Birthdays and parties go together. It is a time of celebration for the one who is having a birthday, as well as his or her friends and family. At some point during the festivities, someone will inevitably begin singing “Happy Birthday.” This is the cue for the other celebrants to join in.

Wouldn’t it be sad if no one showed up for your birthday? How tragic would it be if the singing of “Happy Birthday” depended entirely upon you? Having to spend your birthday by yourself would probably make you feel as if you are the loneliest person on the planet.

Now you know how the Mars Curiosity rover feels every year.

Curiosity was built to study the soil of Mars. It is a product of the Goddard Space Flight Center and the key component of the Soil Analysis at Mars (SAM) project.

The robotic chemistry lab moves around the surface of Mars and gathers samples of Martian soil. After scooping up a sample, Curiosity’s arm deposits the soil in a receptacle. To help the soil go into the analysis chamber, Curiosity vibrates at various frequencies. If anyone happened to be standing near the device at that time, he or she would hear a discordant rising and falling sound that somewhat resembles that annoying co-worker or classmate who insists upon whistling while you are trying to concentrate.

One day each year, Curiosity sings a different song. That day is August 5. It was on that date in 2012 that Curiosity arrived on Mars. In other words, that is the rover’s birthday. On that day, instead of its usual sound, Curiosity takes a few moments to celebrate its birthday with a lonely rendition of “Happy Birthday.”

In those few moments, Curiosity’s isolation must feel especially poignant. On a planet that is inhabited entirely by robots, no one shows up for a party and not a single voice joins in the celebratory song.

If it is any consolation, there are a few scientists who recognize Curiosity’s birthday, but the closest one is over 65 million miles away.

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