of The British Interplanetary Society, Vol. 51, pp. 181-184, 1998
SYSTEM AS A COLLECTOR OF ALIEN ARTEFACTS
Institute of Radio Astronomy,4
Krasnoznamennaya str., Kharkov 310002 Ukraine.
of conventional SETI-experiments cover only a negligible part of the Galaxy's
age, but more effective approaches could cover billions of years without any
speculations about the desire and means of extraterrestrial intelligence (ETI)
to communicate with us. It is shown that the Moon is a good indicator of
ETI presence in the considerable part of the Galaxy during past 4 Gyr. Moreover,
the Earth is a natural collector of ETI artefacts (debris, trash etc.) which
could spontaneously fall on our planet.
SETI-strategies, the search for signals and radiation leakage  reflect the habit of astronomers to study the radiations
from the celestial bodies. That is why only a negligible part (~3x10-8
) of the Galaxy's lifetime is accessible to modern SETI. Hence the probability
of finding an active ETI is decreased and tied in with the vulnerable speculations
about necessity, direction, magic frequencies, time synchronisation, modulation
etc. of electromagnetic signals. However, the search for alien artefacts,
which could have accumulated on the surfaces of the Moon and the Earth during
4.5 Gyr, seems a promising alternative. Although this approach is mentioned
in the literature (e.g.), it is not considered in detail.
Nevertheless the analysis of this problem is quite pertinent now when classical
SETI is in crisis .
2. LUNAR ETI INDICATOR
oxygen-containing atmosphere of the Earth (a good biosphere indicator) is
detectable from interstellar distances . About 104
stars capable of having inhabited planets approached the Sun to distances
within 1.5 pc during the past 4.5 Gyr  while the Sun turned
16 times round the Galaxy centre. Moreover, ~150 stars of different types
have flown through the Solar System at distances <104
a.u. Hence our unique planet could attract ETI attention. The Moon is
a convenient site for long-term observation of the Earth. There is a variety
of arguments for placing equip-ment for prolonged Earth monitoring on the
Moon rather than in orbit or on the Earth itself, e.g.
screening of at least half of the meteorite flow and ionising radiation, the
equipment lifetime on the lunar surface may be at least twice as long as
that of a spacecraft in orbit.
and orientation of an apparatus on the Moon is simple and possible without
fuel for jets.
can be used to support life of the station personnel, thermal control and
repair of equipment.
mission may be effectively concealed from terrestrial aboriginals where as
an orbital spacecraft is much easier to reveal.
of adverse effects of atmospheric, geological and biological nature will offer
longer lifetime for exploration equipment on the Moon rather than on the
advantages of the Moon as an intermediate base for flights to the Earth and
planets are clearly demonstrated by the rise of NASA, ESA and NASDA lunar
It should be
emphasised that landing on the Moon would be for ETI a necessity more than
a convenience. Thus, the Moon should be an attractor of alien artefacts. Moreover,
about 90 per cent of ETI 10cm-artefacts could survive under meteoroid bombardment
for indefinite period  because of the immersion in the
soil due to meteoroid impacts and dust accumula-tion.
With the Moon
as an attractor and a good accumulator of ETI artefacts our satellite is an
indicator of ETI presence at least for civilisations which were interested
in the Earth, for the past 4 Gyr. That is why the specific principles and
probable targets of lunar archaeology  could be useful
for future missions to the Moon.
of lunar exploration obtained already(e.g. ) show that
the search for alien artefacts on the Moon is a promising SETI-strategy especially
in the context of the lunar colonisation plans.
Fig. 1. The ruin-like formation
near the lunar crater Lovelace photographed by the space probe Clementine
on March 8, 1994 (image LHD 30055.080). This cluster of rectangular depressions
occupied an area of about 13km2.
Fig. 2. Sketch map of fig. 1 (a)
and the probable reconstruction of the ruin-like formation (b). The similar
patterns could be preliminary targets for archaelogical reconnaissance.
an unusual formation near the crater Lovelace (117º W; 82º N), which
was photographed by the HIRES camera of the space probe Clementine, image
LHD30055.080 (fig.1), seems to be a promising candidate
for archaeological reconnaissance. This formation looks like an isolated
quasi-rectangular cluster of rectangular depressions (the collapse of some
subsurface caves?). The vault-like remains appear as two terraces on the
depression slopes (fig.2). It suggests that there
are three storeys of the hypothetical caves. The rectangularity and regularity
of this ruin-like pattern is similar to modern projects for the lunar base
as a subsurface construction pro-tected from meteoroids and radiation.
3. SEARCH FOR ALIEN SPACE DEBRIS
activity in the Solar System could lead to the pollution of space. At least
there are interesting candidates for ETI artefacts in the orbits (e.g. ). Moreover, alien space debris could fall on the Earth spontaneously
like our satellites do. That is why the search for candidates to such events
are worth discussing.
the disintegration of artificial satellites into debris of different chemical
composition shows in the form of multicoloured bolides. Such phenomena were
unknown in meteoric astronomy before 1957. However, I have discovered that
rare multicoloured bolides have been observed before that time too, with artefact-like
disintegrations noticed on:
- 1902, July 13 “several colours
being marked” );
- 1926, December 4 (the meteor
trail was “divided into two longitudinal bands: the upper band of a very clear
blue, sapphire colour, and the lower one of a scarlet colour” );
- 1928, June 13 (“as it moved
it emitted sparks of red, blue, white and green hues” );
- 1933, December 18 (“The
ball of fire resembled fireworks... Colours turned blue, red and green...”
- 1936, October 29 ( “a rocket
black formation throwing sparks of various colours” ).
there are reports about some puzzling formations (“pseudometeorites”) which
fell from bolides before 1957 [15-17]. Thus the Eaton meteorite,
seen to fall on May 10, 1931, was so hot on falling that it burned the fingers
of its finder. However, the composition of that finding corresponds to yellow
brass, and the artificial alloy in terrestrial practice .
The new well-registered case of a similar fall, apparently of nonsatellite
origin, is studied by the author . These strange debris
are collected and kept by the Kharkov Astronomical Observatory. It
is not impossible that similar phenomena occurred millions of years ago, examples
being the problem of “fossil artefacts” (found formerly in prehuman layers)
are described in scientific literature .
the above-mentioned findings cannot be regarded as ETI evidence, rather they
are illustrative of search possibilities. Unfortunately, meteoritics a priori
ignores the “pseudometeorites” as a human trash. However, the search for
isotopic anomalies in such curiosities could be a promising SETI-strategy.
4. TRASH FROM THE STARS?
lead to a lasting pollution of the Solar System . Similarly
the interplanetary space of other inhabited planetary systems could contain
artefacts. Even without inter-stellar flights, the spontaneous leakage of
artefacts into the interstellar medium is inevitable because:
- light pressure expels micron-sized
debris particles (e.g. from rocket engines) out of the planetary system;
- a considerable portion of
any large artefacts would be ejected by gravitational interaction with the
planets. According to computer simulations of the asteroid and comet
motion, 10-30 percent of small bodies leave the Solar System [22-24]);
- Collisions between artefacts
or their explosions (like spontaneous explosions of Earth satellites) in the
outer parts of the planetary system could accelerate their debris up to hyperbolic
activities even within a planetary system lead to a diffusion of artefacts
into the interstellar medium. If there are alien artefacts between the stars,
some of them are likely to fall down to Earth at some time. So it is interesting
to estimate the frequency of such events.
Let the velocity (v) of all artefacts in interstellar medium relative to
the Sun be equal to:
v = [X2
+ Y2+ Z2 +(
3=18 km/s are the orthogonal dispersions in velocity
of nearby stars; X=9 km/a, Y=12 km/s, Z=7 km/s are the components of the velocity
vector of the Sun relatively to nearby stars .
The effective radius of the Earth’s orbit for an interstellar artefact:
is the radius of the Earth orbit; V=42.1km/ s is the escape velocity at 1
a.u. distance from the Sun. The probability of the fall on the Earth
for an artefact at the distance of r
a from the Sun is:
R[1+ u2 /<va2>]1/2
is the typical effective radius of the Earth (R=6371 km is the Earth’s radius;
u=11.2 km/s is the geocentric escape velocity; <va2
>=v2 +1.5V2 is the
average square of geocentric velocity of artefacts).
The number density of artefacts
=4.43x10-42 km-3 is the
stellar density near the Sun ;
=0.3 is the fraction of stars with planets among the nearby stars as estimated
from stellar IR-excesses indicating protoplanetary disks and from statistics
of angular momenta in binaries ; M=2.3x1021
kg is the mass of potential raw material for the artefact manufacturing in
the planetary system (the total mass of asteroids in the Solar System ); C is the part of raw material transformed into the interstellar
artefacts; m is the typical mass of artefact; and e is the fraction of planetary
systems generating interstellar artefacts among the nearby planetary systems.
Then the frequency of ETI artefact
3.5x 10-11 [kg/s]
the upper limit on
could be estimated, taking into account that e
1 and C
1. Then the average time between the falls of such ETI artefacts is 1/f
91yr . Let
=10-2 and C=10-2
(the artificial ~5%-erosion of asteroids could be realised during geological
lime or especially with exponential growth of space manufacture ). Then the Earth could accumulate about five thousand
of 0.1kg-artefacts during 4.5x109 years.
They could survive breaking in the atmosphere, at least in part Thus, according
to the known Fisher’s equation (m/mo=exp[-
v*2/2], where: m and mo
are the final and initial meteoroid’s masses, respectively;
is the ablation coefficient; v* is the initial geocentric velocity of the
artefact), the survived part of the artefact is m/mo
> 0.01 if v*2<9.2/
. Assuming accidental orientation of the heliocentric velocity of artefact
near the Earth (vh =[u2
km/s), we can estimate the probability of the survival condition v* = |vh
)1/2 (where ve=29.9km/s
is the Earth orbital velocity):
+ ve2 -9.2/
)/(2vh ve )]/2
finding is possible (W>0) at
For the common meteorites it is accepted that
. Nevertheless, there are materials where the heat of
destruction (Q) differs considerably from that of meteorites (Qo
=8x106 J/kg ). For example,
the boron artefact has the heat of fusion and sublimation Q=5.53x107 J/kg
. Hence s=so Qo/Q=2.9x10-9 s2/m2 and W=0.40. Therefore, the finding of
alien heatproof artefacts on the Earth is not excluded even without interstellar
There are interesting
nonclassical SETI possibilities which look more effective and promising than
the conventional search for radio/laser signals. Unfortunately, new approaches
conflict with the mental habits of astronomers, geologists and geochemists
in studying natural formations and processes. This habit factor leads
most specialists to an a priori rejection of search for alien artefacts on
the surfaces of the Moon and the Earth. Nevertheless, invaluable information
about inhabitabil-ity (or uninhabitability) of our Galaxy during its total
lifetime may be found just there.
The author is grateful to Dr. F. G. Graham and the Lawrence Livermore National
Laboratory for the Clementine data.
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