FUTURES NATURE|Vol 436|25 August 2005 
MAXO signals
A new and unfortunate solution to the Fermi paradox.
Charles Stross 

SIR — In the three years since the publica
tion and confirmation of the first micro
wave artefact of xenobiological origin
(MAXO), and the subsequent detection
of similar signals, interdisciplinary teams
have invested substantial effort in object
frequency analysis, parsing, symbolic
encoding and signal processing. The
excitement generated by the availability of such close
evidence of extraterrestrial intelligence proximity.
has been enormous. However, after the We have formu
initial, easily decoded symbolic represenlated an explana
tational map was analysed, the semantics tory hypothesis that
of the linguistic payload were found to cultural variables unfa
be refractory.

A total of 21 confirmed MAXO signals
have been received to date. These super
ficially similar signals originate from
planetary systems within a range of 11 par
secs, median 9.9 parsecs1. It has been spec
ulated that the observed growth of the
MAXO horizon at 0.5 c can be explained as
a response to one or more of: the deploy
ment of AN/FPS-50 and related ballistic
missile warning radars in the early 1960s1,
television broadcasts11
GHz microwave leakage from ovens2, and
optical detection of atmospheric nuclear
tests3. All MAXO signals to this date share
the common logic header. The payload
data are multiply redundant, packetized
and exhibit both simple checksums and
message-level cryptographic hashing. The
ratio of header to payload content varies
between 1:1 and 2,644:1 (the latter perhaps
indicating a truncated payload1). Some
preliminary syntax analysis delivered
promising results4 but seems to have
foundered on high-level semantics. It has
been hypothesized that the transforma
tional grammars used in the MAXO pay
loads are variable, implying dialectization
of the common core synthetic language4. 

The new-found ubiquity of MAXO 
signals makes the Fermi paradox — now
nearly 70 years old — even more pressing.
Posed by Enrico Fermi, the paradox can
be paraphrased thus: if the Universe has
many technologically advanced civiliza
tions, why have none of them directly 
visited us? The urgency with which orga
nizations such as ESA and NASDA are
now evaluating proposals for fast interstel
lar probes, in conjunction with the exis
tence of the MAXO signals, renders the
non-appearance of aliens incomprehensi
ble, especially given the apparent presence
of numerous technological civilizations in
miliar to the majority of researchers may account both for the semantic ambiguity of the MAXO payloads, and the non-appearance of aliens. This hypothesis was tested (as described below) and resulted in a plausible translation, on the basis of which we would like to recommend a complete, permanent ban on further attempts to decode or respond to MAXOs. 

Our investigation resulted in MAXO payload data being made available to the Serious Fraud Office (SFO) in Nigeria. Bayesian analysis of payload symbol sequences and sequence matching against the extensive database maintained by the SFO has made it possible to produce a tentative transcription of Signal 1142/98 (ref. 1), the ninth MAXO hit confirmed by the IAU. Signal 1142/98 was selected because of its unusually low headerto-content ratio and good redundancy. Further bayesian matching against other MAXO samples indicates a high degree of congruence. Far from being incomprehensibly alien, the MAXO payloads seem to be dismaFUTURES NATURE|Vol 436|25 August 2005 
MAXO signals
A new and unfortunate solution to the Fermi paradox.
Charles Stross 

SIR — In the three years since the publica
tion and confirmation of the first micro
wave artefact of xenobiological origin
(MAXO), and the subsequent detection
of similar signals, interdisciplinary teams
have invested substantial effort in object
frequency analysis, parsing, symbolic
encoding and signal processing. The
excitement generated by the availability of such close
evidence of extraterrestrial intelligence proximity.
has been enormous. However, after the We have formu
initial, easily decoded symbolic represenlated an explana
tational map was analysed, the semantics tory hypothesis that
of the linguistic payload were found to cultural variables unfa
be refractory.

A total of 21 confirmed MAXO signals
have been received to date. These super
ficially similar signals originate from
planetary systems within a range of 11 par
secs, median 9.9 parsecs1. It has been spec
ulated that the observed growth of the
MAXO horizon at 0.5 c can be explained as
a response to one or more of: the deploy
ment of AN/FPS-50 and related ballistic
missile warning radars in the early 1960s1,
television broadcasts11
GHz microwave leakage from ovens2, and
optical detection of atmospheric nuclear
tests3. All MAXO signals to this date share
the common logic header. The payload
data are multiply redundant, packetized
and exhibit both simple checksums and
message-level cryptographic hashing. The
ratio of header to payload content varies
between 1:1 and 2,644:1 (the latter perhaps
indicating a truncated payload1). Some
preliminary syntax analysis delivered
promising results4 but seems to have
foundered on high-level semantics. It has
been hypothesized that the transforma
tional grammars used in the MAXO pay
loads are variable, implying dialectization
of the common core synthetic language4. 

The new-found ubiquity of MAXO 
signals makes the Fermi paradox — now
nearly 70 years old — even more pressing.
Posed by Enrico Fermi, the paradox can
be paraphrased thus: if the Universe has
many technologically advanced civiliza
tions, why have none of them directly 
visited us? The urgency with which orga
nizations such as ESA and NASDA are
now evaluating proposals for fast interstel
lar probes, in conjunction with the exis
tence of the MAXO signals, renders the
non-appearance of aliens incomprehensi
ble, especially given the apparent presence
of numerous technological civilizations in
miliar to the majority of researchers may account both for the semantic ambiguity of the MAXO payloads, and the non-appearance of aliens. This hypothesis was tested (as described below) and resulted in a plausible translation, on the basis of which we would like to recommend a complete, permanent ban on further attempts to decode or respond to MAXOs. 

Our investigation resulted in MAXO payload data being made available to the Serious Fraud Office (SFO) in Nigeria. Bayesian analysis of payload symbol sequences and sequence matching against the extensive database maintained by the SFO has made it possible to produce a tentative transcription of Signal 1142/98 (ref. 1), the ninth MAXO hit confirmed by the IAU. Signal 1142/98 was selected because of its unusually low headerto-content ratio and good redundancy. Further bayesian matching against other MAXO samples indicates a high degree of congruence. Far from being incomprehensibly alien, the MAXO payloads seem to be disma