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"Take one last look at your precious human moon. Because it cannot help you now!"

Earth's Moon (often referred to as simply The Moon or Luna) is Earth's only natural satellite, and the setting of the final sequence of Portal 2. It is also the latest known location of Wheatley.


Moon 2

The surface of the Moon seen with the Apollo landing site with Earth in the background.

At some point in the late 1970s or early 1980s, Cave Johnson, CEO of Aperture Science, somehow managed to acquire roughly $70 million worth of Moon rock. Upon grinding up and mixing it into gel, he discovered two things: one being that it made a great portal conductor, and the other being that ground Moon rock was "pure poison." He then put it to use in testing, under the name Conversion Gel.

An undefined amount of time later, when Wheatley had taken over the Enrichment Center and allowed it to fall into serious disrepair, part of the ceiling collapsed from the Central AI Chamber. This allowed the Moon to be viewed through the opening made. Chell took advantage of this, and the Moon's portal conducive properties, and shot a portal at the moon. This caused both herself and Wheatley to be sucked into the near-total vacuum of the Moon's atmosphere. Chell was returned to Earth when GLaDOS, newly restored to power, pulled her back in through the portal. However, Wheatley was left to drift through space indefinitely, along with a corrupt Personality Core.

The Moon and in the context of Portal 2

The Moon takes on major importance in Portal 2, as it allows Chell to defeat Wheatley and gives the player the Lunacy achievement. And while some may argue that the use of the Moon was unique, the presentation of the Moon and the subsequent view of the Earth when seen from the Moon have unfortunately resulted in extremely flawed basic physics and astronomy and contradictions in the overall Half-Life 2 universe, as noted below:

  • The moon has gravity approximately 1/6 of Earth's gravity, meaning that an object on its surface would remain on the surface unless acted upon, but the force needed is much less than that of Earth. And unlike Earth, its atmosphere is near-inexistent (3×10−15 atm, meaning 3 trillion times less air than on the planet). Due to the bi-directional teleportation nature of the portal Chell launched to the moon, Wheatley and Chell were both blown away from the surface by the negative pressure vacuum resulting.
  • Chell always fires a blue portal at the surface, regardless of what portal one tries to fire.
  • This is a goof during the brief moon sequence. Chell fires the portal near the middle of the side of the Moon facing the Earth. So to see the planet, she would have had to look at least 60 degrees up. Yet when she is on the Moon, the Earth is just above the horizon. For that to happen, she would have had to fire at the "edge" of the Moon.

However, while the above point is intriguing, it ought to be noted that it is completely moot when the following is considered: since Chell is able to observe almost a full moon from the surface of the Earth, this would necessarily cause the Earth to be almost invisible when viewed from the Moon, i.e., a "new earth" or a waning crescent earth." If we are to hold the notion that Chell views a full moon, this would make things very interesting and it is of a most confusing issue why the creators of this game made such a mistake. As a new earth, we may have enjoyed the opportunity to view a seemingly dark earth illuminated by city lights. In addition, we may have been able to view a red glow (due to refraction from Earth's atmosphere, the terminator would not be black like the rest of the planet, but red) around the terminator edges of the planet as sunrise occurred on one-side and sunset on the other. Furthermore, had the creators chosen to have the endgame events occur during a lunar eclipse, players may have enjoyed looking at a blood red moon when they opened the portal on the Moon and witnessed a solar eclipse (this time caused by the Earth eclipsing the Sun). It is unknown why the creators goofed up such a simple concept as the phases of the Earth and Moon given the many references to the Moon's phases in wall pictures left by Doug Rattmann.

If we are instead to assume that Earth is near her full phase and take that the Moon should be in its crescent phase, we learn that it is summer in the northern hemisphere on Earth from the given image. The strange part in assuming that the Earth should be the correct object represented and not the Moon is that it limits where the GLaDOS facility is located. The eastern coast of the US has yet to experience its sunset and thus it would make it impossible for the facility to be located in the midwestern states and furthermore, in any place in the United States.

  • Another goof is that the escape velocity from the Moon's surface is 1.4 km/s, which is faster than an artillery shell as it leaves the barrel. GLaDOS is not hitting Wheatley that hard, nor is the air escaping that fast. If it did, there is no chance Chell could hold on since it would be equivalent to holding on to an aircraft at three times the speed of sound. This means Wheatley would fall to the Moon's surface within a couple of minutes at most instead of floating around in space. But, we also must take into account the Moon's own orbital velocity, which is about 1.02 km/s; assuming Moon as a "fixed point" in calculation, we could see that relative to the Moon surface all Earth-connected objects are moving with the same velocity. With the combination of other factors, like air pressure and differences of gravity on the end of Earth-Moon portal, it is theoretically possible for Wheatley to achieve the escape velocity.
  • The Earth looks similar to what our Earth looks like today, despite the draining of the world's oceans by the Combine as seen in Half-Life 2. This suggests that either the Combine has been overthrown and/or the oceans were somehow restored. This may not be true, as in the credits the photo of Earth is credited to NASA, indicating that it was not created by the developers, and therefore does not have further-reaching implications.
  • It is unknown how the Moon could be seen from the Central AI Chamber. The end credits show that the Enrichment Center's location is hidden deep underground underneath a shed. However, given the modular and internally mobile nature of the Enrichment Center, it is possible that Wheatley moved the chamber closer to the surface and that GLaDOS moved it back deeper underground while Chell was unconscious.
  • Inhaling Moon dust is in fact deadly to humans, which explains Cave Johnson's fatal condition. Due to the Moon's near lack of atmosphere, the jagged texture of the dust is not worn away as it would be by Earth's natural processes. Breathing it in causes lung conditions similar to anything between hay fever and emphysema, depending on how much exposure there was.
  • According to an interview with Erik Wolpaw in the Portal 2 Official Guide, they were originally going to place signs in old Aperture that read things such as "The moon is not your friend." They were even going to put skeletons on the moon during the ending sequence. This was cut with Wolpaw calling it "A good gag that didn't make it in." This connects with Cave Johnson's recording where he says Aperture Science was called to a congressional hearing on "missing astronauts".
  • Doug Rattmann has an extreme obsession with the Moon, as it is seen in all of his drawings and murals. He also states in Portal: Lab Rat that he would have rather have gone to the Moon than help build GLaDOS. The Moon is often referenced in the game as well, including an image hidden in his final transmission showing a companion cube on the Moon. It is unknown if this is foreshadowing, or the Moon serves a greater purpose.
  • During the Moon sequence, a portal is fired at a point on the Moon which is approx. 275 miles (442 km) from the nearest moon landing site which is Apollo 17; making it impossible for a moon landing site to be seen in-game, unless it is an Aperture owned lunar module, or the history of Moon exploration is different in this world.
  • The time it takes the portal beam to reach the moon from the moment the portal gun is fired is roughly the same time it would take a beam of light to reach the moon. This implies the portal gun doesn't violate the Principle of Locality. This also implies the portal gun either fires mass zero particles, which would travel at the speed of light, or it fires highly relativistic, massive particles, which would travel at nearly the speed of light (provided it works by firing particles that adhere to the Standard Model of particle physics).
  • When Chell falls to the ground when the Stalemate Button is pressed, in 3rd person view only her arms and the Portal Gun are shown.

List of appearances

Preceded by
Central AI Chamber (3)
Portal 2 journey (4) Succeeded by
Central AI Chamber (4)
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