
Figure 2b caption reads, "The Termoscan also produced a visible, or near-
infrared, version of the same image, as seen here in Figure 2b."]
"Last year I noticed more than one mention in the media of a 'mystery object'
that appeared in the last images returned by the Russian spacecraft Phobos 2.
It was suggested that aliens were responsible for the object and perhaps even
for the demise of the mission. What actually happened?" -Len Seymour, Elko,
The "mystery object" was actually the shadow of one of Mars' moons. The
spacecraft Phobos 2 reached Mars orbit and began to approach the martian
satellite Phobos in February 1989. In the middle of March, Phobos and the
spacecraft were several hundred meters apart, and they moved synchronously in
the same orbit. At that time there were several surveys of the martian surface
by the Termoscan equipment on board the spacecraft.
Termoscan is a two-channel scanning radiometer that can receive images in the
visible and near-infrared region of the spectrum and at the same time in the
thermal, or far-infrared, region. A Termoscan image is produced by a scanning
mirror moving perpendicular to the spacecraft trajectory with a frequency of
one scan line per second. Thus a picture is generated by the motion of the
spacecraft in its orbit.
The survey of the martian surface was made with a constant Sun-to-spacecraft
orientation. The centerline of the image is in the anti-Sun direction to an
accuracy of one to two scan lines. Since the spacecraft was near Phobos and the
Sun-Phobos directions was approximately the same as the Sun-spacecraft
direction, the Phobos shadow on the Mars surface can be seen in the Termoscan
field of view (Figure 1).
The length of this shadow was about 21 kilometers (13 miles). Termoscan's field
of view on the martian surface was 650 kilometers (400 miles) wide, and the
resolution was 1.8 kilometers (about 1 mile). The moonlet's shadow came into
Termoscan's field of view when the spacecraft was 200 kilometers (about 120
miles) away from Phobos. At this point the termoscan instrument was pointed at
Mars' surface in the same direction as the Sun's rays. On March 26, 1989, the
shadow appeared as shown in Figure 2.
The factors that influenced the form and dimensions of the shadow included
Phobos' orientation (Phobos has an irregular shape); distortion from Mars'
surface curvature, especially near the planet's limb (the edge of its disk as
seen from the Phobos spacecraft); and the dispersion of radiation and other
Another factor -- and probably a more important one -- was deviation of the
axis caused by the spacecraft's instability. The spacecraft's axis moved about
40 minutes of arc during the experiments.
If the spacecraft's orientation and the distance from it to Phobos had been
perfectly constant, Phobos' shadow would have been an even line. But because of
the deviation of the spacecraft's axis, Termoscan's lines moved ahead of the
shadow or dropped behind it as the shadow moved on the planet's surface. The
scanning line overtook the shadow, going through its center, then passed it
(see Figure 2).
This process caused 250-to-300-kilometer (155-185-mile) motion on the Mars
surface in the direction of motion, and the shadow was elliptically stretched
in the resulting picture.
Figure 2 shows images from two different spectral regions. Figure 2a, taken in
the infrared part of the spectrum, shows Phobos' shadow. In Figure 2b, a
visible image, the shadow image drops behind. This image indicates that the
shadow lowered the local surface temperature 4 to 6 degrees Celsius.
The temperature variation depends on how fast Mars' thin surface layer (several
millimeters) cools. After analyzing the results from the two spectral channels,
we were able to calculate the thermal inertia (the measure of the object's
resistance to changes in temperature) of the surface layer and draw conclusions
about its physical characteristics.
The calculations showed that almost all of the observed surface is covered with
a layer of dust. The thermal inertia is two to three times lower than it would
be without the dust. Further analysis will tell us more about Mars' surface
The death of Phobos 2 resulted from a failure in the control system of its
onboard computer. this caused reorientation of the solar cells such that they
did not receive sunlight power. The storage battery was drained of its charge,
and all the spacecraft's subsystems lost power. Phobos 1 went out of control
earlier when its control lock with Earth was lost after an operator's error.
* Origin: MICAP Georgia State Chapter & Georgia Skeptics (9:1012/25.0)