Tesla's Colorado Springs Signals

Summary

Between June 1899 and January 1900 Nikola Tesla operated an experimental station at Colorado Springs, built around a coil more than forty-nine feet across. He wrote afterwards that his instruments had registered periodic disturbances he could not attribute to the sun, to the aurora, or to earth currents, and that the feeling had grown on him that he had been the first to hear the greeting of one planet to another.

The account he wrote for publication named no planet and gave no date. Elsewhere he did name one: a newspaper quoted him in January 1901 saying he believed the inhabitants of Mars were signalling, and in 1921 he wrote that the signals must have come from Mars. Of six scientists a newspaper put the claim to in January 1901, five rejected it and one declined to comment. He published no instrument record, and none has surfaced since.

What is documented

The station. Tesla reached Colorado Springs on 17 May 1899 and began experiments on 15 June, his first spark running about five inches. He left on 13 January 1900. The laboratory stood on North Foote Avenue, and the marker that now commemorates it says it held "the largest Tesla coil ever built, over 49 feet in diameter". Several years later, the marker records, the building was torn down and the lumber reused, and the laboratory equipment was sold at a sheriff’s auction.

The claim, in his own words. In Collier’s Weekly for 9 February 1901, in an article titled "Talking With the Planets", Tesla wrote: "The feeling is constantly growing on me that I had been the first to hear the greeting of one planet to another." On when it happened he said only that "I was alone in my laboratory at night". He also wrote: "My first observations positively terrified me."

What he said the disturbances were like. They occurred, he wrote, "periodically, and with such a clear suggestion of number and order that they were not traceable to any cause then known to me". He added that he "could not decipher their meaning".

What he ruled out. Tesla stated that he had excluded disturbances "produced by the sun, Aurora Borealis and earth currents", and that his experiments "precluded the possibility of the changes being produced by atmospheric disturbances". He also claimed he could note "every electrical change that occurred within a radius of eleven hundred miles".

Mars, and where he named it. The Collier’s article names no source. Tesla writes there of "the inhabitants of whatever planet had signalled to us", and Mars appears in his text only in a passage about habitability: "In the solar system, there seem to be only two planets, Venus and Mars, capable of sustaining life such as ours." The magazine’s editorial note offered "a call from the inhabitants of Mars, or Venus, or some other sister planet!" Tesla did name Mars elsewhere. A newspaper report datelined New York, 4 January 1901, a month before the article, quotes him: "Inhabitants of Mars, I believe, are trying to signal the earth." In a letter to Electrical World published on 24 September 1921 he wrote that "subsequent study convinced me that they must have emanated from Mars, this planet having been just then close to the earth." In the same letter he put the planetary signals others had reported around 1919 down to "interfering undertones of wireless transmitters", without applying that verdict to his own.

The December 1900 letter. Writing to the Red Cross Society that December, Tesla imagined humanity receiving a message "from another world, unknown and remote. It reads: one ... two ... three ..." It is the earliest dated statement of the claim the Registry could read. An earlier mention, in a letter to the reporter Julian Hawthorne dated 8 December 1899, is referred to in secondary accounts; the Registry could not reach the letter itself or a scholarly citation of its text, and does not treat it as established.

The answer from scientists. On 4 January 1901 the New York Journal and Advertiser put the claim to six named scientists under the headline "Astronomers Discuss Tesla’s Alleged Message From Mars". Professor S. I. Brown of the US Naval Observatory called it "remote even to the point of impossibility". Professor A. S. Skinner, of the same observatory, said "You can rest assured it is imaginative and visionary." Professor T. J. J. See declined: "I do not care to say anything about it." Father John B. Hagan of Georgetown said "Astronomers do not look forward to the discovery of communication between the planets." John H. Kedzie called the theory "utterly visionary and impossible". Professor George W. Hough of Dearborn Observatory offered a local cause instead: "A dynamo when running will show a disturbance on any magnetic instrument located a block away." Not one of the six supported the reading.

The instruments. On the Corums’ technical reconstruction, Tesla’s receivers responded primarily between 8 and 22 kHz, and his working frequencies ran from about 5 to 20 kHz. The detector used a coherer stressed to breakdown. These figures are a later reconstruction from his apparatus, not a measurement recorded at the time.

What does not exist. No waveform, chart or instrument reading of the signals has been produced, and there is no second observer and no replication. The whole case rests on Tesla’s own retrospective testimony, the earliest of it written eleven months or more after he left Colorado Springs. His Colorado Springs diary, whose last entry is dated 7 January 1900, is cited by the Corums only for a coherer description and for that date; no source the Registry retrieved places the observation in it.

Leading explanations

Jovian kilometric emission (Corum and Corum, 1996; hypothesis, untested). Kenneth and James Corum proposed that Tesla detected intense natural radio emission from Jupiter at very low frequency, inside the band his receivers covered, and that the apparent link to Mars arose because the predicted Jovian Io-A emission ceased at nearly the moment Mars set behind the western mountains. Their conclusion is that "it is entirely within reason to identify Tesla’s signals" as "the detection of intense kilometric (VLF) emissions originating from Jupiter". The account is internally coherent and rests on real Jovian emission, but it is a reconstruction made ninety-seven years later with no 1899 data to test against. The authors concede that not everyone will agree with them.

A local electrical source (Hough, 1901; hypothesis, untested). George W. Hough of Dearborn Observatory suggested at the time that an ordinary running dynamo nearby would disturb a magnetic instrument a block away. Nothing was done to test this, then or since.

Another experimenter’s wireless (hypothesis; rejected on technical grounds). It has been suggested that Tesla picked up Marconi’s transmissions of July 1899. Secondary accounts attribute the suggestion to Marc Seifer’s biography of Tesla, which the Registry could not open. The Corums reject it on frequency grounds, noting that Marconi’s equipment worked at low and medium frequency and that "there would have been no 1899 VLF signals emanating from the English Channel".

Atmospheric noise (an objection, not an attributed hypothesis). Lightning static and similar natural radio noise would produce pulses in Tesla’s band. The Corums raise and answer this, arguing that Tesla knew the difference and that the signals were not correlated with the weather. No modern proponent is named in any source the Registry retrieved, so it is recorded here as the objection the Corums address.

An intelligent transmission (Tesla, 1901 and 1921; rejected). Tesla’s own reading, which by 1921 he had fixed on Mars. None of the six scientists a newspaper asked in January 1901 supported it, and no evidence has supported it since.

Current status

Unsolved. What Tesla’s receivers responded to has never been established, and probably cannot be. No reading of the signals has been produced, there was no second observer and there has been no replication, so none of the explanations proposed has anything to be tested against, the Corums’ Jovian hypothesis included. Tesla’s own reading, a signal from another planet that he later placed on Mars, drew no support from any of the six scientists a newspaper asked at the time and has found none since. The defensible statement is that Tesla reported periodic disturbances he could not attribute. A contemporaneous chart or dated notebook entry describing the pulses, the surfacing of the Hawthorne letter in a citable archive, or a peer-reviewed analysis of whether his documented receiver could have responded to Jovian emission at that latitude would change this record.

Last reviewed: November 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.