The Yip Yips: Sesame Street's Martians, the Telephone and Jim Henson's Aliens

The Yip Yips arrived on Sesame Street in 1971, in the show's third season, and have done the same thing in every appearance since. Two aliens descend, in a shimmer of sound, on an ordinary Earth object, a telephone, a radio, a clock, a computer, a cat; they announce themselves in a chatter of yips and confirmations; they consult a large book, running a finger down the page, to identify the thing; they guess wrong, address a telephone as a cow, then a cat, and are thrown into panic when it rings; and they leave, satisfied, in the same shimmer. The sketches are two or three minutes long and among the most repeated the show has made, and the aliens have never learned anything.

Jim Henson designed and, with Jerry Nelson, performed them: two shaggy puppets, pink and blue, with round bulging eyes, antennae with small balls, and a mouth that is the whole lower body, a fringe of fabric that flaps open to a wide lip, so that the Yip Yip's speech is its body folding. The voices are the yips, the uh-huhs, a repeated "nope" and the occasional recognisable word, and the humour is in rhythm: the two speak in unison, break into disagreement and reunite. They are the only Martians in the field guide with no plot at all.

The Yip Yips are from Mars, according to the show's own materials, and nothing else about them is fixed. They float rather than walk, arrive and depart in a beam that the sketches render as a sound and a wobble, and seem to be visitors on a schedule of research, each sketch a field trip to a single object; their book, a large volume they carry with them, is an Earth guide that they consult with total confidence and that has never once helped. Their emotional range is curiosity, delight, alarm and reassurance, and the sketches' structure is that alarm and reassurance are the same word said at different speeds.

They are also Henson's purest aliens. The Muppets had used monsters, birds and a frog to look at the world from outside, and the Yip Yips are the device reduced to its parts: a pair of intelligences that know nothing about the ordinary, confront it with a manual and a method, and are defeated by a ringing phone. Preschool audiences, the show's research found, understood the joke immediately, because it was their joke, a world of objects whose names are learned by guessing; the aliens are the child, and the phone is the phone. The sketches have been remade several times, most recently with a computer, and the aliens have gone on to Muppet specials, video games and a cameo in The Muppets (2011).

The company's other extraterrestrial took twenty years to admit it. Gonzo, the hook-nosed daredevil of The Muppet Show, had been introduced in 1976 as a creature of no identifiable species, called a whatever, and the question of what he was became a running gag, answered in 1999 by Muppets from Space: Gonzo is an alien, his family arrives in a ship after contacting him through his breakfast cereal, and a government agent, played by Jeffrey Tambor, kidnaps him for study before the Muppets stage a rescue. The film ended with Gonzo choosing to stay on Earth with Rizzo and the others, which the franchise has treated as settled.

The two properties do not meet. The Yip Yips belong to Sesame Street, owned since 2000 by Sesame Workshop; Gonzo belongs to the Muppets, owned since 2004 by Disney; and the Henson company's aliens have been divided by contract for a quarter of a century. What they share is the design philosophy. Henson's aliens are never threatening and never wise; they are fuzzy, wide-eyed, easily alarmed and eager, the visitor as a toddler, and it is the version of the alien that a generation of Americans met before it met any other.

The Martians of Sesame Street arrived in the year the real Mars was first orbited. Mariner 9 reached the planet on November 14, 1971, the first spacecraft to orbit another world, waited out a global dust storm and then mapped the surface, finding the great volcano Olympus Mons, the canyon system that bears the spacecraft's name and the dry riverbeds that have driven the search for Martian life since; three weeks later the Soviet Mars 3 lander touched down and transmitted for twenty seconds before falling silent. The life on Mars article covers what the orbiters and rovers have found, which is a cold desert with a wet past and no telephones; the Yip Yips are the last Martians of children's television to have arrived before the planet was known.

Their nearest relatives in the sitcom tradition are Mork, who also came to study and report, and Uncle Martin, the earlier Martian who understood the objects perfectly and hid what he knew. The Yip Yips are what the observer alien looks like with the mission removed: no report, no home planet on the line, only the book and the phone. The aliens on TV article follows the observer from Martin to the streaming era, and the first contact entry in the glossary describes the meeting the sketches perform, forty seconds at a time, with a clock.